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The electrolyte is one of the components that releases the most heat during the thermal runaway (TR) and combustion process of lithium-ion batteries (LIBs). Therefore, the thermal hazard of the electrolyte has a significant impact on the safety of LIBs. In this paper, the combustion characteristics of the electrolyte such as parameters of heat release rate (HRR), mass loss rate (MLR) and total heat release (THR) have been investigated and analyzed. In order to meet the current demand of plateau sections with low-pressure and low-oxygen areas on LIBs, an electrolyte with the most commonly used lithium salts, LiPF6, was chosen as the experimental sample. Due to the superior low-temperature performance, an electrolyte containing LiBF4 was also selected to be compared with the LiPF6 sample. Combustion experiments were conducted for electrolyte pool fire under various altitudes. According to the experimental results, both the average and peak values of MLR in the stable combustion stage of the electrolyte pool fire had positive exponential relations with the atmospheric pressure. At the relatively higher altitude, there was less THR, and the average and peak values of HRR decreased significantly, while the combustion duration increased remarkably when compared with that at the lower altitude. The average HRR of the electrolyte with LiBF4 was obviously lower than that of solution containing LiPF6 under low atmospheric pressure, which was slightly higher for LiBF4 electrolyte at standard atmospheric pressure. Because of the low molecular weight (MW) of LiBF4, the THR of the corresponding electrolyte was larger, so the addition of LiBF4 could not effectively improve the safety of the electrolyte. Moreover, the decrease of pressure tended to increase the production of harmful hydrogen fluoride (HF) gas.

The purpose of a battery thermal management system (BTMS) is to maintain the battery safety and efficient use as well as ensure the battery temperature is within the safe operating range. The traditional air-cooling-based BTMS not only needs extra power, but it could also not meet the demand of new lithium-ion battery (LIB) packs with high energy density, while liquid cooling BTMS requires complex devices to ensure the effect. Therefore, phase change materials (PCMs)-based BTMS is becoming the trend. By using PCMs to absorb heat, the temperature of a battery pack could be kept within the normal operating range for a long time without using any external power. PCMs could greatly improve the heat dissipation efficiency of BTMS by combining with fillers such as expanded graphite (EG) and metal foam for their high thermal conductivity or coordinating with fins. In addition, PCMs could also be applied in construction materials, solar thermal recovery, textiles and other fields. Herein, a comprehensive review of the PCMs applied in thermal storage devices, especially in BTMS, is provided. In this work, the literature concerning current issues have been reviewed and summarized, while the key challenges of PCM application have been pointed out. This review may bring new insights to the PCM application.

In applications of lithium ion batteries, it is a requisite to precisely appraise their fire and explosion hazards. In the current study, a fire calorimeter is utilized to test the combustion performance of two commercial 18650 lithium ion batteries (LiCoO 2 and LiFePO 4 ) at different state of charge (SOC). Characteristics on thermal hazards of lithium ion batteries including surface temperature, time to ejection, mass loss, and heat release rate (HRR) are measured and evaluated. In case of thermal runaway, all the lithium ion batteries will rupture the can and catch fire even explode automatically. The solid electrolyte interface layer decomposition and the polymer separator shrinking are direct causes of the lithium ion battery fire. The experimental results show that the HRR and total heat generally rise as the SOC increases, whereas the time to first ejection and the time gap between first and second ejection decrease. LiCoO 2 18650 battery shows higher explosion risk than LiFePO 4 18650, as the former has released much more oxygen. The experimental combustion heats calculated and modified in the oxygen consumption method reveal that the internally generated oxygen have significant effect on the estimate of the heat, where the largest modified rate is 29.9 for 100 % SOC LiCoO 2 18650 battery. The results can provide scientific basis for fire protection during the storage and distribution of lithium ion batteries.