Progress in three-dimensional (3D) Li-ion microbatteries

Progressing from 2D to 3D thin-film microbattery structures represents an important paradigm shift in the development of electrochemical power sources. The development process of three-dimensional microbatteries (3D-MB) on a perforated substrate has to solve complicated technical barriers, such as insertion and deposition of a sandwich of high-capacity thin cathode and ion-conducting membrane in long (500 mu m) and narrow (< 50 mu m) channels. In this study, we investigate composite thin-film cathodes that allow 2.0 - 3.5 times increase of MB capacity for a given footprint over our previous 3D-MB with conventional thin-film battery cathodes. The composite cathodes are obtained by electrodeposition from the bath modified by PEGDME and PEO additives of different molecular weights and concentrations. SEM, XPS, TOFSIMS and electrochemical characterizations were performed to elucidate the source of the improved MB performance. Experimental results obtained in this work show that the addition of polymeric compounds to the electrolytes significantly improves the structure and electrochemical behavior of electrodeposited molybdenum sulfide cathode materials. A semi-3D-on-MCP cell with a composite cathode exhibits a stable cycle life with about 3.5 mA h/cm(2) reversible capacity, 20 to 30 times that of a planar 2D thin-film cell with the same footprint and about twice that of semi-3D cells with pristine cathodes. (c) 2006 Elsevier B.V. All rights reserved.