A fire-retarding electrolyte using triethyl phosphate as a solvent for sodium-ion batteries.

We introduce a fire-retarding phosphate-based electrolyte, 1 M NaBF4 in triethyl phosphate with 3% vinylene carbonate as an SEI-forming additive, for sodium-ion batteries. With this electrolyte formulation, we achieved stable cycling performance with a capacity of 80.5 mA h g-1 and a retention of 77.8% after 200 cycles in the Na-ion full cell of Na3.2V1.8Zn0.2(PO4)3vs. hard carbon.

Impact of Synthesis Conditions in Na-Rich Prussian Blue Analogues.

Sodium-rich iron hexacyanoferrates were prepared by coprecipitation, hydrothermal route, and under reflux, with or without dehydration. They were obtained with different structures described in cubic, orthorhombic, or rhombohedral symmetry, with variable compositions in sodium, water, and cationic vacancies and with a variety of morphologies. This series of sodium-rich Prussian blue analogues allowed addressing the relationship between synthesis conditions, composition, structure, morphology, and electrochemical properties in Na-ion batteries. A new orthorhombic phase with the Na1.8Fe2(CN)6·0.7H2O composition synthesized by an hydrothermal route at 140 °C is reported for the first time, whereas a phase of Na2Fe2(CN)6·2H2O composition obtained under reflux, previously described with a monoclinic structure, shows in fact a rhombohedral structure.

Investigations of Thermal Stability and Solid Electrolyte Interphase on Na2Ti3O7/C as a Non-carbonaceous Anode Material for Sodium Storage Using Non-flammable Ether-based Electrolyte.

In order to become commercially viable, sodium-ion batteries need to deliver long cycle life with good capacity and energy density while still ensuring safety. Electrolyte plays a key role forming solid electrolyte interphase (SEI) layers at low potential, which affects the thermal stability and cycle life of the anode materials under consideration. In this study, an ether-based non-flammable electrolyte, 1 M NaBF4 in tetraglyme, is tested for sodium storage using a non-carbonaceous anode material Na2Ti3O7/C, and the results are compared with those obtained with the popularly used carbonate-based electrolyte, 1 M NaClO4 in ethylene carbonate (EC) and propylene carbonate (PC) (v/v = 1:1). The Na2Ti3O7/C versus Na cells using 1 M NaBF4 in tetraglyme show a much higher first cycle Coulombic efficiency (73%) than those using 1 M NaClO4 in EC/PC (33%). Thermal stability studies using differential scanning calorimetry (DSC) conclusively show that Na2Ti3O7/C electrodes cycled with 1 M NaBF4 in tetraglyme are more thermally stable than the one cycled with 1 M NaClO4 in EC/PC. Further investigations on the formation of SEI layers were performed using attenuated total reflection-Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and DSC studies. These studies unambiguously demonstrate that the SEI formed on Na2Ti3O7/C using 1 M NaBF4 in tetraglyme is not only less resistive but also more stable than the SEI formed using 1 M NaClO4 in EC/PC.

Introducing Na-sufficient P3-Na0.9Fe0.5Mn0.5O2 as a cathode material for Na-ion batteries.

P3-Na0.9Fe0.5Mn0.5O2 is reported as a new P-type cathode material for Na-ion batteries. The P3 structure can accommodate 0.9 mole of Na-ions leading to a high discharge capacity of 155 mA h g-1 and does not require sacrificial salts for full-cell operation. Operando X-ray diffraction and ex situ X-ray absorption studies are also reported.

Electronic Coupling of Cobalt Nanoparticles to Nitrogen-Doped Graphene for Oxygen Reduction and Evolution Reactions.

The rational design of nonprecious-metal electrocatalysts with activities comparable to or greater than that of platinum is extremely valuable to the development of high energy density metal-air batteries. Herein, the two-step preparation of a highly active oxygen electrocatalyst based on ultrasmall cobalt nanoparticles stabilized in a nitrogen-doped graphene matrix is reported. The catalyst performs as well as the commercial Pt/C catalyst in the oxygen reduction reaction, and better than the Pt/C catalyst in the oxygen evolution reaction. This particular electrocatalyst could significantly lower the overpotentials of oxygen electrochemical reactions in aqueous lithium-air batteries to attain a round-trip efficiency of about 79.0 % at a current density of 0.1 mA cm-2 , thereby surpassing the performance of the commercial Pt/C catalyst. The good performance may be attributed to strong metal-support interactions, maximized by a high dispersion of ultrasmall cobalt nanocrystals in a nitrogen-doped graphene matrix, which yields electrocatalytic properties greater than the sum of its parts.

