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The static and dynamic magnetic behavior of β-LiFeO2 has been investigated by measuring dc and ac susceptibilities. The zero-field-cooled (ZFC) and field-cooled (FC) curves reveal an irreversibility behavior at about 156 K and a broad peak at 129 K, indicating a spin glass transition. However, the dc susceptibility of β-LiFeO2 in FC mode differs from a flat curve as expected for a homogeneous spin glass by an increase below Tirr, which is the characteristic magnetic behavior of a cluster spin glass. The real part of the ac susceptibility shows a broad maximum at 135 K, which shifts to higher temperatures and becomes less pronounced with increasing frequency. The corresponding parameter δ=ΔTf/TfΔlogω = 0.005 is calculated for β-LiFeO2, suggesting a spin glass state rather than superparamagnetism. In addition, three models (the Néel-Arrhenius law, the Vogel-Fulcher law, and the power law) have also been employed to analyze the frequency dependence of Tf, which confirm a cluster spin glass state in β-LiFeO2. [ABSTRACT FROM AUTHOR]

Spinel-type Li2NiF4 has been synthesized by a novel sol-gel synthesis process without HF, LiF or F2 as fluorine source. In an easily scalable process a solution of water containing Ni(CH3COO)2 ⋅ 4H2O, Li(CH3COO) ⋅ 2H2O, and CF3COOH was spray-dried to form a precursor powder. It was pyrolyzed to directly result in Li2NiF4. The Li2NiF4 powder was ball-milled with carbon and a binder to produce an Li2NiF4/carbon/binder composite suitable for electrochemical investigation as a positive electrode in a lithium-ion battery. During cycling, the discharge capacity confirmed that at least 2 eq. of lithium had been inserted into the initial Li2NiF4/carbon/binder composite. The electrochemical behavior of this composite cathode and the associated structural changes of the host material during cycling against lithium metal were investigated by in situ X-ray powder diffraction, X-ray photoelectron spectroscopy, and 7Li nuclear magnetic resonance spectroscopy. [ABSTRACT FROM AUTHOR]

The ternary dilithium diboron carbide, Li2B2C (tetragonal, space group P m2, tP10), crystallizes as a new structure type and consists of structural fragments which are typical for structures of elemental lithium and boron or binary borocarbide B13C2. The symmetries of the occupied sites are . m. and 2 mm. for the B and C atoms, and m2 and 2 mm. for the Li atoms. The coordination polyhedra around the Li atoms are cuboctahedra and 15-vertex distorted pseudo-Frank-Kasper polyhedra. The environment of the B atom is a ten-vertex polyhedron. The nearest neighbours of the C atom are two B atoms, and this group is surrounded by a deformed cuboctahedron with one centred lateral facet. Electronic structure calculations using the TB-LMTO-ASA method reveal strong B...C and B...B interactions. [ABSTRACT FROM AUTHOR]

To replace common commercial lithium metal oxides or polyanionic cathode materials, lithium transition metal fluorides are of particular interest, as they potentially provide a high energy density, safety, and cyclability. The quaternary fluoride LiMnFeF6 that crystallizes in the Na2SiF6-type structure was synthesized without toxic chemicals by a sol-gel process with trifluoroacetic acid as fluorine source. After structural and morphological characterization, the as-synthesized material was ball-milled with carbon. The novel composite cathode material produced in this way was cycled versus lithium. The electrochemical potential range, cycling ability, and rate performance were investigated and the electrochemically active redox couple Fe3+/Fe2+ was confirmed by Mössbauer spectroscopy. Structural changes of the LiMnFeF6 host structure after Li insertion were investigated by X-ray powder diffraction. [ABSTRACT FROM AUTHOR]

Lithium transition metal oxides are commonly used as cathode materials in modern mobile and stationary power supplies. Lithium transitionmetal fluorides are an interesting newclass ofmaterials for lithium ion batteries featuring a higher voltage due to substitution of oxygen by the more electronegative fluorine. A sol-gel based process with trifluoroacetic acid as fluorine source was used to synthesize LiNiFeF6. Ball-milling with carbon and binder was applied to obtain an electrochemical active LiNiFeF6/carbon/binder nano composite. In this study we report on the first electrochemical characterization of a quaternary lithium transition metal fluoride as positive electrode for lithium ion batteries, containing two different transition metals. After 20 cycles of galvanostatic cycling a reversible specific capacity of 88 mAh/g, which is 92% of the initial specific capacity, was retained. In a rate performance test with rates of up to 1C a reversible capacity of 53 mAh/g was obtained. The electrochemically active redox couple Fe3+/Fe2+ was identified by Mössbauer spectroscopy and cyclic voltammetry. [ABSTRACT FROM AUTHOR]

