Phosphonium Poly(Ionic Liquid) Electrolytes for Fast Lithium-Ion Conduction.

<p indent="0mm">Since the commercialization of lithium-ion batteries in the 1990s, lithium-ion batteries have been successfully applied in portable electronics, electric vehicles, and grid energy storage. Although current organic liquid electrolytes have high ionic conductivities, they are inherently flammable, volatile, and prone to leakage. Moreover, severe side reactions and dendrite growth on the surface of the lithium anode during the charge-discharge process can cause safety hazards, which greatly impede their applications in lithium metal batteries. Solid electrolytes, including inorganic solid electrolytes and polymer electrolytes, are regarded as effective alternatives to organic liquid electrolytes for the construction of lithium metal batteries with high energy density and safety. Among them, solid polymer electrolytes offer excellent flexibility, processability, and interfacial compatibility over inorganic solid electrolytes, and they are extraordinarily promising for lithium metal batteries with high energy density and safety. Ideal solid polymer electrolytes should have following features: (1) High ionic conductivity (&gt; <sc>10 ^–4 S cm ^–1) </sc> at room temperature; (2) high lithium ion transference number (~1) to reduce the concentration polarization and improve the rate performance of batteries; (3) intimate contact at the electrode/electrolyte interfaces; (4) wide electrochemical window <sc>(&gt;4.5 V</sc> vs. Li/Li ⁺) to match high-voltage cathodes and improve the energy density of batteries; (5) good mechanical stability to resist processing, buffer electrode volume change and inhibit dendrite growth; (6) good thermal stability to withstand environmental changes. Generally, the ionic conductivity of pure solid polymer electrolytes at room temperature is low <sc>(~10 ^–6 S cm ^–1). </sc> Researchers have tried to improve the ionic conductivities by adjusting the lithium salt concentration, such as developing “polymer-in-salt” solid electrolytes. However, increasing the concentration of lithium salt leads to the deterioration of the mechanical strength. Strategies such as developing novel lithium salts, modifying polymer matrix, and incorporating inorganic fillers into solid polymer electrolytes are proposed to promote ionic conductivities of solid polymer electrolytes. In particular, composite polymer electrolytes, fabricated by dispersing a certain amount of inorganic fillers into solid polymer electrolytes, have improved ionic conductivities without sacrificing their mechanical performances. Poor interfacial property between electrodes and electrolytes is also a critical issue for solid polymer electrolytes. On one hand, poor and uneven solid/solid contacts at the electrode/electrolyte interfaces lead to high resistance and sluggish ionic transport kinetics. Furthermore, the volume change of the positive and negative electrodes in the charge/discharge process deteriorates the interfacial contacts, blocks the ion and electron transport through the interfaces, and greatly reduces the electrochemical reaction kinetics. On the other hand, the electrochemical windows of solid polymer electrolytes are usually narrow <sc>(＜4.5 V).</sc> During cycling, redox reactions are prone to occur at the electrode/electrolyte interfaces, causing battery failure. Solid polymer electrolytes have also poor thermal and mechanical stabilities. Therefore, design and synthesis of polymer-based solid electrolytes with excellent comprehensive performances and construction of fast and stable ion transport channels at the electrolyte/electrode interfaces are of great significance for the successful development of solid-state lithium metal batteries. This paper presents a brief review of the research progress in solid polymer electrolytes from two aspects: Improving the ionic conductivities of solid polymer electrolytes and enhancing the interfacial performance at electrolyte/electrode interfaces. First, targeted optimization strategies on ionic conductivities of solid polymer electrolytes, including constructing continuously aligned ionic transport paths and shortening the ionic transport distance, are summarized. Second, interface optimization strategies, including constructing wetting interfaces and synthesizing asymmetric electrolytes, are presented to reduce the interface resistance and improve the interfacial contact. Finally, perspectives on the development of solid polymer electrolytes and high-performance solid-state lithium metal batteries are discussed, and key research directions and advanced test methods are proposed. This review may provide a comprehensive understanding and further guidance for not only the material design of solid polymer electrolytes, but also the structural design of lithium metal batteries with favorable electrochemical and interfacial performances.

