Gradient Phosphatized Interphase for Ultra-Stable and Low-Temperature Zinc Metal Batteries

Gradient Phosphatized Interphase for Ultra-Stable and Low-Temperature Zinc Metal Batteries | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Gradient Phosphatized Interphase for Ultra-Stable and Low-Temperature Zinc Metal Batteries Wei Wang, Shan Chen, Xuelong Liao, Rong Huang, Jialei Chen, Yaxin Wang, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2143664/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Sep, 2023 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract In situ formation of a stable solid electrolyte interphase (SEI) layer on zinc (Zn) surface is an effective solution to suppress dendrite growth. However, the fast transport of bivalent Zn-ions within the solid interlayer remains very challenging. Herein, we engineer the SEI components and enable a superior kinetic of Zn metal under harsh conditions. Trimethyl phosphate was employed as a cosolvent, which decreases the freezing point of water and spontaneously generate a gradient ZnF 2 –Zn 3 (PO 4 ) 2 interphase. Mechanistic studies reveal the outer ZnF 2 facilitates Zn 2+ desolvation and inner Zn 3 (PO 4 ) 2 serves as channels for Zn 2+ transport, contributing to long-term cycling at subzero temperatures. Impressively, the gradient SEI enables a record lifespan of symmetric Zn cells over 6000 hours (~ 8 months) at − 50 o C. Furthermore, the Zn–KVOH full cell achieves a superhigh areal capacity (9.42 mAh cm − 2 ) under a practical cycling condition (high cathode loading: 33.75 mg cm − 2 ; lean electrolyte: 6.76 µL mAh − 1 ), and delivers a capacity retention of 86.1% after 12000 cycles at − 50 o C. This work provides a feasible route for low-temperature aqueous Zn metal batteries. Physical sciences/Energy science and technology/Energy storage/Batteries Physical sciences/Materials science/Materials for energy and catalysis/Batteries Zn metal anodes Gradient phosphatized SEI Low temperature Rapid interfacial kinetics Long-term stability Aqueous Zn batteries Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The ever-increasing demand of renewable energy sources (such as solar and wind) and their fluctuating nature necessitate the development of grid-scale energy storage technologies to minimize the fossil fuel consumption. Aqueous zinc (Zn) metal batteries (ZMBs) have been prospected as appealing choices for enabling more economical and large-scale battery systems due to their abundant reserves, low manufacturing cost, high safety and intrinsic merits of Zn metal including high theoretical capacity (820 mAh g − 1 and 5855 mAh mL − 1 ) and low redox potential (− 0.76 V versus the standard hydrogen electrode) 1 – 5 . However, in terms of the stationary energy storage applications in cold climates or high-latitude regions rich in renewable energy, the ZMBs suffer from severe performance degradation and even fail to work due to the solidification of the aqueous electrolyte and deteriorated electrode/electrolyte interphase at subzero temperatures 6 – 9 . The hydrogen (H)-bonds between water molecules become stronger as temperature drops, which drives the disordered water into ordered ice 10 , 11 . Thus, tuning the electrolyte compositions to break the intermolecular H-bonds in water has been regarded as a general principle to prevent water from solidifying. In this respect, the prevailing research focuses on the following three approaches: i ) employing concentrated aqueous electrolyte that can provide abundant ions to bond with O–H in water 7,12−14 ; ii ) introducing additives/cosolvents to reform H-bonds with water 8,15−18 ; iii ) fabricating hydrogel composed of cross-linked hydrated polymer to intensify the interaction with water 19 , 20 . These strategies have enabled the water-based electrolyte with good low-temperature adaptability, but the cycling life of low-temperature Zn metal anode is generally limited to hundreds of hours, which is far from satisfactory for practical implementation. The chemically instable nature of Zn metal against water causes the continuous and slow H 2 reaction at low temperatures. This can result in the local enhancement of OH − concentration, which in turn corrodes the Zn metal surface through formation of loose and plate-like passivation film, leading to uncontrolled Zn dendrite growth and eventual cell failure 21 – 23 . In this scenario, building dense solid electrolyte interphase (SEI) that can block water penetration is the most effective route to suppress the parasitic reactions and ensure durable Zn metal anodes 2 , 12 . However, learning from the former experiences on low-temperature lithium (Li) batteries 24 – 26 , the interface kinetics associated with Zn 2+ desolvation and conduction are extremely sluggish at low temperatures, which are mainly responsible for the poor cycling performance. Compared with Li-ions, it is more challenging for the bivalent Zn-ions to cross the as-formed SEI at subzero temperatures, thus resulting in huge cell impedance, non-uniform deposition and severe capacity decay. Therefore, regulating the components and distribution of the as-formed SEI on Zn surface to lower the kinetic barrier of Zn 2+ desolvation and its transport through the SEI is the key premise for achieving ultra-stable cycling behaviors under low-temperature condition, however, has rarely been explored. The engineering of electrolyte chemistry can simultaneously mitigate the two issues of low-temperature ZMBs including water solidification and SEI-related kinetics, which is also the simplest approach that could be easily adapted to practical applications. Herein, trimethyl phosphate (TMP) was selected as a cosolvent into the aqueous electrolyte for safe and anti-freezing ZMBs in view of its high Gutmann donor number, fire retardance, low viscosity and miscibility with water 27 – 29 . With a volume ratio of 40%, TMP can greatly break the H-bonds in water through interacting with water that endows the hybrid electrolyte with a low freezing point of − 56.8 o C and a high ionic conductivity of 0.85 mS cm − 1 at − 50°C. Both the experimental characterizations and calculation results reveal that the TMP addition can regulate the Zn 2+ solvation structure to in situ form gradient SEI composed of outer ZnF 2 and inner Zn 3 (PO 4 ) 2 (Fig. 1 ), which can promote the desolvation of Zn 2+ on the interface and facilitate rapid transport across the SEI, respectively. As a result of the joint effects, it achieves an average Coulombic efficiency of 99.9% over 3800 cycles at − 30°C and remarkable durability over 6000 hours at − 50°C, which represent the best low-temperature ZMBs performance to the best of our knowledge. Furthermore, high-capacity full cells with KVOH as cathode were also demonstrated with superb capacity retention ability. Results Exploring optimal formulation for low-temperature aqueous electrolyte A series of TMP/water hybrid electrolytes with 2 M zinc trifluoromethanesulfonate (Zn(OTf) 2 ) were prepared, where the volume percentage of TMP ranges from 0%, 5%, 10%, 20%, 40%, 60%, 80–100%, and the corresponding electrolyte is marked as TMP–0, TMP–5, TMP–10, TMP–20, TMP–40, TMP–60, TMP–80 and TMP–100, respectively. After 3 h of resting at − 50 o C, the TMP–40, TMP–60 and TMP–80 can maintain the liquid state without deposit or phase separation, whereas crystallization/solidification was observed in the other counterparts (Fig. 2 a). Further, the differential scanning calorimeter (DSC) curves show the freezing points of the hybrid electrolytes are lowered to − 56.8°C as the TMP content reaches 40% (Fig. 2 b and Supplementary Fig. 1), which can be explained by the breakage of H-bonds network in water molecules by TMP co-solvent. On the other hand, the ionic conductivity negatively correlates to the content of TMP in the temperature ranging from − 30 o C to 60 o C (Fig. 2 c, Supplementary Fig. 2 and Supplementary Table 1), possibly due to a slight increase in electrolyte viscosity. However, the TMP–0 exhibits a sudden drop in ionic conductivity below − 30 o C, because of the high freezing point (− 34.8 o C in DSC) that causes the electrolyte solidification. In sharp contrast, the TMP–40 exhibits a slow decline in ionic conductivity as the temperature decreases and achieves a high ionic conductivity of 0.85 mS cm − 1 even at − 50°C (> 0.1 mS cm − 1 ) 26 , several orders of magnitude higher than that of TMP–0. To explore the molecular interaction within the hybrid electrolytes, a series of spectroscopic characterizations were performed. The Raman peaks associated with O–H stretching vibration of water molecules are visible within the range from 3100 to 3800 cm − 1 , which can be divided into three peaks including strong, weak and non H-bonds (Fig. 2 d, e, and Supplementary Figs. 3–4) 7 , 30 . It was found that the probability of non-H bonds increases with TMP content, while the change of strong-H bonds shows the opposite trend (Fig. 2 f). Notably, as the TMP content was increased to 40%, the percentage of non H-bond almost reaches the maximum. Moreover, the Fourier transform infrared (FTIR) results in Supplementary Fig. 5 show that the O–H and C–H stretching vibration modes experience significant blueshifts and redshifts with the increase of TMP, respectively, largely ascribed to the breakage of H-bond in water along with the H-bond formation between TMP and water in the hybrid electrolyte 8 . This can be further confirmed by the 1 H nuclear magnetic resonance (NMR) spectra (Fig. 2 g and Supplementary Fig. 6), wherein the 1 H from H 2 O and TMP both chemical shift to low field with the increase of TMP. These results reveal that the TMP can interact with water to reform H-bonds, during which the H-bonds in water were largely destroyed, thus affording a low freezing point and high ionic conductivity of the hybrid electrolyte at low temperatures. To maximally inherit the unique merits of aqueous electrolyte, TMP–40 is considered as the optimal electrolyte formulation for low-temperature ZMBs. Also, the TMP–40 endows the separator with high fire retardance (Supplementary Fig. 7), indicating the hybrid electrolyte is safe enough to operate. Solvation Structure And Sei Characterization Since the SEI components highly depend on the solvation sheath of Zn 2+ , we furthered the study of Zn 2+ solvation structure in a series of TMP/H 2 O electrolytes through theoretical calculations and experimental characterizations. The Raman characterizations shows the SO 3 stretching band in the OTf − –anions experiences a gradual shift with the increase of TMP concentration (Fig. 3 a and Supplementary Fig. 8). The broad peaks can be well fitted into three peaks at ~ 1028 cm − 1 , ~ 1033 cm − 1 and ~ 1040 cm − 1 , corresponding to the free anion (FA, OTf − ), solvent-separated ion pairs (SSIP, Zn 2+ –(H 2 O) x (TMP) y –OTf − ) and contact ion pairs (CIP, Zn 2+ –OTf − ), respectively 31 , 32 , as shown in Supplementary Fig. 9. By calculating the peak area ratio, the CIP percentage increases with the increase of TMP concentration and reaches the maximum value of 51.92% with 40% of TMP (Supplementary Fig. 10), indicating OTf − anion is involved in the Zn 2+ solvation sheath. Afterwards, the CIP content decreases with the increase of TMP, possibly due to the strong binding of TMP and Zn 2+ that causes more TMP to enter the Zn 2+ solvation sheath by substituting partial OTf − anions. Meanwhile, there is a V-shape relationship between FA percentage and TMP concentration, where the lowest FA ratio is 6.59%, suggestive of more OTf − involved in the solvated structure of Zn 2+ . This also confirms that TMP–40 is the optimized electrolyte formulation for in-situ formation of favorable SEI to suppress side reactions and facilitate Zn 2+ transport. For the Raman spectra of the TMP, the P–O–(C) symmetric stretching vibration gradually blueshifts as the increase of TMP (Fig. 3 b and Supplementary Fig. 11), indicating more TMP participates in the Zn 2+ solvation shell 33 , 34 , according well with the above results. This is also supported by the higher binding energy of Zn 2+ –TMP complex (− 200.36 KJ mol − 1 ) compared with Zn 2+ –H 2 O complex (− 104.54 KJ mol − 1 ), as shown in Supplementary Fig. 12. To ascertain the coordination number of anions and solvents in the solvation sheath of TMP–40, molecular dynamic (MD) simulations were carried out. The numbers of Zn 2+ , OTf − , TMP and H 2 O in the hybrid electrolytes are summarized in Supplementary Table 2. As shown by the snapshots from the simulated solvation structure (Supplementary Figs. 13–14), some water molecules are squeezed out of the Zn 2+ solvation shell in the TMP–40 electrolyte and partially replaced with TMP solvent and OTf − anions. According to the radial distribution functions (RDF) in Fig. 3 c, the Zn–O peak in OTf − , TMP and H 2 O correspond to the distance of 0.19, 0.25 and 0.23 nm, respectively, further validating that the OTf − , TMP and H 2 O molecules incorporate into the first solvation shell of Zn 2+ . Accordingly, the respective coordination number was calculated to be 0.85, 0.14 and 5.01, constituting a CIP–type solvation shell of Zn 2+ [H 2 O] 5.01 [TMP] 0.14 [OTf − ] 0.85, which favors the in-situ formation of SEI on Zn surface through reductive decomposition. Note that the small amount of TMP and OTf − involved in the solvation shell is beneficial to form a thin SEI layer, which facilitates fast Zn 2+ transfer. Moreover, the Zn 2+ desolvation energy of TMP–0 and TMP–40 can be obtained by extracting the respective R ct before cycling, where no SEI was formed on Zn surface. As shown in Supplementary Fig. 15, the addition of TMP causes a slight increase in