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By accelerating the naturally-occurring carbonation of magnesian silicates, it would be possible to sequester some of the anthropogenic excess of CO2 in more geologically-stable solid magnesium carbonates. Reaction rates can be accelerated by decreasing the particle size, raising the reaction temperature, increasing the pressure, using a catalyst, and hypothetically, by bacterial addition. We aimed here at assessing quantitatively the added value of photosynthetic microbial activity on the efficiency of Mg-silicates carbonation processes. Synechococcus PCC 7942 (freshwater cyanobacteria) was selected for this study. Two magnesian silicate minerals (substrates) were chosen: a synthetic forsterite with nanometer-sized grains and an industrial ultramafic slag (scoria). All tests were performed at 20 ± 1 °C in closed and sterile 1L Schott® glass bottle reactors. With the aim to elucidate the interaction between mineral phases and bacteria, we used pH and concentration measurements, scanning and transmission electron microscopy along with Raman spectroscopy. The results show that, at ambient temperature, cyanobacteria Synechococcus can accelerate silicate dissolution (i.e. Mg2+ release) and then magnesium carbonate nucleation and precipitation by adsorption on the produced exopolymeric substances and local pH increase during photosynthesis, respectively.

Ionothermal synthesis was recently reported as a very attractive method to design new electrode materials for lithium ion batteries. Here, we report the use of hydrothermal synthesis, using water or a water-ionic liquid (IL) mixture as reacting medium, to prepare hexagonal shaped micrometric LiMPO 4 (M = Fe, Mn and Co) single crystals oriented along the b direction at 260°C. The influence of the reacting medium and the reaction time on the size of single crystals has been ascertained with the feasibility of growing after one month reacting time 700 μm LiFePO 4 single crystals in water-IL media and smaller ones (80-120 μm) in water. The latter exhibit electrochemical capacities of 145 mAh/g at C/2 rate with excellent capacity retention when cycled at 100°C. Last, we show a novel way to decorate the surface of LiFePO 4 crystals through the reduction of silver nitrate into metallic silver. This enables an easy determination of the crystal growth directions while providing insights in the lithium diffusion processes. © 2012 Elsevier B.V.

Polyanionic electrode materials offer an attractive combination of safety benefits and tunable redox potentials. Thus far, phosphate-based phases have drawn the most interest with a subsequent surge of activity focused on the newly discovered family of fluorosulfate phases. Here, we report the preparation of a new potassium-based fluorosulfate, KFeSO4F, which, with removal of K, leads to a new polymorph of FeSO4F crystallizing in the high-temperature structure of KTiOPO4. This new phase which contains large, empty channels, is capable of reversibly inserting 0.9 Li+ per unit formula and can accommodate a wide variety of alkali ions including Li+, Na+, or K+. This finding not only expands the rich crystal chemistry of the fluorosulfate family but further suggests that a similar strategy can apply to other K-based polyanionic compounds in view of stabilizing new attractive host structures for insertion reactions. © 2012 American Chemical Society.

Our work in metal fluorosulphate chemistry, which was triggered by the discovery of the tavorite-phase of LiFeSO 4F, has unveiled many novel Li- and Na-based phases with desirable electrochemical and/or transport properties. Further exploring this rich crystal chemistry, we have synthesized the Na-based magnesium, copper and zinc fluorosulphates, which crystallise in the maxwellite (tavorite-like framework) structure just as their Fe and Co counterparts, which were previously reported. These phases show ionic conductivities in the range of ∼10 -7 S cm -1 or ∼10 -11 S cm -1 depending upon their synthesis process and no reversible electrochemical activity versus Na. © 2011 Elsevier Masson SAS. All rights reserved.

