(Li/Ag)CoO2: a new intergrowth cobalt oxide composed of rock salt and delafossite layers

Predictions of delafossite-hosted honeycomb and kagome phases

Delafossites, typically denoted by the formula ABO2, are a class of layered materials that exhibit a wide range of electronic and optical properties. Recently, the idea of modifying these delafossites into ordered kagome or honeycomb phases via strategic doping has emerged as a potential way to tailor these properties. In this study, we use high-throughput density functional theory calculations to explore many possible candidate kagome and honeycomb phases by considering dopants selected from the parent compounds of known ternary delafossite oxides from the inorganic crystal structure database. Our results indicate that while A-site in existing delafossites can host a limited range of elemental specifies, and display a low propensity for mixing or ordering, the oxide sub-units in the BO2 much more readily admit guest species. Our study identifies four candidate B-site kagome and fifteen candidate B-site honeycombs with a formation energy more than 50 meV f.u.-1 below other competing phases. The ability to predict and control the formation of these unique structures offers exciting opportunities in materials design, where innovative properties can be engineered through the selection of specific dopants. A number of these constitute novel correlated metals, which may be of interest for subsequent efforts in synthesis. These novel correlated metals may have significant implications for quantum computing, spintronics, and high-temperature superconductivity, thus inspiring future experimental synthesis and characterization of these proposed materials.

Mixed alkali-ion transport and storage in atomic-disordered honeycomb layered NaKNi2TeO6

Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms (Na and K) to produce a mixed-alkali honeycomb layered oxide material, namely, NaKNi2TeO6. Via transmission electron microscopy measurements, we reveal the local atomic structural disorders characterised by aperiodic stacking and incoherency in the alternating arrangement of Na and K atoms. We also investigate the possibility of mixed electrochemical transport and storage of Na+ and K+ ions in NaKNi2TeO6. In particular, we report an average discharge cell voltage of about 4 V and a specific capacity of around 80 mAh g-1 at low specific currents (i.e., < 10 mA g-1) when a NaKNi2TeO6-based positive electrode is combined with a room-temperature NaK liquid alloy negative electrode using an ionic liquid-based electrolyte solution. These results represent a step towards the use of tailored cathode active materials for "dendrite-free" electrochemical energy storage systems exploiting room-temperature liquid alkali metal alloy materials.

Structure Recovery and Recycling of the Used LiCoO2 Cathode Material

The large number of lithium batteries have been retiring from the market of energy storage. Thus, the recycling of the used electrode materials is becoming urgent. In this study, the industrial machinery processing was used to recover the crystal structure of the waste LiCoO 2 materials with the combination of small-scale equipment repair technology. The results show that the crystal parameters of the repaired LiCoO 2 material become small, the unit cell volume is reduced, and the crystal structure tends to be stable. The Co-O bond length of 1.9134 nm, O-Co-O bond angle of 94.72º, the (003) interplanar spacing of 0.467 nm indicate the excellent recovery level of the repaired LiCoO 2 . In addition, the electrochemical performance of the repaired LiCoO 2 material is greatly improved, compared with the waste material. The capacity of the repaired electrode material can be maintained at 120 mAh g -1 after 100 cycles at the current density of 0.2 C. The promising rate performance of the repaired electrode material demonstrates the stable structure. This research work provides a large-scale method for the direct recovery of LiCoO 2 with the reduction of unnecessary energy and reagent consumption, which will be beneficial to the environmental protection.