Introduction of capacity difference analysis (CDA) for analyzing lateral lithium-ion flow to determine the state of covering layer evolution

In this contribution a simple in-situ method named capacity difference analysis (CDA) is introduced to characterize lateral flow of lithium-ions within the anode. Therefore, simply the difference between two capacity measurements, which are determined at significantly different current rates, are evaluated for each check-up. During aging the initial capacity difference of 2-3% is reducing for all calendaric and cyclic aged cells until they reach a value which is close to zero difference. The initial capacity difference can be explained by lithium-ion flow between active and passive anode, whereby passive represents the excess anode without counter cathode (passive electrode effect). The successive reduction is likely caused by particle disconnection between active and passive anode and/or dry out of electrolyte in the anode overhang. Furthermore some cyclic aged cells reveal an increase after the initial decrease which can be associated to a process of forming a vertical deposition layer on top of the anode facing the separator that is not permeable to lithium-ions applying reasonable discharge currents. The CDA results are validated by laser microscope imaging after disassembling representative cells. The method is applied on a test matrix presented in our previous publication [1].