Influence of orientation on ageing of large-size pouch lithium-ion batteries during electric vehicle life

In the electric vehicle (EV) battery packs, large-size lithium-ion pouch batteries (LiBs) are mostly used and to miniaturise the battery pack's volume, some manufacturers put the LiBs in different orientations. It is well established that temperature gradients over large-size LiBs surface cause ageing non-uniformities, but the influence of the LiBs orientation on the ageing has to date received little attention. Here, we present an analysis of orientation influence on the large-size pouch LiB's ageing on eight batteries from two differently orientated modules from the dismantled first-generation Nissan Leaf retired battery pack. The influence of orientation is also analysed for brand-new second-generation Nissan Leaf battery which has almost the same geometry as batteries from the retired pack. By utilising infrared (IR) thermography and electrochemical impedance spectroscopy (EIS) techniques, the influence of orientation on the LiBs ageing non-uniformity is detected. Whilst temperature maps analysis shows different LiBs' thermal behaviour depends on their orientation, EIS measurements show that ageing non-uniformity can be identified by analysing the solid-electrolyte-interphase and charge-transfer resistances. Presented results show that different LiBs orientation in EV battery packs should be avoided because it can cause ageing non-uniformities over the battery surface and their second-life applications should be applied with caution.