PVDF-HFP/PAN/PDA@LLZTO Composite Solid Electrolyte Enabling Reinforced Safety and Outstanding Low-Temperature Performance for Quasi-Solid-State Lithium Metal Batteries

Ceramic-Polymer Composite Solid-State Electrolytes for Solid-State Lithium Metal Batteries: Mechanism, Strategy, and Prospect

The low energy density and safety problems of lithium-ion batteries based on liquid electrolyte have set off a new wave of high specific capacity and high safety battery design to meet the need of future market. Solid-state lithium metal battery has been widely concerned for its high energy density, safety, and electrochemical stability. Especially, polymer-based solid-state electrolytes (polymer SSEs) have attracted much attention due to the good interfacial contact, flexible mechanical properties, and physical/chemical stability. However, the deficiencies of low ionic conductivity and weak mechanical strength limit the further development of polymer SSEs. Here, hybrid ceramic-polymer composite solid-state electrolytes (CSSEs), specifically consisted of polymers and inorganic ceramic active fillers, can achieve good interfacial contact, high ionic conductivity, excellent mechanical properties, and Li dendrite growth inhibition. Based on the intrinsic characteristics of polymers, this review expounds the strategies to improve the performance of ceramic-polymer CSSEs. Especially, the screening and modification strategies of polymer and ceramic active fillers in recent years, including structural design, surface modification, and interface engineering, are reviewed. Finally, the core ideas of the existing designs, and proposed feasible solutions, aiming at providing future development and industrialization of ceramic-polymer CSSEs are summarized.

Regulating cation-solvent interactions in PVDF-based solid-state electrolytes for advanced Li metal batteries

Poly(vinylidene fluoride) (PVDF)-based solid-state electrolytes (SSEs) have been considered promising candidates for advanced Li metal batteries due to their adequate mechanical strength and acceptable thermal stability. However, the poor compatibility between residual solvent and Li metal inevitably leads to fast capacity decay. Herein, we propose a multifunctional cation-anchor strategy to regulate solvation chemistry in PVDF-based SSEs to boost the electrochemical performance of Li metal batteries. The strong interaction between N,N-dimethylformamide (DMF) and Zn2+ decreases the participation of DMF in the inner solvation sheath of Li+, inducing an anion-reinforced solvation structure. The unique solvation structure facilitates the formation of a robust LiF-rich solid electrolyte interphase layer to eliminate interfacial side reactions. In addition, a continuous ion-conducting network is constructed by introducing extra TFSI- anions, enabling accelerated Li+ transport. As a result, the corresponding Li‖Li symmetrical cells achieve stable lithium plating/stripping over 780 h, and the rate performance and cycling stability of Li‖LiFePO4 cells are significantly improved. This work highlights the key role of regulation of solvation chemistry in PVDF-based SSEs for Li metal batteries.

In Situ Coordinated MOF-Polymer Composite Electrolyte for Solid-State Lithium Metal Batteries with Exceptional High-Rate Performance

The integration of metal organic frameworks (MOFs) and electrospun polymer fibers offers the potential to achieve uniform dispersion and high loading of fillers, providing a unique perspective for advancing composite solid electrolytes in solid-state lithium metal batteries. In this work, a composite solid electrolyte is fabricated through a combination of electrospinning and chemical immersion, facilitating the in situ nucleation and growth of HKUST-1 on polyacrylonitrile (PAN) electrospun nanofibers. The in situ coordinated HKUST-1 particles not only modify the solvation structure of Li+ and the coordination environment of TFSI-, but also encapsulate PAN fibers to mitigate interfacial side reactions with lithium metal, thereby improving interfacial stability. Consequently, the solid-state electrolyte achieves a high Li ion transference number of 0.77 and an impressive critical current density of 4.5 mA cm-2. The assembled Li||Li symmetric cell exhibits stable operation for over 4000 h at 4.0 mA cm-2, while Li||LFP and Li||NCM811 cells demonstrate exceptional rate capability and cycling stability. This work provides valuable insights into the design and fabrication of MOF/polymer-based composite solid electrolytes.

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.