The recent discovery of electrochemical activity at 3.6 V vs Li +/Li 0 in LiFeSO 4F has generated widespread research activity in this new family of fluorosulfate electrode materials aiming at either increasing the Fe 3+/Fe 2+ redox potential, searching for new active members, or extending this family to hydroxyl-fluorosulfates. Here we present a new low temperature single step synthesis of FeSO 4F 1-yOH y phases using FeF 3 and Fe 2(SO 4) 3•nH 2O as precursors. Using thorough chemical analytical techniques to test for F - content in conjunction with Mössbauer measurements, we demonstrate the existence of a limited solid solution (0.35 < y<1) within this system. Members pertaining to this solid solution have a redox activity ranging from 3.2 to 3.6 V vs Li +/Li 0 and show sustained reversible capacity retention of 130 mAh/g which makes them potentially interesting for Li-based polymer batteries. We demonstrate that the Li-insertion-deinsertion mechanism depends markedly on the sample F -content by using joint in situ XRD and Mössbauer spectroscopy. Moreover, we show the versatility of our synthetic approach by extending it to the elaboration of Fe 1-zM zSO 4F 1-yOH y phases with M = Ti and V. © 2012 American Chemical Society.

Low temperature solvothermal synthesis routes are increasingly being pursued as energy-savvy ways, as opposed to conventional solid-state synthesis, to produce electrode materials. This current work reports ionothermal synthesis, using pristine ionic liquids (ILs) as reacting media, to produce LiMnPO 4 (LMP) in the temperature range of 220-250 °C at ambient pressure. The role of various processing parameters and different types of ionic liquids on the structure and morphology of LiMnPO 4 has been reported. Further, ionothermal synthesis can be modified by altering the nature of reacting media by addition of partially miscible solvent to ionic liquids. Here, in addition, we demonstrate three modified versions of ionothermal synthesis, namely (a) water-micelles (nano-reactors) entrapped in ILs, yielding nanoparticles, (b) carbon-assisted IL synthesis as a one-step production of carbon-coated LiMnPO 4 and (c) diol-assisted ionothermal synthesis forming platelet-morphology. The resulting IL-synthesized LiMnPO 4 olivines were found to deliver reversible capacity close to 100 mA h g -1 (at a rate of C/20) with excellent cycling stability involving standard two-phase lithium (de)insertion mechanism. © 2010 The Royal Society of Chemistry.

Searching for possible new cathode materials with the ability to outperform LiFePO 4, our group has recently discovered LiFeSO 4F, a novel metal fluorosulphate compound. Needing no further optimization, it delivers excellent reversible capacity (∼140 mAh/g) involving a 3.6 V Fe II/III redox plateau. This parent fluorosulphate phase has been synthesized by three different routes; namely ionothermal synthesis, solid-state synthesis and polyol-assisted synthesis. These low temperature synthesis routes are described focusing on synthesis of LiFeSO 4F. Furthermore, these methods were successfully employed to unravel other LiMSO 4F compounds (M =Co/Ni/Mn/Zn) as well as sodium-based metal fluorosulphate NaMSO 4F compounds (M = Fe/Co/Ni/Mn). These syntheses were realized at temperature not exceeding 300°C. We have discovered many interesting and at times intriguing structural, electrochemical and transport properties in these fluorosulphate materials. A few of these findings are illustrated to show the richness of the metal fluorosulphate chemistry. ©The Electrochemical Society.

Dissolution of fayalite has been monitored in a small size batch reactor at a constant pressure of 30MPa and temperatures of 50, 65, 80 and 100°C, either in dilute HCl or in acetate buffered solutions. The technique, based on in situ X-ray absorption spectroscopy measurements, allowed simultaneous measurements of aqueous iron concentration and speciation as a function of time under high pressure and high temperature conditions. Far from equilibrium, dissolution rate normalised to geometric surface area (Rnet) can be described in dilute HCl solutions by:Rnet=k0exp-Ea/RTaH+nwith log(k0)=0.17±0.63 (k0 being expressed in molcm-2s-1); Ea=45,100±4200Jmol-1; n=0.74±0.15, so that Rnet is expressed in molcm-2s-1. These results are found to be consistent with some previous fayalite dissolution studies. In acetate buffered solutions, the dissolution rate was found to be enhanced and positively correlated with the activity of acetate. Whereas speciation of Fe2+ in HCl solutions is dominated by hexahydrated octahedral species, the combination of ab initio XANES calculations, measurement of X-ray absorption spectra, and thermodynamic modelling allowed us to determine that aqueous Fe2+ was complexed octahedrally with two acetate ligands, each bonded to iron through one oxygen atom, the corresponding formula being Fe(CH3COO)2·4H2O. Supposing that surface complexes resemble the major complex species in solution, this solvation by acetate ions would explain the observed enhancement of the dissolution rate, because of the nucleophilic attack of acetate ligands at the silicate surface. © 2010.