The synthesis, structural characterization, and chemical bonding peculiarities of three new binary Li-In intermetallides are reported. The crystal structures of these compounds were determined by single-crystal X-ray diffraction analysis. The compositions obtained after structure refinements were Li22- xIn8+ x ( x = 0.1) [new structure type, monoclinic crystal system, Pearson symbol mS30, space group C2/ m, a = 14.156(3), b = 4.729(1), c = 8.617(2) Å, β = 105.89(1)°, R1 = 0.0279, wR2 = 0.0583 for 669 reflections], Li11- xIn4+ x ( x = 1.05) [new structure type, trigonal, P $\bar {3}$ m1, hP15, a = 4.7480(7), c = 14.283(3) Å, R1 = 0.0323, wR2 = 0.0741 for 277 reflections], and Li10- xIn2+ x ( x = 1.59) [new structure type, hexagonal, P6/ mmm, hP12, a = 4.6975(7), c = 11.526(2) Å, R1 = 0.0680, wR2 = 0.1358 for 127 reflections]. The Li22- xIn8+ x ( x = 0.1) structure is related to the structure of lithium (W-type). The structure of Li11- xIn4+ x ( x = 1.05) can be described as a derivative of the CdI2 type. Li10- xIn2+ x ( x = 1.59) can be derived from the Li2Pt structure. [In2@Li20] clusters composed of 20 lithium atoms, which surround a In-In pair, are detected in the structure of all three investigated compounds. TB-LMTO (Tight-Binding Linear Muffin-Tin Orbital) calculations indicate strong covalent In-In interactions and the presence of [In2@Li20] clusters in these new binary indides. [ABSTRACT FROM AUTHOR]

Abstract: Precise structural data have been determined from a combined Rietveld refinement, based on neutron and X-ray powder diffraction data simultaneously, for the three phases LiCoPO4, Li z CoPO4 with a specific intermediate Li-content z =0.60(10) and CoPO4, which are obtained by electrochemical Li-extraction from LiCoPO4. All three phases are isopointal. Therefore, the transitions between these phases are necessarily of first order, in agreement with their observed coexistence. The same collinear antiferromagnetic structures with magnetic moments nearly parallel to the [010] direction are observed for LiCoPO4 and Li z CoPO4, but with a significantly higher Néel temperature of 76K for the latter compound in comparison with 23K for LiCoPO4. Olivine-type CoPO4 can only be prepared from LiCoPO4 by delithiation and its physical properties were investigated for the first time. An antiferromagnetic arrangement along the [100] direction is observed for CoPO4 with an additional weak ferromagnetic component along the [001] direction (magnetic space group Pn′m′a and T C =45K). The magnetic moment of 3.1(2)μB per Co-ion indicates a mainly high-spin state for Co3+ in the octahedral coordination of CoPO4, which is exceptional and probably the first example in a phosphate. The easy axes and the magnetic exchange interactions between Co-ions change dramatically with the Co2+ ↔Co3+ transition. A continuous change of the formal oxidation state of a transition element by electrochemical Li-extraction and a quasi-continuous in situ observation of the resulting magnetic structure by neutron diffraction appear feasible. [Copyright &y& Elsevier]

The cubic face-centered structure of LiAl (Fd3¯m, a=6.35971(3) A˚ at 290 K) transforms into a tetragonal body-centered structure (I41/amd, a=4.47831(1) A˚, c=6.34435(2) A˚ at 12 K). This first-order phase transition at about 93(2) K during heating is probably the reason for the so-called “100 K anomalies” in some physical properties like specific heat, electrical resistivity and nuclear-spin lattice relaxation. This transition seems to be correlated with the composition Li:Al of the alloy and the amount of Li vacancies. [Copyright &y& Elsevier]

