Under extreme conditions such as rapid heating and deceleration at high temperatures, high-current charging of aluminum busbar CCS modules, and high-rate fast charging, battery cells generate a large amount of heat. Traditional cooling methods can no longer meet the cooling power requirements of battery cells under extreme conditions. In this paper, high heat storage density and high thermal conductivity composite phase change materials are coupled into the traditional battery cooling system, and the heat storage and thermal conductivity of the composite phase change materials are utilized to cool and homogenize the battery. The simulation method is adopted to study the influence of a new thermal management mode that couples phase change materials with traditional cooling methods on the maximum temperature and temperature difference of battery cells under extreme working conditions. This research provides a direction for the study of thermal management strategies of battery systems under extreme working conditions.