In the quest for next-generation cathodes for Li-ion batteries, our group has come up with a novel metal fluorosulphate material LiFeSO 4F tying the benefits of sulphate polyanions with fluorine chemistry. It delivers excellent capacity (∼140 mAh/g) involving a 3.6 V Fe +2/+3 redox plateau along with good rate capability and capacity retention. Following, we have discovered various isostructural LiMSO 4F compounds (M = Co, Ni, Mn) as well as sodium-based metal fluorosulphate NaMSO 4Fcompounds (M = Fe, Co, Ni, Mn). All these novel compounds have been prepared using low temperature synthesis, not exceeding 300°C and their structures have been solved. In an effort to examine and improve the electrochemical properties of electrochemically active AFeSO 4F (A = Li, Na) homologues, we hereby investigate the synthesis, crystal structure, conductivity and electrochemical behaviour of 3d-metal substituted fluorosulphates A(Fe 1-xM x)SO 4F (A = Li, Na; M = Co, Ni, Mn) compounds. ©The Electrochemical Society.

Nanostructured LiMnPO 4 was synthesized via a low temperature ionothermal synthesis route using various ionic liquids as reacting media. After due optimization of different processing parameters, LiMnPO 4 of varied size and morphology were processed at temperature as low as 200-250°C Further, a modified ionothermal synthesis using a mixture of ionic liquid with propanediols was performed to yield platelet-shaped nanoscale LiMnPO 4. The structure, morphology and electrochemical properties of these LiMnPO 4 have been reported showing reversible capacity of 95 mAh/g with good cycling stability. This study shows the versatility and novelty of ionothermal synthesis method to tailor the size, orientation and morphology of olivine-LiMnPO 4. ©The Electrochemical Society.

3d-metal fluorosulphates that have a tavorite-type structure (e.g., LiFeSO4F) were recently reported as attractive positive electrode candidates for future Li-ion batteries aimed at large volume markets. These new fluorosulphates had to be synthesized via ionothermal synthesis owing to both their thermal instability at temperatures greater than 300 °C and their water solubility. In an attempt to depart from ionothermal synthesis, low-temperature solid-state reactions and solvothermal processes were successfully tried.The latter technique,which is reported herein, proceedswithwater as the solvent and has led to a new family of fluorosulphatesNaMSO4F3 2H2Othat crystallize in amonoclinic unit cell (SG=P21/m) similar to the uklonskovite-type structure earlier proposed for NaMgSO4F3 2H2O. These new phases show no electrochemical activity with either Li or Na metal and have room temperature ionic conductivities on the order of 1 × 10-9 S cm-1. Additionally, we have discovered the feasibility, upon controlled dehydration of the NaMSO4F.2H2O phases, to prepare NaMSO4F phases adopting a derived tavoritetype structure and displaying ionic conductivities around 10-7 S cm-1. Finally, this finding opens the possibility to achieve Li-based fluorosulphates via two-step synthetic pathways. © 2010 American Chemical Society.

