Long-cycle stable operation of fluoride-ion batteries at room temperature enabled by an advanced interface engineering and ion diffusion kinetics regulation strategy

Abstract

Fluoride-ion batteries (FIBs) offer a high theoretical energy density of 5000 W h L⁻¹ and superior safety, but they face significant challenges such as electrode material dissolution and volume changes during cycling. Herein, this study presents an advanced interface engineering strategy to enhance the stability of the electrolyte–electrode interface. Through plasma treatment, substrate surface energy and adhesion are increased, while a co-deposition device generates a high-energy ion beam (Bi³⁺ and F⁻), depositing atoms densely and uniformly on CuF₂ to form a protective layer. Additionally, regulating the BiO_xF_y crystal structure via controlled O²⁻ ion injection optimizes F⁻ transport and diffusion barriers. This modulation, driven by O-2p and F-2p electron density states, retards F⁻ diffusion kinetics and mitigates volume changes in CuF₂ during cycling. The resulting battery showed stable performance in N,N,N-dimethyl-N,N-dineopentylammonium fluoride liquid electrolyte at room temperature, including a specific capacity of 110 mA h g⁻¹ and a fiftyfold longer cycling life than that of existing Cu@LaF₃ core–shell batteries. Furthermore, X-ray absorption fine structure analysis reveals the pivotal role of a BiOF film in mitigating the lattice recombination effect by assimilating excess F⁻. These findings highlight the importance of this advanced interface strategy for advancements in FIBs.