Recent Development in Topological Polymer Electrolytes for Rechargeable Lithium Batteries

Garnets Initiate Grafting of Methyl Methacrylate Brushes onto Fluoropolymers for Electrochemically Stable and Fast-Ion-Conducting Composite Solid-State Electrolytes

Fluoropolymer-based solid-state electrolytes (SSEs) promise next-generation all-solid-state Li metal batteries but suffer poor stability against Li metal anodes and sluggish Li+ transport. Herein, a garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) is proposed as a bifunctional mediator to enable the in-situ grafting and compositing for poly(vinylidene fluoride-co-hexafluoropropylene) (PVH), aiming at electrochemically stable and superionic SSEs. The LLZTO not only induces the formation of CC bonds as active sites for effectively grafting methyl methacrylate (MMA) brush chains to PVH but also acts as an ion-conducting filler to enhance mechanical properties and ion transport. In addition, the grafted MMA brush chains improve electrochemical stability against Li metal anodes and weaken polymer crystallinity to create amorphous domains for Li+ transport. Therefore, the resulting composite SSEs, PVH-graft-MMA/LLZTO (PVHML), achieves an impressive ionic conductivity of 0.94 mS cm-1 at 25 °C, high mechanical strength (2.02 MPa), and exceptional cycling stability in Li symmetric cells (2800 h at 0.1 mA cm-1, 25 °C). Furthermore, PVHML-based all-solid-state LiFePO4|Li full cells demonstrate superior cyclability with 89.8% capacity retention at 0.2C after 200 cycles (25 °C). This strategy provides an efficient solution to the challenges of fluoropolymer-based SSEs, paving the way for their practical applications in high-performance all-solid-state lithium metal batteries.

Quasi-Solid Gel Electrolytes for Alkali Metal Battery Applications

Alkali metal batteries (AMBs) have undergone substantial development in portable devices due to their high energy density and durable cycle performance. However, with the rising demand for smart wearable electronic devices, a growing focus on safety and durability becomes increasingly apparent. An effective strategy to address these increased requirements involves employing the quasi-solid gel electrolytes (QSGEs). This review focuses on the application of QSGEs in AMBs, emphasizing four types of gel electrolytes and their influence on battery performance and stability. First, self-healing gels are discussed to prolong battery life and enhance safety through self-repair mechanisms. Then, flexible gels are explored for their mechanical flexibility, making them suitable for wearable devices and flexible electronics. In addition, biomimetic gels inspired by natural designs are introduced for high-performance AMBs. Furthermore, biomass materials gels are presented, derived from natural biomaterials, offering environmental friendliness and biocompatibility. Finally, the perspectives and challenges for future developments are discussed in terms of enhancing the ionic conductivity, mechanical strength, and environmental stability of novel gel materials. The review underscores the significant contributions of these QSGEs in enhancing AMBs performance, including increased lifespan, safety, and adaptability, providing new insights and directions for future research and applications in the field.

Organic Radical-Boosted Ionic Conductivity in Redox Polymer Electrolyte for Advanced Fiber-Shaped Energy Storage Devices

Fiber-shaped energy storage devices (FSESDs) with exceptional flexibility for wearable power sources should be applied with solid electrolytes over liquid electrolytes due to short circuits and leakage issue during deformation. Among the solid options, polymer electrolytes are particularly preferred due to their robustness and flexibility, although their low ionic conductivity remains a significant challenge. Here, we present a redox polymer electrolyte (HT_RPE) with 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HT) as a multi-functional additive. HT acts as a plasticizer that transforms the glassy state into the rubbery state for improved chain mobility and provides distinctive ion conduction pathway by the self-exchange reaction between radical and oxidized species. These synergetic effects lead to high ionic conductivity (73.5 mS cm-1) based on a lower activation energy of 0.13 eV than other redox additives. Moreover, HT_RPE with a pseudocapacitive characteristic by HT enables an outstanding electrochemical performance of the symmetric FSESDs using carbon-based fiber electrodes (energy density of 25.4 W h kg-1 at a power density of 25,000 W kg-1) without typical active materials, along with excellent stability (capacitance retention of 91.2% after 8,000 bending cycles). This work highlights a versatile HT_RPE that utilizes the unique functionality of HT for both the high ionic conductivity and improved energy storage capability, providing a promising pathway for next-generation flexible energy storage devices.

