Titanium oxide based materials, including both Li-titanates and various TiO2 polymorphs are promising alternatives to carbonaceous anode materials for Li-ion rechargeable batteries because of their higher voltage operation (enhanced safety), relatively small volume expansion upon lithiation, minimal electrode/electrolyte interface reactivity (nonexistent SEI layer), inexpensive and biocompatible non-toxic nature. Nanoscale three-dimensional (3D) architectures of current collectors for microbatteries would significantly increase the areal capacity over their planar counterparts, if the active Li-insertion electrode material could be coated conformally. The nanoscale thickness of the active electrode layer in combination with an electronically conducting 3D nanoarchitecture of the current collector should enable high areal capacity and fast charge-discharge rates.

Atomic layer deposition (ALD) is capable of growing conformal ultra thin films on complex 3D surface morphologies. We have used ALD to grow conformal layers of titanium oxide and lithium titanium oxide on various 3D nanoarchitectures including high aspect ratio nanoporous Al2O3 templates, template-electrodeposited 3D metal nanowire arrays and carbon nanotube buckeypapers. The precursors for ALD used in this study include lithium t-butoxide, tetrakis(dimthylamido)titanium (TDMAT) and water. We have been able to grow conformal layers with controllable thickness at nanometer scale uniformly coated around the high aspect ratio features.

A significant increase in areal capacity (up to two orders of magnitude) was obtained in anatase TiO2 coated Ni nanowire arays over 2D thin film electrodes of a similar footprint. ALD TiO2 coated buckeypapers showed specific capacities in excess of 200 mAh/g at C/10, with 70% of the capacity retained at 5C. At 1C, 95% of the initial capacity is retained after 500 charge/discharge cycles. ALD deposition of LiOx and TiOx and subsequent thermal annealing leads to a combination of TiO2 and spinel lithium titanium oxide (Li4Ti5O12) phases. The presence of these phases is reflected in XRD as well as electrochemical charge-discharge curves. This presentation will discuss a systematic study of the ALD growth of 3D titanium oxide and lithium titanium oxide nanostructures and their electrochemical characterization.