The first study on relationship between the cation pre-intercalation amount in MnO₂ matrix and electrochemical performances of AZIBs are provided.

Lithium-rich disordered rocksalt cathodes display high capacities arising from redox chemistry on both transition-metal ions (TM-redox) and oxygen ions (O-redox), making them promising candidates for next-generation lithium-ion batteries. However, the atomic-scale mechanisms governing O-redox behaviour in disordered structures are not fully understood. Here we show that, at high states of charge in the disordered rocksalt Li₂MnO₂F, transition metal migration is necessary for the formation of molecular O₂ trapped in the bulk. Density functional theory calculations reveal that O₂ is thermodynamically favoured over other oxidised O species, which is confirmed by resonant inelastic X-ray scattering data showing only O₂ forms. When O-redox involves irreversible Mn migration, this mechanism results in a path-dependent voltage hysteresis between charge and discharge, commensurate with the hysteresis observed electrochemically. The implications are that irreversible transition metal migration should be suppressed to reduce the voltage hysteresis that afflicts O-redox disordered rocksalt cathodes.

The search for new nanostructural topologies composed of elemental carbon is driven by technological opportunities as well as the need to understand the structure and evolution of carbon materials formed by planetary shock impact events and in laboratory syntheses. We describe two new families of diamond-graphene (diaphite) phases constructed from layered and bonded sp³ and sp² nanostructural units and provide a framework for classifying the members of this new class of materials. The nanocomposite structures are identified within both natural impact diamonds and laboratory-shocked samples and possess diffraction features that have previously been assigned to lonsdaleite and postgraphite phases. The diaphite nanocomposites represent a new class of high-performance carbon materials that are predicted to combine the superhard qualities of diamond with high fracture toughness and ductility enabled by the graphitic units and the atomically defined interfaces between the sp³- and sp²-bonded nanodomains.

Dark-colored shiny flakes of graphitic carbon nitride materials produced by reacting dicyandiamide C2N4H4 in a KBr/LiBr molten salt medium were determined to have a C:N ratio near 1.2:1. The compounds also contained 2.3-2.5 wt% H incorporated within N-H species identified by FTIR spectroscopy. One recent study revealed analogous results for thin films produced by an similar synthesis method, while a previous investigation instead reported formation of crystalline gC3N4 flakes with a triazine-based graphitic carbon nitride (TGCN) structure. The structures of the materials produced here were studied using a combination of high resolution transmission electron microscopy, X-ray diffraction, IR and Raman and X-ray photoelectron spectroscopy, along with series of density functional (DFT) calculations carried out for a range of model layered structures. The results indicate the graphitic layered gCxNy materials contain a mixture of sp2-hybridized C-N and C-C bonded structures, with TGCN to graphene-like domains existing within the layers. Paramagnetic centers localized on the C3N3 rings revealed by EPR spectroscopy correspond to potential defect structures within the graphitic layers predicted by DFT calculations. Our results combined with those of previous researchers indicate that a range of graphitic carbon nitride materials could exist with different C:N:H ratios leading to tunable electronic properties for catalysis, semiconducting, spintronics and energy applications, that could be targeted by controlling the synthesis and thin film deposition procedures.