Bioinspired gel polymer electrolyte for wide temperature lithium metal battery

Stable operation of Li metal batteries with gel polymer electrolytes in a wide temperature range is highly expected. However, insufficient dynamics of ion transport and unstable electrolyte-electrode interfaces at extreme temperatures greatly hinder their practical applications. We report a bioinspired gel polymer electrolyte that enables high-energy-density Li metal batteries to work stably in a wide temperature range from -30 to 80 °C. The wide-temperature gel polymer electrolyte is fabricated by using a branched polymer of which side chains are double coupled with their asymmetric analogues. The double dipole coupling regulates the Li+ coordination environment to form a weak solvation structure that offers fast and uniform Li+ deposition at extreme temperatures. Consequently, the non-flammable gel polymer electrolyte displays an ionic conductivity of 1.03 × 10-4 S cm-1 at -40 °C and a Li+ transference number of 0.83. The Li metal batteries with LiNi0.8Co0.1Mn0.1O2 positive electrode deliver initial specific discharge capacities of 121.4 mAh g-1 at -30 °C and 172.2 mAh g-1 at 80 °C, with corresponding discharge currents of 18.8 mA g-1 and 188 mA g-1, respectively. Additionally, a pouch cell delivers a specific energy up to 490.8 Wh kg-1.

Closed-Loop Recyclable Solid-State Polymer Electrolytes Enabled by Reversible Lithium Salt Catalysis

The rapid expansion in lithium battery production and disposal presents considerable sustainability challenges, emphasizing the critical need for recycling. However, current methods predominantly focus on metals from cathodes, while electrolytes have rarely been recycled. Here, we propose an innovative closed-loop design for solid polymer electrolytes (SPEs), enabled by reversible catalysis of lithium bis(trifluoromethane) sulfonimide (LiTFSI) in both polymerization and depolymerization. The formation of a hydrogen-bonded adduct between TFSI- and alcohol initiates the in situ ring-opening polymerization of Li+-activated trimethylene carbonate (TMC), generating well-defined SPEs. With delicate structural optimization, the SPE achieves an outstanding ionic conductivity of 1.62 × 10-3 S cm-1 at room temperature with robust high-voltage stability up to 4.7 V. The assembled Li||NCM811 demonstrates promising cycling stability with 88% capacity retention over 100 cycles. Upon end-of-life, LiTFSI facilitates selective depolymerization of the polycarbonate-based SPE at 180 °C without introducing external catalysts, recovering both TMC monomer (>90%) and LiTFSI (>98%) for reuse. This work highlights a significant advance in closed-loop recyclable SPEs and a vital step toward sustainable lithium battery technology.

Intrinsic Structural and Coordination Chemistry Insights of Li Salts in Rechargeable Lithium Batteries

Lithium batteries, favored for their high energy density and long lifespan, are staples in electric vehicles, portable electronics, and aerospace. A key component, Li salts, aids lithium ion migration and electrode protection, significantly impacting battery performance. Developing an ideal Li salt, balancing stability, solubility, dissociation, solvation, and eco-friendliness, remains challenging. Given the scarcity of relevant reviews, it is endeavored here to present a novel perspective on Li salt chemistry, offering a concise roadmap for future designs and innovations. It is delved into the trends, opportunities, design principles, and evaluation methodologies related to Li salt chemistry, with a particular emphasis on organic anionic compositions. Furthermore, the latest and most representative organic Li salts from their intrinsic structure and coordination chemistry, highlighting their unique features and contributions are organized and presented. Finally, a visionary outlook is articulated for this field, exploring avenues, such as customizing Li salts for specific applications, synthesizing Li salts on demand, and discussing the potential of F-free Li salts alongside with their electrochemical window challenges. Here it is served as a strategic compass, addressing the shortcomings of existing reviews and guiding the design of functionalized Li salts.

