Investigation of Stresses Generated during Lithium Transport through the RF Sputter-Deposited Li1 − δCoO2 Film by a DQCR Technique

Abstract

In this work, stresses generated during lithium transport through radio-frequency (rf) sputter-deposited films with different thicknesses were investigated by a double quartz crystal resonator (DQCR) technique. For this purpose, in situ resonant frequency changes of the -coated AT- and BT-cut quartz crystals were first recorded along with the galvanostatic charge (lithium deintercalation) and discharge (lithium intercalation) curves obtained in a 1 M -propylene carbonate solution. From the measured resonant frequency changes, the lateral stresses of the films were then estimated as a function of lithium stoichiometry, (1−δ). Compressive and tensile stresses were developed in the films during the lithium deintercalation and intercalation, respectively. The remarkable variation of compressive and tensile stresses with lithium stoichiometry appeared in a two-phase (a Li-poor α-phase and a Li-rich β-phase) region. Compressive and tensile stresses decreased in absolute magnitude with increasing film thickness. The contribution of the electrostrictive stress to the total stress was theoretically calculated to be about From the extremely small contribution of the electrostrictive stress, it is strongly suggested that the stresses result mainly from the volume contraction and expansion of the films due to the lithium intercalation and deintercalation, respectively. Furthermore, the relaxation of the compressive stress was developed during the lithium deintercalation in a single α-phase region, causing the cracking of the films. © 2003 The Electrochemical Society. All rights reserved.