A High-Performance PEO-Based Composite Solid Electrolyte via Facile Hot-Pressing for High-Voltage Lithium Metal Batteries

A High-Performance PEO-Based Composite Solid Electrolyte via Facile Hot-Pressing for High-Voltage Lithium Metal Batteries | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 6 November 2025 V1 Latest version Share on A High-Performance PEO-Based Composite Solid Electrolyte via Facile Hot-Pressing for High-Voltage Lithium Metal Batteries Authors : Hong-Yu Wang , Yu-Hang Zhang 0000-0003-1552-3376 [email protected] , Kun-Rong Lu , Yue-Xi Han , Dong-Yang Li , Jia-Ming Chuai , Jia-He Lu , Hong-Fei Gu , Jun-Tian Luo , Fa-Nian Shi , and Peng-Fei Wang Authors Info & Affiliations https://doi.org/10.22541/au.176242334.42225265/v1 Published Materials Today Energy Version of record Peer review timeline 561 views 169 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) face challenges including high room-temperature crystallinity, low ionic conductivity, and limited compatibility with high-voltage cathodes. To overcome these limitations, this work develops a multi-strategy modified composite polymer electrolyte fabricated via a ”one-step solvent-free hot-pressing” technique, incorporating tetraethylene glycol dimethyl ether (TEGDME) as plasticizer, LiTFSI and LiDFOB dual salts, and tris(2,2,2-trifluoroethyl) phosphate (TFP) as flame retardant. This rational design significantly suppresses PEO crystallization and reconstructs lithium-ion transport pathways, achieving remarkable room-temperature performance with an ionic conductivity of 7.33 × 10 -4 S cm -1 , a lithium-ion transference number of 0.55, and an electrochemical stability window up to 4.4 V. The performance improvement is attributedto competitive coordination and anion-anchoring effects, as confirmed by theoretical and spectroscopic analyses. The electrolyte promotes the formation of stable solid electrolyte interphase/cathode electrolyte interphase (SEI/CEI) layers enriched with LiF and Li x PO y F z components, enabling stable Li||Li symmetric cell operation for over 800 hours. Assembled Li||LiFePO 4 cells maintain 81.59% capacity retention after 950 cycles at 1 C rate, while demonstrating excellent compatibility with high-voltage cathodes such as LiCoO 2 and NCM622 at voltages up to 4.4 V. This work provides an efficient and eco-friendly strategy for developing next-generation polymer electrolytes for high-voltage lithium metal batteries. 1.Introduction Lithium metal stands out as an ideal anode material for high-energy-density lithium batteries, owing to its exceptionally high theoretical specific capacity (3860 mAh g -1 ) and low redox potential (-3.04V vs SHE). [1-2] However, conventional liquid electrolytes introduce safety concerns such as flammability and leakage. [3-5] Moreover, the substantial volume variation of lithium metal during repeated cycling can trigger internal short circuits, further compromising battery reliability. Replacing liquid electrolytes with solid alternatives has thus emerged as a promising strategy to mitigate these issues. [6-11] Among various solid electrolytes, inorganic ceramic and organic polymer electrolytes have attracted the most extensive research interest. Inorganic ceramic electrolytes exhibit high ionic conductivity and excellent thermal stability, yet their practical application is hindered by intrinsic brittleness and poor interfacial compatibility with electrodes. [12-14] In contrast, solid polymer electrolytes (SPEs) offer greater potential due to superior flexibility and ease of processing. [15-18] Poly(ethylene oxide) (PEO), one of the earliest and most thoroughly studied polymer matrices, still faces persistent challenges such as limited ionic conductivity and narrow electrochemical stability window, which restrict its broader application. [19-23] It is widely recognized that lithium-ion migration in PEO occurs predominantly through amorphous regions, and the high degree of crystallinity at room temperature remains a major factor impeding ion transport. [24] To address this, the incorporation of plasticizers or inorganic fillers has been commonly adopted to suppress crystallization