Effect of Carbon Nanohorns on the Electrochemical Performance of Orthorhombic, Hexagonal and Monoclinic Tungsten Trixode Nanoplatelets As High-Energy Anode Material for Lithium-Ion Batteries

Lithium-ion batteries (LIB) are currently the most promising energy storage systems used in a wide range of applications from portable electronic devices to electric vehicles. Tungsten trioxide (WO 3 ), has recently been studied as anode material for LIB due to its high theoretical capacity of 693 mAhg -1 , high melting point (1473 °C) and strong mechanical stability. However, the large first cycle irreversibility as well as the long-term cyclic stability, are the major challenges associated with the application of WO 3 . Several approaches like controlling morphology, creating oxygen vacancy and composite with carbon materials have been tried to overcome those problems and obtain a stable electrochemical performance. It is well-known that the electrochemical performance of the electrode materials is strongly influenced by the microstructure and morphology of the material. Thus, the synthesis of nanostructured WO 3 with controlled crystal structure, morphology and dimensionality is a vital task. Though WO 3 has been demonstrated as an anode material for LIB in different type of crystal structure and morphology, the effect of the crystal structure with a specific morphology on the electrochemical performance of WO 3 has not been reported so far. Herein, we have investigated the electrochemical performance of orthorhombic, hexagonal and monoclinic WO 3 nanoplatelets. The effect of carbon nanohorns (CNH) on the enhancement of capacity and long-term cyclic stability of orthorhombic, hexagonal and monoclinic WO 3 nanoplatelets have also been studied. CNH is a well-studied material as a composite with metal oxides. It enhances the cyclic stability of metal oxides due to its good electric conductivity, large surface area and good mechanical strength. Orthorhombic, hexagonal and monoclinic WO 3 nanoplatelets were synthesized via microwave synthesis method and CNH were prepared by the arc-discharge method. The materials were characterized by XRD, FTIR, Raman spectroscopy, TGA, SEM and TEM. WO 3 showed plates like morphology with a uniform size of ~150 nm and a thickness of ~15 nm. Electrochemical performance of WO 3 and WO 3 /CNH composites were studied by the addition of 10-30 wt% of CNH. Pure orthorhombic WO 3 nanoplatelets showed a first discharge and charge capacity of ~890 and ~400 mAhg -1 respectively at a current density of 50 mAg -1 with a capacity retention of ~260 mAhg -1 after 100 cycles (voltage range of 3.0 to 0.05 V). Whereas, the composite electrode of orthorhombic WO 3 with 30 wt % CNH exhibited a first discharge and charge capacity of ~1100 and ~540 mAhg -1 at a current density of 50 mAg -1 with a capacity retention of ~450 mAhg -1 after 100 cycles. The electrochemical performance of the hexagonal and monoclinic WO 3 and its composites with CNH have also been studied. The results of the rate capability and long-term stability of the composites will be discussed in detail during the presentation.