Three-Dimensional Amorphous TiO2 Thin-Film Electrodes Deposited on Micro-Pillars By Spatial Atomic Layer Deposition for Li+-Ion Batteries

Abstract

A promising route to improve Li+-ion batteries in terms of capacity and rate-performance, is the development of all solid-state three-dimensional (3D) thin-film Li+-ion batteries. For this, the use of amorphous TiO2 (am-TiO2) as a 3D thin-film electrode was investigated. Using spatial atomic layer deposition (s-ALD), ~100 nm thick am-TiO2 films were deposited on high aspect ratio silicon micro-pillars. Due to the self-limiting nature of atomic layer deposition, high quality, uniform and conformal films can be deposited even on 3D structures. Spatial ALD is a fast and upscaleable technique which can significantly lower the cost above conventional ALD. The role of the am-TiO2 s-ALD deposition parameters were investigated for optimal conformal coating. With the optimized process, the thickness variation was at most ~20% for layers deposited on an aspect ratio of 25. Furthermore, the am-TiO2 layers using our process are shown to have a very high capacity and rate-performance, far above that for traditional anatase TiO2 thin-films. At a rate of 1C, near theoretical lithium insertion/extraction (i.e. Li1TiO2) is achieved of ~1150 mAh /cm3. Increasing the rate to 20C (theoretical charging in 3 minutes), results in a capacity of ~890 mAh/cm3, which is still above the average capacity of anatase TiO2 of 769 mAh/cm3 (i.e. Li0.6TiO2), which can typically only be achieved for slow C-rates (C-rate << 1C). This report shows for the first time the use of s-ALD to deposit am-TiO2 thin-films on 3D structures with ultra-fast lithium-ion insertion/extraction capabilities. Figure 1