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Abstract: In this work, we studied the local environment of a series of LiNi y Mn y Co1−2y O2 materials synthesized by wet chemistry via oxalate route. Measurements included the temperature dependence of the magnetic susceptibility χ m (T), the magnetization M(H), and the electron spin resonance. The influence of the synthesis conditions on the magnetic and electronic properties is presented and discussed. Magnetic properties and electron spin resonance spectroscopy provides further information on Ni2+, Mn4+ ion distribution in LiNi y Mn y Co1−2y O2. The magnetic data allows the determination of the cationic disorder, i.e. the concentration of Ni2+ ions in the 3a lithium sites, as a function of the composition, in quantitative agreement with the results of XRD experiments. We find that the lithium extraction proceeds by different steps. In a first step, Ni2+ in converted first in Ni3+, then in Ni4+ as x decreases from x =1, while Co remains in the Co3+ valence state. The ESR spectra show a resonance due to Mn4+, which is analyzed self-consistently with magnetic experiments. [Copyright &y& Elsevier]

This paper addresses the synthesis structural and electrochemical properties of LiFe0.5Mn0.5PO4 electrode materials for Li-ion batteries. The charge–discharge reaction of Li/LiPF6-EC–DEC/LiFe0.5Mn0.5PO4 cell carried out at the 1-C rate shows a capacity retention of 128 mAh/g. The local structure of the delithiated Li x Fe0.5Mn0.5PO4 phases have been studied by Fourier transform infrared spectroscopy and magnetometry. Spectral features indicate that the structure of the delithiated phase remains in the orthorhombic system. The compositional dependence of the magnetic moment is found to be in quantitative agreement with the theoretical value predicted for oxidation of M 2+ ions in the high spin state. [ABSTRACT FROM AUTHOR]

This work is devoted to the study of fundamental properties of LiFePO4 (LFP) olivine in view of the optimization of this material for its use as a positive electrode material in Li-ion batteries. The investigation of the electronic and magnetic properties appears to be successful for the detection of a small amount of impurities. By the combination of X-ray diffraction, optical spectroscopy, and magnetometry, we characterize the local structure and the morphology of LFP particles. The impact of the ferromagnetic clusters (γ-Fe2O3 or Fe2P) on the electrochemical response is examined. The electrochemical performance of the optimized LFP powders investigated at 60 °C is excellent in terms of capacity retention (153 mAh/g at 2 C) as well as cycling life. No iron dissolution was observed after 200 charge–discharge cycles at 60 °C for cells containing Li foil, Li4Ti5O12, or graphite as negative electrodes. [ABSTRACT FROM AUTHOR]

A series of LiNi x Mn y Co z O2 ( x = y, z = 1 − 2 y) oxides have been synthesized by “chimie douce” and investigated as positive electrodes in rechargeable lithium batteries. Layered LiNi y Mn y Co1 − 2 y O2 materials with high homogeneity and crystallinity were synthesized using the wet-chemical method assisted by carboxylic acid as the polymeric agent. The long range and local structural properties are investigated with experiments including X-ray diffraction, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectroscopy. The evolution of the structure is discussed as a function of the cobalt content that confers layer-like behavior on the framework. Electrochemical performance of LiNi y Mn y Co1 − 2 y O2 oxides is tested in cells using nonaqueous 1 M LiPF6 dissolved in ethylene carbonate–diethyl carbonate. Charge–discharge profiles are investigated as a function of the rate capability and the voltage window. A relation is found between the gravimetric capacity and the cation disorder of the positive electrode as indicated by structural analysis. Fast lithium extraction attributed to the larger interslab space has been observed in the cobalt-rich oxides. [ABSTRACT FROM AUTHOR]

We present a review of the structural properties of LiFePO4. Depending on the mode of preparation, different impurities can poison this material. These impurities are identified and a quantitative estimate of their concentrations is deduced from the combination of X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy, and magnetic measurements. An optimized preparation provides samples with carbon-coated particles free of any impurity phase, insuring structural stability and electrochemical performance that justify the use of this material as a cathode element a new generation of lithium secondary batteries. [ABSTRACT FROM AUTHOR]

