In situ polymerization of hydrogel electrolyte on electrode enabling the flexible all-hydrogel supercapacitors with low-temperature adaptability

In situ polymerization of hydrogel electrolyte on electrode enabling the flexible all-hydrogel supercapacitors with low-temperature adaptability | 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 Research Article In situ polymerization of hydrogel electrolyte on electrode enabling the flexible all-hydrogel supercapacitors with low-temperature adaptability Yijing Zhang, Yue Sun, Jingya Nan, Fusheng Yang, Zihao Wang, Yuxi Li, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3365097/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Feb, 2024 Read the published version in Small → Version 1 posted You are reading this latest preprint version Abstract All-hydrogel supercapacitors are emerging as promising power sources for next-generation wearable electronics due to their intrinsically mechanical flexibility, eco-friendliness, and enhanced safety. However, the insufficient interfacial adhesion between electrode and electrolyte and the frozen hydrogel matrices at subzero temperatures largely limit the practical applications of all-hydrogel supercapacitors. Here, we report an all-hydrogel supercapacitor with robust interfacial contact and anti-freezing property, which is fabricated by in situ polymerizing hydrogel electrolyte onto hydrogel electrode. The robust interfacial adhesion is developed by the synergistic effect of tough hydrogel matrix and topological entanglements. Meanwhile, the incorporation of ZnCl 2 in the hydrogel electrolyte prevents water solvents from freezing and endows the all-hydrogel supercapacitor with mechanical flexibility and fatigue resistance across a wide temperature range of 20°C to − 60°C. Such all-hydrogel supercapacitor demonstrates satisfactory low-temperature electrochemical performance, delivering high energy density of 11 mWh cm –2 and excellent cycling stability with capacitance retention of 99% over 5000 cycles at − 40°C. Notably, the fabricated all-hydrogel supercapacitor can endure dynamic deformations and operate well under 2000 tension cycles even at − 40°C, without delamination and electrochemical failure. This work offers a promising strategy for flexible energy storage devices with low-temperature adaptability. Robust interface Flexible supercapacitors Low-temperature All-hydrogel Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1 Introduction The rapid development of wearable electronics has posed new challenges to flexible energy storage devices, which are required to accommodate various mechanical deformations [ 1 – 3 ]. At present, flexible supercapacitors are emerging as a promising candidate due to their excellent mechanical flexibility, high power density, fast charging and discharging, and long cycle life[ 4 – 7 ]. In particular, all-hydrogel supercapacitors are increasingly attractive since hydrogel matrices possess unique merits, including intrinsic flexibility, environmental friendliness and flame-retardant property [ 2 , 8 – 11 ]. Most of the reported all-hydrogel supercapacitors have been prepared by sandwiching a hydrogel electrolyte between two hydrogel electrodes to form three-layer configurations, in which the similar mechanical properties between the electrode and electrolyte enable the supercapacitors to withstand certain deformations, such as bending, stretching, twisting, and folding[ 12 , 13 ]. Despite recent advances, there are two major limitations. First, the interfacial adhesion between the electrode and electrolyte can be weakened because of high water contents existing on the hydrogel surface, thus leading to a poor interfacial contact. As a result, interlayer slippage or irreversible layer delamination may occur for all-hydrogel supercapacitors when being under dynamic deformations [ 14 – 16 ]. Second, water solvents in hydrogel matrices will be inevitably frozen at subzero temperatures, hence deteriorating the flexibility and electrochemical performance of the all-hydrogel supercapacitors at low temperatures[ 17 – 19 ]. Therefore, how to design and construct an all-hydrogel supercapacitor that combines the robust electrode/electrolyte interface and anti-freezing property is highly desirable. Until now, hydrogel adhesion mainly depends on physical interactions[ 20 , 21 ], covalent anchorages[ 22 – 26 ], mechanical interlocking[ 27 ], and topological entanglements[ 28 – 31 ]. Among them, topological entanglements can obtain strong interfacial interactions by penetrating the stitching polymer network into porous adherends, showing its effectiveness in adhesion between two hydrogels[ 31 – 34 ]. However, the unique electrical and mechanical properties of hydrogel-based electrodes and electrolytes make it challenging to realize the device-level interfacial integration only using topological adhesion. In other words, the all-hydrogel supercapacitors need not only a stable interface but also appropriate mechanical properties. Hence, the combination of tough hydrogel matrix and topological entanglements is of great importance to achieve robust integration between hydrogel electrodes and electrolytes. To solve the problem that the device cannot work at low temperatures, the ions often are introduced because that metal ions can form solvation configurations through strong electrostatic interactions with water molecules and inhibit the formation of hydrogen bonds in water, the introduction of inorganic salts containing metal ions into hydrogels has been demonstrated as an effective approach to suppress water solvents freezing and lower the freezing point of hydrogels[ 18 , 35 – 40 ]. However, the mechanical performance of these hydrogels is inevitably deteriorated since ionic aggregations dissociate the intermolecular interactions between the polymer chains[ 17 , 18 , 41 – 45 ]. Therefore, developing anti-freezing all-hydrogel supercapacitors without sacrificing their mechanical flexibility is highly expected in practical applications. Here, we report a new type of all-hydrogel flexible supercapacitors with robust interfacial contact and anti-freezing property, which is fabricated by in situ polymerizing hydrogel electrolyte onto hydrogel electrode. The robust interface is developed by the synergistic effect of the tough hydrogel matrix and strong interfacial interaction, in which the hydrogel matrix is toughened by organic-inorganic integration, the interfacial interaction mainly comes from topological entanglements of the PAAm network penetrating into the hydrogel electrolyte and electrode. Meanwhile, the introduction of zinc chloride (ZnCl 2 ) imparts low-temperature mechanical flexibility to the hydrogel electrolyte, enabling the fabricated all-hydrogel supercapacitor to own fatigue resistance across a vast temperature range of 20~–60°C. More encouragingly, the all-hydrogel supercapacitor possesses excellent low-temperature electrochemical performance, exhibiting stable operation under dynamic deformations at low temperatures. This strategy of designing the all-hydrogel supercapacitor promotes the low-temperature adaptability of flexible energy storage system at the device level. 2 Experimental Section 2.1 Preparation of Ag-Lignin NPs dispersion Ag-Lignin NPs were prepared via a redox reaction between lignin macromolecules and the silver-ammonia complex (Ag[(NH 3 ) 2 ] + ) according to our previously reported method [ 46 ]. Typically, lignin dispersion (50 mg mL –1 ) was first formed by dispersing lignin powder (0.5 g, Aladdin) in deionized water (10 mL) with ultrasonication (130 W, 20 kHz) for 5 min. The silver-ammonia complex was obtained by adding ammonia solution (NH 3 ·H 2 O, Macklin) into the aqueous solution of AgNO 3 (15 mg mL –1 , 10 mL) until the solution to be clear. Lignin dispersion was then added dropwise to silver-ammonia complex and stood in the dark room for 1 h, thus obtaining the Ag-Lignin NPs dispersion. 2.2 Synthesis of PAAm-HAp hydrogel matrix The PAAm-HAp hydrogel matrix was synthesized by free radical polymerizations. In detail, HAp powder (0.63 g, Aladdin), acrylamide (3.15 g, AAm, Aladdin), N,N′ -methylenebisacrylamide (0.00945 g, MBAA, Sigma-Aldrich), and ammonium persulfate (0.0378 g, APS, Sigma-Aldrich) were completely dissolved in deionized water (15 mL) to prepare AAm-HAp solution. Then, the Ag-Lignin NPs dispersion (1.575 mL) was added into the AAm-HAp solution to obtain the pre-gel solution. After degassing, the pre-gel solution was poured into a mold and cured at room temperature for 12 h to fabricate the PAAm-HAp hydrogel matrix. 2.3 Formation of PAAm-HAp/CNTs-PPy hydrogel electrode The PAAm-HAp/CNTs-PPy hydrogel electrode was formed by introducing CNTs-PPy conductive materials into the hydrogel matrix. Firstly, the carbon nanotubes dispersion (6.3 g, CNTs, XFNANO) was dissolved into the above pre-gel solution of hydrogel matrix with ultrasonication (130 W, 20 kHz) for 15 min in a bath of ice water. Later, this degassed pre-gel solution containing CNTs was poured into a mold and cured at room temperature for 12 h to synthesize the PAAm-HAp/CNTs hydrogel. Followingly, the hydrogel was immersed in pyrrole solution (0.5 mol L − 1 , Aladdin) for 3 h, and then placed into the FeCl 3 solution (0.5 mol L − 1 , Aladdin) for 3 h, thus obtaining the PAAm-HAp/CNTs-PPy hydrogel electrode. Finally, the semi-dehydrated gel electrode was formed by dehydrating part of water from the hydrogel electrode at 40°C for 6 h. The final water content of the semi-dehydrated gel electrode was ~ 30%. 2.4 Fabrication of the all-hydrogel supercapacitor The all-hydrogel supercapacitor was fabricated by in situ polymerization of hydrogel electrolyte on electrodes. Firstly, the pre-gel solution of hydrogel electrolyte was obtained by dissolving zinc chloride (15.3 g, ZnCl 2 , Aladdin) into the above pre-gel solution of hydrogel matrix under an ice-water bath. Then, this degassed pre-gel solution was poured onto one semi-dehydrated gel electrode at room temperature for 5 min to form the semi-solid gel electrolyte. Subsequently, another semi-dehydrated gel electrode was placed onto the upper side of the semi-solid gel electrolyte at room temperature for 12 h. Thus, the hydrogel electrolyte polymerized in situ onto two electrodes simultaneously, forming topological entanglements with both pre-existing networks. 2.5 Material characterizations The structures of Lignin NPs and Ag-Lignin NPs were observed by a transmission electron microscope (TEM; FEI Talos F200X G2, America). Size distributions of the Lignin NPs dispersion and Ag-Lignin NPs dispersion were examined using Malvern Nano-ZS90. The morphologies of hydrogel matrix, hydrogel electrode and hydrogel electrolyte were analyzed using a scanning electron microscope (SEM; Hitachi Regulus 8100, Japan) equipped with an energy dispersive X-ray spectroscopic detector (Ultim Max 170, OXFORD). The cross-sectional morphologies of electrode/electrolyte interfaces were obtained using a scanning electron microscope (SEM; Hitachi Regulus 8100, Japan). 2.6 Mechanical tests All mechanical tests were carried out using a universal testing machine (1 kN load cell, UTM 4304GD, Shenzhen SUNS) equipped with an environmental chamber (WGDN-7150S, Shenzhen SUNS). All temperature-dependent mechanical measurements were performed in an environmental chamber with specific temperatures. For the fracture toughness, unnotched and notched hydrogel matrices with a rectangular shape (50 mm length × 20 mm width × 2 mm thickness) were prepared for the pure-shear tensile test. The notched samples were prepared by cutting unnotched samples into a 10 mm-long notch with a knife blade. The tests were conducted at a constant tension rate of 50 mm min − 1 , and the distance between the two clamps was fixed as 10 mm. The fracture energy was calculated from the tensile force-distance curves of the unnotched and notched samples, as shown in Fig. S2 . For the cyclic tensions, the hydrogel electrolyte with a rectangular shape (50 mm length × 20 mm width × 2 mm thickness) were prepared before tests. The mechanical elasticity of the hydrogel electrolyte was evaluated by conducting tension-release tests for 100 successive cycles at 100% strain. The fatigue behaviors of the all-hydrogel supercapacitor (50 mm length × 20 mm width) were assessed by performing cyclic tensions for 1000 successive cycles at 30% strain. All cyclic tensions were conducted at the specific temperature ranging from 20°C to − 60°C with a constant tension rate of 50 mm min − 1 . 2.7 Adhesion tests The adhesion performances of all-hydrogel supercapacitors were evaluated by 180-degree peel tests and lap-shear tests using a universal testing machine (1 kN load cell, UTM 4304GD, Shenzhen SUNS), All tests were proceeded with a constant tension rate of 50 mm min − 1 . For the 180-degree peel tests, the samples with an adhesion area of 25 mm width × 70 mm length were prepared. The interfacial toughness was calculated by doubling the plateau force and dividing by the adhesion width. The 3M double coated tissue tape was applied as a stiff backing onto the hydrogel sample to prevent stretching along the peeling direction. For the shear strength tests, the samples with an adhesion area of 25 mm width ×15 mm length were prepared. The shear strength was calculated by dividing the maximum force by the adhesion area. The 3M double coated tissue tape was applied as a stiff backing onto the hydrogel sample to prevent its elongation along the shear direction. 