Thermal testing of battery packs with nano-enhanced bio-based phase change materials in EVs under driving cycles

Electric vehicle lithium-ion batteries experience severe transient thermal loads during real-world driving, where elevated temperatures and cell-to-cell nonuniformity accelerate aging and can precipitate thermal runaway. This study proposes a sustainable, passive battery thermal management system based on a nano-enhanced bio-based phase change material (NE-BBPCM) from paraffin wax, walnut shell biochar, and reduced graphene oxide (rGO). rGO was incorporated at 0.1, 0.3, 0.5, and 1.0 wt% via probe ultrasonication, and the composite was microencapsulated to mitigate leakage. DSC and microscopy confirmed preserved phase change behavior and a conductive filler network, while thermophysical testing showed a conductivity rise from 0.25 to 1.5-1.85 W/m·K with latent heat retained at 2.5-220 kJ/kg. Increasing rGO reduced the melt time from 1850 s to 1580 s, increased the maximum temperature suppression from 8.4°C to 12.8°C, shortened the recovery time from 620 s to 530 s, and improved cycling stability to 490 cycles. A3S2P Samsung 18650 module with a 2 mm PCM layers was tested under WLTP and UDDS profiles using thermocouples and IR thermography and was simulated in ANSYS fluent and a UDF heat generation model. Model validation yielded RSME of 1.51°C (WLTP peak), 1.32°C (UDDS peak), and 1.16°C (WLTP PCM average), within the estimated ±1.9°C experimental uncertainty. With rGO PCM, cell temperature decreased from 57.8–58.6°C to 53.7–54.2°C, WLTP/UDSS peak reduction reached 4.4/3.6°C, and cooling time from 55°C to °C dropped from 840 to 545 s (11.4Wh saved) under high speed 35°C ambient, NE-BBPCM reduced peak temperature from 62.4°C to 56.7°C. Overall, NE-BBPCM enables a robust, validated, and scalable passive battery thermal management system for EV duty cycles with improved uniformity and safety.