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A nanocomposite of sodium titanate/titania nanotrees self-organized in a parallel fashion to form nanoforests is successfully prepared and used as high-performance anode for Na-ion microbatteries. The first step of the synthesis is the anodic oxidation of Ti foils to form self-organized amorphous TiO 2 nanotubes followed by insertion of sodium in aqueous media at room temperature. Then the composite is thermally dehydrated and crystallized as monoclinic Na 2 Ti 6 O 13 /rutile nanotrees. EPR spectra evidence a significant increase in Ti 3+ content during sodium/proton insertion and a decrease on heating. SEM images reveal that while the height of the nanotubes is similar to the nanoforest (c.a. 8.0 μm) the morphology changes from aligned nanotubes to nanotrees of complex texture. The electrochemical results of sodium test cells in non-aqueous electrolyte using the Na 2 Ti 6 O 13 /TiO 2 nanocomposite electrodes show flat profiles of sodium insertion and de-insertion at 0.7 and 0.9 V, respectively. The observed reversible capacity of 130 μA h cm −2 over 150 cycles is almost threefold the value of titania nanotubes annealed at a same temperature. Both characteristics are of great interest to achieve safe and efficient Na-ion microbatteries. [ABSTRACT FROM AUTHOR]

A 3D mesoporous TiO 2 material with well-developed mesostructure is prepared in the form of a binder-free thin (100 nm) film and studied as potential candidate for the negative electrode in lithium microbatteries. By appropriate thermal treatments, the selected crystal structure (anatase, rutile, or amorphous), and micro-/mesostructure of the materials was obtained. The effects of voltage window and prelithiation treatment improved first cycle reversibility up to 86% and capacity retention of 90% over 100 cycles. After a prolonged intercalation of lithium ions in ordered mesoporous TiO 2 appeared small particles assigned to Li 2 Ti 2 O 4 with cubic structure as observed from ex-situ TEM micrographs. This study highlights the flexibility of the potential window to which the electrode can operate. Maximum capacity values over 100 cycles of 470 μA h cm −2 μm −1 and 177 μA h cm −2 μm −1 are obtained for voltage ranges of 0.1–2.6 V and 1.0–2.6 V, respectively. The observed values are between 6 and 2 times higher than those obtained for films with 600 nm (80 μA h cm −2 μm −1 ) and 900 nm (92 μA h cm −2 μm −1 ) lengths. This indicates that 100 nm thin TiO 2 films with high accessibility show finite-length type diffusion which is interesting for this particular application. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cu–Sn nanowires with 80–100nm diameter and 2μm length are made by electrodeposition. [•] A stable areal capacity of 70μAhcm− 2 over 100 cycles is obtained for η′-Cu5Sn6 phase. [•] The nanowire morphology minimizes volume variations of Sn–Li alloys. [•] The conductive Cu matrix facilitates electrical contact and cycling stability. [Copyright &y& Elsevier]

Abstract: A thin film electrode consisting of a mixture of iron and nickel oxides is prepared by a single route. Electrochemical deposition from Fe2+ and Ni2+ solutions on a titanium substrate and further thermal treatment at low temperature allowed obtaining a nanocomposite thin film of NiO and Fe2O3. The electrochemical studies performed on lithium cells assembled with this electrode material revealed the smallest irreversibility from first to second discharge ever reported during the conversion reactions of metal oxides at ∼0.8 V. Unlike bulk transition metal oxides, the poorly-crystalline oxidized material exhibited an unusually low discharge polarization. The 57Fe Mössbauer spectra of partially discharged and charged electrodes evidenced the reversibility of the conversion reaction with lithium and the efficiency of the recovery of the local environment of iron after the first cycle. [Copyright &y& Elsevier]

Abstract: Electrochemical deposition from Ni2+ and Fe2+ using sulfate and nitrate solutions is carried out under galvanostatic regime. The resulting films are oxidized and examined in lithium test cells as potential anode materials for lithium-ion batteries. X-ray diffraction, XPS and SAED–TEM analyses revealed a thin film based on nanocomposite NiO and Fe2O3. Cycling studies show the smallest discharge polarization ever reported during the conversion reactions of metal oxides at ∼0.8V. Unlike typical transition metal oxides, the amorphous oxidized material exhibited low irreversibility from first to second discharge (∼15%) and a distinctive plateau on consecutive discharge branches. The changes in the film thickness on increasing deposition time and the crystallization phenomena on annealing the deposits strongly affect the electrochemical behavior. The present approach allows preparing a powder free electrode with improved coulombic efficiency directly on the current collector and opens a set of novel preparation routes in this field with intriguing results. [Copyright &y& Elsevier]

Co-P alloy films were electrodeposited on a titanium electrode. The controlled addition of phosphorous acid or sodium hypophosphite to a Co2+-containing solution leads to the formation of amorphous or crystalline CoP phases. Particularly, the orthorhombic Co2P phase is obtained at 80°C with a current density of 37.5 mA cm-2 during 10 and 20 min as determined by XRD and XPS analysis. The morphology of Co2P can be controlled from leopard-like spots to hexagonal symmetric particles as confirmed by SEM. This phase is for first time used as a negative electrode in rechargeabte batteries. The electrochemical results in a lithium test cell of this unique product differ significantly from other metal phosphides reported in the literature. A high potential reaction at 1.3 W is observed in the first discharge. Successive charge/discharge branches are quite different to those reported so far. The preliminary results suggest that the Co to P ratio may affect the redox properties of the materials. In view of the limited amount of reports dealing with performances of cobalt phosphides in Li-cells, the properties presented here justify further effort to be done to evaluate their real potential application in Li-ion batteries with a predefined voltage operation. [ABSTRACT FROM AUTHOR]

Abstract: The preparation of thin films of x Fe2O3–(1−x) NiO (x=0.38–0.49) is reported. A single two-step process including metal electrodeposition and thermal oxidation was performed. The nanocrystalline character of the electrode material was evidenced by X-Ray diffraction and electron microscopy. The electrochemical properties of sodium batteries assembled with these electrode materials were studied for the first time. The synergic effects of both transition metal elements along with the nano-crystalline character are responsible for the good electrochemical performance. The coulombic efficiency of sodium cell improved drastically up to 68%. The post-mortem analysis of discharged and charged electrodes by 57Fe Mössbauer spectroscopy allowed determining the redox mechanism on the probe atom during the first cycle. [Copyright &y& Elsevier]