2.8 Electrochemical tests The electrochemical performances of the hydrogel electrolyte and all-hydrogel supercapacitor device were measured on an electrochemical working station (CHI 760E). All temperature-dependent electrochemical tests were performed with the aid of a Meiling refrigerator (DW-HL100, − 86~–10°C) or Suns environmental chamber (WGDN-7150S, − 70 ~ 150°C). The ionic conductivities of hydrogel electrolytes were determined by electrochemical impedance spectroscopy (EIS) tests of the Pt|hydrogel electrolyte|Pt symmetric cells. The galvanostatic charge/discharge (GCD) and cyclic voltammetry (CV) tests were conducted in the voltage range of 0 ~ 0.8 V at current densities of 0.5 ~ 3 mA cm − 2 and scan rates of 1 ~ 20 mV s –1 , respectively. EIS tests of the supercapacitor device were performed in the frequency range of 0.01 ~ 10 5 Hz with a potential amplitude of 5 mV at an open-circuit voltage. The temperature-dependent capacitive performance of the supercapacitor device under cyclic tensions were evaluated with assistance of the universal testing machine equipped with an environmental chamber. The supercapacitor device with an adhesion area of 25 mm width × 15 mm length was cyclically tensioned for 2000 successive cycles at 20% strain (concerning the adhesion length) at different temperatures of 20, − 20 and − 40°C, respectively. Meanwhile, the corresponding charge/discharge curves were recorded. 2.9 Computational methods The MD simulations in the GROMACS 2021 software package[ 47 – 49 ] used three aqueous solutions (0 m, 7.5 m and 15 m) containing ZnCl 2 to simulate ion-water interactions to investigate the relationship between the ionic solvation configuration and ionic interactions. The model of water molecule is TIP3P [ 50 ]. The OPLSS-AA force field [ 51 ] was used to parametrize all atoms. Leapfrog algorithm was used to integrate the Newtonian equation of motion [ 52 ]. The MD simulation was processed in an NPT ensemble and the simulation time is 20 ns.In NPT simulations, the pressure was maintained at 1 bar by the Berendsen barostat in an isotropic manner [ 53 ] and the temperature was maintained by the V-rescale thermostat at 298.15 K. The LINCS algorithm [ 54 ] was performed for constrain bond lengths of hydrogen atoms. The Particle-Mesh-Ewald (PME) with a fourth-order interpolation was used to evaluate the electrostatic interactions and the grid spacing is 1.0 Å [ 55 ], whereas a cutoff of 1.0 Å was employed to calculate the short-range van der Waals interactions. The initial and final state models of the simulated system were plotted by VMD [ 56 ] (Visual Molecular Dynamics) software. 2.10 Electrochemical calculations The specific capacitance ( C , in the unit of F cm − 2 ) of the supercapacitor device is calculated from the GCD curves based on the following equations: \(\text{C}\text{=3.6*}\frac{\text{Q}}{\text{∆U}\text{*}\text{s}}\) (Eq. 1) where Q is the discharge capacity, Δ U is the voltage after IR drop, and s is the total contact area of the two electrodes. The energy density ( E , in the unit of Wh cm –2 ) and power density ( P , in the unit of W cm –2 ) of the supercapacitor device are calculated based on the following equations: \(\text{E}\text{=}\frac{\text{1}}{\text{2}}\text{C}\text{*}\text{∆U}\) (Eq. 2) \(\text{P=}\frac{\text{E}}{\text{∆t}}\) (Eq. 3) Where Δ t is the discharge time, Δ U is the voltage after IR drop, and C is the specific capacitance of the supercapacitor device. 3 Results and Discussion 3.1 Constructing tough hydrogel matrix The tough hydrogel matrix was constructed by integrating organic polymers and inorganic fillers, in which polyacrylamide (PAAm) polymer chains were cross-linked to form the network skeleton, and hydroxyapatite (3Ca 3 (PO 4 ) 2 ·Ca(OH) 2 , HAp) inorganic fillers were absorbed around the polymer chains by hydrogen bonds. In detail, Ag-Lignin nanoparticles (NPs) were first generated by a redox reaction between lignin macromolecules and the silver-ammonia complex (Ag[(NH 3 ) 2 ] + )[ 46 , 57 ], in which Ag atoms were embedded by lignin shell clusters to form the core-shell nanostructure (Fig. 1 a,b and Fig. S1 ). Acrylamide monomers (AAm), HAp and Ag-Lignin NPs dispersion were then dissolved into deionized water and polymerized to form the PAAm-HAp hydrogel matrix (Fig. 1 c). Because Ag-Lignin NPs could interoperate with ammonium persulfate (APS) to generate a lot of free radicals[ 57 ], AAm monomers were spontaneously polymerized at room temperature to form a cross-linked network without UV or thermal initiation. Scanning electron microscope (SEM) and Energy dispersive X-ray spectroscopy (EDS) elemental mapping images (Fig. 1 d) show that the hydrogel matrix has a typical network structure, in which carbon (C) and nitrogen (N) of the PAAm polymer present a network skeleton, while phosphorus (P) of the HAp inorganic fillers is homogeneously distributed around the polymer chains. Meanwhile, silver (Ag) and sulfur (S) of the Ag-Lignin NPs are well-dispersed within the network. The integration of organic-inorganic structure endows the hydrogel matrix with high toughness, reaching the fracture energy of more than 340 J m –2 (Fig. 1 e and Fig. S2 ), which is crucial for achieving tough adhesion[ 22 ]. In addition, the hydrogel matrix also exhibits excellent adhesion to various material surfaces, including skin tissue, nitrile, glass, polypropylene (PP), polytetrafluoroethylene (PTFE), wood, steel and rubber (Fig. S3 ). We can attribute this adhesion ability to the catechol groups of Ag-Lignin NPs, which can be continuously generated by the redox of silver, thus adhering to various substrates through covalent and noncovalent bonds[ 57 ]. To investigate the toughening mechanism of the hydrogel matrix, we synthesized a series of hydrogels by varying the AAm:HAp mass ratio from 1:0 to 1:0.5, and performed tensile tests. As the AAm:HAp mass ratio increases from 1:0 to 1:0.2, the Young’s modulus, fracture stress and fracture strain gradually increase; When the AAm:HAp mass ratio further increasing to 1:0.5, the fracture strain decreases, but the Young’s modulus and fracture stress slightly increase (Fig. 1 f and Fig. S4 a). This result indicates that the introduction of high-modulus HAp fillers improves the stiffness of polymer skeleton by adsorbing to PAAm chains. Meanwhile, the tension-release hysteresis loops of hydrogels show that the dissipated energy increases with increasing HAp content (Fig. S4 b and Fig. 1 g), suggesting that the sliding of HAp fillers facilitates tension to transmit and distributes mechanical energy among polymer chains. Because a certain content of HAp fillers benefits the stiffness and energy dissipation simultaneously, the fracture energy of hydrogel reaches the highest as the AAm:HAp mass ratio increases to 1: 0.2 (Fig. 1 e, Fig. S4 c and Fig.S5). However, a higher content of inorganic fillers has a negative effect on the fracture energy, which results from the fact that adding more fillers may confine the mobility of polymer chains and break the balance between the organic and inorganic phase[ 58 ]. Thus, we attribute high toughness of the hydrogel matrix to its organic-inorganic integration. On one hand, HAp fillers improve the stiffness of PAAm network. On the other, when the external force is applied, the mechanical energy concentration is effectively suppressed by sliding HAp fillers, preventing the hydrogel from crack propagation and being collapsed [ 59 , 60 ]. 3.2 Fabricating an all-hydrogel supercapacitor On the basis of the tough hydrogel matrix, carbon nanotubes-polypyrrole (CNTs-PPy) conductive materials and ZnCl 2 salts were respectively introduced into the PAAm-HAp hydrogel, thus obtaining the PAAm-HAp/CNTs-PPy hydrogel electrode and the PAAm-HAp/ZnCl 2 hydrogel electrolyte (Fig. 2 a and Fig.S6). An all-hydrogel supercapacitor was fabricated by in situ polymerization of the hydrogel electrolyte on electrodes, as shown in Fig. 2 b. Specifically, when being spread on the semi-dehydrated gel electrodes, the pre-gel solution of hydrogel electrolyte could penetrate into the polymer networks of gel electrodes and polymerize in situ, forming topological entanglements with both pre-existing networks. As a comparison, we used the ex situ adhesion method to prepare the other two types of all-hydrogel supercapacitors. The one is assembled by directly stacking the hydrogel electrolyte between two hydrogel electrodes (defining as ‘direct stacking’), and the other is obtained through stacking the hydrogel electrolyte between two semi-dehydrated gel electrodes (defining as ‘semi-dehydration & stacking’). We compare the SEM images of these three electrode/electrolyte interfaces (Fig. 2 c). The direct stacking-formed interface exists a clear gap, resulting from the fact that high water contents between the electrode and electrolyte would weaken intermolecular interactions at the interface[ 16 , 61 – 63 ] (Fig. 2 c[i]). The interface formed by semi-dehydration & stacking presents a fused state, since the semi-dehydrated gel electrodes enable a close contact with hydrogel electrolyte to strengthen interfacial interactions[ 59 ] (Fig. 2 c[ii]). In contrast, for the interface formed by in situ-polymerization, a dense interface zone appears, which originates from the formation of PAAm stitching network localized at the interface[ 32 ] (Fig. 2 c[iii]). This result confirms that in situ-polymerization enables the PAAm stitching network to be topologically entangled with preexisting networks, leading to a seamless contact between hydrogel electrode and electrolyte. We then performed 180-degree peel tests and lap-shear tests to measure the adhesion performance of these all-hydrogel supercapacitors. For peel tests, the supercapacitor with in situ-polymerization reaches the highest interfacial toughness (639 J m –2 ), the supercapacitor formed by semi-dehydration & stacking lies second (416 J m –2 ), and the supercapacitor with direct stacking is at the lowest (88 J m –2 ) (Fig. 2 d and Fig.S7). At the same time, the supercapacitor with in situ-polymerization undergoes a cohesive failure near the interface during the peeling test (Fig. 2 e). In addition, lap-shear tests show that the supercapacitor with in situ-polymerization also demonstrates the highest shear strength of 54.4 kPa (Fig. 2 d). These results indicate that the adhesion energy between hydrogel electrode and electrolyte strongly relates with the fracture toughness of hydrogel matrix and the interfacial interaction. Thus, we can attribute the robust adhesion to the synergy of topological entanglements and tough hydrogel matrix. For the in situ polymerization process: First, the semi-dehydrated gel electrodes urge the pre-gel solution to penetrate and diffuse into the electrodes by osmotic pressure[ 16 ]. Then, the diffused pre-gel solution can polymerize in situ and form a cross-linked network of PAAm, in topological entanglements with polymer networks of electrodes[ 31 ]. The topological network serving as a molecular suture stitches the electrode and electrolyte together, leading to a strong interfacial interaction[ 33 , 64 ]. Furthermore, the intermolecular interactions between the Ag-Lignin NPs and PAAm polymer also enhance the interfacial interaction. Meanwhile, the tough hydrogel matrix is beneficial to a higher interfacial adhesion because it can amplify energy dissipation through hysteresis at the interface[ 15 ]. Overall, the combination of tough hydrogel matrix and robust interfacial interaction allows our hydrogel electrolyte and hydrogel electrode to obtain a distinguished adhesion energy, which is superior to existing hydrogel adhesion (Table S1 ). 