Nickel-rich LiNi x Mn y Co z O 2 materials (x + y + z = 1, x ≥ 0.6) (NMC) are one of the most promising positive electrode candidates for lithium-ion cells due to their high specific capacity, ease of production, and moderate cost. Conventional NMC materials such as LiNi 0.4 Mn 0.4 Co 0.2 O 2 (NMC442), LiNi 0 . 5 Mn 0 . 3 Co 0 . 2 O 2 (NMC532), Li-Ni 0.6 Mn 0.2 Co 0.2 O 2 (NMC622), etc. have 20% of costly Co among the transition metal atoms. To lower the Co content while maintaining good electrochemical performance, three series of materials with different transition metal ratios, LiNi 0.6 Mn 0.4−x Co x O 2 (x = 0, 0.1, 0.2), LiNi 0.9−x Mn x Co 0.1 O 2 (x = 0.1, 0.2, 0.25), and LiNi 0.8 Mn 0.2−x Co x O 2 (x = 0, 0.1, 0.2), were studied. The materials were synthesized via a coprecipitation/solid state sintering method. Powder X-ray diffraction and electrochemical measurements using coin-type cells were made to characterize the materials. Accelerating rate calorimetry was used to study the reactivity of charged NMC positive electrode materials in the presence of electrolyte at elevated temperatures. NMC721, NMC631, and NMC6.5:2.5:1, which have 50% less Co content than current commercialized NMC622, exhibited excellent specific capacity and thermal stability and therefore deserve careful consideration as next generation materials.
As one of the most promising new energy sources, the lithium-ion battery (LIB) and its associated safety concerns have attracted great research interest. Herein, a comprehensive review on the thermal hazards of LIBs and the corresponding countermeasures is provided. In general, the thermal hazards of the LIB can be caused or aggravated by several factors including physical, electrical and thermal factors, manufacturing defect and even battery aging. Due to the activity and combustibility of traditional battery components, they usually possess a relatively high thermal hazard and a series of side reactions between electrodes and electrolytes may occur under abusive conditions, which would further lead to the thermal failure of LIBs. Besides, the thermal hazards generally manifest as the thermal runaway behaviors such as high-temperature, ejection, combustion, explosion and toxic gases for a single battery, and it can even evolve to thermal failure propagation within a battery pack. To decrease these hazards, some countermeasures are reviewed including the application of safety devices, fire-retardant additives, battery management systems, hazard warnings and firefighting should a hazard occur.
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.
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