A Sandwich-Structure Composite Polymer Electrolyte Based on Poly(vinyl alcohol)/Poly(4-lithium styrene sulfonic acid) for High-Voltage Lithium Batteries

High-performance all-solid-state lithium-metal batteries (ASSLMBs) require solid electrolytes displaying high electrochemical stability, high ion conductivity, a high lithium transference number, excellent compatibility with the electrodes, and the ability to work at room temperature. In this study, we used a solution-casting technique to prepare a flexible composite polymer electrolyte (CPE) having a high lithium transference number and applied it within ASSLMBs. The CPE comprised a poly(vinyl alcohol) (PVA)/poly(4-lithium styrene sulfonic acid) (PLSS) blend with an Al-doped Li7La3Zr2O12 (LLZO) filler sandwiched on both sides by poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)–lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) skin layers. The PVDF-HFP-LiTFSI skin layers not only lowered the interfacial resistance between the electrodes and the sandwich-CPE electrolyte but also suppressed lithium dendrite growth. The sandwich-CPE membrane exhibited high ionic conductivity (3.82 × 10–4 S cm–1) and a high lithium transference number (0.776) at room temperature. A CR2032 coin cell having the structure Li/sandwich-CPE/LMO@T-LNCM811 delivered excellent rate performance and cycle stability (discharge capacity of 130.55 mA h g–1 with 85.63% capacity retention after 100 cycles at a rate of 0.5C at room temperature). A pouch cell having the structure Li/sandwich-CPE/LMO@T-LNCM811 achieved a discharge capacity of 18.1 mA h with a capacity retention of 90.46% after 30 cycles at 0.2C at room temperature. This strategy for fabricating sandwich-CPE structures has potential for application in the preparation of high-voltage cathodes for ASSLMBs.