ALD Al₂O₃‑Coated TiO₂ Nanotube Layers as Anodes for Lithium-Ion Batteries

The utilization of the anodic TiO₂ nanotube layers, with uniform Al₂O₃ coatings of different thicknesses (prepared by atomic layer deposition, ALD), as the new electrode material for lithium-ion batteries (LIBs), is reported herein. Electrodes with very thin Al₂O₃ coatings (∼1 nm) show a superior electrochemical performance for use in LIBs compared to that of the uncoated TiO₂ nanotube layers. A more than 2 times higher areal capacity is received on these coated TiO₂ nanotube layers (∼75 vs 200 μAh/cm²) as well as higher rate capability and coulombic efficiency of the charging and discharging reactions. Reasons for this can be attributed to an increased mechanical stability of the TiO₂ nanotube layers upon Al₂O₃ coating, as well as to an enhanced diffusion of the Li⁺ ions within the coated nanotube layers. In contrast, thicker ALD Al₂O₃ coatings result in a blocking of the electrode surface and therefore an areal capacity decrease.