3.3 Investigating anti-freezing properties of hydrogel electrolyte and all-hydrogel supercapacitor We envision that by introducing critical concentration of ZnCl 2 salts into the hydrogel electrolyte, the anti-freezing property of the all-hydrogel supercapacitor could be realized. We firstly investigate the effect of ZnCl 2 concentration on the ionic conductivity of the hydrogel electrolyte at low temperatures. As shown in Fig. 3 a, when the environmental temperature drops from 20°C to − 60°C, the hydrogel electrolytes with ZnCl 2 concentration of 0 ~ 5 m (molality, mol kg − 1 ) are obviously frozen, but the hydrogel electrolytes with ZnCl 2 concentration above 7.5 m still remain unfrozen, which indicates that the freezing of water solvent can be suppressed by the introduction of ZnCl 2 .The ionic conductivities of hydrogel electrolytes with different molality concentrations of ZnCl 2 were tested at 20~–60°C (Fig. 3 b). At the low concentration of ZnCl 2 (0 ~ 2 m), the ionic conductivities show fast decay with temperature dropping; When further adding ZnCl 2 (above 5 m), the ionic conductivities present gentle decrease. This result suggests that the addition of ZnCl 2 can favor the ionic movements of hydrogel electrolytes at low temperatures. We then calculated the activation energy of ionic conductivity based on the Arrhenius equation[ 36 ] to elucidate the ionic conductivity temperature dependence. As the ZnCl 2 concentration raising, the activation energy shows a sharp decrease and then a slight increase, reaching the minimum value of 0.349 eV at 7.5 m ZnCl 2 (Fig. 3 c). Thus, adding a critical ZnCl 2 concentration of 7.5 m is beneficial to improve the temperature-independence of ionic conductivity for the hydrogel electrolyte. At the same time, the ionic conductivity of the hydrogel electrolyte with 7.5 m ZnCl 2 can keep a high value of 0.292 mS cm − 1 even at − 60°C (Table S2 ). We investigated the hydrogen bonding intensity of hydrogel electrolytes with different ZnCl 2 concentrations by Raman spectra (Fig.S8). As shown in Fig. 3 d, the O − H stretching vibration of water (3000 ~ 3700 cm − 1 ) gradually blueshifts with increasing ZnCl 2 concentration, indicating the weakening of hydrogen bonding interactions among water molecules [ 65 – 67 ]. The water ratios with different hydrogen bonding states, including strong, weak and non- hydrogen bonds, were calculated from the fitted peak areas (Fig. 3 e). Obviously, as the ZnCl 2 concentration increases from 0 m to 15m, the strong hydrogen bonds decrease but the non-hydrogen bonds increase. This result suggests that the introduction of ZnCl 2 into the hydrogel progressively disrupts the hydrogen bonds among water clusters, thus preventing water from freezing at low temperatures [ 37 , 68 ]. We then performed molecular dynamics (MD) simulations of ZnCl 2 aqueous solutions with different concentrations (0 m, 7.5 m, 15 m) to further investigate the interactions between Zn 2+ /Cl − and water. Snapshots of MD simulations display a significant reduction of hydrogen bonds with the addition of ZnCl 2 (Fig. 3 f). In particular, the average number of hydrogen bonds among water clusters decreases from ~ 1683 to ~ 470 as the ZnCl 2 concentration increases from 0 m to 15 m (Fig. 3 g). This result reveals that the addition of ZnCl 2 favors ions solvation configuration and breaks hydrogen bonding in water. In addition, when the ZnCl 2 concentration increases from 7.5 m to 15 m, the average coordination number of Zn 2+ –O w decreases, but the Zn 2+ –Cl − significantly increases (Fig. 3 h and Fig.S9), which suggests that higher concentration of ZnCl 2 would cause ions aggregation. Meanwhile, with the ZnCl 2 increasing from 7.5 m to 15 m, the diffusion coefficient of Zn 2+ remarkably decreases from 0.0825×10 − 5 cm 2 s − 1 to 0.0013×10 − 5 cm 2 s − 1 , indicating that higher concentration of ZnCl 2 negatively affects Zn 2+ movement (Fig. 3 i). Therefore, we selected 7.5 m ZnCl 2 as an appropriate addition to further explore the low-temperature mechanical performance of the hydrogel electrolyte. We performed tension cycles for the hydrogel electrolyte in the temperature range of 20~–60°C (Fig.S10). Apparently, as the environmental temperature drops from 20°C to − 60°C, the hydrogel electrolyte demonstrates excellent mechanical elasticity without being frozen and structural damage when undergoing cyclic tensions (Fig. 3 j). In particular, at the temperature ranging from 20°C to − 40°C, the hydrogel electrolyte can endure 100 tension cycles at 100% strain, exhibiting a slight fluctuation in stress remaining (> 90%), low plastic deformation ( 91%) during 100 cycles. Even at − 60°C, the hydrogel electrolyte still shows high elastic recovery of 88% and resilience of 75% after 100 tension cycles (Fig. 3 k and Fig.S10e). Thus, we stem this excellent low-temperature mechanical elasticity from two reasons: First, solvation configurations of ZnCl 2 inhibits hydrogen bonding between water molecules[ 37 ], improving the freezing resistance of the hydrogel electrolyte. Second, moderate addition of ZnCl 2 can avoid the ions aggregation and remain the strong interactions among the polymer chains[ 35 ], enabling the polymer skeleton to maintain favorable elasticity even at low temperatures. Based on above results, we further study the low-temperature fatigue resistance of the fabricated all-hydrogel supercapacitor, which was tensioned for 1000 cycles at 30% strain across a temperature range of 20~–60°C (Fig.S11 and Fig. 3 l). As shown in Fig. 3 m, the all-hydrogel supercapacitor exhibits remarkable fatigue resistance at the temperature ranging from 20°C to − 40°C, in which retaining more than 70% of maximum stress, featuring low plastic deformation of less than 8.5% and high resilience of over 80% after undergoing 1000 tension cycles. Even when the temperature drops to − 60°C, the all-hydrogel supercapacitor can still tolerant multiple tension cycles without fatigue damage, maintaining high elastic recovery of 86% and resilience of ~ 50% after 1000 tension cycles (Fig.S11f). Hence, the fabricated all-hydrogel supercapacitor presents a satisfactory low-temperature fatigue resistance, which mainly results from the fact that the high osmotic pressure between electrode and electrolyte facilitates ZnCl 2 to be solvated throughout the all-hydrogel supercapacitor. To the best of our knowledge, such remarkable fatigue resistance across a wide temperature range of 20~–60°C, has rarely been reported for any all-hydrogel supercapacitors. 3.4 Analyzing low-temperature electrochemical performance Considering the anti-freezing property of the fabricated all-hydrogel supercapacitor, this supercapacitor device is expected to demonstrate promising low-temperature capacitive performance. We systematically analyzed the low-temperature capacitive performance of the supercapacitor device in the temperature range of 20~–50°C. As shown in Fig. 4 a and b, when the environmental temperature drops from 20°C to − 40°C, the device presents a slow reduction in charge/discharge time, delivering the specific capacitance of 93, 77, 49 and 21 mF cm − 2 with a current density of 1 mA cm − 2 at 20, 0, − 20, and − 40°C, respectively; Even at − 50°C, the device can still run well and deliver the specific capacitance of 37 mF cm − 2 with 0.15 mA cm − 2 (Fig.S12). Further electrochemical impedance spectroscopy (EIS) tests and the equivalent circuit fitting were carried out to reveal the low-temperature effect on the electrochemical process of the device. As shown in Fig.S13a and Table S3 , when the temperature drops from 20°C to − 40°C, both the internal resistance (R s ) and charge-transfer resistance (R ct ) present a sluggish increase, indicating that the anti-freezing all-hydrogel supercapacitor could ensure ions transport and charge transfer at low temperatures (Fig. 4 c). In addition, the linear relationship between ln(1/R ct ) and 1000/T further reveals that the electrode/electrolyte interface could maintain unfrozen and stable across a temperature range of 20°C to − 40°C (Fig.S13b), enabling the charge transfer at the interface to be little affected by temperature dropping [ 69 ]. We also tracked the diffusion coefficients of Zn 2+ (D Zn2+ ) with the temperature dropping through the Warburg diffusion calculation (Fig.S13c and d). The fitting result between ln (D Zn2+ ) and 1000/T obeys a linear relationship, indicating that Zn 2+ can effectively diffuse in the electrode at the temperature of 20~–40°C. However, as the temperature further drops to − 50°C, the corresponding values of R s , R ct and D Zn2+ show significant deterioration, which means that the electrochemical behavior of the supercapacitor device would be weakened below − 50°C. Based on the above electrochemical analysis, the combined merits of satisfactory ion transport in the electrolyte, stable charge transfer at the electrolyte/electrode interface and effective ions diffusion in the electrode endow the all-hydrogel supercapacitor device with remark capacitive performance across a temperature range of 20°C to − 40°C. At the same time, specific capacitances of the supercapacitor device with different current densities at low temperatures were summarized in Fig. 4 d, presenting excellent low-temperature rate performance. The detailed information on the energy densities and power densities at various temperatures shows that the device can deliver a maximum energy density of 36 mWh cm –2 with a power density of 608 mW cm –2 at 20°C, and maintain 11 mWh cm –2 with a high power density of 85 mW cm –2 at − 40°C (Fig. 4 e). These values are much competitive compared with previously reported low-temperature hydrogel-based supercapacitor devices[ 4 , 9 , 70 ]. Besides, the supercapacitor device demonstrates excellent low-temperature cycling stability, maintaining high capacitance retention of 99% with an average Coulomb efficiency of 98% after 5000 charge/discharge cycles at 0.35 mA cm –2 (Fig. 4 f). 3.5 Operating stability Featuring with the robust interfacial contact between electrode and electrolyte and the distinct anti-freezing property, our all-hydrogel supercapacitor would be promised to demonstrate capacitive stability under extreme conditions. Before testing, we encapsulated the all-hydrogel supercapacitor and Pt current collectors into an integrated device (30 mm broad × 15 mm high) with the silicone rubber (Fig.S14), as schematically shown in Fig. 5 a. Then, we performed charge/discharge cycles of the device under dynamic deformations, such as bending, compressing, and twisting. Figure 5 b shows the charge/discharge traces and the corresponding capacitance retention of the device undergoing various mechanical deformations. The device is able to handle different deformations and deliver non-deteriorated capacitances, without interlayer slippage, delamination, or crack. We further investigated the operating stability of the device under cyclic tensions at low temperatures. Figure 5 c and d and Movie S1-S3 record the change of mechanical and charge/discharge behaviors of the device which was subjected to tension cycles at 20% strain in the temperature range of 20~–40°C. During continuous tension for 2000 cycles, the device demonstrates stable capacitive performances at low temperatures, maintaining the average capacitance of 93, 32, and 60 mF cm − 2 at 20, − 20, and − 40°C, respectively (Fig. 5 e). The corresponding tension-release traces also indicate that the device can endure 2000 tension cycles, showing satisfactory mechanical flexibility at temperature of 20~–40°C (Fig.S15). These results suggest that the flexible device can be steadily operated under dynamic deformations across a temperature range of 20°C to − 40°C. Compared with previously-reported all-hydrogel supercapacitors, our all-hydrogel supercapacitor device achieves a more distinguished combination of capacitive stability and mechanical flexibility across a temperature range of 20°C to − 40°C (Fig. 5 f and Table S4 ). Finally, we demonstrate its practical applications. For the flammability concern, we directly exposed the device to be flaming. Encouragingly, the device shows the flame retardancy and thermal stability, which cannot be ignited upon exposure to flame above 300°C for 10 s (Fig. 5 g). As a power supply demonstration, we connected six all-hydrogel supercapacitors in series to assemble an integrated module, as depicted in Fig. 5 h. This module could continue powering a digital watch even at the lowest environmental temperature of − 35°C (This temperature is the lowest temperature that the digital watch could be tolerated.) (Fig. 5 i), indicating that the module can steadily supply electricity under low temperatures. 4. Conclusion We develop a type of all-hydrogel flexible supercapacitor obtained by in situ polymerization of hydrogel electrolyte onto the hydrogel electrode, which is featured with stable interface and low-temperature electrochemical performance. The stable interface results from the synergistic effect between tough hydrogel matrix and topological entanglements, reaching high interfacial toughness of 639 J m –2 . The introduction of moderate ZnCl 2 in the hydrogel electrolyte enables the all-hydrogel supercapacitor to maintain mechanical flexibility across a wide temperature range of 20 to − 60°C, demonstrating high elastic recovery of 86% after 1000 tensile cycles even at − 60°C. The all-hydrogel supercapacitor exhibits satisfactory low-temperature electrochemical performance, delivering a high energy density of 11 mWh cm –2 and excellent cycling stability (with an average Coulomb efficiency of 98.1% and capacitance retention of 99.1% over 5000 cycles) at − 40°C. More importantly, the device can endure dynamic deformations and maintain high capacitance retention after 2000 tension cycles in the temperature range of 20 to − 40°C, without delamination and electrochemical failure. We expect that this type of the all-hydrogel supercapacitor would provide a feasible way for enabling stable operation of low-temperature flexible energy storage system. Declarations Conflict of interest The authors declare no conflict of interests. Author contributions Jingya Nan, Yupeng Liu and Chunpeng Wang proposed the concept and supervised the work. Yijing Zhang, Yue Sun and Fusheng Yang performed the experiments, data collections and calculations. Zihao Wang, Yuxi Li, Chuchu Wang and fuxiang Chu helped to discuss and analyze the data. All authors discussed and revised the manuscript. Supplementary Information The online version contains supplementary material available at Funding This work was supported by the Natural Science Foundation of China (32071724), the Natural Science Foundation of Jiangsu Province (BK20220213), and the Fundamental Research Funds of Jiangsu Key Laboratory of Biomass Energy and Material (JSBEM-S-202210, JSBEM-S-202102). 