Anatase nanotubes showed preferred orientation and high capacityversussodium after many electrochemical cycles.

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a Rechargeable batteries based on the intercalation of aluminium ions may be competitive against lithium-ion batteries, but their development and comprehension are full of difficulties. The charge/discharge processes are particularly complex in aqueous electrolyte solutions. The electrochemical behaviour of orthorhombic V2O5, obtained from xerogel, in aluminium cell is studied here by using electrochemical cycling, impedance spectroscopy, XRD and XPS results. After electrochemical intercalation of aluminium, the resulting (Al 3+ )x/3[(V 4+ )x,(V 5+ )2-x]O5.nH2O is XRD-amorphous at approximately x=1.5. The reversible capacity is ca. 120 mAh g -1 (equivalent to Al0.27V2O5). The loss of crystallinity induced by the electrochemical intercalation enhances the chemical exchange between the electrode material and the electrolyte solution. In the presence of acidic water solution, besides the faradic electrochemical process driven by the electrical current, aluminium, proton and water also can be intercalated into V2O5 by chemical reactions or ion exchange. Please do not adjust margins Please do not adjust margins redox activity in the voltage range between -1.3 and +0.5 V. In comparison with anatase, 2 the voltage of V 2 O 5 is higher, and discharge: solid symbols charge: open symbols (B)

To modify the morphology and electrochemical properties of the resulting titanium oxide layer, we have applied high-intensity ultrasonication during the potentiostatic anodization of metallic titanium, and the applied voltage and anodizing time has been changed. The influence of the imposed voltage, anodizing time, and ultrasonication on the nanotubes growth has been studied. Additional dissolution process takes place under ultrasonication, as is observed in the anodizing curves (current density vs time) that show values on the order of ca. 200 A/m 2 . After only 30 min of ultrasound-assisted anodization at 42 V, the resulting nanotubes length is ca. 4 μm and, in contrast, in the case of non ultrasound-assisted anodization, the length is only ca. 1 μm. Further prolonged anodization under ultrasound induced the complete dissolution of the titanium. After anodization at 60 V during 20 h (no ultrasounds), the observed length of the nanotubes is as long as ca. 45 μm. The nanotube TiO 2 aspect ratio has been tailored between 40 and 320. The obtained nanotubes of TiO 2 exhibit high areal capacity (up to ca. 2 mAh/cm 2 and stabilized around 0.3 to 0.5 mAh/cm 2 ) and good cycling behavior in lithium batteries. A nonlinear relationship between the nanotubes length and the resulting capacity has been revealed.

The direct observation of real time electrochemical processes is of great importance for fundamental research on battery materials. Here, we use electron paramagnetic resonance (EPR) spectroscopy to monitor the electrochemical reaction of sodium ions with few-layer MoS2 and its composite with carbon nanotubes (CNTs), thereby uncovering new details of the reaction mechanism. We propose that the sodiation reaction takes place initially in structural defects at the MoS2 surface that have been created during the synthetic process (ultrasonic exfoliation), leading to a decrease in the density of Mo5+ at low symmetry sites that can be related to the electrochemical irreversibility of the process. In the case of the few-layer MoS2/CNTs composite, we found metallic-type conduction behavior for the electrons associated with the Mo paramagnetic centers and improved electrochemical reversibility. The reversible nature of the EPR spectra implies that adsorption/desorption of Na+ ions occurs on the Mo5+ defects, or that they are neutralized during sodiation and subsequently created upon Na+ extraction. These effects help us to understand the higher capacities obtained in the exfoliated samples, as the sum of electrosorption of ions and faradaic effects, and support the suggestion of a different reaction mechanism in the few-layer chalcogenide, which is not exclusively an insertion process.