Electrochemical quartz crystal microbalance investigations of LiMn2O4 thin films at elevated temperatures

Electrochemical properties of a LiMn2O4 Blm in 1 M LIPF6/PC + EC solution was studied by means of the electrochemical quartz crystal microbalance (QCM) at an elevated temperature (50 degrees C). The film preparation was conducted by an electrostatic spray deposition, which enabled us to obtain a uniform and dense film of LiMn2O4 on a QCM electrode at low temperature (400 degrees C) to avoid the thermal damage of the quartz. During the galvanostatic charge-discharge experiment, the mass of electrode specimen increased, most likely due to the formation of a passivation film. If an as-prepared electrode was only immersed in the LiPF6 solution at 50 degrees C, the mass of electrode decreased steadily, resulting eventually in extinction of the manganese film. Such manganese dissolution was attended by a shift of open circuit voltage from 3.8 to 4.3 V vs. Li, suggesting a formation:for lambda-MnO2 as an intermediate in the dissolution reaction. (C) 2000 The Electrochemical Society. S0013-4651(99)09-053-9. All rights reserved.