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

Abstract

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/cm2), 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/cm2 and peak power density of 129.68 mW/cm2 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.