The effect of ultrasound on lithium surfaces in propylene carbonate

Ultrasonic irradiation of lithium metal electrodes is demonstrated to erode surface layers and subsequently reduce the interfacial resistance. Dynamic impedance measurements were employed to monitor the erosion and reformation of surface layers formed on lithium electrodes placed in a propylene carbonate electrolyte in the presence and absence of ultrasound, respectively. In the presence of ultrasound a marked decrease in the resistance (ca. 310 Omega cm(2) to 225 Omega cm(2)) was observed over a 400 s period. Other experiments employing a 50 mu m diameter Cu microelectrode showed that ultrasound had a marked effect on both lithium plating and stripping. It was found that the stripping efficiency was reduced from ca. 60% under silent conditions to only ca. 18% in the presence of ultrasound. Subsequent experiments demonstrated that ultrasound efficiently removes lithium from a lithium coated copper microelectrode in the absence of any stripping or plating processes. The results demonstrate that ultrasound, under the conditions reported here, removes lithium from the surface of the microelectrode, increases the voltage required for lithium plating, reduces the interfacial resistance of films formed on lithium within a propylene carbonate electrolyte and decreases the efficiency of the stripping/plating process. (C) 1999 Elsevier Science S.A. All rights reserved.