effectively. [25-27] Notably, plasticizers not only enhance ionic mobility but also improve the mechanical flexibility of PEO, thereby contributing to more robust electrolyte performance. [28-31] Despite its prevalence, the solution-casting method for preparing polymer electrolytes relies heavily on large quantities of organic solvents. This not only raises environmental concerns but also compromises electrolyte quality, as solvent evaporation can leave behind residual bubbles that impede ionic conduction. [32-33] More critically, incomplete solvent removal often induces side reactions at lithium metal anode, leading to increased interfacial resistance and severe polarization. [34] In response, solvent-free alternatives like UV-initiated polymerization and in-situ thermal polymerization have been developed. [35-39] These methods create electrolytes by directly crosslinking or polymerizing the matrix, offering a more environmentally benign pathway for the polymer segments. However, their complex processing requirements continue to pose challenges for scalable manufacturing. This study presents a one-step, solvent-free hot-pressing strategy for the fabrication of high-performance SPEs. In contrast to conventional solution casting, this approach is more environmentally benign and efficient. It also offers a simpler processing route and greater potential for commercial scalability compared to other solvent-free techniques such as UV-initiated polymerization and in-situ thermal polymerization. Using this method, we designed a PEO-based electrolyte system incorporating tetraethylene glycol dimethyl ether (TEGDME) as a plasticizer to expand amorphous regions and facilitate chain segment motion, tris(2,2,2-trifluoroethyl) phosphate (TFP) as a flame retardant to enhance safety, and a LiTFSI/LiDFOB dual-salt system to increase free lithium-ion concentration and improve interfacial stability with electrodes. These multi-component synergies collectively suppress PEO crystallinity, promote EO chain mobility, and generate abundant mobile Li⁺ carriers, leading to a PEO-based electrolyte with a high room-temperature ionic conductivity of 7.33 × 10 -4 S·cm -1 and a Li + transference number of 0.55. The inclusion of TFP further imparts excellent flame-retardant characteristics. When assembled into Li||LiFePO 4 cells, the electrolyte enables stable cycling at 0.5 C and delivers an initial discharge capacity of 122.54 mAh·g -1 at 1 C with 81.59% capacity retention after 950 cycles. Moreover, owing to the intrinsic oxidation resistance of the polymer matrix and the formation of a stable cathode-electrolyte interphase (CEI) during cycling, the electrolyte demonstrates compatibility with high-voltage cathodes, supporting operation at cut-off voltages up to 4.4 V. These results significantly broaden the application horizon of PEO-based polymer electrolytes in high-voltage lithium metal batteries. 2.Results and discussion Addressing the critical challenges of traditional PEO-based electrolytes—such as high room-temperature crystallinity, low ionic conductivity, and poor interfacial stability—this study develops a composite polymer electrolyte (denoted as PEO-TTL) through the incorporation of small-molecule TEGDME, flame-retardant TFP, and dual lithium salts (LiTFSI/LiDFOB) into the PEO matrix. The resulting electrolyte exhibits outstanding ion transport properties, excellent interfacial stability, and intrinsic safety. Structural analyses confirm the formation of an amorphous matrix conducive to ion conduction. Scanning electron microscopy (SEM) images ( Figure 1a , S1–S3 ) reveal a continuous three-dimensional network architecture within the composite electrolyte, which not only facilitates efficient ion migration but also restricts lithium dendrite growth via physical confinement. [40] X-ray diffraction (XRD) patterns ( Figure 1b ) show the characteristic crystalline peaks of PEO at 19° and 23° in all composites, while no diffraction signals from lithium salts are detected, confirming their complete dissolution and homogeneous distribution in the polymer matrix and the formation of a predominantly amorphous