Electrochemical STM Observation of Li1 + xMn2 − xO4 Thin Films Prepared by Pulsed Laser Deposition

Abstract

Spinel ( and 0.03) thin films were prepared by pulsed laser deposition (PLD). The ratio of thin films were controlled by the energy fluence of the laser beam in the PLD method. Changes in surface morphology of the thin films after potential cycling in different potential ranges were observed in /propylene carbonate by electrochemical scanning tunnel microscopy (STM). The discharge capacities of the nearly stoichiometric electrode faded rapidly upon charge/discharge cycling in a higher potential region . After repeated cycling in the higher potential region, smaller round-shaped particles of around in diameter were newly formed on the electrode, and the entire surface was covered with them. These small particles were likely to be newly formed from the electrolyte solution through dissolution/precipitation reactions. Capacity-fading with repeated cycling was suppressed for the lithium-ion excess thin film electrode compared to . In addition, no small, round-shaped particles appeared on even after the 75th cycle. Based on these results, it was concluded that the observed changes in morphology in the higher potential region are closely related to the observed capacity-fading of the nearly stoichiometric .