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The synthesis and the electrochemical behavior of Al,Mg-doped Na y TiO 2 , i.e. (Na y [Ti (1−x) Al x ]O 2 , 0.05 ≤ x ≤ 0.40, and Na y [Ti (1−x) Mg x ]O 2, 0.15 ≤ x ≤ 0.35) layered oxide phases as potential anodes for Na-ion batteries have been investigated. They were synthesized by solid state route with controlled sodium vapor pressure in inert atmosphere. The study of the crystal structure by XRD revealed that a maximum of 10% Al and 15% Mg were doped in the O3-type structure without important structural changes associated with the replacement of Ti by Al/Mg ion. 23 Na solid state NMR measurements were performed to confirm the Mg doping, its effects on the local structure, and the disordered disposition of Mg in the compound. The synthesized phases were electrochemically active at low voltages (1.6–0.08 V vs. Na + /Na). The high Mg-doped phase demonstrated improved high rate performance and a capacity of 107 mAh g −1 at C/20 rate with a voltage profile smoother than the undoped material.

Composite electrode materials offer some of the best electrochemical performances available for Li-based batteries. However, the development of economical and scalable synthetic methods for their production remains a significant challenge, especially for submicron and nano-sized composites. In this work, we demonstrate a novel synthetic method which combines galvanic displacement and cationic polymerization in a one-pot synthesis. The materials obtained are Sn-based organic–inorganic micro-composites whose morphology and chemical composition can be altered by changing a few key synthetic parameters. Extensive characterization of the materials by micro-analytical and bulk methods (SEM-SE, SEM-BSE, SEM-EDS, XRD, ATR-FTIR, TGA-DSC, ICP, and SSNMR), revealed the presence of crystalline phases of Sn, of Li-containing Sn-alloys, other crystalline inorganic phases, and carbonate-based polymer. Preliminary electrochemical evaluation revealed that the Sn-containing micro-composite shows better stability than commercial micro-crystalline Sn when cycled in a lithium half-cell.

Organic carbonates are the predominant electrolyte base used in the best Li- and Na-ion battery systems. However, to date, their precise interactions with the electrode are not fully understood. Here, we elucidate the role of a prototypical electrolyte additive, fluoroethylene carbonate (FEC), in Na-ion batteries and illustrate its influence on the solid electrolyte interphase (SEI) composition. Through the use of bulk and surface analytical techniques, we find that early FEC decomposition forms a surface-passivating constituent (Na2CO3), reduces the rate of decomposition of the propylene carbonate electrolyte, and supports the preservation of the polyvinylidene difluoride (PVDF) binder. Furthermore, we observe that NaF is formed by the decomposing PVDF binder when no additive is present, resulting in the early degradation of battery performance. This new understanding of the SEI offers greater chemical insight into the selection of binder and electrolyte combinations, allowing better targeted use of thes...

Among the various possible earth abundant electrode materials, P2-Na2/3[Fe1/2Mn1/2]O2 is one of the most promising cathode materials for sodium ion batteries. Most transition metal oxide materials undergo various structural transitions during the sodiation/desodiation process and it is crucial to understand such transitions for further development of these materials. In the present research, in situ X-ray diffraction (XRD), in situ Raman spectroscopy and ex situ solid-state Nuclear Magnetic Resonance (NMR) were used as tools to understand such transitions for the specific case of P2-Na2/3[Fe1/2Mn1/2]O2. Both in situ Raman spectroscopy and X-ray diffraction measurements, together with ex situ solid-state NMR studies revealed that the synthesized P2-Na2/3[Fe1/2Mn1/2]O2 hexagonal crystal structure undergoes P2–OP4 reversible phase transitions at the end of the charge process and at the end of the discharge process a biphasic mechanism follows. Moreover, ex situ solid state NMR measurements revealed the fast diffusion of Na+ ions in the 2D layers of P2-Na2/3[Fe1/2Mn1/2]O2, which led to an average 23Na NMR signal that reflects very accurately the average oxidation state of the metal centres. Solid state NMR data also shows that the diffusion of sodium ions is frozen at high levels of sodiation, at low voltages and that at the end of the charge process the prismatic coordinated sites are preferentially populated in the OP4 phase.

A pulsed electrodeposition technique has been used for the synthesis of iron-based compounds as catalytic precursors for the growth of carbon nanofilaments via chemical vapor deposition (CVD). Iron-based nanoparticles were electrodeposited on a three-dimensional and electron conducting Al–Mg alloy substrate. A systematic control of the chemical composition, size and density of the iron-based nanoparticles was achieved by varying the nature of the electrolytic bath and the plating conditions. The results show that the as-prepared iron deposits synthesized at room temperature (FeCl3·6H2O) and at 50 °C (FeCl2 and Fe(NO3)3·9H2O) are catalytically active for the growth of different carbon nanostructures. The structure of the catalyst precursor as well as their chemical composition has a direct influence on the final carbon nanostructure. Nanocarbons produced by this route exhibit a more disordered microstructure and higher concentration of defects than other carbon nanostructures like nanotubes also produced by CVD. These filamentous nanocarbons could be of practical and fundamental interest as electrodes in batteries, supercapacitors, fuel cells and sensors.

Keywords:Lithium-ion battery, conversion reaction, hysteresis, composite material In order to expand the Li-ion battery (LIB) technology and to enlarge energy demanded applications such as the electrical vehicle, an increase in their energy storage density is needed. An alternative to common intercalation materials are the so-called conversion materials which undergo a multi-electron redox process [1]. Instead of inserting Li, these materials undergo reversible reduction to form metal nanoparticles M0 and binary Li compounds: Mn+Xy + nLi++ ne- ↔ M0 + yLiz/yX [2]. Transition metal oxides such as Fe2O3 or Fe3O4are examples of this type of materials and have largely been studied these last years due to their high capacity values, good cycleability, capacity retentions and low toxicity and cost [2]. However, they present some drawbacks such as large voltage hysteresis between charge and discharge, which would lead to an enormous loss of energy efficiency of the battery. In this work we present a synergistic approach to reduce the hysteresis in conversion materials. To do so, C- FeOxcomposites with tailored microstructure are prepared using low cost methods. In the literature, carbon-metal oxide nanocomposites has already been used as a strategy to improve the cycleablity of conversion materials but no hysteresis reduction effect was previously observed [2, 3]. In our work, a significant hysteresis voltage reduction ( ≥ 0.3 V) will be shown through the combination of two materials reacting through different mechanisms (intercalation and conversion). The reduction of polarisation through a dual mechanism has been observed in the nanocomposite formed during the electrochemical reaction of titanium hydroxyfluoride [4] and is herein applied to abundant and low cost materials able to deliver much higher capacities. Insights about the electrochemical reactions and mechanisms taking place in these composite materials will be shown by means of TEM, XPS and in-situ Raman spectroscopy data. References [1] Armand, M.; Tarascon, J.-M. Nature 2008, 451, 652. [2] Cabana, J.; Monconduit, L.; Larcher, D. ; Palacin, M. R. Adv. Mater. 2010, 22, E170. [3] Zhang W.M. ; Wu X.L. ; Hu J.S. ; Guo Y.G : Wan L.J. Adv. Funct. Mater. 2008, 18, 3941. [4] Dambournet, D. ; Chapman, K. W. ; Chupas P.J. ; Gerald, R.E.; Penin, N.; Labrugere, C.; Demourgues, A.; Tressaud, A.; Amine, K. J. Am. Chem. Soc. 2011, 133, 13240.

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