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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-3365097","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":234664410,"identity":"9baf09ac-8c8e-4493-bf91-6c9906962a04","order_by":0,"name":"Yijing Zhang","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yijing","middleName":"","lastName":"Zhang","suffix":""},{"id":234664411,"identity":"f574b6e4-4e8c-4606-b789-09d32915b6f2","order_by":1,"name":"Yue Sun","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yue","middleName":"","lastName":"Sun","suffix":""},{"id":234664412,"identity":"21039879-9742-4a0b-8860-3783dde328a0","order_by":2,"name":"Jingya Nan","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYJACgwQQyd7YwJBgQ5IWnoNALWkk2SUB0kiMFnP2swcKHu6oTeyf+bjxw4OEOwz8sxvwa7HsyUswSDxzPHHG7cRmiYSEZwwSdw7g12JwIMfAILHtWGLD7cQ2hsQfhxkMwC7Ep+X8G4iW+TcPtjEkJBCj5QbYlprEDTcYidYCtuWA8cYzEL/wSNwg6LAcM8OfbXWy844ff/jxR8IdOf4ZBLQAAZsBA8NhxwYI5wAPQfVAwPyAgaHOHso5QIyOUTAKRsEoGGEAAN1jTsKDInuXAAAAAElFTkSuQmCC","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Jingya","middleName":"","lastName":"Nan","suffix":""},{"id":234664413,"identity":"3f4c0b06-59a6-474f-9642-fa337aaa0976","order_by":3,"name":"Fusheng Yang","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Fusheng","middleName":"","lastName":"Yang","suffix":""},{"id":234664414,"identity":"55b3f431-001c-48c7-9530-2ffee58c3fd3","order_by":4,"name":"Zihao Wang","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zihao","middleName":"","lastName":"Wang","suffix":""},{"id":234664415,"identity":"b9b2996a-0883-4e9b-8958-3389d467ae8b","order_by":5,"name":"Yuxi Li","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuxi","middleName":"","lastName":"Li","suffix":""},{"id":234664416,"identity":"2b28926b-a8e3-45b1-a89a-b1a1112734ac","order_by":6,"name":"Chuchu Wang","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Chuchu","middleName":"","lastName":"Wang","suffix":""},{"id":234664417,"identity":"376376e2-9e25-4c8f-81f3-68f186b8a289","order_by":7,"name":"Fuxiang Chu","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Fuxiang","middleName":"","lastName":"Chu","suffix":""},{"id":234664418,"identity":"88a56824-2426-4f12-838b-0adf89f7b2fe","order_by":8,"name":"Yupeng Liu","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yupeng","middleName":"","lastName":"Liu","suffix":""},{"id":234664419,"identity":"6479694a-b53f-44e4-b94a-0e9ed0885913","order_by":9,"name":"Chunpeng Wang","email":"","orcid":"","institution":"Chinese Academy of Forestry","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Chunpeng","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2023-09-18 07:59:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3365097/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3365097/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1002/smll.202309900","type":"published","date":"2024-02-05T12:16:11+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":43706131,"identity":"582a2664-90a3-42cf-ae0d-c3b69203a416","added_by":"auto","created_at":"2023-09-26 14:53:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":7853329,"visible":true,"origin":"","legend":"\u003cp\u003eDesign of PAAm-HAp hydrogel matrix. \u003cstrong\u003ea \u003c/strong\u003eAg-Lignin NPs dispersion was produced through a redox reaction between lignin and the Ag[(NH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e; \u003cstrong\u003eb \u003c/strong\u003eTransmission electron microscopy (TEM) images reveal core-shell nanostructures from Ag-Lignin NPs; \u003cstrong\u003ec \u003c/strong\u003eDiagram of the preparation of the PAAm-HAp hydrogel matrix; \u003cstrong\u003ed \u003c/strong\u003eScanning electron microscope (SEM) and Energy dispersive X-ray spectroscopy (EDS) elemental mapping images show a typical network structure of the hydrogel matrix; \u003cstrong\u003ee \u003c/strong\u003eThe fracture energy of hydrogel with AAm: HAp mass ratio=1:0.2; \u003cstrong\u003ef \u003c/strong\u003eTensile stress versus strain curves of hydrogel with different AAm: HAp mass ratios; \u003cstrong\u003eg\u003c/strong\u003e Tension-release hysteresis loops of various hydrogel at 100% tensile strain.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/4b24bbfe7217dcd9cf4ac18b.png"},{"id":43705099,"identity":"47ff9a8c-c1b5-4dc4-a22d-7124784287c7","added_by":"auto","created_at":"2023-09-26 14:45:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":8596437,"visible":true,"origin":"","legend":"\u003cp\u003eDesign of an all-hydrogel supercapacitor. \u003cstrong\u003ea \u003c/strong\u003eDiagram of the preparation of the PAAm-HAp/CNTs-PPy hydrogel electrode and PAAm-HAp/ZnCl\u003csub\u003e2\u003c/sub\u003e hydrogel electrolyte; \u003cstrong\u003eb \u003c/strong\u003eDiagram of the assembly process of an all-hydrogel supercapacitor. The all-hydrogel supercapacitor is fabricated by in situ polymerization of a hydrogel electrolyte on dehydrated hydrogel electrodes; \u003cstrong\u003ec \u003c/strong\u003eScanning electron microscope (SEM) images and diagram of cross sections of three hydrogel electrolyte/electrode interfaces (Direct stacking, Semi-dehydration \u0026amp; stacking, In situ-polymerization); \u003cstrong\u003ed\u003c/strong\u003e Interfacial toughness and shear strength of three all-hydrogel supercapacitors: (ⅰ) Direct stacking, (ⅱ) Semi-dehydration \u0026amp; stacking, (ⅲ) In situ-polymerization.\u003cstrong\u003e e \u003c/strong\u003eOptical images of the 180° peel test procedure for the three interfaces.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/295932ebff02d3be9617ed25.png"},{"id":43705096,"identity":"3007f704-f98f-4b8f-b16d-eba139ee4b25","added_by":"auto","created_at":"2023-09-26 14:45:29","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":7800172,"visible":true,"origin":"","legend":"\u003cp\u003eLow-temperature resistance of hydrogel electrolytes and all-hydrogel supercapacitors \u003cstrong\u003ea\u003c/strong\u003e Optical images of hydrogel electrolytes with different concentration of ZnCl\u003csub\u003e2\u003c/sub\u003e at 20, –60 °C; \u003cstrong\u003eb \u003c/strong\u003eIonic conductivity of different hydrogel electrolytes in the temperature range of 20~–60 °C; \u003cstrong\u003ec \u003c/strong\u003eActivation energy of ionic conductivity of different hydrogel electrolytes at the temperature range of 20~–60 °C;\u003cstrong\u003e d\u003c/strong\u003e The O-H stretching vibration regions of different ZnCl\u003csub\u003e2\u003c/sub\u003e concentration; \u003cstrong\u003ee \u003c/strong\u003eTrends in the proportions of strong, weak and non- hydrogen bonds with increasing\u003cstrong\u003e \u003c/strong\u003eZnCl\u003csub\u003e2\u003c/sub\u003e concentration; \u003cstrong\u003ef\u003c/strong\u003e Snapshots of the electrolyte structure in MD simulations for ZnCl\u003csub\u003e2\u003c/sub\u003e concentrations of 0 m, 7.5 m and 15 m; \u003cstrong\u003eg \u003c/strong\u003eThe average number of hydrogen bonds among water clusters in different ZnCl\u003csub\u003e2\u003c/sub\u003e aqueous solution systems (0 m, 7.5 m and 15 m); \u003cstrong\u003eh \u003c/strong\u003eThe radial distribution function (RDF) and the corresponding average coordination number (N) for 7.5 m; \u003cstrong\u003ei \u003c/strong\u003eFor the last 1 ns, the root mean square displacements of Zn\u003csup\u003e2+\u003c/sup\u003e in different ZnCl\u003csub\u003e2\u003c/sub\u003e aqueous solution systems (0 m, 7.5 m and 15 m); \u003cstrong\u003ej\u003c/strong\u003e Optical images of hydrogel electrolytes in the tensile cycle in the temperature range from 20 to –60 °C. \u003cstrong\u003ek \u003c/strong\u003eTensile stress versus strain curves of the hydrogel electrolyte under 100% strain for 100 cycles at 20, −20, −40 and −60 °C, respectively; \u003cstrong\u003el \u003c/strong\u003eOptical images of the all-hydrogel supercapacitor in tensile cycles in the temperature range of 20~–60 °C. \u003cstrong\u003em\u003c/strong\u003e Tensile stress versus strain curves of the all-hydrogel supercapacitor in 1000 tensile cycles at 30% strain at 20, −20, −40 and −60 °C.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/027ae4f7b71ced4ce7faaf28.png"},{"id":43705094,"identity":"679fb7d5-8099-4625-a5d3-e29e4474322e","added_by":"auto","created_at":"2023-09-26 14:45:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1179913,"visible":true,"origin":"","legend":"\u003cp\u003eLow-temperature electrochemical performance of all-hydrogel supercapacitors.\u003cstrong\u003e a \u003c/strong\u003eCharge and discharge curves of all-hydrogel supercapacitors in the temperature range of 20~–40 °C; \u003cstrong\u003eb \u003c/strong\u003eDischarge capacitance of all-hydrogel supercapacitors with a current density of 1 mA cm\u003csup\u003e–2\u003c/sup\u003e at temperatures from 20 °C to –40 °C; \u003cstrong\u003ec \u003c/strong\u003eNyquist plot of the temperature dependence of all-hydrogel supercapacitors. The solid line corresponds to the fitted equivalent circuit; \u003cstrong\u003ed \u003c/strong\u003eDischarge capacitance of all-hydrogel supercapacitors with different current densities at different temperatures; \u003cstrong\u003ee \u003c/strong\u003eRagone plots of all-hydrogel supercapacitors at different temperatures. The energy density and power density are measured based on the area of distribution of active material in the hydrogel electrodes; \u003cstrong\u003ef \u003c/strong\u003eCycling performance of all-hydrogel supercapacitors at different temperatures. Capacitance and coulombic efficiency as a function of number of cycles at 20 °C with 2 mA cm\u003csup\u003e–2\u003c/sup\u003e, and –40 °C with 0.35 mA cm\u003csup\u003e–2\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/1f94489ff70139dcb131d304.png"},{"id":43705097,"identity":"89c42079-1c64-4fb9-84aa-3103780696d5","added_by":"auto","created_at":"2023-09-26 14:45:29","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":7673712,"visible":true,"origin":"","legend":"\u003cp\u003eCapacitive stability of all-hydrogel supercapacitor under dynamic deformation and flame retardancy of all-hydrogel supercapacitor. \u003cstrong\u003ea \u003c/strong\u003eDiagram of the configuration the all-hydrogel supercapacitor; \u003cstrong\u003eb \u003c/strong\u003eCapacitance retention of all-hydrogel supercapacitor cyclically charge/discharge under different deformations (bending, compression and twisting); \u003cstrong\u003ec \u003c/strong\u003eForce and strain curves for an all-hydrogel supercapacitor undergoing 2000 tensile cycles at 20, –20 and –40 °C at 20% strain; \u003cstrong\u003ed \u003c/strong\u003eCharge/discharge curves for all-hydrogel supercapacitor undergoing 2000 tensile cycles at 20% strain at different temperatures; \u003cstrong\u003ee \u003c/strong\u003eCorresponding variation in discharge specific capacitance of all-hydrogel supercapacitor undergoing cyclic tension at different temperatures; \u003cstrong\u003ef \u003c/strong\u003eA comparison of the low-temperature deformation stability of our all-hydrogel supercapacitor with previously reported aqueous-based energy storage devices in terms of capacitance retention versus number of deformation cycles. The type of deformation is indicated next to the corresponding symbol. The numbers in brackets represent the operating temperature. Details seen in Table S4; \u003cstrong\u003eg \u003c/strong\u003eOptical images of all-hydrogel supercapacitor at different burning times and infrared temperature images of the device in flame retardant test;\u003cstrong\u003e h \u003c/strong\u003eDiagram of all-hydrogel supercapacitor connected in series to provide power at low temperatures; \u003cstrong\u003ei\u003c/strong\u003e. Demonstration of six all-hydrogel supercapacitor connected in series to power a digital watch at low temperatures.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/359e87520370f851cd0603be.png"},{"id":57348301,"identity":"220f4137-425a-45e3-b917-5386b26a4154","added_by":"auto","created_at":"2024-05-29 12:16:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":32487021,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/e34789de-045d-4035-9588-2fcb7fb0d6a7.pdf"},{"id":43705103,"identity":"39871a4b-0bf9-4088-9044-02662ebf00de","added_by":"auto","created_at":"2023-09-26 14:45:30","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":20144341,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/6e0bbf3c0c906f7dff0c5076.docx"},{"id":43705101,"identity":"fd8a9dae-93b4-4fff-a840-0f6f7a8bebb8","added_by":"auto","created_at":"2023-09-26 14:45:30","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":13871043,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS120.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/cdcef30150c7a1bb470378cf.mp4"},{"id":43705102,"identity":"57e12bf9-79ab-485c-99ac-be27534ae73c","added_by":"auto","created_at":"2023-09-26 14:45:30","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":15703886,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS220.