Polyacrylonitrile Porous Membrane-Based Gel Polymer Electrolyte by In Situ Free-Radical Polymerization for Stable Li Metal Batteries

Construction of weakly solvating solid polymer electrolytes for high-voltage and stable lithium metal batteries

Industrial applications of in-situ polymerized solid-state electrolytes still face major challenges, such as low ionic conductivity, electrochemical instability, and incompatibility with high-voltage cathode. Herein, the fluorine-containing weakly solvating solid polymer electrolytes are designed to regulate the solvation structure, Li+ conductivity, and electrode/electrolyte interface. The strong electron-withdrawing effect and localization ability of fluorine atoms alter the electrostatic potential and charge distribution of the ether oxygen groups in monomer and solvent. This weakens the coordination between Li+ and the monomer/solvent while enhancing the coordination with the salt anion, leading to the formation of more contact ion pairs (CIPs) and aggregates (AGGs). This promotes the formation of inorganic-rich solid electrolyte interphase (SEI), enhancing the ionic conductivity of electrolytes and ameliorating the electrode/electrolyte interface. Furthermore, the introduction of fluorine lowers the HOMO of electrolyte, effectively improving its oxidative stability. Herein, a stable lithium stripping/deposition is achieved in Li||Li symmetric cells, maintaining 6420 h at 0.05 mA cm-2. Furthermore, the Li||LiCoO2 cells stably work 281 cycles with a capacity retention of 89.3 % at 0.5 C during a high voltage of 3-4.5 V. This strategy paves the way for the practicability of lithium metal batteries.

Scalable and Ultrathin Dual Entangled Network Polymer Electrolytes for Safe Solid-State Sodium Batteries

Identifying ultrathin and flexible solid-state electrolytes with high ionic conductivity and low interfacial resistance is crucial for scale-up production of solid-state sodium (Na) metal batteries (SSMBs). However, the challenges of poor processing scalability, insufficient intrinsic mechanical strength, and limited ionic transport capacity remain unaddressed. Herein, an ultrathin 9.7 µm solid-state electrolyte membrane featuring a dual-polymer entangled network is meticulously engineered through an arrayed multi-nozzle electrospinning technique with a swelling and hot pressing process using polyacrylonitrile and poly(ether-block-amide), which exhibits an exceptional voltage tolerance, enhanced tensile strength, and superior thermal stability. The soft ether oxygens segments in multiblock copolymers complex with Na+ to promote the rapid hopping transport of Na+. Meanwhile, interconnected electronegative channels based on carbonyl and cyanogen groups serve as Na+ conduits to smooth ion fluctuations and accelerate Na+ selective conduction simultaneously. The obtained inorganic-organic composite solid electrolyte interface with the improved mechanical strength of ultrathin solid-state electrolytes effectively suppresses Na dendrites with low overpotential over 500 h. The solid-state cells paired with layered oxides deliver a capacity retention of over 91.1% between 25 °C and 65 °C, and assembled pouch cells exhibit impressive energy density over 100 cycles, showing great potential for large-scale application of ultrathin structure in the SSMBs.

Gel polymer electrolytes based on sulfonamide functional polymer nanoparticles for sodium metal batteries

In this work, we investigate the development of polymer electrolytes for sodium batteries based on sulfonamide functional polymer nanoparticles (NaNPs). The synthesis of the polymer NaNPs is carried out by emulsion copolymerization of methyl methacrylate and sodium sulfonamide methacrylate in the presence of a crosslinker, resulting in particle sizes of 50 nm, as shown by electron microscopy. Then, gel polymer electrolytes are prepared by mixing polymer NPs and different organic plasticizers including carbonates, glymes, sulfolanes and ionic liquids. The chemical nature of the plasticizer resulted in different effects on the sodium coordination shell, which in turn impacted the properties of each membrane as investigated by FTIR. The transport properties were investigated by EIS and solid-state NMR. Among the organic gel polymer electrolytes (GPEs), the system comprising NaNPs and sulfolanes achieved the best ionic conductivity (1.1 × 10-4 S cm-1 at 50 °C) and sodium single-ion properties while for the ionogels, the best ionic conductivity was obtained by NaNPs mixed with pyrrolidinium-FSI IL (4.7 × 10-4 S cm-1 at 50 °C). From sodium metal symmetrical cell cycling, the use of ILs as plasticizers proved to be more beneficial for SEI formation and its evolution during cell cycling compared to the systems based on NPs and organic solvents. However, NPs + PC led to lower cell overvoltage than NPs + ILs (<0.4 V vs. >0.5 V). This study shows the potential of using Na-sulfonamide functional polymer nanoparticles to immobilize different plasticizers and thereby obtain soft-solid electrolytes for Na metal batteries.

