Electrogravimetric study of the stress developed during lithium transport through the RF sputtered Li1-delta CoO2 film electrode

Abstract

The present work involves the stress change in the oxide during the lithium intercalation into and deintercalation from the sputter-deposited Li1-deltaCoO2 film in a 1 M solution of LiClO4 in propylene carbonate measured by using electrochemical quartz crystal microbalance (EQCM) technique. The changes in the resonant frequency of the Li1-deltaCoO2-coated quartz crystal were first simultaneously recorded along with the galvanostatic discharge curve and the cyclic voltammogram (CV). Next, under the assumptions that the pure lithium ion intercalation and deintercalation occurs and that the resonant frequency change is due only to the true mass of the intercalated lithium ion, the resonant frequency changes were theoretically calculated. The stress changes during the lithium intercalation and deintercalation were quantitatively determined from the difference between the measured and the calculated frequency changes. The stress changes remained almost constant in the presence of a single phase, whereas they showed a steep change in the coexistence of Li-poor alpha- and Li-rich beta-phases. This result indicates that the phase transformation of alpha to beta and vice versa accompanies the large amount of the lateral stress in the deposited film.