Although chemical doping has been extensively employed to improve the electrochemical performance of Li-rich layered oxide (LLO) cathodes for Li ion batteries, the correlation between the electrochemical kinetics and local structure and chemistry of these materials after chemical doping is still not fully understood. Herein, gradient surface Si/Sn-doped LLOs with improved kinetics are demonstrated. The atomic local structure and surface chemistry are determined using electron microscopy and spectroscopy techniques, and remarkably, the correlation of local structure-enhanced kinetics is clearly described in this work. The experimental results suggest that Si/Sn substitution decreases the TMO2 slab thickness and enlarges the interslab spacing, and the concentration gradient of Si/Sn affects the magnitude of these structural changes. The expanded interslab spacing accounts for the enhanced Li+ diffusivity and rate performance observed in Si/Sn-doped materials. The improved understanding of the local structure-enhanced kinetic relationship for doped LLOs demonstrates the potential for the design and development of other high-rate intercalated electrode materials.Keywords: cathode materials; gradient chemical doping; HAADF-STEM; interslab spacing; lithium-rich layered oxide;

Polyanion doping shows great potential to improve electrochemical performance of Li-rich layered oxide (LLO) materials. Here, by optimizing the doping content and annealing temperature, we obtained boron-doped LLO materials Li1.2Mn0.54Ni0.13Co0.13BxO2 (x = 0.04 and 0.06) with comprehensively improved performance (94% capacity retention after 100 cycles at 60 mA/g current density and a rate capability much higher compared to that of the pristine sample) at annealing temperatures of 750 and 650 °C, respectively, which are much lower than the traditional annealing temperature of similar material systems without boron. The scenario of the complex crystallization process was captured using Cs-corrected high-angle annular dark field scanning transmission electron microscopic (HAADF-STEM) imaging techniques. The existence of layered, NiO-type, and spinel-like structures in a single particle induced by boron doping and optimization of annealing temperature is believed to contribute to the remarkable improvement of cycling stability and rate capability.Keywords: annealing temperature; boron doping; cathode materials; complex crystallization; HAADF-STEM; lithium-rich layered oxide;

•Compositional characteristics of precipitates at different stage of heat treatment were determined by STEM-EDS.•Precipitates having stable crystal structures but changing compositions during service are demonstrated.•Phenomenon of forming precipitates with elemental diffusion and segregation in T92 steel was found.•The subtle scenarios of compositional evolution of precipitate in the T92 steel were revealed.A detailed characterization of the composition and evolution of precipitates during thermal exposure (0–10000 h at 650 °C) of T92 steel was carried out using a combination of transmission electron microscopy (TEM), high angle annular dark field (HAADF) imaging, energy-dispersive X-ray spectrometry (EDS) analysis, scanning electron microscopy (SEM) and first-principles calculations. It is shown that MX in T92 steel can be expressed as V/Nb(C,N) rather than complete solid-solution (V,Nb)(C,N) in terms of composition. The segregation of P and S elements in the MX precipitates was found after normalization. Meanwhile the slow segregation of Si from the matrix into the MX took place during a long-term thermal exposure. The nucleation and growth of M23C6 carbides adjacent to the MX micrograin boundary carbonitrides always accompany by the diffusion of C and S from the neighboring MX, and the segregation of W and Mo from the matrix, respectively. Similarly this elemental diffusion behavior of W and Mo, as well as the segregation of Si, P and S were also found for the nucleation and growth of Laves phase in contact with M23C6. Our results indicate that these precipitates formation in T92 steel is a special process with self-adaptive elemental diffusion and segregation.

•The enhanced photoactivity on Bi/BiOCl catalyst was studied.•Bi/BiOCl photocatalyst was prepared in TEM in situ.•The LSPR absorption of Bi NPs was confirmed by Mono-STEM-EELS and simulation.•The direct Eg value of single Bi nanoparticle was determined by Mono-STEM-EELS.•The possible charge transfer between Bi and BiOCl was investigated.State-of-the-art electron microscopy has enabled us to investigate microstructural details down to sub-subångström and milli-electron-volt resolution level. The enhanced photoreactivity over bismuth hybridized BiOCl catalyst (Bi/BiOCl) has been reported recently, however, the mechanistic understandings of this improved photoreactivity especially the optical behavior of bismuth nanoparticles (Bi NPs) are still obscured and in debate. The optical absorption features of Bi NPs and the charge transfer characteristic between bismuth and BiOCl have been considered as the major physicochemical origin for the promoted photoreactivity. Based on the advanced (in-situ) electron microscopy of monochromated electron energy loss spectroscopy in scanning transmission electron microscopy imaging mode (Mono-STEM-EELS) along with related theoretical investigations, in this work, we for the first time distinguished and explained the optical absorption originated from the localized surface plasmon resonances (LSPR) effect and direct band gap transition in an individual bismuth nanoparticle as well as transportation of photogenerated carriers at the interface of Bi/BiOCl. These findings could provide better understandings about the origin of the improved photoreactivity of various bismuth-hybridized photocatalysts.The optical absorption of a single bismuth nanoparticle caused by the LSPR effect and direct band gap transition has been distinguished by means of Mono-STEM-EELS technique.Download high-res image (138KB)Download full-size image

