Development of Carbon Nanomaterials/Transition Metal Oxides Based Hybrid Composites as High Performance Anode Materials for Lithium- Ion Batteries

Abstract

There has been a substantial increase in the use of lithium-ion batteries in a variety of portable electronics and electric gadgets. Graphite is most commercially used anode material in LIBs owing to ecofriendliness, long cycle life, good electronic conductivity, low cost, abundance and low volume changes. However, it displays unsatisfying theoretical specific capacity of 327 mAhg- 1 and volumetric capacity of 850 mAhcm- 1 which, hardly meet the requirements for large scale applications (e.g., electric vehicles). Therefore, research is constantly conducted to find good substitute of graphite as anode material. In this context, two dimensional materials such as transition metal oxides (TMOs) have drawn considerable attention as a better substitute of graphite owing to superior electrochemical performance, good specific capacity (between 700 and 1200 mAh g- 1) and chemical activity, but application of TMOs is hindered by the capacity decay due to huge volume variation, poor electrical conductivity and slow ion diffusion. Multiple strategies have been proposed to avoid these kinds of problems and to improve electrochemical performance. One attractive approach is to prepare variety of nanostructures including nanorods, nanosheets, porous spheres and nanowires with controlled morphology and dimension and other effective method is to combine TMOs with carbonaceous materials such as multi-walled carbon nanotubes (MWCNTs). MWCNTs is attractive owing to its high aspect ratio, good mechanical properties, high electrical conductivity, remarkable thermal conductivity, good mechanical and chemical stability that can effectively reduce volume expansion and improve the electrode’s rate capability and reversible capacity. The structure and tensile strength of MWCNTs not only provide high electrical conductivity, structural flexibility, high surface to volume ratio and chemical stability but also prevent aggregation of nanoparticles and volume expansion/contraction. Therefore, nanocomposite of electrically conductive and flexible MWCNTs anchored with TMO can prove to be a good candidate with superior electrochemical performance in LIBs. In order to overcome further limitations and to increase cyclic stability of anode materials, polyaniline (PANI) has been considered one of the promising polymers due to its high conductivity, low cost, chemical and environmental stability, distinctive physical and electrochemical properties. In this work, a suitable amount of conducting PANI coating was achieved to increase the surface electrical conductivity and to prevent cracking and pulverization of TMOs electrode. PANI coating also promotes Li+ ion conductivity, vi buffers volume changes, maintains structural integrity during cycling, prevents side reactions between electrode and electrolyte, enhance electronic/ ionic transport, suppresses overproduction of SEI and facilitates high electron transportation because of its large surface area and small size. Co-precipitation method was used to synthesize MoO3, and multi-walled CNTs (MWCNTs) were introduced into the active material. Moreover, these materials were uniformly coated with PANI using in situ chemical polymerization. MoO3-(CNT)12%- PANI exhibited high discharge capacities of 1382 mAhg-1 and 961 mAhg-1 at current densities of 50 mAg-1 and 100 mAg-1, respectively. The homogenous nanocomposite of Cr2O3-MWCNTs and PANI exhibit good electrochemical performance. A discharge capacity of Cr2O3-MWCNTs(12%) -PANI is found to be 815 mAh g-1 at 100 mA g-1 with coulombic efficiency of 97.5 %. Moreover, the nanocomposite exhibits good rate capability and cyclic stability. A discharge capacity of 840 mAhg-1 was observed in case of WO3-(CNT)12%-PANI nanocomposite at current density of 100 mAg-1 with coulombic efficiency of 90.40%. Furthermore, WO3-(CNT)12%-PANI nanocomposite showed stable rate and cycling performance at higher current densities. Hence, WO3- (CNT)12%-PANI nanocomposite could be a good anode material for lithium-ion batteries. Similarly, Cr2O3, WO3 and MoO3 anode materials were also synthesized with reduced graphene oxides and PANI coating. The WO3-(RGO)12%-PANI composite electrode exhibited remarkable reversible discharge capacity (~1188 mAhg-1 at 100mAg-1), and excellent cycling stability (770.23 mAhg-1 at 400mAg-1 after 30 cycles). Hence, WO3- (RGO)12%-PANI nanocomposite could be a good anode material for lithium-ion batteries. Cr2O3-(RGO)12%-PANI exhibited discharge capacity of 891.81mAhg-1 at 100mAg-1 and 535.8mAhg-1 at 400mAg-1 after 30 cycles, while MoO3 –(RGO)12%- PANI showed discharged capacity of 1027.6 mAhg-1 at 100 mAg-1 and 656.8 mAhg-1 at 400 mAg-1 after 30 cycles.