Why does the lithium battery capacity become low in winter?

Since the lithium-ion battery entered the market, it has been widely used due to its advantages of long life, large specific capacity, and no memory effect. Low-temperature use of lithium-ion batteries has problems such as low capacity, severe attenuation, poor cycle rate performance, obvious lithium evolution, and unbalanced lithium deintercalation. However, with the continuous expansion of application areas, the restrictions brought by the low-temperature performance of lithium-ion batteries have become more and more obvious. 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 aerospace, electric vehicles and other fields, batteries are required to work normally at -40°C. Therefore, improving the low-temperature properties of lithium-ion batteries is of great significance. Factors restricting the low-temperature performance of lithium-ion batteries Under low-temperature environments, the viscosity of the electrolyte increases, and even partially solidifies, resulting in a decrease in the conductivity of lithium-ion batteries. The compatibility between the electrolyte, the negative electrode and the separator becomes poor in a low temperature environment. In low temperature environments, lithium-ion battery negative electrodes are severely precipitated lithium, and the precipitated metallic lithium reacts with the electrolyte, and the product deposition causes the thickness of the solid electrolyte interface (SEI) to increase. In a low temperature environment, the diffusion system of the lithium ion battery in the active material decreases, and the charge transfer resistance (Rct) increases significantly. Discussion on the decisive factors affecting the low-temperature performance of lithium-ion batteries 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 the lithium ion conduction, and RSEI is the main impedance of the lithium ion battery in the low temperature environment. Expert 2: The main factor limiting the low-temperature performance of lithium-ion batteries is the sharply increased Li+ diffusion resistance at low temperatures, not the SEI film.