Multiphase modelling of bubbling in phase change material for battery thermal safety management

Abstract

The thermal runaway and fire hazards of lithium-ion batteries remain critical safety concerns, so battery thermal management systems with phase change material (PCM) have been widely applied. Commonly used organic PCMs like paraffin wax are combustible, which can be ignited during battery thermal runaway and fire. However, the ignition risks of combustible PCMs under battery abused conditions have not been well simulated and discussed. This work simulates the mass loss of paraffin wax under the specific boundary temperatures with detailed bubbling phenomenon. First, the model adopts the Volume of Fluid (VOF) method to simulate the time-dependent evaporation and bubbling processes of the liquid paraffin wax when it is exposed to the hot boundary up to 550 °C. As the boundary temperature increases from 400 °C to 500 °C, the modelled peak mass flux of paraffin wax increases three folds, which agrees with the trend of hot-plate experiments. Then, the phase-change and bubbling of wax layer attached to a thermal-runaway battery are explored computationally. For battery SOC values higher than 50%, the chance of igniting wax during thermal runaway is high. The probability of ignition changes with the PCM thickness and boiling point, which are critical parameters for safe battery thermal management design. This work establishes a valuable computational framework to quantify ignition risks of organic PCM in battery thermal runaway.