Comb-like poly(β-amino ester)-integrated PEO-based self-healing solid electrolytes for fast ion conduction in lithium-sulfur batteries

All-solid-state lithium-sulfur batteries (ASSLSBs) using poly(ethylene oxide) (PEO) electrolytes offer significant advantages in energy density and safety. However, their development is hampered by the slow Li+ conduction in solid polymer electrolytes and sluggish electrochemical conversion at the cathode-electrolyte interface. Herein, we fabricate a self-healing poly(β-amino ester) with a comb-like topological structure and multiple functional groups, synthesized through a Michael addition strategy. This material modifies the PEO-based solid-state electrolyte, creating fast Li+ transport channels and improving polysulfides conversion kinetics at the electrode surface. Consequently, both modified all-solid-state lithium symmetric cells and lithium-sulfur batteries exhibit improved electrochemical performance. This work demonstrates an expanded interpenetrating macromolecular engineering approach to develop highly ion-conductive solid polymer electrolytes for ASSLSBs.

Organic Cationic-Coordinated Perfluoropolymer Electrolytes with Strong Li+-Solvent Interaction for Solid State Li-Metal Batteries

The practical application of solid-state polymer lithium-metal batteries (LMBs) is plagued by the inferior ionic conductivity of the applied polymer electrolytes (PEs), which is caused by the coupling of ion transport with the motion of polymer segments. Here, solvated molecules based on ionic liquid and lithium salt with strong Li+-solvent interaction are inserted into an elaborately engineered perfluoropolymer electrolyte via ionic dipole interaction, extensively facilitating Li+ transport and improving mechanical properties. The intensified formation of solvation structures of contact ion pairs and ionic aggregates, as well as the strong electron-withdrawal properties of the F atoms in perfluoropolymers, give the PE high electrochemical stability and excellent interfacial stability. As a result, Li||Li symmetric cells demonstrate a lifetime of 2500 h and an exceptionally high critical current density above 2.3 mA cm-2, Li||LiFePO4 batteries exhibit consistent cycling for 550 cycles at 10 C, and Li||uncoated LiNi0.8Co0.1Mn0.1O2 cells achieve 1000 cycles at 0.5 C with an average Coulombic efficiency of 98.45 %, one of the best results reported to date based on PEs. Our discovery sheds fresh light on the targeted synergistic regulation of the electro-chemo-mechanical properties of PEs to extend the cycle life of LMBs.

Interfacial Engineering of Polymer Solid-State Lithium Battery Electrolytes and Li-Metal Anode: Current Status and Future Directions

A combination of material innovations, advanced manufacturing, battery management systems, and regulatory standards is necessary to improve the energy density and safety of lithium (Li) batteries. High-energy-density solid-state Li-batteries have the potential to revolutionize industries and technologies, making them a research priority. The combination of improved safety and compatibility with high-capacity electrode materials makes solid-stateLi-batteries with polymer solid-electrolytes an attractive option for applications where energy density and safety are critical. While polymer-based solid-state Li-batteries hold enormous promise, there are still several challenges that must be addressed, particularly regarding interface between polymer solid-electrolyte and Lianode. There are significant advancements in improving the performance of solid-state Li batteries, and researchers continue to explore new methods to address these challenges. These improvements are critical for enabling the widespread adoption of solid-state Li-batteries invariety of applications, from electrical vehicles to portable electronics. Here, common polymer solid-electrolyte and its interface challenges with Lianode are first introduced, highlighting the trend in polymer solid-state-electrolyte research toward enhancing stability, safety, and performance of solid-state Li-batteries. This includes developing novel polymer materials with improved properties, exploring advanced fabrication techniques, and integrating these electrolytes into battery designs that optimize both safety and energy density.

