ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY OF LITHIUM-TITANIUM DISULFIDE RECHARGEABLE CELLS

The two-terminal alternating current impedance of lithium-titanium dis ulfide (Li/TiS2) rechargeable cells has been studied as a function of frequency, state-of-charge, and extended cycling. Analysis based on a plausible equivalent circuit model for the Li/TiS2 cell leads to evalu ation of kinetic parameters for the various physicochemical processes occurring at the electrode/electrolyte interfaces. To investigate the causes of cell degradation during extended cycling, the parameters eva luated for cells cycled five times have been compared with the paramet ers of cells that have been cycled over 600 times. The findings are th at the combined ohmic resistance of the electrolyte and electrodes suf fers a ten-fold increase after extended cycling, while the charge-tran sfer resistance and diffusional impedance at the TiS2/electrolyte inte rface are not significantly affected. The results reflect the morpholo gical change and increase in area of the anode due to cycling. The stu dy also shows that overdischarge of a cathode-limited cell causes a de crease in the diffusion coefficient of the lithium ion in the cathode. The study demonstrates the value of electrochemical impedance spectro scopy in investigating failure mechanisms. The approach and methodolog y followed here can be extended to other rechargeable lithium battery systems.