Geometric optimization of passive liquid-immersion housing to mitigate thermal runaway propagation in high energy density battery modules

With the rapid growth of the micro-mobility and electric vehicle (EV) markets, high-density packaging of lithium-ion batteries (LIBs) and suppression of thermal runaway propagation (TRP) have become critical challenges. Although conventional indirect liquid-immersion cooling offers effective thermal management and TRP suppression, it suffers from a volumetric energy-density penalty due to the required fluid space. In this study, we propose a geometrically optimized liquid-immersion housing battery module that maintains a high energy density above 430 Wh/L while improving thermal management and TRP suppression. The increased volumetric energy density was primarily achieved by reducing inactive housing and FPM volume through geometric optimization, while maintaining the same FPM formulation. Computational fluid dynamics (CFD) analysis and lab-scale 6S1P module discharge and TRP evaluations showed that minimizing the external gap and adopting a staggered cell arrangement enhanced heat dissipation and induced natural convection of the fire prevention material (FPM), mitigating local heat accumulation. This structural optimization promoted heat redistribution during both normal operation and single-cell TR events, thereby suppressing sequential TRP. In addition, driving tests using a scaled-up 10S2P module in an actual e-kickboard environment showed that the proposed housing design reduced the maximum cell temperature from 31.1 °C to 28.1 °C and maintained an inter-cell temperature deviation of 1.25 °C during operation. These results demonstrate that geometric optimization of passive immersion housing can provide an effective strategy for improving thermal stability in high energy density cylindrical-cell modules.