Ionothermal synthesis has recently been used to prepare a fluorosulfate (LiFeSO4 F) capable of reversibly intercalating Li at 3.6 V vs Li, making this material a serious contender to LiFePO4 for HEV and electric vehicle applications. Although fluorosulfates are made from low cost and abundant starting materials, their synthesis is costly because of the use of ionic liquids as synthetic medium. Herein, we report a solid-state process by which LiFeSO4 F can be synthesized without the use of ionic liquids but at the expense of both longer reaction time and weakly contaminated samples. Additionally, we show how powerful Mössbauer spectroscopy can be in the optimization of the various stages of electrode preparation as shown through the synthesis of LiFeSO4 F and its implementation into an electrode. The importance of having Fe3+-free hydrated precursors to routinely obtain pure LiFeSO4 F samples is shown together with the need to optimize ballmilling conditions to preserve Fe3+-free LiFeSO 4 F composites. Samples prepared via this low temperature solid-state process show battery performances approaching those of samples prepared using ionic liquids as synthetic medium. Furthermore, this process can be extended to the synthesis of the other members of the fluorosulfates AMSO4 F family with A=Li, Na and M=Fe, Co, and Ni. © 2010 The Electrochemical Society.

Li-ion batteries have contributed to the commercial success of portable electronics, and are now in a position to influence higher-volume applications such as plug-in hybrid electric vehicles. Most commercial Li-ion batteries use positive electrodes based on lithium cobalt oxides. Despite showing a lower voltage than cobalt-based systems (3.45 V versus 4 V) and a lower energy density, LiFePO 4 has emerged as a promising contender owing to the cost sensitivity of higher-volume markets. LiFePO 4 also shows intrinsically low ionic and electronic transport, necessitating nanosizing and/or carbon coating. Clearly, there is a need for inexpensive materials with higher energy densities. Although this could in principle be achieved by introducing fluorine and by replacing phosphate groups with more electron-withdrawing sulphate groups, this avenue has remained unexplored. Herein, we synthesize and show promising electrode performance for LiFeSO 4 F. This material shows a slightly higher voltage (3.6 V versus Li) than LiFePO 4 and suppresses the need for nanosizing or carbon coating while sharing the same cost advantage. This work not only provides a positive-electrode contender to rival LiFePO 4, but also suggests that broad classes of fluoro-oxyanion materials could be discovered. © 2010 Macmillan Publishers Limited. All rights reserved.

We have recently reported a promising 3.6 V metal fluorosulphate (LiFeSO4F) electrode, capable of high capacity, rate capability, and cycling stability. In the current work, we extend the fluorosulphate chemistry from lithium to sodium-based systems. In this venture, we have reported the synthesis and crystal structure of NaMSO4F candidates for the first time. As opposed to the triclinic-based LiMSO4F phases, the NaMSO4F phases adopt a monoclinic structure. We further report the degree and possibility of forming Na(Fe1-xMx)SO 4F and (Na1-xLix)MSO4F (M = Fe, Co, Ni) solid-solution phases for the first time. Relying on the underlying topochemical reaction, we have successfully synthesized the NaMSO4F, Na(Fe1-xMx)SO4F, and (Na1-xLi x)MSO4F products at a low temperature of 300 °C using both ionothermal and solid-state syntheses. The crystal structure, thermal stability, ionic conductivity, and reactivity of these new phases toward Li and Na have been investigated. Among them, NaFeSO4F is the only one to present some redox activity (Fe2+/Fe3+) toward Li at 3.6 V. Additionally, this phase shows a pressed-pellet ionic conductivity of 10 -7 S·cm-1. These findings further illustrate the richness of the fluorosulphate crystal chemistry, which has just been recently unveiled. © 2010 American Chemical Society.

Fluoride-based materials have regained interest within the field of Li-ion batteries largely due to the advent of nanosizing which has transformed the insulating insertion compounds into attractive electrode materials. Herein we demonstrate the effectiveness of ionothermal synthesis in the preparation of nanometric LiFePO(4)F and LiTiPO(4)F phases with structures isotopic to tavorite LiFePO(4)(OH) at temperatures of only 260 degrees C, while temperatures of 600-700 degrees C are required to obtain coarse powders via the ceramic method. However, the red ox-active phases, which are obtained in a high state of division, have lower redox voltages than LiFePO(4) despite the presence of fluorine. Additionally, LiTiPO(4)F shows staircase charge/discharge profiles with Ti(2/3+) and Ti(3/4+) couples. Though quite unusual in lithium intercalation oxides, a hint of a Li-driven Fe(3/4+) transition has been detected in LiFePO(4)F.

