Performance and aging of a lithium-ion battery in a non-uniform temperature distribution condition

Inhomogeneous temperature distribution in a large-format lithium-ion cell or between cells in a module/pack may cause a non-uniform current distribution, causing a local difference in aging, and potentially faster global aging (capacity fade and impedance rise) of the module. To study this effect, LiNi_1/3Mn_1/3Co_1/3O₂/graphite lithium-ion pouch cells were cycled at 32, 36, and 40 °C as single cells and in parallel connection, representing uniform and non-uniform temperature distributions. The results show that the current distribution becomes less uniform after cycling at a higher rate and in a narrower state-of-charge range. Cycling with non-uniform temperature at 3C rate results in aging similar to that at the maximum uniform temperature, while at 1C rate the non-uniform aging follows the trend at the average temperature. The performance decay of the cells cycled at 3C is mainly driven by the cell at 40 °C which shows 30 % more capacity loss than the corresponding cell cycled singularly. This leads to additional considerations when designing for cycle life and reliability in fast charging applications and high-power applications such as in electric vehicles or frequency regulation in stationary storage.