Kowsalya Palanisamy

Porous V2O5/RGO/CNT hierarchical architecture as a cathode material: Emphasis on the contribution of surface lithium storage

A three dimensional vanadium pentoxide/reduced graphene oxide/carbon nanotube (3D V2O5/RGO/CNT) composite is synthesized by microwave-assisted hydrothermal method. The combination of 2D RGO and 1D CNT establishes continuous 3D conductive network, and most notably, the 1D CNT is designed to form hierarchically porous structure by penetrating into V2O5 microsphere assembly constituted of numerous V2O5 nanoparticles. The highly porous V2O5 microsphere enhances electrolyte contact and shortens Li+ diffusion path as a consequence of its developed surface area and mesoporosity. The successive phase transformations of 3D V2O5/RGO/CNT from α-phase to ε-, δ-, γ-, and ω-phase and its structural reversibility upon Li+ intercalation/de-intercalation are investigated by in situ XRD analysis, and the electronic and local structure reversibility around vanadium atom in 3D V2O5/RGO/CNT is observed by in situ XANES analysis. The 3D V2O5/RGO/CNT achieves a high capacity of 220 mAh g−1 at 1 C after 80 cycles and an excellent rate capability of 100 mAh g−1 even at a considerably high rate of 20 C. The porous 3D V2O5/RGO/CNT structure not only provides facile Li+ diffusion into bulk but contributes to surface Li+ storage as well, which enables the design of 3D V2O5/RGO/CNT composite to become a promising cathode architecture for high performance LIBs.

Ultrasonicated double wall carbon nanotubes for enhanced electric double layer capacitance

An intense ultrasonication of the double wall carbon nanotubes (DWCNTs) causes fractures and splitting of the individual tubes. This not only generates open tips and edges in DWCNTs but also incorporates defects in the tube walls. The electric double layer capacitor (EDLC) electrodes of intensively ultrasonicated DWCNTs (U-DWCNTs) form organized layered-porous structures. The EDLC behavior of U-DWCNTs electrodes shows dramatic improvements (specific capacitance 10 times and 222 times larger than the pristine DWCNTs at scan rates 5 mV s−1 and 500 mV s−1, respectively) due to the increased wettability of electrodes and accessibility of the electrolyte ions.

Structural and Electrochemical Properties of Doped LiFe 0.48 Mn 0.48 Mg 0.04 PO 4 as Cathode Material for Lithium ion Batteries

The electrochemical properties of Mg-doped and pure olivine cathodes are examined and the lattice parameters are refined by Rietveld analysis. The calculated atomic parameters from the refinement show that doping has a significant effect in the olivine structure. The unit cell volume is 297.053(2) for pure and is decreased to 296.177(1) for Mg-doped sample. The doping of cation with atomic radius smaller than and ion induces longer Li-O bond length in octahedra of the olivine structure. The larger interstitial sites in octahedra facilitate the lithium ion migration and also enhance the diffusion kinetics of olivine cathode material. The sample with larger Li-O bond length delivers higher discharge capacities and also notably increases the rate capability of the electrode.