Regulated solvation structure and solid electrolyte interfaces via imidazolium ionic gel electrolytes with high Li-ion transference number for Li-metal batteries

Abstract

Solid lithium metal batteries (LMBs) are faced with problems such as the solvation structure of lithium ion and the instability of solid electrolyte interface (SEI), which lead to poor cycling stability and anode interface damage. Here, the introduced 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMIM][FSI]) ionic liquid (IL) interacts strongly with Lithium salt to form a new ionic gel electrolyte (IGE) based on the poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), which facilitates the excellent Li-ion transference number up to 0.506 and improves the mechanical properties. The reconstruction of Li-ion solvation environment by [EMIM][FSI] and PVDF-HFP functional groups, as well as the formation of SEI protective layer rich in LiF and Li3N, make the IGE with excellent electrochemical properties and interfacial stability. As a result, the Li||Li symmetric batteries demonstrate outstanding cycle stability, while the LiFePO4||Li batteries exhibit a superior capacity of 154.04 mAh/g at 0.2 C, maintaining a capacity retention rate as high as 94.5 % even after 200 cycles. The results not only demonstrate a new approach to improve Li-ion transference number in IGEs, but also open a potential avenue to achieve LMBs with high performance.