Currently, electrolytes used in lithium-ion batteries are flammable and leaky, causing safety problems when used under high temperatures or extreme conditions. Solid electrolytes can fundamentally avoid the occurrence of such issues, at the same time, it can significantly increase the energy density of solid state lithium batteries. Solid electrolytes are classified into inorganic solid electrolytes and solid polymer electrolytes. Although inorganic solid electrolytes have the high mechanical strength and room temperature ionic conductivity, it has poor flexibility and complicated preparation process. In contrast, solid polymer electrolyte has good elasticity and good interface contact, which can overcome many disadvantages of the inorganic solid electrolyte. Among them, polyethylene oxide (PEO) is first proposed as a polymer electrolyte. Due to its excellent mechanical properties, electrochemical stability and thermal stability, it has been a hot topic for polymer solid electrolytes for decades. However, its low room temperature ionic conductivity limits practical application. Given the problems existing in PEO-based polymer electrolytes, several methods for improving ionic conductivity have been proposed. The primary methods include plasticization, the organic-inorganic composite, and polymer blending. Comparing these methods, it can be seen that adding plasticizers to the polymer can effectively increase the conductivity of the electrolyte, but at the same time it will cause a decrease in the mechanical properties, and the safety issues limit its application in lithium-ion batteries. Inorganic fillers can balance the problems of ionic conductivity and mechanical properties, but the construction of a good filler-polymer dispersion system is complicated in preparing such composite electrolytes, design a new type of multi-dimensional the ion transport network also face tremendous challenges. Undoubtedly, in the future research, inorganic fillers will be the dominant means in the modification of composite electrolytes. Compared with the former two modification methods, polymer blending is easy to operate and friendly to industry, but low ionic conductivity at room temperature still exist. To give full play to the advantages of polymer blending, using it as an auxiliary means to improve the performance of composite electrolytes will be the primary development direction of such modification methods. PEO is the most widely studied polymer electrolyte. Even though a large number of modification methods have emerged in its development history, the ionic conductivity at room temperature is still limited to a relatively low level. To meet the needs of the application in lithium-ion batteries, a high operating temperature (50−70℃) is still needed, the biggest problem remains exist. To solve the problems in polymer solid electrolytes, the research directions in the future may mainly focus on: Expanding the modification method of PEO to other polymer electrolyte host materials, broadening the scope of research, and finding the available polymer electrolytes at room temperature. Concerned about the preparation of ultra-thin polymer electrolytes, reducing the ion transmission path to increase the transmission efficiency of lithium ions between positive and negative electrodes. Effectively combines inorganic solid electrolytes and solid polymer electrolytes to give full play to their advantages. In addition, exploring the effect of inorganic filler morphology on the conductivity of the composite electrolyte will also deserve attention. Many one-dimensional, two-dimensional materials can build ion transport networks so that lithium ions can travel rapidly along the path. With the deepening of research, it is expected that PEO-based polymer electrolytes may replace liquid electrolytes and become an essential cornerstone for building the next generation of safe and reliable lithium-ion batteries.

Graphitic carbon nitride assisted PVDF-HFP based solid electrolyte to realize high performance solid-state lithium metal batteries

For the growth of electric vehicle market, lithium-ion batteries (LIBS) used in the EVs still requires safety and reliability. Unfortunately, large-scale application of the LIBs is being challenged due to the fact that the use of flammable liquid electrolytes has caused safety issues such as leakage and fire explosion. In this respect, all-solid-state batteries (ASSBs) have been intensively studied to ensure the safety and mileage that are superior to the current LIBs. In terms of solid electrolytes, oxide electrolytes not only shows high ionic conductivity (10-4 ~ 10-3 S/cm) but also high mechanical strength to suppress surface dendrite formation. In addition, the oxide electrolytes possess advantages such as non-flammability, high thermal stability, and excellent electrochemical stability (~ 6 V), enabling high temperature/high voltage operations of oxide-based ASSBs. However, most of oxide materials require a sintering process at high temperatures to form a planar solid electrolyte. And a lack of flexibility results in non-uniform electrolyte/electrode contact in the battery, which makes it difficult to apply the rigid oxide electrolyte directly. On the other hand, solid polymer electrolytes have also been actively investigated due to no leakage, good electrolyte/electrode contact, easy processing, flexibility, and good film formability. However, the solid polymer electrolytes have critical disadvantages such as low ionic conductivity at room temperature and low thermal/mechanical stability, which precludes commercialization of solid polymer-based ASSBs despite their advantages. To overcome each disadvantages of oxide and polymer electrolytes, we developed hybrid electrolytes for improved ionic conductivity, easy processing, and formation of continuous electrolyte/electrode interface. In this presentation, pragmatic approach and current challenges related to solid batteries will be discussed including innovative manufacturing process. Hybrid electrolytes and their synergistic effect on the battery performance as a promissing solution will be presented [Fig. 1]

