Coupled electro-thermal investigation of series-parallel lithium-ion battery packs with phase change materials-based cooling at high discharge rates

Owing to their extended cycle life, high energy density, superior power-to-weight ratio, and low self-discharge, the lithium-ion batteries (LIBs) are widely adopted in next-generation electric vehicles (EVs). However, excessive heat generation at high discharge rates can compromise safety and performance. This study investigates the electro-thermal behaviour of pouch-type LiMn 2 O 4 cells in six series-parallel configurations (12S1P, 6S2P, 4S3P, 3S4P, 2S6P, and 1S12P) at discharge rates of 3C 9C using a Multi-Scale Multi-Domain (MSMD) framework coupled with the Newman-Tiedemann-Gu-Kim (NTGK) battery model. Increasing parallel connections improved thermal stability by reducing the current per cell, thereby lowering heat generation and extending discharge duration. In contrast, the series-dominant configurations delivered higher voltage and power output at the expense of elevated battery temperatures. Among all configurations, 12S1P exhibited the highest thermal stress, whereas 1S12P demonstrated superior thermal uniformity and the lowest peak temperature. Phase change material (PCM)-based thermal management was subsequently implemented using PCM1 (n-octadecane) and PCM2 (n-eicosane) with a 3 mm encapsulation layer across models M-I to M-VI. PCM1 was more effective up to 5C, while PCM2 provided better thermal regulation at higher C-rates (7C 9C) owing to its higher latent heat capacity. Notably, M-II achieved the best thermal performance, reducing the maximum temperature by 23 K at 5C and achieving excellent thermal uniformity (Δ T ≈ 1.1 K). Response Surface Methodology (RSM) optimization coupled with ANOVA revealed a progressive increase in the minimum required PCM1 and PCM2 thickness with C-rate while satisfying the prescribed thermal limits. These findings demonstrated the importance of jointly optimizing electrical configuration, PCM selection, and encapsulation thickness for effective thermal regulation and reliable high-power EV battery operation.