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This study reports on the electrochemical alloying-dealloying properties of Mg2Sn intermetallic compounds. 119Sn Mössbauer spectra of β-Sn powder, thermally alloyed cubic-Mg2Sn, and an intermediate MgSn nominal composition are used as references. The discharge of a Mg/micro-Sn half-cell led to significant changes in the spectra line shape, which is explained by a multiphase mechanism involving the coexistence of c-Mg2Sn, distorted Mg2-δSn, and Mg-doped β-Sn. Capacities and capacity retention were improved by using nanoparticulate tin electrodes. This material reduces significantly the diffusion lengths for magnesium and contains surface SnO and SnO2, which are partially electroactive. The half-cell potentials were suitable to be combined versus the MgMn2O4 cathodes. Energy density and cycling properties of the resulting full Mg-ion cells are also scrutinized. [ABSTRACT FROM AUTHOR]

Abstract: A new Na3+xV2(PO4)3−x(SiO4)x (0≤x≤0.5) series is examined as the positive electrodes for sodium‐ion cells. The substitution of P by Si is evidenced by an increase in the lattice parameters and a significant modification of the particle morphology. These structural and morphological changes significantly affect the electrochemical performance. Thus, samples with low Si contents reveal better rate capabilities and cyclabilities than the Si‐free sample. A full ion cell assembled with a selected sample provides an energy density of 342 W h kg−1 after 140 cycles, demonstrating that Si doping on Na3V2(PO4)3 could be an interesting strategy for high‐performance Na‐ion cells. [ABSTRACT FROM AUTHOR]

A novel design of a sodium-ion cell is proposed based on the use of nanocrystalline thin films composed of transition metal oxides. X-ray diffraction, Raman spectroscopy and electron microscopy were helpful techniques to unveil the microstructural properties of the pristine nanostructured electrodes. Thus, Raman spectroscopy revealed the presence of amorphous NiO, α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite). Also, this technique allowed the calculation of an average particle size of 23.4 Å in the amorphous carbon phase in situ generated on the positive electrode. The full sodium-ion cell performed with a reversible capacity of 100 mA h g−1 at C/2 with an output voltage of about 1.8 V, corresponding to a specific energy density of about 180 W h kg−1. These promising electrochemical performances allow these transition metal thin films obtained by electrochemical deposition to be envisaged as serious competitors for future negative electrodes in sodium-ion batteries. [ABSTRACT FROM AUTHOR]

Searching for optimized electrode materials in alkali ion batteries we have prepared a large number of titania nanotubes (nt-TiO2) electrodes by using different voltages in the 42-100 V range and Ti-anodization times and studied their behavior in test batteries. As a result of the high current densities observed in the transient curves for a fixed electrolyte composition, high anodization voltages allow the rapid growth of self-organized and amorphous nanotube arrays with up to 200 µm in length. The growth of nt-TiO2 follows the parabolic rate law (L² = kt). Titania nanotubes with different lengths were used as electrode materials in lithium and sodium test cells. In lithium cells, the areal capacities depend on the nanotube length independently of the anodization voltage used to obtain a particular length. The very high areal capacities that are observed in lithium (around 2-4 mAh/cm²) and sodium (ca. 1 mAh/cm²) cells are attributed to the high length of the nanotubes. However, the longer titania nanotubes exhibit lower gravimetric capacity values (mAh/g) due to the longer ion diffusion path. The capacity to react with sodium is lower than with lithium, probably due to the poor conductivity of nt-NaxTiO2. [ABSTRACT FROM AUTHOR]

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: Oxidised FeCoNi alloys are prepared by an electrodeposition-annealing method. The performances of this type of nanostructured electrode are studied by the combination of structural techniques (transmission electron microscopy and X-ray diffraction) and electrochemical tests in lithium cells. The oxidised FeCoNi alloy achieves an excellent Coulombic efficiency in first cycle (85–90%) as well as a minimal discharge polarization on subsequent cycles because the voltage plateau ascribable to metal reduction is kept invariable at around 0.8V. These results disclose new pathways to fabricate low-cost and high-performance conversion electrodes as anode material for Li-ion secondary batteries. [Copyright &y& Elsevier]

