An Analytical study on Methods to Detect Degraded Cells in a Multi-Cell Lithium-ion Battery Pack

In most applications where electricity is utilised, storing energy and using that energy when the demand is high is important. As the most common energy storage, Lithium-Ion batteries are used in many applications. Such batteries are comprised of modules and the modules consist of series connected and parallel connected cells. When the batteries are in frequent operation, the State-of-health of the cells deteriorate. As a result, the cells will lose their storage capacity and cell voltages will deviate from their nominal values. Therefore, there is a possibility of having damaged cells within a battery. Identifying such damaged cells is important to maintain the battery at high state-of-health and thus to make sure the battery can be operated to its full expected life time, while delivering the expected performance. For that, accurate methods must be available in locating the degraded cells within the battery. This paper reviews the state of the art to detect degraded cells, where almost all of them are limited to one dimensional cases; i.e., either parallel connected cell arrays or series connected cell arrays. Since such approaches have limited applications to this two dimensional problem, this paper proposes a new method to identify faulty cells in a two dimensional array of cells in a battery by measuring array voltage, current and the temperatures.