The impact of low-temperature charging on lithium batteries is irreversible

Charging or discharging batteries at low temperatures will cause irreversible damage to the battery, causing capacity drops and serious safety risks. Long-term storage at ultra-low temperatures (-20°C) will also cause irreversible damage to the battery and reduce its capacity.

1. The whole process of charging lithium-ion battery at low temperature

The positive stage of lithium-ion batteries is generally ternary (NCM), lithium iron phosphate battery (LFP) and lithium cobalt oxide battery (LCO), and the negative electrode is graphite (Gr). When the battery is being charged, lithium ions move from the positive lattice constant across the lithium battery electrolyte diaphragm to the negative electrode and are placed in the graphite solid layer. When charging and discharging, it can be understood that it goes out from the solid layer of the graphite negative electrode and then returns to the positive lattice constant.

When the temperature of the lithium-ion battery structure and the charging and discharging process is low, the molecular motion performance decreases, the entire reaction rate and the material transfer process will slow down, so the most obvious slowness in the battery is the lithium-ion/ Transport of lithium molecules in graphite (negative electrode) solid layer and positive order lattice constant. Therefore there is a lot of lithium deposited in the electrical stage and lithium battery electrolyte page. When the battery is being charged, lithium ions cannot be squeezed into the graphite layer and will remain on the surface of the negative electrode, turning into metallic lithium and accumulating into lithium dendrites. During charging and discharging, lithium ions are squeezed on the surface of the positive stage lattice constant, which can easily cause the positive stage to crack.

2. Low-temperature battery charging causes lithium precipitation, resulting in obvious safety risks

The growth process of lithium dendrites: When charging a normal battery, lithium ions enter the solid layer of graphite in an orderly manner, causing an intercalation reaction. However, when charging a low-temperature battery, lithium ions cannot squeeze into the graphite layer and will always be absorbed by the electronic device on the surface of the negative electrode and become metallic lithium, resulting in a conversion reaction (the reaction potential difference is lower than the intercalation reaction, which can be understood as more difficult to occur. However, it is difficult for the substances in the intercalation reaction to spread, causing the conversion reaction to occur easily at low temperatures) and accumulate into lithium dendrites. As we all learned in ninth-grade chemistry, metallic lithium is very reactive and can react immediately with the lithium battery electrolyte. The resulting chemical components are also irreversible, causing capacity loss. In addition, metal lithium continues to grow and develop, and it is very easy to puncture the diaphragm and connect with the positive stage, causing internal short circuit failure and easily causing more serious safety accidents.

3. Low-temperature charging and discharging induce cracking of positive-level particles

During low-temperature charging and discharging, lithium ions are squeezed on the surface of the positive-level lattice constant, which can easily lead to the cracking of positive-level active particles. On the one hand, it causes damage to positive energy raw materials, causing capacity damage. In addition, the precipitation of excess chemical elements in the positive electrode will be transferred to the surface of the negative electrode and converted into metallic particles, inducing the formation of lithium accumulation.

4. Low temperature storage reduces battery capacity

Recently, some researchers discovered that the battery was only stored at low temperature for 48 hours, and then placed at room temperature for rest, and then the capacity was tested. It was found that for batteries soaked in high temperature for a long time, the capacity will be reduced by 3.2% when charged at a small rate (slow charge), but when charged at a large rate (fast charge), the capacity will be reduced by 6%.

Factors leading to capacity impairment are:

1) Low temperature aggravates the cracking of the positive stage.

2) Low temperature is likely to cause positive-level particles to rotate, thereby causing them to break away from the adhesive and lose photoelectrocatalytic activity.