Abstract: The lithium double diphosphates LiCr y Fe1− y P2O7 have been investigated by X-ray diffraction, SQUID measurements and vibrational spectroscopy. The Rietveld refinements based on the XRD patterns show the existence of a continuous solid solution over the whole composition range (0⩽y⩽1.0) with a continuous evolution of the monoclinic unit cell parameters (S.G. P21). The transition metal ions connect the diphosphate anions forming a three-dimensional network with channels filled by Li+ cations expected to exhibit high mobility. All compounds order magnetically at low temperatures due the Fe–Fe interactions. The ordering temperature decreases with increasing Cr content. The slope in Curie–Weiss fits to the 1/χ vs T data in the paramagnetic domain clearly shows the existence of Fe3+ and Cr3+ in their high spin states, and a ferromagnetic component is clearly detected for y=0, 0.2 and 0.4. IR spectra have been interpreted using factor group analysis. The small shift of the frequencies is due to the influence of the chromium amount. The POP angles were estimated using the Lazarev''s relationship. [Copyright &y& Elsevier]

In this work, the electrostatic self-assembly of LiFePO 4 particles coated with polyelectrolytes on a three-dimensional carbon substrate is described. This new fabrication method allows precise control of ionic and electronic conduction pathways as well as the interfaces between the different electrode components, thus enabling new strategies for tailored electrode designs. Further, it is shown that the polyelectrolytes used to build up the electrode by electrostatic self-assembly can be converted into a conductive matrix by a simple carbonization step. This leads to a firmly adhering carbon film on the surface of LiFePO 4 , which further improves electron transport. The three-dimensional composite cathode exhibits a high specific capacity even at high current rates as well as a long cycle life. The excellent electrochemical performance can be attributed to the improved three-dimensional structure of the electrode as well as to the obtained intrinsic carbon coating of LiFePO 4 particles. [ABSTRACT FROM AUTHOR]

In this work, the LiCoMnO 4 spinel has been synthesized by a two-step sol-gel based method, followed by sintering at temperatures up to 750 °C in oxygen. After structural characterization of the pristine material via synchrotron and neutron diffraction, the material was characterized via SEM and 6 Li-MAS-NMR spectroscopy. 6 Li-MAS-NMR spectroscopy in different states of charge revealed, that manganese and cobalt are distributed homogenously throughout the material and the delithiation primary occurs from the manganese environments. It was also shown, that it is not possible to fully delithiate the material in a practical voltage range of an electrolyte. Electrochemical cycling results reveal that about 70% of the lithium can be extracted and reinserted electrochemically in the voltage window from 4.5 to 5.4 V against lithium from/into LiCoMnO 4 . In situ synchrotron powder diffraction results show that lithium extraction/insertion occurs via a single-phase mechanism over the whole range of lithium contents and that the discharge capacity is mainly restricted by the voltage-window of the electrolyte. Furthermore it was shown, that the delithiation occurs up to a potential of 5.6 V. [ABSTRACT FROM AUTHOR]

A new zero-strain LiCaFeF 6 cathode material for reversible insertion and extraction of lithium ions is presented. LiCaFeF 6 is synthesized by a solid-state reaction and processed to a conductive electrode composite via high-energy ball-milling. In the first cycle, a discharge capacity of 112 mAh g −1 is achieved in the voltage range from 2.0 V to 4.5 V. The electrochemically active redox couple is Fe 3+ /Fe 2+ as confirmed by Mössbauer spectroscopy and X-ray absorption spectroscopy. The compound has a trigonal colquiriite-type crystal structure (space group P 3 ¯ 1 c ). By means of in situ and ex situ XRD as well as X-ray absorption fine structure spectroscopy a reversible response to Li uptake/release is found. For an uptake of 0.8 mol Li per formula unit only minimal changes occur in the lattice parameters causing a total change in unit cell volume of less than 0.5%. The spatial distribution of cations in the crystal structure as well as the linkage between their corresponding fluorine octahedra is responsible for this very small structural response. With its zero-strain behaviour this material is expected to exhibit only negligible mechanical degradation. It may be used as a cathode material in future lithium-ion batteries with strongly improved safety and cycle life. [ABSTRACT FROM AUTHOR]

