Viscosity changes of Li battery electrolytes and their long-term effect on the frequency of EQCM electrodes

The resonant frequency of electrochemical quartz crystal microbalance (EQCM) electrodes (carbon, nickel, and aluminum) decreases gradually with time in 1 M LiCIO4/ethylene carbonate (EC) dimethyl carbonate (DMC) after the immediate frequency shift due to the presence of liquid column on the quartz crystals. It is found that the viscosity change of electrolyte is the main reason for the frequency decrease. The viscosities of five liquids (1 M LiClO4/EC + DMC, 1 M LiPF6/EC + DMC, EC + DMC, DMC, and propylene carbonate) have been measured. Systems with EC + DMC as the solvent of the lithium salt or with the solvent alone show viscosity increase in contact with the electrode, whereas none of the above liquids show viscosity change if they arc stored in glass vials. (C) 2002 The Electrochemical Society.