We present the synthesis, characterization, and electrode behavior of LiNi0.5Mn1.5O4 spinels prepared by the wet-chemical method via citrate precursors. The phase evolution was studied as a function of nickel substitution and upon intercalation and deintercalation of Li ions. Characterization methods include X-ray diffraction, SEM, Raman, Fourier transform infrared, superconducting quantum interference device, and electron spin resonance. The crystal chemistry of LiNi0.5Mn1.5O4 appears to be strongly dependent on the growth conditions. Both normal-like cubic spinel [ Fd3m space group (SG)] and ordered spinel ( P4 1 32 SG) structures have been formed using different synthesis routes. Raman scattering and infrared features indicate that the vibrational mode frequencies and relative intensities of the bands are sensitive to the covalency of the (Ni, Mn)-O bonds. Scanning electron microscopy (SEM) micrographs show that the particle size of the LiNi0.5Mn1.5O4 powders ranges in the submicronic domain with a narrow grain-size distribution. The substitution of the 3d8 metal for Mn in LiNi0.5Mn1.5O4 oxides is beneficial for its charge–discharge cycling performance. For a cut-off voltage of 3.5–4.9 V, the electrochemical capacity of the Li//LiNi0.5Mn1.5O4 cell is ca. 133 mAh/g during the first discharge. Differences and similarities between LiMn2O4 and LiNi0.5Mn1.5O4 oxides are discussed. [ABSTRACT FROM AUTHOR]

Abstract: The structural properties of LiFePO4 prepared by the hydrothermal route and chemically delithiated have been studied using analytical electron microscopy and Raman spectroscopy. High-resolution transmission electron microscopy and selected area electron diffraction measurements indicate that the partially delithiated particles include LiFePO4 regions with cross-sections of finite size along the ac-plane, as a result of tilt grain boundary in the bc-plane, and dislocations in other directions. Only the boundary along the bc-plane is accompanied by a disorder over about 2nm on each side of the boundary. The Raman spectrum shows the existence of both LiFePO4 and FePO4 phases in the shell of the particles at a delithiation degree of 50%, which invalidates the core–shell model. This result also invalidates the recent model according to which each particle would be single-domain, i.e. either a LiFePO4 particle or a FePO4 particle. On the other hand, our results, like prior ones, can be understood within the framework of a model similar to the spinodal decomposition of a two-phase system, which is discussed within the framework of morphogenesis of patterns in systems at equilibrium. Both end-members, however, are well crystallized, suggesting a recovery similar to that observed in superplastic alloys, with dynamics that are due to the motion of nucleation fronts and dislocations, and not due to a diffusion phenomenon associated with a concentration gradient. [Copyright &y& Elsevier]

Abstract: Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 layered materials were synthesized by the co-precipitation method with different Li/M molar ratios (M =Ni+Mn+Co). Elemental titration evaluated by inductively coupled plasma spectrometry (ICP), structural properties studied by X-ray diffraction (XRD), Rietveld analysis of XRD data, scanning electron microscopy (SEM) and magnetic measurements carried out by superconducting quantum interference devices (SQUID) showed the well-defined α-NaFeO2 structure with cationic distribution close to the nominal formula. The Li/Ni cation mixing on the 3b Wyckoff site of the interlayer space was consistent with the structural model [Li1−y Ni y ]3b [Li x+y Ni(1−x)/3−y Mn(1−x)/3Co(1−x)/3]3a O2 (x =0.02, 0.04) and was very small. Both Rietveld refinements and magnetic measurements revealed a concentration of Ni2+-3b ions lower than 2%; moreover, for the optimized sample synthesized at Li/M =1.10, only 1.43% of nickel ions were located into the Li sublattice. Electrochemical properties were investigated by galvanostatic charge–discharge cycling. Data obtained with Li1+x (Ni1/3Mn1/3Co1/3)1−x O2 reflected the high degree of sample optimization. An initial discharge capacity of 150mAhg−1 was delivered at 1C-rate in the cut-off voltage of 3.0–4.3V. More than 95% of its initial capacity was retained after 30 cycles at 1C-rate. Finally, it is demonstrated that a cation mixing below 2% is considered as the threshold for which the electrochemical performance does not change for Li1+x (Ni1/3Mn1/3Co1/3)1−x O2. [Copyright &y& Elsevier]