Hypercrosslinked Metal-Organic Polyhedra Electrolyte with High Transference Number and Fast Conduction of Li Ions

Solid-state electrolytes (SSEs) with high Li-ion transference numbers and fast ionic conductivity are urgently needed for technological innovations in lithium-metal batteries. To promote the dissociation of ion pairs and overcome the mechanical brittleness and interface defects caused by traditional fillers in polymeric electrolytes, we designed and fabricated a cationic hypercrosslinking metal-organic polyhedra (HCMOPs) polymer as SSE. Benefiting a three-component synergistic effect: cationic MOPs, branched polyethyleneimine macromonomer and polyelectrolyte units, the Li-HCMOP electrolyte possesses a high Li-ion conductivity, a high Li-ion transference number and a low activation energy. The LiFePO4/Li battery exhibits high capacity with superior rate performance and cycling stability. Moreover, soluble MOPs serve as high crosslinking nodes to provide excellent mechanical strength for electrolytes and good compatibility with polymers. This work highlights an effective idea of high-performance MOP-based solid-state electrolytes applied in LMBs.

In-Situ Polymerized Solid/Quasi-Solid Polymer Electrolyte for Lithium-Metal Batteries: Recent Progress and Perspectives

In pursuit of high energy density, lithium metal batteries (LMBs) are undoubtedly the best choice. However, leakage and inevitable dendrite growth in liquid electrolytes seriously hinder its practical application. Solid/quasi-solid state electrolytes have emerged as an answer to solve the above issues. Especially, polymer electrolytes with excellent interface compatibility, high flexibility, and ease of machining have become a research hotspot for LMBs. Nevertheless, the interface contact between polymer electrolyte and inorganic electrode materials and the low ionic conductivity restrict its development. On account of these, in situ polymerized polymer electrolyte is proposed. Polymer solid electrolytes produced through in situ polymerization promote robust interface contact between the electrolyte and electrode while simplifying the preparation steps. This review summarized the latest research progress in in situ polymerized solid electrolytes for LMBs. These electrolytes were divided into three parts according to their polymerization methods: thermally induced polymerization, chemical initiator polymerization, ionizing radiation polymerization, and so on. Furthermore, we concluded the major challenges and future trends of in situ polymerized solid electrolytes for LMBs. It's hoped that this review will provide meaningful guidance on designing high-performance polymer solid electrolytes for LMBs.

Heterogenization of Palladium Trimer and Nanoparticles Through Polymerization Boosted Catalytic Efficiencies in Recyclable Coupling and Reduction Reactions

The development of heterogeneous palladium catalysts has shown continuous vitality in the field of catalysis and materials. In this work, we report one concise free radical polymerization approach to accomplish the aromatic palladium trimer functionalized polymers PSSy-[Pd3]+ (2) and its derived palladium nanoparticles (3). Full characterizations could confirm the successful combination of cationic [Pd3]+ or nanoparticles with poly(p-sulfonated styrene) skeleton. Compared to their monomeric tri-palladium precursor (1) and common Pd(dba)2, Pd(PPh3)4, Pd(OAc)2, heterogeneous PSSy-[Pd3]+ (2) shows much superior catalytic activities (0.15 mol %, TOF=1333.3 h-1) in the SMCC reaction. The identically ligated PdNPs (3) are formed in-suit in the presence of NaBH4 and accomplish quantitative reduction of 4-nitrophenol in just 320 s (0.50 mol %, TOF=2250 h-1). Moreover, these heterogeneous catalysts are reused for 5-6 times without significant loss of catalytic activity. Their superior catalytic ability is probably attributed to the synergistic effect of polymer entanglement and the tri-palladium fragment. This work enlightens that the immobilization of palladium clusters or nanoparticles by polymerization could offer multiple advantages in stability, efficiency and recyclability for their involved catalyses and show far-reaching future implications.

