Two-phase immersion cooling with microcapsule phase-change material particle slurries for heat-transfer enhancement in battery thermal management

Abstract

Heat generation in high power lithium ion battery modules exceeds the capability of air cooling and single phase liquid cooling to maintain a low peak temperature and tight temperature uniformity. Although two phase immersion cooling leverages latent heat, module scale, gravity driven studies that isolate the role of coolant formulation remain limited. This study incorporates a microencapsulated phase-change material (MPCM) slurry into SF33 (Novec 7000) and benchmarks thermal control of a 3s3p 21,700 module at C rates from 1 to 4 with an ambient temperature of 20 °C. A condenser using gravity reflux enables pump free operation. Four baselines were compared: air, silicone oil, SF33, and SF33 with MPCM at 1, 5, 10, and 15 wt%. Metrics include peak surface temperature, maximum cell to cell temperature difference, and the heat transfer coefficient. All two phase cases outperformed air and silicone oil. The best performance occurred at 5 wt% MPCM, yielding peak temperatures of 22.6, 27.4, 30.5, and 33 °C at 1, 2, 3, and 4C, a cell to cell spread of 0.05 to 0.20 °C, and a heat transfer coefficient as high as 6.9 kW m-2 K-1. Performance declined at 10 to 15 wt% because increased viscosity and particle agglomeration weakened natural circulation and reduced boiling uniformity. The combined effects of latent heat temperature clamping by the phase change material and capsule induced early pool boiling explain the observed optimum near 5 wt%. © 2026 Elsevier Ltd.