High areal energy density and super durable aqueous rechargeable NiCo//Zn battery with hierarchical structural cobalt–nickel phosphate octahydrate as binder-free cathode

Bimetallic cobalt-nickel phosphate octahydrate (NCP) with hierarchical structure was prepared in situ on nickel foam by a simple one-step hydrothermal method. The areal energy density and peak power density of NCP//Zn batteries are much higher than most of the aqueous Zn-based batteries reported so far. By coating the electrodes with carbon materials and adding potassium phosphate buffer salt to the electrolyte, the cycling stability of NCP//Zn batteries is greatly improved. Quasi-solid NCP-C//Zn batteries can still charge a mobile phone even under hammer strokes, demonstrating excellent safety and promising energy storage applications. • (Co 0.5 Ni 0.5 ) 3 (PO 4 ) 2 ·8H 2 O with hierarchical structure was prepared in situ on nickel foam. • The NCP sample exhibited an ultrahigh areal capacity of 3.2 mAh/cm 2 at a current density of 5 mA/cm 2 . • The NCP//Zn battery showed superior areal energy densities (5.42 mWh/cm 2 ) and peak power densities (129.68 mW/cm 2 ). • The cycling durability of NCP//Zn battery reached to 98.31% after 2000 cycles. Aqueous rechargeable Zn-based alkaline batteries combine the advantages of battery-level energy density and capacitance-level power density, showing bright prospects. However, their energy density and cycling life were restricted by the low areal capacity and poor cycling tolerance of cathodes. Herein, bimetallic cobalt-nickel phosphate octahydrate (NCP) with hierarchical structure was prepared in situ on nickel foam by a simple one-step hydrothermal method. The NCP cathode achieved an ultrahigh areal capacity (3.2 mAh/cm 2 ), which was far more than twice that of the single metallic cobalt/nickel phosphate octahydrate due to its larger surface area, smaller electrode/electrolyte interface resistance, higher electrochemical reaction activity and kinetics process. The NCP//Zn battery showed much higher areal energy density of 5.42 mWh/cm 2 and peak power density of 129.68 mW/cm 2 than most aqueous Zn-based batteries currently reported. The cycling durability of NCP//Zn battery increased from 58.59% to 98.31% after 2000 cycles by coating carbon material on electrode and adding potassium phosphate buffer salt into electrolyte. Quasi-solid NCP-C//Zn batteries can still charge a mobile phone even under hammer strokes, demonstrating excellent safety and promising energy storage applications. This work might shed light on the construction of phosphate based energy storage devices with high energy density, power density and long life.