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/0ed6a4ce03d4b874c74ea9be.mp4"},{"id":43705105,"identity":"ee3b3cf1-669c-41da-a07a-0f6f8301d723","added_by":"auto","created_at":"2023-09-26 14:45:30","extension":"mp4","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":15822794,"visible":true,"origin":"","legend":"","description":"","filename":"MovieS340.mp4","url":"https://assets-eu.researchsquare.com/files/rs-3365097/v1/a04288dca3fe193918bbc6af.mp4"}],"financialInterests":"No competing interests reported.","formattedTitle":"In situ polymerization of hydrogel electrolyte on electrode enabling the flexible all-hydrogel supercapacitors with low-temperature adaptability","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe rapid development of wearable electronics has posed new challenges to flexible energy storage devices, which are required to accommodate various mechanical deformations [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. At present, flexible supercapacitors are emerging as a promising candidate due to their excellent mechanical flexibility, high power density, fast charging and discharging, and long cycle life[\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In particular, all-hydrogel supercapacitors are increasingly attractive since hydrogel matrices possess unique merits, including intrinsic flexibility, environmental friendliness and flame-retardant property [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Most of the reported all-hydrogel supercapacitors have been prepared by sandwiching a hydrogel electrolyte between two hydrogel electrodes to form three-layer configurations, in which the similar mechanical properties between the electrode and electrolyte enable the supercapacitors to withstand certain deformations, such as bending, stretching, twisting, and folding[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Despite recent advances, there are two major limitations. First, the interfacial adhesion between the electrode and electrolyte can be weakened because of high water contents existing on the hydrogel surface, thus leading to a poor interfacial contact. As a result, interlayer slippage or irreversible layer delamination may occur for all-hydrogel supercapacitors when being under dynamic deformations [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Second, water solvents in hydrogel matrices will be inevitably frozen at subzero temperatures, hence deteriorating the flexibility and electrochemical performance of the all-hydrogel supercapacitors at low temperatures[\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Therefore, how to design and construct an all-hydrogel supercapacitor that combines the robust electrode/electrolyte interface and anti-freezing property is highly desirable.\u003c/p\u003e \u003cp\u003eUntil now, hydrogel adhesion mainly depends on physical interactions[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], covalent anchorages[\u003cspan additionalcitationids=\"CR23 CR24 CR25\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], mechanical interlocking[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], and topological entanglements[\u003cspan additionalcitationids=\"CR29 CR30\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Among them, topological entanglements can obtain strong interfacial interactions by penetrating the stitching polymer network into porous adherends, showing its effectiveness in adhesion between two hydrogels[\u003cspan additionalcitationids=\"CR32 CR33\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. However, the unique electrical and mechanical properties of hydrogel-based electrodes and electrolytes make it challenging to realize the device-level interfacial integration only using topological adhesion. In other words, the all-hydrogel supercapacitors need not only a stable interface but also appropriate mechanical properties. Hence, the combination of tough hydrogel matrix and topological entanglements is of great importance to achieve robust integration between hydrogel electrodes and electrolytes. To solve the problem that the device cannot work at low temperatures, the ions often are introduced because that metal ions can form solvation configurations through strong electrostatic interactions with water molecules and inhibit the formation of hydrogen bonds in water, the introduction of inorganic salts containing metal ions into hydrogels has been demonstrated as an effective approach to suppress water solvents freezing and lower the freezing point of hydrogels[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan additionalcitationids=\"CR36 CR37 CR38 CR39\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. However, the mechanical performance of these hydrogels is inevitably deteriorated since ionic aggregations dissociate the intermolecular interactions between the polymer chains[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan additionalcitationids=\"CR42 CR43 CR44\" citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. Therefore, developing anti-freezing all-hydrogel supercapacitors without sacrificing their mechanical flexibility is highly expected in practical applications.\u003c/p\u003e \u003cp\u003eHere, we report a new type of all-hydrogel flexible supercapacitors with robust interfacial contact and anti-freezing property, which is fabricated by in situ polymerizing hydrogel electrolyte onto hydrogel electrode. The robust interface is developed by the synergistic effect of the tough hydrogel matrix and strong interfacial interaction, in which the hydrogel matrix is toughened by organic-inorganic integration, the interfacial interaction mainly comes from topological entanglements of the PAAm network penetrating into the hydrogel electrolyte and electrode. Meanwhile, the introduction of zinc chloride (ZnCl\u003csub\u003e2\u003c/sub\u003e) imparts low-temperature mechanical flexibility to the hydrogel electrolyte, enabling the fabricated all-hydrogel supercapacitor to own fatigue resistance across a vast temperature range of 20~\u0026ndash;60\u0026deg;C. More encouragingly, the all-hydrogel supercapacitor possesses excellent low-temperature electrochemical performance, exhibiting stable operation under dynamic deformations at low temperatures. This strategy of designing the all-hydrogel supercapacitor promotes the low-temperature adaptability of flexible energy storage system at the device level.\u003c/p\u003e"},{"header":"2 Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Preparation of Ag-Lignin NPs dispersion\u003c/h2\u003e \u003cp\u003eAg-Lignin NPs were prepared via a redox reaction between lignin macromolecules and the silver-ammonia complex (Ag[(NH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e) according to our previously reported method [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Typically, lignin dispersion (50 mg mL\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) was first formed by dispersing lignin powder (0.5 g, Aladdin) in deionized water (10 mL) with ultrasonication (130 W, 20 kHz) for 5 min. The silver-ammonia complex was obtained by adding ammonia solution (NH\u003csub\u003e3\u003c/sub\u003e\u0026middot;H\u003csub\u003e2\u003c/sub\u003eO, Macklin) into the aqueous solution of AgNO\u003csub\u003e3\u003c/sub\u003e (15 mg mL\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, 10 mL) until the solution to be clear. Lignin dispersion was then added dropwise to silver-ammonia complex and stood in the dark room for 1 h, thus obtaining the Ag-Lignin NPs dispersion.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of PAAm-HAp hydrogel matrix\u003c/h2\u003e \u003cp\u003eThe PAAm-HAp hydrogel matrix was synthesized by free radical polymerizations. In detail, HAp powder (0.63 g, Aladdin), acrylamide (3.15 g, AAm, Aladdin), \u003cem\u003eN,N\u0026prime;\u003c/em\u003e-methylenebisacrylamide (0.00945 g, MBAA, Sigma-Aldrich), and ammonium persulfate (0.0378 g, APS, Sigma-Aldrich) were completely dissolved in deionized water (15 mL) to prepare AAm-HAp solution. Then, the Ag-Lignin NPs dispersion (1.575 mL) was added into the AAm-HAp solution to obtain the pre-gel solution. After degassing, the pre-gel solution was poured into a mold and cured at room temperature for 12 h to fabricate the PAAm-HAp hydrogel matrix.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Formation of PAAm-HAp/CNTs-PPy hydrogel electrode\u003c/h2\u003e \u003cp\u003eThe PAAm-HAp/CNTs-PPy hydrogel electrode was formed by introducing CNTs-PPy conductive materials into the hydrogel matrix. Firstly, the carbon nanotubes dispersion (6.3 g, CNTs, XFNANO) was dissolved into the above pre-gel solution of hydrogel matrix with ultrasonication (130 W, 20 kHz) for 15 min in a bath of ice water. Later, this degassed pre-gel solution containing CNTs was poured into a mold and cured at room temperature for 12 h to synthesize the PAAm-HAp/CNTs hydrogel. Followingly, the hydrogel was immersed in pyrrole solution (0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, Aladdin) for 3 h, and then placed into the FeCl\u003csub\u003e3\u003c/sub\u003e solution (0.5 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, Aladdin) for 3 h, thus obtaining the PAAm-HAp/CNTs-PPy hydrogel electrode. Finally, the semi-dehydrated gel electrode was formed by dehydrating part of water from the hydrogel electrode at 40\u0026deg;C for 6 h. The final water content of the semi-dehydrated gel electrode was ~\u0026thinsp;30%.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Fabrication of the all-hydrogel supercapacitor\u003c/h2\u003e \u003cp\u003eThe all-hydrogel supercapacitor was fabricated by in situ polymerization of hydrogel electrolyte on electrodes. Firstly, the pre-gel solution of hydrogel electrolyte was obtained by dissolving zinc chloride (15.3 g, ZnCl\u003csub\u003e2\u003c/sub\u003e, Aladdin) into the above pre-gel solution of hydrogel matrix under an ice-water bath. Then, this degassed pre-gel solution was poured onto one semi-dehydrated gel electrode at room temperature for 5 min to form the semi-solid gel electrolyte. Subsequently, another semi-dehydrated gel electrode was placed onto the upper side of the semi-solid gel electrolyte at room temperature for 12 h. Thus, the hydrogel electrolyte polymerized in situ onto two electrodes simultaneously, forming topological entanglements with both pre-existing networks.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Material characterizations\u003c/h2\u003e \u003cp\u003eThe structures of Lignin NPs and Ag-Lignin NPs were observed by a transmission electron microscope (TEM; FEI Talos F200X G2, America). Size distributions of the Lignin NPs dispersion and Ag-Lignin NPs dispersion were examined using Malvern Nano-ZS90. The morphologies of hydrogel matrix, hydrogel electrode and hydrogel electrolyte were analyzed using a scanning electron microscope (SEM; Hitachi Regulus 8100, Japan) equipped with an energy dispersive X-ray spectroscopic detector (Ultim Max 170, OXFORD). The cross-sectional morphologies of electrode/electrolyte interfaces were obtained using a scanning electron microscope (SEM; Hitachi Regulus 8100, Japan).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.6 Mechanical tests\u003c/h2\u003e \u003cp\u003eAll mechanical tests were carried out using a universal testing machine (1 kN load cell, UTM 4304GD, Shenzhen SUNS) equipped with an environmental chamber (WGDN-7150S, Shenzhen SUNS). All temperature-dependent mechanical measurements were performed in an environmental chamber with specific temperatures.\u003c/p\u003e \u003cp\u003eFor the fracture toughness, unnotched and notched hydrogel matrices with a rectangular shape (50 mm length \u0026times; 20 mm width \u0026times; 2 mm thickness) were prepared for the pure-shear tensile test. The notched samples were prepared by cutting unnotched samples into a 10 mm-long notch with a knife blade. The tests were conducted at a constant tension rate of 50 mm min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the distance between the two clamps was fixed as 10 mm. The fracture energy was calculated from the tensile force-distance curves of the unnotched and notched samples, as shown in Fig.\u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFor the cyclic tensions, the hydrogel electrolyte with a rectangular shape (50 mm length \u0026times; 20 mm width \u0026times; 2 mm thickness) were prepared before tests. The mechanical elasticity of the hydrogel electrolyte was evaluated by conducting tension-release tests for 100 successive cycles at 100% strain. The fatigue behaviors of the all-hydrogel supercapacitor (50 mm length \u0026times; 20 mm width) were assessed by performing cyclic tensions for 1000 successive cycles at 30% strain. All cyclic tensions were conducted at the specific temperature ranging from 20\u0026deg;C to \u0026minus;\u0026thinsp;60\u0026deg;C with a constant tension rate of 50 mm min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.7 Adhesion tests\u003c/h2\u003e \u003cp\u003eThe adhesion performances of all-hydrogel supercapacitors were evaluated by 180-degree peel tests and lap-shear tests using a universal testing machine (1 kN load cell, UTM 4304GD, Shenzhen SUNS), All tests were proceeded with a constant tension rate of 50 mm min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFor the 180-degree peel tests, the samples with an adhesion area of 25 mm width \u0026times; 70 mm length were prepared. The interfacial toughness was calculated by doubling the plateau force and dividing by the adhesion width. The 3M double coated tissue tape was applied as a stiff backing onto the hydrogel sample to prevent stretching along the peeling direction.