Lithium-ion batteries have been widely used in consumer electronics, electric vehicles and energy storage due to their high specific energy and power density, long cycle life and environmental friendliness. As the power source of new energy vehicles, lithium-ion batteries still have many problems in practical applications. For example, the energy density is significantly reduced under low temperature conditions, and the cycle life is also affected accordingly, which also severely limits the scale of lithium-ion batteries.
At present, researchers have debated the main factors causing poor low-temperature performance of lithium-ion batteries, but the reasons are as follows:
1. The viscosity of the electrolyte increases at a low temperature, and the electrical conductivity decreases;
2. Electrolyte/electrode interface membrane impedance and charge transfer impedance increase;
3. The migration rate of lithium ions in the bulk of the active material is reduced. As a result, the polarization of the electrode is intensified at a low temperature, and the charge and discharge capacity is reduced.
In addition, during low-temperature charging, especially at low temperature and large rate charging, lithium metal precipitation and deposition will occur in the negative electrode. The deposited metal lithium easily reacts with the electrolyte irreversibly, consuming a large amount of electrolyte, and further increasing the thickness of the SEI film, resulting in a battery. The impedance of the surface film of the negative electrode is further increased, and the polarization of the battery is again enhanced, which will greatly deteriorate the low temperature performance, cycle life and safety performance of the battery.