Date: 2024-02-01 hits: 237
Since entering the market, lithium-ion batteries have been widely used for their advantages such as long life, large specific capacity and no memory effect. However, the low temperature use of lithium-ion batteries has some problems, such as low capacity, serious attenuation, poor cycle rate performance, obvious lithium evolution, and unbalanced lithium removal. However, with the continuous expansion of application fields, the constraints brought by the poor low-temperature performance of lithium-ion batteries have become more obvious.
It is reported that the discharge capacity of lithium-ion batteries at -20 ° C is only about 31.5% of that at room temperature. Traditional lithium-ion batteries operate at temperatures between -20 and +55 ° C. However, in aerospace, military, electric vehicles and other fields, the battery is required to work normally at -40 ° C. Therefore, it is of great significance to improve the low-temperature properties of lithium-ion batteries.
First, the factors that restrict the low-temperature performance of lithium-ion batteries
1, at low temperatures, the viscosity of the electrolyte increases, and even partially solidifies, resulting in a decrease in the conductivity of lithium-ion batteries.
2, the compatibility between the electrolyte and the negative electrode and the diaphragm becomes worse at low temperature.
3, at low temperatures, the negative electrode of the lithium-ion battery precipitates lithium seriously, and the precipitated metal lithium reacts with the electrolyte, and the product deposition leads to the increase in the thickness of the solid electrolyte interface (SEI).
4, At low temperatures, the internal diffusion system of lithium-ion batteries in active substances is reduced, and the charge transfer impedance (Rct) is significantly increased.
Second, the low-temperature characteristics of lithium-ion battery cathode materials
1, Low temperature characteristics of layered cathode materials
2, Low temperature characteristics of spinel structure cathode materials
3, low temperature characteristics of phosphate system cathode materials
Third, the low-temperature characteristics of lithium-ion battery anode materials
Compared with the positive electrode material, the low-temperature deterioration of the negative electrode material of lithium-ion battery is more serious, mainly for the following three reasons:
1, When charging and discharging at low temperature and high rate, the battery polarization is serious, a large amount of metal lithium is deposited on the surface of the negative electrode, and the reaction product of metal lithium and electrolyte is generally not conductive;
2, From the perspective of thermodynamics, the electrolyte contains a large number of polar groups such as C-O and C-N, which can react with the negative electrode material, and the SEI film formed is more susceptible to low temperature;
3, It is difficult to embed lithium in carbon negative electrode at low temperature, and there is asymmetry of charge and discharge.
Four, the study of low temperature electrolyte
1, Preparation process. Effect of electrode load and coating thickness on low temperature performance of LiNi0.6Co0.2Mn0.202 /Graphite cells It was found that in terms of capacity retention, the lower the electrode load and the thinner the coating layer, the better the low temperature performance.
2, charge and discharge state. The effect of low temperature charging and discharging state on battery cycle life is found that when the discharge depth is larger, it will cause greater capacity loss and reduce cycle life.
3, Other factors. The surface area, pore size, electrode density, the wettability of electrode and electrolyte and the diaphragm all affect the low-temperature performance of lithium-ion batteries. In addition, the impact of material and process defects on the low-temperature performance of the battery can not be ignored.
Five, Summary
In order to ensure the low-temperature performance of lithium-ion batteries, the following points need to be done:
(1) Forming thin and dense SEI film;
(2) Ensure that Li+ has a large diffusion coefficient in the active substance;
(3) The electrolyte has high ionic conductivity at low temperatures.
