Solid polymer electrolytes with dual salts enhance lithium-metal interfacial stability for long cycle performance of lithium batteries

Abstract

Solid-state lithium metal batteries (LMBs) are considered to be the ideal energy storage system for achieving higher energy density and high safety. However, poor physical contact at the interface between the solid-state electrolyte and lithium metal, as well as the growth of dendrites make the cycling stability of LMBs challenging. Therefore, we developed a multifunctional ionic liquid-based polymer electrolyte including montmorillonite (MMT) and double salts (NaFSI and LiTFSI). The self-concentration effect of MMT lithium ions, combined with the electrostatic shielding effect of the double salts, resulted in homogeneous ion deposition, reducing dendritic lithium generation and improving lithium battery performance, with lithium batteries achieving a stable cycling rate of 1000 cycles at 1 C. Moreover, Due to the integrated assembly of the battery assembly process using light curing, the physical interface between the positive electrode-electrolyte-negative electrode achieves good contact and wettability. NaFSI achieves the enhancement of solid electrolyte interface (SEI) by introducing NaF/LiF to SEI of lithium metal, and the optimization of ion deposition pattern at the interface can be achieved by electrostatic shielding effect. Ultimately, stable ion transport at the solid-solid interface for lithium metal solid-state batteries can be realized. Notably, the ionic liquid-based polymer electrolyte with high ionic conductivity (1.2 × 10−3 S cm−1) and high oxidative stability (5.2 V vs. Li/Li+) at room temperature. In addition, the good flame retardant properties of the electrolytes indicate that dual-salt polymer electrolytes are an effective strategy for achieving high safety and long cycle stability of LMBs.