Overcharge Protection of Liquid Lithium-Ion Batteries

　　Overcharging is a critical issue for liquid lithium-ion batteries, as it can lead to serious safety hazards and significant degradation of battery performance. When a lithium-ion battery is overcharged, lithium ions accumulate excessively on the anode, causing lithium plating. This plating not only reduces the battery's capacity and lifespan but also poses a risk of internal short circuits, potentially leading to thermal runaway and even fires or explosions.

　　To prevent overcharging, multiple protection mechanisms are employed. At the hardware level, battery management systems (BMS) play a crucial role. BMS continuously monitors the battery's voltage, current, and temperature during the charging process. Once the battery voltage reaches the preset overcharge threshold, usually around 4.2V per cell, the BMS will immediately cut off the charging current, stopping the charging process. Additionally, some advanced chargers are equipped with smart charging algorithms. These algorithms adjust the charging current according to the battery's state of charge (SoC). For example, in the initial stage of charging, a larger current is applied to quickly increase the SoC, and as the battery approaches full charge, the current gradually decreases to a trickle charge, ensuring a more stable and safe charging process.

　　Furthermore, cell - level protection devices, such as positive temperature coefficient (PTC) thermistors and safety vents, are also essential. PTC thermistors increase their resistance as the temperature rises. In case of abnormal heat generation during overcharging, the PTC thermistor's resistance increases significantly, reducing the charging current. Safety vents are designed to release excessive pressure inside the battery if a dangerous situation occurs, preventing the battery from bursting due to overpressure.

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