Cobalt-Doped NiS₂ Micro/Nanostructures with Complete Solid Solubility as High-Performance Cathode Materials for Actual High-Specific-Energy Thermal Batteries

Abstract

Transition-metal sulfides are key cathode materials for thermal batteries used in military applications. However, it is still a big challenge to prepare sulfides with good electronic conductivity and thermal stability. Herein, we rapidly synthesized a Co-doped NiS₂ micro/nanostructure using a hydrothermal method. We found that the specific capacity of the Ni_1-<i>x</i>Co<i>_x</i>S₂ micro/nanostructure increases with the amount of Co doping. Under a current density of 100 mA cm^-2, the specific capacity of Ni_0.5Co_0.5S₂ was about 1565.2 As g^-1 (434.8 mAh g^-1) with a cutoff voltage of 1.5 V. Owing to the small polarization impedance (5 mΩ), the pulse voltage reaches about 1.74 V under a pulse current of 2.5 A cm^-2, 30 ms. Additionally, the discharge mechanism was proposed by analyzing the discharge product according to the anionic redox chemistry. Furthermore, a 3.9 kg full thermal battery is assembled based on the synthesized Ni_0.5Co_0.5S₂ cathode materials. Notably, the full thermal battery discharges at a current density of 100 mA cm^-2, with an operating time of about 4000 s, enabling a high specific energy density of around 142.5 Wh kg^-1. In summary, this work presents an effective cathode material for thermal battery with high specific energy and long operating life.