Molecular Control Based on Electrostatically Driven Modification for Solid-State Lithium Metal Batteries

With the rapid development of energy vehicles, the demand for high-safety and high-energy-density battery systems, such as solid-state lithium metal batteries, is becoming increasingly urgent. Polyethylene oxide (PEO), as a commonly used electrolyte in solid-state batteries, has the advantages of easy processing and good interface compatibility but also faces the issue of poor ionic conductivity. In this study, we have enhanced the mechanical properties and ion conductivity of PEO electrolytes significantly, stabilizing electrochemical cycling, utilizing positively charged MXene as a modifying material for PEO solid electrolytes and leveraging stronger electrostatic forces. With these enhanced properties, the modified solid electrolyte in Li/Li cells demonstrates excellent cycling stability of over 430 h at 0.1 mA cm-2. Furthermore, the Li/LiFePO4 cells show excellent cycling performance, and the capacity retention rate is 92.1%.

Bilayer Heterostructure Electrolytes Were Prepared by a UV-Curing Process for High Temperature Lithium-Ion Batteries

Solid-state electrolytes are widely anticipated to revitalize high-energy-density and high-safety lithium-ion batteries. However, low ionic conductivity and high interfacial resistance at room temperature pose challenges for their practical application. In this work, the dual-matrix concept is applied to the design of a bilayer heterogeneous structure. The electrolyte in contact with the cathode blends PVDF-HFP and oxidation-resistant PAN. In contrast, the electrolyte in contact with the anode blends PVDF-HFP and reduction-resistant PEO. A UV-curing process was used to fabricate the bilayer heterostructure electrolyte. The heterostructure electrolyte exhibits an ionic conductivity of 4.27 × 10-4 S/cm and a Li+ transference number of 0.68 at room temperature. Additionally, when assembled into LiFePO4/CPEs/Li batteries, it shows a high initial discharge capacity at room temperature (168 mAh g-1 at 0.1 C and 60 mAh g-1 at 2 C), with a capacity retention of 93.3% after 100 cycles at a current density of 0.2 C. Notably, at 60 °C, the battery maintains a discharge capacity of 90 mAh g-1 at 2 C, with a capacity retention of 97.4% after 100 cycles at 0.2 C. Therefore, solid-state batteries using this bilayer heterogeneous structure electrolyte demonstrate promising performance, including effective capacity output and cycling stability.

Electrolytes for High-Safety Lithium-Ion Batteries at Low Temperature: A Review

As the core of modern energy technology, lithium-ion batteries (LIBs) have been widely integrated into many key areas, especially in the automotive industry, particularly represented by electric vehicles (EVs). The spread of LIBs has contributed to the sustainable development of societies, especially in the promotion of green transportation. However, the high demand for battery performance and safety in these fields has made the high viscosity, volatility, and potential leakage inherent in traditional organic liquid electrolytes a constraint on their further expansion. Especially at low temperature, the increased viscosity of the electrolyte, reduced solubility of lithium salts, crystallization or solidification of the electrolyte, increased resistance to charge transfer due to interfacial by-products, and short-circuiting due to the growth of anode lithium dendrites all affect the performance and safety of LIBs. Therefore, improving the safety performance of LIBs under low-temperature environments has become a focus of current research. This paper primarily reviews the progress made in utilizing different types of electrolytes in LIBs to enhance safety and optimize low temperature performance and discusses the current research progress as well as the future development direction of the field.

Accelerating the Development of LLZO in Solid-State Batteries Toward Commercialization: A Comprehensive Review

Solid-state batteries (SSBs) are under development as high-priority technologies for safe and energy-dense next-generation electrochemical energy storage systems operating over a wide temperature range. Solid-state electrolytes (SSEs) exhibit high thermal stability and, in some cases, the ability to prevent dendrite growth through a physical barrier, and compatibility with the "holy grail" metallic lithium. These unique advantages of SSEs have spurred significant research interests during the last decade. Garnet-type SSEs, that is, Li7La3Zr2O12 (LLZO), are intensively investigated due to their high Li-ion conductivity and exceptional chemical and electrochemical stability against lithium metal anodes. However, poor interfacial contact with cathode materials, undesirable lithium plating along grain boundaries, and moisture-induced chemical degradation greatly hinder the practical implementation of LLZO-based SSEs for SSBs. In this review, the recent advances in synthesis methods, modification strategies, corresponding mechanisms, and applications of garnet-based SSEs in SSBs are critically summarized. Furthermore, a comprehensive evaluation of the challenges and development trends of LLZO-based electrolytes in practical applications is presented to accelerate their development for high-performance SSBs.

