Reductive solvothermal synthesis of MgMn2O4 spinel nanoparticles for Mg-ion battery cathodes

Rechargeable Mg-ion batteries have gained significant attention as promising alternatives to Li-ion batteries. Owing to its high theoretical energy density and relatively high Mg-ion diffusivity, spinel oxide MgMn2O4 is a viable candidate as a cathode material; however, its poor rate capability limits its applicability. Decreasing the particle size can effectively address this problem by enhancing Mg-ion diffusion. In this paper, we demonstrate the conventional solvothermal synthesis of MgMn2O4 spinel nanoparticles. Solvothermal process is one of the most fundamental methods for nanoparticle synthesis because of its simple and flexible synthetic conditions. In the alcohol solvothermal conditions, spinel type MgMn2O4 nanoparticles of approximately 10–15 nm are successfully synthesized using amorphous MnO2 as a precursor. We note that controlling Mg2+ solvation and oxidation/reduction conditions in the reaction solution is crucial for the effective intercalation of Mg2+ into the MnO6 octahedral framework. Although the obtained MgMn2O4 nanoparticles aggregate to form submicron secondary particles, the aggregation can be suppressed by compositing them with the carbon nanotubes dispersed in the reaction solution. The composite exhibits a discharge capacity of 60 mAh g−1 with maintaining 80% of capacity retention after the 10th cycle.