structure. Differential scanning calorimetry (DSC) was used to further quantitatively assess the crystallinity of the samples ( Figure 1c , S4 ). The results show that PEO-TTL has the lowest melting temperature (24.15 °C) among all samples; moreover, the crystallinity calculated from the melting enthalpy ( Table S1 ) also confirms that its crystallinity (24.43%) is the lowest of all samples. These results unequivocally demonstrate that the designed composite effectively disrupts the ordered arrangement of PEO molecular chains, resulting in a significantly expanded amorphous phase. This structural modification establishes a robust foundation for enhanced polymer segmental motion and rapid ion transport. Figure 1. a) SEM image of PEO-TTL electrolyte. b) XRD patterns, c) DSC curves, and d) Contact angles of PEO-T, PEO-TT, and PEO-TTL electrolytes. e) Flame tests of PEO-T, PEO-TT, and PEO-TTL electrolytes. f) Binding energies of polymer/solvent (PEO, TEGDME, TFP) interactions with Li⁺, TFSI⁻, and DFOB⁻. g) FTIR spectra of PEO-T, PEO-TT, and PEO-TTL electrolytes. h) HOMO and LUMO energy levels of relevant molecules and ions. Concurrently with structural optimization, the interfacial compatibility and intrinsic safety of the electrolyte were systematically evaluated. Contact angle measurements ( Figure 1d ) reveal superior wettability of the PEO-TTL electrolyte on the electrode surface, as evidenced by a low contact angle of 19.8°, indicating favorable interfacial adhesion conducive to constructing a low-impedance ion-transport interface. In addition, combustion tests ( Figure 1e ) highlight the practical safety merits of the electrolytes incorporating flame-retardant TFP (PEO-TT and PEO-TTL), which exhibit rapid self-extinguishing behavior upon flame removal. This result underscores their significantly improved thermal safety, a critical attribute for real-world battery applications. To unravel the mechanistic origin of the improved structural and interfacial properties, the ion coordination chemistry within the electrolyte was systematically probed through theoretical modeling and spectroscopic analysis. Binding energy calculations ( Figure 1f , S5, Table S2 ) uncovered a competitive coordination mechanism, wherein TEGDME and TFP exhibit higher binding energies with Li⁺ (-2.041 eV and -2.932 eV, respectively) than the PEO chain (-2.021 eV), enabling them to preferentially solvate Li + . This effectively weakens the intrinsic Li + -ether oxygen interaction, leading to decoupling of Li⁺ from the polymer backbone and enhanced segmental mobility. In parallel, PEO chains show stronger affinity toward TFSI - and DFOB - anions, an effect described as “anion-anchoring”, which effectively restricts anion migration and is critical for achieving a high Li + transference number. Fourier transform infrared (FTIR) spectroscopy shown in Figure 1g offers direct experimental validation of the competitive coordination and anion-anchoring mechanisms. In the PEO-T electrolyte, the C-O-C stretching vibration of the PEO backbone appears at 1100.21 cm -1 . Upon introduction of TFP and LiDFOB (in PEO-TT and PEO-TTL), this peak redshifts to 1099.24 cm -1 and 1099.73 cm -1 , respectively, indicating a altered local chemical environment around the ethylene oxide (EO) segments, increased conformational disorder, and further suppression of crystallinity-consistent with the Li + -polymer decoupling phenomenon. Moreover, the S=O stretching vibration of TFSI - at 1196.63 cm -1 in PEO-T shifts markedly to 1181.21 cm -1 in both PEO-TT and PEO-TTL, reflecting improved Li-salt dissociation and increased free Li⁺ availability. Additional features near 1760.24 cm -1 and 1793.50 cm -1 are assigned to solvated and dissociated DFOB - species, respectively. Their distinct positions confirm that LiDFOB inclusion reshapes the solvation structure. Collectively, these systematic spectral shifts verify the multifaceted coordination interplay among Li + , polymer host, small-molecule additives, and anions. The emergence of DFOB - -related bands further attests to its active role in establishing more continuous Li + transport pathways. The molecular orbital energy