Marine Reynaud

LiZnSO4F Made in an Ionic Liquid: A Ceramic Electrolyte Composite for Solid-State Lithium Batteries

The search for good solid electrolytes constitutes a major goal towards the development of safer lithium batteries. A few candidates do exist, but they suffer either from narrow electrochemical window stability or too low ionic conductivity. Herein we report the ionic-liquid-assisted synthesis of a novel LiZnSO4F fluorosulfate phase having a sillimanite LiTiOPO4-type structure, which on simply pressed samples shows a room-temperature ionic conductivity of 10 – 10 7 Scm 1 together with a 0–5 V electrochemical stability window range, while ionic-liquid-free LiZnSO4F shows an ionic conductivity four orders of magnitude lower (10 11 Scm ). While robustly reproducible but not yet fully understood, this finding offers new opportunities to tailor inorganic composites with higher ionic conductivity. The origin of such results is demonstrated to be rooted in a surface effect associated with the grafting of a lithium-containing ionic liquid layer. This finding opens up new opportunities for the design of ceramic composites with higher ionic conductivity and should serve as an impetus for further exploiting the chemistry of ionic liquid grafting on oxides. Renewable energy sources and electric automotive transportation are popular topics in today s energy-conscious society, hence placing rechargeable batteries as one of the major technological sciences in this new century. Advances in energy storage are a tribute to chemists abilities to design new and better materials. In the hunt for novel electrode materials, notions of sustainability must be considered. This is the reason why LiFePO4, which is made of inexpensive and abundant chemical elements, has attracted the attention of the research community despite its poor conducting properties. By particle downsizing and carbon nanocoating, LiFePO4/C composite overcomes transport limitations and is capable of reversibly and rapidly intercalating 0.9 Li (ca. 160 mA hg ) at a redox voltage of 3.43 V versus Li. Thus, it has become one of the most praised electrode materials for the next generation of rechargeable batteries for high-volume applications. Further exploring the chemistry of polyanionic-based insertion electrodes, we recently synthesized, by an ionothermal process, a novel 3.6 V LiFeSO4F electrode showing a reversible capacity nearing 140 mAh g 1 (theoretical capacity = 151 mAh g ), good rate capability, and cycling stability. This fluorosulfate was found to crystallize in a tavorite structure (space group P 1) with three-dimensional channels for Li diffusion as opposed to the one-dimensional channels in LiFePO4. Most likely, from the 3D versus 1D change in the conduction path, the use of LiFeSO4F powders will obviate the need for nanosizing or carbon coating, while the same cost and environmental advantages are maintained. Since our early report, we have considerably enlarged the fluorosulfate family with the discovery of AMSO4F (A = Li, Na and M = Co, Ni, Mn, etc.) homologues. This new family of materials, practically unknown a year ago, counts no less than 20 members showing related structures with either promising electrochemical or attractive ionic properties. Among them, the sodium-based 3d-metal fluorosulfates, which crystallize in a titanite structure (derived from the tavorite structure, space group P21/c) and have localized positions for the Na ions, were found to show a four-fold increase in ionic conductivity as compared to their Li-based counterparts on cold-pressed powders (10 7 S cm 1 for Na vs. 10 11 Scm 1 for Li at room temperature). While far from the hallmark solid-state electrolytes for future Li batteries such as Li1.5Al0.5Ge1.5(PO4)3 (LAG), Li1.3Al0.3Ti1.7(PO4)3 (LAT), and Li3+xPO4 xNx (LIPON), which have room-temperature conductivities of 2.8 10 4 Scm , 10 3 S cm , and 10 6 S cm , respectively, such a finding was an impetus to look for further fluorosulfate members as part of the effort to develop new ceramic electrolyte materials with increased conductivity, thus allowing a switch from thin-film to bulk technology in all solid-state batteries. Besides high ionic conductivity, a pivotal figure of merit for solid-state electrolytes is the width of their electrochemical stability window. This window is limited for ionic conducting ceramics containing 3d-metal elements, such as Li1.3Al0.3Ti1.7(PO4)3, owing to the reduction of Ti 4+ in Ti at approximately 2.4 V. So our strategy was to search for other members of the fluorosulfate AMSO4F family containing divalent metals that cannot be easily reduced or oxidized. Besides LiMgSO4F, the first reported fluorosulfate, [7] other attractive candidates could enlist lead, tin, or zinc to prepare AMSO4F phases. Mindful of the previously reported struc[*] Dr. P. Barpanda, Dr. J.-N. Chotard, Dr. C. Delacourt, M. Reynaud, Prof. M. Armand, Prof. J.-M. Tarascon Laboratoire de R activit et Chimie des Solides Universit de Picardie Jules Verne, CNRS UMR 6007 33, rue Saint Leu, 80039 Amiens (France) E-mail: jean-marie.tarascon@sc.u-picardie.fr Homepage: http://jmtarascon.tech.officelive.com