With the rapid development of energy storage technology, solid‐state lithium batteries with high energy density, power density, and safety are considered as the ideal choice for the next generation of energy storage devices. Solid electrolytes have attracted considerable attention as key components of solid‐state batteries. Compared with inorganic solid electrolytes, solid polymer electrolytes have better flexibility, machinability, and more importantly, better contact with the electrode, and low interfacial impedance. However, its low ionic conductivity, narrow electrochemical stability window (ESW), and poor mechanical properties at room temperature limit its development and practical applications. In recent years, many studies have focused on improving the ionic conductivity of polymer electrolytes; however, few systematic studies and reviews have been conducted on their ESWs. A polymer electrolyte with wide electrochemical window will aid battery operation at a high voltage, which can effectively improve their energy density. Moreover, their stability toward lithium metal anode is also important. Therefore, this review summarizes the recent progress of solid polymer electrolytes on the ESW, discusses the factors affecting ESW of polymer electrolytes, and analyzes a strategy to broaden the window from the perspective of molecular interaction, polymer structural design, and interfacial tuning. The development trends of polymer electrolytes with wide electrochemical windows are also presented.image

Solid-state sodium ion batteries are frequently referred to as the most promising technology for next-generation energy storage applications. However, developing a suitable solid electrolyte with high ionic conductivity, excellent electrolyte–electrode interfaces, and a wide electrochemical stability window, remains a major challenge. Although solid-polymer electrolytes have attracted great interest due to their low cost, low density and very good processability, they generally have significantly lower ionic conductivity and poor mechanical strength. Here, we report on the development of a low-cost composite solid polymer electrolyte comprised of poly(ethylene oxide), poly(vinylpyrrolidone) and sodium hexafluorophosphate, mixed with indium arsenide nanowires. We show that the addition of 1.0% by weight of indium arsenide nanowires increases the sodium ion conductivity in the polymer to 1.50 × 10−4 Scm−1 at 40 °C. In order to explain this remarkable characteristic, we propose a new transport model in which sodium ions hop between close-spaced defect sites present on the surface of the nanowires, forming an effective complex conductive percolation network. Our work represents a significant advance in the development of novel solid polymer electrolytes with embedded engineered ultrafast 1D percolation networks for near-future generations of low-cost, high-performance batteries with excellent energy storage capabilities.