levels of electrolyte components were further calculated to assess their interfacial reactivity. Following frontier orbital theory, species with lower LUMO energies are more reducible at the anode, while those with higher HOMO energies are more easily oxidized at the cathode. As plotted in Figure 1h , LiDFOB exhibits the lowest LUMO energy (-1.96 eV), and DFOB - shows the highest HOMO energy (-2.74 eV) among the components. This suggests that LiDFOB preferentially undergoes reduction at the anode and DFOB - participates in oxidation at the cathode, thereby promoting the in situ formation of a stable and ion-conductive interphase. The macro-scale electrochemical implications of the structural and mechanistic optimizations were systematically evaluated. Time-evolution impedance spectra of Li||Li symmetric cells with PEO-TTL ( Figure S6 ) reveal stable bulk resistance over 30 days, while the interfacial resistance progressively decreased before stabilizing after 8 days-a behavior ascribed to improved electrode wettability. Variable-temperature impedance measurements further demonstrate outstanding ion-transport properties, with PEO-TTL achieving a high ionic conductivity of 7.33 × 10 -4 S cm -1 at 30 °C ( Figure S7–S9 , Table S3 ), significantly surpassing other counterparts. Fitting of the Arrhenius plot ( Figure 2a ) yielded two activation energy values for PEO-TTL: 0.284 eV and 0.224 eV, substantially lower than those of PEO-T and PEO-TT. This energetically validates the reduced barrier for Li + migration within the PEO-TTL matrix. Moreover, DC polarization measurements ( Figure 2b , S10 , S11 ) confirm a high Li + transference number of 0.55 for PEO-TTL, compared to 0.38 for PEO-T and 0.31 for PEO-TT. This enhancement stems from the synergistic effects of DFOB - -assisted segmental mobilization, PEO-anion anchoring, and increased free Li + concentration, which collectively suppress anionic mobility. Additionally, linear sweep voltammetry (LSV) ( Figure 2c ) reveals an extended electrochemical stability window up to 4.4 V for PEO-TTL, indicating promising compatibility with high-voltage cathode systems. Figure 2. a) Arrhenius plots of the ionic conductivity for PEO-T, PEO-TT, and PEO-TTL electrolytes. b) Chronoamperometry profile of a Li||Li symmetric cell under a 10 mV polarization potential (Inset: EIS spectra before and after polarization). c) LSV curves of Li||SS cells scanned from 3 to 6 V at 1.0 mV s -1 . d) Tafel plots of Li||Li symmetric cells scanned from -0.2 to 0.2 V at 1 mV s -1 . e) CV curve of Li||SS cells scanned between -0.2 and 1.0 V at a scan rate of 1 mV s -1 (Inset: corresponding enlarged view from -0.2 to 0 V). f) CV curves of Li||LiFePO 4 cells employing PEO-T, PEO-TT, and PEO-TTL electrolytes at a scan rate of 1 mV s -1 . Corresponding DRT plots of Li||LiFePO 4 cells for (g) PEO-T, (h) PEO-TT, and (i) PEO-TTL. Contour plots of the corresponding DRT for Li||LiFePO 4 cells with (j) PEO-T, (k) PEO-TT, and (l) PEO-TTL. The interfacial kinetics play a pivotal role in determining the overall battery performance. Tafel analysis was employed to quantify the charge-transfer behavior of lithium ions at the electrode/electrolyte interface. As shown in Figure 2d , PEO-TTL exhibits the highest exchange current density (27.2 μA cm -2 ), indicating significantly accelerated lithium deposition/dissolution kinetics under equivalent overpotential. Such enhanced kinetics correspond to lower charge-transfer resistance, a finding consistent with subsequent in situ impedance results. Collectively, these results confirm that PEO-TTL enables highly efficient ion transport across the interface. The nucleation overpotential, a key kinetic descriptor for initial lithium deposition, was quantified using cyclic voltammetry (CV). PEO-TTL demonstrates a notably low value of 48 mV ( Figure 2e ), reflecting an energetically favorable nucleation process. Such a low barrier facilitates the formation of abundant and well-dispersed nucleation sites, leading to homogeneous spatial distribution of lithium deposition and effectively avoiding dendrite formation caused by localized high current density. The mechanism by