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Many carbon allotropes can act as host materials for reversible lithium uptake.sup.1,2, thereby laying the foundations for existing and future electrochemical energy storage. However, insight into how lithium is arranged within these hosts is difficult to obtain from a working system. For example, the use of in situ transmission electron microscopy.sup.3-5 to probe light elements (especially lithium).sup.6,7 is severely hampered by their low scattering cross-section for impinging electrons and their susceptibility to knock-on damage.sup.8. Here we study the reversible intercalation of lithium into bilayer graphene by in situ low-voltage transmission electron microscopy, using both spherical and chromatic aberration correction.sup.9 to enhance contrast and resolution to the required levels. The microscopy is supported by electron energy-loss spectroscopy and density functional theory calculations. On their remote insertion from an electrochemical cell covering one end of the long but narrow bilayer, we observe lithium atoms to assume multi-layered close-packed order between the two carbon sheets. The lithium storage capacity associated with this superdense phase far exceeds that expected from formation of LiC.sub.6, which is the densest configuration known under normal conditions for lithium intercalation within bulk graphitic carbon.sup.10. Our findings thus point to the possible existence of distinct storage arrangements of ions in two-dimensional layered materials as compared to their bulk parent compounds.Using a double-aberration-corrected transmission electron microscope, intercalation of lithium between two graphene sheets is found to produce a dense, multilayer lithium phase, rather than the expected single layer., Author(s): Matthias Kühne [sup.1] [sup.6] , Felix Börrnert [sup.2] , Sven Fecher [sup.1] , Mahdi Ghorbani-Asl [sup.3] , Johannes Biskupek [sup.2] , Dominik Samuelis [sup.1] [sup.7] , Arkady V. Krasheninnikov [...]

In this report, we discuss the Li-storage performance of niobium-doped TiO2 nanostructures (Ti1−yNbyO2+δ), with a special focus on the effects of ionic/electronic charge carrier concentration (defect chemistry) on Li storage and transport properties. By Nb-doping, Li storage kinetics of titania electrode material is significantly improved mainly due to the increased electronic charge carrier concentration (n-type doping). However, it was found that there is a maximum beyond which further doping is rather detrimental to Li diffusion kinetics. Defect chemical analysis indicates that this limited doping effect is due to the trapping of free lithium ions by the critical electron–ion association reactions at room temperature such as UGRAPHIC DISPLAY="INLINE" ID="UGT1" SRC="UGT1"/ and UGRAPHIC DISPLAY="INLINE" ID="UGT2" SRC="UGT2"/. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the point defect chemistry of lithium storage in TiO2 and emphasize its great importance to lithium battery applications. Not only charge carrier concentration but also lithium diffusivity is successfully interpreted in terms of lithium content and activity as well as oxygen stoichiometry. A detailed defect chemical analysis reveals that ionic-electronic defect associations (Li i • + e′⇌ Li i X and V O •• +2e′⇌ V O • + e′⇌ V O X ) play a significant role in determining the concentration of defects and lithium diffusivity, and hence can have large impact on overall lithium storage performance of oxide based electrode materials. [Copyright &y& Elsevier]

We present the thermodynamic modeling and experimental evidence of the occurrence of lithium storage at abrupt junctions, which describes the transition from an electrostatic capacitor to a chemical capacitor. In both Ru:Li2O and Ni:LiF systems, the functionalities and extracted parameters are in good agreement with the thermodynamic model, based on the dependence of the storage capacity on open-circuit voltage. Moreover, it is set out that a complete understanding of a conventional storage mechanism requires unifying both the space charge and bulk storage for a nanocrystalline electroactive electrode. [ABSTRACT FROM AUTHOR]