P2-Type Mn-Based Oxide Cathode for Chlorine-Free Mg–Na Hybrid Battery Devices

Abstract

P2-type manganese-based oxides possess high voltage and open layered structures, showing promise for high-energy-density rechargeable magnesium batteries (RMBs), but they suffer from sluggish Mg²⁺ diffusion and a lack of adaptable noncorrosive electrolytes. Herein, a Mg–Na hybrid battery with a dual-salt electrolyte containing amine chelators is developed to enable voltage-enhanced and reversible cathode operation. Na⁺ improves the reaction kinetics at high voltage, while amine chelators enhance Mg anode interface compatibility. The battery achieves 150 mAh g^–1 and 1.8 V at 20 mA g^–1, with 66.8% capacity retention over 100 cycles at 50 mA g^–1, outperforming most reported oxide cathodes due to improved kinetics in the high-voltage region, as evidenced by the galvanostatic intermittent titration technique and the distribution of relaxation time analyses. Moreover, a magnesium-based pouch cell is also demonstrated for the first time, delivering ∼162 Wh kg^–1 (based on the cathode active mass). This work verifies the practical potential of oxide-based magnesium batteries and establishes a key design principle for the development of high-performance RMBs.