March 14, 2024
How to handle lithium battery overcharge: A complete safety guide
As the core energy source of modern devices such as electric motorcycles, smartphones, and laptops, the performance of lithium batteries directly affects the user experience and safety of the devices. However, if lithium batteries are not handled properly during use, they are easily overcharged, which in turn causes a series of problems.
This article will deeply analyze the potential hazards of lithium battery overcharge, introduce effective preventive measures, and explore the repair solutions after different types of batteries are overcharged, to help users better understand and maintain lithium batteries, extend their service life, and ensure safe use.
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Definition and hazards of lithium battery overcharge
What is lithium battery overcharge?
Overcharge of lithium batteries refers to the behavior of continuing to charge after the actual remaining power (SOC, State of Charge) of the lithium battery exceeds the set protection threshold (for example, 95%), or the charging voltage of the battery pack exceeds the upper limit of the cut-off voltage (explore what is lithium battery state of charge). Simply put, it means that the battery is already full, but it continues to charge.
Potential hazards of overcharging lithium batteries
The hazards of lithium battery overcharge cannot be ignored. At the least, it shortens the battery life, and at the worst, it may cause safety accidents. The following are the main hazards of overcharging:
Heat accumulation and thermal runaway
When the lithium battery is close to full charge, continuing to charge will cause a lot of heat to accumulate inside the battery cell. The battery voltage continues to rise, which may cause battery bulging (find swollen lithium battery), fire, or even explosion. The larger the overcharge current, the shorter the time for the battery to have thermal runaway, the higher the critical temperature, the greater the regional temperature difference, and the temperature difference between the inside and outside will also increase accordingly.
Irreversible damage to the battery
Lithium battery overcharge will cause irreversible damage to the battery pack and cells, significantly shortening the cycle life of the battery. The internal structure of the battery changes, resulting in accelerated capacity decay and performance degradation.
Safety hazards
If the battery management system (BMS) cannot provide effective protection, the thermal runaway of a single cell may spread rapidly, causing heat diffusion, and ultimately leading to serious safety accidents such as fire or explosion of the entire vehicle (understand BMS hardware).
Internal chemical reactions
When lithium batteries are overcharged, a series of complex chemical reactions will occur. Excessive lithium ions embedded in the negative electrode may lead to the growth of lithium dendrites and increase the risk of short circuit (explore lithium battery internal short circuit). At the same time, excessive lithium ions are released from the positive electrode, which may cause the positive electrode structure to collapse, release heat and oxygen, and further accelerate the decomposition of the electrolyte.
Analysis of the mechanism of lithium battery overcharge
Chemical reactions during overcharging
During the overcharging process of lithium batteries, the electrolyte will undergo different reactions at the positive and negative electrodes, resulting in the generation of gas and heat.
- Positive electrode reaction
For batteries using LiCoO2, LiMn2O4 or ternary materials as the main positive electrode materials, when overcharging, the positive electrode active material that is over-de-lithiated is prone to decomposition reaction and generate oxygen. More commonly, due to the high positive electrode potential and strong oxidizing property during overcharging, the electrolyte is prone to oxidative decomposition and gas production at the positive electrode. The electrolyte will also react with the O2 decomposed by the positive electrode material, further decomposing and producing gas.
- Negative electrode reaction
When overcharging, lithium is easily deposited at the negative electrode, causing the negative electrode potential to shift to the negative potential. The deposited lithium layer will react with the electrolyte, causing the battery voltage to drop slightly. The solid product generated by this reaction is a component of the SEI film, and gas is produced at the same time. If the overcharge causes the internal temperature of the battery to reach 90°C, the SEI film will decompose and produce gas. In addition, at a higher voltage, the electrolyte will be oxidized at the positive electrode to generate R-H+, which will be reduced to generate H2 after migrating to the negative electrode.
Effect of overcharging on the internal structure of the battery
- Lithium dendrite growth
Overcharging causes too many lithium ions to deposit on the surface of the negative electrode, which is easy to form lithium dendrites. Lithium dendrites are a needle-like structure of metallic lithium that will pierce the battery separator, causing a short circuit and triggering thermal runaway.
- Positive electrode structure collapse
Overcharging causes too many lithium ions to escape from the positive electrode, causing the structure of the positive electrode material to be unstable or even collapse. This will reduce the capacity and cycle life of the battery.
- SEI membrane changes
Overcharging will affect the composition and stability of the SEI membrane, causing the SEI membrane to thicken or decompose, affecting the transmission of lithium ions and increasing the internal resistance of the battery.
How to prevent lithium battery overcharge?
In order to avoid the risks of lithium battery overcharge, multiple protection mechanisms need to be adopted during the design and use process.
The importance of BMS (battery management system)
The battery management system (BMS) is a core component of electric vehicles and other equipment using lithium batteries. Its main function is to monitor the status of the battery in real time and take corresponding protection measures to prevent overcharging and over-discharging (explore battery over discharge).
- Voltage monitoring: BMS monitors the voltage of the battery module and battery pack in real time. When the voltage exceeds the set threshold, the system will automatically stop charging to ensure battery safety.
- SOC (remaining power) monitoring: BMS calculates and monitors the available energy state (SOC) of the battery. When the SOC exceeds the set threshold, the system will automatically stop charging or remind the owner to charge.
- SOH (health state) monitoring: BMS also monitors the health state (SOH) of the battery, evaluates the performance and life of the battery, and adjusts the charging strategy according to the SOH.
