Reliability Analysis of a PCM–Liquid Hybrid Battery Thermal Management System for Electric Vehicles

Electric vehicles (EVs) utilize batteries that generate thermal energy during charging and discharging processes. Inadequate heat management can result in thermal runaway, which is marked by a rapid and uncontrolled increase in battery temperature and may lead to fire or explosion. Battery Thermal Management Systems (BTMSs) are implemented to reduce the risk of thermal runaway by maintaining battery temperature within a defined safe operating range. Hybrid BTMS configurations integrate multiple cooling methods to enhance operational effectiveness and reliability, surpassing the performance of conventional liquid coolant systems. This work investigates the enhanced efficiency of an integrated phase change material (PCM)–liquid hybrid approach evaluated under severe 3C discharge conditions over a 10,000 h operational reliability window. Our study carefully investigates the system-level reliability using a Functional Fault Tree Analysis (FTA) framework to classify top, intermediate, and basic events. Multi-physics and probabilistic evaluation results demonstrate that the hybrid system achieves a 5 °C reduction in peak cell temperature and a 3 °C improvement in spatial temperature uniformity compared to standard liquid cooling. Reliability assessment establishes a system top-event failure probability of 6% over the 10,000 h window, identifying the coolant pump as the primary failure bottleneck with an individual contribution of 27%. These quantitative insights advance our understanding of hybrid safety architectures, providing essential baseline metrics for future electric vehicle thermal management development.