Electrochemical behaviour of coated lithium-carbon electrodes

On lithium-carbon intercalation electrodes a thin protective layer on the electrode surface is formed during the first charge/discharge cycle. This film formation is investigated by means of impedance spectroscopy and cyclic voltammetry. Uncoated LiCn electrodes show a continuous increasement of the low frequency semicircles during the first charge/discharge cycle. The protective films can be simulated by a polymer precoating. But any coating of the electrode should influence the behaviour due to modification of the film and/or modification of the surface in general. The influence of different coatings like poly-2-vinylpyridine, poly(ethylene oxide) and TiO2 on the electrochemical behaviour of lithium-carbon electrodes is demonstrated in propylene carbonate electrolyte. Inpedance studies during charge and discharge show that the low frequency semicircles decrease due to a modification of the resistances and the capacities. Cyclic voltammograms are also clearly influenced by the coatings and demonstrate differences in the electrode kinetics and the film formation from decomposition products of the electrolyte.