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We present the results of our in situ X-ray diffraction (XRD) and Raman spectroscopy measurements for the first Li-ion extraction/insertion (charge/discharge) processes of nickel-rich Li1+ x(Ni yCo zMn z) wO2 (0.005< x<0.03; y: z=8:1, w is nearly 1) electrodes in Li cells. These cells were of a special design that provide in situ (at-work) measurements during electrochemical polarization and can be used for regular cycling tests of practical Li-battery electrodes. By using XRD measurements, it was established that, upon Li+ extraction, these cathode materials demonstrate structural transformations of the hexagonal phase (space group R-3 m) H1 to another hexagonal phase H2 (with a lower Li-ion content in the lattice) and to domains comprising both of these two phases, coexisting at potentials E≈4.2-4.3 V. The above phases differ by the a and c lattice constants, which is in agreement with literature results. Evolution of the lattice constants with the electrode potential upon charge/discharge is shown to be in correlation with the differential capacity d Q/d E versus E plots and with some Raman parameters calculated from complementary in situ studies of these cathode materials by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

We report herein on the study of Li and Mn rich Lix[MnNiCo]O2 cathode materials with an emphasis on the effect of AlF3 coating on their electrochemical performance. The initial stoichiometry of these materials was xLi2MnO3.(1-x)LiMnyNizCowO2 where x is in the range 0.4-0.5 and the y:z:w ratio was as we previously reported. Their structure was considered on the basis of two-components model, namely monoclinic Li2MnO3 (C2/m) and rhombohedral LiMO2 (R-3m) (M = Mn, Ni, Co) that are structurally compatible and closely integrated phases. Based on TEM studies we concluded that the coating had a crystalline tetragonal structure t-AlF3 (P4nmm symmetry) and AlF3 nano-crystals were regularly distributed over the particles surface. Amorphous clusters of AlF3 and/or other Al-containing species, like AlFxOy, Al[FOH], etc. may also present, as it follows from solid-state NMR measurements. It was shown that electrodes comprising the AlF3-coated material exhibited higher reversible capacities of ∼250 mAh/g at a C/5 rate, more stable cycling behavior, higher lithium storage capability at 60°C, and lower impedance measured during Li-deinteraclation comparing to electrodes prepared from the uncoated material. An important finding is that Lix[MnNiCo]O2 /AlF3 materials revealed much higher thermal stability both in the pristine (lithiated) and cycled (delithiated) states than their uncoated counterparts. [ABSTRACT FROM AUTHOR]

The thermal behavior and structural changes of representative types of lithiated graphitic materials were investigated in solutions comprising ethylene carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC) and LiPF6. We show that the protective films formed on intercalated graphite electrodes upon cathodic polarization are stable in these electrolyte solutions up to ∼80°C, in DSC experiments. Upon increasing the temperature, between 80 and 120°C, reactions of the surface films with solution species take place and the level of the graphite lithiation is reduced. After destruction of the surface films on lithiated graphite at higher temperatures >120°C, solvent molecules diffuse into the graphite particles and interact with Li ions therein thus forming reduction products. The later decompose upon further heating at temperatures >200°C, with the formation of gaseous products. This results in an internal pressure within the graphite particles that causes their partial exfoliation in an endothermic process. While the protective surface films on the lithiated graphite are removed from the particles in the course of the thermal reactions, we have indications that surface films on fully delithiated graphite do not react with the electrolyte solution at least up to 200°C. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we studied the cycling performance of initially inactive Li2MnO3 electrodes prepared from micron-sized particles, at 30°C and 60°C and possible structural transitions that this material can undergo due to de-lithiation. It was found that being activated at elevated temperatures, Li2MnO3 electrodes demonstrate a steady-state cycling behavior and reasonable capacity retention after aging at 60°C. The main gases evolved during polarization of the Li2MnO3 electrodes are O2 evolved from the structure and CO2 and CO that can be formed due the reaction of oxygen with carbon black. It was found that a transformation of the Li2MnO3 layered structure into a spinel-like phase occurred during the initial charging of the Li2MnO3 electrodes, which were characterized as possessing domains of both layered and spinel-like structures. The results of the structural studies of these electrodes obtained by the X-ray diffraction and transmission electron microscopy were found to be in agreement with their Raman spectroscopic responses. We suggest that the mechanism of the charge compensation during the extraction of lithium at 60°C involves both oxygen removal from the Li2MnO3 structure and the exchange between Li+ and protons formed during the anodic oxidation of ethylene carbonate or dimethyl carbonate solvents in LiPF6 solutions at high potentials (>4.5V). It is assumed that the proton-containing structure Li2−x H x−y MnO3−0.5y is retained in a discharged state of the electrode and may decompose above 500°C with the formation of Li2O and manganese oxides accompanied by the release of water and CO2. [Copyright &y& Elsevier]