18650 lithium battery.What is a ternary lithium battery?

　　What is a ternary lithium battery? Why is the nominal voltage of ternary lithium batteries 3.6V or 3.7V?

　　The potential difference between the positive and negative electrodes of a secondary battery is called the nominal voltage of the battery. The nominal voltage is determined by the electrode potential of the electrode material and the concentration of the internal electrolyte.

　　The lithium battery discharge chart is parabolic, with a rapid change from 4.3V to 3.7V and from 3.7V to 3.0V. Only a discharge time of around 3.7V is the longest, accounting for almost three-quarters of the time. Therefore, the nominal voltage of a lithium battery refers to the voltage that maintains the longest discharge time.

　　Taking the typical constant current discharge test current and voltage curves of a common commercial lithium-ion battery brand as an example. During the charging and discharging test, the equipment applies a certain load to the battery, and records the evolution process of voltage over time and current over time based on the set data recording conditions.

　　The voltage curve of lithium-ion batteries during the entire discharge process can be divided into three stages:

　　1) In the initial stage, the terminal voltage of the battery drops rapidly, and the larger the discharge rate, the faster the voltage drops;

　　2) The battery voltage enters a stage of slow change, which is called the platform area of the battery. The smaller the discharge rate, the longer the platform area lasts, the higher the platform voltage, and the slower the voltage drop.

　　3) As the battery level approaches full discharge, the load voltage of the battery begins to drop sharply until it reaches the discharge cut-off voltage. The disadvantages of lithium cobalt oxide are relatively short lifespan, low thermal stability, and limited load capacity (specific power). Like other cobalt mixed lithium-ion batteries, lithium cobalt oxide uses a graphite anode, and its cycle life is mainly limited by the solid electrolyte interface (SEI), mainly manifested in the gradual thickening of the SEI film and the anode lithium plating problem during rapid or low-temperature charging processes. Newer material systems have added nickel, manganese, and/or aluminum to improve lifespan, load capacity, and reduce costs.

　　Lithium cobalt oxide should not be charged or discharged at a current higher than its capacity. This means that 18650 batteries with 2400mAh can only charge and discharge at 2400mA or less. Forcing fast charging or applying loads higher than 2400mA can cause overheating and overload stress. For optimal fast charging, the manufacturer recommends a charging rate of 0.8C or approximately 2000mA. The battery protection circuit limits the charging and discharging rates of the energy unit to a safe level of approximately 1C.

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