Axial expansion of Ni-doped TiO2 nanorods grown on carbon nanotubes for favourable lithium-ion intercalation

Abstract

The serious worldwide competition of energy efficient materials has led the pathway for many materials previously not focused on energy storage applications. In this report, Ni-doped TiO2/MWCNTs (NixTi1−xO2/MWCNTs) nanocomposites were synthesized by surfactant-assisted controlled hydrolysis approach taking advantage of the synergistic interplay between MWCNTs and Ni-doped TiO2 leveraging both the electrode performance and stability. At an optimal 5% doping of Ni the electrode showed 241.3 mAh g−1 capacity at C/10 for 80 cycles, moreover an excellent rate capacity (154.1 mAh g−1) is also demonstrated even at a high rate of 20 C. The lower angle shift and enlargement of TiO2 unit cell from XRD results indicate that Ni is occupying Ti position in TiO2 matrix. The increase in the intensity of t2g and eg bands in O K edge NEXAFS point to the effective hybridization between Ni 3d and O 2p orbitals. Ni and Ti L3,2 edge from NEXAFS spectra clearly reflect 2+ and 4+ valence states of Ni and Ti, respectively. C K edge NEXAFS provides clear evidence for a charge distribution and chemical bonding between NixTi1−xO2 nanorods and MWCNTs. Ex-situ XANES studies of lithiated samples have proved that Ti and Ni K edge shifts to lower energy upon increased doping concentration while ex-situ XRD points towards the lattice expansion upon Li-insertion that seems to be most favoured for Ni0.05Ti0.95O2/MWCNTs sample. This work offers new outlooks for electrode fabrication with a deep insight into structural alterations associated with the charging-discharging behaviour in the nanocomposite electrodes for battery applications.