High Cycling Stability for Solid‐State Li Metal Batteries via Regulating Solvation Effect in Poly(Vinylidene Fluoride)‐Based Electrolytes

Abstract

Solid polymer electrolytes have emerged as promising alternatives to current liquid electrolytes due to their advantages in battery safety and stability. Among various polymer electrolytes, poly(vinylidene fluoride) (PVDF)‐based electrolytes with high ionic conductivity, large mechanical strength, and excellent electrochemical and thermal stability have a great potential for practical applications. However, fundamental issues, such as how the Li ions transport in the PVDF‐based electrolytes and how the residual solvent affects the cell performance, are unclear. Here, we demonstrate that the solvation effect due to a small amount of residual N,N‐dimethylformamide (DMF) bound into the electrolytes plays a critical role in ionic transport, interface stability, and cell performance. With the residual DMF existing in the electrolytes in a bound state not as free solvent, the ionic conduction could be realized by the Li‐ion transport among the interaction sites between the bound DMF and PVDF chains. Regulating the solvation effect in the electrolytes can make the PVDF‐based solid‐state Li metal batteries a significantly improved cycling performance at 25 °C (e. g., over 1000 cycles with a capacity retention of more than 94 %). These findings would promote the development of next‐generation Li metal batteries with high energy density and safety.

Sandwich-like solid composite electrolytes employed as bifunctional separators for safe lithium metal batteries with excellent cycling performance

“…For PVDF/PP and PVDF–DBDPO/PP separators, the synchronously gentle mass reduction in the initial low-temperature range is mainly ascribed to the gradual volatilization of the bound DMF molecules complexed in PVDF polymer networks (Fig. S4†), 49 and a sudden weight loss doesn't occur until about 310 °C though the thermal decomposition of PVDF polymers can be slightly accelerated due to the oxidation by LiClO 4 , 50 demonstrating a good decomposition resistance at high temperature.…”

Double-Layer Solid Composite Electrolytes Enabling Improved Room-Temperature Cycling Performance for High-Voltage Lithium Metal Batteries

“…The EA result shows that the calculated mass percentage of remaining DMF is about 20 wt % in all the electrolyte membranes (Table S1). More importantly, this low content of DMF is confirmed to exist as [Li(DMF) x ] + complexes in the polymer networks but not free molecules, since only the absorption band at 658 cm −1 that corresponds the bound DMF appears in the FT-IR spectra (Figure 2d), 39,40 which can strongly illustrates the solid-state characteristics of the PVDF/(PEO+PVDF)-L SCEs. 41 Electrochemical Properties of PVDF/(PEO+PVDF)-L SCEs.…”

Structure Code for Advanced Polymer Electrolyte in Lithium‐Ion Batteries

“…Additional polyethers, such as poly(propylene oxide) (PPO), [ 38 ] as well as PEO and PPO [ 39 ] with various molecular weights, have also been used as host polymers for ion transfer. To date, several homopolymers, such as poly(acrylonitrile) (PAN), [ 40 ] poly(methyl methacrylate) (PMMA), [ 41 ] poly(vinyl chloride) (PVC), [ 42 ] and poly(vinylidene fluoride) (PVDF) [ 43 ] have been used as PEs, which can either be assembled with lithium salts to form polymer in salt electrolytes, or form ternary or quaternary gel mixtures with liquid plasticizers such as ethylene carbonate (EC) or propylene carbonate (PC). [ 44 ] In addition, the blend of two homopolymers, or a homopolymer with other polymer types can also moderate the defects of individual PEs, realizing a balance between their physical properties and ionic conductivity.…”