Overcharging and over-discharging are two common problems that can severely impact the lifespan and safety of lithium batteries. This article explores the meaning of these terms, their effects on battery health, and practical tips for avoiding them.
Lithium battery overcharge
Overcharging a lithium battery refers to the charging voltage exceeding the battery's maximum cutoff voltage during the charging process, typically 4.2-4.4 volts (for mobile phone lithium-ion batteries). Overcharging causes changes in the internal positive electrode material structure, resulting in a loss of total battery capacity. Overcharging also promotes electrolyte decomposition, producing gases (such as hydrogen and oxygen), increasing internal battery pressure, and potentially leading to battery swelling, leakage, or casing rupture.
Will charging a phone for an extended period of time cause it to overcharge?
Contrary to many people's expectations, charging a smartphone for a long time will not lead to overcharging. This is mainly due to the charging protection of the phone system, the BMS in the phone's lithium battery, and the fast charging protocol in the charger.
Charging protection in mobile phone system
Some smartphones, such as iPhones, offer optimized battery charging and temperature management features in their systems to effectively prevent overcharging and slow down battery aging.
Optimized Battery Charging: Taking iPhones as an example, iOS 13 and later versions introduced the "Optimized Battery Charging" feature. This feature learns the user's charging habits and pauses charging or reduces the charging current after the battery reaches 80%, until it predicts that the user will use the device, then charges it to 100%.
Stop charging when the temperature is too high: iPhones are equipped with a temperature monitoring function in the system. If the phone temperature is too high while charging, the charging speed will be reduced or charging will be temporarily stopped.
BMS in mobile phone lithium batteries
The BMS built into the mobile phone lithium battery can monitor the battery voltage, temperature and charging status to ensure the charging process is safe. Once the battery is fully charged, the system will automatically stop charging to prevent overcharging.
Fast charging protocol in the charger
The original charger supports QC (Qualcomm Quick Charge) and PD (USB Power Delivery) protocols, which allow the charger to communicate with the phone and adjust the current and voltage according to the phone's needs.
Mobile phone lithium batteries are charged in two stages when using a charger.
Constant current charging (CC): When the battery charge percentage is low (at which point the voltage will also be low), it is charged with a constant current, and the voltage gradually increases.
Constant voltage charging (CV): When the battery voltage approaches the maximum rated voltage (e.g., 4.2 volts), the charger switches to constant voltage charging, and the current gradually decreases until the current drops to a small value (usually the termination current, and charging ends).
In summary, with the triple protection of the phone system, lithium battery, and charger, the phone will not overcharge. However, you should still try to avoid charging the phone for a long time, as this will cause the battery to age prematurely.
How to prevent overcharging of mobile phone batteries?
If your phone and accessories are all original, then you don't need to worry about overcharging the lithium battery. However, if you replace them with third-party accessories, you need to pay attention to the quality of the accessories.
Replacing a lithium battery: It is recommended to choose a high-quality mobile phone battery. Although very cheap counterfeit batteries may also have a BMS, they are prone to failure during use, causing the battery to swell soon after use.
Third-party chargers: Choose certified chargers. Many third-party manufacturers now produce chargers that also support QC and PD protocols, making them just as safe as original chargers.
Over-discharge of lithium batteries
Lithium-ion batteries release stored energy during use. When the discharge voltage falls below the manufacturer's specified cutoff voltage (typically 2.5V or 2.8V), it is considered over-discharge. Frequent over-discharge accelerates battery aging, shortens battery life, and causes excess heat and gas buildup inside the battery, leading to swelling or leakage.
Is it considered over-discharge if a phone is allowed to shut down completely?
A phone battery level below 0 does not necessarily indicate over-discharge. The energy stored in a battery is usually greater than the level displayed on the phone's system. This means that when your phone shows 0% battery, the lithium battery may actually have 5% charge remaining. Since the battery voltage is above the minimum cutoff voltage, over-discharge will not occur. When a phone discharges to the point of shutdown, the battery management system (BMS) in the lithium battery is functioning. The BMS automatically cuts off power when the battery level drops to a certain level to prevent battery damage.
However, frequent deep discharges will cause the capacity of lithium batteries to gradually decrease. The active materials inside the battery will be irreversibly lost during deep discharge, resulting in reduced battery capacity and shortened cycle life.
in conclusion
By understanding the concepts of overcharging and over-discharging, users can take proactive steps to prevent these problems. Using original chargers and batteries, leveraging the built-in protection features of modern devices, and following recommended charging habits can help maximize battery performance and lifespan.
