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 reformatio
n of surface layers formed on lithium electrodes placed in a propylene carb
onate 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 exp
eriments employing a 50 mu m diameter Cu microelectrode showed that ultraso
und had a marked effect on both lithium plating and stripping. It was found
that the stripping efficiency was reduced from ca. 60% under silent condit
ions to only ca. 18% in the presence of ultrasound. Subsequent experiments
demonstrated that ultrasound efficiently removes lithium from a lithium coa
ted copper microelectrode in the absence of any stripping or plating proces
ses. The results demonstrate that ultrasound, under the conditions reported
here, removes lithium from the surface of the microelectrode, increases th
e voltage required for lithium plating, reduces the interfacial resistance
of films formed on lithium within a propylene carbonate electrolyte and dec
reases the efficiency of the stripping/plating process. (C) 1999 Elsevier S
cience S.A. All rights reserved.