\u003c/p\u003e \u003cp\u003eFor the shear strength tests, the samples with an adhesion area of 25 mm width \u0026times;15 mm length were prepared. The shear strength was calculated by dividing the maximum force by the adhesion area. The 3M double coated tissue tape was applied as a stiff backing onto the hydrogel sample to prevent its elongation along the shear direction.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.8 Electrochemical tests\u003c/h2\u003e \u003cp\u003eThe electrochemical performances of the hydrogel electrolyte and all-hydrogel supercapacitor device were measured on an electrochemical working station (CHI 760E). All temperature-dependent electrochemical tests were performed with the aid of a Meiling refrigerator (DW-HL100, \u0026minus;\u0026thinsp;86~\u0026ndash;10\u0026deg;C) or Suns environmental chamber (WGDN-7150S, \u0026minus;\u0026thinsp;70\u0026thinsp;~\u0026thinsp;150\u0026deg;C). The ionic conductivities of hydrogel electrolytes were determined by electrochemical impedance spectroscopy (EIS) tests of the Pt|hydrogel electrolyte|Pt symmetric cells.\u003c/p\u003e \u003cp\u003eThe galvanostatic charge/discharge (GCD) and cyclic voltammetry (CV) tests were conducted in the voltage range of 0\u0026thinsp;~\u0026thinsp;0.8 V at current densities of 0.5\u0026thinsp;~\u0026thinsp;3 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and scan rates of 1\u0026thinsp;~\u0026thinsp;20 mV s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively. EIS tests of the supercapacitor device were performed in the frequency range of 0.01\u0026thinsp;~\u0026thinsp;10\u003csup\u003e5\u003c/sup\u003e Hz with a potential amplitude of 5 mV at an open-circuit voltage.\u003c/p\u003e \u003cp\u003eThe temperature-dependent capacitive performance of the supercapacitor device under cyclic tensions were evaluated with assistance of the universal testing machine equipped with an environmental chamber. The supercapacitor device with an adhesion area of 25 mm width \u0026times; 15 mm length was cyclically tensioned for 2000 successive cycles at 20% strain (concerning the adhesion length) at different temperatures of 20, \u0026minus;\u0026thinsp;20 and \u0026minus;\u0026thinsp;40\u0026deg;C, respectively. Meanwhile, the corresponding charge/discharge curves were recorded.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.9 Computational methods\u003c/h2\u003e \u003cp\u003eThe MD simulations in the GROMACS 2021 software package[\u003cspan additionalcitationids=\"CR48\" citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] used three aqueous solutions (0 m, 7.5 m and 15 m) containing ZnCl\u003csub\u003e2\u003c/sub\u003e to simulate ion-water interactions to investigate the relationship between the ionic solvation configuration and ionic interactions. The model of water molecule is TIP3P [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. The OPLSS-AA force field [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e] was used to parametrize all atoms. Leapfrog algorithm was used to integrate the Newtonian equation of motion [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. The MD simulation was processed in an NPT ensemble and the simulation time is 20 ns.In NPT simulations, the pressure was maintained at 1 bar by the Berendsen barostat in an isotropic manner [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e] and the temperature was maintained by the V-rescale thermostat at 298.15 K. The LINCS algorithm [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e] was performed for constrain bond lengths of hydrogen atoms. The Particle-Mesh-Ewald (PME) with a fourth-order interpolation was used to evaluate the electrostatic interactions and the grid spacing is 1.0 \u0026Aring; [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], whereas a cutoff of 1.0 \u0026Aring; was employed to calculate the short-range van der Waals interactions. The initial and final state models of the simulated system were plotted by VMD [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e] (Visual Molecular Dynamics) software.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e2.10 Electrochemical calculations\u003c/h2\u003e \u003cp\u003eThe specific capacitance (\u003cem\u003eC\u003c/em\u003e, in the unit of F cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) of the supercapacitor device is calculated from the GCD curves based on the following equations:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\text{C}\\text{=3.6*}\\frac{\\text{Q}}{\\text{∆U}\\text{*}\\text{s}}\\)\u003c/span\u003e \u003c/span\u003e (Eq.\u0026nbsp;1)\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eQ\u003c/em\u003e is the discharge capacity, Δ\u003cem\u003eU\u003c/em\u003e is the voltage after IR drop, and \u003cem\u003es\u003c/em\u003e is the total contact area of the two electrodes.\u003c/p\u003e \u003cp\u003eThe energy density (\u003cem\u003eE\u003c/em\u003e, in the unit of Wh cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e) and power density (\u003cem\u003eP\u003c/em\u003e, in the unit of W cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e) of the supercapacitor device are calculated based on the following equations:\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\text{E}\\text{=}\\frac{\\text{1}}{\\text{2}}\\text{C}\\text{*}\\text{∆U}\\)\u003c/span\u003e \u003c/span\u003e (Eq.\u0026nbsp;2)\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\text{P=}\\frac{\\text{E}}{\\text{∆t}}\\)\u003c/span\u003e \u003c/span\u003e (Eq.\u0026nbsp;3)\u003c/p\u003e \u003cp\u003eWhere Δ\u003cem\u003et\u003c/em\u003e is the discharge time, Δ\u003cem\u003eU\u003c/em\u003e is the voltage after IR drop, and \u003cem\u003eC\u003c/em\u003e is the specific capacitance of the supercapacitor device.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Constructing tough hydrogel matrix\u003c/h2\u003e \u003cp\u003eThe tough hydrogel matrix was constructed by integrating organic polymers and inorganic fillers, in which polyacrylamide (PAAm) polymer chains were cross-linked to form the network skeleton, and hydroxyapatite (3Ca\u003csub\u003e3\u003c/sub\u003e(PO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;Ca(OH)\u003csub\u003e2\u003c/sub\u003e, HAp) inorganic fillers were absorbed around the polymer chains by hydrogen bonds. In detail, Ag-Lignin nanoparticles (NPs) were first generated by a redox reaction between lignin macromolecules and the silver-ammonia complex (Ag[(NH\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e]\u003csup\u003e+\u003c/sup\u003e)[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e], in which Ag atoms were embedded by lignin shell clusters to form the core-shell nanostructure (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea,b and Fig.\u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Acrylamide monomers (AAm), HAp and Ag-Lignin NPs dispersion were then dissolved into deionized water and polymerized to form the PAAm-HAp hydrogel matrix (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). Because Ag-Lignin NPs could interoperate with ammonium persulfate (APS) to generate a lot of free radicals[\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e], AAm monomers were spontaneously polymerized at room temperature to form a cross-linked network without UV or thermal initiation. Scanning electron microscope (SEM) and Energy dispersive X-ray spectroscopy (EDS) elemental mapping images (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) show that the hydrogel matrix has a typical network structure, in which carbon (C) and nitrogen (N) of the PAAm polymer present a network skeleton, while phosphorus (P) of the HAp inorganic fillers is homogeneously distributed around the polymer chains. Meanwhile, silver (Ag) and sulfur (S) of the Ag-Lignin NPs are well-dispersed within the network. The integration of organic-inorganic structure endows the hydrogel matrix with high toughness, reaching the fracture energy of more than 340 J m\u003csup\u003e\u0026ndash;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee and Fig.\u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e), which is crucial for achieving tough adhesion[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In addition, the hydrogel matrix also exhibits excellent adhesion to various material surfaces, including skin tissue, nitrile, glass, polypropylene (PP), polytetrafluoroethylene (PTFE), wood, steel and rubber (Fig.\u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e). We can attribute this adhesion ability to the catechol groups of Ag-Lignin NPs, which can be continuously generated by the redox of silver, thus adhering to various substrates through covalent and noncovalent bonds[\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo investigate the toughening mechanism of the hydrogel matrix, we synthesized a series of hydrogels by varying the AAm:HAp mass ratio from 1:0 to 1:0.5, and performed tensile tests. As the AAm:HAp mass ratio increases from 1:0 to 1:0.2, the Young\u0026rsquo;s modulus, fracture stress and fracture strain gradually increase; When the AAm:HAp mass ratio further increasing to 1:0.5, the fracture strain decreases, but the Young\u0026rsquo;s modulus and fracture stress slightly increase (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef and Fig.\u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003ea). This result indicates that the introduction of high-modulus HAp fillers improves the stiffness of polymer skeleton by adsorbing to PAAm chains. Meanwhile, the tension-release hysteresis loops of hydrogels show that the dissipated energy increases with increasing HAp content (Fig.\u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003eb and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg), suggesting that the sliding of HAp fillers facilitates tension to transmit and distributes mechanical energy among polymer chains. Because a certain content of HAp fillers benefits the stiffness and energy dissipation simultaneously, the fracture energy of hydrogel reaches the highest as the AAm:HAp mass ratio increases to 1: 0.2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee, Fig.\u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003ec and Fig.S5). However, a higher content of inorganic fillers has a negative effect on the fracture energy, which results from the fact that adding more fillers may confine the mobility of polymer chains and break the balance between the organic and inorganic phase[\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. Thus, we attribute high toughness of the hydrogel matrix to its organic-inorganic integration. On one hand, HAp fillers improve the stiffness of PAAm network. On the other, when the external force is applied, the mechanical energy concentration is effectively suppressed by sliding HAp fillers, preventing the hydrogel from crack propagation and being collapsed [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Fabricating an all-hydrogel supercapacitor\u003c/h2\u003e \u003cp\u003eOn the basis of the tough hydrogel matrix, carbon nanotubes-polypyrrole (CNTs-PPy) conductive materials and ZnCl\u003csub\u003e2\u003c/sub\u003e salts were respectively introduced into the PAAm-HAp hydrogel, thus obtaining the PAAm-HAp/CNTs-PPy hydrogel electrode and the PAAm-HAp/ZnCl\u003csub\u003e2\u003c/sub\u003e hydrogel electrolyte (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and Fig.S6). An all-hydrogel supercapacitor was fabricated by in situ polymerization of the hydrogel electrolyte on electrodes, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. Specifically, when being spread on the semi-dehydrated gel electrodes, the pre-gel solution of hydrogel electrolyte could penetrate into the polymer networks of gel electrodes and polymerize in situ, forming topological entanglements with both pre-existing networks. As a comparison, we used the ex situ adhesion method to prepare the other two types of all-hydrogel supercapacitors. The one is assembled by directly stacking the hydrogel electrolyte between two hydrogel electrodes (defining as \u0026lsquo;direct stacking\u0026rsquo;), and the other is obtained through stacking the hydrogel electrolyte between two semi-dehydrated gel electrodes (defining as \u0026lsquo;semi-dehydration \u0026amp; stacking\u0026rsquo;). We compare the SEM images of these three electrode/electrolyte interfaces (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). The direct stacking-formed interface exists a clear gap, resulting from the fact that high water contents between the electrode and electrolyte would weaken intermolecular interactions at the interface[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan additionalcitationids=\"CR62\" citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec[i]). The interface formed by semi-dehydration \u0026amp; stacking presents a fused state, since the semi-dehydrated gel electrodes enable a close contact with hydrogel electrolyte to strengthen interfacial interactions[\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec[ii]). In contrast, for the interface formed by in situ-polymerization, a dense interface zone appears, which originates from the formation of PAAm stitching network localized at the interface[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec[iii]). This result confirms that in situ-polymerization enables the PAAm stitching network to be topologically entangled with preexisting networks, leading to a seamless contact between hydrogel electrode and electrolyte.