All-solid-state lithium batteries (ASSBs) are considered like the next generation of electrochemical energy storage devices because of their safety and their high energy density up to 400Wh/kg. The all-solid-state battery is composed of a positive electrode (e.g., NMC (Li(Ni1∕3Mn1∕3Co1∕3)O2)), a negative one (Li), and a solid electrolyte, which is the critical component, composed of inorganic compound and/or solid polymer electrolyte (SPE) [1]. On the one hand, SPE have the advantage of an easy shaping with the technique already used in the manufacture of batteries and their flexibility allows obtaining a good interface with the electrode materials [2]. On the other hand, inorganic compounds generally have high ionic conductivity (10-3S/cm), they are stable electrochemically vs Li/Li+ and their transport number is close to 1 to promote the diffusion/migration of Li+ ions only. In order to combine the advantages of both types of materials, hybrid materials have been designed [3].First, a new adaptable polymer matrix based on PEO derivatives has been developed. A solvent-free synthesis has been designed from liquid and commercial precursors Poly(ethylene glycol) methyl methacrylate (PEGM) and Poly(ethylene glycol) dimethacrylate (PEGDM). These latter were copolymerized with Lithium 3-[(trifluoromethane)sulfonamidosulfonyl] propyl methacrylate (MTFSLi). The anion TFSI- is thus grafted to the PEO network, allowing exclusively the diffusion of the Li+ ion. This polymer matrix can be thus classified as single-ion conductor. In addition, the proportions between PEGM and PEGDM, acting as crosslinker, can be easily tuned. The PEGDM proportion controls the cross-linking density which modifies not only the glass transition temperature (Tg), but also the storage modulus (E’) and the free volume, and consequently the ionic conductivity of the polymer matrix which is the main property required for SPE. Finally, a ratio of PEGM:PEGDM (80:20) allows obtaining homogeneous SPE, self-standing and soft at room temperature, amorphous with a Tg of -41°C. The EO/Li ratio was then modulated in single-ion networks with the MTFSLi proportion, and an optimum in ionic conductivity of 2.10-7 S/cm @25°C has been measured for EO/Li ratio of about 20. The transport number measured by the Bruce and Vincent method [4] was t+=1,0 for the single ion conductor, demonstrating the effective grafting of the counter anion. This value has been validated by measuring the diffusion coefficients of 7Li and 19F in NMR. To our knowledge, this is the first time a real unity transport number is reported in the literature for a polymer electrolyte. Moreover, the electrochemical stability of this single ion system extends from 0 to 6V vs Li+/Li. These experiments suggest the interest of using the single-ion polymer in the formulation of composite positive electrode with high potential cathode materials, due to its stability in potential. Li metal is considered the ultimate anode for Li-batteries. The long-term electrochemical stability has been evaluated in symmetric Li/polymer electrolyte/Li cell. The cell is cycled at a constant current density of 0.2 mA/cm2. After 200 h of cycling the voltage reaches solely 2V. Accordingly, the grafting of the anion to the network limits an overpotential in the cell, allowing a more stable system over time.Second, the garnet Li6.4La3Zr2Al0.2O12 (LLZO) of the oxide family was associated to the previous polymer matrix. This garnet presents a high conductivity (10-4 S/cm @ 25°C), a good chemical stability not only against lithium metal but also against air and humidity, which is not the case of sulphides homologues. A 3D-fibrous network obtained by the electrospinning method was carried out with a solution containing the inorganic precursors, a polymer and an appropriate solvent [5]. Then this membrane is calcined at 850°C to obtain the 3D fibrous network of LLZO. The resulting self-standing porous inorganic material (~80% of porosity) exhibits a conductivity of the order of 10-6 S/cm @25°C. It was then impregnated with the polymer matrix precursors by capillarity and following by a polymerization. A self-standing membrane as thin as 80 µm containing 9%vol of LLZO was obtained. The conductivity of this hybrid membrane is comparable to that of the polymer (10-7S/cm @ 25°C). The resulting hybrid is mainly polymeric where the ionic conduction was realized by the polymeric matrix and the inorganic acts as a mechanical reinforcement. Preliminary results on high content of LLZO hybrid will also be presented, where a synergy of the both components is observed.[1] Janek. Nature Energy. 2016. Vol 1(9)p.16141. [2] Yue. Energy Storage Materials. 2016. Vol 5p.139-164. [3] Zheng. Chem Soc Rev. 2020. Vol 49p.8790-8839. [4] Bruce. Solid State Ion. 1988. Vol 28–30p.918–922. [5] A. La Monaca. Electrochemistry Communications. 2019. Vol 104p.106483. Figure 1

