Search

Lithium diffusion coefficient (D) in LiyFeSO4F is investigated by means of three electrochemical techniques, namely potentiostatic intermittent titration technique (PITT), galvanostatic intermittent titration technique (GITT), and galvanostatic charge/discharge at different C-rates. The analytic equations used for analyzing PITT and GITT are based on radial diffusion in spherical particles, which is more suitable to the type of electrode studied here than the original equations derived by Wen [J. Electrochem. Soc., 126, 2258 (1979).] for a slab geometry. While PITT and GITT analyses with the analytic equations are only valid in the partial solid solution regions (y ≤ 0.29 and y ≥ 0.83 in LiyFeSO 4F), the analysis of galvanostatic charge/discharge with a mathematical model allows for the determination of D over the entire lithium composition range. The average D values found with PITT and GITT analyses are in good agreement with each other, and of the same order as those reported for LiyFePO4 in the literature (ca. 10-14 cm 2/s); However, D is larger for LiyFeSO4F in the Li-rich composition range than in the Li-poor one, whereas it is the opposite for LiyFePO4. This result could explain why Li yFeSO4F has a better rate capability on discharge than LiyFePO4. © 2011 The Electrochemical Society.

Searching for possible new cathode materials with the ability to outperform LiFePO 4, our group has recently discovered LiFeSO 4F, a novel metal fluorosulphate compound. Needing no further optimization, it delivers excellent reversible capacity (∼140 mAh/g) involving a 3.6 V Fe II/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 synthesis routes are described focusing on synthesis of LiFeSO 4F. Furthermore, these methods were successfully employed to unravel other LiMSO 4F compounds (M =Co/Ni/Mn/Zn) as well as sodium-based metal fluorosulphate NaMSO 4F 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. ©The Electrochemical Society.

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. © 2010 Macmillan Publishers Limited. All rights reserved.

We have recently reported a promising 3.6 V metal fluorosulphate (LiFeSO4F) 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 NaMSO4F candidates for the first time. As opposed to the triclinic-based LiMSO4F phases, the NaMSO4F phases adopt a monoclinic structure. We further report the degree and possibility of forming Na(Fe1-xMx)SO 4F and (Na1-xLix)MSO4F (M = Fe, Co, Ni) solid-solution phases for the first time. Relying on the underlying topochemical reaction, we have successfully synthesized the NaMSO4F, Na(Fe1-xMx)SO4F, and (Na1-xLi x)MSO4F products at a low temperature of 300 °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, NaFeSO4F is the only one to present some redox activity (Fe2+/Fe3+) toward Li at 3.6 V. Additionally, this phase shows a pressed-pellet ionic conductivity of 10 -7 S·cm-1. These findings further illustrate the richness of the fluorosulphate crystal chemistry, which has just been recently unveiled. © 2010 American Chemical Society.

An electrochemical cell designed to perform high temperature lithium battery tests has been developed adapting a typical Swagelok ® cell. The high temperature cell is intended to work in a wide temperature range, namely from room temperature up to 300 °C. It has been successfully tested at 250 °C using LiFePO 4 as cathode, LiTFSI as molten salt electrolyte and metallic lithium as anode. © 2006 Elsevier B.V. All rights reserved.

The intriguingly fast electrochemical response of the insulating LiFePO4 insertion electrode toward Li is of both fundamental and practical importance. Here we present a comprehensive study of its deinsertion/ insertion mechanism by high-resolution electron energy loss spectroscopy on thin platelet-type particles of LixFePO4 (bPnma axis normal to the surface). We find that the lithium deinsertion/insertion process is not well-described by the classical shrinking core model. Compositions of the same x value obtained by both deinsertion and insertion gave the same results, namely that the LixFePO4 so formed consists of a core of FePO4 surrounded by a shell of LiFePO 4 with respective ratios dependent on x. We suggest that lattice mismatch between the two end members may be at the origin of the peculiar microstructure observed. Furthermore, because of the appearance of isosbestic points on the overlaid EELS spectra, we provide direct experimental evidence that the nanometer interface between single-phase areas composed of LiFePO 4 or FePO4 is the juxtaposition of the two end members and not a solid solution. One future prospect of such knowledge is to determine strategies on how to control, on a large scale, the synthesis of nanometersized thin platelet-type particles to prepare high-rate LiFePO4 electrodes for future energy storage devices. © 2006 American Chemical Society.

