ALD Al2O3 Coated TiO2 Nanotube Layers As Anodes for Lithium Ion Batteries

Abstract

Alumina coatings produced by Atomic layer deposition (ALD) on electrode materials have been explored extensively. Alumina coatings generally, have been used as a protective layer for the suppression of the solid electrolyte interphase (SEI) in various electrode materials.1 But its influence on increasing the electronic conductivity of the electrode material has not been explored. TiO2 nanotubes have been recently explored due to its low volume expansion, good capacity retention even at faster kinetics.2 The utilization of anodic TiO2 nanotube layers with uniform Al2O3 coatings of different thicknesses (prepared by atomic layer deposition, ALD) as new electrode material for lithium-ion batteries (LIBs) is reported. Electrodes with very thin Al2O3 coatings (~1 nm) show a superior electrochemical performance for the use in lithium ion batteries compared to uncoated TiO2 nanotube layers. A more than two times higher capacity is received on these coated TiO2 nanotube layers (~75 µAh/cm2 vs 200 µAh/cm2 at 1 C) as well as a higher rate capability and coulombic efficiency. Reasons for this can be attributed to a better diffusion of Li+ ions within the coated nanotube layers. However, thicker ALD Al2O3 coatings result in a passivation of the electrode surface and, therefore, in a capacity decrease. Fig. 1(a) shows the influence of alumina coating with different thickness on the capacity of the TiO2 nanotube layer. Fig.1(b) shows the long term cycling of the 1 nm alumina coated and the uncoated TiO2nanotube layers at 1C. In this work, factors influencing the increase in capacity due to the alumina coating will be discussed using results from different electrochemical characterization methods. Fig. 1 (a) Galvanostatic cycling of the uncoated and the coated TiO2 nanotube layers at 1C (b) Long term galvanostatic cycling of the 1 nm thick alumina coated and uncoated TiO2nanotube layers at 1 C for 100 cycles. References 1) Jung, Y. S.; Cavanagh, A. S.; Riley, L. A.; Kang, S.-H.; Dillon, A. C.; Groner, M. D.; George, S. M.; Lee, S.-H. Ultrathin Direct Atomic Layer Deposition on Composite Electrodes for Highly Durable and Safe Li-Ion Batteries. Adv.Mater. 2010, 22, 2172-2176. 2) Ortiz, G. F.; Hanzu, I.; Djenizian, T.; Lavela, P.; Tirado, J. L.; Knauth, P.; Alternative Li-Ion Battery ElectrodeBased on Self-Organized Titania Nanotubes. Chem. Mater. 2009, 21, 63-67. Figure 1