Boosting High Energy Density for Aqueous Ni–Zn Batteries by Synergetic Engineering of Bimetal Doping and Se Vacancy in Ni3Se2

Abstract

Developing transition metal selenide materials with high capacity, excellent rate capability, and satisfactory durability presents significant challenges due to their sluggish electrochemical kinetics, limited electrical conductivity, and detrimental volume change. To address these challenges, we have prepared four Ni₃Se₂-based cathode materials, named as Ni₃Se₂, Mo-Ni₃Se₂, V-Ni₃Se₂, and MoV-Ni₃Se₂, with selenium vacancies through a one-step hydrazine-hydrothermal process. Co doping with Mo and V demonstrates the synergistic effects of the bimetallic dopants and induces the generation of a higher density of selenium vacancies. The incorporation of Mo/V codoping and rich selenium vacancies confers upon MoV-Ni₃Se₂ obvious advantages, such as improved electrical conductivity, enhanced structural flexibility, sufficient redox reaction sites, and reduction of charge-transfer resistance. Consequently, the MoV-Ni₃Se₂ electrodes achieve a peak specific capacity of 1.78 mAh cm^–2 at a current density of 2 mA cm^–2 and sustain a high rate capability of 0.96 mAh cm^–2 at 50 mA cm^–2. The MoV-Ni₃Se₂//Zn battery delivers an impressive surface energy density of 2.93 mWh cm^–2 and a remarkable power density of 51.55 mW cm^–2 with outstanding cycling stability (capacity retention of 87.44% at 20 mA cm^–2 after 3000 cycles). This study provides valuable insights for the development of high-performance cathode electrodes by synergetic engineering of doping and defects for aqueous nickel–zinc batteries.