Investigation of thermal runaway Inhibition in NCM811 Lithium-Ion Batteries under Overcharge Conditions via Immersion Cooling

This paper investigates the overcharge-thermal runaway (TR) behavior of Li[Ni 0.8 Co 0.1 Mn 0.1 ]O 2 (NCM811) lithium-ion batteries under immersed liquid cooling conditions. Overcharge tests were conducted under various immersion liquid heights and different coolant conditions to study the behavior characteristics, parameter evolution patterns, and response characteristics of the immersion liquid during the overcharge-TR process. The findings provide critical data and technical support for the safe application of immersed liquid-cooled battery energy storage systems. First, experiments were designed to investigate thermal runaway induced by overcharging in pouch-type NCM811 batteries under immersion conditions at different immersion heights. Key data such as temperature, voltage, and capacity were measured, and the overcharging process was clearly divided into five stages based on key voltage and temperature characteristics. Compared to non immersion conditions, the t TR was extended by approximately 515 s under full immersion condition, and T onset decreased from 109°C under to 68°C. This indicates that a full immersion condition can effectively reduce the risk of TR to a certain extent. However, experimental observations revealed that the coolant can act as an accelerant for battery combustion. Subsequently, overcharging experiments were conducted on ternary lithium batteries using two types of coolants: natural esters and synthetic hydrocarbons. The results indicate that overcharging and thermal runaway in high-energy-density NCM batteries can easily trigger the combustion of immersion fluids with low flash points. Flame propagation and sustained liquid combustion are two typical combustion behaviors resulting from thermal runaway in ternary pouch batteries under immersion conditions. Complete immersion conditions environment can delay the risk of thermal runaway in ternary lithium-ion batteries, but it does not reduce the severity of the thermal runaway. Coolants with a low flash point carry the risk of ignition if a ternary lithium-ion battery experiences thermal runaway.