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

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 (Ni_xTi_1−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 t_2g and e_g bands in O K edge NEXAFS point to the effective hybridization between Ni 3d and O 2p orbitals. Ni and Ti L_3,2 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 Ni_xTi_1−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 Ni_0.05Ti_0.95O₂/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.