Karim Djellab

Ionothermal Synthesis of Sodium-Based Fluorophosphate Cathode Materials

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 (Na 2 MPO 4 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, Na 2 FePO 4 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 Na 2 MnPO 4 F powders, which crystallize in a three-dimensional (3D) tunnel structure rather than in the two-dimensional (2D)-layered structure of Na 2 FePO 4 F, were poorly electroactive. Substituting 0.25 Fe for Mn in Na 2 Fe 1-x Mn x PO 4 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.

Structure and electrochemical properties of novel mixed Li(Fe1−xMx)SO4F (M = Co, Ni, Mn) phases fabricated by low temperature ionothermal synthesis

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−xCox)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.

Direct and modified ionothermal synthesis of LiMnPO4 with tunable morphology for rechargeable Li-ion batteries

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 LiMnPO4 (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 LiMnPO4 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 LiMnPO4 and (c) diol-assisted ionothermal synthesis forming platelet-morphology. The resulting IL-synthesized LiMnPO4 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.

Enzymatic hydrolysis of ionic liquid-pretreated celluloses: contribution of CP-MAS 13C NMR and SEM.

The supramolecular structure of four model celluloses was altered prior to their enzymatic saccharification using two ionic liquid pretreatments: one with the commonly used 1-ethyl-3-methylimidazolium acetate ([Emim](+)[CH(3)COO](-)) and the other with the newly developed 1-ethyl-3-methylimidazolium methylphosphonate ([Emim](+)[MeO(H)PO(2)](-)). The estimation of crystallinity index (CrI) by solid state (13)C nuclear magnetic resonance for each untreated/pretreated celluloses was compared with the performances of their enzymatic hydrolysis. For α-cellulose, both pretreatments led to a significant decrease in CrI from 25% to 5% but had no effect on glucose yields. In contrast, The [Emim](+)[MeO(H)PO(2)](-) pretreatment on the long fibers of cellulose had no significant effect on the CrI although a conversion yield in glucose of 88% is obtained versus 32% without pretreatment. However, scanning electron microscopy analysis suggested a loss of fiber organization induced by both ionic liquid pretreatments leading to a larger accessibility by cellulases to the cellulose surface.

Mild pretreatment and enzymatic saccharification of cellulose with recycled ionic liquids towards one-batch process.

The development of second-generation bioethanol involves minimizing the energy input throughout the processing steps. We report here that efficient ionic liquid pretreatments of cellulose can be achieved with short duration times (20 min) at mild temperature (45°C) with [Emim](+)[MeO(H)PO(2)](-) and at room temperature (25 °C) with [Emim](+)[CH(3)COO](-). In these conditions, yields of glucose were increased by a factor of 3. In addition, the recycling of these two imidazolium-based ILs can be performed in maintaining their efficiency to pretreat cellulose. The short time and mild temperature of cellulose solubilization allowed a one-batch processing of [Emim](+)[MeO(H)PO(2)](-) IL-pretreatment and saccharification. In the range from 0 to 100% IL in an aqueous enzymatic medium, the glucose yields were improved at IL proportions between 10 and 40%. The maximum yield at 10% IL is very promising to consider one batch process as efficient as two-step process.

An inconvenient influence of iridium(III) isomer on OLED efficiency

The recently reported heteroleptic cyclometallated iridium(III) complex [Ir(2-phenylpyridine)(2)(2-carboxy-4-dimethylaminopyridine)] N984 and its isomer N984b have been studied more in detail. While photo- and electrochemical properties are very similar, DFT/TDDFT calculations show that the two isomers have different HOMO orbital characteristics. As a consequence, solution processed OLEDs made using a mixture of N984 and isomer N984b similar to vacuum processed devices show that the isomer has a dramatic detrimental effect on the performances of the device. In addition, commonly used thermogravimetric analysis is not suitable for showing the isomerization process. The isomer could impact performances of vacuum processed OLEDs using heteroleptic cyclometallated iridium(III) complexes as dopant.

Fluorosulfate Positive Electrode Materials Made with Polymers as Reacting Media

LiFeS0 4 F, which can be synthesized either via an ionothermal or solid-state route, stands as a possible alternative to LiFeP0 4 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 FeSO 4 F·nH 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.

Crystal structures and sodium/silver distributions within the ionic conductors Na5Ag2Fe3(As2O7)4 and Na2Ag5Fe3(P2O7)4

The crystal structures of new Na5Ag2Fe3(As2O7)4 and Na2Ag5Fe3(P2O7)4 compounds, prepared through ion exchange from Na7Fe3(X2O7)4 (X = P, As) are reported. They crystallize in the monoclinic C2/c space group and exhibit a Na/Ag ordering on cooling. Crystal structures were determined from single crystal X-ray diffraction at 100 and 298 K for each composition. The structure consists of FeO6 octahedra sharing their corners with X2O7 dimers (X = P, As) to form a three-dimensional framework [Fe3(X2O7)4]7− into which the sodium/silver ions are located. The differences between the four structures lie on the distribution of the sodium/silver ions within this framework giving a developed insight of the ionic diffusion paths.

Ionothermal Synthesis and Electrochemical Characterization of Nanostructured Lithium Manganese Phosphates

Nanostructured LiMnPO4 was synthesized via a low temperature ionothermal synthesis route using various ionic liquids as reacting media. After due optimization of different processing parameters, LiMnPO4 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 LiMnPO4. The structure, morphology and electrochemical properties of these LiMnPO4 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-LiMnPO4.