For years, the space charge layer formation in Li-conducting solid electrolytes and its relevance to so-called all solid-state batteries have been controversially discussed from experimental and theoretical perspectives. In this work, we observe the phenomenon of space charge layer formation using impedance spectroscopy at different electrode polarizations. We analyze the properties of these space charge layers using a physical equivalent circuit describing the response of the solid electrolytes and solid/solid electrified interfaces under blocking conditions. The elements corresponding to the interfacial layers are identified and analyzed with different electrode metals and applied biases. The effective thickness of the space charge layer was calculated to be ∼60 nm at a bias potential of 1 V. In addition, it was possible to estimate the relative permittivity of the electrolytes, specific resistance of the space charge layer, and the effective thickness of the electric double layer (∼0.7 nm).

Fast-charging is a key requirement for customer acceptance of battery electric vehicles. In this work, various methods for lithiumplating detection are applied to prismatic hard-case lithium-ion cells to demonstrate their applicability for large-format automotive cells despite possible thermal and electrochemical inhomogeneities. Different fast-charging profiles with a charging time of less than 30 min from 10% to 80% state-of-charge are examined with methods based on coulombic efficiency, cell voltage analysis and swelling force. To validate these results, a lifetime cycling test with a subsequent cell opening is performed, followed by a discussion on lithium-plating detectability and the restrictions of each method.In order to further illustrate the applicability of the lithium-plating detection methods, the fast-charging ability of two cells with the same format but different cathode active materials, namely NMC622 and NMC811, are compared. Furthermore, a coupled electrochemical-thermal simulation is performed to study the effect of the cell design on the fast-charging ability and to elucidate why a higher cell energy density does not necessarily lead to a worse fast-charging ability.

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