Li metal batteries based on solid polymer electrolytes offer the benefits of high energy density and safety, as well as extended cycling life, making them an excellent candidate for the next‐generation battery system. However, current solid polymer electrolytes still suffer from low ion conductivity and Li+ transfer number, which seriously restricts its practical application. Herein, a self‐supporting composite solid polymer electrolyte was prepared, where phenolic resin rich in hydroxyl groups (BR) and polyethylene oxide (PEO) are mixed evenly and poured onto a cellulose membrane in one step. In such an electrolyte, PEO and BR combine to form intermolecular hydrogen bonds, lowering the crystallinity of PEO and increasing the Li+ transfer number. Lastly, the obtained solid electrolytes exhibited a high ion conductivity (1.1×10−4 S cm−1) and Li+ transfer number (0.53), as well as improved electrochemical window. Consequently, Li || Li symmetrical cells can run stably for more than 700 h at 0.1 mA cm−2/0.25 mAh cm−2. And full cells with LiFePO4 cathode can also demonstrate high discharge capacity of 152.12 mAh g−1 and rate performance. We believe that such a design based on supramolecular interaction offer a new avenue to advanced solid polymer electrolytes.

Solid polymer electrolytes (SPEs) or ionic conductors were proposed by Gray in 1997 and are typically composed by polymer with salts in its constitution, finding applications in the areas of batteries, sensors/actuators and supercapacitors, among others. Recently, salts have been substituted by ionic liquid (ILs) due to their excellent properties, including high ionic conductivity (~10-3 – 10-2 S.cm-1), almost null volatility, null flammability, thermal stability, wide electrochemical windows (~4-6 V) and being environmental friendly [1-2].The excellent properties of poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE), as solid polymer electrolyte with (N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N111 2(OH)][NTf2] where demonstrated in [3], where the addition of the ILs affects the microstructure, thermal stability and ionic conductivity of the polymer membrane.In this work, the effect of different anions within the ionic liquid for the development of SPE based on P(VDF-TrFE) has been investigated. 1-ethyl-3-methylimidazolium acetate, [C2mim][OAc], 1-ethyl-3-methylimidazolium triflate, [C2mim][(CF3SO3)3], 1-ethyl-3-methylimidazolium lactate, [C2mim][Lactate], 1-ethyl-3-methylimidazolium thiocyanate, [C2mim][SNC] and 1-ethyl-3-methylimidazolium hydrogen sulphate [C2mim][HSO4] have been used for this purpose and the SPE were prepared by thermaly induced phase separation (TIPS). The thermal and electrical properties of the SPE strongly depend on the selected IL through their different interactions with the polymer matrix. The room temperature ionic conductivity increasing in the following way for the different anions: [SNC] > [CF3SO3)3] > [HSO4] > [Lactate] > [OAc]. Acknowledgments This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011, PEST-C/QUI/UI0686/2013, PEST-OE/EQB/LA0004/2011, and grants SFRH/BD/68499/2010 (C.M.C.) and SRFH/BD/90366/2012 (R.L.). The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). The authors thank Solvay for kindly supplying the high quality materials.

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) incorporating lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) offer excellent potential for solid-state lithium metal batteries (SSLMBs) due to their wide electrochemical stability window and high lithium salt solubility. LiTFSI supplies Li+ ions and also acts as a plasticizer, promoting the formation of the amorphous phase, which is vital for ionic conduction. Reduced ionic conductivity can result from very high crystallinity, spherulitic morphology, and secondary crystallization disrupting the ion pathways. The [EO:Li] molar ratio critically governs crystallization behavior and ionic transport; a ratio of 10:1, close to the stable amorphous eutectic composition (9:1), promotes amorphous phase formation and high ionic conductivity while limiting excessive crystallization. However, high salt content at this ratio leads to membrane stickiness, low mechanical strength, and handling difficulties. Here, we present a parafilm-assisted peeling technique that enables the fabrication of freestanding PEO/LiTFSI membranes while preserving their structural integrity. SEM analysis shows that conventional Teflon-mold peeling yields cracked, stretched surfaces, whereas parafilm-assisted films are smooth and defect-free. FTIR confirms Li+–PEO coordination with no parafilm–electrolyte interaction. Both methods deliver similar electrochemical performance: ∼4.30 V stability window, ionic conductivity 3.96 × 10−3 S cm−1 at 50 ° C (E a ∼ 0.898 eV), and Li+ transference number ∼0.14–0.15. Symmetric Li|SPE|Li cells cycle stably for 300 h at 50 ° C , while LiFePO4 full cells retain ∼161 mAh g−1 and >98% Coulombic efficiency over 30 cycles, confirming parafilm-assisted peeling as an effective fabrication method. This approach presents an effective means to address processing difficulties, thereby extending the viability of PEO based SPEs in next-generation energy storage devices.