Low temperature aqueous electrodeposited TiO(x) thin films as electron extraction layer for efficient inverted organic solar cells.

Organic solar cells based on poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester were fabricated with electrodeposited TiOx electron extraction layers 5-180 nm thick. Electrodeposition under ambient conditions is an attractive, facile and viable approach to prepare metal oxide interfacial layers. The TiOx films obtained displayed a linear relationship between thickness and deposition time when fabricated under ambient conditions using an aqueous air stable peroxotitanium precursor. The precursor solution was prepared from titanium isopropoxide using a chelate process, which allowed water to be used as solvent due to considerably decreased sensitivity of the precursor solution towards hydrolysis. Highly conformal TiOx films, typically observed with vacuum deposition techniques, were obtained on the indium tin oxide substrate upon electrogeneration of OH(-) ions using H2O2 additive. Conversely, significantly rougher films with spherical growths were obtained using NO3(-) additives. Low temperature annealing at 200 °C in air was found to greatly improve purity and O stoichiometry of the TiOx films, enabling efficient devices incorporating the electrodeposited TiOx to be made. Using MoOx as the hole extraction layer, the maximum power conversion efficiency obtained was 3.8% (Voc = 610 mV; Jsc = 10.6 mA/cm(2); FF = 59%) under simulated 100 mW/cm(2) (AM1.5G) solar irradiation, whereas an efficiency of 3.4% was achieved with fully solution processed interfacial layers comprising the electrodeposited TiOx films and a surfactant-modified PEDOT:PSS hole extraction layer.

Enhancing the electrochemical kinetics of high voltage olivine LiMnPO4 by isovalent co-doping.

We report here doping of Fe(2+) and/or Mg(2+) in LiMnPO4 cathode material to enhance its lithium storage performance and appraise the effect of doping. For this purpose, LiMn0.9Fe(0.1-x)MgxPO4/C (x = 0 and 0.05) and LiMn0.95Mg0.05PO4/C have been prepared by a ball mill assisted soft template method. These materials were prepared with similar morphology, particle size and carbon content. Amongst them, the isovalent co-doped LiMn0.9Fe0.05Mg0.05PO4/C sample shows better electrochemical performance compared to LiMn0.9Fe0.1PO4/C and LiMn0.95Mg0.05PO4/C samples. For instance, a lithium storage capacity of 159 mA h g(-1) is obtained at 0.1 C for LiMn0.9Fe0.05Mg0.05PO4/C material with a relatively low polarization of ~139 mV. This is in sharp contrast to LiMn0.9Fe0.1PO4/C and LiMn0.95Mg0.05PO4/C which show only 136.8 and 128.4 mA h g(-1) at 0.1 C with the polarization of ~222 and 334 mV respectively. Further, the LiMn0.9Fe0.05Mg0.05PO4/C electrode delivers discharge capacities of 155.8, 141.4, 118.8, 104.6, 81.4 and 51.8 mA h g(-1) at 0.2, 0.5, 1, 2, 5 and 10 C respectively. This electrode material also retains a capacity of 116 mA h g(-1) at 1 C after 200 cycles, which is 96% of its initial capacity. Such improved cycling stability of LiMn0.9Fe0.05Mg0.05PO4/C is attributed to the suppressed Mn dissolution in the electrolyte compared to the other samples. Further, during the Li extraction process, delithiated phases created from the Fe(2+)/Fe(3+) redox reaction (~3.45 V) favor enhanced electrochemical activity of the succeeding Mn(2+)/Mn(3+) redox couples. The fully charged state (4.6 V) contains a partially lithiated phase owing to the presence of electrochemically inactive Mg(2+). The presence of such lithiated phase provides a favourable environment for the subsequent lithium insertion process. We also observe improved electronic conductivity and Li-ion diffusion for the co-doped sample compared to LiMnPO4 doped with either Fe(2+) or Mg(2+) by impedance measurements. The improved storage performance of co-doped LiMnPO4 is thus explained in terms of (i) favorable extraction and insertion reactions and (ii) enhanced transport properties.

Na2Ti6O13: a potential anode for grid-storage sodium-ion batteries.

The ultra-fast (30C or 2 min) rate capability and impressive long cycle life (>5000 cycles) of Na2Ti6O13 are reported. A stable 2.5 V sodium-ion battery full cell is demonstrated. In addition, the sodium storage mechanism and thermal stability of Na2Ti6O13 are discussed.

