Lithium batteries can get hot for multiple reasons. The most common reasons are too high current either while discharging or charging for the ambient temperature conditions or poor ventilation around the batteries. Lithium battery overcharge protection allows the battery to shut off and the current goes away.
Root cause 1: High self-discharge, which causes low voltage. Solution: Charge the bare lithium battery directly using the charger with over-voltage protection, but do not use universal charge. It could be quite dangerous. Root cause 2: Uneven current.
However, this is only partially true. The lithium-ion battery’s voltage increases as it charges, but the relationship is not linear. It can vary based on several factors, including the battery’s age and temperature. For instance, a typical lithium-ion cell might show a voltage of 3.7V at 50% charge.
Case 1: Lithium battery expands when charging. When charging lithium battery, it will naturally expand, but generally not more than 0.1 mm. However, overcharging will cause electrolyte decomposition, increase internal pressure, and finally lithium batteries expansion.
Temperature extremes can indeed affect lithium-ion batteries. Charging batteries at temperatures below 0°C (32°F) can cause permanent plating of metallic lithium on the anode, while high temperatures during charging can degrade the battery more rapidly.
However, charging beyond 1C, like at 2C or higher, can significantly reduce the battery’s lifespan. Rapid discharge can indeed be harmful if it leads to excessive heat buildup. However, lithium-ion batteries are designed to handle certain levels of immediate dismissal without damage.