which PEO-TTL exceptionally suppresses lithium dendrites is elucidated by these kinetic insights, which are further corroborated by the observed densely deposited lithium morphology. CV tests of Li||LiFePO 4 cells was employed to evaluate the interfacial kinetics under near-practical conditions. As shown in Figure 2f , the PEO-TTL-based cell exhibits the smallest voltage hysteresis, with an oxidation peak at 3.69 V and a reduction peak at 3.16 V, corresponding to a potential separation of only 0.54 V. In comparison, larger polarizations are observed for cells with PEO-T (3.91 V/3.08 V) and PEO-TT (3.79 V/2.98 V). The minimized voltage gap in PEO-TTL indicates significantly improved interfacial reaction reversibility. To dynamically investigate the electrolyte-electrode interfacial evolution, in-situ electrochemical impedance spectroscopy (EIS) was performed on Li||LiFePO 4 cells during the charging process. The acquired spectra ( Figure S12-S14 ) were deconvoluted using MATLAB to successfully resolve the individual impedance components ( Figure 2g-i ). Within the relaxation time range of 10 -5 to 10 seconds, the impedance was categorized into: interfacial contact resistance ( R C ), solid electrolyte interphase resistance ( R SEI ), charge transfer resistance ( R CT ) at the electrode/electrolyte interface, and diffusion resistance in the LiFePO 4 cathode ( R D ). The PEO-TTL system exhibited the lowest values in R C , R SEI , and R CT , demonstrating superior interfacial adhesion and chemical compatibility with the electrodes-consistent with the contact angle measurements shown in Figure 1d . The minimal R CT and significantly reduced R SEI are primarily attributed to the reconfigured coordination environment, which not only weakens Li⁺-polymer interactions but also promotes the formation of a highly ion-conductive interphase. Furthermore, the contour maps derived from the distribution of relaxation times (DRT) analysis ( Figure 2j-l ) provide intuitive visualization of the impedance characteristics. For the PEO-TTL system, the R SEI peak shifts toward shorter relaxation times, reflecting accelerated ion transport kinetics. Simultaneously, both the R C and R CT signals were significantly attenuated, becoming virtually undetectable in the contour maps. These features collectively demonstrate effective suppression of interfacial resistance and charge transfer barriers, thereby confirming the superior interfacial properties of PEO-TTL for high-performance lithium metal batteries. Having established the superior electrochemical properties of the electrolyte, we further evaluated its long-term cycling stability and lithium metal compatibility under more stringent conditions using Li||Li symmetric cells. Galvanostatic cycling tests ( Figure 3a ) reveal that the cell with PEO-TTL sustains stable operation for over 800 hours at 0.2 mA cm -2 , with a consistently low polarization voltage. In contrast, the PEO-T cell failed after 117 hours due to interfacial degradation, and the PEO-TT cell experienced a rapid voltage surge to 3 V after 400 hours, a behavior attributed to continuous side reactions between TFP and lithium metal. To correlate these performance trends with interfacial morphology, post-cycling lithium anodes were examined by SEM ( Figure 3b ). The PEO-TTL electrolyte promotes a compact and uniform lithium deposition layer, indicative of favorable plating/stripping behavior. Conversely, PEO-T leads to extensive crack formation, and PEO-TT results in granular, fragmented deposits. These morphologies underscore the detrimental effects of irreversible lithium reactions and non-uniform deposition, which ultimately cause cell failure. Figure 3. a) Voltage profiles of Li||Li symmetric cells at a constant current density of 0.2 mA cm -2 . b) SEM images of the Li metal anode surface after cycling for various durations at 0.2 mA cm -2 . c) CCD test for cells with different electrolytes. d) Rate capability of Li||Li symmetric cells measured at increasing current densities. e) Voltage profiles of Li||Li symmetric cells at a constant current density of 0.4 mA cm -2 . The polarization tolerance and rate performance