Rechargeable Mg–Na and Mg–K hybrid batteries based on a low-defect Co3[Co(CN)6]2 nanocube cathode

Abstract

Rechargeable Mg–Li hybrid batteries have the merits of a Mg metal anode and a Li⁺ intercalation cathode, but the limited availability of Li resources hinders their large-scale application. Herein, rechargeable Mg–Na and Mg–K hybrid batteries are constructed with a low-defect Co₃[Co(CN)₆]₂ nanocube cathode. The large redox active cavities of Co₃[Co(CN)₆]₂ are highly favorable for reversible Na⁺ and K⁺ intercalations. The Mg–Na and Mg–K hybrid batteries provide reversible capacities of 123 and 126 mA h g⁻¹, respectively, and a stable long-term cycling over 600 cycles. By contrast, the Mg–Li hybrid battery delivers a much lower capacity of 55 mA h g⁻¹. It is also demonstrated that controlled crystallization of well-defined nanocubes with few lattice defects is important for these high-capacity Mg–Na and Mg–K hybrid battery cathodes. The low-defect Co₃[Co(CN)₆]₂ nanocube cathode shows good rate capability, providing specific capacities of 45 and 53 mA h g⁻¹ at 1000 mA g⁻¹ in Mg–Na and Mg–K hybrid batteries, respectively. This study illustrates that low-defect Prussian blue analogs of Co₃[Co(CN)₆]₂ are highly compatible and promising cathodes for Mg–Na and Mg–K hybrid batteries. The present study also provides a new method for the development of low-cost and high-performance batteries based on Mg metal anodes.