Low-cost MgMn_2-xNi_xO₄ cathode synthesized by electrochemical method for high-performance aqueous magnesium ion batteries

Aqueous magnesium ion batteries (AMIBs) have aroused enormous concern on account of their high intrinsic safety, low manufacturing budget, and eco-friendliness for large-scale storage application. Although the spinel-type manganese oxides presented good storage properties of Mg ion, their poor diffusion kinetics greatly limited their further application. In this work, MgMn_2-xNi_xO₄ was synthesized via electrochemical conversion from LiMn_2-xNi_xO₄ precursors. Their electrochemical properties were affected by the stoichiometric ratio of Mn:Ni. MgMn_1.5Ni_0.5O₄ displayed good rate capability with a discharge specific capacity of 221.8 mAh g⁻¹ at a current density of 50 mA g⁻¹ and stable cycling of 500 laps with a capacity retention of 92.9% at a current density of 1000 mA g⁻¹. Substituting Ni ion for partial Mn ion could raise the content of Mn⁴⁺ and the electrical conductivity, which was in favor of the redox reaction in the discharge/charge processes. Moreover, spinel MgMn_1.5Ni_0.5O₄ achieved a high Mg ion diffusion ability, generating good electrochemical behavior.