What are the effects of temperature changes on the charging and discharging of lithium batteries?

　　People in the battery industry generally know that the stability of the charging and discharging state of lithium batteries is greatly influenced by temperature changes. When lithium batteries are charged and discharged in high and low temperature environments, their capacity retention rate decreases. Among all environmental factors, temperature has a significant impact on the charging and discharging performance of lithium batteries. The electrochemical reactions at the electrode/electrolyte interface are related to the ambient temperature, and the electrode/electrolyte interface is considered the heart of the battery.

　　If the temperature decreases, the reaction rate of the electrode also decreases. Assuming the battery voltage remains constant and the discharge current decreases, the power output of the lithium battery will also decrease. If the temperature rises, the opposite is true, that is, the output power of the battery will increase, and the temperature will also affect the transmission speed of the electrolyte. If the temperature rises, it will accelerate, but if the transmission temperature drops, it will slow down, and the charging and discharging performance of the battery will also be affected.

　　But the temperature is too high, exceeding 45 ℃. Lithium ion batteries are increasingly being used in people's production and life, making their temperature environment a key concern. Relatively speaking, lithium batteries are more prone to safety issues in high temperature environments. Therefore, it is necessary to conduct high-temperature performance tests on lithium batteries and compare them with their room temperature test data.

　　The change in temperature directly affects the discharge performance and capacity of lithium batteries. The temperature decreases, the internal resistance of the battery increases, the electrochemical reaction rate slows down, the polarization internal resistance rapidly increases, the discharge capacity and discharge platform of the battery decrease, affecting the output of battery power and energy.

　　For lithium-ion batteries, the discharge capacity drops sharply at low temperatures, but at high temperatures, the discharge capacity is not lower than at room temperature, and sometimes slightly higher than at room temperature. This is mainly due to the accelerated migration rate of lithium ions at high temperatures. Unlike nickel electrodes and hydrogen storage electrodes, lithium electrodes do not decompose or form hydrogen gas at high temperatures, resulting in a decrease in capacity.

　　When the battery module is discharged at low temperature, heat is generated due to resistance and other reasons as the discharge progresses, causing the battery temperature to rise, manifested as a voltage rise phenomenon. As the discharge progresses, the voltage gradually decreases again.

　　At present, there is no clear theoretical support for the inevitable relationship between internal resistance, discharge platform, lifespan, capacity, and other temperature performance in the lithium battery industry. The relevant calculation formulas and mathematical models are still in the exploratory stage.

　　In practical experiments, it has been proven that lithium batteries are not sensitive to temperatures in the range of 0-40 ℃. If the temperature changes below 0 ℃ or above 40 ℃ during charging and discharging, the cycle life and capacity of lithium batteries will be lower than normal values. The larger the temperature range exceeds, the less capacity and life there will be. For example, in winter, especially in colder northern regions, the battery life of mobile phones is much shorter than in summer. This is related to temperature changes, not the reason why mobile phone batteries are not durable.

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