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Thin-film LiMn2O4 electrodes, which were exposed to pure dimethyl carbonate (DMC) or to a mixture of ethylene carbonate (EC) and DMC (1:1 by volume) containing 1 M LiPF6 at elevated temperatures, were studied by using X-ray diffraction, current-sensing atomic force microscopy (CSAFM), cyclic voltammetry, ordinary Raman spectroscopy, and surface-enhanced Raman spectroscopy (SERS). Thin, electronically insulating surface layers were detected by CSAFM and SERS on all electrodes. The surface layer formed by exposure to DMC at 70°C was uniform and preserved the electrode structure, however, it led to complete electrode deactivation, probably due to loss of surface electronic conductivity and slower lithium-ion transport rates through the surface layer. A similar surface layer was formed when the electrodes were exposed to EC­DMC­LiPF6, however, the layer formed at 70°C did not prevent LiMn2O4 decomposition and consequent electrode capacity loss. In this case, manganese dissolution was observed, accompanied by the formation of λ­MnO2. SER spectra of the surface layers suggest that they were formed as a result of DMC decomposition at the LiMn2O4 surface. The SER spectra displayed bands characteristic of Li-O-R, carbonate, and carboxyl groups. Derivatives of carbon-oxygen triple bonds or silver-carbon-oxygen groups, which are possibly a result of interactions between the surface layer and silver microparticles, were also detected. © 2001 The Electrochemical Society. All rights reserved.

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Here we propose the use of a carbon material called graphene-like-graphite (GLG) as anode material of lithium ion batteries that delivers a high capacity of 608 mAh/g and provides superior rate capability. The morphology and crystal structure of GLG are quite similar to those of graphite, which is currently used as the anode material of lithium ion batteries. Therefore, it is expected to be used in the same manner of conventional graphite materials to fabricate the cells. Based on the data obtained from various spectroscopic techniques, we propose a structural GLG model in which nanopores and pairs of C-O-C units are introduced within the carbon layers stacked with three-dimensional regularity. Three types of highly ionic lithium ions are found in fully charged GLG and stored between its layers. The oxygen atoms introduced within the carbon layers seem to play an important role in accommodating a large amount of lithium ions in GLG. Moreover, the large increase in the interlayer spacing observed for fully charged GLG is ascribed to the migration of oxygen atoms within the carbon layer introduced in the state of C-O-C to the interlayer space maintaining one of the C-O bonds.