Ni₃S₂ Nanocomposite Structures Doped with Zn and Co as Long-Lifetime, High-Energy-Density, and Binder-Free Cathodes in Flexible Aqueous Nickel-Zinc Batteries

Flexible rechargeable Zn//Ni batteries are attractive owing to their high energy density, good safety, inexpensive cost, and simple manufacturing process. However, the effects of metal doping on the properties of Ni₃S₂ cathodes in Zn/Ni batteries are not well understood. Herein, a binder-free Ni₃S₂ electrode is doped with Zn and Co and the nanocomposite structures are prepared on nickel foam (named ZCNS/NF) by a simple two-step hydrothermal technique. The ZCNS/NF//Zn battery delivers excellent electrochemical performance such as a working voltage window can be as high as 2.05 V, a capacity of 2.3 mAh cm^-2 at 12 mA cm^-2, and 82% retention going through 2000 cycles at 20 mA cm^-2. The battery has a maximum output area energy density of 1.8 mWh cm^-2 (462 Wh kg^-1) and a power density of 36.8 mW cm^-2 (9.2 kW kg^-1). In addition, the flexible battery remains operational while being bent at a large angle and even punctured. The high performance and robustness of the composite cathode suggest that the design principle and materials have large commercial potential in Ni//Zn batteries.