MultiElement-Doped Ni-Based Disulfide Enhances the Specific Capacity of Thermal Batteries by High Thermal Stability

With the high theoretical capacity and the ability of large current discharge, NiS₂ has been expected as a new cathode material for thermal batteries. However, its lower decomposition temperature (∼500 °C) restricts its application on thermal batteries because of the high operating temperature of thermal batteries (500-600 °C). In this case, Cr, Fe, Co, and Cu multielement-doped NiS₂ (NiS₂-d) has been successfully prepared by low-temperature solid-phase sintering. Owing to the effect of high entropy, the multielement doping improved the thermodynamic system stability of NiS₂, and the decomposition temperature (2NiS₂ → 2NiS + S₂) increased from 482 to 610 °C. Interestingly, doping also reduces the particle size of NiS₂, resulting in defects on the surface of NiS₂ particles and improving the conductivity of NiS₂.The actual discharge capacity of NiS₂ enhanced significantly from 516 to 643 mA h g^-1 at 500 °C, with a current density of 100 mA cm^-2 and a cut-off voltage of 1.5 V. This is due to a more complete release of the first discharge reaction (NiS₂ + 2Li⁺ + 2e^- → NiS + Li₂S) as the decomposition temperature rises. The enhancement of conductivity, meanwhile, lessens polarization during the discharge process, raises the voltage of the NiS₂ discharge platform, and improves the stability of the NiS₂ later discharge platform. Additionally, the smaller particle size enables improved contact between the cathode and the electrolyte interface, allowing electrolyte ions to quickly come into touch with the NiS₂ surface. These results show that the discharge performance of NiS₂ at high temperatures could be effectively improved by multielement doping. It provides a new method for improving the stability of a metal sulfide and its application at high-temperature discharge.