To address the thermal safety control of high-capacity lithium-ion battery energy storage systems, this study combined theoretical analysis and experimental testing and adopted a immersion liquid cooling scheme to investigate the thermal runaway behavior of energy storage modules under overcharging conditions. It explored the influence of factors such as the type of immersion liquid and the spacing between batteries on the voltage, temperature, and heat propagation of the module during thermal runaway and compared the results with those of conventional non-immersion modules. The study reveals that severe thermal runaway propagation occurs in conventional non-immersion energy storage modules, whereas no thermal runaway propagation is observed in immersion modules. Additionally, the maximum temperature of the battery undergoing thermal runaway is reduced by 85% compared to that of the non-immersion module. By using a immersion liquid with higher thermal conductivity and specific heat capacity, the maximum temperature of the module can be controlled within 237 ℃. Meanwhile, the gestation period before thermal runaway is extended, delaying the thermal runaway onset by 150 s. Besides, the temperature rise of the overcharged battery is also small (approximately 12.9 ℃). Increasing the battery spacing from 1.5 mm to 2.0 mm reduces the maximum module temperature by 40.3 ℃. No fire, explosion, or thermal runaway propagation is observed during the thermal runaway process of the immersion energy storage module. The findings of this study can provide valuable reference points for the design and optimization of thermal safety management systems in large-scale lithium-ion energy storage.