As is well known, lithium batteries cannot be charged at low temperatures. At excessively low temperatures, lithium deposits within the battery can cause internal short circuits. Simply put, at low temperatures, the lithium battery doesn't actually run out of power; rather, it has charge but cannot release it properly. A typical lithium battery's capacity decreases by 20% at 0°C, and at -10°C, its capacity may be reduced to only about half.
Charging lithium batteries in low-temperature environments poses several risks:
1. Increased electrolyte viscosity: At low temperatures, the viscosity of lithium battery electrolyte decreases, which affects conductivity and the activity of active materials, resulting in a slower diffusion rate of lithium ions at the carbon anode and increasing the risk of lithium deposition.
2. Formation of lithium dendrites: When lithium-ion batteries are charged at low temperatures, the diffusion of lithium ions on the graphite negative electrode is inhibited, leading to the growth of lithium dendrites. These dendrites may penetrate the separator and cause internal short circuits, or react with the electrolyte to cause exothermic reactions, further triggering battery thermal runaway or even fire.
3. Impaired structural stability: At low temperatures, the chemical reactions inside lithium batteries become more active, which may lead to a decrease in the stability of the battery structure.
4. Increased internal resistance: The internal resistance of the battery increases significantly as the temperature decreases, which increases energy loss, especially heat loss during discharge, resulting in a shorter driving time.
5. Discharge capacity degradation: In low-temperature environments, the discharge capacity of lithium batteries will decrease significantly due to the drop in temperature. This is different from the normal operating state of the battery and affects the battery's performance and lifespan.
6. Safety issues: Low-temperature charging may also lead to lithium plating on the negative electrode, which is a serious safety hazard because it may cause rapid degradation of battery capacity and, in extreme cases, short circuits and other safety problems.
To address these risks, researchers have proposed several solutions, such as optimizing charging strategies to reduce the risk of lithium plating and using non-destructive methods to monitor potential changes at the negative electrode to determine the presence of lithium plating.
According to reliable statistics, lithium batteries only retain about 30% of their nominal capacity when discharged at -20°C. Some traditional low-temperature lithium batteries can discharge normally between -20°C and +55°C. However, in fields such as aerospace, polar research, and special equipment, lithium batteries are required to operate normally at -40°C. Therefore, the emergence of low-temperature lithium batteries is of great significance.
