Overview of cell balancing methods for Li-ion battery technology

Li-ion batteries are influenced by numerous features such as over-voltage, undervoltage, overcharge and discharge current, thermal runaway, and cell voltage imbalance. One of the most significant factors is cell imbalance which varies each cell voltage in the battery pack overtime and hence decreases battery capacity rapidly. To increase the lifetime of the battery pack, the battery cells should be frequently equalized to keeps up the difference between the cells as small as possible. There are different techniques of cell balancing have been presented for the battery pack. It is classified as passive and active cell balancing methods based on cell voltage and state of charge (SOC). The passive cell balancing technique equalizing the SOC of the cells by the dissipation of energy from higher SOC cells and formulates all the cells with similar SOC equivalent to the lowest level cell SOC. The active cell balancing transferring the energy from higher SOC cell to lower SOC cell, hence the SOC of the cells will be equal. This review article introduces an overview of different proposed cell balancing methods for Li-ion battery can be used in energy storage and automobile applications.