• NiS2/SiO2 composite cathodes achieve a stable discharge voltage at 200 mA/cm² and reduce activation time by nearly 20% compared to bare NiS2.
• SiO2 doping raises the initial decomposition temperature of NiS2 by 30 °C, significantly improving thermal stability.
• Spherical SiO2 acts as a filler and lubricant, enhancing the cold-pressing formability and thermal conductivity of NiS2 electrodes.
• The NiS2/SiO2 composite is a promising cathode material for high-stability, fast-response thermal batteries in advanced weapon systems.