Au-doped Co3O4 Nanotubes as Electrode Materials for Lithium Ion Batteries
The use of transition metal oxides, such as Co3O4, as positive electrode materials in lithium ion batteries (LIBs) has attracted great interest due to their high discharge-charge capacity. However, the poor capacity retention of the materials caused by large volume changes during the cycling process limits their cycle life time. Therefore I propose gold nanoparticles doped Co3O4 nanotubes as a new electrode material to improve the battery life time, which largely depends on the size and shape of the anode materials. This proposed study aims at synthesizing Au-doped Co3O4 nanotubes and investigating the effect of the nanotubular structure on the battery performance. In this proposal, Co3O4 nanotubes will be synthesized by a surfactant-assisted method for the first time. The nanotubular structure with a high surface area and porous wall surfaces can provide increased active sites for lithium ion diffusion, which will greatly elongate the cycling lifetime. The Au nanoparticles incorporated in the nanostructure are expected to further enhance the electrochemical performance by facilitating the lithium ions intercalation. This noble-metal-doped nanotubular structure can also be applied to other transition metal oxides as electrode materials to facilitate the development of LIBs with higher rate capacity and longer cycle life. 1. Introduction
Lithium ion batteries (LIBs) have been the dominant power source for portable electronics because of their high energy density and design flexibility. However, the ever-growing global need for high-power energy source, especially for large-scale applications, such as electric cars, has driven much research efforts towards the development of next generation LIBs with better performance electrode materials.1-3 As a member of spinel-type transition metal oxides, Co3O4 possesses excellent electronic and chemical properties. In particular, Co3O4 is an important ceramic material in electrochemical, catalytic and magnetic applications. As anode materials for LIBs, Co3O4 can deliver capacity three times that of the commonly used graphite (350 mA h g-1) in theory. However, they usually suffer from poor capacity retention upon cycling and poor rate capability, which remains major challenges in cell applications.4,5 These problems have been attributed to the large volume changes during repeated lithium uptake and removal reactions, which can cause local stress and eventually lead to electrode failure. One promising remedy is to prepare nanomaterials with designed structures, as growing evidence shows that the nanostructured materials can improve the electrochemical properties compared to the bulk counterpart.6-11 It is also consistent with the current trend to develop batteries in smaller dimensions. Recently researchers demonstrated that Co3O4 nanomaterials with different shapes possessed different electrochemical properties as anode materials in LIBs.12Tuning the morphology to obtain porous and high surface area can greatly enhance the capacity of the electrode.13 Therefore it is desirable to investigate Co3O4 nanostructures with different parameters, such as shape and size, to find out the optimum Co3O4 anode materials. The creation of pores and channels is a natural way to the thermodynamic stabilization of complex structures. Correspondingly, material researchers have made a lot of effort in porous materials14,15 and nanotubular structures16,17. Mesoporous materials are known for their ultra large surface areas and highly ordered pore structures, and they have shown potential applications in catalysis, gas storage and optics.15 Shaju and coworkers synthesized mesoporous Co3O4 for electrochemical use5, however, after several cycles, the materials lost their mesoporosity and become more like bulk Co3O4, therefore the fragile mesoporosity did not practically improve the...