Boron nitride nanofluids for immersion cooling mitigation of lithium-ion battery thermal runaway: roles of dispersion stability and thermophysical properties

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Abstract
To improve immersion cooling for mitigating thermal runaway in lithium-ion batteries, boron nitride (BN) nanofluids with different volume fractions were prepared using deionized water/2-methyl-1,3-propanediol as the base fluid and polyvinylpyrrolidone as the dispersant. The dispersion stability, thermophysical properties, and thermal runaway suppression performance of the nanofluids were systematically evaluated. Results showed that BN concentration strongly affected both long-term stability and heat transfer performance. Nanofluids with 0.1-0.2 vol% BN remained uniformly dispersed without visible sedimentation after 120 days, while the 0.4 vol% BN nanofluid exhibited only slight sedimentation after 14 days but still maintained acceptable dispersion stability. Meanwhile, 0.4 vol% BN delivered the highest thermophysical enhancement, with thermal conductivity and specific heat capacity increased by 8.1% and 11.0%, respectively, compared with the base fluid. During battery thermal runaway tests, the 0.4 vol% BN nanofluid reduced the peak battery temperature by 2.4-4.3% and the temperature rise rate by 9.7-9.9%, and also suppressed battery mass loss and smoke temperature, with more pronounced effects at high state of charge. Therefore, rather than simply showing the best overall performance, the 0.4 vol% BN nanofluid achieved the most favorable compromise between dispersion stability, thermophysical enhancement, and thermal runaway mitigation, demonstrating strong potential as an immersion-cooling medium for lithium-ion battery safety applications.

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