Flexible PVDF-HFP based hybrid composite solid electrolyte membrane co-filled with hydroxypropyl methyl cellulose and Li6.4La3Zr1.4Ta0.6O12 for high-performance solid-state lithium batteries

Solid polymer electrolytes (SPEs) have sparked attention due to their superior mechanical robustness and excellent security in solid-state lithium batteries. However, intrinsic limitations, such as poor ionic transport properties and large interface impedance, severely hinder their practical applications. Herein, a novel composite solid electrolyte (PLHL-CSE) membrane, which consists of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), hydroxypropyl methyl cellulose (HPMC), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and Li6.4La3Zr1.4Ta0.6O12 (LLZTO), was prepared by solution-casting technique. The incorporation of HPMC into PVDF-HFP-based electrolyte played crucial roles in reducing the crystallinity of PVDF-HFP, promoting the dissociation of lithium salt, and increasing the amount of mobile Li+. With synergistic effects of HPMC and LLZTO, the mechanical and electrochemical performance of PVDF-HFP-based electrolytes were greatly enhanced. The obtained PLHL-CSE membrane showed better mechanical strength (3.0 MPa), enhanced ionic conductivity (0.25 mS/cm at 25 °C), greater lithium-ion transference number (0.7), and broadened electrochemical window of 5.0 V (vs. Li+/Li) than the PVDF-HFP/LiTFSI solid polymer electrolyte (PL-SPE) membrane. After 300 cycles at 1 C, the assembled LiFePO4/PLHL-CSE/Li cell with PLHL-CSE membrane as the hybrid composite solid electrolyte displayed a high capacity retention (95.6%). In addition, the positive effects of HPMC and LLZTO on promoting the generation of stable SEI and the uniform lithium deposition were also confirmed by the SEM results of cycled lithium metals. These findings point to the good potential of PLHL-CSE membrane as a hybrid composite solid electrolyte for practical application in lithium batteries.