Date: 2024-05-17 hits: 439
As an important energy storage device, lithium battery has been widely used in modern electronic products. In order to ensure the safe operation and best performance of lithium batteries, reasonable setting of cut-off voltage and current is very critical.
A. The working principle of lithium batteries is based on the movement of lithium ions back and forth between the positive and negative electrodes.
During the charging process, lithium ions are removed from the positive electrode and migrated to the negative electrode through the electrolyte solution, while electrons flow from the external circuit to the negative electrode to achieve battery charging.
The discharge process is reversed, with lithium ions returning from the negative electrode to the positive electrode, and electrons flowing from the negative electrode to the external circuit.
B. Discharge cut-off voltage
1. Discharge cut-off voltage refers to the lowest voltage that can be achieved when the battery is discharged.
Setting the appropriate discharge cut-off voltage can avoid excessive discharge of the battery, thus extending the battery life.
In general, the discharge cutoff voltage of lithium batteries is usually set between 3.0V and 3.2V.
The exact number depends on the type of battery, the application scenario and the manufacturer's requirements. A lower discharge cutoff voltage allows the battery to release more energy, but it also increases the risk of battery loss and shortened life. Higher discharge cutoff voltages can extend battery life, but may sacrifice some battery capacity. When setting the discharge cutoff voltage, there is a trade-off between energy output and battery life.
2. Charging cut-off voltage
The charging cut-off voltage refers to the highest voltage that can be reached when the battery is charged. The setting of the charge cutoff voltage takes into account a number of factors, including battery chemistry, safety and longevity. The charging cutoff voltage of the general lithium battery is usually set at about 4.2V.
This voltage value is determined based on the rated voltage and charging characteristics of the battery. Charging beyond the charging cut-off voltage may cause the battery to overcharge, causing problems such as electrolyte decomposition, heating, and even causing the battery to explode or catch fire.
In order to ensure the safety and adequacy of charging, constant current - constant voltage charging mode is usually adopted during the charging process.
In the constant current charging phase, the battery is charged at a constant current until the voltage reaches the charge cut-off voltage. Then switch to the constant voltage charging phase, charging at a constant voltage until the current drops to a certain value, at which point the battery is considered full.
C. The cut-off current refers to the current value that is considered to be the end of charging when the current drops to a certain value during the charging process.
Setting the appropriate cut-off current ensures that the battery is fully charged while avoiding overcharging. The national standard usually stipulates that the charging cutoff current shall not exceed 0.01 times of the battery capacity, that is, 0.01C.
For example, if the capacity of the battery is 2000mAh, the cutoff current should not exceed 2mA. Such a setting can ensure that the battery reaches a higher charging level at the end of charging and improves the capacity utilization of the battery.
D. Infulence of other factors
1. Temperature
Temperature has an important impact on the performance and safety of lithium batteries. In high temperature environments, the battery life may be shortened, while the risk of overcharge and overdischarge will also increase. When setting the cut-off voltage and current, it is necessary to consider the temperature factor and take corresponding temperature control measures.
2. Battery aging As a battery is used and aged, its performance may change.
Aging batteries may require lower discharge cut-off voltages and charge cut-off voltages to ensure safety and performance. During the use of the battery, it is necessary to make appropriate adjustments according to the actual condition of the battery.
3. Load characteristics Different load characteristics may affect the cutoff voltage and current setting of the battery.
For example, high load conditions may require a higher discharge cutoff voltage to meet power requirements, while low load conditions can be appropriately reduced to extend battery life.
E. Precautions
The correct cut-off voltage and current setting is very important for the safety and life of lithium batteries.
Improper Settings can result in battery damage, safety risks, or shortened battery life. When setting the cut-off voltage and current, it is important to follow the relevant standards of the battery and make reasonable adjustments according to the specific application to ensure the safety and performance of the battery.
F. Application of Battery Management System (BMS)
Battery Management System (BMS): In some complex systems, such as electric vehicles or large energy storage systems, a BMS may be used to monitor and control the status of the battery. BMS can automatically adjust the cut-off voltage and current based on the temperature, voltage, current and other parameters of the battery to ensure its safety and optimal performance. Its function is as follows:
1. Battery status monitoring: BMS can monitor the voltage, current, temperature and other parameters of the battery in real time, ensuring that the battery is within the normal working range.
2. Battery protection: When the battery encounters abnormal situations such as overcharging, over discharging, high temperature, etc., the BMS will promptly cut off the power or take other protective measures to prevent battery damage.
3. Battery balancing: The balancing function of BMS can avoid inconsistent battery usage, thereby improving the overall performance of the battery pack and extending its service life.
4. Battery usage optimization: BMS can allocate power reasonably based on the actual situation of the battery, optimize battery usage, and improve battery utilization.
G. Summary
The setting of cutoff voltage and current for lithium batteries is a complex process that requires comprehensive consideration of factors such as battery performance, lifespan, safety, and application scenarios. Following relevant standards and specifications, and making reasonable adjustments based on actual situations, can ensure the best performance and longest lifespan of lithium batteries. At the same time, users should also pay attention to the correct charging and discharging methods when using lithium batteries, avoid overcharging and discharging, to ensure the safety and stability of the battery.
