Modern microelectronic devices such as backup power for computer memories, MicroElectroMechanical Systems (MEMS), medical implants, smart cards, Radio-Frequency Identification (RFID) tags and remote sensors have necessitated the development of high performance power sources at the microscale. In this context, the development of three-dimensional (3D) microbatteries forms a viable alternative to provide high volumetric energy densities to meet the demands of these devices.¹ The development of nanoarchitectured electrodes is one of the most promising approaches to realize the 3D paradigm of microbatteries.² Among all the potential anode materials, TiO₂ nanotubes (TiO₂-NTs) possess some remarkable characteristics for the design of 3D Li-ion microbatteries. Self-organized porous nano-architecture allows a good diffusion of Li ions in the pores of the structures and the 1D morphology allows an efficient charge transfer along the axis of the tube that results in a good apparent electronic conductivity of the TiO₂-NTs layer when compared to a film composed of nanoparticleS ^{3, 4}. TiO₂ (anatase or rutile) can accommodate only 0.5 Li⁺ per formula unit, corresponding to a theoretical capacity of 168 mAh g^-1. Hence, several approaches have been investigated to improve the overall performance of TiO₂-NTs for the design of high-performance Li-ion microbatteries. Doping with aliovalent ions like Niobium (Nb⁵⁺) is also a facile strategy to modify the electronic properties of titanium oxide and thereby enhance the electrochemical performance.^5,6

We report the fabrication of self-supported Nb doped TiO₂-NTs by anodization of Nb/Ti alloys devoid of any carbon additives or binders. An increase in the capacity of the TiO₂-NTs was observed as the doping concentration for Nb was increased. Such a composition of 10 wt.% Nb doped TiO₂-NTs (Nb10-TiO₂-NTs) showed a first cycle capacity of 200 mAh.g^-1 (144 µAh.cm^-2) compared to pristine TiO₂-NTs which gave a capacity of 115 mAh.g^-1 (78 µAh.cm^-2) at C/10 rate. Galvanostatic cycling tests at various C rates revealed the influence of Nb doping in the TiO₂-NTs which is shown in Fig.1 (a) and (b). Compared to pristine TiO₂-NTs, the discharge capacities of doped nanotubes are improved and almost doubled when the Nb concentration reaches 10 wt.%. Besides a good cycling behaviour at multiple C-rates, an overall capacity retention of 86.7 % is achieved after 100 cycles. In this work, we will discuss the synthesis, and various characterization techniques like XRD, XPS, Impedance spectroscopy results of the pristine and the Nb doped TiO₂-NTs. ⁷

References

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