Based on the thermal runaway reaction heat generation models of 314Ah lithium iron phosphate batteries, it is proposed that absorbing heat through phase change materials to break the positive feedback cycle of “temperature rise-reaction acceleration” is an effective approach to delay the thermal runaway process. The study designed a “phase change material and aerogel” thermal runaway protection structure for energy storage battery packs and discussed the division of roles between phase change materials and aerogels in thermal runaway prevention. Focusing on phase change materials suitable for thermal runaway protection within the 100–200 °C phase change temperature range, the study screened four types of materials, including high-carbon paraffin-based, modified hydrated salt-based, polymer-based, and eutectic mixture-based materials. By comparing the delay and inhibition effects of typical phase change materials, it was clarified that absorbing the heat generated by the negative electrode–electrolyte reaction is the key factor affecting the protection effect. Additionally, optimization recommendations were proposed for four parameters of phase change materials: material quantity, latent heat of phase change, phase change temperature range, and material thermal conductivity.