Influence of diffusion plane orientation on electrochemical properties of thin film LiCoO2 electrodes

Submicrometer LiCoO2 films have been prepared on silicon substrates with RF sputtering and pulsed laser deposition (PLD). The electrochemical activity of both types of thin film electrodes is compared using scanning cyclic voltammetry, galvanostatic and potentiostatic intermittent titration, and electrochemical impedance spectroscopy. The RF films exhibit a axis orientation and have an accessible diffusion plane alignment, unlike the c axis oriented PLD films. The preferential orientation of the host crystal lattice toward the electrolyte solution is critical for the intercalation rate and cycling efficiency. The RF films show superior electrochemical performance and faster relaxation characteristics than the PLD films. Based on the analysis of the time and frequency domain measurements a model for the electrode response is proposed. Apparently, the intercalation rate of the RF films is not diffusion-limited, but hindered by the large charge-transfer resistance, the phase boundary movement, and the hindrance by the solid electrolyte interface. (C) 2002 The Electrochemical Society.