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Solid state electrolytes could address the current safety concerns of lithium-ion batteries as well as provide higher electrochemical stability and energy density. Among solid electrolyte contenders, garnet-structured Li7La3Zr2O12 appears as a particularly promising material owing to its wide electrochemical stability window; however, its ionic conductivity remains an order of magnitude below that of ubiquitous liquid electrolytes. Here, we present an innovative dual substitution strategy developed to enhance Li-ion mobility in garnet-structured solid electrolytes. A first dopant cation, Ga3+, is introduced on the Li sites to stabilize the fast-conducting cubic phase. Simultaneously, a second cation, Sc3+, is used to partially populate the Zr sites, which consequently increases the concentration of Li ions by charge compensation. This aliovalent dual substitution strategy allows fine-tuning of the number of charge carriers in the cubic Li7La3Zr2O12 according to the resulting stoichiometry, Li7–3x+yGaxLa3Zr2–yScyO12. The coexistence of Ga and Sc cations in the garnet structure is confirmed by a set of simulation and experimental techniques: DFT calculations, XRD, ICP, SEM, STEM, EDS, solid state NMR, and EIS. This thorough characterization highlights a particular cationic distribution in Li6.65Ga0.15La3Zr1.90Sc0.10O12, with preferential Ga3+ occupation of tetrahedral Li24d sites over the distorted octahedral Li96h sites. 7Li NMR reveals a heterogeneous distribution of Li charge carriers with distinct mobilities. This unique Li local structure has a beneficial effect on the transport properties of the garnet, enhancing the ionic conductivity and lowering the activation energy, with values of 1.8 × 10–3 S cm–1 at 300 K and 0.29 eV in the temperature range of 180 to 340 K, respectively.

6 pags., 9 figs., 1 tab., The chlorination of ferrocene at 900 °C yields very interesting carbon hollow nanospheres (CHNSs) with diameters of ∼50-150 nm and ∼12-25 nm thick walls. X-ray energy-dispersive spectroscopy shows no traces of chlorine or iron and the π*/σ* ratio of the carbon bonding was quantified by electron energy-loss spectroscopy with 80% sp2 (100% sp2 for pure graphite). Energy-filtered transmission electron microscopy has been used to establish the hollow nature of the CHNSs by thickness mapping. Electron energy loss spectroscopy, high-resolution TEM, and Raman microspectroscopy techniques have stated that the CHNS carbon walls are composed of disordered and independent curved graphene nanoflakes ∼3-4 nm long that tend to graphitize with longer reaction times. © 2007 American Chemical Society., The authors are thankful for financial support from the UCM-Santander project with reference PR 27/05-13982.