Electrochemical Impedance Spectroscopy of Lithium‐Titanium Disulfide Rechargeable Cells

The two‐terminal alternating current impedance of lithium‐titanium disulfide 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 cell leads to evaluation 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 evaluated for cells cycled five times have been compared with the parameters of cells that have been cycled over 600 times. The findings are that the combined ohmic resistance of the electrolyte and electrodes suffers a ten‐fold increase after extended cycling, while the charge‐transfer resistance and diffusional impedance at the interface are not significantly affected. The results reflect the morphological change and increase in area of the anode due to cycling. The study also shows that overdischarge of a cathode‐limited cell causes a decrease in the diffusion coefficient of the lithium ion in the cathode. The study demonstrates the value of electrochemical impedance spectroscopy in investigating failure mechanisms. The approach and methodology followed here can be extended to other rechargeable lithium battery systems.