Preparation of electrodes based on WO3 nanostructures for Li-ion batteries

The data are related with the preparation of electrodes based on WO3 nanostructures used as anode materials for Li-ion batteries. The nanostructured WO3 thin film was effectively synthesized by an electrochemical procedure. Then, an annealing treatment at 600◦C in air environment for 4 h was carried out. In the second electrode synthesized, a carbon layer was uniformly deposited on WO3 nanostructures to obtain a WO3/C electrode. Finally, WO3/WS2 electrodes were prepared by means of in situ sulfurization of WO3 one-step solid-state synthesis using tungsten trioxide (WO3) and thiourea as precursor material. By using X-ray photoelectron spectroscopy, X-ray diffraction analysis and Raman spectra, the three electrodes have been morphologically characterized. Electrochemical properties were analysed by cyclic voltammogram, galvanostatic charge/discharge cycling, and electrochemical impedance spectroscopy. METHODOLOGICAL INFORMATION WO3 andWO3/C nanostructures synthesis: The pure WO3 nanostructures were synthesized using the electrochemicalanodization method using CH4O3S as anelectrolyte. After the anodization, a thinblue layerwas formed, and itwas annealed at 600◦C for 4hin air to obtain a crystalline structure.In order to prepare the WO3/C electrodes, an evaporationmethod was chosen. This method consists in applying8 V and vacuum pressure until reaching 10−5 mbar usingthe LEICA MED 20 equipment on the WO3 nanostructurespreviously synthesized, as specified in ourwork.Finally, a solid-state synthesis was used to prepare theWO3/WS2 electrodes from basicWO3 nanostructures. TheWS2 layer was obtained by heating tungsten oxide nanostructuresin the presence of thiourea with aWO3/thiourearatio of 1:48 during 3 h at 773 K under argon. Once these3 h had elapsed, the nanostructures were cooled to roomtemperature in an inert atmosphere, resulting in a blackproduct. After the annealing treatment, the nanostructures wereused in Li-ion batteries as an anode. Structure characterization: The crystal structure was examined by XRD (Bruker D8Advance) with Cu Kα radiation (λ = 1.5406 Å) at a scanrate of 10◦ min−1. Raman spectroscopy was performed ina range of 0–2000 cm−1 on a WITec alpha300 R confocalRaman microscope.The electronic structure and the chemical state of theelements that exist in the samples were analyzed by XPS.The K-Alpha Thermo Scientific systemwith an Al-Kα radiation(1486.6 eV) was used to obtain the composition data.The pass energy and the pressurewere 50 eV and 10−7 Torr,respectively. Electrochemical tests: The electrochemical analyses were realized with a twoelectrodecell configuration. These batteries were setup byusing the WO3 nanostructures layers as the working electrode(the mass of active material used in each batterywas 6.5 mg). The counter electrode used in this test was alithium sheet. The solution used as an electrolyte (Merck)was 1 M LiPF6 in a nonaqueous solution of dimethyl carbonate,and ethylene carbonate with a volume relationof 1:1 and fiberglass were used as spacers. The cells wereconstructed in a glove box with an inert atmosphere, andthe electrolyte volume incorporated in each battery was300 μl. Charge–discharge experiments were carried outwith an Autolab PGSTAT302N potentiostat. The rangepotential between the charge and discharge tests that havebeen carried out was 0.01–4 V versus Li/Li+ at a currentdensity of 100 mA g−1. The cyclic voltammogram (CV)measurements were performed at a scan rate of 0.5mV s−1of between 0.01 and 4.0 V on an Autolab PGSTAT302Npotentiostat.The EIS was examined at open circuit potential. Thefrequency range used was 0.1–10 kHz, and the signalperturbation had an amplitude of 10 mV.