A Gel Polymer Electrolyte with High Uniform Na+ Flux and its Constructed Hybrid Interface Synergistically to Facilitate High-Performance Sodium Batteries

Sodium metal batteries (SMBs) can be developed on a large scale to achieve low-cost and high-capacity energy storage systems. Gel polymer electrolyte (GPE) can relieve volatilization of liquid electrolyte, adapt to volume changes in electrodes, and better satisfy the requirements of long-term SMBs. Herein, a dense polyurethane-based GPE modified with polyacrylonitrile is synthesized by rapidly swelling two-component polyurethane/polyacrylonitrile electrospun fiber film. Compared to traditional porous GPEs obtained by swelling porous matrixes, the fiber film provides uniform high Na+ flux inside GPE due to its partial solubility property and ability to dissociate salts. Therefore, it can reduce the polarization effect and induce uniform metal deposition under high current in conjunction with its constructed hybrid N/F-containing solid electrolyte interface (SEI) that possesses low ionic diffusion barrier. The study demonstrates that GPE has an ionic conductivity of 1.816 mS cm-1 at 20 °C and an ion transference number of 0.53. The full battery (NVP/GPE/Na) assembled with this GPE and Na3V2(PO4)3 (NVP) cathode shows 90.8% capacity retention rate after 1000 cycles at 10 C. Considering the convenient preparation and outstanding electrochemical performances of the obtained GPE, it can also be matched with other electrodes in the future to expand the application of sodium-based batteries.

Composite Polymer Electrolyte Based on PAN/TPU for Lithium-Ion Batteries Operating at Room Temperature

Lithium-ion batteries have garnered significant attention owing to their exceptional energy density, extended lifespan, rapid charging capabilities, eco-friendly characteristics, and extensive application potential. These remarkable features establish them as a critical focus for advancing next-generation battery technologies. However, the commonly used organic liquid electrolytes in batteries are explosive, volatile, and possess specific toxic properties, resulting in persistent safety concerns that remain to be addressed. Composite polymer electrolytes (CPEs) exhibit enhanced safety and stable electrochemical performance, emerging as one of the most promising alternatives. However, single polymers often need to meet the multifaceted performance requirements of batteries. In this study, a composite polymer electrolyte was prepared using solution casting, consisting of a blend of polyurethane (TPU) and polyacrylonitrile (PAN), along with the ceramic filler Li1.3Al0.3Ti1.7(PO4)3 (LATP) and lithium perchlorate (LiClO4). The optimal formulation, which included 40 wt% TPU, 60 wt% PAN, and 10 wt% LATP, exhibited a commendable ionic conductivity of 2.1 × 10-4 S cm-1, a lithium-ion transference number (tLi+) of 0.60, and notable electrochemical stability at 30 °C. The LiFePO4/Li battery assembled with this CPE demonstrated excellent cycling stability and rate capability at room temperature. It delivered a discharge specific capacity of 130 mAh g-1 at 1C. Under a charge-discharge rate of 0.2C, the battery achieved a discharge specific capacity of 168 mAh g-1, retaining 98% of its capacity after 100 cycles at 25 °C. Additionally, the CPE exhibited robust safety performance. Consequently, this composite polymer electrolyte holds significant promise for application in lithium-ion batteries.

An In Situ Polymerization Gel Polymer Electrolyte Based on Pentaerythritol Tetracrylate for High-Performance Lithium-Ion Batteries

Problems occur frequently during the application of traditional liquid electrolyte batteries, such as fluid leakage and low energy density. As a product of liquid electrolyte transition to solid electrolyte, gel polymer electrolyte has its own advantages for achieving high conductivity and good thermal stability. In this study, pentaerythritol tetracrylate (PETEA) was used as the precursor to prepare polymer-based materials with the assistance of azobis(isobutyronitrile) (AIBN) as the initiator. Because fluorine is beneficial to improving the migration efficiency of Li+ and the electrochemical performance of the gel polymer electrolyte, dodecafluoroheptyl methacrylate (DFHMA) is introduced to the PETEA-based gel polymer electrolyte (GPE) system. The DFHMA-introduced GPE shows better electrochemical performance, battery cycle performance, conductivity, and lithium-ion migration number compared with the pristine PETEA-based GPE. In particular, the DFHMA-introduced GPE exhibits the best performance because the molar ratio of PETEA to DFHMA is 5:1. Herein, the electrochemical window is 4.6 V, the ionic conductivity reaches 1.207 mS cm-1, and the number of lithium-ion migrations reaches the value of 0.663. Because the electric current density is 2 C, the specific capacity of LiNi0.5Co0.2Mn0.3O2 (NCM523)/GPE/Li reaches 143.1 mAh g-1 after 100 cycles.