Abstract: A series of LiMn y Fe1−y PO4 samples have been prepared in the whole range 0≤ y ≤1. Chemical delithiation could be achieved to obtain Mn y Fe1−y PO4 in the range 0≤ y ≤0.8, keeping the same crystal phase (olivine structure, space group Pnma). The composition y =0.8 is the limit where the delithiated phase is still crystallized, but abruptly suffers strains at the molecular scale evidenced by both optical spectroscopy and X-ray diffraction. The analysis of the magnetic properties shows that in all the samples the concentration of impurities is negligible. The concentration of polarons, either holes associated to Li vacancies in LiMn y Fe1−y PO4 or electrons associated to the existence of Li left in the matrix of Mn y Fe1−y PO4, is found to be small (≤1%) in all the samples. For y ≤0.6, all the Mn3+ ions Mn y Fe1−y PO4 are in the high-spin state (S =2). At larger manganese concentration, however, the Mn3+ ions in excess of the critical concentration y c =0.6 undergo a transition to the low-spin state (S =1). As a consequence, and in contrast with prior works, we find that Mn0.8Fe0.2PO4 has magnetic interactions that are much smaller, and no antiferromagnetic ordering in this compound is detected, at least above 20K. Antiferromagnetic ordering that had been reported so far for Mn y Fe1−y PO4 at large y-composition might come from incomplete delithiation. The spin-transition of Mn3+ in concentration (y–y c) to the low-spin state is at the origin of the strain fields at the molecular scale that increase with y for y >0.6, and ultimately prevents the full delithiation for y >0.8. This result sheds light on the reason for the degradation of cathode properties in Mn-rich compounds of the heterosite–purpurite series, while the electrochemical properties are good in the range y ≤0.6 but only at slow rates, due to the very small hopping mobility of the small polaron. [Copyright &y& Elsevier]

Abstract: The effect of H2O on carbon-coated LiFePO4 particles was investigated by chemical analysis, structural analysis (X-ray diffraction, SEM, TEM), optical spectroscopy (FTIR, Raman) and magnetic measurements. Upon immersion in water, part of the product floats while the main part sinks. Both the floating and the sinking part have been analyzed. We find that the floating and sinking part only differ by the amount of carbon that partly detaches from the particles upon immersion in water. Exposure to H2O results in rapid attack, within minutes, of the surface layer of the particles, because the particles are no longer protected by carbon. The deterioration of the carbon coat is dependent on the synthesis process, either hydrothermal or solid-state reaction. In both cases, however, the carbon coat is permeable to water and fails to protect the surface of the LiFePO4 particles. The consequence is that this immersion results in the chemical attack of LiFePO4, but is restricted to the surface layer of the particles (few nanometers-thick). In case the particles are simply exposed to humid air, the carbon coat protects the particles more efficiently. In this case, the exposure to H2O mainly results in the delithiation of the surface layer, due to the hydrophilic nature of Li, and only the surface layer is affected, at least for a reasonable time of exposure to humid air (weeks). In addition, within this timescale, the surface layer can be chemically lithiated again, and the samples can be dried to remove the moisture, restoring the reversible electrochemical properties. [Copyright &y& Elsevier]

Abstract: We report the structural and electronic characterization of Li2FeSiO4 synthesized by solid-state reaction. X-ray diffraction, Raman scattering, Fourier transform infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and magnetization measurements are analyzed. Magnetic susceptibility experiments give evidence that Li2FeSiO4 powders possess an antiferromagnetic ordering below T N =25K due to long range Fe–O–Li–O–Fe interactions. Analysis of the paramagnetic region giving the Curie–Weiss parameters θ p =−93.5K and C p =4.13emuKmol−1 shows the divalent state of Fe cations. Electron paramagnetic resonance experiments confirm this electronic configuration. Electrochemical measurements were carried out in lithium cells with LiTFSI in a poly(ethylene oxide) (PEO) polymer electrolyte at 80°C. The resulting cyclic voltammogram indicates a stable structure for the first cycle with redox peaks at 2.80 and 2.74V versus Li0/Li+. [Copyright &y& Elsevier]

Abstract: An experimental relationship between local structure and electrochemical properties is established for lithium metal phosphates LiMePO4 (Me = Fe, Co, Mn), LiFeP2O7 and Li3Fe2(PO4)3 which crystallise with either the olivine-like or the Nasicon-like structure. Structural features of several lithium metal phosphates are investigated by a local probe such as the FTIR spectroscopy in order to explain the influence of either or covalent bonds on redox energies. The local cationic arrangement is also discussed with the aid of a molecular vibration model to figure out the strong covalent bonds within a complex for glassy Nasicon compounds. [Copyright &y& Elsevier]