Introduction to the low-temperature performance of lithium-ion batteries, the factors restricting the low-temperature performance of lithium-ion batteries. Since its commercialization, lithium-ion batteries have been widely used due to their advantages such as long life, large specific capacity, and no memory effect. In the past, more attention was paid to the cycle life and safety of lithium-ion batteries. With the continuous expansion of application fields, lithium The restriction brought by the poor low-temperature performance of ion batteries has become more and more obvious.

With the rapid development of lithium-ion batteries in electric vehicles and military applications, the disadvantage that their low-temperature performance cannot adapt to special low-temperature weather or extreme environments has become more and more obvious. Under low temperature conditions, the effective discharge capacity and effective discharge energy of lithium-ion batteries will be significantly reduced, and at the same time, they are almost non-rechargeable in an environment below -10°C, which severely restricts the application of lithium-ion batteries.

Introduction to low-temperature performance of lithium-ion batteries

Among all the environmental factors, temperature has the greatest impact on the charge and discharge performance of the battery, and the electrochemical reaction of the lithium battery at the electrode/electrolyte interface is related to the ambient temperature. At low temperatures, the viscosity of the electrolyte decreases and the conductivity decreases, and the activity of the active material will also decrease, which will increase the concentration difference of the electrolyte, increase the polarization, and terminate the charging earlier. More importantly, the diffusion rate of lithium ions in the carbon negative electrode will be slower, and the temperature will decrease, and the reaction rate of the electrode will also decrease.

Lithium-ion batteries work under low temperature conditions, and the capacity of the battery drops sharply and the polarization increases. Under low temperature conditions, it is difficult for lithium ions to be inserted into the negative electrode and relatively easy to be extracted from the negative electrode, which leads to a decrease in capacity and discharge of the battery. The chemical change is related to the decrease in the conductivity of the electrolyte at low temperatures, the decrease in the diffusion rate of lithium ions in the electrode, and the increase in impedance due to the formation of a new SEI film on the surface of the negative electrode due to the deposition of lithium metal during the charging process.

Before charging or using lithium-ion batteries in low temperature environments, the batteries must be preheated. The way the battery management system in electric vehicles heats the battery can be roughly divided into two categories: external heating and internal heating. These heating methods are generally located in the battery pack, or set in the container of the thermal cycle medium. The internal heating method heats the battery by exciting the electrochemical substances inside the battery through alternating current, so that the battery itself generates heat.

Factors restricting the low-temperature performance of lithium-ion batteries

1. The three-dimensional structure of the cathode material restricts the diffusion rate of lithium ions. Different cathode materials have different three-dimensional structures, and the effect is particularly obvious at low temperatures;

2. The compatibility between the electrolyte and the negative electrode and the diaphragm becomes poor at low temperature; the viscosity of the electrolyte increases, and even partially solidifies, resulting in low ion conductivity;

3. At low temperature, the diffusion coefficient of lithium ions in the active material decreases, and the charge transfer resistance increases significantly;

4. Under the low temperature environment, the SEI film of the negative electrode of the lithium ion battery is thickened, and the impedance of the SEI film increases, which causes the conduction rate of lithium ions in the SEI film to decrease;

5. The negative electrode lithium is severely precipitated at low temperature, and the precipitated metallic lithium reacts with the electrolyte, and the product deposition causes the thickness of the solid electrolyte interface to increase.

Faced with the limited use of lithium batteries at low temperatures, the response strategy is to charge and warm up. Although it is a stopgap measure, it has a significant effect on improving the low temperature performance of lithium batteries. Compared with conventional lithium-ion batteries, all-solid-state lithium-ion batteries, especially all-solid-state thin-film lithium-ion batteries, are expected to completely solve the problem of capacity degradation and cycle safety when the battery is used at low temperatures.