Solid-State Electrolytes by Electrospinning Techniques for Lithium Batteries

Solid-state lithium batteries (SSLBs) are regarded as next-generation energy storage devices because of their advantages in terms of safety and energy density. However, the poor interfacial compatibility and low ionic conductivity seriously hinder their development. Electrospinning is considered as a promising method for fabricating solid-state electrolytes (SSEs) with controllable nanofiber structures, scalability, and cost-effectiveness. Numerous efforts are dedicated to electrospinning SSEs with high ionic conductivity and strong interfacial compatibility, but a comprehensive summary is lacking. Here, the history of electrospinning SSEs is overeviewed and introduce the electrospinning mechanism, followed by the manipulation of electrospun nanofibers and their utilization in SSEs, as well as various methods to improve the ionic conductivity of SSEs. Finally, new perspectives aimed at enhancing the performance of SSEs membranes and facilitating their industrialization are proposed. This review aims to provide a comprehensive overview and future perspective on electrospinning technology in SSEs, with the goal of guiding the further development of SSLBs.

In Situ Characterizations of the Dynamics of Cathode Electrolyte Interfaces at Different Current Densities

LiNi0.8Mn0.1Co0.1O2 with high nickel content plays a critical role in enabling lithium metal batteries (LMBs) to achieve high specific energy density, making them a prominent choice for electric vehicles (EVs). However, ensuring the long-term cycling stability of the cathode electrolyte interfaces (CEIs), particularly at fast-charge conditions, remains an unsolved challenge. The decay mechanism associated with CEIs and electrolytes in LMB at high current densities is still not fully understood. To address this issue, in situ Fourier transform infrared (FTIR) is employed to observe the dynamic process of formation/disappearance/regeneration of CEIs during charge and discharge cycles. These dynamic processes further exacerbate the instability of CEIs as current density increases, leading to rupture and dissolution of CEIs and subsequent deterioration in battery performance because of continuous electrolyte reactions. Additionally, the dynamic changes occurring within individual components of CEIs at different cycling stages and various current densities are also discussed. The results demonstrate that excellent capacity retention at small current density is attributed to enrichment of inorganic compounds (Li2CO3, LiF, etc.) and rendering better stability and smaller expansion of CEIs. The key to achieving excellent electrochemical performance at high current densities lies on protecting CEIs, mainly inorganic components.

Solid Electrolyte Interphase on Lithium Metal Anodes

Lithium metal batteries (LMBs) represent the most promising next-generation high-energy density batteries. The solid electrolyte interphase (SEI) film on the lithium metal anode plays a crucial role in regulating lithium deposition and improving the cycling performance of LMBs. In this review, we comprehensively present the formation process of the SEI film, while elucidating the key properties such as electronic conductivity, ionic conductivity, and mechanical performance. Furthermore, various approaches for constructing the SEI film are discussed from both electrolyte regulation and artificial coating design perspectives. Lastly, future research directions along with development recommendations are also provided. This review aims to provide possible strategies for the further improvement of SEI film in LMBs and highlight their inspiration for future research directions.

Gel polymer electrolytes for rechargeable batteries toward wide-temperature applications

Rechargeable batteries, typically represented by lithium-ion batteries, have taken a huge leap in energy density over the last two decades. However, they still face material/chemical challenges in ensuring safety and long service life at temperatures beyond the optimum range, primarily due to the chemical/electrochemical instabilities of conventional liquid electrolytes against aggressive electrode reactions and temperature variation. In this regard, a gel polymer electrolyte (GPE) with its liquid components immobilized and stabilized by a solid matrix, capable of retaining almost all the advantageous natures of the liquid electrolytes and circumventing the interfacial issues that exist in the all-solid-state electrolytes, is of great significance to realize rechargeable batteries with extended working temperature range. We begin this review with the main challenges faced in the development of GPEs, based on extensive literature research and our practical experience. Then, a significant section is dedicated to the requirements and design principles of GPEs for wide-temperature applications, with special attention paid to the feasibility, cost, and environmental impact. Next, the research progress of GPEs is thoroughly reviewed according to the strategies applied. In the end, we outline some prospects of GPEs related to innovations in material sciences, advanced characterizations, artificial intelligence, and environmental impact analysis, hoping to spark new research activities that ultimately bring us a step closer to realizing wide-temperature rechargeable batteries.

