Direct evidence on anomalous expansion of graphite-negative electrodes on first charge by dilatometry

Dilatometer was fabricated and applied to measure change in electrode thick ness of the graphite-negative electrode for Lithium-ion batteries. Anomalou s expansion was observed in the initial part of the first reduction, i.e. s o-called irreversible capacity region in voltages of 1.1-0.5 V versus Li. D uring further reduction to 0 V versus Li, the thickness of electrode increa sed monotonously as the lithium-intercalation reaction proceeded. The obser ved change in electrode thickness was larger than that of 10% expected from XRD data, due mainly to the expansion at the initial part of the first red uction. One-to-one correspondence between the electrochemical and dilatomet ric data was observed. The acoustic events occurring inside the Li/graphite cells were also measured. The effect of electrolyte on the anomalous expan sion was also examined by dilatometry in relation to the irreversible capac ity for the first reduction of graphite, and the significance of introducin g the dilatometry together with acoustic emission technique to insertion ma terials research for advanced lithium-ion batteries was discussed. (C) 2001 Elsevier Science B.V. All rights reserved.