What is the decisive factor affecting the low temperature performance of lithium-ion batteries

According to reports, the discharge capacity of lithium-ion batteries at -20°C is only about 31.5% of that at room temperature. The operating temperature of traditional lithium-ion batteries is between -20°C and +55°C. However, in the fields of aerospace, military industry, and electric vehicles, batteries are required to work normally at -40°C. Therefore, improving the low-temperature properties of lithium-ion batteries is of great significance. In a low temperature environment, the viscosity of the electrolyte increases, and even partially solidifies, resulting in a decrease in the conductivity of the lithium-ion battery. The compatibility between the electrolyte, the negative electrode and the separator becomes poor in a low temperature environment. In the low temperature environment, the lithium ion battery negative electrode is severely precipitated, and the precipitated metal lithium reacts with the electrolyte, and the product deposition causes the thickness of the solid electrolyte interface (SEI) to increase. In the low temperature environment, the diffusion system of the lithium ion battery in the active material decreases, and the charge transfer resistance (Rct) increases significantly. Expert opinion 1: The electrolyte has the greatest impact on the low-temperature performance of lithium-ion batteries, and the composition and physical and chemical properties of the electrolyte have an important impact on the low-temperature performance of the battery. The problems faced by the battery cycle at low temperatures are: the viscosity of the electrolyte will increase, the ion conduction speed will slow down, and the electron migration speed of the external circuit will not match, so the battery will be severely polarized and the charge and discharge capacity will drop sharply. Especially when charging at low temperature, lithium ions can easily form lithium dendrites on the surface of the negative electrode, causing the battery to fail. The low temperature performance of the electrolyte is closely related to the conductivity of the electrolyte itself. The high conductivity of the electrolyte transports ions faster, and it can exert more capacity at low temperatures. The more the lithium salt in the electrolyte is dissociated, the greater the number of migration and the higher the conductivity. The higher the electrical conductivity, the faster the ion conductivity, the smaller the polarization, and the better the performance of the battery at low temperatures. Therefore, higher electrical conductivity is a necessary condition for achieving good low-temperature performance of lithium-ion batteries. The conductivity of the electrolyte is related to the composition of the electrolyte, and reducing the viscosity of the solvent is one of the ways to improve the conductivity of the electrolyte. The good fluidity of the solvent at low temperature is the guarantee of ion transport, and the solid electrolyte membrane formed by the electrolyte on the negative electrode at low temperature is also the key to affecting lithium ion conduction, and RSEI is an important impedance of lithium ion batteries in low temperature environments. Expert 2: The important factor limiting the low-temperature performance of lithium-ion batteries is the sharply increased Li+ diffusion resistance at low temperatures, not the SEI film. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.