Design of new electrode materials for Li-ion and Na-ion batteries from the bloedite mineral Na2Mg(SO4)2·4H2O

Mineralogy offers a large database to search for Li- or Na-based compounds having suitable structural features for acting as electrode materials, LiFePO4 being one example. Here we further explore this avenue and report on the electrochemical properties of the bloedite type compounds Na2M(SO4)2·4H2O (M = Mg, Fe, Co, Ni, Zn) and their dehydrated phases Na2M(SO4)2 (M = Fe, Co), whose structures have been solved via complementary synchrotron X-ray diffraction, neutron powder diffraction and transmission electron microscopy. Among these compounds, the hydrated and anhydrous iron-based phases show electrochemical activity with the reversible release/uptake of 1 Na+ or 1 Li+ at high voltages of ∼3.3 V vs. Na+/Na0 and ∼3.6 V vs. Li+/Li0, respectively. Although the reversible capacities remain lower than 100 mA h g−1, we hope this work will stress further the importance of mineralogy as a source of inspiration for designing eco-efficient electrode materials.

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.

Chemical and structural indicators for large redox potentials in fe-based positive electrode materials

Li-ion batteries have enabled a revolution in the way portable consumer-electronics are powered and will play an important role as large-scale electrochemical storage applications like electric vehicles and grid-storage are developed. The ability to identify and design promising new positive insertion electrodes will be vital in continuing to push Li-ion technology to its fullest potential. Utilizing a combination of computational tools and structural analysis, we report new indicators which will facilitate the recognition of phases with the desired redox potential. Most importantly of these, we find there is a strong correlation between the presence of Li ions sitting in close-proximity to the redox center of polyanionic phases and the open circuit voltage in Fe-based cathodes. This common structural feature suggests that the bonding associated with Li may have a secondary inductive effect which increases the ionic character of Fe bonds beyond what is typically expected based purely on arguments of electronegativity associated with the polyanionic group. This correlation is supported by ab initio calculations which show the Bader charge increases (reflecting an increased ionicity) in a nearly linear fashion with the experimental cell potentials. These features are demonstrated to be consistent across a wide variety of compositions and structures and should help to facilitate the design of new, high-potential, and environmentally sustainable insertion electrodes.

FAULTS: a program for refinement of structures with extended defects

The FAULTS program is a powerful tool for the refinement of diffraction patterns of materials with planar defects. A new release of the FAULTS program is herein presented, together with a number of new capabilities, aimed at improving the refinement process and evolving towards a more user-friendly approach. These include the possibility to refine multiple sets of single-crystal profiles of diffuse streaks, the visualization of the model structures, the possibility to add the diffracted intensities from secondary phases as background and the new DIFFaX2FAULTS converter, among others. Three examples related to battery materials are shown to illustrate the capabilities of the program.

Order and disorder in NMC layered materials: a FAULTS simulation analysis

The program FAULTS has been used to simulate the X-ray powder diffraction (XRD), neutron powder diffraction (NPD), and electron diffraction (ED) patterns of several structural models for LiNi 1/3 Mn 1/3 Co 1/3 O 2 , including different types of ordering of the transition metal (TM) cations in the TM slabs, different amounts of Li + /Ni II+ cation mixing and different amounts of stacking faults. The results demonstrate the relevance of the structural information provided by NPD and ED data as compared with XRD to characterize the microstructure of NMC (LiNi 1− y-z Mn y Co z O 2 ) compounds.

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.