The development of low-cost electrode devices from conductive materials has recently attracted considerable attention as a sustainable means to replace the existing commercially available electrodes. In this study, two different electrode surfaces (surfaces 1 and 2, denoted as S1 and S2) were fabricated from chocolate wrapping aluminum foils. Energy dispersive X-Ray (EDX) and field emission scanning electron microscopy (FESEM) were used to investigate the elemental composition and surface morphology of the prepared electrodes. Meanwhile, cyclic voltammetry (CV), chronoamperometry, electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) were used to assess the electrical conductivities and the electrochemical activities of the prepared electrodes. It was found that the fabricated electrode strips, particularly the S1 electrode, showed good electrochemical responses and conductivity properties in phosphate buffer (PB) solutions. Interestingly, both of the electrodes can respond to the ruthenium hexamine (Ruhex) redox species. The fundamental results presented from this study indicate that this electrode material can be an inexpensive alternative for the electrode substrate. Overall, our findings indicate that electrodes made from chocolate wrapping materials have promise as electrochemical sensors and can be utilized in various applications. [ABSTRACT FROM AUTHOR]

In this study, Li4Ti5O12 (LTO) electrodes with different types of water-soluble binders are successfully coated upon aluminum foil. Electrodes containing solely sodium alginate (SA) as a binder or a mixed PVDF/carboxymethyl cellulose (CMC) binder show the most stable performance in 1 M LiPF6 in EC/DMC 1:1 in half cell vs. Li, with respect to cycle stability over 100 cycles at 1 C. The electrodes processed with a mixture of PVDF/SA show considerable fading and slightly worse values for rate capability. Each one of the different binders used is eco-friendly, and the whole processing can be performed without the use of organic solvents. Further advantages covering the whole production and recycling process, as well as safety issues during operation, encourage deeper research in this area. [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]

The use of iron-, tin- and antimony-containing carbon fibres as potential candidates for the negatives electrode of advanced lithium-ion batteries is described. Two different types of fibres are used: non-graphitic and partially graphitized carbon. EPR results show that both carbon and dispersed iron participate in redox processes during the electrochemical reaction with Li. Lithium test cells evidence higher capacities for partially graphitized fibres. The addition of dispersed tin or antimony is used to improve the capacity of the non-graphitic fibres by formation of lithium-tin and lithium-antimony compounds. Reversible capacity values close to 300 mA h g-1 are achieved in both partially graphitized and composite electrodes containing Li-alloying elements. The use of nanodispersed transition metals, i.e. iron, in a carbon matrix is proposed here as an alternative to carbon composites containing Li-alloying elements. [Copyright &y& Elsevier]

Abstract: Heterostructures composed of reduced graphene oxide and self-organized titania nanotubes (nt-TiO2) are examined as novel electrode material for lithium-ion batteries. The novelty here resides in the deposition of a graphene-like film on self-organized nanotubes and that, as compared with previous materials, the differences in behavior are significant as the heterostructure combines previously reported advantages of self-organized nt-TiO2 with those emerging from the graphene composites. The preparation of this nt-TiO2/graphene hybrid electrode material is described here. The deposition of a graphene film on self-arranged amorphous nt-TiO2 was confirmed by using SEM, Raman spectroscopy and mapping of composition. Lithium test cells display capacities that can exceed 300 mAh g−1 over 100 cycles and that are therefore superior to those of bare nt-TiO2 and anatase or rutile TiO2–graphene hybrid nanostructures. The excellent rate performance of these electrodes makes charge–discharge possible up to at least 300 C-rate. The impedance spectra show that the graphene-like film improves the interface properties in the hybrid electrode. In addition to the environmentally friendly nature of the active electrode material, the moderate working voltage offers an important safety advantage in that it protects the battery from the electroplating phenomena. [Copyright &y& Elsevier]