Structure modification of nickel sulfide cathode for enhanced performance in lithium thermal batteries

Nickel sulfide (NiS₂) is a promising cathode material for Lithium (Li) thermal batteries due to its abundant resources and high theoretical capacity (870 mAh/g). However, its practical discharge capacity is much lower than the theoretical capacity, especially at high current densities. Structure modification is a feasible strategy for optimizing its electrochemical performance. Hence, a Co doping NiS₂ (Ni_1-xCo_xS₂, x = 0.03, 0.05 and 0.08) cathode was designed and constructed using a structural modification strategy. The Ni_0.95Co_0.05S₂ cathode demonstrates an optimal specific capacity of 729.3 mAh/g in comparison with NiS₂ (641.6 mAh/g) with a cut-off voltage of 0.5 V at 100 mA/cm² at 500 °C. Even at a high current density of 500 mA/cm², the specific capacity of Ni_0.95Co_0.05S₂ can reach 671.6 mAh/g. Pulse test and electrochemical impedance spectroscopy (EIS) reveal that Co doping can effectively reduce internal resistance and elevate electron conductivity and ionic transfer rate of NiS₂. Moreover, ex-situ X-ray diffraction (XRD) of discharge products of NiS₂ and Ni_0.95Co_0.05S₂ suggests that Co doping facilitates the sufficient reaction of NiS₂, boosting the discharge performance of Li thermal batteries.