1. Introduction
Elevated and non-uniform temperatures across a lithium-ion battery pack accelerate capacity fade and, in extreme cases, contribute to thermal runaway risk, and while active liquid cooling is effective it adds parasitic power draw and system complexity that passive phase change material approaches can partially offset.
2. Methodology
A paraffin-based phase change material composite enhanced with 8 percent expanded graphite for improved thermal conductivity was cast around a scaled eight-cell 21700 battery module and instrumented with twelve thermocouples, then subjected to a repeated 2C discharge cycling protocol and compared against an identical module relying on natural convection alone, with peak temperature and inter-cell temperature standard deviation as the primary comparison metrics.
3. Results
The PCM-equipped module limited peak cell temperature to 41.2 degrees Celsius versus 52.6 degrees Celsius for the natural-convection baseline under the 2C discharge protocol, an 11.4 degree Celsius reduction, while inter-cell temperature standard deviation dropped from 3.8 to 1.4 degrees Celsius, a 63 percent improvement in thermal uniformity across the module.
4. Conclusion
Expanded-graphite-enhanced PCM composites provide meaningful passive thermal management benefits for EV battery modules under moderate discharge rates without added parasitic power draw. Future work will evaluate performance under fast-charging thermal loads and across repeated melt-freeze cycles for material degradation.
References
[1] Al-Hallaj S. and Selman J. R., A novel thermal management system for electric vehicle batteries using phase-change material, Journal of the Electrochemical Society, 2000. [2] Ling Z. et al., Review on thermal management systems using phase change materials for electronic components, Renewable and Sustainable Energy Reviews, 2014.