A low-cost Mg2+/Na+ hybrid aqueous battery

Abstract

A Mg²⁺/Na⁺ hybrid aqueous battery with high energy density and low cost is constructed using commercial Mn₃O₄ as a cathode and NaTi₂(PO₄)₃ as an anode for the first time. During electrochemical cycling, spinel Mn₃O₄ experiences a transition to layered MnO₂ hosting Mg²⁺/Na⁺ with a high specific capacity and a long cycling life in Mg²⁺/Na⁺ hybrid electrolytes. The battery delivers a discharge potential above 1.2 V and an energy density over 47 W h kg⁻¹ (based on the total mass of electrode materials) at a power density of 48 W kg⁻¹; even at a high power density of 400 W kg⁻¹, it delivers an energy density of 23.6 W h kg⁻¹. What is more, the battery shows an excellent cycling performance with 94% capacity retention after 6000 cycles at 10C. The performances drop only very slightly for batteries prepared by an economic and scalable method. The excellent electrochemical properties, combined with the low cost of raw materials and the ease of scaling up which many aqueous batteries lack, make this approach a very promising cost-effective environment-friendly solution for large-scale energy storage.