Topology crafting of polyvinylidene difluoride electrolyte creates ultra-long cycling high-voltage lithium metal solid-state batteries

Abstract

Solid-state polymer electrolytes (SPEs) present poor anti-oxidation ability, low ionic conductivity and high flammability, which greatly restrict their applications in high-voltage solid-state lithium metal batteries. Herein, we uniformly graft the lithium phenyl phosphate (LPPO) on polyvinylidene difluoride (PVDF) by dehydrofluorination and Friedel-Crafts alkylation reactions to create a multifunctional PVDF-LPPO SPE with branched topology. The LPPO serves as a single ion conductor, flame retardant and cathode electrolyte interface formation agent not only greatly improves the ionic conductivity, fireproof property and electrochemical stability of SPE, but also remarkably suppresses the side reactions with both cathode and lithium metal anode. An additional and uniform Li-ion transmission path is constructed by LPPO to remarkably reduce the activation energy and enhance the lithium-ion transference number of PVDF-LPPO SPE. The solid-state LiNi0.8Co0.1Mn0.1O2||PVDF-LPPO||Li batteries stably cycle for 1550 times between 2.8 and 4.3 V at 1 C and 1000 times under a high charging voltage of 4.5 V. The transformation of layered structure to rock-salt phase of NCM811 particles is greatly suppressed during long cycling by a stable and uniform LPPO derived cathode electrolyte interface. This work provides a precise operation method for modifying structure of polymer electrolyte to achieve outstanding special properties of lithium metal solid-state batteries.