High-temperature oxide melt solution calorimetry was performed on the battery material LiFePO4 and the orthorhombic and trigonal polymorphs of its delithiated form, FePO4. The enthalpies of formation from oxides and from elements at 25°C were determined. The phase transition of FePO4 from orthorhombic symmetry to trigonal symmetry was investigated using differential scanning calorimetry. The enthalpies of formation from oxides at 25°C for LiFePO4, o-FePO4, and t-FePO4 are -151.52±1.68, -113.68±1.26, and -102.01±1.26 kJ/mol, respectively. The enthalpy of transition from o-FePO4 to t-FePO4 is 11.67±1.56 kJ/mol. Thus the orthorhombic form of FePO4 is energetically more stable than the trigonal phase and is therefore stable at low temperatures. The equilibrium temperature of the o-t transition is probably sufficiently above room temperature, so that under the operating conditions of a battery, it is themodynamically impossible that o-FePO4 will decompose to t-FePO4. The t-o transition on cooling is kinetically hindered. © 2005 The Electrochemical Society. All rights reserved.

LiFePO4-based powders prepared through various synthesis conditions are presented. Depending on whether the precursors contain carbon or not, LiFePO4-based composites obtained contain significant amounts of carbon as well. We did not succeed in doping LiFePO4 with Nb and produced, instead, crystalline β-NbOPO4 and/or an amorphous (Nb,Fe,C,O,P) matrix around LiFePO4 particles. The total electrical conductivity is of ∼10-9S.cm-1 at 25°C with an activation energy of ca. 0.65 eV for pure LiFePO4 and LiFePO 4/β-NbOPO4 composite. C-containing LiFePO4 samples, including those that had been tentatively doped with Nb, are much more conductive (up to 1.6.10-1 S.cm-1) with an activation energy ΔE ∼ 0.08 eV. © 2005 Materials Research Society.

To better understand the factors responsible for the poor electrochemical performances of the olivine-type LiMnPO 4, various experiments such as chemical delithiation, galvanostatic charge and discharge, cyclic voltamperometry, and impedance conductivity, were carried out on both LiFePO 4 and LiMnPO 4. Chemical delithiation experiments confirmed a topotactic two-phase electrochemical mechanism between LiMnPO 4 and the fully delithiated phase MnPO 4 (a = 5.909(5) Å, b = 9.64(1) Å, and c = 4.768(6) Å). We conclude that the limiting factor in the MnPO 4/LiMnPO 4 electrochemical reaction is nested mostly in the ionic and/or electronic transport within the LiMnPO 4 particles themselves rather than in charge transfer kinetics or structural instability of the MnPO 4 phase. For instance, the electrical conductivity of LiMnPO 4 (σ ∼ 3.10 -9 S cm -1 at 573 K, ΔE ∼ 1.1 eV) was found to be several orders of magnitude lower than that of LiFePO 4 (σ ∼ 10 -9 S cm -1 at 298 K, ΔE ∼ 0.6 eV). © 2005 The Electrochemical Society. All rights reserved.

An experimental evidence of a solid solution LixFePO4 for 0 ≤ x ≤ 1 at 450 °C was discussed. Two metastable phases at room temperature with Li0.75FePO4 and Li0.5FePO 4 composition were analyzed. The unit-cell parameters for all the members of the LixFePO4 series were obtained from full pattern-matching refinements of x-ray diffraction (XRD) data recorded at 350 °C. The results may also lead to improved performances of these electrodes at elevated temperatures.

The crystal chemistry of two initial mixtures of LiFePO4 and heterosite FePO4 (0.5LiFePO4 + 0.5FePO4; 0.75LiFePO4 + 0.25FePO4) was investigated through Neutron diffraction at 350 and 370 °C, respectively, and at room temperature after cooling. At 350 and 370 °C, Li0.5FePO4 and Li 0.75FePO4 are refined as olivine-type single phases, in which Li+ ions are disordered. Significant anisotropic microstrains, within the (001)Pmnb planes, occur, which may be accounted for by heterogeneous distance distributions within and between the [100]Pmnb Li+ channels. On cooling back to room temperature, Li 0.5FePO4 and Li0.75FePO4 single phases separate into mixtures of FePO4 + Li ∼0.64FePO4 and LiFePO4 + Li ∼0.64FePO4, respectively. The Li content of this metastable intermediate phase may correspond to the occupancy of 2 out of 3 Li sites within [100]Pmnb Li+ channels. In Li 0,64FePO4, average LiO bonds are longer than in LiFePO4, whereas FeO bond lengths are shortened, due to a fraction of Fe(III). This may be at the origin of the metastability of such intermediate phase, and thus of the two-phase mechanism between LiFePO4 and FePO4.

