An electrochemical activation strategy boosted alkaline Zinc-ion battery with Ultra-high energy density

Aqueous zinc ion batteries (AZIBs) have broad prospects in many fields because of their high theoretical capacity, high hydrogen overpotential, low equilibrium potential, low cost and high safety. However, the surface chemical reactivity of cathode is usually limited by the utilization of active materials, resulting in insensitive edge position and unsatisfactory capacity. In this paper, a simple and convenient strategy is reported, in which the bimetallic phosphide nano-interfaces are constructed only by electrochemical high-voltage activation, so as to increase the electrode capacity of about 150 % (compared to the original NiCoP electrode). Under the combined action of water and oxygen, a coating of NiCo-OH nanosheet is formed on the NiCoP nano-wall, and the surfaces are rich in low-priced mixed state with remarkable reactivity and structural stability, which is theoretically confirmed by density functional theory (DFT). As a result, the 3D cathode has an ultra-high capacity of 544.9 mAh g^-1 and excellent rate performance (still about 69.5 % at 30 A g^-1). The assembled NCPOH//Zn battery has excellent reversibility and long life (maintained 97 % of initial capacity after 2000 cycles) and achieves a remarkable energy density of 933.5 Wh kg^-1. Our work explores the relationship between interface corrosion mechanism and corrosion surface activity, which is a powerful strategy to build metal phosphides with high surface electrochemical activity as advanced energy storage devices.