Aqueous Magnesium Zinc Hybrid Battery: An Advanced High-Voltage and High-Energy MgMn₂O₄ Cathode

Driven by energy demand and commercial necessities, rechargeable aqueous metal ion batteries (RAMBs) have gained increasing attention over the last few decades as high-power and high-energy hubs for large-scale and ecofriendly energy storage devices (ESDs). However, recently explored RAMBs still do not provide the performance needed in order to be realized in grid-scale storage operations due to their poor electrochemical stability, low capacity, low working voltage, and apparently low specific energies. Herein, we have fabricated a new RAMB using MgMn₂O₄ as the cathode and zinc as the anode for the first time. The stable electrochemical performance of this RAMB at high current rates (∼80% capacity retention at 500 mA g^-1 after 500 cycles) and a very high specific energy of 370 Wh kg^-1 at a specific power of 70 W kg^-1 make this newcomer to the family of RAMBs a serious contender for the exploration of safe and green ESDs in the near future.