Li Dendrite Formation on the Side of Cu Current Collector during Charging in Misaligned Pouch-Type Lithium-Ion Batteries

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Not only high-capacity electrode materials but also electrode/cell design greatly governs the electrochemical performance of LIBs. For instance, there are systematic works to unravel the effect of area or capacity ratio between anode and cathode or the electrolyte amount. [1,2,3] Especially, our research group has already reported the effect of electrode misalignment, which can frequently occur during the coin cell assembly, on the electrochemical properties, where Li dendrites formed on the coin cell bottom mainly deteriorated the cell performance. [4] However, considering the commercial cell configurations like pouch-type LIBs, which have insulating polypropylene inner layer, those negative phenomena should be evaluated in misaligned LIB cells.For this purpose, three pouch-type cells (well-aligned, slightly misaligned, and largely misaligned) using LixNi0.6Co0.2Mn0.2O2 cathode and graphite anode were fabricated in a dry room. Surprisingly, a similar misalignment effect to coin cells was also observed in the pouch-type cell, even though the inner layer of the Al-pouch is insulative. When we disassembled the misaligned cell after precycling, we could observe Li dendrites formed on the side of the Cu current collector (CC) of the anode. That is, the Li ions from the cathode are able to be plated on the metal side of Cu CC of a few micrometer thickness. Thus, even in pouch cells, the electrode misalignment can lead to Li inventory loss. To solve this problem, an insulating coating was applied to the side of the Cu CC, and as a result, the cycle performance of the misaligned cell was improved by suppressing the Li dendrite formation. In addition, the electrochemical characteristics were compared as a function of the lithiation state (SOL, x in LixNi0.6Co0.2Mn0.2O2) using EIS, DC-IR, XRD, etc.Reference B. Son, Y. M. Lee et al., J. Power Sources , 243 (2013) 641-647R. Xue et al., J. Power Sources , 55 (1995) 111-114B. R. Long, J. R. Croy et al., J. Electrochem. Soc. , 163 (2016) A2999N. Kim, Y. M. Lee et al., J. Electrochem. Soc. , 169 (2022) 023502