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The configuration of positive charge alignments in a poled-BaTiO3 functionalized separator, and the mechanism for anchoring polysulfides and accelerating Li-ion transportation.

Li-rich layered oxides (LLOs) are considered promising candidates for new high-energy-density cathode materials for next-generation power batteries. However, their large-scale applications are largely hindered by irreversible Li/O loss, structural degradation, and interfacial side reactions during cycling. Herein, we demonstrate an integration strategy that tunes the electronic structure by La/Al codoping and constructs a ferroelectric interface on the LLOs surface through Bi

Lithium-rich manganese-based layered oxides (LLOs) are considered to be the most promising cathode materials for next-generation lithium-ion batteries (LIBs) for their higher reversible capacity, higher operating voltage, and lower cost compared with those of other commercially available cathode materials. However, irreversible lattice oxygen release and associated severe structural degradation that exacerbate under high temperature and deep delithiation hinder the large-scale application of LLOs. Herein, we propose a strategy to stabilize the layered lattice framework and improve the thermal stability of cobalt-free Li1.2Mn0.53Ni0.27O2 by doping with 4d transition metal niobium (Nb). Detailed atomic-scale imaging, in situ characterization, and DFT simulations confirm that the induced strong Nb-O bonds stabilize the oxygen lattice framework and restrains the fracture of TM-O bonds, thereby inhibiting the release of lattice oxygen and the continuous migration of TM ions to the lithium layer during the cycle. Furthermore, Nb doping also promotes the surface rearrangement to form a Ni-enrichment layered/rocksalt heterogeneous interface to enhance surface structural stability. As a result, the Nb-doped material delivers a capacity of 181.7 mAh g-1 with retention of 85.5% after 200 cycles at 1C, extraordinary thermal stability with a capacity retention of 80.7% after 200 cycles at 50 °C, and superior rate capability.

Two new eight-layer hexagonal perovskites with the composition Ba8MNb6O24 (M = Fe and Cu) are synthesized by solid-state reaction at 1350-1400 °C. Their crystal structures have been investigated using X-ray and electron diffractions as well as high-resolution transmission electron microscopy. Although both compounds have similar M2+ size, Ba8FeNb6O24 and Ba8CuNb6O24 adopt shifted and twinned structures, respectively. Through comparison with the reported shifted Ba8MNb6O24 (M = Mn, Co, and Zn) and twinned Ba8NiNb6O24 as well as inexistent Ba8Mg(Nb/Ta)6O24, we elucidate that the twin-shift competition of Ba8MNb6O24 family could be related with multiple chemical factors including tolerance factors, B-cationic size difference, entropy variation with B-cation and vacancy disorder, Jahn-Teller distortion, and FSO B-B d orbit interactions.

Recently honeycomb-ordered Na3M2XO6 (M = Ni, Cu, Co; X = Sb, Bi etc.) layered oxide cathode materials have attracted significant interest because of their excellent voltage platform and high energy density. Despite their excellent prospects, they still suffer from insufficient rate capability and poor structure stability. Herein, we find that the specific capacity, electronic conductivity and structural stability of honeycomb-ordered Na3Ni2SbO6 cathode material can be well promoted through partial Ru substitution. By combining the experimental analyses and theoretical calculations, we reveal that the partial substitution of Sb(V) with low valence Ru(IV) generated a strong Ru-O covalency reduces the bandgap, leading to a decreased redox potential and enhanced electrochemical kinetics. Meanwhile, the formed honeycomb RuNi6-ring superstructure with structural distortion can adapt large strain fluctuation during cycling and eventually enhance the electrochemical cyclability. Such a proposed strategy provides valuable insights into further developments of the high-performance honeycomb layered oxides cathodes.

Formation of quasicrystal structures has always been mysterious since the discovery of these magic structures. In this work, the nucleation of decagonal, dodecagonal, heptagonal, and octagonal quasicrystal structures controlled by the coupling among multiple length scales is investigated using a dynamic phase-field crystal model. We observe that the nucleation of quasicrystals proceeds through local rearrangement of length scales, i.e., the generation, merging and stacking of 3-atom building blocks constructed by the length scales, and accordingly, propose a geometric model to describe the cooperation of length scales during structural transformation in quasicrystal nucleation. Essentially, such cooperation is crucial to quasicrystal formation, and controlled by the match and balance between length scales. These findings clarify the scenario and microscopic mechanism of the structural evolution during quasicrystal nucleation, and help us to understand the common rule for the formation of periodic crystal and quasicrystal structures with various symmetries.

