Planting Repulsion Centers for Faster Ionic Diffusion in Superionic Conductors

The successful launch of solid-state batteries relies on the discovery of solid electrolytes with remarkably high ionic conductivity. Extensive efforts have identified several important superionic conductors (SICs) and broadened our understanding of their superionic conductivity. Herein, we propose a new design strategy to facilitate ionic conduction in SICs by planting immobile repulsion centers. Our ab initio molecular dynamics simulations on the model system Na₁₁Sn₂PS₁₂ demonstrate that the sodium ionic conductivity can be increased by approximately one order of magnitude by simply doping large Cs ions as repulsion centers in the characteristic vacant site of Na₁₁Sn₂PS₁₂. Planting immobile repulsion centers locally induces the formation of high-energy sites, leading to a fast track for ionic conduction owing to the unique interactions among mobile ions in SICs. Seemingly non-intuitive approaches tailor the ionic diffusion by exploiting these immobile repulsion centers.     

Metallic mono-layered C4N as a potential anode material for Na-ion batteries: A first-principles investigation

First-principles calculations based on density functional theory were used to study the adsorption behaviors of Na on metallic mono-layered C₄N as electrode materials for Na-ion batteries. The adsorption energy of Na atom was calculated to be 2.05 eV, which is much higher than Na bulk cohesive energy and sufficiently ensure stability and safety. It is worth noting that the Dirac-type band structure of mono-layered C₄N has a ultrahigh capacity of 1945.89 mAh/g for Na-ion batteries anode in theory. Remarkably, 2D C₄N has a low diffusion barrier 0.071 and 0.075 eV for path I and path II, respectively. The average open circuit voltage is 1.383 eV when nine Na ions adsorbed on one side of mono-layered C₄N. All the excellent properties show that the mono-layered C₄N will be a potential development of anode materials for Na-ion batteries.     

On the Origin of the Non-Arrhenius Na-ion Conductivity in Na3OBr

The sodium-rich antiperovskites (NaRAPs) with composition Na₃OB (B=Br, Cl, I, BH₄, etc.) are a family of materials that has recently attracted great interest for application as solid electrolytes in sodium metal batteries. Non-Arrhenius ionic conductivities have been reported for these materials, the origin of which is poorly understood. In this work, we combined temperature-resolved bulk and local characterisation methods to gain an insight into the origin of this unusual behaviour using Na₃OBr as a model system. We first excluded crystallographic disorder on the anion sites as the cause of the change in activation energy; then identified the presence of a poorly crystalline impurities, not detectable by XRD, and elucidated their effect on ionic conductivity. These findings improve understanding of the processing-structure-properties relationships pertaining to NaRAPs and highlight the need to determine these relationships in other materials systems, which will accelerate the development of high-performance solid electrolytes.     

Na3SbS4: A Solution Processable Sodium Superionic Conductor for All‐Solid‐State Sodium‐Ion Batteries

All‐solid‐state sodium‐ion batteries that operate at room temperature are attractive candidates for use in large‐scale energy storage systems. However, materials innovation in solid electrolytes is imperative to fulfill multiple requirements, including high conductivity, functional synthesis protocols for achieving intimate ionic contact with active materials, and air stability. A new, highly conductive (1.1 mS cm^?1 at 25 °C, E_a=0.20 eV) and dry air stable sodium superionic conductor, tetragonal Na₃SbS₄, is described. Importantly, Na₃SbS₄ can be prepared by scalable solution processes using methanol or water, and it exhibits high conductivities of 0.1–0.3 mS cm^?1. The solution‐processed, highly conductive solidified Na₃SbS₄ electrolyte coated on an active material (NaCrO₂) demonstrates dramatically improved electrochemical performance in all‐solid‐state batteries.     