the energy barrier for dissociation of Zn 2+ , largely ascribed to the strong interaction of Zn 2+ –TMP and Zn 2+ –OTf − , which in turn allows for the stepwise formation of ZnF 2 –Zn 3 (PO 4 ) 2 . With the TMP–40 as the optimal electrolyte formulation, the linear sweep voltammetry (LSV) measurements were first performed to examine the electrochemical stability. It was found that the TMP–40 electrolyte can effectively suppress the water decomposition over a wide electrochemical window and prevent Zn surface corrosion (Supplementary Figs. 16–17). Moreover, the disappearance of the cathodic peak at ~ 0.1 V accompanied with the decrease in current density after five cycles also indicates the SEI was formed at the initial plating and can inhibit the hydrogen evolution reaction (HER) (Supplementary Fig. 18). After 40 cycles of stripping/plating of Zn metal, X-ray diffraction (XRD) peaks corresponding to the zinc triflate hydroxide hydrate (Zn x OTf y (OH) 2x−y ·nH 2 O, ZOTH) were detected on the Zn surface in TMP–0 (Supplementary Fig. 19), which can largely restrict the transport of Zn 2+ and lead to dendrite growth 31 , 35 . In contrast, no byproduct was observed in TMP–40. X-ray photoelectron spectroscopy (XPS) with Ar ion sputtering was further employed to determine the depth distribution of composition in SEI formed on Zn surface. As shown in Fig. 3 d, the top SEI layer (before sputtering) is rich in –CF 3 species (~ 688.8 eV) and inorganic ZnF 2 (~ 684.1 eV) with a tiny amount of Zn 3 (PO 4 ) 2 (~ 134.3 eV). Accordingly, the lattice fringes in the high-resolution transmission electron microscopy (HRTEM) corresponding to the planes of ZnF 2 and Zn 3 (PO 4 ) 2 were clearly observed with uniform distribution (Fig. 3 e, f and Supplementary Fig. 20), consistent with the XPS results. Based on the previous reports 28 , 31 , the –CF 3 species arises from either the incomplete reduction of OTf − or the residual salt on Zn surface, while ZnF 2 and Zn 3 (PO 4 ) 2 are attributed to the decomposition product of Zn 2+ –OTf − and Zn 2+ –TMP complexes. As the sputtering continues, the peak intensity of Zn 3 (PO 4 ) 2 distinctly becomes stronger along with the decrease in ZnF 2 peak (Fig. 3 d and Supplementary Fig. 21). After 310 s of sputtering, the Zn 3 (PO 4 ) 2 gradually becomes the major composition in the SEI. In sharp contrast, no F or P signals related to ZnF 2 or Zn 3 (PO 4 ) 2 was detected in TMP–0 (Supplementary Fig. 22). The XPS analyses provide strong evidences that the TMP–40 electrolyte favors the in-situ formation of gradient interlayer on Zn surface, where ZnF 2 and Zn 3 (PO 4 ) 2 dominates the surface layer and inner layer, respectively. The Kinetic Behavior Of Bivalent Zn On The Electrode/electrolyte Interface As aforementioned, the SEI with rapid Zn 2+ transport kinetics and low Zn 2+ desolvation energy is beneficial for ZMBs to stably work at low temperatures. Thus, we performed temperature-dependent electrochemical impedance spectroscopy (EIS) of Zn||Zn cells at temperature ranging from 20 o C to − 30 o C in TMP–0 and TMP–40 after 40 cycles (Supplementary Fig. 23), where a dense SEI should be formed in TMP–40. The charge transfer resistance (R ct ) and the resistance associated with Zn 2+ crossing SEI (R SEI ) can be extracted from the semicircles in mid-frequency region and the high-frequency region, respectively 24 – 26 . By Arrhenius-fitting R ct and R SEI over 1000/T, the activation energy of each interface process were obtained, as shown in Fig. 4 a, b. Compared with TMP–0, the desolvation energy of Zn 2+ in the TMP–40 was greatly reduced (70.2 KJ mol − 1 vs 54.8 KJ mol − 1 ), indicating the outer ZnF 2 facilitate Zn 2+ desolvation, agreeing with the reported results 36 , 37 . Moreover, the activation energy for Zn 2+ transport through the SEI in TMP–40 (E a,SEI =52.7 KJ mol − 1 ) is significantly lower than in TMP–0 (E a,SEI =64.3 KJ mol − 1 ). This can be well explained by the density functional theory (DFT) calculation results that the Zn 3 (PO 4 ) 2 delivers a much smaller migration energy barrier for Zn 2+ (0.38 eV) (Fig. 4 d) and higher affinity with Zn 2+ (− 1.15 eV) (Fig. 4 c) compared with those of ZnF 2 (1.12 eV for Zn 2+ transport and weak binding energy of − 0.85 eV with Zn 2+ ). That is, the rich Zn 3 (PO 4 ) 2 in the inner SEI serves as the dominant channels for the desolvated Zn 2+ across the SEI to deposit on the Zn surface, which can facilitate fast Zn 2+ conduction to mitigate voltage polarization under cold environments 38 , 39 . Moreover, we prepared SEI containing single ZnF 2 or Zn 3 (PO 4 ) 2 to confirm their respective role (Supplementary Fig. 24). Besides, the interface impedance of Zn||Zn cells in the TMP–40 electrolyte can remain stable after 500 cycles, indicating the stable interface due to the formation of ZnF 2 –Zn 3 (PO 4 ) 2 interlayer (Fig. 4 e). In sharp contrast, the TMP–0 electrolyte shows a sharp decrease in the interfacial impedance after 100 cycles, possibly due to the dendrite growth that causes the cell short circuit (Fig. 4 f). In addition, a high mechanical integrity is indispensable for SEI to ensure the long-term cycling and high-capacity plating. To this end, in-situ optical microscopy was performed to observe the morphology evolution at different plating stages. As shown in Fig. 4 g, the TMP–40 electrolyte enables the dense deposition without dendrite formation during the whole deposition process and can maintain a smooth surface even at a colossal loading of 50 mAh cm − 2 . While for the case of TMP–0, uneven spots appear at 10 mAh cm − 2 and gradually evolve into discontinuous islands as the plating capacity increases, which is consistent with the scanning electron microscopy (SEM) results (Supplementary Fig. 25). The striking contrast in morphology evolution demonstrates that the gradient SEI can effectively suppress the dendrite growth and is highly stable to accommodate the high-loading Zn plating, largely ascribed to the strong bulk modulus of Zn 3 (PO 4 ) 2 37 . Taken together, we reasonably conclude that the rich ZnF 2 on the top layer of SEI favors the desolvation of Zn 2+ and the robust Zn 3 (PO 4 ) 2 predominating the inner SEI layer facilitates rapid Zn 2+ transport. With these admirable characters, it is expected that the as-formed gradient ZnF 2 –Zn 3 (PO 4 ) 2 SEI can guarantee stable and long-term cycling of Zn metal at low temperatures. Electrochemical Performance Of Zn Metal Anodes Under Harsh Conditions It is worth mentioning that these features of the gradient SEI can allow the symmetric Zn cells to stably cycle in the TMP–40 electrolyte at a high current density of 5 mA cm − 2 at 25 o C and 45 o C (Fig. 5 a and Supplementary Fig. 26). In sharp contrast, the cells in TMP–0 quickly failed due to severe Zn dendrite formation and aggravated side reactions. This also manifests that the gradient ZnF 2 –Zn 3 (PO 4 ) 2 SEI is ultra-stable against the high-temperature and high-rate cycling, underscoring the significance of SEI formation on the interface. Then the galvanostatic cycling stability of Zn metal in the TMP–40 electrolyte was studied at low temperatures with different rates. When the operation temperature was fixed at − 30 o C, the cell in TMP–40 exhibits a stable voltage profile at 2 mA cm − 2 with an ultralong cycling life up to 3600 hours, which is around 40–fold improvement in cycle life (Fig. 5 b). With the superior kinetics in the electrolyte/electrode interface, the TMP–40 electrolyte enables the symmetric cells to operate over long-term cycles with high rates ranging from 5 mA cm − 2 to 15 mA cm − 2 through a transient activation (Supplementary Fig. 27). Then the cycling temperature was decreased to − 50 o C. Not surprisingly, the cell in TMP–0 cannot work due to the electrolyte solidification (Fig. 5 c). While the TMP–40 electrolyte achieves an ultralong lifespan at 0.4 mA cm − 2 and 0.4 mAh cm − 2 without obvious fluctuation in overpotential over 6000 hours (~ 8 months). As the discharge depth was increased to 1 mAh cm − 2 , it is amazing to find that the cell can still maintain an impressive stability without voltage fluctuation over 6000 hours (Supplementary Fig. 28). These observations convectively demonstrate that the as-formed gradient ZnF 2 –Zn 3 (PO 4 ) 2 SEI with the unique configurations can accelerate the rapid Zn 2+ desolvation and conduction at low temperatures, which guarantees the ultra-stable cycling with a negligible polarization at rather extreme conditions (low temperatures with high rates). Notably, the Zn||Zn symmetric cells in TMP–40 achieve a rather competitive cumulative capacity over a wide temperature range (Fig. 5 d and Supplementary Table 3), far outperforming those of reported low-temperature aqueous Zn metal anodes 8 , 13 , 17 , 19 , 40 , 41 . Both top and side views reveal that the surface of Zn electrode after 100 plating/stripping cycles in TMP–40 is highly homogeneous and tightly packed, while the one with TMP–0 exhibits severe cracks (Fig. 5 e, f), indicating the gradient SEI layer can effectively suppress the Zn dendrite growth. The reversibility of Zn plating/stripping was further studied by calculating the Coulombic efficiency (CE) of Zn metal onto titanium (Ti) substrate. At − 30°C with a current density of 1 mA cm − 2 and a capacity of 0.5 mAh cm − 2 , the CE in TMP–40 electrolyte quickly increases to 99% within 20 cycles and stabilizes at 99.9% over 3800 cycles along with flat voltage profiles (Fig. 5 g and Supplementary Fig. 29). Conversely, the cell with TMP–0 electrolyte exhibits a low CE of around 60% and quickly short circuited at the 9th cycle due to dendrite formation. These contrasts can be maximized at different temperatures ranging from 45°C to − 50°C (Supplementary Fig. 30), well illustrating that the gradient SEI layer is stable against the severe side reaction and maintains superior kinetics at low temperatures. Electrochemical Performance Of Zn–kvoh Full Cells Under Practical Conditions To evaluate the practical applications of TMP–40 electrolyte, KVOH was employed as cathode to pair with Zn metal for full cells in the TMP–40 electrolyte due to its superior kinetics (Supplementary Fig. 31). The Zn–KVOH full cell with TMP–40 electrolyte delivers an initial capacity of 329.1 mAh g − 1 at 5 A g − 1 and retains a capacity of 323.6 mAh g − 1 after 2300 cycles at room temperature (Fig. 6 a), corresponding to a capacity retention of 98.3%. In contrast, the cell with TMP–0 electrolyte exhibits a slightly higher initial capacity of 344.4 mAh g − 1 at 5 A g − 1 possibly due to a higher ionic conductivity, but quickly dropped to 211 mAh g − 1 after 500 cycles, along with a larger polarization in the charge–discharge voltage profiles (Supplementary Fig. 32). The significant performance improvement is also revealed with high loadings of KVOH (6.37 mg cm − 2 and 17.6 mg cm − 2 ), at various rates (1 A g − 1 , 2 A g − 1 and 10 A g − 1 ) or even at a higher temperature (45 o C, 5 A g − 1 ), as shown in Supplementary Figs. 33–35. Impressively, with a high areal loading of KVOH up to 17.6 mg cm − 2 , the full cell still maintains an areal capacity of 4.37 mAh cm − 2 after 100 cycles, which meets the requirements of a typical commercial Li-ion battery (4.0 mAh cm − 2 ) 42 . In view of the inspiring performance, we further evaluated the application of TMP–40 electrolyte in practical situation by controlling lean electrolyte and low Zn excess. As shown in Fig. 6 b, when the KVOH loading increases to 33.75 mg cm − 2 , the cell still delivers a superhigh initial areal capacity of 9.42 mAh cm − 1 with lean E/C (6.76 µL mAh − 1 , the ratio of electrolyte volume to capacity) ratio and low N/P (3.1, the ratio of negative to positive). The corresponding energy density is calculated to be 251.2 Wh kg − 1 (based on the KVOH mass) with a high capacity retention of 93.3% after 50 cycles. The outstanding performance can be ascribed to the superior kinetics and great robustness of the ZnF 2 –Zn 3 (PO 4 ) 2 SEI that can allow large amounts of Zn 2+ to repeatedly strip and plate. Electrochemical Performance Of Zn–kvoh Full Cells At Low Temperature By virtue of the favorable SEI formation, the TMP–40 electrolyte can enable the Zn–KVOH full cells to sustain remarkable long lifespan and prominent stability at subzero temperatures. Specifically, when the temperature was decreased to − 30 o C (Supplementary Fig. 36), the discharge capacity of the cell in the TMP–40 electrolyte remains at 120.6 mAh g − 1 after 4000 cycles at 1 A g − 1 , far exceeding that without TMP. Even at a higher rate of 2 A g − 1 and 5 A g − 1 , the 40% of TMP addition can prompt the cell to charge/discharge reversibly over 10000 cycles and 1500 cycles, respectively. In stark contrast, the cell with TMP–0 electrolyte failed to work, underscoring the critical role of the gradient SEI formed in the TMP–40 electrolyte. These contrasts are more evident at − 50 o C, where the cell with TMP–0 cannot provide any capacities due to the electrolyte solidification. Comparatively, the TMP–40 electrolyte can render the full cell to deliver a stable capacity of 50.8 mAh g − 1 at 0.5 A g − 1 over 12000 cycles (Fig. 6 c). The fluctuations at the 800th, 5000th and 9800th cycle are ascribed to the sudden power outages during the long-term test, which also confirm the good temperature adaptivity of the gradient SEI formed in the TMP–40 electrolyte. Compared with the published works on electrolyte modification for aqueous Zn batteries, this work is undoubtedly prominent in achieving long-cycle stability over a wide temperature range (Fig. 6 d, Supplementary Tables 4–5) 4,8,12,14–17,19,22,40,41,43−46 . Post-mortem analyses show that the Zn