(71c) Engineering Lithium-Containing Ionic Conductive Thin Films By Atomic Layer Deposition for Lithium-Ion Battery Applications

Lithium (Li)-ion batteries have drawn much attention for their outstanding performance in portable electronic applications. These batteries have the potentials to function as miniaturized power source for microelectromechanical (MEMS) devices through the fabrication of 3-dimensional configurations. To fabricate a fully functional 3D Li-ion microbattery, however, an ultra-thin and highly conformal electrolyte layer is required to coat the 3D electrodes. The solid oxide Li-ion conductor, lithium aluminosilicate (Li_xAl_ySi_zO, LASO), synthesized by atomic layer deposition (ALD) is a promising electrolyte material for 3D battery applications owing its adequate ionic conductivity as well as improved electrode stability.

The self-limiting characteristic of ALD allows for precise control of thickness and composition of complex oxides and results in a highly conformal and pinhole-free coating even on highly complex structures such as high aspect ratio 3D electrodes. The metal precursors, lithium t-butoxide (LTB), trimethylaluminum (TMA), tris(tert-butoxy)silanol (TTBS), and tetraethylorthosilicate (TEOS) were used to form Li_xAl_ySi_zO via ALD. In-situ FTIR was implemented to study the incubation time and growth mechanisms of each constituent oxide on the other to improve the controllability of deposited films. In-situ FTIR studies revealed that the growth mechanism of silicon oxide is strongly affected by the underlying oxide layer, exhibiting different surface reaction mechanisms during the incubation stage.

Li-ion conductivities and the activation energy of as-deposited LASO/LAO/LSO films with respect to lithium contents and the film thickness were studied. The LASO ALD coating on 3D carbon array posts were confirmed to be conformal and uniform using transmission electron microscopy (TEM) imaging. A Li-ion half-cell consisting of LASO coated on 3D carbon array electrode has shown promising improvement in efficiency when compared to bare electrode. Lithiation cycling tests of thin LASO/LAO/LSO films were found to be functions of both composition and thickness. The reversibility and kinetics of insertion as well as the effect on the cycling stability from the direct deposition of LASO/LAO/LSO on potential anode materials, SiNWs were also investigated using in-situTEM observations during lithiation.