An Air‐Stable Na3SbS4 Superionic Conductor Prepared by a Rapid and Economic Synthetic Procedure

All‐solid‐state sodium batteries, using solid electrolyte and abundant sodium resources, show great promise for safe, low‐cost, and large‐scale energy storage applications. The exploration of novel solid electrolytes is critical for the room temperature operation of all‐solid‐state Na batteries. An ideal solid electrolyte must have high ionic conductivity, hold outstanding chemical and electrochemical stability, and employ low‐cost synthetic methods. Achieving the combination of these properties is a grand challenge for the synthesis of sulfide‐based solid electrolytes. Design of the solid electrolyte Na₃SbS₄ is described, realizing excellent air stability and an economic synthesis based on hard and soft acid and base (HSAB) theory. This new solid electrolyte also exhibits a remarkably high ionic conductivity of 1 mS cm^?1 at 25 °C and ideal compatibility with a metallic sodium anode.     

Graphitic Carbon Nitride (g‐C3N4): An Interface Enabler for Solid‐State Lithium Metal Batteries

Solid‐state Li metal batteries (SSLMBs) have attracted considerable interests due to their promising energy density as well as high safety. However, the realization of a well‐matched Li metal/solid‐state electrolyte (SSE) interface remains challenging. Herein, we report g‐C₃N₄ as a new interface enabler. We discover that introducing g‐C₃N₄ into Li metal can not only convert the Li metal/garnet‐type SSE interface from point contact to intimate contact but also greatly enhance the capability to suppress the dendritic Li formation because of the greatly enhanced viscosity, decreased surface tension of molten Li, and the in situ formation of Li₃N at the interface. Thus, the resulting Li‐C₃N₄|SSE|Li‐C₃N₄ symmetric cell gives a significantly low interfacial resistance of 11 Ω cm² and a high critical current density (CCD) of 1500 μA cm^?2. In contrast, the same symmetric cell configuration with pristine Li metal electrodes has a much larger interfacial resistance (428 Ω cm²) and a much lower CCD (50 μA cm^?2).     

A First-Principles Study of C3N Nanostructures: Control and Engineering of the Electronic and Magnetic Properties of Nanosheets,Tubes and Ribbons

Using first-principles calculations we systematically investigate the atomic, electronic and magnetic properties of novel two-dimensional materials (2DM) with a stoichiometry C₃N which has recently been synthesized. We investigate how the number of layers affect the electronic properties by considering monolayer, bilayer and trilayer structures, with different stacking of the layers. We find that a transition from semiconducting to metallic character occurs which could offer potential applications in future nanoelectronic devices. We also study the affect of width of C₃N nanoribbons, as well as the radius and length of C₃N nanotubes, on the atomic, electronic and magnetic properties. Our results show that these properties can be modified depending on these dimensions, and depend markedly on the nature of the edge states. Functionalization of the nanostructures by the adsorption of H adatoms is found induce metallic, half-metallic, semiconducting and ferromagnetic behavior, which offers an approach to tailor the properties, as can the application of strain. Our calculations give insight into this new family of C₃N nanostructures, which reveal unusual electronic and magnetic properties, and may have great potential in applications such as sensors, electronics and optoelectronic at the nanoscale.     

Stable Crystalline Forms of Na Polysulfides: Experiment versus Ab Initio Computational Prediction

For the design of light‐metal–sulfur batteries and for the understanding of their performance, knowledge on the stable crystalline polysulfides is very important. We confronted experimental and ab initio crystal structure prediction studies on the stability of Na polysulfides. The selected evolutionary‐based structure‐prediction algorithm was able to quickly and correctly predict the thermodynamically stable crystalline forms of Na polysulfides with small unit cells. For Na polysulfides with large unit cells, the algorithm correctly proposed short unbranched polysulfide chains to be energetically favorite structural motifs, but could not find proper three‐dimensional structures in the limited number of generations. Experimentally, the polysulfides were studied by X‐ray diffraction and ²³Na solid‐state NMR spectroscopy. Complemented by calculations of the isotropic chemical shifts and quadrupolar coupling constants, NMR spectroscopy proved to be an excellent tool for the examination of Na polysulfides, because it allowed easy distinction and quantification of components in the samples.     

