The protection of lithium batteries mainly involves the following aspects:

Overcharge protection: Principle During the charging process of lithium batteries, when the battery voltage rises to the set upper limit voltage (the overcharge protection voltage varies for different types of lithium batteries; for instance, the single-cell overcharge protection voltage for ternary lithium batteries is generally around 4.2V, while that for lithium iron phosphate batteries is approximately 3.65V), the protection circuit will cut off the charging circuit. Prevent the charger from continuing to charge the battery to avoid safety issues caused by overcharging, such as battery swelling, overheating, and even fire and explosion. This is because overcharging causes the electrolyte inside the battery to decompose, generating a large amount of gas and leading to an increase in the internal pressure of the battery. Implementation method: Overcharge protection is usually achieved by adding a protection board to the lithium battery pack. The control chip on the protection board will monitor the battery voltage in real time. Once the voltage reaches the overcharge protection threshold, the chip will control the switching devices such as the field-effect transistor (MOSFET) to turn off the charging circuit.

2. Over-discharge protection: Principle: When a lithium battery discharges, its voltage gradually drops. If the battery voltage drops to the set lower limit voltage (for example, the single-cell over-discharge protection voltage of a ternary lithium battery is generally around 2.5V, and that of a lithium iron phosphate battery is approximately 2.0V), the protection circuit will cut off the discharge circuit to prevent the battery from over-discharging. Excessive discharge can cause irreversible damage to lithium batteries, such as reducing battery capacity, shortening battery life, and in severe cases, it may lead to the battery being unable to be recharged. The implementation method: It also relies on the control chip on the protection board to monitor the battery voltage. When the voltage drops below the over-discharge protection threshold, the control chip will control the switch device to turn off the discharge circuit and stop the battery's discharge.

3. Overcurrent protection: Principle: It is divided into charging overcurrent protection and discharging overcurrent protection. Overcurrent charging refers to the situation where, during the charging process, the current output by the charger is too large, exceeding the maximum charging current that the lithium battery can withstand. Discharge overcurrent refers to the situation where, during the battery discharge process, the current required by the load exceeds the maximum discharge current that the lithium battery can provide. The purpose of overcurrent protection is to prevent excessive current from damaging the battery and to avoid safety issues such as overheating and short circuits caused by excessive current. The implementation method: The current detection circuit on the protection board will monitor the charging and discharging currents in real time. When the current exceeds the set threshold, the protection circuit will quickly cut off the current loop to protect the battery and the load. For instance, in some power tools, electric vehicles and other devices that use lithium batteries, overcurrent protection devices are installed to prevent the large current at the moment of startup from damaging the battery.

4. Short-circuit protection: Principle: When the positive and negative terminals of a lithium battery are directly short-circuited or a short circuit occurs in an external circuit, an extremely large short-circuit current will be generated. The function of short-circuit protection is to detect a short circuit within an extremely short period of time and cut off the connection between the battery and the external circuit to prevent the battery from being damaged due to excessive short-circuit current, and also to avoid safety accidents such as fires caused by short circuits. The implementation method: The protection board determines whether a short circuit has occurred by detecting the changes in voltage and current at the battery output terminal. Once a short circuit is detected, the protection circuit will immediately control the switching device to turn off and cut off the battery output. After the short-circuit fault is eliminated, the protection circuit will automatically resume normal operation, allowing the battery to continue charging or discharging.

5. Temperature protection: Principle: Lithium batteries generate heat during charging and discharging. When the temperature is too high, it will affect the performance and safety of the battery. The purpose of temperature protection is to take corresponding measures to lower the temperature or stop the charging and discharging operations of the battery when the battery temperature exceeds the safe range, to prevent the battery from being damaged due to overheating. Implementation method: Generally, a temperature sensor is used to monitor the temperature of the battery. When the temperature sensor detects that the battery temperature has risen to the set threshold, the protection circuit will take measures based on the specific situation, such as reducing the charging current, stopping charging or discharging, and activating the heat dissipation device, etc. For instance, in some high-end lithium battery packs, cooling fans or heat sinks and other heat dissipation devices are equipped to ensure that the battery operates within a normal temperature range.

6. Balanced protection: Principle: In lithium battery packs, due to the performance differences among individual cells, such as internal resistance and capacity, inconsistent voltages may occur during charging and discharging. Long-term use can lead to overcharging or overdischarging of some individual cells, affecting the performance and service life of the entire battery pack. The purpose of balanced protection is to monitor and adjust the voltage of each individual battery in the battery pack to keep their voltages at a relatively consistent level, thereby enhancing the overall performance and service life of the battery pack. The implementation methods mainly include passive balancing and active balancing. Passive balancing is achieved by connecting a resistor in parallel to each individual battery. When the voltage of a certain battery is too high, the excess energy is consumed through the resistor, reducing the voltage of that battery to a level similar to that of other batteries. Active balancing is achieved by transferring energy from a battery with a higher voltage to one with a lower voltage, thereby balancing the battery pack.