Utilizing the Mn(II) Dissolution‐Induced Vacancy for Optimum Mg ²⁺ Storage of Spinel Mn ₃ O ₄

Manganese-based oxide can theoretically exert the multivalent advantages of an aqueous magnesium-ion cathode due to its redox activity and abundant crystal structure. However, sluggish diffusion kinetics of Mg²⁺ and Mn dissolution limit the rate performance and structure stability. Herein, we successfully utilize the notorious dissolution of Mn(II) tetrahedral site contributed vacancies for packaging optimum Mg²⁺ storage of a popular spinel Mn₃O₄ electrode. Such mechanism reverses the sluggish diffusion kinetics. Moreover, merited by the common ion effect and drug dissolution, a suitable preaddition of Mn²⁺ to electrolyte inhibit Mn(III) dissolution and optimize the integrity of the spinel framework. Impressively, the cathode achieves a reversible capacity of 310 mAh g^-1 and a stable cycle performance of 2000 cycles with 94.9% retention. Our research shows that reversible insertion/extraction at vacancies and effective stabilization of spinel framework is a powerful strategy to achieve Mg²⁺ ion energy storage system with high rate performance and long lifespan.