Interface regulation of Cu₂Se via Cu–Se–C bonding for superior lithium-ion batteries

Transition metal selenides have aroused great attention in recent years due to their high theoretical capacity. However, the huge volume fluctuation generated by conversion reaction during the charge/discharge process results in the significant electrochemical performance reduction. Herein, the carbon-regulated copper(I) selenide (Cu₂Se@C) is designed to significantly promote the interface stability and ion diffusion for selenide electrodes. The systematic X-ray spectroscopies characterizations and density functional theory (DFT) simulations reveal that the Cu–Se–C bonding forming on the surface of Cu₂Se not only improves the electronic conductivity of Cu₂Se@C but also retards the volume change during electrochemical cycling, playing a pivotal role in interface regulation. Consequently, the storage kinetics of Cu₂Se@C is mainly controlled by the capacitance process diverting from the ion diffusion-controlled process of Cu₂Se. When employed this distinctive Cu₂Se@C as anode active material in Li coin cell configuration, the ultrahigh specific capacity of 810.3 mA·h·g⁻¹ at 0.1 A·g⁻¹ and the capacity retention of 83% after 1,500 cycles at 5 A·g⁻¹ is achieved, implying the best Cu-based Li⁺-storage capacity reported so far. This strategy of heterojunction combined with chemical bonding regulation opens up a potential way for the development of advanced electrodes for battery storage systems.