Electrochemical analysis of thin film electrolytes and electrodes for application in rechargeable all solid state lithium microbatteries

The suitability of two important electrochemical experimental methods, impedance spectroscopy and coulometric titration of ion insertion and extraction compounds, has been examined for the investigation of thin film electrolytes and electrodes. These solid electrolytes and electrodes are employed in rechargeable lithium microbatteries which may be integrated into microchips and may serve as power sources for microstructures such as micromotors fabricated by the LIGA technique. Thin solid lithium electrolyte films with thicknesses of the order of 1 mu m have been rf-sputtered from a 4 '' x 1/4 '' uniaxially hot pressed LiBO2 target. The ionic conductivity sigma of the resulting thin solid electrolyte films and their activation energy E-A have been determined by impedance spectroscopy. The investigation of thin solid electrolyte films required the development of a special experimental setup. Thin electrode films with thicknesses in the range of several hundred nm were sputtered from 4 '' x1/4 '' uniaxially hot pressed C and Li4Fe0.5. Ti4.5O11.75 targets. Coulometric titration experiments allow us to conclude that lithium can be reversibly inserted into and extracted from bulk graphite like carbon according to Li + 6C --> LiC6 at nearly 0 V vs Li while in the case of bulk Li4Fe0.5Ti4.5O11.75 2 5 Li per formula unit can be reversibly inserted and extracted at 2.3 V vs Li according to the reduction of iron and at 1.55 V vs Li due to the reduction of titanium. In the present paper we present the effect of thin film electrodes on coulometric titration curves. (C) 1997 Published by Elsevier Science Ltd.