\u003c/p\u003e \u003cp\u003eWe then performed 180-degree peel tests and lap-shear tests to measure the adhesion performance of these all-hydrogel supercapacitors. For peel tests, the supercapacitor with in situ-polymerization reaches the highest interfacial toughness (639 J m\u003csup\u003e\u0026ndash;2\u003c/sup\u003e), the supercapacitor formed by semi-dehydration \u0026amp; stacking lies second (416 J m\u003csup\u003e\u0026ndash;2\u003c/sup\u003e), and the supercapacitor with direct stacking is at the lowest (88 J m\u003csup\u003e\u0026ndash;2\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed and Fig.S7). At the same time, the supercapacitor with in situ-polymerization undergoes a cohesive failure near the interface during the peeling test (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). In addition, lap-shear tests show that the supercapacitor with in situ-polymerization also demonstrates the highest shear strength of 54.4 kPa (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). These results indicate that the adhesion energy between hydrogel electrode and electrolyte strongly relates with the fracture toughness of hydrogel matrix and the interfacial interaction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThus, we can attribute the robust adhesion to the synergy of topological entanglements and tough hydrogel matrix. For the in situ polymerization process: First, the semi-dehydrated gel electrodes urge the pre-gel solution to penetrate and diffuse into the electrodes by osmotic pressure[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Then, the diffused pre-gel solution can polymerize in situ and form a cross-linked network of PAAm, in topological entanglements with polymer networks of electrodes[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The topological network serving as a molecular suture stitches the electrode and electrolyte together, leading to a strong interfacial interaction[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]. Furthermore, the intermolecular interactions between the Ag-Lignin NPs and PAAm polymer also enhance the interfacial interaction. Meanwhile, the tough hydrogel matrix is beneficial to a higher interfacial adhesion because it can amplify energy dissipation through hysteresis at the interface[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Overall, the combination of tough hydrogel matrix and robust interfacial interaction allows our hydrogel electrolyte and hydrogel electrode to obtain a distinguished adhesion energy, which is superior to existing hydrogel adhesion (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Investigating anti-freezing properties of hydrogel electrolyte and all-hydrogel supercapacitor\u003c/h2\u003e \u003cp\u003eWe envision that by introducing critical concentration of ZnCl\u003csub\u003e2\u003c/sub\u003e salts into the hydrogel electrolyte, the anti-freezing property of the all-hydrogel supercapacitor could be realized. We firstly investigate the effect of ZnCl\u003csub\u003e2\u003c/sub\u003e concentration on the ionic conductivity of the hydrogel electrolyte at low temperatures. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, when the environmental temperature drops from 20\u0026deg;C to \u0026minus;\u0026thinsp;60\u0026deg;C, the hydrogel electrolytes with ZnCl\u003csub\u003e2\u003c/sub\u003e concentration of 0\u0026thinsp;~\u0026thinsp;5 m (molality, mol kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) are obviously frozen, but the hydrogel electrolytes with ZnCl\u003csub\u003e2\u003c/sub\u003e concentration above 7.5 m still remain unfrozen, which indicates that the freezing of water solvent can be suppressed by the introduction of ZnCl\u003csub\u003e2\u003c/sub\u003e.The ionic conductivities of hydrogel electrolytes with different molality concentrations of ZnCl\u003csub\u003e2\u003c/sub\u003e were tested at 20~\u0026ndash;60\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). At the low concentration of ZnCl\u003csub\u003e2\u003c/sub\u003e (0\u0026thinsp;~\u0026thinsp;2 m), the ionic conductivities show fast decay with temperature dropping; When further adding ZnCl\u003csub\u003e2\u003c/sub\u003e (above 5 m), the ionic conductivities present gentle decrease. This result suggests that the addition of ZnCl\u003csub\u003e2\u003c/sub\u003e can favor the ionic movements of hydrogel electrolytes at low temperatures. We then calculated the activation energy of ionic conductivity based on the Arrhenius equation[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] to elucidate the ionic conductivity temperature dependence. As the ZnCl\u003csub\u003e2\u003c/sub\u003e concentration raising, the activation energy shows a sharp decrease and then a slight increase, reaching the minimum value of 0.349 eV at 7.5 m ZnCl\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). Thus, adding a critical ZnCl\u003csub\u003e2\u003c/sub\u003e concentration of 7.5 m is beneficial to improve the temperature-independence of ionic conductivity for the hydrogel electrolyte. At the same time, the ionic conductivity of the hydrogel electrolyte with 7.5 m ZnCl\u003csub\u003e2\u003c/sub\u003e can keep a high value of 0.292 mS cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e even at \u0026minus;\u0026thinsp;60\u0026deg;C (Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWe investigated the hydrogen bonding intensity of hydrogel electrolytes with different ZnCl\u003csub\u003e2\u003c/sub\u003e concentrations by Raman spectra (Fig.S8). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, the O\u0026thinsp;\u0026minus;\u0026thinsp;H stretching vibration of water (3000\u0026thinsp;~\u0026thinsp;3700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) gradually blueshifts with increasing ZnCl\u003csub\u003e2\u003c/sub\u003e concentration, indicating the weakening of hydrogen bonding interactions among water molecules [\u003cspan additionalcitationids=\"CR66\" citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. The water ratios with different hydrogen bonding states, including strong, weak and non- hydrogen bonds, were calculated from the fitted peak areas (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). Obviously, as the ZnCl\u003csub\u003e2\u003c/sub\u003e concentration increases from 0 m to 15m, the strong hydrogen bonds decrease but the non-hydrogen bonds increase. This result suggests that the introduction of ZnCl\u003csub\u003e2\u003c/sub\u003e into the hydrogel progressively disrupts the hydrogen bonds among water clusters, thus preventing water from freezing at low temperatures [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e]. We then performed molecular dynamics (MD) simulations of ZnCl\u003csub\u003e2\u003c/sub\u003e aqueous solutions with different concentrations (0 m, 7.5 m, 15 m) to further investigate the interactions between Zn\u003csup\u003e2+\u003c/sup\u003e/Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e and water. Snapshots of MD simulations display a significant reduction of hydrogen bonds with the addition of ZnCl\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). In particular, the average number of hydrogen bonds among water clusters decreases from ~\u0026thinsp;1683 to ~\u0026thinsp;470 as the ZnCl\u003csub\u003e2\u003c/sub\u003e concentration increases from 0 m to 15 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). This result reveals that the addition of ZnCl\u003csub\u003e2\u003c/sub\u003e favors ions solvation configuration and breaks hydrogen bonding in water. In addition, when the ZnCl\u003csub\u003e2\u003c/sub\u003e concentration increases from 7.5 m to 15 m, the average coordination number of Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;O\u003csub\u003ew\u003c/sub\u003e decreases, but the Zn\u003csup\u003e2+\u003c/sup\u003e\u0026ndash;Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e significantly increases (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh and Fig.S9), which suggests that higher concentration of ZnCl\u003csub\u003e2\u003c/sub\u003e would cause ions aggregation. Meanwhile, with the ZnCl\u003csub\u003e2\u003c/sub\u003e increasing from 7.5 m to 15 m, the diffusion coefficient of Zn\u003csup\u003e2+\u003c/sup\u003e remarkably decreases from 0.0825\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to 0.0013\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating that higher concentration of ZnCl\u003csub\u003e2\u003c/sub\u003e negatively affects Zn\u003csup\u003e2+\u003c/sup\u003e movement (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). Therefore, we selected 7.5 m ZnCl\u003csub\u003e2\u003c/sub\u003e as an appropriate addition to further explore the low-temperature mechanical performance of the hydrogel electrolyte.\u003c/p\u003e \u003cp\u003eWe performed tension cycles for the hydrogel electrolyte in the temperature range of 20~\u0026ndash;60\u0026deg;C (Fig.S10). Apparently, as the environmental temperature drops from 20\u0026deg;C to \u0026minus;\u0026thinsp;60\u0026deg;C, the hydrogel electrolyte demonstrates excellent mechanical elasticity without being frozen and structural damage when undergoing cyclic tensions (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej). In particular, at the temperature ranging from 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C, the hydrogel electrolyte can endure 100 tension cycles at 100% strain, exhibiting a slight fluctuation in stress remaining (\u0026gt;\u0026thinsp;90%), low plastic deformation (\u0026lt;\u0026thinsp;8.4%), and high resilience (\u0026gt;\u0026thinsp;91%) during 100 cycles. Even at \u0026minus;\u0026thinsp;60\u0026deg;C, the hydrogel electrolyte still shows high elastic recovery of 88% and resilience of 75% after 100 tension cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ek and Fig.S10e). Thus, we stem this excellent low-temperature mechanical elasticity from two reasons: First, solvation configurations of ZnCl\u003csub\u003e2\u003c/sub\u003e inhibits hydrogen bonding between water molecules[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], improving the freezing resistance of the hydrogel electrolyte. Second, moderate addition of ZnCl\u003csub\u003e2\u003c/sub\u003e can avoid the ions aggregation and remain the strong interactions among the polymer chains[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], enabling the polymer skeleton to maintain favorable elasticity even at low temperatures.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on above results, we further study the low-temperature fatigue resistance of the fabricated all-hydrogel supercapacitor, which was tensioned for 1000 cycles at 30% strain across a temperature range of 20~\u0026ndash;60\u0026deg;C (Fig.S11 and Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003el). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003em, the all-hydrogel supercapacitor exhibits remarkable fatigue resistance at the temperature ranging from 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C, in which retaining more than 70% of maximum stress, featuring low plastic deformation of less than 8.5% and high resilience of over 80% after undergoing 1000 tension cycles. Even when the temperature drops to \u0026minus;\u0026thinsp;60\u0026deg;C, the all-hydrogel supercapacitor can still tolerant multiple tension cycles without fatigue damage, maintaining high elastic recovery of 86% and resilience of ~\u0026thinsp;50% after 1000 tension cycles (Fig.S11f). Hence, the fabricated all-hydrogel supercapacitor presents a satisfactory low-temperature fatigue resistance, which mainly results from the fact that the high osmotic pressure between electrode and electrolyte facilitates ZnCl\u003csub\u003e2\u003c/sub\u003e to be solvated throughout the all-hydrogel supercapacitor. To the best of our knowledge, such remarkable fatigue resistance across a wide temperature range of 20~\u0026ndash;60\u0026deg;C, has rarely been reported for any all-hydrogel supercapacitors.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Analyzing low-temperature electrochemical performance\u003c/h2\u003e \u003cp\u003eConsidering the anti-freezing property of the fabricated all-hydrogel supercapacitor, this supercapacitor device is expected to demonstrate promising low-temperature capacitive performance. We systematically analyzed the low-temperature capacitive performance of the supercapacitor device in the temperature range of 20~\u0026ndash;50\u0026deg;C. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and b, when the environmental temperature drops from 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C, the device presents a slow reduction in charge/discharge time, delivering the specific capacitance of 93, 77, 49 and 21 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with a current density of 1 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 20, 0, \u0026minus;\u0026thinsp;20, and \u0026minus;\u0026thinsp;40\u0026deg;C, respectively; Even at \u0026minus;\u0026thinsp;50\u0026deg;C, the device can still run well and deliver the specific capacitance of 37 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with 0.15 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.S12).