The custom-designed solid–solid phase change material possesses ultra-high thermal stability and exhibits outstanding battery thermal management performance.

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The overcharge of the lithium iron phosphate (LiFePO 4 ) batteries usually leads to the sharp capacity fading and safety issues, especially under low temperature environment. Thus, investigating their root cause originated from the electrode materials is critical for the safety performance optimization and market promotion of the LiFePO 4 batteries. In this work, the electrochemical/thermal behaviors of 18650 LiFePO 4 batteries are investigated after overcharge under room and low temperature of 25°C and −20°C, respectively. The results demonstrate a decreased electrochemical performance and faster heating rate of the overcharged battery, particularly under harsh working environments such as high discharge rate and low temperature. Coupling with the analyses of the internal resistance, the crystal structure, and microstructure of the electrodes, the root cause is attributed to the damage of the crystal structure and microstructure, which reduce the electron/Li + migrating capability and electrolyte diffusion/transfer efficiency. KEYWORDS electrochemical performance, internal resistance, lithium iron phosphate battery, microstructure, overcharge

The development of phase change material (PCM) for battery thermal management poses key limitations on its reliability caused by leakage and shape deformation under high temperature. In this work, a kind of phase changeable and hydrophobic polymer skeleton is grown in situ in a paraffin (PA)/expanded graphite matrix to obtain the leakage-proof composite PCM (CPCM) at the kilogram-level. Benefiting from the additional latent heat provided by the phase changeable alkyl side chains of the polymer skeleton, the obtained CPCM shows a high latent heat of 120.3 J g–1 coupled with a thermal conductivity of 2.92 W m–1 K–1. Most importantly, the three-dimensional cross-linking main chain and the hydrophobic alkyl side chains endow the obtained CPCM with extraordinary shape stability under high temperatures up to 250 °C and high PA adsorbing capability, respectively. As a consequence, the CPCM presents excellent antileakage performance for the battery module (21 V/16 Ah) under harsh working conditions, i.e., 50 charge–discharge cycles at 3C–4C, thus giving rise to a durable cooling performance. The maximum temperature (T max) and temperature difference (ΔT max) of the battery module can be controlled constant at 50.9 and 5.0 °C during the cycles, respectively. By stark contrast, owing to the obvious leakage phenomenon, the battery module with traditional CPCM adopting a classical low-density polyethylene skeleton shows increasing T max and ΔT max during the cycles.

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