What are the requirements for charging and discharging lithium-ion batteries

1. Lithium battery charging The maximum end-of-charge voltage of a single-cell lithium battery is 4.2V, and it cannot be overcharged, otherwise the battery will be scrapped due to the loss of too much lithium ions in the positive electrode. When charging the lithium battery, a dedicated constant current and constant voltage charger should be used, first charge with constant current until the voltage at both ends of the lithium battery is 4.2V, then switch to the constant voltage charging mode; when the constant voltage charging current drops to 100mA, Charging should be stopped. The charging current (mA) can be 0.1 to 1.5 times the battery capacity, for example: a 1350mAh lithium battery, the charging current can be controlled between 135mA and 2025mA. The normal charging current can be selected at about 0.5 times the battery capacity, and the charging time is about 2 to 3 hours. 2. Discharge of lithium batteries Due to the internal structure of lithium batteries, all lithium ions cannot move to the positive electrode during discharge, and some lithium ions must be retained in the negative electrode to ensure that lithium ions can be inserted into the channel smoothly during the next charge. Otherwise, the battery life will be shortened. In order to ensure that some lithium ions remain in the graphite layer after discharge, it is necessary to severely limit the minimum discharge termination voltage, which means that the lithium battery cannot be over-discharged. The discharge termination voltage of a single-cell lithium battery is generally 3.0V, and the minimum should not be lower than 2.5V. The length of battery discharge time is related to battery capacity and discharge current. Battery discharge time (hours) u003d battery capacity/discharge current, and lithium battery discharge current (mA) should not exceed 3 times the battery capacity, for example: 1000mAh lithium battery, the discharge current should be strictly controlled within 3A, otherwise it will The battery is damaged. Second, the composition of the maintenance circuit The maintenance circuit is generally composed of control IC, MOs switch tube, blown fuse, resistor, capacitor and other components, as shown in Figure 2. Under normal circumstances, control the IC output signal to control the MOs switch tube to conduct, so that the cell and the external circuit are connected. When the cell voltage or loop current exceeds the specified value, it immediately controls the MOS tube to turn off to maintain the cell’s Safety. The control IC has a built-in high-precision voltage test circuit and a multi-level current test circuit. Among them, the voltage test circuit first tests the charging voltage, once it reaches its set threshold (generally 3.9V ~ 4.4V), it immediately enters the overcharge maintenance condition; the second is to test the discharge voltage, once it reaches its set threshold (Generally 2.0V～3.0V), immediately enter the over-discharge maintenance condition. In this circuit, the thin TSSOP-8 or SOT23-6 package is mostly used for MOS switch tubes, and its appearance is shown in Figure 3. Some of these MOS switch tubes contain an N-channel field effect transistor, such as FDMC7680, whose pins ①～③ are S poles, ④ feet are G poles, and ⑤～⑧ pins are D poles. The internal structure is shown in Figure 4. ; Some include two N-channel field effect transistors, such as FDW9926A, 8205A, etc., whose pin functions are related to the packaging method, as shown in Figure 5. [Prompt] If there is a small circular concave point on the control IC and MOs switch tube, the pin corresponding to the concave point is pin ①; if there is no concave point on the surface, the first pin on the left of the component model label is pin ① , And the rest of the pins are placed in a counterclockwise direction. In addition, when switching to a MOS switch tube, it is necessary to judge its internal circuit according to the actual line direction, and then perform the correct substitution. In addition, part of the lithium battery maintenance circuit is also equipped with NTC and ID signal components. NTC is the abbreviation of NegaTIvetemperaturecoefficient in English, which means negative temperature coefficient resistance. The element in this circuit mainly plays the role of overheating maintenance, that is, when the temperature of the battery itself or the surrounding environment rises, the resistance of the NTC element decreases, and the electrical equipment or charging equipment responds in time. If the temperature exceeds a certain value, the system enters Maintain status and stop charging and discharging. ID is the abbreviation of IdenTIficaTIon, which means identity recognition. There are two types of components for information recognition: one is memory, which is often the animal line interface memory, which stores information such as battery type and processing date; the other is identification resistance, both It can be used to restrict the traceability and use of the product. Disclaimer: Some pictures and content of articles published on this site are from the Internet, please contact to delete if there is any infringement. Previous: What factors affect the service life of lead-acid batteries