Design of Fluorinated Elastomeric Electrolyte for Solid-State Lithium Metal Batteries Operating at Low Temperature and High Voltage

This work demonstrates the low-temperature operation of solid-state lithium metal batteries (LMBs) through the development of a fluorinated and plastic-crystal-embedded elastomeric electrolyte (F-PCEE). The F-PCEE is formed via polymerization-induced phase separation between the polymer matrix and plastic crystal phase, offering a high mechanical strain (≈300%) and ionic conductivity (≈0.23 mS cm-1) at -10 °C. Notably, strong phase separation between two phases leads to the selective distribution of lithium (Li) salts within the plastic crystal phase, enabling superior elasticity and high ionic conductivity at low temperatures. The F-PCEE in a Li/LiNi0.8Co0.1Mn0.1O2 full cell maintains 74.4% and 42.5% of discharge capacity at -10 °C and -20 °C, respectively, compared to that at 25 °C. Furthermore, the full cell exhibits 85.3% capacity retention after 150 cycles at -10 °C and a high cut-off voltage of 4.5 V, representing one of the highest cycling performances among the reported solid polymer electrolytes for low-temperature LMBs. This work attributes the prolonged cycling lifetime of F-PCEE at -10 °C to the great mechanical robustness to suppress the Li-dendrite growth and ability to form superior LiF-rich interphases. This study establishes the design strategies of elastomeric electrolytes for developing solid-state LMBs operating at low temperatures and high voltages.

Diversifying Ion-Transport Pathways of Composite Solid Electrolytes for High-Performance Solid-State Lithium-Metal Batteries

The application of composite solid electrolytes (CSEs) in solid-state lithium-metal batteries is limited by the unsatisfactory ionic conductivity underpinned by the low concentration of free lithium ions. Herein, we propose an interface design strategy where an amine silane linker is employed as a coupling agent to graft the Li7La3Zr2O12 (LLZO) ceramic nanofibers to the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer matrix to enhance their interaction. The hydrogen bonding between amino-functionalized LLZO (NH2@LLZO) and PVDF-HFP not only effectively induces a uniform incorporation of high-content nanofibers (50 wt %) into the polymer matrix but also furnishes sufficient continuous surfaces to weaken the complexation between PVDF-HFP and Li-ion carriers. Additionally, introduction of the hydrogen bond and Lewis acid-base interplay strengthens the interfacial interactions between NH2@LLZO and lithium salts that release more free lithium ions for efficient interfacial transport. The impact of the linker's structure on the dissociation capacity of lithium salts is systematically studied from the steric effect perspective, which affords insights into interface design. Conclusively, the composite solid electrolyte achieves a high ionic conductivity (5.8 × 10-4 S cm-1) by synergy of multiple transport channels at ceramic, polymer, and their interface, which effectively regulates the lithium deposition behavior in symmetric cells. The excellent compatibility of the electrolyte with both LiFePO4 and LiNi0.8Co0.1Mn0.1O2 cathodes also results in a long lifetime and a high rate capability for full cells.

Ultrathin, Mechanically Robust Quasi-Solid Composite Electrolyte for Solid-State Lithium Metal Batteries

