Juan Luis Gómez-Cámer

On the performances of CuxO-TiO2 (x = 1, 2) nanomaterials as innovative anodes for thin film lithium batteries.

CuxO-TiO2 (x = 1, 2) nanomaterials are synthesized on polycrystalline Ti substrates by a convenient chemical vapor deposition (CVD) approach, based on the initial growth of a CuxO matrix (at 400 and 550 °C for x = 1 and 2, respectively) and the subsequent overdispersion of TiO2 at 400 °C. All CVD processes are carried out in an oxygen atmosphere saturated with water vapor. The obtained systems are investigated by means of glancing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical experiments. Galvanostatic charge/discharge measurements indicate that Cu2O-TiO2 nanomaterials exhibit very attractive high-rate capabilities (∼400 mA h g(-1) at 1 C; ∼325 mA h g(-1) at 2 C) and good stability after 50 operating cycles, with a retention of 80% of the initial capacity. This phenomenon is mainly due to the presence of TiO2 acting as a buffer material, i.e., minimizing volume changes occurring in the electrochemical conversion. In a different way, CuO-TiO2 systems exhibit worse electrochemical performances as a consequence of their porous morphology and higher thickness. In both cases, the obtained values are among the best ever reported for CuxO-based systems, candidating the present nanomaterials as extremely promising anodes for eventual applications in thin film lithium batteries.

Anchoring Si nanoparticles to carbon nanofibers: an efficient procedure for improving Si performance in Li batteries

Carbon fibers obtained by pyrolysis of tailored resorcinol/formaldehyde polymer particles were used to anchor Si nanoparticles at their surface. The carbonization process, carried out at 1000 °C under nitrogen, induced strong interactions between Si particles and the carbon matrix through a thick amorphous silicon oxide layer as revealed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Therefore, the actual composition of the composites was Si/SiOx/C (fibers). Component contents were determined from thermogravimetric measurements (TG) made under oxygen. The composites delivered specific capacities as high as 2500 mA h gSi−1 at rather high current densities (500 mA gsi−1) and exhibited good capacity retention on cycling. By contrast, a mixture of pristine Si nanoparticles and carbon nanofibers performed considerably worse, their capacity fading abruptly with cycling. The improved performance of composites is ascribed to a combination of the properties of the amorphous SiOx layer, and the texture and morphological properties of carbon, increasing the electrode conductivity and buffering Si expansion and shrinkage during Li insertion and deinsertion.

Precipitation of CoS vs Ceramic Synthesis for Improved Performance in Lithium Cells

An amorphous cobalt sulfide was synthesized by precipitation from aqueous solutions of cobalt nitrate and sodium sulfide, and its chemical composition, CoS 0.92 ·0.9H 2 O, determined from energy dispersive X-ray analysis and thermogravimetric data. X-ray photoelectron spectroscopy measurements confirmed the valence state of Co to be Co 2+ bound to s 2- and O in H 2 O molecules. This amorphous sulfide reacts reversibly with lithium in lithium cells in several steps, which exhibited some coincidence with those observed for crystalline CoS 0.89 , as revealed by step potential curves. However, the cycling properties are rather different. Thus, the capacity of the cell made from the crystalline compound fades rapidly with cycling; by contrast, the amorphous compound exhibits better capacity retention upon cycling, with capacity values almost four times greater than those for cells made from CoS 0.89 . Supplementary experimental results are consistent with the improved performance being a result of the role played by the water content rather than the amorphous structure of the compound.

Influence of Conversion Material Morphology on Electrochemistry Studied with Operando X-Ray Tomography and Diffraction

X-ray diffraction and X-ray tomography are performed on intermetallic particles undergoing lithiation in a porous electrode. Differences between ensemble phase evolution and that at a single-particle level are explored. It is found that all particles evidence core-shell lithiation; however, particles with internal porosity are more mechanically robust and exhibit less fracture.

Antimony based negative electrodes for next generation Li-ion batteries

Crystalline TiSb2 and NbSb2 prepared by the ceramic route were examined as negative electrodes for lithium-ion batteries. The crystal structures of both materials are different, as well as their electrochemical responses. TiSb2 has a specific charge of 450 mA h g−1 at an average potential of 0.7 V vs. Li+/Li and is able to maintain this specific charge during 70 cycles while NbSb2 has a specific charge of 400 mA h g−1 for the first few cycles which then fades continuously. The reaction mechanism was revisited in this paper by applying high resolution in situ synchrotron X-ray diffraction characterization combined with electrochemical tests.