LiFeSO4 F, which can be synthesized either via an ionothermal or solid-state route, stands as a possible alternative to LiFePO4 for the next generation of Li-ion batteries. Here we demonstrate a different route to prepare this material. It consists of (i) combining stoichiometric amounts of FeSO4 Fn H 2 O and LiF in a powdered polymeric media, which has a low melting point and remains stable up to 300°C, and (ii) recovering and purifying the reacted powder by washing it in organic solvent. This method offers advantages in terms of both cost and kinetics while providing powders that have similar performances vs Li. © 2010 The Electrochemical Society.

A theoretical study of the lithium intercalated LiMSO4F and deintercalated MSO4F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond predictions of structural evolution and average voltages versus a lithium electrode, we have applied partial density of states and Bader's topological analysis of the electron density to the study of lithium deintercalation. Upon lithium extraction, charge rearrangement occurs for nickel between different d-orbitals, but with little net positive charge gain, while cobalt and iron atoms end up with a clear oxidized state. The participation of oxygen ions in accepting the electron of the lithium is thus enhanced for LiNiSO4F. However, this effect does not affect the long-range electrostatic interactions a lot in the lithiated phase, since the valence of all transition metals is very close due to initial lower oxidized state for the Ni atom in the host. It is found that this is not essentially a long-range electrostatic interaction within the lithiated phase but within the host which explains, at least partly, the increase in voltage by passing from Fe to Ni. Our results also shed light upon the possibility of getting an approximate evaluation of the local strain associated with delithiation from the atomic volume evolutions, which are also likely to affect the electrochemical potential. © 2010 the Owner Societies.

In the current scenario, Li-ion batteries are no longer limited to portable electronic devices, but are rapidly gaining momentum to enter the large-scale hybrid automotive market owing to their adequate energy density coupled with their low cost and safety. LiFePO4 is the front-runner candidate in this sector mainly due to its economic cost and operational safety. Recently, our group has discovered a novel 3.6 V metal fluorosulfate (LiFeSO4F) electrode system, which combines sulfate polyanions with fluorine chemistry to deliver excellent conductivity and electrochemical capacity. In the current study, we extend our effort to investigate the structure and electrochemical properties of 3d-transition metal (M = Co, Ni, Mn) substituted fluorosulfates. Toward this goal, we have adopted ionothermal synthesis to fabricate three families of solid-solution systems, namely Li(Fe1-xCo x)SO4F, Li(Fe1-xNix)SO4F and Li(Fe1-xMnx)SO4F at temperatures as low as 300 °C. The structure, thermal stability and electrochemical properties of these mixed sulfate phases along with the end members (LiCoSO4F, LiNiSO4F and LiMnSO4F) have been examined using a suite of characterization techniques. Overall, a 3.6 V Fe2+/3+ redox reaction is observed with no signature of Co2+/3+, Ni2+/3+ or Mn2+/3+ reaction. These metal fluorosulfate systems, delivering near theoretical capacity, stand as an alternative new class of electrodes for varied commercial applications. © 2010 The Royal Society of Chemistry.

LiFeP O4 is presently the most studied electrode material for battery applications. It can be prepared via solution, although it requires well-controlled pH conditions to master the iron valence state in the newly created material. Here we report its synthesis via the use of "latent bases" capable of releasing a nitrogen base upon heating. This way of controlling the reaction pH enables, in the absence of excess Li, the preparation of Fe+3 -free LiFeP O4 powders having various morphologies and showing good electrochemical performance. This approach is shown to offer great opportunities for the low-temperature synthesis of various electrode materials. © 2008 The Electrochemical Society.