In this study, first principles calculations demonstrated that the cohesive energies, atomic volumes, or bulk moduli of the rhombohedral (A7), monoclinic (M), and triclinic (T1 and T2) structures of bismuth are very close to each other, thereby suggesting that these four structures of bismuth will probably coexist with each other, which agrees well with previously reported experimental and theoretical observations. The band structures showed that the A7, M, and T1 structures are semimetals with a small overlap, whereas T2 is a direct semiconductor with a narrow band gap. We also found that the T2 structure has much higher Seebeck coefficients than the A7, M, and T1 structures, mainly because of its larger effective mass and lower carrier density. In addition, the figure of merit was determined as highest for T2 among the four structures, and thus the T2 structure of bismuth should be preferred in actual situations in terms of the thermoelectric properties.

Lithium and oxygen activities can have substantial influences on the kinetics of ion and electron transport and the structural integrity of Li-rich layered oxide (LLO) cathodes, since reversible oxygen redox is ascribed to the extra capacity beyond the theoretical capacity from transition metal redox at high voltages. Herein, we demonstrate a liquid-solid interfacial reaction to generate a heteroepitaxial interface with tunable Li/O activities on LLOs using molten boric acid. The experimental and theoretical analyses indicate that the atomic scale interface is comprised of a disordered rock salt structure containing substantial Li/O vacancies along the layered structure, associated with a segregation tendency of Ni and Co. The formation of this heteroepitaxial interface with Li/O vacancies improves the ionic/electronic conduction and electrochemical/structural stability, leading to a high discharge capacity of 283 mA h g-1 with initial Coulombic efficiency of 91.7% (0.1 C, 2.0–4.7 V vs. Li+/Li), excellent rate performance (246 and 159.7 mAh g-1 at 1 C and 10 C, respectively) and enhanced cyclic performance with a capacity retention of 92% after 100 cycles. The findings highlight the importance of a well-engineered interface for the design of high performance layered cathode materials for Li storage.

A novel continuously graded material that is based on a porosity-graded structure was successfully synthesised via a cold pressing-vacuum sintering-dissolution process (SDP) of powder metallurgy te...

In this study, AlSi10Mg alloy were prepared by powder-delivery laser powder deposition (LPD) process. In order to obtain AlSi10Mg alloy with maximum density, LPD parameters were optimized using Taguchi method. Results were analyzed based on the signal-to-noise (S/N) ratios and analyses of variance (ANOVA). The optimal combination of parameters was laser power of 150 W, scanning speed of 400 mm/min, powder feeding rate of 0.78 g/min and shielding gas flow rate of 7 L/min. The dominant parameter was the laser power which contributes 49.43% to the relative density. Additionally, the regression equation was established based on the output parameter (relative density) and the four input process parameters, and validated by the obtained results. From the experiments, sample with density higher than 99% was obtained. The investigation will help to establish an efficient process for AlSi10Mg alloy fabricated by LPD.

Purpose The purpose of this study is to develop a monolayer surface coating of stearic acid on Sn-Ag-Cu solder powder to limit oxidation. Design/methodology/approach Stearic acid was adsorbed onto Sn-Ag-Cu solder powder through liquid-phase adsorption. The isotherm of adsorption was measured and then the microstructure of coated powder was characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Findings The adsorption isotherm of stearic acid on the powder was “H” type, which revealed the layer-by-layer adsorption on non-porous surface. When the concentration of solution was in the range of 0.001-0.006 mol/L, with an adsorption amount of 0.12 ± 0.1 mg/g, monolayer stearic acid covered the solder powder completely. Uniform and integrated self-assembled monolayer coating was formed through hydrogen bonds between the oxygen ions in surface lattice of Sn3.0Ag0.5Cu solder powder and the —O—H hydroxyl group of stearic acid. The maximum angle of stability of coated powder also reduced by 2.87° compared with that of non-coated powder. The increase rate of oxygen content of coated powder was much slower than that of non-coated powder when they were exposed to humid air. Originality/value As a result, oxidation of fine solder powder was effectively limited. Essentially, this method can also be applied to the coating of other types of solder powder and has reference significance to other coating by liquid-phase method.

