What is the impact of extreme temperature on the safety of lithium batteries?

　　1. High temperature impact: High temperature can accelerate the decomposition of electrolyte, leading to an increase in internal pressure of the battery, which may cause leakage, gas release, smoke and other phenomena. In severe cases, it may even cause violent combustion or explosion. High temperature can also accelerate the oxidation and decomposition of positive electrode materials, producing oxygen that reacts violently with the electrolyte.

　　In addition, the SEI film inside the battery may decompose at high temperatures, leading to direct contact between the negative electrode and the electrolyte, generating more heat and gas. High temperature can also increase the internal resistance of the battery, leading to a decrease in battery performance and a shortened cycle life.

　　2. Low temperature effect: Low temperature will reduce the conductivity of the electrolyte, increase the internal resistance of the battery, reduce the available capacity of the battery, and affect the charging and discharging performance of the battery. Under low temperature conditions, the diffusion rate of lithium ions in electrode materials slows down, resulting in a decrease in the charging and discharging efficiency of the battery. In addition, low temperatures may also lead to uneven deposition of lithium ions inside the battery, forming lithium dendrites and increasing the risk of battery short circuits.

　　3. Risk of thermal runaway: Extreme temperatures, whether high or low, can cause thermal runaway of the battery. Thermal runaway refers to the exothermic reaction and heat accumulation inside the battery reaching a critical point, causing a sharp rise in battery temperature, which may lead to combustion or explosion of the battery.

　　4. Stability of battery structure and materials: Extreme temperatures can also affect the stability of battery structure and materials. For example, high temperatures may cause aging of the battery casing and internal structure, reducing the overall strength of the battery; Low temperature may cause embrittlement of internal materials in batteries, affecting their mechanical stability.

　　5. The challenge of Battery Management Systems (BMS): In extreme temperatures, BMS needs to more accurately control the charging and discharging process of the battery to prevent issues such as overcharging, overdischarging, and temperature anomalies, which puts higher demands on the design and performance of BMS.

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