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

Electrochemical properties of a LiMn₂O₄ film in 1 M LiPF₆/PC + EC solution was studied by means of the electrochemical quartz crystal microbalance (QCM) at an elevated temperature (50°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°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°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 λ-MnO₂ as an intermediate in the dissolution reaction.