Purpose To explore substitutes for traditional Sn-Pb solder, Sn-20In-2.8Ag was considered because of its appropriate melting temperature, good reliability and high ductility at less than 100°C. However, the mechanical properties of Sn-20In-2.8Ag were not satisfactory. The reason for the poor mechanical properties of the Sn-20In-2.8Ag/Cu joint was revealed, and a way to solve the problem was found. Design/methodology/approach The microstructure evolution, characteristics of melting and solidification and joining performance with Cu were investigated using scanning electron microscopy (SEM), electron probe microanalysis, differential scanning calorimetry (DSC) and mechanical testing. Findings SEM results showed that the microstructure of Sn-20In-2.8Ag was composed of coarse dendritic Ag2In and γ phases, with Ag2In distributed at the grain boundaries. DSC measurements revealed that small amount of low temperature eutectic reaction, L → Ag2In + β + γ, occurred at 112.9°C. This reaction was caused by the segregation of indium, which is a process that has a strong driving force. In the lap-shear testing, a crack propagated along the grain boundary of the solder, and failure showed an intergranular fracture. This failure was connected with the three-phase eutectic and coarse Ag2In. Thus, to improve the mechanical properties, segregation of indium should be reduced and coarsening of Ag2In should be prevented. Originality/value The reason for the unsatisfactory mechanical properties of Sn-20In-2.8Ag was revealed via microstructural observations and solidification analysis, and the way to solve this problem was found.

Twinning defects often present in crystalline materials when are subject to mechanical stimuli and are mostly affecting their physicochemical properties. The twinning formation and twin-related degradation upon cycling in sodium layered oxides (SLOs) are poorly understood. Combining atomic-resolution imaging, spectroscopy and first principles calculations, we reveal that growth twinning is unexpectedly common in the SLO materials and the twin boundaries show distinct structural and chemical characters from those identified in lithium layered oxides. A unique O-P-O twinning plane was identified in the O3 type SLO materials. We discover that twin-assisted Na diffusion cause large volume variations and trigger intragranular fracture during electrochemical cycling. The present findings not only establish a robust correlation between growth twinning and intragranular cracking in SLOs, but also offer general implications for the development of high-performing intercalation electrode materials by regulating crystallographic defects.

In this work, braided carbon fiber reinforced carbon matrix composites (3D-C/C composites) are prepared by chemical vapor infiltration process. Their composite structure, mechanical properties, biocompatibility, and in vivo experiments are investigated and compared with those of traditional 2.5D-C/C composites and titanium alloys TC4. The results show that 3D-C/C composites are composed of reinforced braided carbon fiber bundles and pyrolytic carbon matrix and provide 51% open pores with a size larger than 100 μm for tissue adhesion and growth. The Young’s modulus of 3D-C/C composites is about 5 GPa, much smaller than those of 2.5D-C/C composites and TC4, while close to the autogenous bone. 3D-C/C composites have a higher tensile strength (167 MPa) and larger elongation (5.0%) than 2.5D-C/C composites (81 MPa and 0.7%), and do not show obvious degradation after 1 × 106 cyclic tensile loading. The 3D-C/C composites display good biocompatibility and have almost no artifacts on CT imaging. The in vivo experiment reveals that 3D-C/C composites artificial ribs implanted in dogs do not show displacement or fracture in 1 year, and there are no obvious proliferation and inflammation in the soft tissues around 3D-C/C composites implant. Our findings demonstrate that 3D-C/C composites are suitable for chest wall reconstruction and present great potentials in artificial bones.

In this work, the Li ordering and its influence on Li intercalation and plating on graphite, bilayer, and single-layer graphene are investigated by first-principles calculation with two-dimensional cluster expansion and van der Waals corrections. The results show that Li intercalation has a multistage feature for graphite and bilayer graphene at Li concentrations from C2 to LiC6. Beyond LiC6, Li atoms are crowded in graphite and bilayer graphene, resulting in a negative discharge voltage. The calculated overpotential indicates Li plating easily happens on graphite but is unlikely on bilayer graphene. For single-layer graphene, Li atoms uniformly cover the graphene surface from C2 to LiC4 with the presence of voltage stages, while forming an atomic island at a higher Li concentration. Our findings not only give a good recount on recent Li plating phenomena in Li-ion batteries but also provide a rationale for circumventing those side reactions on graphene and its variants.

