Charge-discharge stability of graphite anodes for lithium-ion batteries

A graphite powder disk sandwiched between two nickel screens was used as a lithium-insertion working electrode. Electrochemical impedance spectroscopy (EIS), galvanostatic intermittent titration (GIT) using pulsed microcurrent, and in-situ intrinsic resistance measurements were used for the evaluation of kinetics and intrinsic (i.e. physical) resistance changes during charge-discharge cycling from room temperature to elevated temperatures. The investigation of the thermal stability of the electrolyte at elevated temperature used an EIS study of a palladium electrode in the electrolyte. EIS measurements for electrochemical reaction and intrinsic resistances of a graphite electrode show that the first high-frequency depressed semicircle is due to the 'solid electrolyte interphase' (SEI) film, although it is also influenced by the electrode contact impedance. The growth of the SEI film on the MCMB 10-28 graphite electrode surface with cycling, results in a decline in kinetic rate and a corresponding increase in contact resistance giving rapid capacity fade. The high stability of the capacity of JM 287 electrodes is due to the slow increase in SEI film thickness on their surfaces. Although new SEI films were formed on the originals at elevated temperature, the kinetics were still more rapid than at room temperature in the initial cycling. (C) 2001 Elsevier Science B.V. All rights reserved.