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Insulator–metal transitions are well known in transition-metal oxides, but inducing an insulator–metal transition in the oxide of a main group element is a major challenge. Here, we report the observation of an insulator–metal transition, with a conductivity jump of seven orders of magnitude, in highly non-stoichiometric, amorphous gallium oxide of approximate composition GaO 1.2 at a temperature around 670 K. We demonstrate through experimental studies and density-functional-theory calculations that the conductivity jump takes place at a critical gallium concentration and is induced by crystallization of stoichiometric Ga 2 O 3 within the metastable oxide matrix—in chemical terms by a disproportionation. This novel mechanism—an insulator–metal transition driven by a heterogeneous solid-state reaction—opens up a new route to achieve metallic behaviour in oxides that are expected to exist only as classic insulators. Inducing and understanding insulator–metal transitions in binary oxide can be challenging. A transition driven chemically by an internal redox reaction is now observed in a non-stoichiometric, amorphous gallium oxide.

Many carbon allotropes can act as host materials for reversible lithium uptake 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 3 – 5 to probe light elements (especially lithium) 6 , 7 is severely hampered by their low scattering cross-section for impinging electrons and their susceptibility to knock-on damage 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 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 6 , which is the densest configuration known under normal conditions for lithium intercalation within bulk graphitic carbon 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.

LiFePO 4 is one of the most frequently studied positive electrode materials for lithium-ion batteries during the last years. Nevertheless, there is still an extensive debate on the mechanism of phase transformation. On the one hand this is due to the small energetic differences involved and hence the great sensitivity with respect to parameters such as size and morphology. On the other hand this is due to the lack of in situ observations with appreciable space and time resolution. Here we present scanning transmission X-ray microscopy measurements following in situ the phase boundary propagation within a LiFePO 4 single crystal along the (010) orientation during electrochemical lithiation/delithiation. We follow, on a battery-relevant timescale, the evolution of a two-phase-front on a micrometre scale with a lateral resolution of 30 nm and with minutes of time resolution. The growth pattern is found to be dominated by elastic effects rather than being transport-controlled. The phase transformation of LiFePO 4 /FePO 4 is an intriguing problem in lithium-ion battery research. Here, the authors use scanning transmission X-ray microscopy to reveal in-situ phase evolution of LiFePO 4 /FePO 4 in a micrometer scale battery cell with well characterised single-crystalline electrodes.

The use of regenerative energy in many primary forms leads to the necessity to store grid dimensions for maintaining continuous supply and enabling the replacement of fossil fuel systems. Chemical energy storage is one of the possibilities besides mechano-thermal and biological systems. This work starts with the more general aspects of chemical energy storage in the context of the geosphere and evolves to dealing with aspects of electrochemistry, catalysis, synthesis of catalysts, functional analysis of catalytic processes and with the interface between electrochemistry and heterogeneous catalysis. Top-notch experts provide a sound, practical, hands-on insight into the present status of energy conversion aimed primarily at the young emerging research front.

In this chapter the relationship between nanoarchitecture and electrochemical properties of composite cathode materials based on LiFePO4 will be discussed in detail. We start out from studies of the inherent materials properties based on single crystal experiments. These will provide insight into defect chemistry, mass and charge transport as well as into phase transition behavior of the FePO4/LiFePO4 two phase system. Then the possibilities of optimizing the performance (e.g., by doping) will be discussed, out of which nanostructuring appears to be most promising. Diff erent nanoarchitectures, their significance as well as their preparation will be discussed. The detailed understanding of the transport and storage aspects allows us to deduce appropriate nanoarchitectures that comprise both electroactive material and electrochemical wiring.

We report measurements of the dynamics of isolated \\(^8\\)Li\\(^+\\) in single crystal rutile TiO\\(_2\\) using \\(\\)-detected NMR. From spin-lattice relaxation and motional narrowing, we find two sets of thermally activated dynamics: one below 100 K; and one at higher temperatures. At low temperature, the activation barrier is \\(26.8(6)\\) meV with prefactor \\(1.23(5) 10^10\\) s\\(^-1\\). We suggest this is unrelated to Li\\(^+\\) motion, and rather is a consequence of electron polarons in the vicinity of the implanted \\(^8\\)Li\\(^+\\) that are known to become mobile in this temperature range. Above 100 K, Li\\(^+\\) undergoes long-range diffusion as an isolated uncomplexed cation, characterized by an activation energy and prefactor of \\(0.32(2)\\) eV and \\(1.0(5) 10^16\\) s\\(^-1\\), in agreement with macroscopic diffusion measurements. These results in the dilute limit from a microscopic probe indicate that Li\\(^+\\) concentration does not limit the diffusivity even up to high concentrations, but that some key ingredient is missing in the calculations of the migration barrier. The anomalous prefactors provide further insight into both Li\\(^+\\) and polaron motion.