Synthesis and Electrochemical Properties of ZnO Nanotube Materials

Abstract

Zinc oxide (ZnO) is one of the widely used metal oxide materials in industry. It is cheap and chemically stable. In addition, it has a wide bandgap (3.37 eV) and a high binding energy in a crystalline state (60 meV), which ensure efficient exciton emission. Based on these characteristics, ZnO has been applied from traditional industry such as white pigment and sunscreen to high technology industry that includes semiconductors, optical materials, conductive films, solar cells, biosensors, and light emitting diodes. Nanostructured ZnO materials can be synthesized by various methods such as hydrothermal, vapor deposition, and vapor-liquid-solid processes. The shapes of the nanostructure are rod, wire, tube, ring, spring, sheet, propeller, etc. These various nanostructures can be beneficial for enabling fast electronic and ionic transport in electrochemical energy storage device applications such as rechargeable batteries and supercapacitors. However, the low electronic conductivity of ZnO is still a problem when it is used as electrode materials for lithium rechargeable batteries. In the present work, carbon coated ZnO nanotube materials were formed by a simple one-pot synthesis method. Conventional ZnO nanotube structures have been synthesized by relatively complex methods and have usually grown on the substrates. Here, free-standing ZnO nanorod materials were prepared by a hydrothermal process and then they were transformed into nanotubes with simultaneous carbon-coating during annealing process. The ZnO nanotube structure is suitable for alleviating volume changes for Li insertion and extraction during cycling and carbon coating enables fast electronic transport with a buffering effect for volume changes of the active materials.