A 3D Cross-Linked Metal-Organic Framework (MOF)-Derived Polymer Electrolyte for Dendrite-Free Solid-State Lithium-Ion Batteries

Lithium metal batteries (LMBs) with high energy density have received widespread attention; however, there are usually issues with lithium dendrite growth and safety. Therefore, there is a demand for solid electrolytes with high mechanical strength, room-temperature ionic conductivity, and good interface performance. Herein, a 3D cross-linked metal-organic framework (MOF)-derived polymer solid electrolyte exhibits good mechanical and ionic conductive properties simultaneously, in which the MOF with optimized pore size and strong imidazole cation sites can restrict the migration of anions, resulting in a uniform Li+ flux and a high lithium-ion transference number (0.54). Moreover, the MOF-derived polymer solid electrolytes with the 3D cross-linked network can promote the rapid movement of Li+ and inhibit the growth of lithium dendrites. Lithium symmetric batteries assembled with the 3D MOF-derived polymer solid electrolytes are subjected to lithium plating/stripping and cycled over 2000 h at a current density of 0.1 mA cm-2 and over 800 h at a current density of 0.2 mA cm-2. The Li/P-PETEA-MOF/LiFePO4 batteries exhibit excellent long-cycle stability and cycle reversibility.

In-situ construction of poly(tetraisopentyl acrylate) based gel polymer electrolytes with Lix La2-x TiO3 for high energy density lithium-metal batteries

As promising alternatives to liquid electrolytes, polymer electrolytes attract much research interest recently, but their widespread use is limited by the low ionic conductivity. In this study, we use electrostatic spinning to introduce particles of an ionic conductor into polyacrylonitrile (PAN) fibers to prepare a porous membrane as the host of gel polymer electrolytes (GPEs). The relevant in-situ produced GPE performs a high ionic conductivity of 6.0×10-3  S cm-1 , and a high lithium transfer number (tLi + ) of 0.85 at 30 °C, respectively. A symmetrical Li cell with this GPE can cycle stably for 550 h at a current density of 0.5 mA cm-2 . While the capacity retention of the NCM|GPE|Li cell is 79.84 % after 500 cycles at 2 C. Even with an increased cut-off voltage of 4.5 V, the 1st coulomb efficiency reaches 91.58 % with a specific discharge capacity of 213.4 mAh g-1 . This study provides a viable route for the practical application of high energy density lithium metal batteries.

Toluene Tolerated Li9.88GeP1.96Sb0.04S11.88Cl0.12 Solid Electrolyte toward Ultrathin Membranes for All-Solid-State Lithium Batteries

Sulfide solid electrolyte membranes employed in all-solid-state lithium batteries generally show high thickness and poor chemical stability, which limit the cell-level energy density and cycle life. In this work, Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 solid electrolyte is synthesized with Sb, Cl partial substitution of P, S, possessing excellent toluene tolerance and stability to lithium. The formed SbS₄^3- group in Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 exhibits low adsorption energy and reactivity for toluene molecules, confirmed by first-principles density functional theory calculation. Using toluene as the solvent, ultrathin Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 membranes with adjustable thicknesses can be well prepared by the wet coating method, and an 8 μm thick membrane exhibits an ionic conductivity of 1.9 mS cm^-1 with ultrahigh ionic conductance of 1860 mS and ultralow areal resistance of 0.68 Ω cm^-2 at 25 °C. The obtained LiCoO₂|Li_9.88GeP_1.96Sb_0.04S_11.88Cl_0.12 membrane|Li all-solid-state lithium battery shows an initial reversible capacity of 125.6 mAh g^-1 with a capacity retention of 86.3% after 250 cycles at 0.1 C under 60 °C.