Proton Switch Enabled Rich (100) Crystal Facet of Cu₃VS₄ Microspheres for Efficient Intercalation‐Transformation Ion Storage

Rechargeable magnesium batteries (RMBs) are receiving great attention due to their abundant resources and high intrinsic safety. However, the strong interaction between Mg²⁺ ions and slow diffusion kinetics in electrochemical reaction result in poor Mg²⁺-storage performance. Herein, Cu₃VS₄ microspheres with rich (100) crystal facets and cubic primary particles are constructed by the precise regulation of the proton switch. The cubic morphology and rich (100) facets provide sufficient active sites for redox reactions, facilitating the diffusion of energy storage ions within a 3D channel. The optimized Cu₃VS₄ cathode exhibits a high discharge specific capacity of 240 mAh g^-1 at a current density of 50 mA g^-1 and a retention rate of 77% over 500 cycles at 1 A g^-1, which is superior to most of the reported cathode materials. The experimental investigation and DFT theoretical computation demonstrate that the facet induces a novel reaction mechanism of intercalation reaction followed by a transformation process, involving the joint contribution of Mg²⁺/Na⁺ ions. Moreover, the pouch cell prototypes are assembled with decent capacity and cycle characteristics to confirm the practical prospect. This work provides new crystal facet engineering for structural optimization of cathode materials for RMBs.