metal anode after 1000 cycles in the TMP–40 electrolyte can maintain a much flatter and denser surface (Supplementary Fig. 37). The significant performance improvement achieved in the TMP–40 electrolyte at low temperatures strongly validates the gradient SEI with the favorable kinetics can effectively suppress the Zn dendrite growth and ensure the superb cycling behaviors in full cells under extreme conditions. The exceptional performance of the ZMBs inspired us to further evaluate the low-temperature performance of pouch cell with a size of 4.3 × 5.6 cm in the TMP–40 electrolyte. As shown in Fig. 6 e, a reversible capacity of 340.5, 159.4, 122.2 mAh g − 1 was achieved at 25 ℃ (room temperature), − 30 ℃ and − 50 ℃, respectively. Notably, the pouch cell achieves a superior cycling stability at a low temperature of − 30°C with a high capacity retention of 88.6% after 1200 cycles at 0.25 mA cm − 2 (Fig. 6 f). Even at − 50°C, it can stably cycle for 180 cycles with nearly 100% of capacity retention (Supplementary Fig. 38). Moreover, five series connected pouch cells with a voltage of ~ 5 V can drive an electro-calculagraph normally working for more than 3 min at an extreme temperature of − 50°C (Fig. 6 g and Supplementary Fig. 39), further demonstrating its promising potential in the practical applications under harsh conditions. Discussion In summary, we have successfully in-situ constructed gradient SEI layer on Zn surface to enable long-cycling and dendrite-free ZMBs at low temperatures by introducing TMP into the aqueous electrolyte. It was found that 40% of TMP addition can regulate the Zn 2+ solvation sheath and promote the formation of ZnF 2 –Zn 3 (PO 4 ) 2 gradient SEI, which effectively suppress the parasitic reaction and Zn dendrite growth. Moreover, a combination study of computational and experimental characterizations reveals the outer ZnF 2 can facilitate Zn 2+ desolvation and the inner Zn 3 (PO 4 ) 2 can serve as channels for fast Zn 2+ conduction, synergistically leading to continuous cycling under cold environments. Remarkably, a record stability was achieved in the symmetric Zn cell at − 50 o C with a lifespan of 6000 hours at a relatively high current density of 0.4 mA cm − 2 . Furthermore, the Zn–KVOH full cell delivers a stable capacity of 50.8 mAh g − 1 at 0.5 A g − 1 over 12000 cycles at − 50 o C. Full cells with lean electrolyte and low Zn excess also demonstrate the practical feasibility. This work provides a feasible route to achieve highly stable ZMBs under extreme conditions. Methods Electrolyte preparation Zinc trifluoromethanesulfonate (Zn(OTf) 2 , > 99%) and trimethyl phosphate (TMP, 98%) was purchased from Adamas and Sigma-Aldrich, respectively. A series of electrolytes were formulated by dissolving 2 M Zn(OTf) 2 in deionized (DI) water with different volume ratios of TMP from 0%, 5%, 10%, 20%, 40%, 60%, 80–100%. The corresponding electrolyte is marked as TMP–0, TMP–5, TMP–10, TMP–20, TMP–40, TMP–60, TMP–80 and TMP–100, respectively. Fabrication Of Kvoh Cathode The synthesis of KVOH was based on a previous method, as reported by Gao 1 . Specifically, 0.364 g of vanadium pentoxide (V 2 O 5 , 99%, Sigma Aldrich) in 50 ml DI water was mixed with 0.0745 g of potassium chloride (KCl, 99.9%, Sigma Aldrich) in 30 mL DI water, followed by addition of 1.7 mL hydrogen peroxide (H 2 O 2 , 35%, Fisher Scientific) and 0.5 h of stirring. Then the mixture was transferred into 100 mL Teflon autoclave and heated at 120°C for 6 h. The green powder was collected by centrifugation, repeated wash with DI water and ethanol, and drying overnight at 60°C. Preparation Of Znf@zn And Zn(Po)@zn According to the previous report 2 , ZnF 2 @Zn was obtained by chemically treating Zn foil with Ammonium fluoride (NH 4 F, 99.99%, Aladdin) dispersed in the dimethyl sulfoxide (DMSO, 99.9%, Innochem) solvents. First, 5 mg NH 4 F was dispersed in 6 mL DMSO under vigorous stirring for 3 days and then dropped onto the Zn surface, followed by rapidly drying in glove box at 180°C for 10 min. The above operation was repeated 10 times to obtain uniform ZnF 2 @Zn. The Zn 3 (PO 4 ) 2 @Zn was obtained through the chemical reaction between Zn and Diammonium hydrogen phosphate aqueous solution. First, 66 mg Diammonium hydrogen phosphate ((NH 4 ) 2 HPO 4 , 99.9%, Macklin) was dissolved in 10 mL deionized water to obtain 0.05 M (NH 4 ) 2 HPO 4 aqueous solution. Second, Zn plates (φ = 12 mm) were immersed into the above solution under stirring for 5 h, followed by repeated washing and drying at 80°C for standby. Material Characterizations Differential scanning calorimetry (DSC, METTLER TOLEDO DSC3) was used to measure the freezing point of the hybrid electrolyte at a temperature range from − 150 o C to 25 o C, which was carried out in a liquid nitrogen cooling system with a heating rate of 5°C min − 1 . Fourier Transform Infrared (FT-IR) analysis was conducted on Nicolet iS50. Raman spectroscopy was recorded on LabRAM HR Evolution with an excitation wavelength of 633 nm. The changes of hydrogen bonds were analyzed by nuclear magnetic resonance (NMR, AVANCE III 400MHz) with deuterated DMSO. Scanning electron microscopy (SEM) images were collected using FEI Microscope (JSM-7900F). Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were performed on Talos F200X G2. X-ray diffraction (XRD) measurements were obtained on diffractometer (Smart Lab 9 KW) with a Cu-target X-ray tube (λ = 0.154 nm) at 150 mA and 40 kV. The compositions of solid electrolyte interphase (SEI) were determined by X-ray photoelectron spectroscopy (XPS, Axis Ultra DLD) using monochromatic 1486.7 X-ray source. Electrode Preparation For the coin cell, the as-prepared KVOH was mixed with super P carbon black (SUPER P, TIMCAL) and polyvinyldifluoride (PVDF, Sinopharm) based on a weight ratio of 7:2:1 (routine test) or 8:1:1 (high loading test), which was dispersed in N-methyl-2-pyrrolidinone (NMP, Sinopharm) to form a slurry. Then the slurry was casted onto carbon paper disks with a diameter of 10 mm and dried overnight at 60°C in a vacuum oven. The preparation procedures of KVOH cathode for punch cells were similar to the above description, except the electrode size is 4.3 × 5.6 cm. Electrochemical Measurements 2032-type coin cells were assembled to measure the Coulombic efficiency and cycling stability of Zn metal anode (100 µm) on standard battery tester (LAND-CT2001A) at different temperatures controlled by cryostat (− 50 o C), fridge (− 30 o C) and oven (25 o C, 45 o C). The separator used was glass fiber (90 µm in thickness, Waterman GF/D). The cycling stability was evaluated in symmetric cells composed of two identical Zn disks in the electrolyte of TMP–0 and TMP–40 at different current densities and capacities. For the measurement of Coulombic efficiency, the coin cells were composed of a titanium (Ti) foil as working electrode (substrate for Zn plating and stripping), and a piece of Zn foil as counter and reference electrode. A constant current with a constant capacity (the amount of Zn deposited) was applied to the electrode, followed by Zn stripping via charging to 1 V (versus Zn/Zn 2+ ). The Coulombic efficiency of each cycle was calculated as the amount of Zn stripped (based on capacity extracted) divided by the amount of Zn plated (based on capacity deposited) onto the Ti foil. Linear sweep voltammetry (LSV) of the hybrid electrolytes was measured using Ti||Zn asymmetric at a scan rate of 5 mV s − 1 in a voltage range of − 0.5 ~ 3 V (versus Zn/Zn 2+ ) on an electrochemical workstation (Ivium-n-Stat, Nederlanden). The ionic conductivity of hybrid electrolytes at different temperatures was measured by EIS via symmetrical cells consisted of two parallel Pt-plate electrodes (10 mm×10 mm). The distance between two electrodes is 10 mm and the applied frequency range was from 10 5 Hz to 10 − 1 Hz with 5 mV AC amplitude. The ionic conductivity of hybrid electrolyte was calculated by the following equation: Where σ is the ionic conductivity of the electrolyte (S cm − 1 ), R s is the electrolyte resistance (Ω), which corresponds to the intercept of Nyquist plot. L (cm) is the distance between two Pt-plate electrodes. A (cm 2 ) stands for the area of Pt electrode. The electrochemical performance of Zn–KVOH full cell was evaluated by using both 2032-type coin-cell and pouch-cell. For the routine test of coin-type full cell, the typical mass loading of active materials (KVOH) is around 1.2 ~ 1.5 mg cm − 2 , glass fiber (GF/D, 90 µm in thickness) as separator and 100 µm Zn metal as anode. The electrolyte was fixed to around 130 µL. The galvanostatic discharge/charge tests were performed using LAND-CT2001A instruments in a voltage range of 0.2–1.6 V (vs Zn/Zn 2+ ). Electrochemical impedance spectroscopy (EIS) measurements were carried out on an electrochemical workstation (Ivium-n-Stat, Nederlanden) from 10 5 Hz to 10 − 2 Hz, and the perturbation amplitude was 5 mV. All the tests at different temperatures were carried out after 2 hours of resting. For the test of coin-type full cell with high-loading cathode (33.75 mg cm − 2 ), we used carbon cloth as current collector, thin glass fiber (GF/A, 55 µm in thickness) as separator, 50 µm Zn metal as anode and the lean electrolyte (50 µL) is dropped on the cathode side. Computational Details Molecular dynamics simulations In this work, the solvation environment of TMP–0 (molar ratio, Zn(OTf) 2 :H 2 O = 1:27.79) and TMP–40 (molar ratio, Zn(OTf) 2 :TMP:H 2 O = 1:1.74:16.67) were simulated. The TMP–0 model system involves 70 Zn(OTf) 2 salt molecules and 1945 H 2 O molecules, while the TMP–40 one contains 70 Zn(OTf) 2 salt molecules, 122 TMP molecules, and 1167 H 2 O molecules. Packmol 3 was used to build initial configuration of the two model systems. LAMMPS 4 was used to perform the molecular simulations. All atom molecular dynamics simulations were carried out using PCFF-INTERFACE force field 5 . Constant NVT conditions are enforced using a Nosé-Hoover thermostat with a relaxation time of 100 fs and a temperature of 300 K 6 . The density of each electrolyte solution was determined from 500 ps molecular dynamics simulation in the NPT ensemble at the same thermodynamic conditions. Equations of motions were integrated using the velocity–Verlet method with a 1.0 fs time step. The cut-offs for all the non-bonded interactions are 12 Å. All results reported here are statistical averages taken from runs of 1000 ps in length, each preceded by 1500 ps of equilibration. The atomic coordinates were collected every 1.0 ps for statistical analysis. Quantum Chemistry Calculations For the relative binding energy of Zn 2+ with different species, the structures were fully optimized by using the B3LYP 7 , 8 method in the level of 6–31 + + G (d, p) basis set. Analytical vibrational frequency was calculated at the same level. The Zn 2+ cation carries two unit of positive charge. The interaction energy was calculated as following: ΔE inter = E total – (E Zn + E solvent ) (2) ΔE inter represents the interaction energy, E total , E zn and E solvent are the energies of the complex, Zn 2+ cation, and solvent (H 2 O or TMP), respectively. The more negative the magnitude of interaction energy, the more favorable the interaction between the Zn 2+ cation and the solvent is. All calculations were performed with the Gaussian 09 program. For the migration energy barrier of zinc ions between different components, we have employed the Vienna Ab initio Simulation Package (VASP) to perform all density functional theory (DFT) calculations within spin-polarized frame 9 , 10 . The elemental core and valence electrons were represented by the projector augmented wave (PAW) method and plane–wave basis functions with a cutoff energy of 400 eV. Generalized gradient approximation with the Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation functional was employed in all the calculations 11 , 12 . Geometry optimizations were performed with the force convergency smaller than 0.05 eV/Å, where the same convergency were applied for the locating of transition states through the constrained optimizations (NEB). The atoms at bottom of Zn 3 (PO 4 ) 2 (− 121) surfaces (43 atoms) and the ZnF 2 (111) surfaces (44 atoms) were fixed in all the calculations. Monkhorst-Pack k-points of 3×2×1 and 2×2×1 were applied for all the surface calculations for Zn 3 (PO 4 ) 2 (− 121), and ZnF 2 (111), respectively. To obtain transition states, the bulk structures of Zn 3 (PO 4 ) 2 and ZnF 2 (111) have been optimized with the Monkhorst-Pack k-point of 3×3×3 and 5×3×8, respectively. Declarations Acknowledgements This work was supported by the Ministry of Science and Technology of China (2021YFA1201900), National Natural Science Foundation of China (No. 22105107) and Fundamental Research Funds for the Central Universities (No. 020/C029201005). We thank the Haihe Laboratory of Sustainable Chemical Transformations for financial support. H.W. acknowledge the Young Elite Scientists Sponsorship Program by Tianjin. Author contributions H.W. and W.W. conceived the original idea. W. W., F. W. and H. W. designed all the experiments. W. W., S. C., X. L. and J. C. carried out the experiments. W. W., S. C., X. L., R. H., Y. W., F. W. and H. W. analyzed the experimental data. W. W., F. W. and H. W. co-wrote the paper. All authors were involved in discussion of the experimental results and preparing of the manuscript. Competing interests The authors declare no competing interests. References Wang, F. et al. Highly reversible zinc metal anode for aqueous batteries. Nat. 