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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]

Solid-electrolyte interface (SEI) between the active material and the electrolyte is critically important to the electrochemical performance of a lithium-ion battery. In this work, a depth profile measurement of the SEI layer after prolonged electrochemical cycling is reported in order to quantify the influence of conducting additives in the development of this layer in mesocarbon microbeads (MCMB) electrodes. It is shown that the SEI in the electrodes having multiwalled carbon nanotubes (CNT) as conductive additive is primarily a multi-layered structure consisting of an outer organic layer near the electrolyte/SEI interface and an inner inorganic layer near the SEI/electrode interface. The chemical analysis of such electrodes exhibits that the inorganic layer is made up of compounds such as Li 2 O, LiF and Li 2 CO 3, while the outer layer consists mainly of organic carbonates, oligomers, traces of randomly distributed Li x PO y F z and undissociated LiPF 6. The chemical analysis of electrodes with carbon black (CB) as conducting additive reveals a similar composition of the outer layer, whereas the inner layer shows a relatively uniform molar amount of organic and inorganic carbonates and species like Li x PO y F z and Li x PO y , resulting in a porous SEI layer which as confirmed in AFM and SEM characterizations. On the other hand, the electrodes containing hybrid (CB-CNT) conducting additives show a relatively higher oligomer content than the electrodes with CNT only. The SEI formed on electrodes with CB-CNT as additives is shown to offer increased flexibility to accommodate partial strain generated due to volume change with narrow cracks exhibited in the SEM micrographs. Further, the variation in surface features and roughness augment the XPS findings. [ABSTRACT FROM AUTHOR]