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Title: Synthesis, Characterization and Electrochmical Performance of Modified Titania/Carbon Nanotube Composites as Anode Material for Lithium-ion Btteries
Authors: , Ata-ur-Rehman
Keywords: Chemistry
Issue Date: 2019
Publisher: Quaid-i-Azam University, Islamabad.
Abstract: The present efforts in energy storage are directed more towards modifying the secondary battery systems. Titania (TiO2) is an appropriate substitute for anode material in lithium ion batteries (LIBs) owing to its surpassed structural stability and high safety during the prolonged charge/discharge cycles. The low conductivity issues associated with this material has been a constraining factor influencing its rate capability and cycling performance. From this viewpoint, multiwalled carbon nanotubes (MWCNTs), a zero gap semiconductor, with distinctive electronic properties, together with superb electrochemical, thermal, optical, and mechanical properties that are much more than the other carbon allotropes such as diamond, graphite and fullerene. More importantly, MWCNTs has also proved their effectiveness upon compositing with a metal oxide or metallic nanoparticles to augment the electrochemical performance. In this work, M-TiO2/MWCNTs (M = Mn, Ni, Co, Cu) were synthesized by surfactant assisted controlled hydrolysis approach taking the advantage of the synergistic interplay between MWCNTs and M-doped TiO2 leveraging both the electrode performance and stability. Exploiting synchrotron-based spectroscopy (NEXAFS, XANES and ex-situ XRD) and microscopy techniques, we examined the structure of metal-doped TiO2/MWCNTs nanocomposites characterized by varied morphology and structural order at the nanoscale. This entire investigation of the electronic, morphological, and structural properties enabled us to recognize and unveil the electrochemical transformations upon cycling. A convenient, cheap and mild covalent functionalization route for multiwalled carbon nanotubes (MWCNTs) has been developed for the first time. The results consistently iv confirmed the formation of carboxyl functionalities on MWCNTs, while the structure of MWCNTs has remained relatively intact. At an optimal 5% doping of Mn, Ni, Cu and 7% doping of Co the electrode showed 176.4, 241.3, 214.1 and 177.6 mAh g‒1 capacity at C/10 for 80 cycles, moreover an excellent rate capacity is also demonstrated at a sufficiently high rate of 20 C. The lower angle shift and enlargement of TiO2 unit cell from XRD results indicate that metal dopants are substituting Ti atoms from the pure anatase TiO2 matrix. The increase in the intensity of t2g and eg bands in O K-edge NEXAFS point to the effective hybridization between metal 3d and O 2p orbitals. Metal and Ti L3,2 edge from NEXAFS spectra clearly reflect 2+ and 4+ valence states of metal and Ti, respectively. C K-edge NEXAFS provides clear evidence for a charge distribution and chemical bonding between MxTi1-xO2 nanoparticles and MWCNTs. Ex-situ XANES studies of lithiated samples have proved that Ti and metal K edge shifts to lower energy upon increased doping concentration while ex-situ XRD points towards the lattice expansion upon Li-insertion. This work offers new outlooks for electrode fabrication with a deep insight into structural alterations associated with the charging-discharging behaviour in the composite electrodes for battery applications.
Gov't Doc #: 19141
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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