Self-assembly formation of solid-electrolyte interphase in gel polymer electrolytes for high performance lithium metal batteries

Abstract

Lithium-metal batteries (LMBs) using limited-Li anodes are imperative for realizing high-energy storage. Proper solid-electrolyte interphase (SEI) design to control Li-deposition behavior and enhance deposition reversibility is challenging. We engineer the self-assembly formation of SEI in a gel polymer electrolyte (GPE) comprising poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-co-HFP) dissolved in a LiPF6-LiNO3 dual-salt solution with multiple solvents. The components of this GPE present critical functions: (1) dielectric (PVDF‐co-HFP) dissociates ion pairs to facilitate Li+ transport in the electrolyte and regulate Li+ diffusion in the SEI to lower Li deposition overpotentials, and endows soft characteristics to the SEI; (2) dual-anion PF6−-NO3− in the Li+ solvation sheath facilitates facile Li+ desolvation and formation of rigid and ion-conductive Li3N–LiF-rich SEI. This GPE exhibits higher ionic conductivity and Li+ transference number than the corresponding liquid electrolytes. The capacity retention of an anode-free Cu|GPE|NMC811 battery, i.e., at an anodic-to-cathodic Li ratio (A/C) of 0, reaches 44% after 100 charge-discharge cycles. An LMB with limited-Li at A/C = 2, having energy of 616 Wh kg−1 based on electrode-material mass, exhibits a retention of 85% after 100 cycles. The strategy to regulate Li+-transport and Li-deposition through GPE is promising for realizing the application of LMBs.