Due to their high specific surface area and advanced properties, TiO₂ nanotubes (TiO₂ NTs) have a great significance for production and storage of energy. In this paper, TiO₂ NTs were synthesized from anodization of Ti-6Al-4V alloy at 60 V for 3 h in fluoride ethylene glycol electrolyte by varying the water content and further annealing treatment. The morphological, structural, optical and electrochemical performances of TiO₂ NTs were investigated by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), UV-Visible spectroscopy and electrochemical characterization techniques. By varying the water content in the solution, a honeycomb and porous structure was obtained at low water content and the presence of (α + β) phase in Ti-6Al-4V alloy caused not uniform etching. With an additional increase in water content, a nanotubular structure is formed in the (α + β) phases with different morphological parameters. The anatase TiO₂ NTs synthesized with 20 wt% H₂O shows an improvement in absorption band that extends into the visible region due the presence of vanadium oxide in the structure and the effective band gap energy (Eg) value of 2.25 eV. The TiO₂ NTs electrode also shows a good cycling performance, delivering a reversible capacity of 82 mAh.g⁻¹ (34 μAh.cm⁻².μm⁻¹) at 1C rate over 50 cycles.

Carbon nanotubes (CNT) are used as anodes for flexible Li-ion micro-batteries. However, one of the major challenges in the growth of flexible micro-batteries with CNT as the anode is their immense capacity loss and a very low initial coulombic efficiency. In this study, we report the use of a facile direct pre-lithiation to suppress high irreversible capacity of the CNT electrodes in the first cycles. Pre-lithiated polymer-coated CNT anodes displayed good rate capabilities, studied up to 30 C and delivered high capacities of 850 mAh g⁻¹ (313 μAh cm⁻²) at 1 C rate over 50 charge-discharge cycles.

The increasing demands from micro-power applications call for the development of the electrode materials for Li-ion microbatteries using thin-film technology. Porous Olivine-type LiFePO₄ (LFP) and NASICON-type Li₃Fe₂(PO₄)₃ have been successfully fabricated by radio frequency (RF) sputtering and post-annealing treatments of LFP thin films. The microstructures of the LFP films were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the LFP films were evaluated by cyclic voltammetry and galvanostatic charge-discharge measurements. The deposited and annealed thin film electrodes were tested as cathodes for Li-ion microbatteries. It was found that the electrochemical performance of the deposited films depends strongly on the annealing temperature. The films annealed at 500 °C showed an operating voltage of the porous LFP film about 3.45 V vs. Li/Li⁺ with an areal capacity of 17.9 µAh cm⁻² µm⁻¹ at C/5 rate after 100 cycles. Porous NASICON-type Li₃Fe₂(PO₄)₃ obtained after annealing at 700 °C delivers the most stable capacity of 22.1 µAh cm⁻² µm⁻¹ over 100 cycles at C/5 rate, with an operating voltage of 2.8 V vs. Li/Li⁺. The post-annealing treatment of sputtered LFP at 700 °C showed a drastic increase in the electrochemical reactivity of the thin film cathodes vs. Li⁺, leading to areal capacity ~9 times higher than as-deposited film (~27 vs. ~3 µAh cm⁻² µm⁻¹) at C/10 rate.

Self-organized Titanium dioxide (TiO₂) nanotubes grown on Ti grid acting as anode for Li-ion microbatteries were prepared via an electrochemical anodization. By tuning the anodization time, the morphology and length of the nanotubes were investigated by scanning electron microscope. When the anodization time reached 1.5 h, the TiO₂nts/Ti grid anode showed a well-defined nanotubes, which are stable, well-adherent ~90 nm with a length of 1.9 ± 0.1 μm. Due to their high surface utilization, surface area, and material loading per unit area, TiO₂nts/Ti grid anode using polymer electrolyte exhibited a high areal capacity of 376 μAh cm⁻² at C/10 rate and a stable discharge plateau at 1.8 V without using a polymer binder and conductive additive. The storage capacity of the TiO₂nts/Ti grid after 10 cycles is 15 times higher compared to previous reports using planar Ti foils.

We report the electrochemical performance of porous NASICON-type Li3Fe2(PO4)3 thin films to be used as a cathode for Li-ion microbatteries. Crystalline porous NASICON-type Li3Fe2(PO4)3 layers were obtained by radio frequency sputtering with an annealing treatment. The thin films were characterized by XRD, SEM, and electrochemical techniques. The chronoamperometry experiments showed that a discharge capacity of 88 mAhg−1 (23 μAhcm−2) is attained for the first cycle at C/10 to reach 65 mAhg−1 (17 μAhcm−2) after 10 cycles with a good stability over 40 cycles.