The improved ionic conductivity (1.64 × 10(-4) S cm(-1) at room temperature) and excellent electrochemical stability of nanoporous β-Li3PS4 make it one of the promising candidates for rechargeable all-solid-state lithium-ion battery electrolytes. Here, elastic properties, defect thermodynamics, phase diagram, and Li(+) migration mechanism of Li3PS4 (both γ and β phases) are examined via the first-principles calculations. Results indicate that both γ- and β-Li3PS4 phases are ductile while γ-Li3PS4 is harder under volume change and shear stress than β-Li3PS4. The electrochemical window of Li3PS4 ranges from 0.6 to 3.7 V, and thus the experimentally excellent stability (>5 V) is proposed due to the passivation phenomenon. The dominant diffusion carrier type in Li3PS4 is identified over its electrochemical window. In γ-Li3PS4 the direct-hopping of Lii(+) along the [001] is energetically more favorable than other diffusion processes, whereas in β-Li3PS4 the knock-off diffusion of Lii(+) along the [010] has the lowest migration barrier. The ionic conductivity is evaluated from the concentration and the mobility calculations using the Nernst-Einstein relationship and compared with the available experimental results. According to our calculated results, the Li(+) prefers to transport along the [010] direction. It is suggested that the enhanced ionic conductivity in nanostructured β-Li3PS4 is due to the larger possibility of contiguous (010) planes provided by larger nanoporous β-Li3PS4 particles. By a series of motivated and closely linked calculations, we try to provide a portable method, by which researchers could gain insights into the physicochemical properties of solid electrolyte.

Using a structural search method in combination with first-principles calculations, we found lots of low energy 2D carbon allotropes and examined all possible Dirac points around their Fermi levels. Three amazing 2D Dirac carbon allotropes have been discovered, named as S-graphene, D-graphene and E-graphene. By analyzing the topology correlations among S-, T, net W graphene and graphene, we found that a general rule is valuable for constructing 2D carbon allotropes that are keen to possess Dirac cones in their electronic structures. Based on this rule, we have successfully designed many new 2D carbon allotropes possessing Dirac cones. Their energy order can be well described by an Ising-like model, and some allotropes are energetically more stable than those recently reported. The related electronic structures of these Dirac allotropes are anisotropy distinguished from those of graphene. Moreover, the fact that D- and E-graphene present Dirac cones suggests that sp hybridization or sp(3) hybridization could not suppress the emerging of Dirac features. Our results demonstrate that the Dirac cone and carrier linear dispersion is a very common feature in 2D carbon allotropes and can exist beyond the limitations of fundamental structure features of graphene.

Cathodes of lithium-rich layered oxides for highenergy Li-ion batteries in electrically powered vehicles are attracting considerable attention by the research community. However, current research is insufficient to account for their complex reaction mechanism and application. Here, the structural evolution of lithium−manganese-rich layered oxides at different temperatures during electrochemical cycling has been investigated thoroughly, and their structural stability has been designed. The results indicated structure conversion from the two structures into a core−shell structure with a single distorted-monoclinic LiTMO 2 structure core and disorderedspinel/rock salt structure shell, along with lattice oxygen extraction and lattice densification, transition-metal migration, and aggregation on the crystal surface. The structural conversion behavior was found to be seriously temperature sensitive, accelerated with higher temperature, and can be effectively adjusted by structural design. This study clarifies the structural evolution mechanism of these lithium-rich layered oxides and opens the door to the design of similar high-energy materials with better cycle stability.

Photodegradable hydrogels that allow 3D encapsulation of cells are important biomaterials to modulate cellular microenvironments with temporal and spatial resolution. Herein we report a photodegradable hydrogel formed by the self-assembly of short peptides modified with a novel phototrigger. The phototrigger is a biaryl-substituted tetrazole moiety that, upon mild light irradiation, undergoes rapid intramolecular photoclick ligation to form a highly fluorescent pyrazoline moiety. Short peptides linked with a tetrazole-containing moiety, Tet(I) or Tet(II), are able to self-assemble into hydrogels, among which the Tet(I)-GFF and Tet(II)-GFRGD gels show good mechanical strength and biocompatibility for 3D encapsulation and prolonged culture of live cells. The phototriggered tetrazole-to-pyrazoline transformation generates a highly fluorescent reporter and induces the disassembly of the hydrogel matrix by disturbing the balance between hydrophilic interaction and π-π stacking of the self-assembled system. Photomodulation of cellular microenvironments was demonstrated not only for the cells grown on top of the gel but also for stem cells encapsulated inside the hydrogels.

Bring to light: The first visible‐light‐promoted somophilic isocyanide insertion occurs using an iridium photocatalyst. This efficient synthetic approach provides a rapid entry to 6‐alkylated phenanthridine derivatives (see scheme). The reactions proceed at room temperature in good to excellent yields with broad substrate scope and under environmentally friendly conditions.

Hafnium disulfide (HfS2) has attracted significant interest because of the predicted excellent electronic properties superior to group VIB transition metal dichalcogenides. On the other hand, atomically thin hexagonal boron nitride (h-BN) is an ideal dielectric substrate for optoelectronic applications of other 2D materials. Here, for the first time, we report the direct growth of high-quality atomic layered HfS2 on few-layer h-BN transferred on SiO2/Si substrates by chemical vapor deposition. It was found that the HfS2 layers are selectively grown on h-BN rather than on SiO2/Si. Density functional theory calculations are performed to help understand the mechanism of selective growth of HfS2. Furthermore, the photodetectors based on the HfS2/h-BN heterostructures exhibit excellent visible-light sensing performance, such as a high on/off ratio of more than 105, an ultrafast response rate of about 200 μs, a high responsivity of 26.5 mA W–1, and a competitive detectivity exceeding 3 × 1011 Jones, superior to the vast majority of the reported 2D materials based photodetectors. The remarkable performance of the HfS2/h-BN photodetector is attributed to the unique features of 2D h-BN substrate.

A novel two-dimension carbon allotrope, rectangular graphyne (R-graphyne) with tetra-rings and acetylenic linkages, is proposed by first-principles calculations. Although the bulk R-graphyne exhibits metallic property, the nanoribbons of R-graphyne show distinct electronic structures from the bulk. The most intriguing feature is that band gaps of R-graphene nanoribbons oscillate between semiconductor and metal as a function of width. Particularly, the zigzag edge nanoribbons with half-integer repeating unit cell exhibits unexpected Dirac-like fermions in the band structures. The Dirac-like fermions of the R-graphyne nanoribbons originate from the central symmetry and two sub-lattices. The extraordinary properties of R-graphene nanoribbons greatly expand our understanding on the origin of Dirac-like point. Such findings uncover a novel fascinating property of nanoribbons, which may have broad potential applications for carbon-based nano-size electronic devices.

No abstract