Research progress on safety of lithium-ion batteries

Lithium-ion batteries, now widely used in many fields, have a long cycle life, low self-discharge rate, high capacity and energy efficiency, no memory effect, and are environment-friendly. While enhancing everyday life, this new energy source comes with a number of serious safety risks. Due to the wide variety of battery materials used, the performance and safety features of these batteries also vary greatly. Capacity degradation and thermal runaway occur under extreme conditions such as high temperatures and over-charging, thus limiting their further promotion and use. With the large-scale application of the lithium-ion battery, the number of safety-related incidents have shown an increasing trend each year. To date, research on the safety of this battery has made great progress, especially with respect to thermal decomposition of the electrolyte and electrode materials. This paper reviews the factors influencing the thermal stability of the electrolyte, the thermal runaway process as it relates to the product composition, and the monomer and battery-pack safety and fire-extinguishing measures. It is found that the thermal stability of the electrolyte is affected by both the lithium salt and the organic solvent. When the internal temperature of the battery reaches about 120℃, an exothermic reaction begins to appear. Thermal runaway will spontaneously proceed with the continuous accumulation of heat, and at the same time, hydrogen and alkane gas products are produced that have combustion and explosion risks. Compared with carbon dioxide and dry powder fire extinguishing agents, the fire-extinguishing effect of heptafluoropropane and water is better. Lastly, the paper considers the application prospects of the lithium-ion battery and describes the directions of future research, including the thermal runaway process under the different abuse conditions, the product formation mechanism of the thermal runaway, the development of a new electrolyte, and the search for a high-efficiency fire-extinguishing medium.