No abstract

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.

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 LiFePO 4 (LFP) and NASICON-type Li 3 Fe 2 (PO 4 ) 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 Li 3 Fe 2 (PO 4 ) 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.

Polymer-coated Carbon Nanotube (CNT) tissues are very flexible and lightweight and have high potential as an anode material for flexible Li-ion microbatteries. The electrochemical deposition of p-sulfonated poly(allyl phenyl ether) (SPAPE) polymer electrolyte into CNT tissues has been accomplished using a cyclic voltammetry (CV) technique. When compared to a pristine CNT tissue, the capacity of SPAPE-coated CNT tissue after 10 cycles of CV is improved about 67% at 1C rate. The enhancement of electrochemical performance is obtained when the CNT tissues are coated with the SPAPE polymer electrolyte. The higher capacity of the SPAPE-coated CNT tissue is attributed to the increased surface area and the improved quality of the electrode/electrolyte interfaces between the nanotubes and the polymer electrolyte. The SPAPE-coated CNT tissue delivers a higher reversible capacity of 750 mAh g−1 (276 µAh cm−2) compared to a pristine CNT tissue, which solely provides a reversible capacity of 450 mAh g−1 (166 µAh cm−2) after 110 cycles at 1C rate. Remarkably, the SPAPE-coated CNT tissue reaches a high capacity up to 12C rate while observing that the capacity can be significantly recovered.