In order to apply low conductive materials, such as LiFePO 4 , in lithium-ion batteries, a conductive additive like carbon black is commonly used to build an electronic transport path between the active particles. The connection between active phase and conductive media has a dominant influence on electrochemical properties and lifetime of batteries. We compare the performance and properties of electrodes which were prepared in two different ways with the same LiFePO 4 nanopowder as the active phase. The electrodes were prepared in a conventional route, based on the commonly used powder-suspension coating on metallic foils and in an alternative route, based on the electrospinning method. As a result, the obtained electrodes have different structures and connections between the active and conductive phase, which has an influence on the electrode behavior during cycling. The accessible high thickness and variable density of the electrodes are the main advantages of the electrodes prepared by electrospinning. [ABSTRACT FROM AUTHOR]

The Al-substituted LiTi2(PO4)3 powders Li1+xAlxTi2-x(PO4)3 (LATP) were successfully prepared by a water-based sol-gel process with subsequent calcination and sintering. The crystal structure of obtained samples was characterized at different temperatures using high-resolution synchrotron-based X-ray and neutron powder diffraction. Possible lithium diffusion pathways were initially evaluated using the difference bond-valence approach. Experimental 3D lithium diffusion pathway in LATP was extracted from the negative nuclear density maps reconstructed by the maximum entropy method. Evaluation of the energy landscape determining the lithium diffusion process in NASICON-type superionic conductor is shown for the first time. [ABSTRACT FROM AUTHOR]

Lithium transition metal fluorides (Li 3 MF 6 ; M = Fe, V) with cryolite structure are investigated as positive electrode materials for lithium-ion batteries. A novel sol–gel process with trifluoroacetic acid as fluorine source was used to synthesize monoclinic and orthorhombic Li 3 CrF 6 . A ball milling process with Li 3 CrF 6 , binder, and conductive agent was applied to form a Li 3 CrF 6 composite, which was electrochemically characterized against lithium metal for the first time. The electrochemical properties of two different modifications are quite similar, with a reversible specific capacity of 111 mAhg −1 for monoclinic Li 3 CrF 6 and 106 mAhg −1 for orthorhombic Li 3 CrF 6 (1 eq. Li ≙ 143 mAhg −1 ). The electrochemically active redox couple Cr III /Cr II was confirmed by X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of LiNi 0.5 Mn 0.5 O 2 were studied by synchrotron X-ray diffraction, dc and ac susceptibilities. The material showed a continuous magnetic transition from paramagnetism into ferrimagnetism, followed by a spin glass with the decrease of temperature. Using a criterion given by Banerjee to distinguish first-order magnetic transition from second-order ones, it is shown that the ferrimagnetic transition at 108 K belongs to the second-order type. The frequency dependence of peak intensity and the shift in ac susceptibility at 14 K suggest a reentrant spin glass transition in LiNi 0.5 Mn 0.5 O 2 . [ABSTRACT FROM AUTHOR]

The citric acid-assisted sol–gel method was used to produce the high-voltage cathodes LiNi 0.5 Mn 1.5 O 4 and LiNi 0.4 Ru 0.05 Mn 1.5 O 4 at 800 °C and 1000 °C final calcination temperatures. High resolution powder diffraction using synchrotron radiation, inductively coupled plasma – optical emission spectroscopy and scanning electron microscopy analyses were carried out to characterize the structure, chemical composition and morphology. X-ray absorption spectroscopy studies were conducted to confirm Ru doping inside the spinel as well as to compare the oxidation states of transition metals. The formation of an impurity Li x Ni 1− x O in LiNi 0.5 Mn 1.5 O 4 powders annealed at high temperatures ( T ≥ 800 °C) can be suppressed by partial substitution of Ni 2+ by Ru 4+ ion. The LiNi 0.4 Ru 0.05 Mn 1.5 O 4 powder synthesized at 1000 °C shows the highest performance regarding the rate capability and cycling stability. It has an initial capacity of ∼139 mAh g −1 and capacity retention of 84% after 300 cycles at C/2 charging–discharging rate between 3.5 and 5.0 V. The achievable discharge capacity at 20 C for a charging rate of C/2 is ∼136 mAh g −1 (∼98% of the capacity delivered at C/2). Since the electrode preparation plays a crucial role on parameters like the rate capability, the influence of the mass loading of active materials in the cathode mixture is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Osmium tetroxide (OsO4) staining, commonly used to enhance scattering contrast in electron microscopy of biologic tissue and polymer blends, has been adopted for studies of graphite anodes in lithium-ion batteries. OsO4 shows a coordinated reaction with components of the solid electrolyte interphase (SEI) and lithium dendrites, thereby increasing material contrast for scanning electron microscopy investigations. Utilizing the high affinity of lithium metal to react with osmium tetroxide it was possible to localize even small lithium deposits on graphite electrodes. In spite of their reaction with the OsO4 fume, the lithium dendrite morphology remains almost untouched by the staining procedure, offering information on the dendrite growth process. Correlating the quantity of osmium detected with the amount of residual (“dead”) lithium of a discharged electrode, it was possible to obtain a practical measure for lithium plating and stripping efficiencies. EDX mappings allowed for a localization of electrochemically stripped lithium dendrites by their residual stained SEI shells. Cross sections, prepared by focused ion beam (FIB) of cycled graphite electrodes treated with OsO4, revealed important information about deposition and distribution of metallic lithium and the electrolyte reduction layer across the electrode. [Copyright &y& Elsevier]

