Faced with the limited use of lithium-ion batteries at low temperatures, the found coping strategy is charging and preheating. Although it is an expedient measure, it has a significant effect on improving the low-temperature performance of lithium-ion batteries.
Li-ion batteries must be preheated before charging or using them in low temperature environments. The battery management system (BMS) onboard an electric vehicle can generally be divided into two categories: external heating and internal heating.
External heating methods include air heating, liquid heating, phase change material heating, and thermal resistance heaters or heat pump heating. These heating means are generally located in the battery pack, or in the container of the thermal cycle medium. The internal heating method heats the battery, which excites the electrochemical substances inside the battery through the alternating current, so that the battery itself generates heat.
The key to improving the low-temperature performance of lithium-ion batteries lies in the improvement of the low-temperature performance of the electrolyte. The viscosity of conventional commercial lithium-ion battery electrolytes will increase rapidly at low temperatures. Therefore, the key to improving the low-temperature performance of lithium-ion batteries is to improve the low-temperature performance of the electrolyte.
Electrolyte salt is one of the important components of the electrolyte and a key factor to obtain excellent low temperature performance. At present, the commercial electrolyte salt is lithium hexafluorophosphate, and the SEI film formed has a large impedance, resulting in poor low temperature performance. The development of new lithium salts is imminent. Lithium tetrafluoroborate anion has a small radius, is easy to associate, and has a lower electrical conductivity than LiPF6, but has low charge transfer resistance at low temperature, and has good low temperature performance as an electrolyte salt.
By optimizing the composition and film-forming conditions of the SEI film, improving the ionic conductivity of the SEI film at low temperature is beneficial to the improvement of the low-temperature performance of the battery. Therefore, the development of film-forming additives with excellent low-temperature performance is a current research focus.