of the electrolyte were further evaluated in symmetric cells. Critical current density (CCD) measurements ( Figure 3c ) demonstrate that PEO-TTL achieves a value of 0.55 mA cm -2 , substantially surpassing those of PEO-T (0.2 mA cm -2 ) and PEO-TT (0.4 mA cm -2 ), indicating its ability to sustain higher current densities and highlighting its promise for high-power applications. In rate capability tests performed at progressively increasing current densities ( Figure 3d ), PEO-TTL consistently maintained the smallest and most stable polarization voltage, underscoring its rapid ion transport and robust interfacial characteristics. Furthermore, as shown in Figure 3e , the PEO-TTL-based battery maintained stable operation for over 300 hours even under a demanding current density of 0.4 mA cm⁻², demonstrating excellent long-term cycling stability. The practical applicability of the electrolyte was evaluated through the rate performance of Li||LiFePO 4 full cells. As illustrated in Figure 4a , the cell incorporating PEO-TTL demonstrates superior rate capability, delivering a maximum discharge capacity of 163.25 mAh g -1 at 0.1 C and retaining 101.16 mAh g -1 even at 2 C. In contrast, the cell with PEO-T exhibits a sharp capacity drop to only 20.78 mAh g -1 at 2 C, indicating that its electrolyte and resulting SEI are incompatible with high-current cycling. Meanwhile, the PEO-TT-based cell shows severe capacity fading from the initial cycles, which is attributed to an unstable SEI layer caused by continuous reactions between TFP and lithium metal, ultimately resulting in full cell failure before reaching the 2 C stage. The charge-discharge profiles of the PEO-TTL cell at different rates ( Figure 4b ) exhibit minimal polarization, indicating highly reversible electrode kinetics. In comparison, cells with PEO-T and PEO-TT show substantially larger voltage polarization ( Figure S15 , S16 ), reflecting their less stable interfacial structures. Furthermore, the PEO-TTL cell demonstrates excellent cycling stability, with no noticeable capacity decay observed over 200 cycles at 0.1C ( Figure 4c ). To probe the chemical composition of the SEI generated by the polymer electrolyte, X-ray photoelectron spectroscopy (XPS) was conducted on lithium metal anodes after cycling. In the C 1s spectrum ( Figure 4d ), the PEO-TTL sample exhibits a further diminished peak at 284.8 eV, associated with C-C bonds, implying a more favorably organized coordination structure. The F 1s spectrum ( Figure 4e ) displays contributions from C-F (688.6 eV) and LiF (684.2 eV), while the P 2p spectrum ( Figure 4f ) reveals a characteristic signal at 134.4 eV corresponding to Li x PO y F z in both PEO-TT and PEO-TTL, with a greater proportion of LiF in the latter. It is documented that LiF improves the mechanical integrity of the SEI, whereas Li x PO y F z serves as an effective conduction pathway for lithium ions. Furthermore, the B 1s spectrum ( Figure 4g ) exhibits characteristic peaks for B-O (191.9 eV) and a minor B-F component (198.5 eV), primarily derived from LiDFOB decomposition. The presence of B-O in the SEI contributes to suppressing electrolyte degradation and effectively scavenges detrimental species such as HF. Concurrently, the B-F bond is prone to further cleavage during extended cycling, transforming into additional LiF and thereby progressively enhancing the interfacial properties. Figure 4. a) Rate capability of Li||LiFePO 4 cells employing PEO-T, PEO-TT, and PEO-TTL electrolytes. b) Representative charge/discharge voltage profile of the cell with PEO-TTL electrolyte. c) Cycling performance of Li||LiFePO 4 cells at 0.1C. XPS spectra of d) C 1s, e) F 1s, f) P 2p, and g) B 1s obtained from cycled Li metal anodes. The anodes were extracted from Li||LiFePO 4 cells with PEO-T, PEO-TT, and PEO-TTL electrolytes after 200 cycles at 0.1C. h) Long-term cycling performance of Li||LiFePO 4 cells at 0.5C. i) Charge–discharge voltage profiles of the Li||LiFePO 4 cell with PEO-TTL electrolyte after 700 cycles at 0.5C. j) Long-term cycling performance of a Li||LiFePO 4 cell at 1C. Furthermore, long-term cycling tests at high rates were