Charging method

　　There are many charging methods for lithium batteries, which can be divided into conventional charging and rapid charging according to charging efficiency. Conventional charging methods include constant current charging, constant voltage charging, stage charging and intermittent charging, while fast charging includes pulse charging and Reflex charging. Finally, intelligent charging is analyzed.

　　1. Constant current charging

　　According to the charging current, constant current charging can be divided into fast charging, standard charging and trickle charging. During the whole charging process, generally adjust the charging voltage of the power supply or change the resistance value in series with the battery to maintain the charging current of the battery unchanged. This method has the advantage of simple control and is suitable for charging battery packs with multiple batteries connected in series. The disadvantage is that the acceptable charging capacity of the lithium battery will gradually decrease with the charging process, and excessive charging current in the late charging period will cause bubbles in the battery, causing damage to the battery. Therefore, constant current charging is often used as a link in stage charging.

　　2. Constant voltage charging

　　Constant voltage charging means that during the whole charging process, the charging voltage remains constant, and the charging current automatically adjusts with the change of battery state. With the charging process, the charging current gradually decreases. Compared with constant current charging, its charging process is closer to the optimal charging curve, simple to control and low in cost. The disadvantage is that the charging time is long, and the charging current of the battery is too large at the initial stage of charging, which directly affects the life and service quality of the lithium battery. Therefore, the constant voltage charging method is rarely used alone, only when the charging power supply voltage is low and the current is high.

　　3. Constant current and voltage charging

　　Figure 2 shows the constant current and constant voltage charging curve. Before charging, first detect the battery voltage. If the battery voltage is lower than the threshold voltage (about 2.5V), then trickle charge the battery with a small current of C/10 to make the battery voltage rise slowly; When the battery voltage reaches the threshold voltage, it will enter into constant current charging. At this stage, the battery will be rapidly charged with a large current (0.5C~1C). The battery voltage will rise rapidly, and the battery capacity will reach about 85% of its rated value; After the battery voltage rises to the upper limit voltage (4.2V), the circuit switches to the constant voltage charging mode. The battery voltage is basically maintained at 4.2V, the charging current gradually decreases, and the charging speed slows down. This stage is mainly to ensure that the battery is fully charged. When the charging current drops to 0.1C or 0.05C, it is determined that the battery is fully charged.

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