Graphene is an outstanding material with ultrahigh thermal conductivity. Its thermal transfer properties under various strains are studied by reverse nonequilibrium molecular dynamics. Based on the unique two-dimensional structure of graphene, the distinctive geometries of graphene sheets and graphene nanoribbons with large flexibility and their intriguing thermal properties are demonstrated under strains. For example, the corrugation under uniaxial compression and helical structure under light torsion, as well as tube-like structure under strong torsion, exhibit enormously different thermal conductivity. The important robustness of thermal conductivity is found in the corrugated and helical configurations of graphene nanoribbons. Nevertheless, thermal conductivity of graphene is very sensitive to tensile strain. The relationship among phonon frequency, strain and thermal conductivity are analyzed. A similar trend line of phonon frequency dependence of thermal conductivity is observed for armchair graphene nanoribbons and zigzag graphene nanoribbons. The unique thermal properties of graphene nanoribbons under strains suggest their great potentials for nanoscale thermal managements and thermoelectric applications.

Using a combination of time-resolved X-ray diffraction (XRD), in situ transmission electron microscopy (TEM), and first principles calculations, we explore the structural origin of the overcharge induced thermal instability of two cathode materials, LiNi 0.8 Co 0.15 Al 0.05 O 2 and LiNi 1/3 -Co 1/3 Mn 1/3 O 2 , which exhibit significant difference in thermal stabilities. Detailed TEM analysis reveals, for the first time, a complex coreÀshell-surface structure of the particles in both materials that was not previously detected by XRD. Structural comparison indicates that the overcharged Li x Ni 0.8 Co 0.15 Al 0.05 O 2 (x < 0.15) particles consist of a rhombohedral core, a spinel shell, and a rock-salt structure at the surface, while the overcharged Li x Ni 1/3 Co 1/3 Mn 1/3 O 2 consists of a similar coreÀshell-surface structure but a very different CdI 2 -type surface structure. The thermal instability of Li x Ni 0.8 Co 0.15 Al 0.05 O 2 can be attributed to the release of oxygen because of the rapid growth of the rock-salt-type structure on the surface during heating. In contrast, the CdI 2 -type surface structure of the overcharged Li x Ni 1/3 Co 1/3 Mn 1/3 O 2 particles delays the oxygen-release reaction to a much higher temperature resulting in better stability. These results gave deep insight into the relationship between the local structural changes and the thermal stability of cathode materials, which is vital to the development of new cathode materials for the next generation of lithium-ion batteries.

LaCoO3 exhibits an anomaly in its magnetic susceptibility around 80 K associated with a thermally excited transition of the Co3+-ion spin. We show that electron energy-loss spectroscopy is sensitive to this Co3+-ion spin-state transition, and that the O K edge prepeak provides a direct measure of the Co3+ spin state in LaCoO3 as a function of temperature. Our experimental results are confirmed by first-principles calculations, and we conclude that the thermally excited spin-state transition occurs from a low to an intermediate spin state, which can be distinguished from the high-spin state.

Since two-dimensional boron sheet (borophene) synthesized on Ag substrates in 2015, research on borophene has grown fast in the fields of condensed matter physics, chemistry, material science, and nanotechnology. Due to the unique physical and chemical properties, borophene has various potential applications. In this review, we summarize the progress on borophene with a particular emphasis on the recent advances.First, we introduce the phases of borophene by experimental synthesis and theoretical predictions. Then, the physical and chemical properties, such as mechanical, thermal, electronic, optical and superconducting properties are summarized. We also discuss in detail the utilization of the borophene for wide ranges of potential application among the alkali metal ion batteries, Li-S batteries, hydrogen storage, supercapacitor, sensor and catalytic in hydrogen evolution, oxygen reduction, oxygen evolution, and CO2 electroreduction reaction. Finally, the challenges and outlooks in this promising field are featured on the basis of its current development.