Nadir Recham

A 3.6 V lithium-based fluorosulphate insertion positive electrode for lithium-ion batteries

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.

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.

Structural, transport, and electrochemical investigation of novel AMSO4F (A = Na, Li; M = Fe, Co, Ni, Mn) metal fluorosulphates prepared using low temperature synthesis routes.

We have recently reported a promising 3.6 V metal fluorosulphate (LiFeSO(4)F) 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 NaMSO(4)F candidates for the first time. As opposed to the triclinic-based LiMSO(4)F phases, the NaMSO(4)F phases adopt a monoclinic structure. We further report the degree and possibility of forming Na(Fe(1-x)M(x))SO(4)F and (Na(1-x)Li(x))MSO(4)F (M = Fe, Co, Ni) solid-solution phases for the first time. Relying on the underlying topochemical reaction, we have successfully synthesized the NaMSO(4)F, Na(Fe(1-x)M(x))SO(4)F, and (Na(1-x)Li(x))MSO(4)F products at a low temperature of 300 degrees 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, NaFeSO(4)F is the only one to present some redox activity (Fe(2+)/Fe(3+)) toward Li at 3.6 V. Additionally, this phase shows a pressed-pellet ionic conductivity of 10(-7) S x cm(-1). These findings further illustrate the richness of the fluorosulphate crystal chemistry, which has just been recently unveiled.

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.

Understanding the roles of anionic redox and oxygen release during electrochemical cycling of lithium-rich layered Li4FeSbO6.

Li-rich oxides continue to be of immense interest as potential next generation Li-ion battery positive electrodes, and yet the role of oxygen during cycling is still poorly understood. Here, the complex electrochemical behavior of Li4FeSbO6 materials is studied thoroughly with a variety of methods. Herein, we show that oxygen release occurs at a distinct voltage plateau from the peroxo/superoxo formation making this material ideal for revealing new aspects of oxygen redox processes in Li-rich oxides. Moreover, we directly demonstrate the limited reversibility of the oxygenated species (O2(n-); n = 1, 2, 3) for the first time. We also find that during charge to 4.2 V iron is oxidized from +3 to an unusual +4 state with the concomitant formation of oxygenated species. Upon further charge to 5.0 V, an oxygen release process associated with the reduction of iron +4 to +3 is present, indicative of the reductive coupling mechanism between oxygen and metals previously reported. Thus, in full state of charge, lithium removal is fully compensated by oxygen only, as the iron and antimony are both very close to their pristine states. Besides, this charging step results in complex phase transformations that are ultimately destructive to the crystallinity of the material. Such findings again demonstrate the vital importance of fully understanding the behavior of oxygen in such systems. The consequences of these new aspects of the electrochemical behavior of lithium-rich oxides are discussed in detail.

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.

LiMSO4F (M = Fe, Co and Ni): promising new positive electrode materials through the DFT microscope

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F 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 Baders 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 LiNiSO(4)F. 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.

Fluorosulfate Positive Electrodes for Li-Ion Batteries Made via a Solid-State Dry Process.

Ionothermal synthesis has recently been used to prepare a fluorosulfate (LiFeSO 4 F) capable of reversibly intercalating Li at 3.6 V vs Li, making this material a serious contender to LiFePO 4 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 LiFeSO 4 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 Mossbauer spectroscopy can be in the optimization of the various stages of electrode preparation as shown through the synthesis of LiFeSO 4 F and its implementation into an electrode. The importance of having Fe 3+ -free hydrated precursors to routinely obtain pure LiFeSO 4 F samples is shown together with the need to optimize ballmilling conditions to preserve Fe 3+ -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 AMSO 4 F family with A = Li, Na and M = Fe, Co, and Ni.

Biomineralized α-Fe2O3: texture and electrochemical reaction with Li

Sustainable batteries call for the development of new eco-efficient processes for preparation of electrode materials based on low cost and abundant chemical elements. Here we report a method based on bacterial iron biomineralization for the synthesis of α-Fe2O3 and its subsequent use as a conversion-based electrode material in Li batteries. This high-yield synthesis approach enlists (1) the room temperature formation of γ-FeOOH via the use of an anaerobic Fe(II)-oxidizing bacterium Acidovorax sp. strain BoFeN1 and (2) the transformation of these BoFeN1/γ-FeOOH assemblies into an alveolar bacteria-free α-Fe2O3 material by a short heat treatment under air. As the γ-FeOOH precursor particles are precipitated between the two membranes of the bacterial cell wall (40 nm-thick space), the final material consists of highly monodisperse nanometric ([similar]40 × 15 nm) and oriented hematite crystals, assembled to form a hollow shell having the same size and shape as the initial bacteria (bacteriomorph). This double level of control (nanometric particle size and particle organization at the micrometric scale) provided powders exhibiting (1) enhanced electrochemical reversibility when fully reacted with Li and (2) an impressive high rate capability when compared to non-textured primary α-Fe2O3 particles of similar size. This bacterially induced eco-efficient and scalable synthesis method opens wide new avenues to be explored at the crossroads of biomineralization and electrochemistry for energy storage.

Eco-Efficient Synthesis of LiFePO4 with Different Morphologies for Li-Ion Batteries

Formula 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 Formula -free Formula 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.