Solid-state electrochemical kinetics of Li-ion intercalation into Li1-xCoO2: Simultaneous application of electroanalytical techniques SSCV, PITT, andEIS

The electroanalytical behavior of thin Li1-xCoO2 electrodes is elucidated b y the simultaneous application of three electroanalytical techniques: slow- scan-rate cyclic voltammetry (SSCV), potentiostatic intermittent titration technique, and electrochemical impedance spectroscopy. The data were treate d within the framework of a simple model expressed by a Frumkin-type sorpti on isotherm. The experimental SSCV curves were well described by an equatio n combining such an isotherm with the Butler-Volmer equation for slow inter facial Li-ion transfer. The apparent attraction constant was -4.2, which is characteristic of a quasi-equilibrium, first-order phase transition. Imped ance spectra reflected a process with the following steps: Li+ ion migratio n in solution, Li+ ion migration through surface films, strongly potential- dependent charge-transfer resistance, solid-state Li+ diffusion, and accumu lation of the intercalants into the host materials. An excellent fit was fo und between these spectra and an equivalent circuit, including a Voigt-type analog (Li+ migration through multilayer surface films and charge transfer ) in series with a finite-length Warburg-type element (Li+ solid-state diff usion), and a capacitor (Li accumulation). In this paper, we compare the so lid-state diffusion time constants and the differential intercalation capac ities obtained by the three electroanalytical techniques. (C) 1999 The Elec trochemical Society. S0013-4651(98)05-018-6. All rights reserved.