A rationally designed dual role anode material for lithium-ion and sodium-ion batteries: case study of eco-friendly Fe3O4.

Identifying dual role electrode materials capable of storing both lithium and sodium are thought to be highly relevant, as these materials could find potential applications simultaneously in lithium and sodium ion batteries. In this regard, the concept of dual alkali storage is demonstrated in Fe(3)O(4) anode material undergoing conversion reaction. To enable improved storage, a rational active material and electrode design is proposed. Accordingly, the following features were simultaneously incorporated into the design: (i) an optimal particle size, (ii) a conducting matrix, (iii) adequately large active material surface area and (iv) strong electrode material-current collector integrity. Electrodes incorporating this rational design exhibit excellent high rate performance and impressive cyclability during lithium storage. For instance, Fe(3)O(4) electrodes deliver a charge capacity of 950 mAh g(-1) at 1.2 C (~2.6 times higher than graphite and 5.4 times higher than Li(4)Ti(5)O(12)). Further, these electrodes show no signs of capacity fade even up to 1100 cycles. Impressively, the cells could also be charged-discharged to 65% of their theoretical capacity in just 5 min or 12 C (11.11 A g(-1)). The rate performance and cyclability of lithium storage achieved here are amongst the highest reported values in the literature for the conversion reaction in Fe(3)O(4). Besides lithium storage, the dual role of this anode is shown by demonstrating its sodium storage ability by conversion reaction for the first time.

Thermodynamics of nano- and macrocrystalline anatase using cell voltage measurements.

In view of increasing scientific and technological interest in nanomaterials, it is important to examine whether or, more exactly, to what extent the thermodynamic parameters change with size. Electrochemical e.m.f. measurements which provide a direct and elegant access to these thermodynamic data have been used in this study to investigate the excess contributions of anatase due to nano-size. The e.m.f. measurements are carried out (250-450 degrees C) on different particle sizes (1.2 microm-5 nm) using the cell: Au, O(2), Na(2)Ti(6)O(13), TiO(2) (anatase) |Na-beta'' alumina |TiO(2) (rutile), Na(2)Ti(6)O(13), O(2), Au. The e.m.f. observed is closely related to the difference of the Gibbs energies of formation (Delta(f)G degrees) of the titania crystals on both sides. Such cell voltage measurements with various sizes of anatase (1200, 100, 15, and 5 nm) as working electrodes enable us to calculate the excess enthalpy and entropy due to surface contributions and to provide refined data for the macroscopic anatase. No electrochemical Ostwald ripening or chemical Ostwald ripening was observed in the case of anatase nanoparticles up to 500 degrees C.

Electrochemical lithiation synthesis of nanoporous materials with superior catalytic and capacitive activity.

Nanoporous materials have attracted great technological interest during the past two decades, essentially due to their wide range of applications: they are used as catalysts, molecular sieves, separators and gas sensors as well as for electronic and electrochemical devices. Most syntheses of nanoporous materials reported so far have focused on template-assisted bottom-up processes, including soft templating (chelating agents, surfactants, block copolymers and so on) and hard templating (porous alumina, carbon nanotubes and nanoporous materials) methods. Here, we exploit a mechanism implicitly occurring in lithium batteries at deep discharge to develop it into a room-temperature template-free method of wide applicability in the synthesis of not only transition metals but also metal oxides with large surface area and pronounced nanoporosity associated with unprecedented properties. The power of this top-down method is demonstrated by the synthesis of nanoporous Pt and RuO2, both exhibiting superior performance: the Pt prepared shows outstanding properties when used as an electrocatalyst for methanol oxidation, and the RuO2, when used as a supercapacitor electrode material, exhibits a distinctly better performance than that previously reported for non-hydrated RuO2 (refs 19,20).

Evidence for interfacial-storage anomaly in nanocomposites for lithium batteries from first-principles simulations.

We present theoretical support for a mass storage anomaly proposed for nanocomposites in the context of lithium batteries which forms the transition between an electrostatic capacitive mechanism and an electrode mechanism. Ab initio atomic and electronic structure calculations, performed on the Ti(0001)/Li2O(111) model interface, indicate the validity of the phenomenological model of interfacial Li storage and provide a deeper insight into the local situation. Beyond the specific applicability to storage devices, the possibility of a two-phase effect on mass storage generally highlights the availability of novel degrees of freedom in materials research when dealing with nanocomposites.