The Role of Solvent on the Mechanism of Proton Transfer to Hydride Complexes: The Case of the [W3PdS4H3(dmpe)3(CO)]+ Cubane Cluster

The kinetics of reaction of the [W₃PdS₄H₃(dmpe)₃(CO)]⁺ hydride cluster ( 1 ⁺) with HCl has been measured in dichloromethane, and a second‐order dependence with respect to the acid is found for the initial step. In the presence of added BF₄^? the second‐order dependence is maintained, but there is a deceleration that becomes more evident as the acid concentration increases. DFT calculations indicate that these results can be rationalized on the basis of the mechanism previously proposed for the same reaction of the closely related [W₃S₄H₃(dmpe)₃]⁺ cluster, which involves parallel first‐ and second‐order pathways in which the coordinated hydride interacts with one and two acid molecules, and ion pairing to BF₄^? hinders formation of dihydrogen bonded adducts able to evolve to the products of proton transfer. Additional DFT calculations are reported to understand the behavior of the cluster in neat acetonitrile and acetonitrile–water mixtures. The interaction of the HCl molecule with CH₃CN is stronger than the W? H???HCl dihydrogen bond and so the reaction pathways operating in dichloromethane become inefficient, in agreement with the lack of reaction between 1 ⁺ and HCl in neat acetonitrile. However, the attacking species in acetonitrile–water mixtures is the solvated proton, and DFT calculations indicate that the reaction can then go through pathways involving solvent attack to the W centers, while still maintaining the coordinated hydride, which is made possible by the capability of the cluster to undergo structural changes in its core.     

ANiN(A=Li,Na,Mg,Ca)的结构、热力学、弹性和电子性质的第一性原理研究

三元过渡金属氮化物ANiN(A=Li,Na,Mg,Ca)是潜在的可充放电池的电极材料.物理性质,比如热稳定性、电子能隙以及弹性稳定性等,对于这些材料的电池应用都是非常重要的.本文使用第一原理方法,对比研究了 ANiN这些材料的结构、动力学、弹性和电子结构性质.对状态方程和声子谱的计算被用来确定体系的稳定结构.对最稳定结...     

Sodium and Manganese Stoichiometry of P2‐Type Na2/3MnO2

To realize a reversible solid‐state Mn^III/IV redox couple in layered oxides, co‐operative Jahn–Teller distortion (CJTD) of six‐coordinate Mn^III (t_2g³–e_g¹) is a key factor in terms of structural and physical properties. We develop a single‐phase synthesis route for two polymorphs, namely distorted and undistorted P2‐type Na_2/3MnO₂ having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na_2/3MnO₂ delivers 216 mAh g^?1 as a 3 V class positive electrode, reaching 590 Wh (kg oxide)^?1 with excellent cycle stability in a non‐aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na_2/3MnO₂. Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na_2/3MnO₂, providing a new insight into utilization of the Mn^III/IV redox couple for positive electrodes of Na‐ion batteries.     

Investigation of 4f-Related Electronic Transitions of Rare-Earth Doped ZnO Luminescent Materials: Insights from First-Principles Calculations

Rare-earth (RE) doped zinc oxides (ZnO) are regarded as promising materials for application in versatile color-tuned devices. However, the understanding of underlying luminescence mechanism and the rule of 4 f-related electronic transition is still limited, which is full of significance for the exploration of advanced RE-based ZnO phosphors. Thus, a series of ZnO : RE (RE=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb) phosphors have been investigated by means of first-principles calculations. Meanwhile, we also consider the effect of native defects (V_O, V_Zn) on the luminescence of ZnO : RE phosphors. Accordingly, four types of electric-dipole allowed transition processes are figured out in ZnO : RE family. Additionally, we manifest that the V_O can further improve the luminescent performance of ZnO : RE phosphors, and give insightful guidance to design desired RE-based ZnO materials with excellent luminescence.     

