Two‐in‐one shell configuration for bimetal selenides toward fast sodium storage within broadened voltage windows

Abstract The shell structure design has been recognized as a highly efficient strategy to buffer the severe volume expansion and consecutive pulverization of conversion‐type anodes. Nevertheless, construction of a functional shell with a stabilized structure that meets the demands of both high electronic conductivity and feasible pathways for Na⁺ ions has been a challenge so far. Herein, we design a two‐in‐one shell configuration for bimetal selenides to achieve fast sodium storage within broadened voltage windows. The hybridized shell, which benefits from the combination of titanium dioxide quantum dots and amorphous carbon, can not only effectively buffer the strain and maintain structural integrity but also allow facile and reversible transport of electrons and Na⁺ uptake for electrode materials during sodiation/desodiation processes, resulting in increased reaction kinetics and diffusion of sodium ions, conferring many benefits to the functionality of conversion‐type electrode materials. As a representative material, Ni‐CoSe₂ with such structural engineering shows a reversible capacity of 515 mAh g⁻¹ at 0.1 A g⁻¹ and a stable capacity of 416 mAh g⁻¹ even at 6.4 A g⁻¹; more than 80% of the capacity at 0.1 A g⁻¹ could be preserved, so that this strategy holds great promise for designing fast‐charging conversion‐type anodes in the future.