Colloidal nanocrystals of lead halide perovskites have recently received great attention due to their remarkable performance in optoelectronic applications (e.g., light-emitting devices, flexible electronics, and photodetectors). However, the use of lead remains of great concern due to its toxicity and bioaccumulation in the ecosystem; herein we report a strategy to address this issue by using tetravalent tin (Sn4+) instead of divalent lead (Pb2+) to synthesize stable Cs2SnI6 perovskite nanocrystals. The shapes of as-synthesized Cs2SnI6 nanocrystals are tuned from spherical quantum dots, nanorods, nanowires, and nanobelts to nanoplatelets via a facile hot-injection process using inexpensive and nontoxic commercial precursors. Spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM) and simulation studies revealed a well-defined face-centered-cubic (fcc) perovskite derivative structure of Cs2SnI6 nanocrystals. The solution-processed Cs2SnI6 nanocrystal-based field effect transistors (FETs) displayed a p-type semiconductor behavior with high hole mobility (>20 cm2/(V s)) and high I-ON/I-OFF ratio (>104) under ambient conditions. We envision that this work will pave the way to produce new families of high-performance, stable, low-cost and nontoxic nanocrystals for optoelectronic applications.

The synthetic techniques for novel photocatalytic crystals had evolved by a trial-and-error process that spanned more than two decades, and an insight into the photocatalytic crystal growth process is a challenging area and prerequisite for achieving an excellent photoactivity. Bismuth nanoparticle based hybrids, such as Bi/BiOCl composites, have recently been investigated as highly efficient photocatalytic systems because of the localized surface plasmon resonance (LSPR) of nanostructured bismuth. In this work, the observation towards the formation and growth of bismuth nanoparticles onto 2D structured BiOCl photocatalysts has been performed using a transmission electron microscope (TEM) directly in real time. The growth of bismuth nanoparticles on BiOCl nanosheets can be emulated and speeded up driven by the electron beam (e− beam) in TEM. The crystallinity, growth and the elemental evolution during the formation of bismuth nanoparticles have also been probed in this work.

•The perturbation energy of electron vortices in electromagnetic fields is studied.•The perturbation energy is dependent on the spatial extent of electron vortices.•Electron–electric potential interaction is the dominant interaction.•The electron–magnetic field/potential interaction is about 10−4 eV.•The spin–orbit coupling interaction is about 10−4–10−3 eV.The novel discovery of electron vortices carrying quantized orbital angular momentum motivated intensive research of their basic properties as well as applications, e.g. structural characterization of magnetic materials. In this paper, the fundamental interactions of electron vortices within infinitely long atomic-column-like electromagnetic fields are studied based on the relativistically corrected Pauli–Schrödinger equation and the perturbation theory. The relative strengths of three fundamental interactions, i.e. the electron–electric potential interaction, the electron–magnetic potential/field interaction and the spin–orbit coupling are discussed. The results suggest that the perturbation energies of the last two interactions are in an order of 103–104 smaller than that of the first one for electron vortices. In addition, it is also found that the strengths of these interactions are strongly dependant on the spatial distributions of the electromagnetic field as well as the electron vortices.

The synthetic techniques for novel photocatalytic crystals had evolved by a trial-and-error process that spanned more than two decades, and an insight into the photocatalytic crystal growth process is a challenging area and prerequisite for achieving an excellent photoactivity. Bismuth nanoparticle based hybrids, such as Bi/BiOCl composites, have recently been investigated as highly efficient photocatalytic systems because of the localized surface plasmon resonance (LSPR) of nanostructured bismuth. In this work, the observation towards the formation and growth of bismuth nanoparticles onto 2D structured BiOCl photocatalysts has been performed using a transmission electron microscope (TEM) directly in real time. The growth of bismuth nanoparticles on BiOCl nanosheets can be emulated and speeded up driven by the electron beam (e− beam) in TEM. The crystallinity, growth and the elemental evolution during the formation of bismuth nanoparticles have also been probed in this work.