Pure and well-crystallized LiMnPO4 powders were obtained by a direct precipitation route in an aqueous medium at 373 K. A thermodynamic study of the system Li+/Mn(II)/phosphate/ H2O identified a pH range in which LiMnPO4 precipitation was the most probable. From these theoretical considerations, the olivine-type compound precipitation turned out to be straightforward, i.e., no further thermal treatment was needed. A systematic study of the influence of synthesis parameters enabled tailoring of the size of the as-obtained particles. The smallest precipitated particles (∼100 nm) led to a global improvement of the electrochemical behavior when used in lithium batteries, consisting in lowering the polarization and enhancement of the reversible capacities (∼70 mAh/g at C/20). A two-phase Li extraction/insertion mechanism was identified, using the potential intermittent titration technique (PITT) and in situ X-ray diffraction, between LiMnPO4 and the delithiated phase MnPO4, indexed in the space group Pmnb with unit cell parameters a = 5.93(2) Å, b = 9.69(6) Å, and c = 4.78(1) Å.

This Perspective highlights, through several snapshot examples, the importance of electrochemically-driven redox reactions in tuning the electronic/ionic as well as magnetic properties of 3d-metal-based inorganic compounds through a careful control of the metal oxidation state. Although such redox reactions usually imply the electron-ionic duality, they can be extended to insulating compounds (LiFePO 4) or semiconductors (CoO) as long as we can combine electrochemistry at the nanoscale to reduce diffusion and migration limitations, and provide the compounds with electrons through metallic coating techniques. A thorough investigation of the composition-structure- property relationships of the Li xCoO 2 system, through the assembly of LiCoO 2/Li electrochemical cells has led to the identification of the CoO 2 phase, whose property and stability are discussed in terms of cationic-anionic redox competition, thus bearing some similarity with the high T c cuprate superconductors. Such a d-sp redox competition could have structural and electronic consequences. Encouraged by the recently reported superconductivity in Na xCoO 2;yH 2O phase, the room temperature Li xCuO 2 phase diagram was reinvestigated through Li-driven electrochemical reactions. A solid solution domain was unravelled but superconductivity was not evident. With Cu-based materials such as Cu 2.33V 4O 11, we have shown the feasibility of a new reversible Li electrochemically-driven copper extrusion/insertion process, owing to the enhanced copper diffusion within the structure.

In southeast Karakorum (northwest Himalaya, Pakistan), kilometric size migmatitic domes were exhumed in a context of north-south shortening during Neogene times. The domes are characterized by a conical shape, and ductile deformation criteria indicate both radial expansion and extrusion of the migmatitic core relative to the surrounding gneisses. Most of the domes are aligned along the dextral, strike-slip Shigar fault that is parallel to the N130°E Karakorum fault. Along the Shigar fault, exhumation of the domes is mainly vertical with a slight dextral component. We propose that the high temperature exhumation of the domes is due to diapiric ascent of the molten mid-crust helped by the compressive regime. The localization of the initial diapir was controlled by crustal-scale vertical structures parallel to the Karakorum fault. The later stage of exhumation in mid to low temperature conditions was related to the uplift and erosion of the whole southeastern Karakorum by crustal-scale east-west folding. In south Tibet, the westward prolongation of south Karakorum, Neogene crustal melting is also supported by geophysical data and volcanism, but mid-crustal rocks have not been exhumed. This difference between the amount of exhumation in south Karakorum and south Tibet could be related to the transpressive context of south Karakorum inducing a strain partitioning between the N130°E faults and east-west folding. Such partitioning produces heterogeneous uplift in this area. Moreover, zones of rapid uplift rate are associated with erosion due to the high incision rate of the large Shyok and Braldu rivers and the large Biafo-Hispar and Concordia glaciers in south Karakorum.