Immersion cooling enhancement using a low-viscosity synthetic ester-based nanofluid for improved thermal safety in lithium-ion battery systems

Effective thermal management is critical for the reliable operation of lithium-ion battery systems, as excessive heat accumulation may lead to performance degradation and safety risks. This study develops a low-viscosity, synthetic ester-based nanofluid as an environmentally friendly immersion coolant for 18650 battery modules. Surface-modified Si 3 N 4 nanoparticles were stably dispersed in the ester base to form a homogeneous nanofluid. Thermal characterization under static and dynamic immersion-cooling conditions demonstrates enhanced thermal conductivity, improved heat-dissipation capability, and reduced temperature gradients, while maintaining low viscosity and favorable pumping performance. Dynamic cooling experiments show a maximum battery temperature reduction of 12.78% compared with conventional transformer oil under identical operating conditions. The interfacial modification of nanoparticles contributes to reduced thermal resistance and improved heat transfer pathways. In addition, the synthetic ester base exhibits good biodegradability and low aquatic toxicity, indicating favorable environmental compatibility. Overall, this work provides a thermally efficient and environmentally benign immersion cooling strategy that improves the operational thermal management performance of lithium-ion battery systems and enhances their thermal safety margin under normal operating conditions. Download: Download high-res image (272KB) Download: Download full-size image