Doping of group IVB elements for nickel-rich cobalt-free cathodes

Hetero-element doping is a promising strategy to improve the cycling stability of nickel-rich cobalt-free cathodes for the next-generation high energy-density Li ion batteries.To make doping effective,it is important to understand the mechanism of how the dopants regulate the electronic band,lattice parameter adjusting,or hetero-phase formation to achieve high stability.In this study,we investigate LiNi_(0.9)Mn_(0.1)O_(2)cathodes doped with IVB grouping elements via multiple characterization techniques.By utilizing in situ XRD and TEM methods,we found that the stronger Ti-O bond effectively improves the cathode stability via a dual protection mechanism.Specifically,the bulk lattice of cathode is wellpreserved during cycling as a result of the suppressed H_(2)-H_(3)phase transition,while a in situ formed Ti-rich surface layer can prevent continuous surface degradation.As a result,the 5%Ti doped LiNi_(0.9)Mn_(0.1)O_(2)cathode exhibits a high capacity retention of 96%after 100 cycles.Whereas,despite IVB group elements Zr and Hf have stronger bonding energy with oxygen,their larger ionic radii actually impede their diffusion into the cathode,thereby they can not improve the cycling stability.Our findings uncover the functional origin of doped elements with their dynamic modification on cathode structure,providing mechanistic insights into the design of nickel-rich cobalt-free cathodes.

Morphology-controlled transformation of Cu@Au core-shell nanowires into thermally stable Cu3Au intermetallic nanowires

Multimetallic nanowires with long-range atomic ordering hold the promise of unique physicochemical properties in many applications.Here we demonstrate the synthesis and study the stability of CU3AU intermetallic nanowires.The synthesis is achieved by using Cu@Au core-shell nanowires as precursors.With appropriate Cu/Au stoichiometry,the Cu@Au core-shell nanowires are transformed into fully ordered Cu3Au nanowires under thermal annealing.Thermally-driven atom diffusion accounts for this transformation as revealed by X-ray diffraction and electron microscopy studies.The twin boundaries abundant in the Cu@Au core-shell nanowires facilitate the ordering process.The resulting CU3AU intermetallic nanowires have uniform and accurate atomic positioning in the crystal lattice,which enhances the nobility of Cu.No obvious copper oxides are observed in fully ordered Cu3Au nanowires after annealing in air at 200℃,a temperature that is much higher than those observed in Cu@Au core-shell and pure Cu nanowires.This work opens up an opportunity for further research into the development and applications of intermetallic nanowires.

Towards next generation white LEDs:opticselectronics synergistic effect in a single-layer heterophase halide perovskite

A novel concept of the heterophase optics-electronics synergistic effect has been demonstrated in a single-layerα/δ-heterophase perovskite CsPbl3 in order to realize white LEDs featuring only one broadband emissive layer.

Insight from in situ microscopy into which precipitate morphology can enable high strength in magnesium alloys

Magnesium alloys, while boasting light weight, suffer from a major drawback in their relatively low strength. Identifying the microstructural features that are most effective in strengthening is therefore a pressing challenge. Deformation twinning often mediates plastic yielding in magnesium alloys. Unfortunately, due to the complexity involved in the twinning mechanism and twin-precipitate interactions, the optimal precipitate morphology that can best impede twinning has yet to be singled out. Based on the understanding of twinning mechanism in magnesium alloys, here we propose that the lamellar precipitates or the network of plate-shaped precipitates are most effective in suppressing deformation twinning. This has been verified through quantitative in situ tests inside a transmission electron microscope on a series of magnesium alloys containing precipitates with different morphology. The insight gained is expected to have general implications for strengthening strategies and alloy design. 2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.