Rechargeable Mg-Ion Full Battery System with High Capacity and High Rate

Thanks to the low cost, free dendritic hazards, and high volumetric capacity, magnesium (Mg)-ion batteries have attracted increasing attention as alternative energy storage devices to lithium-ion batteries. Despite the successful development of electrode materials, the real-life application potential of Mg-ion full battery systems (MIFBSs) is largely hindered by the lack of suitable electrode couples and hence low diffusion kinetics, which induce low specific capacity, poor rate performance, and low working voltage. Herein, we report an aqueous rechargeable MIFBS by employing copper hexacyanoferrate (CuHCF) as the cathode and 3,4,9,10-perylene-tetracarboxylic acid diimide (PTCDI) as the anode in 1 moL L^-1 MgCl₂ electrolyte. The combination of PTCDI//CuHCF allows efficient redox and convenient intercalation/deintercalation of Mg²⁺ at the electrodes while facilitating a fast transfer of Mg²⁺ between the two electrodes. As a result, the system delivers a high capacity of ∼120.3 mAh g^-1 at a current density of 0.5 A g^-1 after 200 operation cycles with a broadened voltage range (0-1.95 V) and maintains a capacity of ∼97.8 mAh g^-1 at 2.0 A g^-1 after 1000 cycles. Even at a high current density of 5.0 A g^-1, the battery provides a steady capacity of ∼81.4 mAh g^-1 over 5000 cycles. Moreover, after being applied at 11.0 A g^-1, the system can deliver a capacity of ∼126.5 mAh g^-1 at 0.5 A g^-1. This work emphasizes the great promise of developing suitable electrode couples for aqueous MIFBSs to achieve high capacity and high rate.