Lifetime of ternary lithium batteries

　　The so-called lifespan of a lithium battery refers to the capacity decay of the battery after a period of use to 70% of its nominal capacity (room temperature 25 ℃, standard atmospheric pressure, and battery capacity discharged at 0.2C), which can be considered as the end of its lifespan. In the industry, the cycle life is generally calculated based on the number of cycles when a lithium battery is fully charged and discharged. During use, irreversible electrochemical reactions occur inside the lithium battery, leading to a decrease in capacity, such as electrolyte decomposition, deactivation of active materials, collapse of positive and negative electrode structures, resulting in a decrease in the number of lithium ion intercalation and de intercalation, and so on. Experiments have shown that higher rate discharge leads to faster capacity decay. If the discharge current is low, the battery voltage will approach the equilibrium voltage, which can release more energy.

　　The theoretical lifespan of ternary lithium batteries is about 800 cycles, which is considered moderate in commercial rechargeable lithium batteries. Lithium iron phosphate is approximately 2000 cycles, while lithium titanate is said to be capable of up to 10000 cycles. At present, mainstream battery manufacturers promise to charge and discharge ternary cells more than 500 times (under standard conditions) in their specifications. However, after the cells are assembled into battery packs, due to consistency issues, the voltage and internal resistance cannot be exactly the same, and their cycle life is approximately 400 times. The manufacturer recommends a SOC usage window of 10%~90% and does not recommend deep charging and discharging, as it may cause irreversible damage to the positive and negative electrode structures of the battery. If calculated based on shallow charging and discharging, the cycle life should be at least 1000 times. In addition, if lithium batteries are frequently discharged at high rates and high temperatures, their lifespan will significantly decrease to less than 200 cycles.

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