Unraveling thickness-dependent lithiation behaviors of boride films for all-solid-state thin-film lithium batteries

The energy density of thin-film lithium batteries (TFLBs) is predominantly determined by average voltage and specific capacity, but how to regulate the voltage plateaus of film electrodes remains inadequately understood. Herein, three boride films (Co-B, Fe-B, and Co-Fe-B alloys) with changing thickness are precisely fabricated to enhance the specific capacity and voltage stability of TFLBs. By analyzing the cycling performance, redox peak evolution, and capacitive contribution, the thickness-dependent lithiation behaviors of thin/thick films are elucidated. Theoretical simulations and electrochemical analysis unravel the mechanisms underlying how lithiation behaviors affect the voltage profiles of film electrodes. Moreover, the various-thickness CoB films are compared in all-solid-state TFLBs, demonstrating the universality and practicability of this simple regulation strategy for developing high-performance energy storage devices.