\u003c/p\u003e \u003cp\u003eFurther electrochemical impedance spectroscopy (EIS) tests and the equivalent circuit fitting were carried out to reveal the low-temperature effect on the electrochemical process of the device. As shown in Fig.S13a and Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e, when the temperature drops from 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C, both the internal resistance (R\u003csub\u003es\u003c/sub\u003e) and charge-transfer resistance (R\u003csub\u003ect\u003c/sub\u003e) present a sluggish increase, indicating that the anti-freezing all-hydrogel supercapacitor could ensure ions transport and charge transfer at low temperatures (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). In addition, the linear relationship between ln(1/R\u003csub\u003ect\u003c/sub\u003e) and 1000/T further reveals that the electrode/electrolyte interface could maintain unfrozen and stable across a temperature range of 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C (Fig.S13b), enabling the charge transfer at the interface to be little affected by temperature dropping [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]. We also tracked the diffusion coefficients of Zn\u003csup\u003e2+\u003c/sup\u003e (D\u003csub\u003eZn2+\u003c/sub\u003e) with the temperature dropping through the Warburg diffusion calculation (Fig.S13c and d). The fitting result between ln (D\u003csub\u003eZn2+\u003c/sub\u003e) and 1000/T obeys a linear relationship, indicating that Zn\u003csup\u003e2+\u003c/sup\u003e can effectively diffuse in the electrode at the temperature of 20~\u0026ndash;40\u0026deg;C. However, as the temperature further drops to \u0026minus;\u0026thinsp;50\u0026deg;C, the corresponding values of R\u003csub\u003es\u003c/sub\u003e, R\u003csub\u003ect\u003c/sub\u003e and D\u003csub\u003eZn2+\u003c/sub\u003e show significant deterioration, which means that the electrochemical behavior of the supercapacitor device would be weakened below \u0026minus;\u0026thinsp;50\u0026deg;C. Based on the above electrochemical analysis, the combined merits of satisfactory ion transport in the electrolyte, stable charge transfer at the electrolyte/electrode interface and effective ions diffusion in the electrode endow the all-hydrogel supercapacitor device with remark capacitive performance across a temperature range of 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C. At the same time, specific capacitances of the supercapacitor device with different current densities at low temperatures were summarized in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed, presenting excellent low-temperature rate performance. The detailed information on the energy densities and power densities at various temperatures shows that the device can deliver a maximum energy density of 36 mWh cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e with a power density of 608 mW cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e at 20\u0026deg;C, and maintain 11 mWh cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e with a high power density of 85 mW cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e at \u0026minus;\u0026thinsp;40\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). These values are much competitive compared with previously reported low-temperature hydrogel-based supercapacitor devices[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e]. Besides, the supercapacitor device demonstrates excellent low-temperature cycling stability, maintaining high capacitance retention of 99% with an average Coulomb efficiency of 98% after 5000 charge/discharge cycles at 0.35 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Operating stability\u003c/h2\u003e \u003cp\u003eFeaturing with the robust interfacial contact between electrode and electrolyte and the distinct anti-freezing property, our all-hydrogel supercapacitor would be promised to demonstrate capacitive stability under extreme conditions. Before testing, we encapsulated the all-hydrogel supercapacitor and Pt current collectors into an integrated device (30 mm broad \u0026times; 15 mm high) with the silicone rubber (Fig.S14), as schematically shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea. Then, we performed charge/discharge cycles of the device under dynamic deformations, such as bending, compressing, and twisting. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows the charge/discharge traces and the corresponding capacitance retention of the device undergoing various mechanical deformations. The device is able to handle different deformations and deliver non-deteriorated capacitances, without interlayer slippage, delamination, or crack. We further investigated the operating stability of the device under cyclic tensions at low temperatures. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and d and Movie S1-S3 record the change of mechanical and charge/discharge behaviors of the device which was subjected to tension cycles at 20% strain in the temperature range of 20~\u0026ndash;40\u0026deg;C. During continuous tension for 2000 cycles, the device demonstrates stable capacitive performances at low temperatures, maintaining the average capacitance of 93, 32, and 60 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 20, \u0026minus;\u0026thinsp;20, and \u0026minus;\u0026thinsp;40\u0026deg;C, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). The corresponding tension-release traces also indicate that the device can endure 2000 tension cycles, showing satisfactory mechanical flexibility at temperature of 20~\u0026ndash;40\u0026deg;C (Fig.S15). These results suggest that the flexible device can be steadily operated under dynamic deformations across a temperature range of 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C. Compared with previously-reported all-hydrogel supercapacitors, our all-hydrogel supercapacitor device achieves a more distinguished combination of capacitive stability and mechanical flexibility across a temperature range of 20\u0026deg;C to \u0026minus;\u0026thinsp;40\u0026deg;C (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef and Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFinally, we demonstrate its practical applications. For the flammability concern, we directly exposed the device to be flaming. Encouragingly, the device shows the flame retardancy and thermal stability, which cannot be ignited upon exposure to flame above 300\u0026deg;C for 10 s (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg). As a power supply demonstration, we connected six all-hydrogel supercapacitors in series to assemble an integrated module, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eh. This module could continue powering a digital watch even at the lowest environmental temperature of \u0026minus;\u0026thinsp;35\u0026deg;C (This temperature is the lowest temperature that the digital watch could be tolerated.) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ei), indicating that the module can steadily supply electricity under low temperatures.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eWe develop a type of all-hydrogel flexible supercapacitor obtained by in situ polymerization of hydrogel electrolyte onto the hydrogel electrode, which is featured with stable interface and low-temperature electrochemical performance. The stable interface results from the synergistic effect between tough hydrogel matrix and topological entanglements, reaching high interfacial toughness of 639 J m\u003csup\u003e\u0026ndash;2\u003c/sup\u003e. The introduction of moderate ZnCl\u003csub\u003e2\u003c/sub\u003e in the hydrogel electrolyte enables the all-hydrogel supercapacitor to maintain mechanical flexibility across a wide temperature range of 20 to \u0026minus;\u0026thinsp;60\u0026deg;C, demonstrating high elastic recovery of 86% after 1000 tensile cycles even at \u0026minus;\u0026thinsp;60\u0026deg;C. The all-hydrogel supercapacitor exhibits satisfactory low-temperature electrochemical performance, delivering a high energy density of 11 mWh cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e and excellent cycling stability (with an average Coulomb efficiency of 98.1% and capacitance retention of 99.1% over 5000 cycles) at \u0026minus;\u0026thinsp;40\u0026deg;C. More importantly, the device can endure dynamic deformations and maintain high capacitance retention after 2000 tension cycles in the temperature range of 20 to \u0026minus;\u0026thinsp;40\u0026deg;C, without delamination and electrochemical failure. We expect that this type of the all-hydrogel supercapacitor would provide a feasible way for enabling stable operation of low-temperature flexible energy storage system.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e The authors declare no conflict of interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e Jingya Nan, Yupeng Liu and Chunpeng Wang proposed the concept and supervised the work. Yijing Zhang, Yue Sun and Fusheng Yang performed the experiments, data collections and calculations. Zihao Wang, Yuxi Li, Chuchu Wang and fuxiang Chu helped to discuss and analyze the data. All authors discussed and revised the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary Information\u003c/strong\u003eThe online version contains supplementary material available at\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e This work was supported by the Natural Science Foundation of China (32071724), the Natural Science Foundation of Jiangsu Province (BK20220213), and the Fundamental Research Funds of Jiangsu Key Laboratory of Biomass Energy and Material (JSBEM-S-202210, JSBEM-S-202102).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLi X, Yuan L, Liu R, He H, Hao J, Lu Y, Wang Y, Liang G, Yuan G, Guo Z (2021) Engineering textile electrode and bacterial cellulose nanofiber reinforced hydrogel electrolyte to enable high-performance flexible all‐solid‐state supercapacitors. 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J Am Chem Soc 34:39404\u0026ndash;39419. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/:10.1021/acsami.2c11973\u003c/span\u003e\u003cspan address=\":10.1021/acsami.2c11973\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Robust interface, Flexible supercapacitors, Low-temperature, All-hydrogel","lastPublishedDoi":"10.21203/rs.3.rs-3365097/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3365097/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAll-hydrogel supercapacitors are emerging as promising power sources for next-generation wearable electronics due to their intrinsically mechanical flexibility, eco-friendliness, and enhanced safety. However, the insufficient interfacial adhesion between electrode and electrolyte and the frozen hydrogel matrices at subzero temperatures largely limit the practical applications of all-hydrogel supercapacitors. Here, we report an all-hydrogel supercapacitor with robust interfacial contact and anti-freezing property, which is fabricated by in situ polymerizing hydrogel electrolyte onto hydrogel electrode. The robust interfacial adhesion is developed by the synergistic effect of tough hydrogel matrix and topological entanglements. Meanwhile, the incorporation of ZnCl\u003csub\u003e2\u003c/sub\u003e in the hydrogel electrolyte prevents water solvents from freezing and endows the all-hydrogel supercapacitor with mechanical flexibility and fatigue resistance across a wide temperature range of 20\u0026deg;C to \u0026minus;\u0026thinsp;60\u0026deg;C. Such all-hydrogel supercapacitor demonstrates satisfactory low-temperature electrochemical performance, delivering high energy density of 11 mWh cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e and excellent cycling stability with capacitance retention of 99% over 5000 cycles at \u0026minus;\u0026thinsp;40\u0026deg;C. Notably, the fabricated all-hydrogel supercapacitor can endure dynamic deformations and operate well under 2000 tension cycles even at \u0026minus;\u0026thinsp;40\u0026deg;C, without delamination and electrochemical failure. This work offers a promising strategy for flexible energy storage devices with low-temperature adaptability.\u003c/p\u003e","manuscriptTitle":"In situ polymerization of hydrogel electrolyte on electrode enabling the flexible all-hydrogel supercapacitors with low-temperature adaptability","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-09-26 14:45:24","doi":"10.21203/rs.3.rs-3365097/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"72fb891c-5910-4d4a-8a3f-378675b152ad","owner":[],"postedDate":"September 26th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-05-29T12:16:11+00:00","versionOfRecord":{"articleIdentity":"rs-3365097","link":"https://doi.org/10.1002/smll.202309900","journal":{"identity":"small","isVorOnly":true,"title":"Small"},"publishedOn":"2024-02-05 12:16:11","publishedOnDateReadable":"February 5th, 2024"},"versionCreatedAt":"2023-09-26 14:45:24","video":"","vorDoi":"10.1002/smll.202309900","vorDoiUrl":"https://doi.org/10.1002/smll.202309900","workflowStages":[]},"version":"v1","identity":"rs-3365097","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3365097","identity":"rs-3365097","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}