Hierarchical-structural design of ultrathin composite electrolytes for high-stability solid-state lithium batteries: from “polymer-in-salt” to “polymer-in-ceramic”

Abstract

The high-voltage solid-state lithium batteries (SSLBs) are promising for breaking through the bottlenecks of high energy density and safety. Therefore, the solid electrolytes are required to make reliable interfaces with both high-voltage cathodes and Li-metal anodes. However, such requirement is usually difficult to be satisfied if using single-type electrolytes. Herein, a polyvinylidene fluoride (PVDF) based composite electrolyte with hierarchical-structural design from “polymer-in-salt” (PIS) to “polymer-in-ceramic” (PIC) is proposed to fulfill the double-side interface stability. Based on PVDF matrix with Li-salt as major component, the “PIS” electrolyte presents electrochemical window of as high as 4.8 V and ionic conductivity of 2.1×10⁻⁴ S cm⁻¹. Meanwhile, through being incorporated with inorganic nanoparticles, the PVDF further endows “PIC” configuration with high mechanical strength of 5.0 MPa and electrochemical stability to restrain dendrite infiltration. Upon coupling of hierarchical electrolyte (~16 μm) with LiNi_0.6Co_0.2Mn_0.2O₂ cathode and Li anode, the resultant LiNi_0.6Co_0.2Mn_0.2O₂/Li cell delivers a remarkable capacity retention of 83.3% after 200 cycles at 0.2 C. Furthermore, an excellent capacity retention of 89.7% after 120 cycles is achieved for the corresponding pouch cell with high cathode loading of 7.6 mg cm⁻² at 0.2 C. This work demonstrates a universal strategy for realizing high-stability SSLBs by adopting hierarchical electrolyte configuration.