High-capacity electrodes based on multiple reaction mechanisms are promising for lithium storage, but the inferior conversion reversibility limits the practical application. Herein, the Cu-Sn-S (CTS) electrodes based on conversion-alloying mechanisms are synthesized with abundant Cu₄SnS₄ (75.98%) and beneficial Cu_7.2S₄ phases. The regulated composition and core-shell nanostructures can effectively mitigate the volume change and improve the lithiation performance of CTS upon cycling. Moreover, the composition evolution of CTS is comprehensively tracked via various in-situ tests, revealing that the abundant Cu₄SnS₄ and the formed Cu₃Sn after lithiation are the key factors to induce uniform phase distribution and enhanced conversion reversibility, which is confirmed by theoretical calculations. This work sheds light on the reaction process of electrodes based on multiple lithiation mechanisms, which could inspire the development of analogous energy materials.

The energy density of thin-film lithium batteries (TFLBs) is predominantly determined by the average voltage and specific capacity, however, the mechanism of regulating the voltage plateaus of the film electrodes is not well understood. In this study, three boride films (Co–B, Fe–B, and Co–Fe–B alloys) with different thicknesses were 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 behavior of the thin/thick films was elucidated. Theoretical simulations and electrochemical analysis were conducted to investigate how the lithiation behaviors affected the voltage profiles of the film electrodes. In addition, the various-thickness CoB films were compared in all-solid-state TFLBs, demonstrating the universality and practicability of this simple regulation strategy to develop high-performance energy storage devices.