Pectin alignment induced changes in ion solvation structure in ethylene carbonate-based liquid electrolytes

Classical molecular dynamics simulations are used to explore the impact of the alignment of pectin over the randomized configuration on ion solvation structure in pectin-loaded ethylene carbonate - lithium bis(trifluoromethanesulfonyl) imide electrolytes. Our study focuses on how biological macromolecules, specifically pectin, influence the behavior of liquid electrolytes, considering their applications in rechargeable batteries due to their ion solvation capabilities and ion transport characteristics. Aligned pectin causes a tightly packed first coordination shell of anions around lithium ions by weakening the long-ranged interactions beyond the first coordination shell compared to a random configuration. Consequently, the number of pectin oxygens around lithium decreases dramatically from 3 to 2, resulting in an overall diluted solvation shell containing fewer numbers of anions and pectin oxygens around lithium ions. With polymer alignment, the non-Gaussianity increases from 3.387 to 6.550 for lithium ions and from 0.475 to 0.621 for TFSI ions, reflecting a 90% increase in dynamic heterogeneity for lithium ions and a 30% increase for TFSI ions. Cation-cation correlations enhance ionic conductivity in randomized pectin, whereas isolated anion motion dominates in aligned pectin due to cation-pectin interactions. Our work not only highlights potential strategies for improving electrolyte performance in rechargeable batteries but also emphasizes the crucial role of molecular orientation in optimizing electrolyte properties, paving the way for more optimized and efficient battery technologies.

Correlating local structure and migration dynamics in Na/Li dual ion conductor Na5YSi4O12

Na5YSi4O12 (NYSO) is demonstrated as a promising electrolyte with high ionic conductivity and low activation energy for practical use in solid Na-ion batteries. Solid-state NMR was employed to identify the six types of coordination of Na+ ions and migration pathway, which is vital to master working mechanism and enhance performance. The assignment of each sodium site is clearly determined from high-quality 23Na NMR spectra by the aid of Density Functional Theory calculation. Well-resolved 23Na exchangespectroscopy and electrochemical tracer exchange spectra provide the first experimental evidence to show the existence of ionic exchange between sodium at Na5 and Na6 sites, revealing that Na transport route is possibly along three-dimensional chain of open channel-Na4-open channel. Variable-temperature NMR relaxometry is developed to evaluate Na jump rates and self-diffusion coefficient to probe the sodium-ion dynamics in NYSO. Furthermore, NYSO works well as a dual ion conductor in Na and Li metal batteries with Na3V2(PO4)3 and LiFePO4 as cathodes, respectively.

Achieving High-Performance Lithium-Sulfur Batteries by Modulating Li+ Desolvation Barrier with Liquid Crystal Polymers

Lithium-sulfur (Li-S) batteries offer high theoretical capacity but are hindered by poor rate capability and cycling stability due to sluggish Li2S precipitation kinetics. Here a sulfonate-group-rich liquid crystal polymer (poly-2,2'-disulfonyl-4,4'-benzidine terephthalamide, PBDT) is designed and fabricated to accelerate Li2S precipitation by promoting the desolvation of Li+ from electrolyte. PBDT-modified separators are employed to assemble Li-S batteries, which deliver a remarkable rate capacity (761 mAh g-1 at 4 C) and cycling stability (500 cycles with an average decay rate of 0.088% per cycle at 0.5 C). A PBDT-based pouch cell even delivers an exceptional capacity of ≈1400 mAh g-1 and an areal capacity of ≈11 mAh cm-2 under lean-electrolyte and high-sulfur-loading condition, demonstrating promise for practical applications. Results of Raman spectra, molecular dynamic (MD) and density functional theory (DFT) calculations reveal that the abundant anionic sulfonate groups of PBDT aid in Li+ desolvation by attenuating Li+-solvent interactions and lowering the desolvation energy barrier. Plus, the polysulfide adsorption/catalysis is also excluded via electrostatic repulsion. This work elucidates the critical impact of Li+ desolvation on Li-S batteries and provides a new design direction for advanced Li-S batteries.

