Synthesis and Electrochemical Study of Spinel MgMn₂O₄ Cathode for Aqueous Magnesium Ion Batteries

In this work, spinel magnesium manganese oxides MgMn₂O₄ were successfully synthesized via a sol-gel method followed by calcination. In order to alleviate the particles aggregation of MgMn₂O₄, carbon spheres (CS) as the sacrificial template were introduced during the sol-gel synthesis process. The addition of CS templates at weight ratios of 5 and 20% relative to Mg²⁺ respectively yields products characterized by well-dispersed nanoparticles and hollow porous nanocages. Galvanostatic charge-discharge tests demonstrated that the MgMn₂O₄ with a 5% CS template could deliver the maximum discharge capacity of 155.5 mA h/g, while still maintaining a reversible capacity of 115 mA h/g after 100 cycles at a current density of 100 mA/g. The MgMn₂O₄ derived from a 20% CS template displays a hollow porous nanocages, with a capacity slightly lower than that of the 5% CS template. However, it exhibits excellent cycling stability, especially at a high current density of 300 mA/g, where after 250 cycles, the capacity retention rate remain as high as 93%.