Graphite fluoride interface blocking for higher capacity fluoride ion thermal batteries

Abstract

Fluoride ion thermal batteries (FITBs) have emerged as a promising next-generation energy storage system attributed to their unique ionic transport characteristics coupled with exceptional theoretical energy density. Nevertheless, nickel fluoride (NiF₂) cathode dissolution in molten halide electrolyte (e.g., formation of Cs_xNiᵧF_x+2ᵧ and other by-products), leading to capacity decay and safety hazards. In this study, we innovatively introduced graphite fluoride (GF) interfacial layer to achieve a specific capacity of 400 mA h g⁻¹ (500 °C, 50 mA cm⁻²) in NiF₂|GF|electrolyte|La system, which is a 2.4-fold increase compared with that of the GF-free system (167 mA h g⁻¹). The GF layer selectivity was confirmed to allow the GF layer to be used in the GF system. Experiments confirm that the GF layer selectively allows F⁻ migration and blocks the diffusion of metal cations, effectively suppressing side reactions. This strategy provides a universal solution for the interface design of molten salt batteries and promotes the development of high-energy thermal batteries.