Multilayered Approach for TiO₂ Hollow-Shell-Protected SnO₂ Nanorod Arrays for Superior Lithium Storage

The ability to control the growth of materials with nanosized precision as well as a complex hollow morphology provides rationale for the study of systems comprising both characteristics. This study explores the design of TiO₂ hollow nanotube shells deposited by atomic layer deposition (ALD) on vertically aligned SnO₂ nanorods grown using the vapor-liquid-solid technique. The sacrificial template approach in combination with highly conformal coating advantages of ALD resulted in a highly reproducible method to create a large surface area covered by TiO₂-protected SnO₂ nanorods, which are about 60-100 nm in diameter and approximately 1 μm in length. ZnO was used as a sacrificial layer to create a 30 nm gap between SnO₂ nanorods and 10 nm of TiO₂ shells. Chemical etching of the sacrificial layer was used to create the desired hollow nanocomposite. A coin half-cell battery has been assembled using the TiO₂-protected SnO₂ nanorods as an anode electrode and lithium foil as a counter electrode and tested for lithium storage during 70 cycles of charge/discharge in a range of 0.5-2.5 V. The TiO₂ hollow shell functioned as a good and robust enhancer for both absolute capacity and current rate capabilities of vertically aligned SnO₂ nanorods; an improvement in cyclic stability was also observed. This advanced self-standing hollow configuration provides several unique advantages for energy storage device applications including enhanced lithiation for superior energy storage performance.