We present a new method to directly detect transport of organic species from cathode to anode using isotope labeling: if the Oxidation and Transport Processes (OTP) do exist between cathode and anode, one could utilize 13C-labelling to differentiate these organic species from the ones directly generated through electrolyte reduction at the anode−electrolyte interface. The conditions for growing and dissolving the electrolyte degradation layer on the cathode were experimentally established. The cathode covered by 13C-labelled electrolyte decomposition layer was prepared and, after washing away an excess of 13C-labelled electrolyte, it was assembled into the cell with non-labelled electrolyte, fresh graphite anode and fresh separator for further cycling. In this case the only source of 13C within the cell was the pre-generated 13C-labelled electrolyte decomposition products present on the cathode surface. This cell was then cycled under the conditions in which the electrolyte decomposition layer is dissolving. If the OTP does occur, the 13C-labelled species would be transported to the anode surface, where they can be detected by surface sensitive techniques, such as ToF-SIMS. Control experiment was done using the same experimental procedure but with nonlabelled 12C-containing electrolyte. As expected, for the non-labelled experiment, the signals from all three 13C-containing ions were weak, and percentages of detected 13C did not exceed natural abundance. For the 13C-experiment, signals from the 13C-containing ions were increased remarkably and were about eight times higher than the levels of natural abundance, directly proving the existence of OTP in Li-ion cells.

Direct proof of Oxidation-and-Transport Processes within Li-ion cells

256th National Meeting (2018)

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