Topological analysis of chemical bonding in the layered FePSe3 upon pressure-induced phase transitions

Two pressure-induced phase transitions have been theoretically studied in the layered iron phosphorus triselenide (FePSe₃ ). Topological analysis of chemical bonding in FePSe₃ has been performed based on the results of first-principles calculations within the periodic linear combination of atomic orbitals (LCAO) method with hybrid Hartree-Fock-DFT B3LYP functional. The first transition at about 6 GPa is accompanied by the symmetry change from to C2/m , whereas the semiconductor-to-metal transition (SMT) occurs at about 13 GPa leading to the symmetry change from C2/m to . We found that the collapse of the band gap at about 13 GPa occurs due to changes in the electronic structure of FePSe₃ induced by relative displacements of phosphorus or selenium atoms along the c-axis direction under pressure. The results of the topological analysis of the electron density and its Laplacian demonstrate that the pressure changes not only the interatomic distances but also the bond nature between the intralayer and interlayer phosphorus atoms. The interlayer P–P interactions are absent in two non-metallic FePSe₃ phases while after SMT the intralayer P–P interactions weaken and the interlayer P–P interactions appear.     

A First-Principles Study on the Adsorption of Small Molecules on Arsenene: Comparison of Oxidation Kinetics in Arsenene,Antimonene, Phosphorene,and InSe

Arsenene, a new group-V two-dimensional (2D) semiconducting material beyond phosphorene and antimonene, has recently gained an increasing attention owning to its various interesting properties which can be altered or intentionally functionalized by chemical reactions with various molecules. This work provides a systematic study on the interactions of arsenene with the small molecules, including H₂, NH₃, O₂, H₂O, NO, and NO₂. It is predicted that O₂, H₂O, NO, and NO₂ are strong acceptors, while NH₃ serves as a donor. Importantly, it is shown a negligible charge transfer between H₂ and arsenene which is ten times lower than that between H₂ and phosphorene and about thousand times lower than that between H₂ and InSe and antimonene. The calculated energy barrier for O₂ splitting on arsenene is found to be as low as 0.67 eV. Thus, pristine arsenene may easily oxidize in ambient conditions as other group V 2D materials. On the other hand, the acceptor role of H₂O on arsenene, similarly to the cases of antimonene and InSe, may help to prevent the proton transfer between H₂O and O− species by forming acids, which suppresses further structural degradation of arsenene. The structural decomposition of the 2D layers upon interaction with the environment may be avoided due to the acceptor role of H₂O molecules as the study predicts from the comparison of common group V 2D materials. However, the protection for arsenene is still required due to its strong interaction with other small environmental molecules. The present work renders the possible ways to protect arsenene from structure degradation and to modulate its electronic properties, which is useful for the material synthesis, storage and applications.     

Functional MXene Materials: Progress of Their Applications

Nowadays, two‐dimensional materials have many applications in materials science. As a novel two‐dimensional layered material, MXene possesses distinct structural, electronic, and chemical properties; thus, it has potential applications in many fields, including battery electrodes, energy storage materials, sensors, and catalysts. Up to now, more than 70 MAX phases have been reported. However, in contrast to the variety of MAX phases, the existing MXene family merely includes Ti₂C, Ti₃C₂, (Ti_1/2, Nb_1/2)₂C, (V_1/2, Cr_1/2)₃C₂, Nb₂C, Ti₃CN, Ta₄C₃, V₂C, and Nb₄C₃. Among these materials, the Ti₃C₂T_x MXene exhibits prominently high volumetric capacitance, and the rate at which it transports electron is suitable for electrode materials in batteries and supercapacitors. Hence, Ti₃C₂T_x is commonly utilized as an electrode material in ion batteries such as Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, and Al³⁺ batteries. What is more, Ti₂C has the biggest specific surface area among all of these potential MXene phases, and therefore, Ti₂C has remarkably high gravimetric hydrogen storage capacities. In addition, Ti₂CO₂ materials display extremely high activity for CO oxidation, which makes it possible to design catalysts for CO oxidation at low temperatures. Furthermore, Ti₃C₂T_x with O, OH, and/or F terminations can be used for water purification owing to excellent water permeance, favorable filtration ability, and long‐time operation ability. This review supplies a relatively comprehensive summary of various applications of MXenes over the past few years.