carried out on cells with different electrolytes ( Figure 4h ). Cells based on PEO-T and PEO-TT showed pronounced capacity fading, resulting from persistent interfacial side reactions driven by their unstable SEI. In contrast, the PEO-TTL cell sustained 81.01% capacity retention after 700 cycles. Corresponding charge-discharge curves ( Figure 4i ) reveal minimal polarization at both the 100th and 700th cycles for PEO-TTL, whereas PEO-T and PEO-TT exhibited severe capacity loss and significantly increased polarization ( Figure S17 , S18 ). To further verify the superior performance of PEO-TTL, cycling tests were conducted at an even higher rate of 1 C ( Figure 4j ). The cell delivered an initial discharge capacity of 122.54 mAh g⁻¹ and retained 81.59% of its capacity after 950 cycles, unambiguously demonstrating exceptional long-term cycling stability under high-rate conditions ( Figure S19 ). To assess the compatibility of the polymer electrolyte with high-voltage cathodes, Li||LCO cells were assembled using PEO-TTL. As shown in Figure 5a , the cell exhibited stable cycling over 200 cycles at a cut-off voltage of 4.3 V and 0.2 C, delivering an initial discharge capacity of 129.32 mAh g -1 that increased to a maximum of 138.71 mAh g -1 after several activation cycles. The compatibility was further verified with NCM622 cathodes. Cells incorporating PEO-TTL and NCM622 ( Figure 5b and S20 ) demonstrated minimal polarization and excellent capacity retention over 400 cycles at 0.5 C, collectively confirming the outstanding compatibility of PEO-TTL with multiple high-voltage cathodes system. Figure 5. a) Cycling performance of Li||LCO cells. b) Long-term cycling performance of a Li||NCM622 cell at 0.5C. c) Representative discharge voltage profile of a Li||NCM622 cell with PEO-T electrolyte. d) Representative discharge voltage profile of a Li||NCM622 cell with PEO-TT electrolyte. e) Cycling performance of a Li||NCM622 cell. XPS spectra of f) F 1s, g) B 1s, and h) P 2p obtained from cycled Li metal anodes. The anodes were extracted from Li||NCM622 cells with PEO-T, PEO-TT, and PEO-TTL electrolytes after 100 cycles at 0.5C. i) Performance comparison between this work and other reported PEO-based polymer electrolytes. Cells based on PEO-T and PEO-TT electrolytes were also assembled with NCM622 cathodes and evaluated under identical conditions (4.3 V, 0.1 C; Figure 5c , d ). The PEO-T cell demonstrated progressive capacity activation yet limited electrochemical stability, reflected in low Coulombic efficiency that remained below 99% after 20 cycles ( Figure S21 ). The PEO-TT cell, meanwhile, showed rapid degradation after a brief activation period, resulting from uncontrolled side reactions between TFP and the lithium metal anode that led to irreversible lithium consumption. To further assess the overall performance of PEO-TTL, Li||NCM622 cells were cycled at an elevated cut-off voltage of 4.4 V ( Figure 5e ). The cells maintained stable operation, confirming the high-voltage endurance of this electrolyte system. Post-cycling XPS analysis of the CEI identified dominant constituents of LiF (685.5 eV), Li x PO y F z (134.4 eV), and B-O (192.2 eV) ( Figure 5f-h ). This demonstrates that the decomposition of LiDFOB not only contributes to the SEI but also cooperatively forms a robust and ion-conductive CEI on the cathode side, thereby effectively suppressing side reactions at the interface under high-voltage conditions. Collectively, these findings confirm the compatibility of the PEO-TTL material system with various high-voltage cathodes, highlighting its multifunctional characteristics and practical application potential. A comparative analysis with other reported PEO-based electrolytes ( Figure 5i, Table S4 ) underscores the superior performance of the present system, which enables long-term cycling stability in full cells. This work thus positions PEO-TTL as a highly competitive candidate for the rapid, green, and scalable production of safe polymer electrolytes. 