Abstract: The crystal structure of Li2−x Ag1+x In3 (x=0.05) has been determined on a single crystal synthesized from the elements in a tantalum crucible. The compound crystallizes in orthorhombic space group Pmma (a=9.325 (3) Å, b=3.198 (1) Å, c=8.043 (3) Å at 296K) with 12atoms per unit cell and represents a new structure type. The structure of Li2−x Ag1+x In3 is closely related to the LaCoAl4 structure and belongs to the structural family, the representative members of which may be derived from the hexagonal AlB2 structure type by a combination of internal deformation and substitution. The strong In–In interaction and close to zero electrons concentration around Li and Ag atoms, calculated by LTMO, allow to suggest high mobility of lithium atoms located within the channels formed by the strongly waved [–In–In–] polyanionic chains. [Copyright &y& Elsevier]

Abstract: Samples with nominal composition LiM 0.5Mn1.5O4 (M = Fe, Co) were synthesized via a sol–gel process with a post thermal treatment at 1000 °C. In contrast to the Ni-analogue Co- and Fe-doped samples show a fast degradation at 55 °C with an average capacity retention at RT of ∼55% for the Co- and of ∼59% for the Fe-substituted samples, respectively after 70 cycles for a C/2 rate. The PITT plots of the Fe doped spinel exhibited a sharp peak in the discharge capacity when cycled with a cut-off current rate C/5, which was assumed due to a kinetic limitation, which disappears when cycled at slower charge–discharge rates. This assumption was checked, and the mechanisms of Li-intercalation/-de-intercalation were investigated in detail for the Fe and Co doped spinels by in situ synchrotron diffraction. The charge–discharge processes take place through a solid-solution mechanism in both cases, though the Fe-doped spinel exhibits a two-phase region during the discharge. [Copyright &y& Elsevier]

Abstract: Structural properties of Li7−xLa3TaxZr2−xO12 garnets with x=0–2 were clarified by means of Rietveld analysis using results of X-ray diffraction and neutron diffraction at room temperature and at low temperature. In this work the controversy between Awaka [1] and Murugan [2] concerning the crystal structure of Li7La3Zr2O12 was solved. It was shown that the tetragonally derived garnet structure of space group I41/acd described by Awaka [1] is the thermodynamically stable structure for Li7La3Zr2O12. In the three-dimensional sub-network of this structure, lithium is ordered and occupies all octahedral sites as well as one third of the tetrahedral sites. Li7−xLa3TaxZr2−xO12 garnets with x=0.125–2 crystallize in the garnet structure, space group Ia d. As the tantalum content increases, the lattice parameter at room temperature decreases from a =12.9833(1) Å for Li6.875La3Ta0.125Zr1.875O12 down to a =12.81224(7) Å for Li5La3Ta2O12. In Li6.5La3Ta0.5Zr1.5O12 garnet, lithium atoms are statistically partitioned among octahedral sites (occ.: 0.80(2)) and tetrahedral sites (occ.: 0.56(4)). In the cases of ordered Li7La3Zr2O12 tetragonally derived garnet and statistically disordered Li6.5La3Ta0.5Zr1.5O12 garnet, lithium partitioning remains unchanged as temperature decreases. [Copyright &y& Elsevier]