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S., Li, D., Deng, T., Li, Q. & Wang, C. S. Hydrophobic organic-electrolyte-protected zinc anodes for aqueous zinc batteries. Angew. Chem. Int. Ed. 59 , 19292–19296 (2020). Zeng, X. H. et al. Electrolyte design for in situ construction of highly Zn 2+ -conductive solid electrolyte interphase to enable high-performance aqueous Zn-ion batteries under practical conditions. Adv, Mater. 33 , 2007416 (2021). Hou, Z., Lu, Z. H., Chen, Q. W. & Zhang, B. Realizing wide-temperature Zn metal anodes through concurrent interface stability regulation and solvation structure modulation. Energy Storage Mater. 42 , 517–525 (2021). Zhou, J. et al. Highly Reversible and Stable Zn Metal Anode under Wide Temperature Conditions Enabled by Modulating Electrolyte Chemistry. Chem. Eng. J. 442 , 136218 (2022). Zhang, L. et al. Enhanced polysulfide regulation via porous catalytic V 2 O 3 /V 8 C 7 heterostructures derived from metal – organic frameworks toward high-performance Li – S batteries. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2143664","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":145521223,"identity":"4b1ed9a3-9c30-406b-a71f-70d9c79fb9cc","order_by":0,"name":"Wei Wang","email":"","orcid":"","institution":"Nankai University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Wei","middleName":"","lastName":"Wang","suffix":""},{"id":145521224,"identity":"9f5ab171-95ea-4a87-9758-10260580ab3b","order_by":1,"name":"Shan Chen","email":"","orcid":"","institution":"Nankai 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ZnF\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e-Zn\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e(PO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e)\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e interlayer formed in the hybrid electrolyte to facilitate the Zn\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+ \u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003edesolvation and conduction across the SEI for dendrite-free Zn deposition at subzero temperatures.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/b8a732771fe26fb8a818630f.jpg"},{"id":28050778,"identity":"de301f48-6cee-4546-950d-8acc4b4ab6ec","added_by":"auto","created_at":"2022-10-20 17:13:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":793533,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterizations of the TMP/water hybrid electrolytes with different TMP contents to explore the optimal formulation for low-temperature ZMBs.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e The photographs of hybrid electrolytes at 25 °C (top) and −50 °C (bottom). \u003cstrong\u003eb\u003c/strong\u003e DSC curves to obtain the freezing points. \u003cstrong\u003ec\u003c/strong\u003e Ionic conductivities at different temperatures. \u003cstrong\u003ed\u003c/strong\u003e The Raman spectra of O–H stretching vibration. \u003cstrong\u003ee\u003c/strong\u003e The fitted O–H stretching vibration of TMP–40 electrolyte. \u003cstrong\u003ef\u003c/strong\u003e Ratios of strong H-bond and non H-bond water with TMP content in the hybrid electrolyte. \u003cstrong\u003eg\u003c/strong\u003e \u003csup\u003e1\u003c/sup\u003eH chemical shift of water with different TMP contents.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/97b6912b070c7603d57294c6.png"},{"id":28050775,"identity":"8473fc70-3c78-45cb-91aa-9216ac972870","added_by":"auto","created_at":"2022-10-20 17:13:45","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1161537,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterizations of Zn\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e solvation structure and the in-situ SEI components.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e SO\u003csub\u003e3\u003c/sub\u003e stretching mode in Raman spectra for different hybrid electrolytes. \u003cstrong\u003eb\u003c/strong\u003e The P–O–(C) symmetric stretching vibration\u003cstrong\u003e \u003c/strong\u003eof\u003cstrong\u003e \u003c/strong\u003edifferent hybrid electrolytes. \u003cstrong\u003ec\u003c/strong\u003e Profiles of radial distribution function g(r) (solid line) and its integral that represents the coordination number (dash-dotted line) of Zn\u003csup\u003e2+ \u003c/sup\u003ewith\u003csup\u003e \u003c/sup\u003eO in different components of TMP–40 electrolyte. \u003cstrong\u003ed\u003c/strong\u003e XPS F 1s and P 2p spectra with increasing sputtering time. \u003cstrong\u003ee\u003c/strong\u003e HRTEM images of Zn surface after cycling by Zn||Zn symmetric cells with TMP–40 electrolyte. \u003cstrong\u003ef\u003c/strong\u003e Element distribution of SEI formed on the Zn surface in TMP–40 electrolyte.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/54764eb6357e60a6bf869a92.png"},{"id":28050774,"identity":"b8786100-54fe-414f-a50a-25892527e9df","added_by":"auto","created_at":"2022-10-20 17:13:45","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1607301,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eProperty and function study of SEI in-situ formed on Zn surface in the electrolyte of TMP–40.\u003c/strong\u003e Arrhenius curves and the activation energies of \u003cstrong\u003ea\u003c/strong\u003e R\u003csub\u003eSEI\u003c/sub\u003e and \u003cstrong\u003eb\u003c/strong\u003e R\u003csub\u003ect\u003c/sub\u003e derived from the Nyquist plots of Zn||Zn cells with TMP–0 or TMP–40 electrolyte after 40 cycles. \u003cstrong\u003ec\u003c/strong\u003e Adsorption energy of Zn\u003csup\u003e2+\u003c/sup\u003e with ZnF\u003csub\u003e2\u003c/sub\u003e and Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e. \u003cstrong\u003ed\u003c/strong\u003e Migration energy barrier of Zn\u003csup\u003e2+\u003c/sup\u003e across ZnF\u003csub\u003e2\u003c/sub\u003e and Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e interlayer. Electrochemical impedance spectra of Zn||Zn symmetric cells in \u003cstrong\u003ee\u003c/strong\u003e TMP–40 electrolyte and \u003cstrong\u003ef\u003c/strong\u003e TMP–0 electrolyte after different cycles. \u003cstrong\u003eg\u003c/strong\u003e In-situ optical observation of Zn deposition process in the electrolyte of TMP–0 (top) and TMP–40 (bottom). The scale bar is 200 μm.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/2adda530259803ae9345f945.png"},{"id":28051145,"identity":"bdd1c0d5-d619-4672-9456-5debcd1e7d38","added_by":"auto","created_at":"2022-10-20 17:18:45","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":736487,"visible":true,"origin":"","legend":"\u003cp\u003eGalvanostatic cycling stability of symmetrical Zn cells with TMP–40 and TMP–0 electrolytes, respectively, at a temperature of \u003cstrong\u003ea\u003c/strong\u003e 25 °C, \u003cstrong\u003eb\u003c/strong\u003e −30 °C and \u003cstrong\u003ec\u003c/strong\u003e −50 °C. \u003cstrong\u003ed\u003c/strong\u003e Comparison of the cumulative capacity at wide temperatures in our work with other reported results.\u003csup\u003e \u003c/sup\u003eTop-view (top) and cross-section (bottom) SEM images of symmetric Zn cells after 100 cycles with electrolytes of \u003cstrong\u003ee\u003c/strong\u003e TMP–0 and \u003cstrong\u003ef\u003c/strong\u003e TMP–40. \u003cstrong\u003eg\u003c/strong\u003e Long-term Zn plating/stripping CE in TMP–40 and TMP–0 electrolytes at −30 °C. Insets: the magnified views of selected cycles.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/392e648a10d5e1653cd09e0b.png"},{"id":28050777,"identity":"d5eab3f6-8d7f-4b18-9375-521fc1a90ff7","added_by":"auto","created_at":"2022-10-20 17:13:45","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1114148,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical performance of Zn–KVOHfull cells.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Cycling performance of Zn–KVOH cells in the electrolyte of TMP–0 and TMP–40 at 25 °C. \u003cstrong\u003eb\u003c/strong\u003eZn–KVOH full cell test under practical conditions with TMP–40 electrolyte. \u003cstrong\u003ec\u003c/strong\u003e Cycling performance of Zn–KVOH cells with TMP–40 electrolyte at −50 °C. \u003cstrong\u003ed\u003c/strong\u003e Comparison of the cycling performance of full cells at wide temperatures achieved in this work with those reported ones in literatures. \u003cstrong\u003ee\u003c/strong\u003e Discharge–charge curves of Zn–KVOH pouch cell with TMP–40 electrolyte at 25 °C, −30 °C and −50 °C. \u003cstrong\u003ef\u003c/strong\u003e Cycling performance of pouch cell with TMP–40 electrolyte at −30 °C. \u003cstrong\u003eg\u003c/strong\u003e Pictures of the five series connected pouch cells to drive the calculagraph working for more than 3 min at −50 °C.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/10575cbfa96e74c3e04c9a02.png"},{"id":43885875,"identity":"e23bccd4-f676-4864-b452-4a24819e90b1","added_by":"auto","created_at":"2023-09-29 15:27:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4057394,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/e5982476-61c5-4874-804c-1e8139616cd1.pdf"},{"id":28050779,"identity":"d2d92e61-18c7-43c0-9f18-3b002580d9ef","added_by":"auto","created_at":"2022-10-20 17:13:47","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":23622205,"visible":true,"origin":"","legend":"\u003cp\u003eSupporting Information\u003c/p\u003e","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-2143664/v1/736a2654f01671f45b2201cf.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Gradient Phosphatized Interphase for Ultra-Stable and Low-Temperature Zinc Metal Batteries","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe ever-increasing demand of renewable energy sources (such as solar and wind) and their fluctuating nature necessitate the development of grid-scale energy storage technologies to minimize the fossil fuel consumption. Aqueous zinc (Zn) metal batteries (ZMBs) have been prospected as appealing choices for enabling more economical and large-scale battery systems due to their abundant reserves, low manufacturing cost, high safety and intrinsic merits of Zn metal including high theoretical capacity (820 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 5855 mAh mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and low redox potential (\u0026minus;\u0026thinsp;0.76 V versus the standard hydrogen electrode)\u003csup\u003e\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. However, in terms of the stationary energy storage applications in cold climates or high-latitude regions rich in renewable energy, the ZMBs suffer from severe performance degradation and even fail to work due to the solidification of the aqueous electrolyte and deteriorated electrode/electrolyte interphase at subzero temperatures\u003csup\u003e\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe hydrogen (H)-bonds between water molecules become stronger as temperature drops, which drives the disordered water into ordered ice\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Thus, tuning the electrolyte compositions to break the intermolecular H-bonds in water has been regarded as a general principle to prevent water from solidifying. In this respect, the prevailing research focuses on the following three approaches: \u003cem\u003ei\u003c/em\u003e) employing concentrated aqueous electrolyte that can provide abundant ions to bond with O\u0026ndash;H in water\u003csup\u003e7,12\u0026minus;14\u003c/sup\u003e; \u003cem\u003eii\u003c/em\u003e) introducing additives/cosolvents to reform H-bonds with water\u003csup\u003e8,15\u0026minus;18\u003c/sup\u003e; \u003cem\u003eiii\u003c/em\u003e) fabricating hydrogel composed of cross-linked hydrated polymer to intensify the interaction with water\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. These strategies have enabled the water-based electrolyte with good low-temperature adaptability, but the cycling life of low-temperature Zn metal anode is generally limited to hundreds of hours, which is far from satisfactory for practical implementation.\u003c/p\u003e \u003cp\u003eThe chemically instable nature of Zn metal against water causes the continuous and slow H\u003csub\u003e2\u003c/sub\u003e reaction at low temperatures. This can result in the local enhancement of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration, which in turn corrodes the Zn metal surface through formation of loose and plate-like passivation film, leading to uncontrolled Zn dendrite growth and eventual cell failure\u003csup\u003e\u003cspan additionalcitationids=\"CR22\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. In this scenario, building dense solid electrolyte interphase (SEI) that can block water penetration is the most effective route to suppress the parasitic reactions and ensure durable Zn metal anodes\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. However, learning from the former experiences on low-temperature lithium (Li) batteries\u003csup\u003e\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, the interface kinetics associated with Zn\u003csup\u003e2+\u003c/sup\u003e desolvation and conduction are extremely sluggish at low temperatures, which are mainly responsible for the poor cycling performance. Compared with Li-ions, it is more challenging for the bivalent Zn-ions to cross the as-formed SEI at subzero temperatures, thus resulting in huge cell impedance, non-uniform deposition and severe capacity decay. Therefore, regulating the components and distribution of the as-formed SEI on Zn surface to lower the kinetic barrier of Zn\u003csup\u003e2+\u003c/sup\u003e desolvation and its transport through the SEI is the key premise for achieving ultra-stable cycling behaviors under low-temperature condition, however, has rarely been explored.