Mg(Al, Fe, Mn, REE)₂O₄ Spinel Prepared from Pelagic REE-Rich Clays and Application as Magnesium-Ion-Battery Cathodes

The oxidation and lattice distortion of spinel oxides used for magnesium-ion battery (MIB) cathodes lead to poor stability and cycling performance. Herein, the highly inverted spinel oxide Mg(Al, Fe, Mn, REE)₂O₄ of <i>i</i> = 0.62 with incorporated rare-earth elements (REE) and decent specific surface area was prepared by utilizing leachate of the pelagic rare-earth-rich clays via a foamed sol-gel/calcination method. Measurements of specific capacity, cycling performance, and multiplicity performance showed that the foamed spinel exhibited distinguished electrochemical performance of MIB. At the current density of 100 mA h^-1, the initial discharge and charge specific capacity were 125.7 mAh g^-1 and 139.7 mAh g^-1, and the reversible discharge and charge specific capacities were maintained as 96.7 mAh g^-1 and 102.4 mAh g^-1 after 200 cycles of charging-discharging. The Mg-ion diffusion rate for MAFMRO was 1.08 × 10^-5 cm² s^-1, which was significantly improved, compared to traditional magnesium spinel anodes. This work highlights an approach for modification of spinel-type cathode materials and the high-value utilization of pelagic clay resources.