Herein, we present the preparation and properties of an ultrathin, mechanically robust, quasi-solid composite electrolyte (SEO-QSCE) for solid-state lithium metal battery (SLB) from a well-defined polystyrene-b-poly(ethylene oxide) diblock copolymer (SEO), Li6.75La3Zr1.75Ta0.25O12 nanofiller, and fluoroethylene carbonate plasticizer. Compared with the ordered lamellar microphase separation of SEO, the SEO-QSCE displays bicontinuous phases, consisting of a Li+ ion conductive poly(ethylene oxide) domain and a mechanically robust framework of the polystyrene domain. Therefore, the 12 μm-thick SEO-QSCE membrane exhibits an exceptional ionic conductivity of 1.3 × 10-3 S cm-1 at 30 °C, along with a remarkable tensile strength of 5.1 MPa and an elastic modulus of 2.7 GPa. The high mechanical robustness and the self-generated LiF-rich SEI enable the SEO-QSCE to have an extraordinary lithium dendrite prohibition effect. The SLB of Li|SEO-QSCE|LiFePO4 reveals superior cycling performances at 30 °C for over 600 cycles, maintaining an initial discharge capacity of 145 mAh g-1 and a remarkable capacity retention of 81% (117 mAh g-1) after 400 cycles at 0.5 C. The high-voltage SLB of Li|SEO-QSCE|LiNi0.5Co0.3Mn0.2O2 displays good cycling stability for over 150 cycles at 30 °C. Moreover, the exceptional robustness of SEO-QSCE enables the high-voltage solid-state pouch cell of Li|SEO-QSCE|LiNi0.5Co0.3Mn0.2O2 with high flexibility and excellent safety features. The current investigation delivers a promising and innovative approach for preparing quasi-solid electrolytes with features of ultrathin design, mechanical robustness, and exceptional electrochemical performance for high-voltage SLBs.

In Situ Polymerization Derived from PAN-Based Porous Membrane Realizing Double-Stabilized Interface and High Ionic Conductivity for Lithium-Metal Batteries

Polymer polyacrylonitrile (PAN), with exceptional mechanical strength and ionic conductivity, is considered a potential electrolyte. However, the huge interfacial impedance of PAN-derived C≡N polar nitrile groups and Li anode limited its application. In this study, a double-stabilized interface was integrated by in situ polymerization of DOL between electrodes and a three-dimensional (3D) porous PAN polymer matrix containing SN plasticizer and LLZTO ceramic fillers to optimize the challenge of interfacial instability. The fabricated PDOL-PAN(SN/LLZTO)-PDOL composite solid electrolyte (CSE) exhibited the maximum ionic conductivities of 1.9 × 10-3 S cm-1 at room temperature and 2.5 × 10-3 S cm-1 at 60 °C, an electrochemical stability window (ESW) of 4.9 V, and a high Li+ transference number (tLi+) of 0.65. In addition, the side reactions of the PAN/Li metal were effectively prevented by inserting PDOL between the 3D porous membrane and Li electrode. Benefiting from the superior interface compatibility and ion conductivity, the Li symmetric battery showed more than 2000 h of cyclability. The solid Li/LiFePO4 full battery delivered excellent cycling performance, showing an original specific capacity of 136.2 mAh g-1 with a capacity retention of 90.1% after 350 cycles at 1C and 60 °C. Furthermore, the cycling of solid-state Li/NCM622 batteries also proved their application potential. This work presents an effective approach to solving interface problems of the PAN electrolyte for solid lithium-metal batteries (LMBs).

An Advanced Gel Polymer Electrolyte for Solid-State Lithium Metal Batteries

All-solid-state lithium metal batteries (LMBs) are regarded as one of the most viable energy storage devices and their comprehensive properties are mainly controlled by solid electrolytes and interface compatibility. This work proposes an advanced poly(vinylidene fluoride-hexafluoropropylene) based gel polymer electrolyte (AP-GPEs) via functional superposition strategy, which involves incorporating butyl acrylate and polyethylene glycol diacrylate as elastic optimization framework, triethyl phosphate and fluoroethylene carbonate as flameproof liquid plasticizers, and Li7La3Zr2O12 nanowires (LLZO-w) as ion-conductive fillers, endowing the designed AP-GPEs/LLZO-w membrane with high mechanical strength, excellent flexibility, low flammability, low activation energy (0.137 eV), and improved ionic conductivity (0.42 × 10-3 S cm-1 at 20 °C) due to continuous ionic transport pathways. Additionally, the AP-GPEs/LLZO-w membrane shows good safety and chemical/electrochemical compatibility with the lithium anode, owing to the synergistic effect of LLZO-w filler, flexible frameworks, and flame retardants. Consequently, the LiFePO4/Li batteries assembled with AP-GPEs/LLZO-w electrolyte exhibit enhanced cycling performance (87.3% capacity retention after 600 cycles at 1 C) and notable high-rate capacity (93.3 mAh g-1 at 5 C). This work proposes a novel functional superposition strategy for the synthesis of high-performance comprehensive GPEs for LMBs.

