Ultralong cycling and wide temperature range of lithium metal batteries enabled by solid polymer electrolytes interpenetrated with a poly(liquid crystal) network

Abstract

Solid polymer electrolytes (SPEs) that can work over a wide temperature range are highly desired to accelerate the commercial applications of solid lithium metal batteries (SLMBs). Herein, novel SPEs were fabricated via the in situ polymerization and immobilization of a nematic liquid crystal (LC) into a poly(vinylidene fluoride-co-hexafluoropropene)–hexafluoropropylene (P(VDF-HFP)) network under in situ UV irradiation in the presence of an ionic liquid (IL). The migration of Li⁺ ions in as-formed SPEs was enhanced intensively on account of the interpretation of the poly(liquid crystal) (PLC) network, which was confirmed by FTIR and DFT calculations. As-developed SPEs exhibit an ultra-high ionic conductivity of 1.79 mS cm⁻¹ at 20 °C, a high lithium-ion transference number of 0.64, and an electrochemical window up to 5.0 V. Due to these outstanding performances, Li/Li symmetrical cells containing as-obtained SPEs delivered an outstanding cycling stability of over 3500 h under a current density of 0.2 mA cm⁻². Moreover, a Li/LiFePO₄ battery showed desirable cycling stability from 0 °C to 100 °C. It exhibited a high discharge capacity of 165.1 mA h g⁻¹, a high capacity retention of 95.1% after 500 cycles, and a high coulombic efficiency above 99.5% even under a 3C rate at 100 °C. Undoubtedly, these novel SPEs have great potential to be used in next-generation SLMBs.