THERMAL MANAGEMENT OF LITHIUM-ION BATTERY PACKS USING PHASE-CHANGE MATERIAL COMPOSITE HEAT SINKS

Abstract

Rising energy density requirements in electric vehicles have placed unprecedented thermal loads on lithium-ion battery packs. Uncontrolled temperature rise accelerates capacity fade, promotes lithium plating, and may trigger thermal runaway. This thesis proposes and experimentally validates a passive thermal management system (TMS) based on paraffin-graphene composite phase-change materials (PCM) integrated into an aluminium heat-sink matrix surrounding cylindrical 18650 cells. A three-dimensional finite-element thermal model was developed in ANSYS Fluent to predict cell surface temperature distributions during standard US06 drive-cycle discharge at ambient temperatures of −20°C, 25°C, and 45°C. The composite PCM (paraffin + 5 wt% expanded graphite) exhibited effective thermal conductivity kᵉᵠᵠ = 4.2 W/m·K versus 0.21 W/m·K for pure paraffin, and latent heat L = 187 J/g. Experimental validation on a 24-cell (4S6P) module demonstrated that peak cell temperature was reduced from 58.3°C (air-cooled baseline) to 37.1°C (−21.2°C reduction) during 3C discharge, with maximum temperature non-uniformity ΔTᵐᵃˣ held below 4.5°C. Cycle life testing over 500 cycles showed 94.2% capacity retention for the PCM-managed module versus 81.7% for the air-cooled baseline, a significant improvement for mobility applications.