\u003c/p\u003e \u003cp\u003eThe engineering of electrolyte chemistry can simultaneously mitigate the two issues of low-temperature ZMBs including water solidification and SEI-related kinetics, which is also the simplest approach that could be easily adapted to practical applications. Herein, trimethyl phosphate (TMP) was selected as a cosolvent into the aqueous electrolyte for safe and anti-freezing ZMBs in view of its high Gutmann donor number, fire retardance, low viscosity and miscibility with water\u003csup\u003e\u003cspan additionalcitationids=\"CR28\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. With a volume ratio of 40%, TMP can greatly break the H-bonds in water through interacting with water that endows the hybrid electrolyte with a low freezing point of \u0026minus;\u0026thinsp;56.8 \u003csup\u003eo\u003c/sup\u003eC and a high ionic conductivity of 0.85 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at \u0026minus;\u0026thinsp;50\u0026deg;C. Both the experimental characterizations and calculation results reveal that the TMP addition can regulate the Zn\u003csup\u003e2+\u003c/sup\u003e solvation structure to in situ form gradient SEI composed of outer ZnF\u003csub\u003e2\u003c/sub\u003e and inner Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which can promote the desolvation of Zn\u003csup\u003e2+\u003c/sup\u003e on the interface and facilitate rapid transport across the SEI, respectively. As a result of the joint effects, it achieves an average Coulombic efficiency of 99.9% over 3800 cycles at \u0026minus;\u0026thinsp;30\u0026deg;C and remarkable durability over 6000 hours at \u0026minus;\u0026thinsp;50\u0026deg;C, which represent the best low-temperature ZMBs performance to the best of our knowledge. Furthermore, high-capacity full cells with KVOH as cathode were also demonstrated with superb capacity retention ability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eExploring optimal formulation for low-temperature aqueous electrolyte\u003c/h2\u003e \u003cp\u003eA series of TMP/water hybrid electrolytes with 2 M zinc trifluoromethanesulfonate (Zn(OTf)\u003csub\u003e2\u003c/sub\u003e) were prepared, where the volume percentage of TMP ranges from 0%, 5%, 10%, 20%, 40%, 60%, 80\u0026ndash;100%, and the corresponding electrolyte is marked as TMP\u0026ndash;0, TMP\u0026ndash;5, TMP\u0026ndash;10, TMP\u0026ndash;20, TMP\u0026ndash;40, TMP\u0026ndash;60, TMP\u0026ndash;80 and TMP\u0026ndash;100, respectively. After 3 h of resting at \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC, the TMP\u0026ndash;40, TMP\u0026ndash;60 and TMP\u0026ndash;80 can maintain the liquid state without deposit or phase separation, whereas crystallization/solidification was observed in the other counterparts (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Further, the differential scanning calorimeter (DSC) curves show the freezing points of the hybrid electrolytes are lowered to \u0026minus;\u0026thinsp;56.8\u0026deg;C as the TMP content reaches 40% (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;1), which can be explained by the breakage of H-bonds network in water molecules by TMP co-solvent. On the other hand, the ionic conductivity negatively correlates to the content of TMP in the temperature ranging from \u0026minus;\u0026thinsp;30 \u003csup\u003eo\u003c/sup\u003eC to 60 \u003csup\u003eo\u003c/sup\u003eC (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, Supplementary Fig.\u0026nbsp;2 and Supplementary Table\u0026nbsp;1), possibly due to a slight increase in electrolyte viscosity. However, the TMP\u0026ndash;0 exhibits a sudden drop in ionic conductivity below \u0026minus;\u0026thinsp;30 \u003csup\u003eo\u003c/sup\u003eC, because of the high freezing point (\u0026minus;\u0026thinsp;34.8 \u003csup\u003eo\u003c/sup\u003eC in DSC) that causes the electrolyte solidification. In sharp contrast, the TMP\u0026ndash;40 exhibits a slow decline in ionic conductivity as the temperature decreases and achieves a high ionic conductivity of 0.85 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e even at \u0026minus;\u0026thinsp;50\u0026deg;C (\u0026gt;\u0026thinsp;0.1 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e26\u003c/sup\u003e, several orders of magnitude higher than that of TMP\u0026ndash;0.\u003c/p\u003e \u003cp\u003eTo explore the molecular interaction within the hybrid electrolytes, a series of spectroscopic characterizations were performed. The Raman peaks associated with O\u0026ndash;H stretching vibration of water molecules are visible within the range from 3100 to 3800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which can be divided into three peaks including strong, weak and non H-bonds (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, e, and Supplementary Figs.\u0026nbsp;3\u0026ndash;4)\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. It was found that the probability of non-H bonds increases with TMP content, while the change of strong-H bonds shows the opposite trend (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). Notably, as the TMP content was increased to 40%, the percentage of non H-bond almost reaches the maximum. Moreover, the Fourier transform infrared (FTIR) results in Supplementary Fig.\u0026nbsp;5 show that the O\u0026ndash;H and C\u0026ndash;H stretching vibration modes experience significant blueshifts and redshifts with the increase of TMP, respectively, largely ascribed to the breakage of H-bond in water along with the H-bond formation between TMP and water in the hybrid electrolyte\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. This can be further confirmed by the \u003csup\u003e1\u003c/sup\u003eH nuclear magnetic resonance (NMR) spectra (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg and Supplementary Fig.\u0026nbsp;6), wherein the \u003csup\u003e1\u003c/sup\u003eH from H\u003csub\u003e2\u003c/sub\u003eO and TMP both chemical shift to low field with the increase of TMP. These results reveal that the TMP can interact with water to reform H-bonds, during which the H-bonds in water were largely destroyed, thus affording a low freezing point and high ionic conductivity of the hybrid electrolyte at low temperatures. To maximally inherit the unique merits of aqueous electrolyte, TMP\u0026ndash;40 is considered as the optimal electrolyte formulation for low-temperature ZMBs. Also, the TMP\u0026ndash;40 endows the separator with high fire retardance (Supplementary Fig.\u0026nbsp;7), indicating the hybrid electrolyte is safe enough to operate.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eSolvation Structure And Sei Characterization\u003c/h3\u003e\n\u003cp\u003eSince the SEI components highly depend on the solvation sheath of Zn\u003csup\u003e2+\u003c/sup\u003e, we furthered the study of Zn\u003csup\u003e2+\u003c/sup\u003e solvation structure in a series of TMP/H\u003csub\u003e2\u003c/sub\u003eO electrolytes through theoretical calculations and experimental characterizations. The Raman characterizations shows the SO\u003csub\u003e3\u003c/sub\u003e stretching band in the OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026ndash;anions experiences a gradual shift with the increase of TMP concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;8). The broad peaks can be well fitted into three peaks at ~\u0026thinsp;1028 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, ~\u0026thinsp;1033 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and ~\u0026thinsp;1040 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to the free anion (FA, OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e), solvent-separated ion pairs (SSIP, Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003ex\u003c/sub\u003e(TMP)\u003csub\u003ey\u003c/sub\u003e\u0026ndash;OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e) and contact ion pairs (CIP, Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e), respectively\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e, as shown in Supplementary Fig.\u0026nbsp;9. By calculating the peak area ratio, the CIP percentage increases with the increase of TMP concentration and reaches the maximum value of 51.92% with 40% of TMP (Supplementary Fig.\u0026nbsp;10), indicating OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e anion is involved in the Zn\u003csup\u003e2+\u003c/sup\u003e solvation sheath. Afterwards, the CIP content decreases with the increase of TMP, possibly due to the strong binding of TMP and Zn\u003csup\u003e2+\u003c/sup\u003e that causes more TMP to enter the Zn\u003csup\u003e2+\u003c/sup\u003e solvation sheath by substituting partial OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e anions. Meanwhile, there is a V-shape relationship between FA percentage and TMP concentration, where the lowest FA ratio is 6.59%, suggestive of more OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e involved in the solvated structure of Zn\u003csup\u003e2+\u003c/sup\u003e. This also confirms that TMP\u0026ndash;40 is the optimized electrolyte formulation for in-situ formation of favorable SEI to suppress side reactions and facilitate Zn\u003csup\u003e2+\u003c/sup\u003e transport. For the Raman spectra of the TMP, the P\u0026ndash;O\u0026ndash;(C) symmetric stretching vibration gradually blueshifts as the increase of TMP (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and Supplementary Fig.\u0026nbsp;11), indicating more TMP participates in the Zn\u003csup\u003e2+\u003c/sup\u003e solvation shell\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e, according well with the above results. This is also supported by the higher binding energy of Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;TMP complex (\u0026minus;\u0026thinsp;200.36 KJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) compared with Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;H\u003csub\u003e2\u003c/sub\u003eO complex (\u0026minus;\u0026thinsp;104.54 KJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), as shown in Supplementary Fig.\u0026nbsp;12.\u003c/p\u003e \u003cp\u003eTo ascertain the coordination number of anions and solvents in the solvation sheath of TMP\u0026ndash;40, molecular dynamic (MD) simulations were carried out. The numbers of Zn\u003csup\u003e2+\u003c/sup\u003e, OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e, TMP and H\u003csub\u003e2\u003c/sub\u003eO in the hybrid electrolytes are summarized in Supplementary Table\u0026nbsp;2. As shown by the snapshots from the simulated solvation structure (Supplementary Figs.\u0026nbsp;13\u0026ndash;14), some water molecules are squeezed out of the Zn\u003csup\u003e2+\u003c/sup\u003e solvation shell in the TMP\u0026ndash;40 electrolyte and partially replaced with TMP solvent and OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e anions. According to the radial distribution functions (RDF) in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, the Zn\u0026ndash;O peak in OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e, TMP and H\u003csub\u003e2\u003c/sub\u003eO correspond to the distance of 0.19, 0.25 and 0.23 nm, respectively, further validating that the OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e, TMP and H\u003csub\u003e2\u003c/sub\u003eO molecules incorporate into the first solvation shell of Zn\u003csup\u003e2+\u003c/sup\u003e. Accordingly, the respective coordination number was calculated to be 0.85, 0.14 and 5.01, constituting a CIP\u0026ndash;type solvation shell of Zn\u003csup\u003e2+\u003c/sup\u003e[H\u003csub\u003e2\u003c/sub\u003eO]\u003csub\u003e5.01\u003c/sub\u003e[TMP]\u003csub\u003e0.14\u003c/sub\u003e[OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e]\u003csub\u003e0.85,\u003c/sub\u003e which favors the in-situ formation of SEI on Zn surface through reductive decomposition. Note that the small amount of TMP and OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e involved in the solvation shell is beneficial to form a thin SEI layer, which facilitates fast Zn\u003csup\u003e2+\u003c/sup\u003e transfer. Moreover, the Zn\u003csup\u003e2+\u003c/sup\u003e desolvation energy of TMP\u0026ndash;0 and TMP\u0026ndash;40 can be obtained by extracting the respective R\u003csub\u003ect\u003c/sub\u003e before cycling, where no SEI was formed on Zn surface. As shown in Supplementary Fig.\u0026nbsp;15, the addition of TMP causes a slight increase in the energy barrier for dissociation of Zn\u003csup\u003e2+\u003c/sup\u003e, largely ascribed to the strong interaction of Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;TMP and Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e, which in turn allows for the stepwise formation of ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eWith the TMP\u0026ndash;40 as the optimal electrolyte formulation, the linear sweep voltammetry (LSV) measurements were first performed to examine the electrochemical stability. It was found that the TMP\u0026ndash;40 electrolyte can effectively suppress the water decomposition over a wide electrochemical window and prevent Zn surface corrosion (Supplementary Figs.\u0026nbsp;16\u0026ndash;17). Moreover, the disappearance of the cathodic peak at ~\u0026thinsp;0.1 V accompanied with the decrease in current density after five cycles also indicates the SEI was formed at the initial plating and can inhibit the hydrogen evolution reaction (HER) (Supplementary Fig.\u0026nbsp;18). After 40 cycles of stripping/plating of Zn metal, X-ray diffraction (XRD) peaks corresponding to the zinc triflate hydroxide hydrate (Zn\u003csub\u003ex\u003c/sub\u003eOTf\u003csub\u003ey\u003c/sub\u003e(OH)\u003csub\u003e2x\u0026minus;y\u003c/sub\u003e\u0026middot;nH\u003csub\u003e2\u003c/sub\u003eO, ZOTH) were detected on the Zn surface in TMP\u0026ndash;0 (Supplementary Fig.