Studies on Composite Solid Electrolytes with a Dual Selective Confinement Interface Structure of Anions for High-Performance Lithium Metal Batteries

Solid-state lithium batteries (SSLBs) have attracted much attention due to their good thermal stability and high energy density. However, solid-state electrolytes with low conductivity and prominent interfacial issues have hindered the further development of SSLBs. In this research, inspired from a selective confinement structure of anions, a novel HMOF-DNSE composite solid electrolyte with a dual selective confinement interface structure is proposed based on the semi-interpenetrating structure generated by poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), poly(di-n-butylmethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMATFSI), and a metal-organic frameworks MOF derivative (HMOF) as a filler. The dual-network structure of PVDF-HFP/PDADMATFSI combined with HMOF formed a dual selective confinement interface structure to confine out the movement of large anions TFSI-, thereby enhancing the transfer ability of Li+. Subsequently, the addition of HMOF further improves the transfer of Li+ by binding up TFSI- through its crystal structure. The results show that HMOF-DNSE possesses a high room-temperature ionic conductivity (0.7 mS cm-1), a wide electrochemical window (up to 4.5 V), and a high Li+ transfer number (tLi+) (0.56). LiFePO4/HMOF-DNSE/Li cell shows an excellent capacity of 141.5 mAh g-1 at 1C rate under room temperature, with a high retention of 80.1% after 500 cycles. The material design strategy, which is based on selective confinement interface structures of anions, offers valuable insights into enhancing the electrochemical performance of solid-state lithium batteries.

MXene-BN-Introduced Artificial SEI to Inhibit Dendrite Growth of Lithium Metal Batteries

Lithiophilic substrates have been shown to improve the electrochemical performance of lithium metal anodes. The MXene-BN/Cu 3D current collector was prepared by a filtration method. The artificial solid electrolyte interface (SEI) layer composed of Li3N and LiF was formed on the surface of MXene-BN/Cu during the Li deposition process. Volume changes can be effectively relieved by this special 3D structure. The artificial SEI film reduced the critical dendrite growth length, inhibited Li dendrite growth, and stabilized the electrochemical cycle. MXene-BN/Cu exhibited highly reversible cycling properties during lithium metal deposition with a high Coulombic efficiency of ∼ 98.0% over 500 cycles. Furthermore, LiBH4 was produced during the Li deposition process. This study presents a promising strategy for developing dendrite-free Li anodes for use in lithium metal batteries.

Introduction of Nanoscale Si3N4 to Improve the Dielectric Thermal Stability of a Si3N4/P(VDF-HFP) Composite Film

In order to improve the dielectric thermal stability of polyvinylidene fluoride (PVDF)-based film, nano silicon nitride (Si3N4) was introduced, and hence the energy storage performance was improved. The introduction of nano Si3N4 fillers will induce a phase transition of P(VDF-HFP) from polar β to nonpolar α, which leads to the improved energy storage property. As such, the discharging energy density of Si3N4/P(VDF-HFP) composite films increased with the amount of doped Si3N4. After incorporating 10wt% Si3N4 in Si3N4/P(VDF-HFP) films, the discharging density increased to 1.2 J/cm3 under a relatively low electric field of 100 MV/m. Compared with a pure P(VDF-HFP) film, both the discharging energy density and thermal dielectric relaxor temperature of Si3N4/P(VDF-HFP) increased. The working temperature increased from 80 °C to 120 °C, which is significant for ensuring its adaptability in high-temperature energy storage areas. Thus, this result indicates that Si3N4 is a key filler that can improve the thermal stability of PVDF-based energy storage polymer films and may provide a reference for high-temperature capacitor materials.