Heat Dissipation and Structural Optimization of Cylindrical Lithium-Ion Batteries with Phase Change Material–Liquid Hybrid Cooling: A Numerical Study

This work explores the thermal management of cylindrical lithium-ion batteries used in electric vehicles by introducing a combined cooling approach that couples phase-change materials (PCM) with a liquid-based cooling loop. Fluent-based numerical simulations are conducted to first examine the effects of battery spacing and ambient temperature on PCM cooling performance, from which the optimal spacing is identified. Building on this foundation, a coupled PCM–liquid cooling model is developed to evaluate the impacts of liquid-channel inlet configuration, coolant flow velocity, and inlet temperature. Results show that varying the inlet position has little impact when the outlet is fixed. Increasing coolant velocity lowers the peak cell temperature and the extent of PCM melting but enlarges the temperature difference, reaching 5.03 °C at 0.0075 m/s, which exceeds the recommended safety threshold. Lowering the coolant inlet temperature further decreases the peak temperature but also deteriorates temperature uniformity. To simultaneously suppress both the maximum temperature (Tmaxi) and temperature gradient, two structural optimization schemes are proposed. Among them, distributing liquid cooling plates evenly above and below the battery pack achieves the best overall performance. The findings demonstrate the strong cooling potential of the PCM–liquid hybrid system and offer theoretical support for the design and optimization of advanced battery thermal management systems.