The use of lithium batteries in low battery temperature environments is limited. In addition to a severe drop in discharge capacity, lithium batteries cannot be charged when the battery temperature is low. When the battery is charged at low temperature, the lithium ion embedment on the battery graphite electrode and the lithium plating reaction exist simultaneously and compete with each other. Under the condition of low battery temperature, the diffusion of lithium ions in graphite is inhibited, the conductivity of the electrolyte decreases, resulting in a decrease in the intercalation rate, and it is easier to plate lithium on the graphite surface. The main reason for the decline in life of lithium-ion batteries when used at low battery temperatures is the increase in internal resistance and capacity loss due to lithium ion precipitation.

1, the impact of low temperature on battery discharge capacity
As the temperature rises, the capacity gradually increases. The capacity at -20℃ is only equivalent to about 60% of the capacity at 15℃. In addition to capacity, the open circuit voltage of the battery also decreases with increasing temperature. We all know that the energy contained in a battery is the product of capacity and terminal voltage. When both multiples fall, the energy in the battery must be a superposition of the declining effects of both. When the battery temperature is lower, the activity of the positive electrode material is reduced, so that the number of lithium ions that can move and bring discharge current is reduced, which is the root cause of the decrease in capacity.
2, the effect of low temperature on the internal resistance of the battery
In any charging situation, the internal resistance of the battery will increase significantly as the temperature decreases. The lower the charge, the greater the internal resistance, and this trend remains constant with temperature. When the temperature of the battery is low, the diffusion and mobility of charged ions in the positive and negative materials becomes poor, and it is difficult to pass through the passivation film between the electrode and the electrolyte. The transfer rate in the electrolyte is also reduced, and a large amount of additional heat is generated during the transfer process. After lithium ions reach the negative electrode, the diffusion inside the negative material also becomes not smooth. Throughout the process, the movement of charged ions becomes very difficult. From the outside, it means that the internal resistance of the cell has increased.
3, low battery temperature lithium ion battery internal side reaction

The performance of lithium-ion batteries will be seriously reduced at low battery temperatures, and some side reactions will occur during the charging and discharging of lithium-ion batteries. These side reactions are mainly irreversible reactions between lithium ions and electrolyte, which will lead to a decrease in lithium battery capacity and further deteriorate battery performance. The consumption of conductive active material leads to capacity attenuation. Given the potential of the positive and negative electrodes in the battery, these side reactions are more likely to occur on the negative side than the positive side. Since the potential of the negative electrode material is much lower than that of the positive electrode material, the side reaction deposits of ions and electrolyte solvents are deposited on the electrode surface to form the SEI film. The impedance of SEI film is one of the factors causing negative overpotential. When the battery is further cycled and aged, the electrode expansion and contraction caused by continuous cycling will lead to the SEI film rupture due to the continuous embedment and deembedment of lithium ions on the negative electrode during continuous cycling. The crack after the SEI film breaks provides a direct contact channel between the electrolyte and the electrode, thus forming a new SEI film to fill the crack and increase the thickness of the SEI film

These reaction processes are repeated with the continuous charging and discharging of the battery, which makes the lithium ions in the reaction continue to decrease, resulting in a decrease in the discharge capacity of the lithium-ion battery. During the charging process, deposits form on the surface of the active material, which increases the resistance. The effective surface area of active particles decreases and the ionic resistance increases. The available capacity and energy of lithium batteries are declining simultaneously. Lithium batteries are more prone to side reactions during charging. At the beginning of the charging of the lithium battery, the lithium ions move to the negative electrode through the electrolyte, so the potential difference between the electrode and the electrolyte is reduced, making it easier for the lithium ions to have irreversible side reactions with the substances in the electrolyte. The relationship curves between the electrode material potential and the concentration fraction of lithium inlay are different for different lithium-ion battery electrode materials
4, lithium battery low temperature preheating technology
Faced with the limited use of lithium batteries in the case of low battery temperatures, technicians have found countermeasures for charging and preheating. Although it is a stopgap measure, it has a significant effect on improving the discharge capacity and long-term life of lithium batteries. Before charging or using a lithium battery in a low battery temperature environment, the battery must be preheated. The way battery management systems (BMS) heat batteries can be broadly divided into two categories: external heating and internal heating.
Compared with external heating methods, internal heating avoids long path heat conduction and the formation of local hot spots close to the heating device. As a result, internal heating can heat the battery more evenly, resulting in better heating with higher efficiency and is easier to implement. At present, most studies on internal AC preheating schemes focus on heating speed and efficiency, and few heating strategies are explicitly considered to prevent side reactions such as lithium deposition. In order to prevent lithium deposition during preheating, it is necessary for BMS to estimate and control the conditions of lithium deposition in real time. In order to realize the above functions, a model based low battery temperature control battery heating technology is needed. With the development of new energy, the use of power lithium batteries is also increasing. The use of lithium batteries at low battery temperatures urgently needs to solve the problem of battery preheating. This is an area that is very close to practical application.