\u0026nbsp;19), which can largely restrict the transport of Zn\u003csup\u003e2+\u003c/sup\u003e and lead to dendrite growth\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. In contrast, no byproduct was observed in TMP\u0026ndash;40. X-ray photoelectron spectroscopy (XPS) with Ar ion sputtering was further employed to determine the depth distribution of composition in SEI formed on Zn surface. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, the top SEI layer (before sputtering) is rich in \u0026ndash;CF\u003csub\u003e3\u003c/sub\u003e species (~\u0026thinsp;688.8 eV) and inorganic ZnF\u003csub\u003e2\u003c/sub\u003e (~\u0026thinsp;684.1 eV) with a tiny amount of Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (~\u0026thinsp;134.3 eV). Accordingly, the lattice fringes in the high-resolution transmission electron microscopy (HRTEM) corresponding to the planes of ZnF\u003csub\u003e2\u003c/sub\u003e and Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e were clearly observed with uniform distribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, f and Supplementary Fig.\u0026nbsp;20), consistent with the XPS results. Based on the previous reports\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e, the \u0026ndash;CF\u003csub\u003e3\u003c/sub\u003e species arises from either the incomplete reduction of OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e or the residual salt on Zn surface, while ZnF\u003csub\u003e2\u003c/sub\u003e and Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e are attributed to the decomposition product of Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;OTf\u003csup\u003e\u0026minus;\u003c/sup\u003e and Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;TMP complexes. As the sputtering continues, the peak intensity of Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e distinctly becomes stronger along with the decrease in ZnF\u003csub\u003e2\u003c/sub\u003e peak (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and Supplementary Fig.\u0026nbsp;21). After 310 s of sputtering, the Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e gradually becomes the major composition in the SEI. In sharp contrast, no F or P signals related to ZnF\u003csub\u003e2\u003c/sub\u003e or Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e was detected in TMP\u0026ndash;0 (Supplementary Fig.\u0026nbsp;22). The XPS analyses provide strong evidences that the TMP\u0026ndash;40 electrolyte favors the in-situ formation of gradient interlayer on Zn surface, where ZnF\u003csub\u003e2\u003c/sub\u003e and Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e dominates the surface layer and inner layer, respectively.\u003c/p\u003e\n\u003ch3\u003eThe Kinetic Behavior Of Bivalent Zn On The Electrode/electrolyte Interface\u003c/h3\u003e\n\u003cp\u003eAs aforementioned, the SEI with rapid Zn\u003csup\u003e2+\u003c/sup\u003e transport kinetics and low Zn\u003csup\u003e2+\u003c/sup\u003e desolvation energy is beneficial for ZMBs to stably work at low temperatures. Thus, we performed temperature-dependent electrochemical impedance spectroscopy (EIS) of Zn||Zn cells at temperature ranging from 20 \u003csup\u003eo\u003c/sup\u003eC to \u0026minus;\u0026thinsp;30 \u003csup\u003eo\u003c/sup\u003eC in TMP\u0026ndash;0 and TMP\u0026ndash;40 after 40 cycles (Supplementary Fig.\u0026nbsp;23), where a dense SEI should be formed in TMP\u0026ndash;40. The charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e) and the resistance associated with Zn\u003csup\u003e2+\u003c/sup\u003e crossing SEI (R\u003csub\u003eSEI\u003c/sub\u003e) can be extracted from the semicircles in mid-frequency region and the high-frequency region, respectively\u003csup\u003e\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. By Arrhenius-fitting R\u003csub\u003ect\u003c/sub\u003e and R\u003csub\u003eSEI\u003c/sub\u003e over 1000/T, the activation energy of each interface process were obtained, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, b. Compared with TMP\u0026ndash;0, the desolvation energy of Zn\u003csup\u003e2+\u003c/sup\u003e in the TMP\u0026ndash;40 was greatly reduced (70.2 KJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e vs 54.8 KJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), indicating the outer ZnF\u003csub\u003e2\u003c/sub\u003e facilitate Zn\u003csup\u003e2+\u003c/sup\u003e desolvation, agreeing with the reported results\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. Moreover, the activation energy for Zn\u003csup\u003e2+\u003c/sup\u003e transport through the SEI in TMP\u0026ndash;40 (E\u003csub\u003ea,SEI\u003c/sub\u003e=52.7 KJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) is significantly lower than in TMP\u0026ndash;0 (E\u003csub\u003ea,SEI\u003c/sub\u003e=64.3 KJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). This can be well explained by the density functional theory (DFT) calculation results that the Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e delivers a much smaller migration energy barrier for Zn\u003csup\u003e2+\u003c/sup\u003e (0.38 eV) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) and higher affinity with Zn\u003csup\u003e2+\u003c/sup\u003e (\u0026minus;\u0026thinsp;1.15 eV) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec) compared with those of ZnF\u003csub\u003e2\u003c/sub\u003e (1.12 eV for Zn\u003csup\u003e2+\u003c/sup\u003e transport and weak binding energy of \u0026minus;\u0026thinsp;0.85 eV with Zn\u003csup\u003e2+\u003c/sup\u003e). That is, the rich Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e in the inner SEI serves as the dominant channels for the desolvated Zn\u003csup\u003e2+\u003c/sup\u003e across the SEI to deposit on the Zn surface, which can facilitate fast Zn\u003csup\u003e2+\u003c/sup\u003e conduction to mitigate voltage polarization under cold environments\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e,\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. Moreover, we prepared SEI containing single ZnF\u003csub\u003e2\u003c/sub\u003e or Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e to confirm their respective role (Supplementary Fig.\u0026nbsp;24). Besides, the interface impedance of Zn||Zn cells in the TMP\u0026ndash;40 electrolyte can remain stable after 500 cycles, indicating the stable interface due to the formation of ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e interlayer (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). In sharp contrast, the TMP\u0026ndash;0 electrolyte shows a sharp decrease in the interfacial impedance after 100 cycles, possibly due to the dendrite growth that causes the cell short circuit (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef).\u003c/p\u003e \u003cp\u003eIn addition, a high mechanical integrity is indispensable for SEI to ensure the long-term cycling and high-capacity plating. To this end, in-situ optical microscopy was performed to observe the morphology evolution at different plating stages. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg, the TMP\u0026ndash;40 electrolyte enables the dense deposition without dendrite formation during the whole deposition process and can maintain a smooth surface even at a colossal loading of 50 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. While for the case of TMP\u0026ndash;0, uneven spots appear at 10 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and gradually evolve into discontinuous islands as the plating capacity increases, which is consistent with the scanning electron microscopy (SEM) results (Supplementary Fig.\u0026nbsp;25). The striking contrast in morphology evolution demonstrates that the gradient SEI can effectively suppress the dendrite growth and is highly stable to accommodate the high-loading Zn plating, largely ascribed to the strong bulk modulus of Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003e. Taken together, we reasonably conclude that the rich ZnF\u003csub\u003e2\u003c/sub\u003e on the top layer of SEI favors the desolvation of Zn\u003csup\u003e2+\u003c/sup\u003e and the robust Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e predominating the inner SEI layer facilitates rapid Zn\u003csup\u003e2+\u003c/sup\u003e transport. With these admirable characters, it is expected that the as-formed gradient ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e SEI can guarantee stable and long-term cycling of Zn metal at low temperatures.\u003c/p\u003e\n\u003ch3\u003eElectrochemical Performance Of Zn Metal Anodes Under Harsh Conditions\u003c/h3\u003e\n\u003cp\u003eIt is worth mentioning that these features of the gradient SEI can allow the symmetric Zn cells to stably cycle in the TMP\u0026ndash;40 electrolyte at a high current density of 5 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 25 \u003csup\u003eo\u003c/sup\u003eC and 45 \u003csup\u003eo\u003c/sup\u003eC (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and Supplementary Fig.\u0026nbsp;26). In sharp contrast, the cells in TMP\u0026ndash;0 quickly failed due to severe Zn dendrite formation and aggravated side reactions. This also manifests that the gradient ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e SEI is ultra-stable against the high-temperature and high-rate cycling, underscoring the significance of SEI formation on the interface. Then the galvanostatic cycling stability of Zn metal in the TMP\u0026ndash;40 electrolyte was studied at low temperatures with different rates. When the operation temperature was fixed at \u0026minus;\u0026thinsp;30 \u003csup\u003eo\u003c/sup\u003eC, the cell in TMP\u0026ndash;40 exhibits a stable voltage profile at 2 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with an ultralong cycling life up to 3600 hours, which is around 40\u0026ndash;fold improvement in cycle life (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). With the superior kinetics in the electrolyte/electrode interface, the TMP\u0026ndash;40 electrolyte enables the symmetric cells to operate over long-term cycles with high rates ranging from 5 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e to 15 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e through a transient activation (Supplementary Fig.\u0026nbsp;27).\u003c/p\u003e\u003cp\u003eThen the cycling temperature was decreased to \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC. Not surprisingly, the cell in TMP\u0026ndash;0 cannot work due to the electrolyte solidification (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). While the TMP\u0026ndash;40 electrolyte achieves an ultralong lifespan at 0.4 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 0.4 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e without obvious fluctuation in overpotential over 6000 hours (~\u0026thinsp;8 months). As the discharge depth was increased to 1 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, it is amazing to find that the cell can still maintain an impressive stability without voltage fluctuation over 6000 hours (Supplementary Fig.\u0026nbsp;28). These observations convectively demonstrate that the as-formed gradient ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e SEI with the unique configurations can accelerate the rapid Zn\u003csup\u003e2+\u003c/sup\u003e desolvation and conduction at low temperatures, which guarantees the ultra-stable cycling with a negligible polarization at rather extreme conditions (low temperatures with high rates). Notably, the Zn||Zn symmetric cells in TMP\u0026ndash;40 achieve a rather competitive cumulative capacity over a wide temperature range (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed and Supplementary Table\u0026nbsp;3), far outperforming those of reported low-temperature aqueous Zn metal anodes\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. Both top and side views reveal that the surface of Zn electrode after 100 plating/stripping cycles in TMP\u0026ndash;40 is highly homogeneous and tightly packed, while the one with TMP\u0026ndash;0 exhibits severe cracks (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee, f), indicating the gradient SEI layer can effectively suppress the Zn dendrite growth.\u003c/p\u003e \u003cp\u003eThe reversibility of Zn plating/stripping was further studied by calculating the Coulombic efficiency (CE) of Zn metal onto titanium (Ti) substrate. At \u0026minus;\u0026thinsp;30\u0026deg;C with a current density of 1 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and a capacity of 0.5 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the CE in TMP\u0026ndash;40 electrolyte quickly increases to 99% within 20 cycles and stabilizes at 99.9% over 3800 cycles along with flat voltage profiles (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg and Supplementary Fig.\u0026nbsp;29). Conversely, the cell with TMP\u0026ndash;0 electrolyte exhibits a low CE of around 60% and quickly short circuited at the 9th cycle due to dendrite formation. These contrasts can be maximized at different temperatures ranging from 45\u0026deg;C to \u0026minus;\u0026thinsp;50\u0026deg;C (Supplementary Fig.\u0026nbsp;30), well illustrating that the gradient SEI layer is stable against the severe side reaction and maintains superior kinetics at low temperatures.\u003c/p\u003e\n\u003ch3\u003eElectrochemical Performance Of Zn–kvoh Full Cells Under Practical Conditions\u003c/h3\u003e\n\u003cp\u003eTo evaluate the practical applications of TMP\u0026ndash;40 electrolyte, KVOH was employed as cathode to pair with Zn metal for full cells in the TMP\u0026ndash;40 electrolyte due to its superior kinetics (Supplementary Fig.