Rechargeable lithium-ion batteries take advantage of solid-state ionic conductors, such as solid polymer electrolytes (SPEs) [1, 2]. Despite the large technological potential of solvent-free SPEs, they suffer from a serious problem: a relatively low ionic conductivity. The addition of ionic liquids (ILs) to SPEs appears as a possible solution due to the enhancement of electrochemical stability (~4-6 V) and ionic conductivity (~10-3 – 10-2 S.cm-1) [3].ILs has two important features for their specific use in battery applications: high concentration of ions and high ion mobility at room temperature. The use of PVDF polymer and its copolymers together with ILs as SPEs still has to be thoroughly explored.This work shows the thermal and electrochemical properties of SPEs based on poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE), and specific amounts (4wt% to 32wt%) of the ionic liquid N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium bis(trifluoromethylsulfonyl)imide, [N1 1 1 2(OH)][NTf2]. The SPE was prepared by thermaly induced phase separation (TIPS).The addition of ILs in P(VDF-TrFE) affects the microstructure, thermal stability and ionic conductivity of the polymer membrane.The ionic conductivity increases as the ionic liquid (IL) content increases with a maximum value at room temperature of 1.7x10-5 S.cm-1for an IL composition of 32wt%. The temperature behavior of the ionic conductivity follows the Arrhenius equation and the electrical response of the membrane is well represented by a Randles modified equivalent circuit. The results prove that the developed SPEs are adequate for energy storage devices. Acknowledgments This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011, PEST-C/QUI/UI0686/2011, PEST-OE/EQB/LA0004/2011, projects PTDC/CTM-NAN/121274/2010 and PTDC/QUI-QUI/117340/2010, grants SFRH/BD/68499/2010 (C.M.C.) and SRFH/BD/90366/2012 (R.L.) and FCT Investigator grant (J.M.S.S.E.). The authors also thank funding from Matepro –Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). The authors thank Solvay for kindly supplying the high quality materials.

Over the past ten years, lithium-ion batteries (LIBs) have become indispensable for powering wearable technology, smart electronics, and electric cars. However, the use of extremely flammable and volatile liquid electrolytes in typical Li-ion rechargeable batteries raises serious safety issues and prevents future advancements in energy density and dependability. Solid electrolytes have been suggested as viable solutions to these problems. In particular, polymer-based solid electrolytes combine high ionic conductivity with advantages such as low flammability, mechanical flexibility, thermal stability, and improved safety. This review highlights recent advances in solid polymer electrolytes for LIBs, with a focus on their fabrication strategies, structural designs, ionic conductivities, and electrochemical/mechanical stabilities. Keywords: Lithium-ion batteries, Solid polymer electrolytes, Ionic conductivity, Safety, Electrochemical stability, Fabrication strategies.

