Passive Thermal Management of Electric Vehicle Batteries Using Enhanced Phase Change Materials

Background/Objectives: This research aims to create, improve, and test a passive thermal management system (TMS) for lithium-ion EV batteries. The goal is to keep cell temperatures below 50°C during high-rate discharges without using extra power. The study focuses on improving the low thermal conductivity of standard phase change materials (PCMs) by developing a composite with expanded graphite (EG) and evaluating its ability to reduce thermal runaway risks and temperature differences within the battery module. Methods: To make the composite PCM, 20% expanded graphite was added to commercial paraffin wax (RT42) using a vacuum process to keep the structure strong and reduce empty spaces. The team measured its properties using Differential Scanning Calorimetry (DSC) and the transient plane source method. They tested the material in an 8-cell LG Chem M50S module set up in a 2×2×2 cube. The tests included constant-rate discharges (1C to 5C), high-current pulses (3C) to mimic acceleration and braking, and a long-term test of 500 charge-discharge cycles. Findings: The optimized EG-PCM composite exhibited a thermal conductivity of 5.9 W/m·K, a 29.5-fold increase over pure paraffin, while maintaining a latent heat capacity of 182 J/g. Module-level testing at a 2C discharge rate and 25°C ambient temperature showed a 50% reduction in peak cell temperatures (38.2°C) compared to the air-cooled baseline (52.3°C). Temperature uniformity improved to ±1.1°C, closely matching the performance of active liquid-cooled systems (±0.3°C). Long-term cycling demonstrated stable latent heat capacity, with no significant material degradation or accelerated battery ageing over 500 cycles. Novelty: This study stands out because it fully tests a high-conductivity composite PCM under sudden fault conditions, like 3C pulse discharges that mimic thermal spikes before a short circuit. Unlike earlier research that focused only on material production or steady-state tests, this work includes long-term reliability data (500 cycles) and a cost analysis. It shows a calculated thermal buffer of ~28°C below the nominal thermal runaway onset temperature (~70°C) under tested conditions. Abuse testing was not conducted. Keywords: Phase Change Materials (PCM), Lithium-Ion Battery, Passive Thermal Management, Expanded Graphite Composite (EG), Thermal Runaway Prevention, Electric Vehicles (EV)