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Abstract: We studied the structural transformations from the layered-type to spinel-type ordering upon galvanostatic charging (Li+ extraction) of Li2MnO3 electrodes. We have determined by X-ray, electron diffraction techniques and Raman spectroscopy analyses that these transformations partially occurred even at the initial states-of-charge, at potentials of 4.3–4.5V, and in fully charged (4.7V) and discharged (2.0V) states as well. The above transformations are evident also from the analysis of the intrinsic magnetic properties of Li2MnO3 electrodes that indicate short-range spin correlations typical for the Li2Mn2O4 and LiMn2O4 spinel-type structures, depending on the state of charge and the C-rates used for the cycling. [Copyright &y& Elsevier]

Abstract: In this work, we synthesized nano-particles (20–80nm) of Li2MnO3 using the self-combustion reaction and studied the electrochemical activity of electrodes prepared from this nano-material at 30, 45, and 60°C. It was shown that the first Li-extraction from nano-Li2MnO3 occurs at much lower potentials (by 180–360mV) in comparison with micron-sized Li2MnO3 electrodes. This can be associated with the higher surface-to-volume ratio, much shorter the diffusion path and the increased surface concentration of the electrochemically active sites. On the basis of magnetic susceptibility studies of nano-Li2MnO3 we proposed a model of disordered surface layer, containing Mn3+ or Mn2+ ions, both at low spin state, at the surface of these nano-particles. From the results of structural analysis (by X-ray and electron diffraction and vibrational Raman spectroscopy) of galvanostatically cycled nano-Li2MnO3 electrodes in Li-cells we came to a conclusion of partial transition of layered LiMO2 to spinel-type ordering. [Copyright &y& Elsevier]

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]

Abstract: A comparative analysis of the electrochemical behavior and Li+ transport characteristics of thin-layer LiNi0.5Mn1.5O4 intercalation electrodes comprised of micro- or nano-sized particles in standard Li salt solutions, was carried out and is reported herein. These electrodes were free of any conductive additives and polymeric binder in order to avoid their complex impact on the electrochemical response of the active mass. It was clearly established that the electrodes prepared from nanoparticles of the active mass show faster kinetics and a more reversible electrochemical behavior compared to the electrodes comprising microparticles. The response of the nanoparticles to electrochemical techniques such as linear sweep voltammetry and potentiostatic intermittent titration (PITT) is characterized by high resolution. Thus D versus E could be calculated very precisely. It was encouraging to realize the good performance of the electrodes comprising nano-LiMn1.5Ni0.5O4, in spite of their high surface area and their high operating voltage. [Copyright &y& Elsevier]