Dispersion stability analysis of surface-modified hexagonal boron nitride in synthetic esters and simulation of immersion cooling for lithium-ion batteries

Immersion cooling improves battery safety and thermal performance via direct contact. Ester oils are regarded as superior alternatives due to biodegradability and thermal stability, but their low thermal conductivity (TC) limits application. A paucity of research has been conducted on the systematic improvement of this property in relation to ester oils. In order to address this limitation, the study selected hexagonal boron nitride (h-BN) with high TC. Through liquid-phase ultrasonic exfoliation and surface modification, h-BNNS-CTAB nanomaterials were successfully synthesized and incorporated into ester oil 1190. The dispersion stability, rheological properties, and TC of nanofluids at different concentrations were investigated. Furthermore, the heat dissipation performance of a 5 wt% h-BNNS-CTAB (BNC-5) nanofluid was evaluated through simulation. Results indicated that h-BNNS-CTAB exhibited significantly enhanced dispersion stability in 1190 compared to h-BN. Moreover, both additives improved the TC of 1190, the enhancement rates differed: 5 wt% h-BN nanofluid increased TC by 17.05 % (20 °C) and 10.71 % (40 °C), while BNC-5 nanofluid achieved increases of 9.87 % and 9.91 %, respectively. The simulation results obtained for a flow rate of 6 L/min indicated that the average battery pack temperature when utilizing BNC-5 nanofluid was 26.55 °C, representing a 40.62 % reduction compared to natural convection conditions. The maximum temperature difference (ΔT max ) recorded was 4.15 °C, which demonstrated a more homogeneous thermal distribution than pure 1190. This study demonstrated the significant potential of BNC-5 nanofluid as an immersion cooling medium for lithium-ion batteries, providing robust experimental data to support the application of immersion cooling technology.