- Balancing function: In order to ensure the consistency of the battery cell state, BMS also detects the voltage, temperature and other states of the module and even the battery cell. If the set threshold is exceeded, the system will stop charging or reduce the charging/output power, and start active or passive balancing to keep the battery SOC state as close to the same baseline as possible, thereby reducing the possibility of overcharging.
Precautions that consumers need to pay attention to
Although modern electric vehicles and electronic devices are equipped with a complete BMS, consumers can still take some additional precautions in daily use to extend battery life and ensure safe use.
- Choose the right charger
Always use original or certified chargers, and avoid using inferior chargers to avoid unstable charging voltage or current, resulting in overcharging.
- Avoid long-term charging
Try to avoid charging for a long time, especially when the battery is already fully charged. It is recommended to use a charger or timer with automatic power-off function to prevent overcharging.
- Avoid charging in high temperature environment
High temperature will accelerate the aging and decomposition of the battery, so try to avoid charging in a high temperature environment and choose a cool and ventilated place for charging.
- Check the battery status regularly
Check the appearance of the battery regularly. If you find that the battery is bulging, deformed or leaking, stop using it immediately and contact a professional for inspection or replacement.
- Set a reasonable charging range
It is recommended to charge the battery SOC to the range of 80% to 90%. Most pure electric models can set this value. In this SOC range, the battery can work in a comfortable environment and the driving range will not shrink too much, which is very beneficial to extend the battery life.
- When not in use for a long time, charge appropriately
When the device is not in use for a long time, do not store it completely exhausted. The battery should be charged to about 50%-60% and charged every few months to maintain the activity of the battery.
Repair plan after lithium battery overcharge
Whether lithium batteries can be repaired after overcharging depends on the battery type, the severity of overcharging and the internal damage. There are large differences in the treatment methods of different battery types. The following is a specific analysis:
Overcharge repair of lead-acid batteries
If the electric motorcycle is equipped with a lead-acid battery (explore lead acid battery vs lithium ion), overcharging may cause intense heating inside the battery, a significant increase in internal resistance, and bulging in severe cases. This type of damage is often irreversible and its performance cannot usually be restored by repair. The only reliable solution is to replace the entire battery pack.
It is worth noting that bulging lead-acid batteries pose serious safety hazards, which may not only cause leakage or explosion accidents, but also greatly reduce the endurance of electric vehicles. Therefore, once a bulging battery is found, it should be stopped and replaced immediately.
Overcharge repair of lithium batteries
After overcharging, if the built-in protection board functions normally, the lithium battery may automatically cut off the power to prevent further damage. In such cases, the battery still has a certain possibility of repair, but the premise is that the fault does not affect the battery body.
Possible repair measures include:
- Replace the protection board: If it is confirmed that the fault is caused by the failure of the protection board, you can try to replace the new protection board module. But before that, be sure to find out the specific cause of overcharging, such as abnormal charger, imbalance of individual cells in the battery pack, short circuit of the line, etc.
- Professional detection and repair: Lithium battery packs are usually composed of multiple 18650 or other types of cells in series and parallel. Any abnormality of any cell may cause system failure. Due to the complex structure of the battery, it is recommended to be tested and repaired by a qualified after-sales service team or professional maintenance personnel.
Special warning: Lithium batteries have high energy density. If they are not handled properly, they may cause serious safety accidents such as combustion and explosion. Non-professionals should not disassemble or repair batteries without authorization to avoid personal injury or property loss.
Common misunderstandings in the use of lithium batteries
| Common Misconception | Correct Practice |
|---|---|
| Misconception 1: New batteries need to be "activated" (fully discharged and charged for 12 hours) | Charge as needed. Recharge when below 20%, and unplug when full. |
| Misconception 2: It's better to recharge only when the battery is empty | Keep the charge level between 20%–80%. Avoid deep discharges. |
| Misconception 3: Fast charging doesn’t harm the battery | Use slow charging for daily use. Reserve fast charging for emergencies. |
| Misconception 4: Storing a fully charged battery is better | For long-term storage, keep the charge at 50%–60% and recharge every 3 months. |
Technical solutions to solve the overcharge problem
In addition to the protection of BMS, the following technical means can also be used to improve the battery’s ability to resist overcharge:
- Material modification: By modifying the positive and negative electrode materials, such as material coating, the structural stability and overcharge resistance of the material can be improved.
- Adding anti-overcharge additives: Adding anti-overcharge additives to the electrolyte, such as redox pairs, can react first when the battery is overcharged to protect the battery.
- Use of voltage-sensitive membrane: Using voltage-sensitive membrane, the membrane resistance is significantly reduced when the battery is overcharged, which plays a shunt role.
- Safety structure design: The use of OSD (Overcharge Safety Device) and CID (Circuit Interrupt Device) design in square aluminum shell batteries is currently a common anti-overcharge design. However, soft-pack batteries cannot achieve similar designs.
Conclusion
Lithium battery overcharge is an issue that needs to be highly valued. It not only shortens the battery life, but may also cause safety accidents. By understanding the mechanism and hazards of lithium battery overcharge, taking effective preventive measures, and choosing appropriate repair solutions, we can better protect lithium batteries, extend their service life, and ensure safe use (find what is lithium battery safety?). I hope this article can help users better understand and maintain lithium batteries, so that lithium batteries can play a greater role in our lives.
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Willow
Willow is a materials engineer with a Master’s degree in Materials Science and Engineering, specializing in lithium-ion battery materials and energy storage technologies.
Her work focuses on EV battery swapping solutions, battery innovation, and new energy industry trends, aiming to translate research insights into practical applications for sustainable transportation.
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