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
Authors: Sahu Sumit Ranjan , Rikka Vallabha Rao , Haridoss Prathap , Gopalan Raghavan , Prakash Raju 
Published: February 2020

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 (WO3), 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 WO3. 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 WO3 with controlled crystal structure, morphology and dimensionality is a vital task. Though WO3 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 WO3 has not been reported so far.

Herein, we have investigated the electrochemical performance of orthorhombic, hexagonal and monoclinic WO3 nanoplatelets. The effect of carbon nanohorns (CNH) on the enhancement of capacity and long-term cyclic stability of orthorhombic, hexagonal and monoclinic WO3 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 WO3 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. WO3 showed plates like morphology with a uniform size of ~150 nm and a thickness of ~15 nm. Electrochemical performance of WO3 and WO3/CNH composites were studied by the addition of 10-30 wt% of CNH. Pure orthorhombic WO3 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 WO3 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 WO3 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.