Solid-state lithium-metal (Li0) batteries are gaining traction for electric vehicle applications because they replace flammable liquid electrolytes with a safer, solid-form electrolyte that also offers higher energy density and better resistance against Li dendrite formation. Solid polymer electrolytes (SPEs) are highly promising candidates because of their tuneable mechanical properties and easy manufacturability; however, their electrochemical instability against lithium-metal (Li0), mediocre conductivity and poorly understood Li0/SPE interphases have prevented extensive application in real batteries. In particular, the origin of the low Coulombic efficiency (CE) associated with SPEs remains elusive, as the debate continues as to whether it originates from unfavoured interfacial reactions or lithium dendritic growth and dead lithium formation. In this work, we use state-of-the-art cryo-EM imaging and spectroscopic techniques to characterize the structure and chemistry of the interface between Li0 and a polyacrylate-based SPE. Contradicting the conventional knowledge, we find that no protective interphase forms, owing to the sustained reactions between deposited Li dendrites and polyacrylic backbones and succinonitrile plasticizer. Due to the reaction-induced volume change, large amounts of cracks form inside the Li dendrites with a stress-corrosion-cracking behaviour, indicating that Li0 cannot be passivated in this SPE system. On the basis of this observation, we then introduce additive engineering, leveraging from knowledge of liquid electrolytes, and demonstrate that the Li0 surface can be effectively protected against corrosion using fluoroethylene carbonate, leading to densely packed Li0 domes with conformal and stable solid-electrolyte interphase films. Owing to the high room-temperature ionic conductivity of 1.01 mS cm-1, the high transference number of 0.57 and the stabilized lithium-electrolyte interface, this improved SPE delivers an excellent lithium plating/stripping CE of 99% and 1,800 hours of stable cycling in Li||Li symmetric cells (0.2 mA cm-2, 1 mAh cm-2). This improved cathodic stability, along with the high anodic stability, enables a record high cycle life of >2,000 cycles for Li||LiFePO4 and >400 cycles for Li||LiCoO2 full cells.

Lithium-metal batteries (LMBs) with high energy densities are highly desirable for energy storage, but generally suffer from dendrite growth and side reactions in liquid electrolytes; thus the need for solid electrolytes with high mechanical strength, ionic conductivity, and compatible interface arises. Herein, a thiol-branched solid polymer electrolyte (SPE) is introduced featuring high Li+ conductivity (2.26 × 10-4 S cm-1 at room temperature) and good mechanical strength (9.4 MPa)/toughness (≈500%), thus unblocking the tradeoff between ionic conductivity and mechanical robustness in polymer electrolytes. The SPE (denoted as M-S-PEGDA) is fabricated by covalently cross-linking metal-organic frameworks (MOFs), tetrakis (3-mercaptopropionic acid) pentaerythritol (PETMP), and poly(ethylene glycol) diacrylate (PEGDA) via multiple CSC bonds. The SPE also exhibits a high electrochemical window (>5.4 V), low interfacial impedance (<550 Ω), and impressive Li+ transference number (tLi+ = 0.44). As a result, Li||Li symmetrical cells with the thiol-branched SPE displayed a high stability in a >1300 h cycling test. Moreover, a Li|M-S-PEGDA|LiFePO4 full cell demonstrates discharge capacity of 143.7 mAh g-1 and maintains 85.6% after 500 cycles at 0.5 C, displaying one of the most outstanding performances for SPEs to date.

Solid polymer electrolytes offer a promising pathway toward safe, high-energy solid-state lithium metal batteries. However, their practical deployment remains limited by insufficient ionic conductivity, narrow oxidative stability windows, and poor interfacial compatibility with metal anodes. In particular, conventional polymer systems such as PEO typically operate below ∼3.8 V and cannot sustain high-voltage cathode chemistry. In this work, a solid polymer electrolyte based on a proprietary carbonate–fluorinated methacrylate copolymer PIRION-F (denoted as PCFMA) is developed and systematically evaluated. Comprehensive FTIR, X-ray diffraction, differential scanning calorimetry, TGA, and scanning electron microscopy analyses confirm the amorphous nature of the polymer, its robust thermal stability, and the dense microstructure of the solid electrolyte membrane. The PCFMA exhibits outstanding LiTFSI solubility, high ionic conductivity (0.1 mS cm–1 at room temperature and 1.2 mS cm–1 at 70 °C), and a wide oxidative stability window up to ∼4.8 V vs Li+/Li, enabling operation with high-voltage cathodes. Li symmetric cells display ultrastable cycling for over 4500 h with low polarization. All-solid-state Li//NCM622 and high-voltage Ni-rich cells further show reversible charge/discharge behavior and strong capacity retention during extended cycling at room temperature. To contextualize broader manufacturability, an independent multilayer pouch-cell prototype fabricated by a technology startup collaborator delivers a cell-level energy density of 523 Wh kg–1. Collectively, these results demonstrate the strong potential of PCFMA-based solid electrolytes for next-generation high-voltage solid-state lithium metal batteries.