\u0026nbsp;31). The Zn\u0026ndash;KVOH full cell with TMP\u0026ndash;40 electrolyte delivers an initial capacity of 329.1 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and retains a capacity of 323.6 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after 2300 cycles at room temperature (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea), corresponding to a capacity retention of 98.3%. In contrast, the cell with TMP\u0026ndash;0 electrolyte exhibits a slightly higher initial capacity of 344.4 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e possibly due to a higher ionic conductivity, but quickly dropped to 211 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after 500 cycles, along with a larger polarization in the charge\u0026ndash;discharge voltage profiles (Supplementary Fig.\u0026nbsp;32). The significant performance improvement is also revealed with high loadings of KVOH (6.37 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 17.6 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), at various rates (1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 2 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) or even at a higher temperature (45 \u003csup\u003eo\u003c/sup\u003eC, 5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), as shown in Supplementary Figs.\u0026nbsp;33\u0026ndash;35. Impressively, with a high areal loading of KVOH up to 17.6 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the full cell still maintains an areal capacity of 4.37 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e after 100 cycles, which meets the requirements of a typical commercial Li-ion battery (4.0 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003csup\u003e42\u003c/sup\u003e. In view of the inspiring performance, we further evaluated the application of TMP\u0026ndash;40 electrolyte in practical situation by controlling lean electrolyte and low Zn excess. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, when the KVOH loading increases to 33.75 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, the cell still delivers a superhigh initial areal capacity of 9.42 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with lean E/C (6.76 \u0026micro;L mAh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the ratio of electrolyte volume to capacity) ratio and low N/P (3.1, the ratio of negative to positive). The corresponding energy density is calculated to be 251.2 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (based on the KVOH mass) with a high capacity retention of 93.3% after 50 cycles. The outstanding performance can be ascribed to the superior kinetics and great robustness of the ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e SEI that can allow large amounts of Zn\u003csup\u003e2+\u003c/sup\u003e to repeatedly strip and plate.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eElectrochemical Performance Of Zn–kvoh Full Cells At Low Temperature\u003c/h3\u003e\n\u003cp\u003eBy virtue of the favorable SEI formation, the TMP\u0026ndash;40 electrolyte can enable the Zn\u0026ndash;KVOH full cells to sustain remarkable long lifespan and prominent stability at subzero temperatures. Specifically, when the temperature was decreased to \u0026minus;\u0026thinsp;30 \u003csup\u003eo\u003c/sup\u003eC (Supplementary Fig.\u0026nbsp;36), the discharge capacity of the cell in the TMP\u0026ndash;40 electrolyte remains at 120.6 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after 4000 cycles at 1 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, far exceeding that without TMP. Even at a higher rate of 2 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the 40% of TMP addition can prompt the cell to charge/discharge reversibly over 10000 cycles and 1500 cycles, respectively. In stark contrast, the cell with TMP\u0026ndash;0 electrolyte failed to work, underscoring the critical role of the gradient SEI formed in the TMP\u0026ndash;40 electrolyte. These contrasts are more evident at \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC, where the cell with TMP\u0026ndash;0 cannot provide any capacities due to the electrolyte solidification. Comparatively, the TMP\u0026ndash;40 electrolyte can render the full cell to deliver a stable capacity of 50.8 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e over 12000 cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The fluctuations at the 800th, 5000th and 9800th cycle are ascribed to the sudden power outages during the long-term test, which also confirm the good temperature adaptivity of the gradient SEI formed in the TMP\u0026ndash;40 electrolyte. Compared with the published works on electrolyte modification for aqueous Zn batteries, this work is undoubtedly prominent in achieving long-cycle stability over a wide temperature range (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed, Supplementary Tables\u0026nbsp;4\u0026ndash;5)\u003csup\u003e4,8,12,14\u0026ndash;17,19,22,40,41,43\u0026minus;46\u003c/sup\u003e. Post-mortem analyses show that the Zn metal anode after 1000 cycles in the TMP\u0026ndash;40 electrolyte can maintain a much flatter and denser surface (Supplementary Fig.\u0026nbsp;37). The significant performance improvement achieved in the TMP\u0026ndash;40 electrolyte at low temperatures strongly validates the gradient SEI with the favorable kinetics can effectively suppress the Zn dendrite growth and ensure the superb cycling behaviors in full cells under extreme conditions.\u003c/p\u003e \u003cp\u003eThe exceptional performance of the ZMBs inspired us to further evaluate the low-temperature performance of pouch cell with a size of 4.3 \u0026times; 5.6 cm in the TMP\u0026ndash;40 electrolyte. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee, a reversible capacity of 340.5, 159.4, 122.2 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was achieved at 25 ℃ (room temperature), \u0026minus;\u0026thinsp;30 ℃ and \u0026minus;\u0026thinsp;50 ℃, respectively. Notably, the pouch cell achieves a superior cycling stability at a low temperature of \u0026minus;\u0026thinsp;30\u0026deg;C with a high capacity retention of 88.6% after 1200 cycles at 0.25 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef). Even at \u0026minus;\u0026thinsp;50\u0026deg;C, it can stably cycle for 180 cycles with nearly 100% of capacity retention (Supplementary Fig.\u0026nbsp;38). Moreover, five series connected pouch cells with a voltage of ~\u0026thinsp;5 V can drive an electro-calculagraph normally working for more than 3 min at an extreme temperature of \u0026minus;\u0026thinsp;50\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eg and Supplementary Fig.\u0026nbsp;39), further demonstrating its promising potential in the practical applications under harsh conditions.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn summary, we have successfully in-situ constructed gradient SEI layer on Zn surface to enable long-cycling and dendrite-free ZMBs at low temperatures by introducing TMP into the aqueous electrolyte. It was found that 40% of TMP addition can regulate the Zn\u003csup\u003e2+\u003c/sup\u003e solvation sheath and promote the formation of ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e gradient SEI, which effectively suppress the parasitic reaction and Zn dendrite growth. Moreover, a combination study of computational and experimental characterizations reveals the outer ZnF\u003csub\u003e2\u003c/sub\u003e can facilitate Zn\u003csup\u003e2+\u003c/sup\u003e desolvation and the inner Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e can serve as channels for fast Zn\u003csup\u003e2+\u003c/sup\u003e conduction, synergistically leading to continuous cycling under cold environments. Remarkably, a record stability was achieved in the symmetric Zn cell at \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC with a lifespan of 6000 hours at a relatively high current density of 0.4 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Furthermore, the Zn\u0026ndash;KVOH full cell delivers a stable capacity of 50.8 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.5 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e over 12000 cycles at \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC. Full cells with lean electrolyte and low Zn excess also demonstrate the practical feasibility. This work provides a feasible route to achieve highly stable ZMBs under extreme conditions.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv class=\"Section2\" id=\"Sec11\"\u003e\n \u003ch2\u003eElectrolyte preparation\u003c/h2\u003e\n \u003cp\u003eZinc trifluoromethanesulfonate (Zn(OTf)\u003csub\u003e2\u003c/sub\u003e, \u0026gt;\u0026thinsp;99%) and trimethyl phosphate (TMP, 98%) was purchased from Adamas and Sigma-Aldrich, respectively. A series of electrolytes were formulated by dissolving 2 M Zn(OTf)\u003csub\u003e2\u003c/sub\u003e in deionized (DI) water with different volume ratios of TMP from 0%, 5%, 10%, 20%, 40%, 60%, 80\u0026ndash;100%. The corresponding electrolyte is marked as TMP\u0026ndash;0, TMP\u0026ndash;5, TMP\u0026ndash;10, TMP\u0026ndash;20, TMP\u0026ndash;40, TMP\u0026ndash;60, TMP\u0026ndash;80 and TMP\u0026ndash;100, respectively.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eFabrication Of Kvoh Cathode\u003c/h3\u003e\n\u003cp\u003eThe synthesis of KVOH was based on a previous method, as reported by Gao\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Specifically, 0.364 g of vanadium pentoxide (V\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, 99%, Sigma Aldrich) in 50 ml DI water was mixed with 0.0745 g of potassium chloride (KCl, 99.9%, Sigma Aldrich) in 30 mL DI water, followed by addition of 1.7 mL hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 35%, Fisher Scientific) and 0.5 h of stirring. Then the mixture was transferred into 100 mL Teflon autoclave and heated at 120\u0026deg;C for 6 h. The green powder was collected by centrifugation, repeated wash with DI water and ethanol, and drying overnight at 60\u0026deg;C.\u003c/p\u003e\n\u003ch3\u003ePreparation Of Znf@zn And Zn(Po)@zn\u003c/h3\u003e\n\u003cp\u003eAccording to the previous report\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, ZnF\u003csub\u003e2\u003c/sub\u003e@Zn was obtained by chemically treating Zn foil with Ammonium fluoride (NH\u003csub\u003e4\u003c/sub\u003eF, 99.99%, Aladdin) dispersed in the dimethyl sulfoxide (DMSO, 99.9%, Innochem) solvents. First, 5 mg NH\u003csub\u003e4\u003c/sub\u003eF was dispersed in 6 mL DMSO under vigorous stirring for 3 days and then dropped onto the Zn surface, followed by rapidly drying in glove box at 180\u0026deg;C for 10 min. The above operation was repeated 10 times to obtain uniform ZnF\u003csub\u003e2\u003c/sub\u003e@Zn. The Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e@Zn was obtained through the chemical reaction between Zn and Diammonium hydrogen phosphate aqueous solution. First, 66 mg Diammonium hydrogen phosphate ((NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e, 99.9%, Macklin) was dissolved in 10 mL deionized water to obtain 0.05 M (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003eHPO\u003csub\u003e4\u003c/sub\u003e aqueous solution. Second, Zn plates (\u0026phi;\u0026thinsp;=\u0026thinsp;12 mm) were immersed into the above solution under stirring for 5 h, followed by repeated washing and drying at 80\u0026deg;C for standby.\u003c/p\u003e\n\u003ch3\u003eMaterial Characterizations\u003c/h3\u003e\n\u003cp\u003eDifferential scanning calorimetry (DSC, METTLER TOLEDO DSC3) was used to measure the freezing point of the hybrid electrolyte at a temperature range from \u0026minus;\u0026thinsp;150 \u003csup\u003eo\u003c/sup\u003eC to 25 \u003csup\u003eo\u003c/sup\u003eC, which was carried out in a liquid nitrogen cooling system with a heating rate of 5\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Fourier Transform Infrared (FT-IR) analysis was conducted on Nicolet iS50. Raman spectroscopy was recorded on LabRAM HR Evolution with an excitation wavelength of 633 nm. The changes of hydrogen bonds were analyzed by nuclear magnetic resonance (NMR, AVANCE III 400MHz) with deuterated DMSO. Scanning electron microscopy (SEM) images were collected using FEI Microscope (JSM-7900F). Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) were performed on Talos F200X G2. X-ray diffraction (XRD) measurements were obtained on diffractometer (Smart Lab 9 KW) with a Cu-target X-ray tube (\u0026lambda;\u0026thinsp;=\u0026thinsp;0.154 nm) at 150 mA and 40 kV. The compositions of solid electrolyte interphase (SEI) were determined by X-ray photoelectron spectroscopy (XPS, Axis Ultra DLD) using monochromatic 1486.7 X-ray source.\u003c/p\u003e\n\u003ch3\u003eElectrode Preparation\u003c/h3\u003e\n\u003cp\u003eFor the coin cell, the as-prepared KVOH was mixed with super P carbon black (SUPER P, TIMCAL) and polyvinyldifluoride (PVDF, Sinopharm) based on a weight ratio of 7:2:1 (routine test) or 8:1:1 (high loading test), which was dispersed in N-methyl-2-pyrrolidinone (NMP, Sinopharm) to form a slurry. Then the slurry was casted onto carbon paper disks with a diameter of 10 mm and dried overnight at 60\u0026deg;C in a vacuum oven. The preparation procedures of KVOH cathode for punch cells were similar to the above description, except the electrode size is 4.3 \u0026times; 5.6 cm.