3.Conclusion This study successfully developed a high-performance PEO-TTL composite polymer electrolyte through strategic incorporation of small-molecule TEGDME, flame-retardant TFP, and dual lithium salts (LiTFSI/LiDFOB) into the PEO matrix. Structural characterization confirmed the formation of a predominantly amorphous three-dimensional network with significantly suppressed crystallinity (24.43%), establishing continuous pathways for rapid ion transport. Mechanism studies revealed a synergistic interplay between competitive coordination of TEGDME/TFP with Li⁺ and anion-anchoring by PEO chains, effectively decoupling Li + from polymer backbones. This unique coordination environment enabled a high ionic conductivity of 7.33 × 10 -4 S cm -1 and a Li + transference number of 0.55 at 30°C. The electrolyte simultaneously exhibited excellent electrode wettability, intrinsic flame retardancy, and a broad electrochemical stability window of 4.4 V (vs. Li/Li⁺). Furthermore, the preferential reaction of LiDFOB facilitated the formation of robust SEI/CEI layers enriched with LiF/Li x PO y F z at electrode interfaces, significantly enhancing interfacial stability and charge transfer kinetics. Electrochemical evaluation demonstrated exceptional cycling stability: Li||Li symmetric cells maintained stable operation for over 800 hours, and Li||LiFePO 4 cells delivered 81.59% capacity retention after 950 cycles at 1C rate. Remarkably, the electrolyte showed excellent compatibility with high-voltage cathodes including LCO and NCM622. This work presents an effective multi-component design strategy addressing the fundamental challenges of PEO-based electrolytes-high crystallinity, inadequate ionic conductivity, and interfacial instability-paving the way for their practical application in high-energy-density lithium metal batteries. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. This work was supported by the Liaoning Provincial Department of Education (LJ212410142081, LJ202410142076) and the Science and Technology Department of Liaoning Province (2024-MSLH-370, 2024-BS-099). References [1] Deng, C.; Yang, B.; Liang, Y.; Zhao, Y.; Gui, B.; Hou, C.; Shang, Y.; Zhang, J.; Song, T.; Gong, X.; Chen, N.; Wu, F.; Chen, R. Bipolar Polymeric Protective Layer for Dendrite‐Free and Corrosion‐Resistant Lithium Metal Anode in Ethylene Carbonate Electrolyte. Angew. chem., Int. Ed. 2024 , 63, e202400619. 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Suppressing Dendritic Lithium Formation Using Porous Media in Lithium Metal-Based Batteries. Nano Lett. 2018 , 18, 2067–2073. Information & Authors Information Version history V1 Version 1 06 November 2025 Peer review timeline Published Materials Today Energy Version of Record 1 Apr 2026 Published Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords competitive coordination flame retardancy hot-pressing oxidation stability peo-based electrolytes Authors Affiliations Hong-Yu Wang Shenyang University of Technology View all articles by this author Yu-Hang Zhang 0000-0003-1552-3376 [email protected] Shenyang University of Technology View all articles by this author Kun-Rong Lu Shenyang University of Technology View all articles by this author Yue-Xi Han Shenyang University of Technology View all articles by this author Dong-Yang Li Shenyang University of Technology View all articles by this author Jia-Ming Chuai Shenyang University of Technology View all articles by this author Jia-He Lu Shenyang University of Technology View all articles by this author Hong-Fei Gu Shenyang University of Technology View all articles by this author Jun-Tian Luo Shenyang University of Technology View all articles by this author Fa-Nian Shi Shenyang University of Technology View all articles by this author Peng-Fei Wang Shenyang University of Technology View all articles by this author Metrics & Citations Metrics Article Usage 561 views 169 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Hong-Yu Wang, Yu-Hang Zhang, Kun-Rong Lu, et al. A High-Performance PEO-Based Composite Solid Electrolyte via Facile Hot-Pressing for High-Voltage Lithium Metal Batteries. Authorea . 06 November 2025. DOI: https://doi.org/10.22541/au.176242334.42225265/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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