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.