The operation of Li-ion batteries is highly dependent on the operating temperature, as chemical processes take place in them. The inside of the cells can be damaged in various ways if the temperature limits are not observed. The inside of the cell can also be damaged due to too much or too little voltage.
Security components
The cells have some safety components built into them. which are described in the article Cell structure type 18650. Built-in components generally provide greater safety for the environment, but their operation generally results in the destruction of the cell. When, for example, an anti-explosion valve opens, the cell is destroyed. This can occur at high temperatures or high currents. In order to protect cells from extreme conditions, battery management systems (BMS) are used in battery packs.Charging and temperatures
At low temperatures, a reduced degree of diffusion (scattering) occurs at the anode, so charging at temperatures below 0°C is generally not allowed. Between 0°C and 10°C, charging is allowed for most cells, but the charging current must be reduced to an appropriate value of 0.25 C, which means 0.25 times the nominal capacity of the battery in Ah. Due to the increased internal resistance of the battery at low temperatures, increased heating of the battery occurs during charging, compensating for some of the heat. Due to the increased internal resistance of the battery at low temperatures, the charging time increases. Charging below 0°C is possible, but such treatment causes permanent damage that cannot be repaired, as lithium plating begins to be permanently deposited on the anode. Damaged cells are then much more sensitive to vibrations and other stressful situations. Internal resistance also increases, which is seen in larger voltage drops under the same loads compared to healthy cells with low internal resistance.Li-ion batteries behave well at high temperatures, but even long exposure to high temperatures has a negative effect on battery life. Most manufacturers have set an upper temperature limit at which the cells can be charged at 45°C. Charging and discharging at higher temperatures can cause gas to escape from the cell. In the worst cases, the valve may open and the cell may ventilate, but it may also swell. The loss of capacity when the cell is exposed to high temperatures is also greatly influenced by the SoC. The battery is most damaged if it is charged to 100% and subjected to high temperatures. Therefore, for a long battery life, it is recommended to charge only up to 80%. If an individual cell is charged above the permitted limit of 4.2V, metallic lithium begins to be loaded onto the anode. Materials at the cathode become the oxidizing agent. The cell becomes unstable as CO2 begins to be produced. The pressure in the cells increases and the anti-explosion valve opens. The cell can also become inflamed.
The Li-ion cell is also affected by under-voltage (discharge below the permissible limit). The permissible limit for most cells is between 2.65V and 2.7V. If the voltage drops below this limit, the materials on the electrodes gradually break down. Current limitations are mostly related to overheating. Larger currents are carried by batteries with lower energy capacities, as they do not heat up as much as batteries with higher energy capacities.