Mohamed Ati

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.

Preparation, Structure, and Electrochemistry of Layered Polyanionic Hydroxysulfates: LiMSO4OH (M = Fe, Co, Mn) Electrodes for Li-Ion Batteries

The Li-ion rechargeable battery, due to its high energy density, has driven remarkable advances in portable electronics. Moving toward more sustainable electrodes could make this technology even more attractive to large-volume applications. We present here a new family of 3d-metal hydroxysulfates of general formula LiMSO4OH (M = Fe, Co, and Mn) among which (i) LiFeSO4OH reversibly releases 0.7 Li(+) at an average potential of 3.6 V vs Li(+)/Li(0), slightly higher than the potential of currently lauded LiFePO4 (3.45 V) electrode material, and (ii) LiCoSO4OH shows a redox activity at 4.7 V vs Li(+)/Li(0). Besides, these compounds can be easily made at temperatures near 200 °C via a synthesis process that enlists a new intermediate phase of composition M3(SO4)2(OH)2 (M = Fe, Co, Mn, and Ni), related to the mineral caminite. Structurally, we found that LiFeSO4OH is a layered phase unlike the previously reported 3.2 V tavorite LiFeSO4OH. This work should provide an impetus to experimentalists for designing better electrolytes to fully tap the capacity of high-voltage Co-based hydroxysulfates, and to theorists for providing a means to predict the electrochemical redox activity of two polymorphs.

Understanding and Promoting the Rapid Preparation of the Triplite-Phase of LiFeSO4F for Use as a Large-Potential Fe Cathode

The development of new electrode materials, which are composed of Earth-abundant elements and that can be made via eco-efficient processes, is becoming absolutely necessary for reasons of sustainable production. The 3.9 V triplite-phase of LiFeSO(4)F, compared to the 3.6 V tavorite-phase, could satisfy this requirement provided the currently complex synthetic pathway can be simplified. Here, we present our work aiming at better understanding the reaction mechanism that govern its formation as a way to optimize its preparation. We first demonstrate, using complementary X-ray diffraction and transmission electron microscopy studies, that triplite-LiFeSO(4)F can nucleate from tavorite-LiFeSO(4)F via a reconstructive process whose kinetics are significantly influenced by moisture and particle morphology. Perhaps the most spectacular finding is that it is possible to prepare electrochemically active triplite-LiFeSO(4)F from anhydrous precursors using either reactive spark plasma sintering (SPS) synthesis in a mere 20 min at 320 °C or room-temperature ball milling for 3 h. These new pathways appear to be strongly driven by the easy formation of a disordered phase with higher entropy, as both techniques trigger disorder via rapid annealing steps or defect creation. Although a huge number of phases adopts the tavorite structure-type, this new finding offers both a potential way to prepare new compositions in the triplite structure and a wealth of opportunities for the synthesis of new materials which could benefit many domains beyond energy storage.

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.

A new room temperature and solvent free carbon coating procedure for battery electrode materials

Carbon coating on battery electrode active material powders is a common practice in order to improve their electronic conductivity and the battery calendar life by limiting side reactions (i.e. active material surface degradation and electrolyte decomposition). Such a coating is currently achieved through chemical procedures involving dispersing the powder in a liquid medium with a carbon precursor followed by thermolysis at high temperatures (ca. 700 °C). This energy consuming procedure has the drawback of not being applicable to materials which may decompose or reduce under such conditions. We present herein an alternative procedure based on physical deposition of carbon, carried out at room temperature under dry conditions, hence avoiding the limitations mentioned above and being generally applicable to any electrode active material. Moreover it allows easy achievement of a homogeneous conformal coating with fine control of the coating thickness. Results on selected materials are reported to exemplify the wide application spectrum and performance improvements induced by the coating.

Synthesis, Structure, and Magnetic Properties of the NaCoXO4F·2H2O Phases Where X = S and Se

A novel hydrated fluoroselenate NaCoSeO(4)F·2H(2)O has been synthesized, and its structure determined. Like its sulfate homologue, NaCoSO(4)F·2H(2)O, the structure contains one-dimensional chains of corner-sharing MO(4)F(2) octahedra linked together through F atoms sitting in a trans configuration with respect to each other. The magnetic properties of the two phases have been investigated using powder neutron diffraction and susceptibility measurements which indicate antiferromagnetic ordering along the length of the chains and result in a G-type antiferromagnetic ground state. Both compounds exhibit a Néel temperature near 4 K, and undergo a field-induced magnetic phase transition in fields greater than 3 kOe.

Synthesis of New Fluorosulphate Materials Using Different Approaches

Searching for possible new cathode materials with the ability to outperform LiFePO4, our group has recently discovered LiFeSO4F, a novel metal fluorosulphate compound. Needing no further optimization, it delivers excellent reversible capacity (~140 mAh/g) involving a 3.6 V FeII/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 processing routes are described focusing on synthesis of LiFeSO4F. Furthermore, these methods were successfully employed to unravel other LiMSO4F compounds (M = Co/Ni/Mn/Zn) as well as sodium-based metal fluorosulphate NaMSO4F 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.

Crystal Structure and Electrochemical Study of A(Fe1-xMx)SO4F (A = Li/Na; M = Co/Ni/Mn) Fluorosulfates Prepared by Low Temperature Ionothermal Synthesis

In the quest for next-generation cathodes for Li-ion batteries, our group has come up with a novel metal fluorosulphate material LiFeSO4F 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 LiMSO4F compounds (M = Co, Ni, Mn) as well as sodium-based metal fluorosulphate NaMSO4Fcompounds (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 AFeSO4F (A = Li, Na) homologues, we hereby investigate the synthesis, crystal structure, conductivity and electrochemical behaviour of 3d-metal substituted fluorosulphates A(Fe1-xMx)SO4F (A = Li, Na; M = Co, Ni, Mn) compounds.