Direct mapping of the lithium spatial distribution and the chemical state provides critical information on structure-correlated lithium transport in electrode materials for lithium batteries. Nevertheless, probing lithium, the lightest solid element in the periodic table, poses an extreme challenge with traditional X-ray or electron scattering techniques due to its weak scattering power and vulnerability to radiation damage. Here, we report nanoscale maps of the lithium spatial distribution in electrochemically lithiated graphite using electron energy loss spectroscopy in the transmission electron microscope under optimized experimental conditions. The electronic structure of the discharged graphite was obtained from the near-edge fine structure of the Li and C K-edges and ab initio calculations. A 2.7 eV chemical shift of the Li K-edge, along with changes in the density of states, reveals the ionic nature of the intercalated lithium with significant charge transfer to the graphene sheets. Direct mapping of lithium in graphite revealed nanoscale inhomogeneities (nonstoichiometric regions), which are correlated with local phase separation and structural disorder (i.e., lattice distortion and dislocations) as observed by high-resolution transmission electron microscopy. The surface solid-electrolyte interphase (SEI) layer was also imaged and determined to have a thickness of 10-50 nm, covering both edge and basal planes with LiF as its primary inorganic component. The Li K-edge spectroscopy and mapping, combined with electron microscopy-based structural analysis provide a comprehensive view of the structure-correlated lithium intercalation in graphite and of the formation of the SEI layer.

No abstract

No abstract

The use of MgB 2 in superconducting applications still awaits for the development of a MgB 2 -based material where both current-carrying performance and critical magnetic field are optimized simultaneously. We achieved this by doping MgB 2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in polycrystalline samples. The optimum nominal DWCNT content for increasing the critical current density, J c is in the range 2.5-10%at depending on field and temperature. Record values of the upper critical field, H c2 (4K) = 41.9 T (with extrapolated H c2 (0) ≈ 44.4 T) are reached in a bulk sample with 10%at DWCNT content. The measured H c2 vs T in all samples are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich et al.