Jean-Noël Chotard

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.

A 3.90 V iron-based fluorosulphate material for lithium-ion batteries crystallizing in the triplite structure

Li-ion batteries have empowered consumer electronics and are now seen as the best choice to propel forward the development of eco-friendly (hybrid) electric vehicles. To enhance the energy density, an intensive search has been made for new polyanionic compounds that have a higher potential for the Fe²⁺/Fe³⁺ redox couple. Herein we push this potential to 3.90 V in a new polyanionic material that crystallizes in the triplite structure by substituting as little as 5 atomic per cent of Mn for Fe in Li(Fe(1-δ)Mn(δ))SO₄F. Not only is this the highest voltage reported so far for the Fe²⁺/Fe³⁺ redox couple, exceeding that of LiFePO₄ by 450 mV, but this new triplite phase is capable of reversibly releasing and reinserting 0.7-0.8 Li ions with a volume change of 0.6% (compared with 7 and 10% for LiFePO₄ and LiFeSO₄F respectively), to give a capacity of ~125 mA h g⁻¹.

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.

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

Structural and Mechanistic Insights into Fast Lithium-Ion Conduction in Li4SiO4–Li3PO4 Solid Electrolytes

Solid electrolytes that are chemically stable and have a high ionic conductivity would dramatically enhance the safety and operating lifespan of rechargeable lithium batteries. Here, we apply a multi-technique approach to the Li-ion conducting system (1-z)Li4SiO4-(z)Li3PO4 with the aim of developing a solid electrolyte with enhanced ionic conductivity. Previously unidentified superstructure and immiscibility features in high-purity samples are characterized by X-ray and neutron diffraction across a range of compositions (z = 0.0-1.0). Ionic conductivities from AC impedance measurements and large-scale molecular dynamics (MD) simulations are in good agreement, showing very low values in the parent phases (Li4SiO4 and Li3PO4) but orders of magnitude higher conductivities (10(-3) S/cm at 573 K) in the mixed compositions. The MD simulations reveal new mechanistic insights into the mixed Si/P compositions in which Li-ion conduction occurs through 3D pathways and a cooperative interstitial mechanism; such correlated motion is a key factor in promoting high ionic conductivity. Solid-state (6)Li, (7)Li, and (31)P NMR experiments reveal enhanced local Li-ion dynamics and atomic disorder in the solid solutions, which are correlated to the ionic diffusivity. These unique insights will be valuable in developing strategies to optimize the ionic conductivity in this system and to identify next-generation solid electrolytes.

Improving the energy density of Na3V2(PO4)3-based positive electrodes through V/Al substitution

The crystal chemistry and the electrochemical properties upon Na+ extraction/insertion of NASICON-type Na3AlyV2−y(PO4)3 compositions (y = 0.1, 0.25 and 0.5) were investigated. It was found that this family of V/Al substituted NASICON materials undergoes multiple reversible phase transitions between −50 °C and 250 °C upon heating, from monoclinic to rhombohedral symmetry, related to progressive disordering of Na+ ions within the framework. Na+ insertion/extraction mechanisms were monitored by operando X-ray diffraction. It is shown for the first time that substitution of aluminum for vanadium in Na3Al0.5V1.5(PO4)3 increases significantly the theoretical energy density of these promising positive electrodes (425 W h kg−1) due to its lighter molecular weight and the possibility of reversible operation on the V4+/V5+ redox couple at 3.95 V vs. Na+/Na.

Preparation, structure and electrochemistry of LiFeBO3: a cathode material for Li-ion batteries

LiMBO3 (M = Fe, Co, Mn) has been identified as an interesting new cathode material for Li-ion batteries. It was shown to be difficult to synthesize the material as a pure phase and in a highly electrochemically active form. Here we report several methods for the successful preparation of LiFeBO3, including traditional ceramic and self-combustion reactions. By decreasing the particle size and introducing in situ carbon coating, conventionally ceramic-synthesized LiFeBO3/C yields a first discharge of 210 mA h g−1 within the 1.5–4.5 V voltage window at a C/20 rate, 55 °C. Using high-resolution synchrotron X-ray diffraction, neutron powder diffraction and single crystal X-ray diffraction in combination with 6Li NMR and 57Fe Mossbauer spectroscopies, we present a “1Fe 2Li” complex cation distribution model for LiFeBO3 powder.

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.

Potassium Silanide (KSiH3): A Reversible Hydrogen Storage Material

KSi silicide can absorb hydrogen to directly form the ternary KSiH(3) hydride. The full structure of α-KSiD(3), which has been solved by using neutron powder diffraction (NPD), shows an unusually short Si-D lengths of 1.47 Å. Through a combination of density functional theory (DFT) calculations and experimental methods, the thermodynamic and structural properties of the KSi/α-KSiH(3) system are determined. This system is able to store 4.3 wt% of hydrogen reversibly within a good P-T window; a 0.1 MPa hydrogen equilibrium pressure can be obtained at around 414 K. The DFT calculations and the measurements of hydrogen equilibrium pressures at different temperatures give similar values for the dehydrogenation enthalpy (≈23 kJ mol(-1) H(2)) and entropy (≈54 J K(-1) mol(-1) H(2)). Owing to its relatively high hydrogen storage capacity and its good thermodynamic values, this KSi/α-KSiH(3) system is a promising candidate for reversible hydrogen storage.