Electrochemical stability of thin film LiMn2O4 cathode in organic electrolyte solutions with different compositions at 55 °C

A survey of the electrochemical stability of electrostatic spray deposited thin film of LiMn2O4 was performed in LiClO4-EC-PC, LiBF4-EC-PC, and LiPF6-EC-PC solutions at 55 C. The solution resistance, the surface film resistance, and the charge-transfer resistance were all found to depend on the electrolyte composition. Among the LiX-salts studied, the lowest charge transfer-resistance, and surface layer resistance were obtained in LiBF4-EC-PC solution. There is no major influence of the electrolyte solution compositions upon lithium ion transport in the LiMn2O4 bulk at 55 degreesC. The diffusion coefficient of lithium in the solid phase varied within 10(-10)-10(-8) cm(2) s(-1) in the three solutions. In general, it seems that in LiBF4 solutions, the surface chemistry is the most stable in the three solutions examined, and hence the electrode impedance in LiBF4 solutions was the lowest. In LiPF6 solutions, HF seems to play an important role, and thus, the electrode impedance is relatively high due to the precipitation of surface LiF. (C) 2002 Elsevier Science Ltd. All rights reserved.