What are the effects of charging at low temperatures on lithium batteries?
Charging lithium batteries at low temperatures carries certain risks. As temperature decreases, the kinetic properties of the graphite anode deteriorate further. During charging, the electrochemical polarization of the anode intensifies significantly, and the deposited metallic lithium is prone to forming lithium dendrites, which can rupture the separator and cause a short circuit between the positive and negative electrodes. Therefore, charging lithium-ion batteries at low temperatures should be avoided whenever possible.
Due to the low temperature, ion crystals will form in the lithium-ion battery nested on the negative electrode, directly piercing the separator. Under normal circumstances, this will cause a micro short circuit, affecting lifespan and performance, and in severe cases, it may explode!
According to expert research, short-term use of lithium batteries in low-temperature environments, or at temperatures not low enough, will only temporarily affect the battery capacity, but will not cause permanent damage. However, prolonged use in low-temperature environments, or in ultra-low-temperature environments of -40°C, may cause lithium-ion batteries to be "frozen" and suffer permanent damage.
Lithium-ion batteries suffer from problems at low temperatures, including low capacity, severe capacity degradation, poor cycle rate performance, significant lithium plating, and imbalanced lithium insertion/extraction. However, as application areas continue to expand, the limitations imposed by the poor low-temperature performance of lithium-ion batteries become increasingly apparent. In aerospace, outdoor equipment, power, security, and robotics fields, batteries are required to operate normally at -40°C. Therefore, improving the low-temperature properties of lithium-ion batteries is of great significance.
For lithium batteries, there is currently no clear theoretical support in the industry to support the necessary correlation between their internal resistance, discharge plateau, lifespan, and capacity at various temperatures. The relevant calculation formulas and mathematical models are still in the exploratory stage. Generally speaking, lithium batteries are not very sensitive to temperatures in the 0-40℃ range; however, once the temperature exceeds this range, their lifespan and capacity will be reduced.
Different lithium battery materials have different low-temperature performance. The most popular lithium iron phosphate battery has the worst low-temperature performance. Our product can release 89% of its maximum capacity at -10℃, which is relatively high in the industry. At 55℃, the capacity can reach 95%, and the degradation at relatively low temperatures is relatively small.
1. The use of lithium-ion batteries is limited in low-temperature environments. In addition to the severe degradation of discharge capacity, lithium-ion batteries cannot be charged at low temperatures.
2. During low-temperature charging, the lithium-ion intercalation and lithium plating reactions on the graphite electrodes of the battery occur simultaneously and compete with each other. Under low-temperature conditions, the diffusion of lithium ions in graphite is suppressed, and the conductivity of the electrolyte decreases, resulting in a reduced intercalation rate. Meanwhile, the lithium plating reaction is more likely to occur on the graphite surface.
3. The internal resistance of the battery increases significantly as the temperature decreases. The lower the charge of the cell, the greater the internal resistance, and this trend remains constant with temperature changes. After reaching the negative electrode, the diffusion of lithium-ion ions within the negative electrode material becomes difficult. Throughout the entire process, the movement of charged ions becomes extremely challenging, which appears externally as an increase in the cell's internal resistance.
4. The impact of low temperature on the charging and discharging efficiency of lithium-ion batteries: During the discharge process, a large amount of electrical energy is consumed by internal resistance heating. When driving an electric vehicle, you will feel that even with seemingly similar battery capacity, the driving range is shorter in low temperatures.
Low-temperature preheating technology: The solution found by technicians is preheating before charging. Although it is a stopgap measure, it has a significant effect on improving the discharge capacity and long lifespan of lithium-ion batteries. Before charging or using lithium-ion batteries in low-temperature environments, the batteries must be preheated.
Improving the low-temperature performance of lithium iron phosphate batteries involves four aspects: positive electrode, negative electrode, electrolyte, and binder. For the positive electrode, nano-scale fabrication is now common, and its particle size, resistivity, and AB plane axial length all affect the overall low-temperature characteristics of the battery. Lithium iron phosphate was prepared using three different processes. From the perspective of the overall preparation conditions, different nano-scale and coating processes for lithium iron phosphate, particularly regarding the AB plane axial length, result in larger lithium-ion migration channels, which is beneficial for improving the battery's rate performance.
