Fluorinated Graphene Fillers for High-Performance Solid-State Lithium Batteries

Abstract

Solid-state batteries (SSBs) are expected to revolutionize the field of energy storage due to their superior safety and high energy density, which result from the use of lithium metal as the negative electrode. However, the development of solid-state electrolytes (SSEs), the key component of SSBs, is quite crucial. SSEs have high thermal stability, high mechanical strength, and a wide electrochemical window but lack enough ionic conductivity; which is one of the most challenging aspects. Incorporating suitable active or inert fillers in the solid polymer electrolyte matrix is one of several methods adopted to improve the ionic conductivity of pure polymer SSEs. Two-dimensional graphene-based fillers are a promising option as they provide a high surface area for creating an abundant interface with the polymer matrix creating a continuous pathway for lithium-ion transport and simultaneously their robust nature improves the mechanical strength of the electrolyte. Pristine graphene is electronically conducting in nature owing to the continuous sp2 carbon linkages, but the electronic conductivity can be suppressed by disrupting the sp2 bonds by heteroatom functionalization on the graphene. This study investigates the heteroatom functionalization of graphene to obtain various graphene-based fillers such as graphene oxide (GO), reduced graphene oxide (rGO), and fluorinated graphene oxide (FGO) and their effectiveness when introduced into a polymer SSE matrix for LiNi0.8Co0.1Mn0.1O2-based SSBs. FGO filler outperforms others in terms of ionic conductivity, thermal stability, enhanced electrochemical potential window, and compatibility of the SSE. The optimized ratio of FGO fillers in SSE demonstrates excellent electrochemical performance, enabling long-term Li plating/stripping with small overpotential and stable cycling of Li/ LiNi0.8Co0.1Mn0.1O2 full cells. This work highlights the notable potential of FGO materials in improving the comprehensive properties of polymer SSEs and promoting the applications of polymer SSEs in high-performance SSBs.