Aliphatic Hyperbranched Polycarbonates Solid Polymer Electrolytes with High Li-Ion Transference Number for Lithium Metal Batteries

In this work, hyperbranched polycarbonate-poly(ethylene oxide) (PEO)-based solid polymer electrolytes (HBPC-SEs) are successfully synthesized via a straightforward organo-catalyzed "A1"+"B2"-ring-opening polymerization approach. The temperature-dependent ionic conductivity of HBPC-SEs, composed of different polycarbonate linkages and various LiTFSI concentrations, is investigated. The results demonstrate that HBPC-SE with an ether-carbonate alternating structure exhibits superior ionic conductivity, attributed to the solubility of Li salts in the polymer matrix and the mobility of the polymer segments. The HBPC1-SE with 30 wt% LiTFSI presents the highest ionic conductivities of 2.15  × 10-5, 1.78 × 10-4, and 6.07 × 10-4 Scm-1 at 30, 60, and 80 °C, respectively. Compared to traditional PEO-based electrolytes, the incorporation of polycarbonate segments significantly enhances the electrochemical stability window (5 V) and Li+ transference number (0.53) of HBPC-SEs. Furthermore, the LiFePO4/HBPC1-SE-3/Li cell exhibits exceptional rate capability and long-cycling performance, maintaining a discharge capacity of 130 mAh g-1 at 0.5C with a capacity retention of 95% after 300 cycles.

Hyperbranched polymers: growing richer in flavours with time

Hyperbranched polymers (HBPs) have been studied for over three decades now; yet several interesting aspects continue to draw the attention of researchers worldwide. This is because of the simplicity of synthesis, their unique globular structure, and the numerous peripherally located functional groups that can be utilised to impart a variety of attributes, such as core-shell amphiphilicity, Janus amphiphilicity, clickable polymeric scaffolds, multifunctional crosslinkers, etc. Several reviews have been written on HBPs with a focus on synthetic strategies, structural diversity, and their potential applications; in this short feature article, we have taken an alternate approach to highlight some of the unique structural features of HBPs and their influence on the properties of HBPs. We also discuss their versatility and adaptability for the generation of several interesting functional polymeric systems. In the latter half, we focus on the utilisation of HBPs as multifunctional scaffolds, that rely on the numerous peripheral terminal groups. We conclude by drawing a structuro-functional analogy between the range of peripherally functionalised HBPs and other analogous, but more complex, polymeric systems. We believe that this review will serve as a visual sounding board that would encourage the development of several other applications for this class of unique polymers.

An Ultrahigh Modulus Gel Electrolytes Reforming the Growing Pattern of Li Dendrites for Interfacially Stable Lithium-Metal Batteries

Gel polymer electrolytes (GPEs) have aroused intensive attention for their moderate comprehensive performances in lithium-metal batteries (LMBs). However, GPEs with low elastic moduli of MPa magnitude cannot mechanically regulate the Li deposition, leading to recalcitrant lithium dendrites. Herein, a porous Li7 La3 Zr2 O12 (LLZO) framework (PLF) is employed as an integrated solid filler to address the intrinsic drawback of GPEs. With the incorporation of PLF, the composite GPE exhibits an ultrahigh elastic modulus of GPa magnitude, confronting Li dendrites at a mechanical level and realizing steady polarization at high current densities in Li||Li cells. Benefiting from the compatible interface with anodes, the LFP|PLF@GPE|Li cells deliver excellent rate capability and cycling performance at room temperature. Theoretical models extracted from the topology of solid fillers reveal that the PLF with unique 3D structures can effectively reinforce the gel phase of GPEs at the nanoscale via providing sufficient mechanical support from the load-sensitive direction. Numerical models are further developed to reproduce the multiphysical procedure of dendrite propagation and give insights into predicting the failure modes of LMBs. This work quantitatively clarifies the relationship between the topology of solid fillers and the interface stability of GPEs, providing guidelines for designing mechanically reliable GPEs for LMBs.