| AVS 62nd International Symposium & Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+EN-WeM |
| Session: | ALD for Energy |
| Presenter: | Trevor Seegmiller, University of California at Los Angeles |
| Authors: | J. Cho, University of California at Los Angeles T. Seegmiller, University of California at Los Angeles J. Lau, University of California at Los Angeles L. Smith, University of California at Los Angeles J. Hur, University of California at Los Angeles B. Dunn, University of California at Los Angeles J.P. Chang, University of California at Los Angeles |
| Correspondent: | Click to Email |
Lithium-ion (Li-ion) batteries have demonstrated their performance in portable electronics for many years. Li-ion batteries also have the potential to be miniature power sources for microelectromechanical systems (MEMS) through 3-dimensional (3D) battery architectures. In order to fabricate a fully functional 3D Li-ion microbattery, an ultra-thin, highly conformal electrolyte layer is required to fully coat 3D electrodes. Lithium aluminosilicate (LixAlySizO, LASO), a solid oxide Li-ion conductor, synthesized by atomic layer deposition (ALD) is a promising electrolyte material for 3D battery applications due to its adequate ionic conductivity (1×10-7 S/cm) in thin film applications as well as improved electrode stability.
The self-limiting nature of ALD allows precise thickness and composition control when applied to complex metal oxides. This results in a highly conformal and pinhole-free coating on complex structures, including high aspect ratio 3D electrodes. Lithium tert-butoxide (LTB), trimethylaluminum (TMA), tris(tert-butoxy)silanol (TTBS), and tetraethylorthosilicate (TEOS) were precursors used to synthesize LASO by ALD. LASO films ranging in thickness from 6 to 12 nm exhibited Li-ion conductivity from 8.2 x 10-8 to 1.4 x 10-9 S/cm. The LASO films were also deposited on anode and cathode materials for evaluating their integration into solid state Li-ion batteries. A Li-ion half-cell consisting of LASO-coated 2D carbon anode showed reversible electrochemical behavior with coulombic efficiency reaching 98%.
Current research on Li-ion batteries is directed at creating next generation anode materials. Both silicon and germanium have received considerable study due to their high theoretical volumetric capacity (8444 A h L-1 for Li15Si4 and 7366 A h L-1 for Li15Ge4 respectively). Upon lithium intercalation, however, these anode materials undergo large volumetric expansion (~300% for Si) which compromises their mechanical integrity. We have started to carry out in situ transmission electron microscopy (TEM) studies in which the structural effects of lithium intercalation and deintercalation on silicon/germanium (Si/Ge) alloy nanowires conformally coated with LASO electrolyte are characterized . These in situ TEM studies show 40% radial expansion of the Si0.4Ge0.6 alloy upon lithium intercalation, and morphological changes upon deintercalation, with the LASO film preserved on the nanowire.