Owing to cost and abundance considerations, Na-based electrode materials are regaining interest, especially those that can be prepared at low temperatures. Here, we report the low temperature synthesis of highly divided Na-based fluorophosphates (Na2 MP O4 F, M = Fe, Mn, or mixtures) in ionic liquid media. We show that this ionothermal approach enables the synthesis of these phases at temperatures as low as 270°C, while temperatures as high as 600°C are needed to obtain similar quality phases by solid-state reactions. Moreover, owing to their highly divided character, Na2 FeP O4 F powders made via such a process show better electrochemical performances vs either Li or Na than their ceramic counterparts. In contrast, regardless of how they were made, the Na2 MnP O 4 F powders, which crystallize in a three-dimensional (3D) tunnel structure rather than in the two-dimensional (2D)-layered structure of Na 2 FeP O4 F, were poorly electroactive. Substituting 0.25 Fe for Mn in Na2 Fe1-x Mnx P O4 F is sufficient to trigger a 2D-3D structural transition and leads to a rapid decay of the materials electrochemical performances. A tentative explanation, based on structural considerations to account for such behavior, is given in this paper. © 2009 The Electrochemical Society.

As opposed to ceramic methods, low-temperature solvothermal-hydrothermal methods using liquid media as reaction support are less energy demanding to design new electrode materials; therefore, they tend to replace ceramic routes. Here, we report the use of ionic liquids as both solvent and template to enable the growth of LiFePO4 (LFP) powders with controlled size and morphology at temperatures at least 200 °C lower than those required for conventional ceramic methods, while showing excellent electrochemical performances versus lithium. An inherent advantage to the use of ionic liquids lies in the feasibility of carrying out the reaction at atmospheric pressure. Besides, the recovery of the powders from the reacting medium is particularly easy, as are the effluents and ionic liquid recycling. Additionally, it is shown that ionic liquids can be used as a structural directing agent to orient crystal growth and obtain powders adopting a single morphology. Needless to say, such a new approach, which is not specific to LiFePO4, offers great opportunities for the low-temperature synthesis of new electrode materials. © 2009 American Chemical Society.

The recent infatuation for LiFePO4 as positive electrode material in Li-ion batteries has prompted a renewed interest in olivine-type structures, with a view to enhance their conduction properties. We show that the dual substitution of Li for Fe and of P for Si in the olivine LiFePO 4 phase leads to a complete solid solution Li1-xFe 1+xP1-xSixO4 as deduced from combined X-ray diffraction, Mössbauer, and NMR experiments. Our findings challenge the common belief that the anionic network cannot be substituted. Moreover, it is found that such a substitution promotes Li intersite mixing between the olivine M1 and M2 sites. Such mixing, together with the worsening of the conducting properties of the dually substituted samples, is believed to be responsible for the poor electrochemical performances of the member's series. Beyond x = 0.20, the samples were electrochemically inactive. While the current materials are disappointing application-wise, such a study provides clues to the rich chemistry remaining to be unveiled with olivine-type structures in particular and polyanionic compounds in general. © 2008 American Chemical Society.

Enhanced sorption properties of ball-milled MgH2 are reported by adding NbF5. Among various catalyst amounts, 2 mol% of NbF5 reveals to be the optimum concentration leading to significant reduction of the desorption temperature as well as faster kinetics of ball-milled MgH2. At 200 °C, temperature at which MgH2 does not show any activity, Mg H2 Nb F5 / 2 mol % composite desorbs 3.2 wt.% of H2 in 50 mins. Interestingly, the addition of NbF5 is also associated with an increase in the desorption pressure. At 300 °C, Mg H2 Nb F5 / 2 mol % composite starts to desorb hydrogen at 600 mbar in comparison with 1 mbar for MgH2. Further improvements were successfully achieved by pre-grinding NbF5 prior to ball-milling the catalyst with MgH2. Such pre-ground NbF5 catalyzed MgH2 composite desorbs 3 wt.% of H2 at 150 °C. Improved properties are associated with smaller activation energies down to values close to the enthalpy of formation of MgH2. Finally, the mechanism at the origin of the enhancement is discussed in terms of catalyst stability, MgF2 formation and electronic density localization. © 2007 Elsevier B.V. All rights reserved.