\u003c/p\u003e\n\u003ch3\u003eElectrochemical Measurements\u003c/h3\u003e\n\u003cp\u003e2032-type coin cells were assembled to measure the Coulombic efficiency and cycling stability of Zn metal anode (100 \u0026micro;m) on standard battery tester (LAND-CT2001A) at different temperatures controlled by cryostat (\u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC), fridge (\u0026minus;\u0026thinsp;30 \u003csup\u003eo\u003c/sup\u003eC) and oven (25 \u003csup\u003eo\u003c/sup\u003eC, 45 \u003csup\u003eo\u003c/sup\u003eC). The separator used was glass fiber (90 \u0026micro;m in thickness, Waterman GF/D). The cycling stability was evaluated in symmetric cells composed of two identical Zn disks in the electrolyte of TMP\u0026ndash;0 and TMP\u0026ndash;40 at different current densities and capacities. For the measurement of Coulombic efficiency, the coin cells were composed of a titanium (Ti) foil as working electrode (substrate for Zn plating and stripping), and a piece of Zn foil as counter and reference electrode. A constant current with a constant capacity (the amount of Zn deposited) was applied to the electrode, followed by Zn stripping via charging to 1 V (versus Zn/Zn\u003csup\u003e2+\u003c/sup\u003e). The Coulombic efficiency of each cycle was calculated as the amount of Zn stripped (based on capacity extracted) divided by the amount of Zn plated (based on capacity deposited) onto the Ti foil. Linear sweep voltammetry (LSV) of the hybrid electrolytes was measured using Ti||Zn asymmetric at a scan rate of 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in a voltage range of \u0026minus;\u0026thinsp;0.5\u0026thinsp;~\u0026thinsp;3 V (versus Zn/Zn\u003csup\u003e2+\u003c/sup\u003e) on an electrochemical workstation (Ivium-n-Stat, Nederlanden).\u003c/p\u003e\n\u003cp\u003eThe ionic conductivity of hybrid electrolytes at different temperatures was measured by EIS via symmetrical cells consisted of two parallel Pt-plate electrodes (10 mm\u0026times;10 mm). The distance between two electrodes is 10 mm and the applied frequency range was from 10\u003csup\u003e5\u003c/sup\u003e Hz to 10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e Hz with 5 mV AC amplitude. The ionic conductivity of hybrid electrolyte was calculated by the following equation:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" height=\"45\" width=\"334\"\u003e\u003c/p\u003e\n\u003cp\u003eWhere \u0026sigma; is the ionic conductivity of the electrolyte (S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), R\u003csub\u003es\u003c/sub\u003e is the electrolyte resistance (Ω), which corresponds to the intercept of Nyquist plot. L (cm) is the distance between two Pt-plate electrodes. A (cm\u003csup\u003e2\u003c/sup\u003e) stands for the area of Pt electrode.\u003c/p\u003e\n\u003cp\u003eThe electrochemical performance of Zn\u0026ndash;KVOH full cell was evaluated by using both 2032-type coin-cell and pouch-cell. For the routine test of coin-type full cell, the typical mass loading of active materials (KVOH) is around 1.2\u0026thinsp;~\u0026thinsp;1.5 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, glass fiber (GF/D, 90 \u0026micro;m in thickness) as separator and 100 \u0026micro;m Zn metal as anode. The electrolyte was fixed to around 130 \u0026micro;L. The galvanostatic discharge/charge tests were performed using LAND-CT2001A instruments in a voltage range of 0.2\u0026ndash;1.6 V (vs Zn/Zn\u003csup\u003e2+\u003c/sup\u003e). Electrochemical impedance spectroscopy (EIS) measurements were carried out on an electrochemical workstation (Ivium-n-Stat, Nederlanden) from 10\u003csup\u003e5\u003c/sup\u003e Hz to 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e Hz, and the perturbation amplitude was 5 mV. All the tests at different temperatures were carried out after 2 hours of resting.\u003c/p\u003e\n\u003cp\u003eFor the test of coin-type full cell with high-loading cathode (33.75 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), we used carbon cloth as current collector, thin glass fiber (GF/A, 55 \u0026micro;m in thickness) as separator, 50 \u0026micro;m Zn metal as anode and the lean electrolyte (50 \u0026micro;L) is dropped on the cathode side.\u003c/p\u003e\n\u003ch2\u003eComputational Details\u003c/h2\u003e\n\u003cdiv class=\"Section2\" id=\"Sec18\"\u003e\n \u003ch2\u003eMolecular dynamics simulations\u003c/h2\u003e\n \u003cp\u003eIn this work, the solvation environment of TMP\u0026ndash;0 (molar ratio, Zn(OTf)\u003csub\u003e2\u003c/sub\u003e:H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;=\u0026thinsp;1:27.79) and TMP\u0026ndash;40 (molar ratio, Zn(OTf)\u003csub\u003e2\u003c/sub\u003e:TMP:H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;=\u0026thinsp;1:1.74:16.67) were simulated. The TMP\u0026ndash;0 model system involves 70 Zn(OTf)\u003csub\u003e2\u003c/sub\u003e salt molecules and 1945 H\u003csub\u003e2\u003c/sub\u003eO molecules, while the TMP\u0026ndash;40 one contains 70 Zn(OTf)\u003csub\u003e2\u003c/sub\u003e salt molecules, 122 TMP molecules, and 1167 H\u003csub\u003e2\u003c/sub\u003eO molecules. Packmol\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e was used to build initial configuration of the two model systems. LAMMPS\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e was used to perform the molecular simulations. All atom molecular dynamics simulations were carried out using PCFF-INTERFACE force field\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Constant NVT conditions are enforced using a Nos\u0026eacute;-Hoover thermostat with a relaxation time of 100 fs and a temperature of 300 K\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. The density of each electrolyte solution was determined from 500 ps molecular dynamics simulation in the NPT ensemble at the same thermodynamic conditions. Equations of motions were integrated using the velocity\u0026ndash;Verlet method with a 1.0 fs time step. The cut-offs for all the non-bonded interactions are 12 \u0026Aring;. All results reported here are statistical averages taken from runs of 1000 ps in length, each preceded by 1500 ps of equilibration. The atomic coordinates were collected every 1.0 ps for statistical analysis.\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003eQuantum Chemistry Calculations\u003c/h3\u003e\n\u003cp\u003eFor the relative binding energy of Zn\u003csup\u003e2+\u003c/sup\u003e with different species, the structures were fully optimized by using the B3LYP\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e method in the level of 6\u0026ndash;31\u0026thinsp;+\u0026thinsp;+\u0026thinsp;G (d, p) basis set. Analytical vibrational frequency was calculated at the same level. The Zn\u003csup\u003e2+\u003c/sup\u003e cation carries two unit of positive charge. The interaction energy was calculated as following:\u003c/p\u003e\n\u003cp\u003e\u0026Delta;E\u003csub\u003einter\u003c/sub\u003e= E\u003csub\u003etotal\u003c/sub\u003e \u0026ndash; (E\u003csub\u003eZn\u003c/sub\u003e + E\u003csub\u003esolvent\u003c/sub\u003e) (2)\u003c/p\u003e\n\u003cp\u003e\u0026Delta;E\u003csub\u003einter\u003c/sub\u003e represents the interaction energy, E\u003csub\u003etotal\u003c/sub\u003e, E\u003csub\u003ezn\u003c/sub\u003e and E\u003csub\u003esolvent\u003c/sub\u003e are the energies of the complex, Zn\u003csup\u003e2+\u003c/sup\u003e cation, and solvent (H\u003csub\u003e2\u003c/sub\u003eO or TMP), respectively. The more negative the magnitude of interaction energy, the more favorable the interaction between the Zn\u003csup\u003e2+\u003c/sup\u003e cation and the solvent is. All calculations were performed with the Gaussian 09 program.\u003c/p\u003e\n\u003cp\u003eFor the migration energy barrier of zinc ions between different components, we have employed the Vienna Ab initio Simulation Package (VASP) to perform all density functional theory (DFT) calculations within spin-polarized frame\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. The elemental core and valence electrons were represented by the projector augmented wave (PAW) method and plane\u0026ndash;wave basis functions with a cutoff energy of 400 eV. Generalized gradient approximation with the Perdew-Burke-Ernzerhof (GGA-PBE) exchange-correlation functional was employed in all the calculations\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Geometry optimizations were performed with the force convergency smaller than 0.05 eV/\u0026Aring;, where the same convergency were applied for the locating of transition states through the constrained optimizations (NEB). The atoms at bottom of Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (\u0026minus;\u0026thinsp;121) surfaces (43 atoms) and the ZnF\u003csub\u003e2\u003c/sub\u003e (111) surfaces (44 atoms) were fixed in all the calculations. Monkhorst-Pack k-points of 3\u0026times;2\u0026times;1 and 2\u0026times;2\u0026times;1 were applied for all the surface calculations for Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (\u0026minus;\u0026thinsp;121), and ZnF\u003csub\u003e2\u003c/sub\u003e (111), respectively. To obtain transition states, the bulk structures of Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e and ZnF\u003csub\u003e2\u003c/sub\u003e (111) have been optimized with the Monkhorst-Pack k-point of 3\u0026times;3\u0026times;3 and 5\u0026times;3\u0026times;8, respectively.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Ministry of Science and Technology of China (2021YFA1201900), National Natural Science Foundation of China (No. 22105107) and Fundamental Research Funds for the Central Universities (No. 020/C029201005). We thank the Haihe Laboratory of Sustainable Chemical Transformations for financial support. H.W. acknowledge the Young Elite Scientists Sponsorship Program by Tianjin.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eH.W. and W.W. conceived the original idea. W. W., F. W. and H. W. designed all the experiments. W. W., S. C., X. L. and J. C. carried out the experiments. W. W., S. C., X. L., R. H., Y. W., F. W. and H. W. analyzed the experimental data. W. W., F. W. and H. W. co-wrote the paper. All authors were involved in discussion of the experimental results and preparing of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWang, F. et al. Highly reversible zinc metal anode for aqueous batteries. Nat. 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An aqueous zinc-ion battery working at \u0026ndash; 50\u0026deg;C enabled by low-concentration perchlorate-based chaotropic salt electrolyte. Ecomat \u003cb\u003e4\u003c/b\u003e, e12165 (2022).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, D. S. et al. Regulating the electrolyte solvation structure enables ultralong lifespan Vanadium-based cathodes with excellent low-temperature Performance. Adv. Funct. Mater. \u003cb\u003e32\u003c/b\u003e, 2111714 (2022).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":false,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Zn metal anodes, Gradient phosphatized SEI, Low temperature, Rapid interfacial kinetics, Long-term stability, Aqueous Zn batteries ","lastPublishedDoi":"10.21203/rs.3.rs-2143664/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2143664/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn situ formation of a stable solid electrolyte interphase (SEI) layer on zinc (Zn) surface is an effective solution to suppress dendrite growth. However, the fast transport of bivalent Zn-ions within the solid interlayer remains very challenging. Herein, we engineer the SEI components and enable a superior kinetic of Zn metal under harsh conditions. Trimethyl phosphate was employed as a cosolvent, which decreases the freezing point of water and spontaneously generate a gradient ZnF\u003csub\u003e2\u003c/sub\u003e\u0026ndash;Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e interphase. Mechanistic studies reveal the outer ZnF\u003csub\u003e2\u003c/sub\u003e facilitates Zn\u003csup\u003e2+\u003c/sup\u003e desolvation and inner Zn\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e serves as channels for Zn\u003csup\u003e2+\u003c/sup\u003e transport, contributing to long-term cycling at subzero temperatures. Impressively, the gradient SEI enables a record lifespan of symmetric Zn cells over 6000 hours (~\u0026thinsp;8 months) at \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC. Furthermore, the Zn\u0026ndash;KVOH full cell achieves a superhigh areal capacity (9.42 mAh cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) under a practical cycling condition (high cathode loading: 33.75 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e; lean electrolyte: 6.76 \u0026micro;L mAh\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and delivers a capacity retention of 86.1% after 12000 cycles at \u0026minus;\u0026thinsp;50 \u003csup\u003eo\u003c/sup\u003eC. This work provides a feasible route for low-temperature aqueous Zn metal batteries.\u003c/p\u003e","manuscriptTitle":"Gradient Phosphatized Interphase for Ultra-Stable and Low-Temperature Zinc Metal Batteries","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-10-20 17:13:43","doi":"10.21203/rs.3.rs-2143664/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"555a4b91-3f93-4782-9c88-c8fb7afa21de","owner":[],"postedDate":"October 20th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":16366368,"name":"Physical sciences/Energy science and technology/Energy storage/Batteries"},{"id":16366369,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Batteries"}],"tags":[],"updatedAt":"2023-09-29T15:27:07+00:00","versionOfRecord":{"articleIdentity":"rs-2143664","link":"https://doi.org/10.1038/s41467-023-41276-9","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2023-09-06 04:00:00","publishedOnDateReadable":"September 6th, 2023"},"versionCreatedAt":"2022-10-20 17:13:43","video":"","vorDoi":"10.1038/s41467-023-41276-9","vorDoiUrl":"https://doi.org/10.1038/s41467-023-41276-9","workflowStages":[]},"version":"v1","identity":"rs-2143664","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2143664","identity":"rs-2143664","version":["v1"]},"buildId":"rHA-KDH7Qsr4HCuvH75dn","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}