What is overcharging, and what impact does it have on battery performance?
Overcharging refers to the act of continuing to charge a battery after it has been fully charged through a certain charging process.
Because the negative electrode has a higher capacity than the positive electrode in the design, the gas generated at the positive electrode recombines with the cadmium generated at the negative electrode through the separator. Therefore, under normal circumstances, the internal pressure of the battery will not increase significantly. However, if the charging current is too high or the charging time is too long, the generated oxygen may not have enough time to be consumed, potentially causing increased internal pressure, battery deformation, leakage, and other adverse phenomena. Simultaneously, its electrical performance will also be significantly reduced.
What is over-discharge, and what impact does it have on battery performance?
Once a battery has discharged its internal stored charge and reached a certain voltage, continuing to discharge it will result in over-discharge. The discharge cutoff voltage is typically determined by the discharge current. For 0.2C-2C discharge, a voltage of 1.0V per cell is generally used; for 3C and above, such as 5C or 10C, the voltage is set at 0.8V per cell. Over-discharging a battery can have disastrous consequences, especially high-current over-discharge or repeated over-discharge. Generally, over-discharge increases the internal pressure of the battery, disrupts the reversibility of the active materials in the positive and negative electrodes, and even charging can only partially restore the battery's capacity, leading to a significant capacity reduction.
What problems might occur if batteries of different capacities are used together?
Mixing batteries of different capacities or old and new batteries together can lead to leakage, zero voltage, and other issues. This is because during charging, the capacity difference causes some batteries to be overcharged while others are not fully charged. During discharging, some high-capacity batteries are not fully discharged while low-capacity batteries are over-discharged. This vicious cycle damages the batteries, resulting in leakage or low (zero) voltage.
I. Overcharging and Hazards of Lithium Batteries
1. Overcharging refers to the charging voltage of a lithium battery exceeding its set operating voltage. For example, the rated current of a rechargeable battery is ±1V. In other words, if the maximum operating voltage exceeds 9V, it is considered overcharging. What are the harmful effects of overcharging on rechargeable batteries?
2. During overcharging, the battery voltage rises rapidly as polarization increases, causing irreversible changes in the structure of the positive electrode active material. This leads to the dissolution of the lithium battery electrolyte, generating a large amount of vapor and releasing a significant amount of heat, drastically increasing the battery temperature and pressure. It can also dissolve or seal the external separator, causing a short circuit between the positive electrode and the positive electrode material, and posing safety hazards such as explosion and fire.
II. Hazards of Over-Discharge of Lithium Batteries
1. Over-discharge refers to the process of discharging after the operating voltage has reached the rated current during the charging and discharging process. For example, if the rated charging and discharging voltage of a ternary lithium battery is lower than the rated charging and discharging voltage, it is considered over-discharge. What are the hazards of excessive discharge to rechargeable batteries?
2. When a battery discharges its externally stored charge and its operating voltage reaches a certain value, further discharge will lead to over-discharge of the rechargeable battery. Over-discharge of the battery will have a devastating adverse effect on the battery, especially the power loss under high current or repeated discharge will cause greater damage to the battery.
III. How to avoid overcharging or over-discharging the battery during daily use
1. It works in conjunction with a dedicated lithium battery protection board (BMS). The lithium battery protection board can charge and maintain rechargeable batteries. The intelligent version can also set the operating voltage for battery charging and discharging, providing better maintenance for rechargeable batteries.
2. The lithium battery chargers used in the supporting facilities do not use fast charging.
3. When the battery voltage reaches the operating voltage set by the lithium battery protection board, the board will shut off the power to protect the rechargeable battery. However, the lithium battery level will decrease, and the operating voltage will increase, slightly exceeding the operating voltage set by the protection board. The battery should not be used at this time; continued use will inevitably damage the rechargeable battery.