Lithium-rich, manganese-based layered oxides are considered one of the most valuable cathode materials for the next generation of high-energy density lithium-ion batteries (LIBs) for their high specific capacity and low cost. However, their practical implementation in LIBs is hindered by the rapid voltage/capacity decay on cycling and the long-standing contradictions between redox kinetics and volumetric energy density due to their poor calendaring compatibility. Herein, a coherent near-zero-strain interphase is constructed on the grain boundaries of cathode secondary particles by infusing LiAlO2 material through the reactive infiltration method (RIM). Theoretical calculations, multi-scale characterizations, and electrochemical tests show that this coherent interphase with near-zero-strain feature upon electrochemical (de)lithiation inhibits volume changes of the lattice and structural degradation of cathode primary particles during cycling. More importantly, the ionically conductive LiAlO2 nanolayer infiltrated in the grain boundaries of cathode secondary particles can not only promote the rapid Li+ migration and act as a barrier to protect the material from the corrosion of the electrolyte but also effectively improve the mechanical strength of the cathode secondary particles. Collectedly, the LiAlO2-infiltrated cathode materials display superior electrochemical cyclability, enhanced rate capability, and industrial calendaring performance, marking a significant step toward commercial implementation.

Transition metal (TM)-based layered oxides NaTMO2 (TM = Fe, Ni, Co, Mn, etc.) have been intensively pursued as high-capacity cathode materials for Na-ion batteries. Nevertheless, they still suffer from fast capacity loss and voltage decay, as a result of the layered structure instability upon extended electrochemical cycling. The mechanism underlying such instability remains poorly understood. Here we unravel the TM migrations and structural evolution of a quaternary NaNi0.3Co0.12Mn0.18Fe0.4O2 compound during electrochemical cycling using atomic-resolution electron microscopy and associated spectroscopies. We discover successive migrations of TM ions to Na layers that account for structure and performance degradations. The Fe ions migrate into the interstices of both tetrahedra and octahedra of the layers; on the contrary, the Ni ions migrate predominantly in the octahedral ones, and the Mn and Co ions mostly remain in the TM layers. Direct atomic-level observations of the TM migration process upon cycling offer deep insight into designing high-capacity and long-life span cathode materials for sodium-ion batteries.

Layered O3-type NaMn0.5Ni0.5O2 has been widely investigated as cathode material for sodium-ion batteries (SIBs). However, it usually suffers from detrimental phase transformation upon high voltage (>4.1 V) and sluggish Na+ migration kinetics, leading to rapid capacity decay and limited rate capability. Herein, guided by the first principles calculations, a structure modulation strategy to construct mechanically robust transition metal oxides (TMO2) layers for O3-NaMn0.5Ni0.5O2 is realized through Mg/Ti co-substitution. After Mg/Ti co-substitution, the capability of the TMO2 layers framework of O3 phase has been significantly improved to go against and tolerant strains and distortions, and thus remarkably enhanced the electrochemical performance of O3 phase upon high voltage. The as-prepared O3-type NaMn0.45Ni0.45Mg0.05Ti0.05O2 exhibits an initial discharge capacity of 177.7 mAh g−1 at a current density of 0.1 C in a voltage range of 2.0–4.2 V, and the detrimental P3-O1 phase transition upon 4.0 V can be effectively suppressed as well as the Na+ diffusion kinetics is enhanced under high voltage, subsequently leading to improved high voltage cycling-stability and rate-capability.

The intrinsic brittleness of tungsten limits the improvement on the comprehensive mechanical properties of tungsten alloys. Starting from the perspective of solid solution toughening, this study innovatively used tungsten-tantalum particles instead of tungsten particles as the sintered core to prepare 90(W-Ta)-Ni-Fe alloy. Tantalum forms a BCC solid solution with tungsten in the process of high-energy ball milling. During the vacuum sintering process, tantalum precipitated and reacted with the matrix to form acicular phase. This precipitation process reduces the liquid phase sintering temperature of the tungsten alloy and refine the tungsten particles. The microstructure of the sintered alloy is composed of tungsten particles, matrix phase, intermediate phase, acicular precipitated phase and oxides. The solid solution of tantalum increases the hardness and reduces the modulus of the tungsten particles. The hardness and modulus of the matrix phase are increased due to the influence of the acicular precipitation phase. These findings indicate that the solid solution of tantalum has the potential to improve the comprehensive mechanical properties of tungsten heavy alloys.

In this study, a compositionally graded Ti Al intermetallic coating has been successfully fabricated by laser powder deposition (LPD) with Ti6Al4V and AlSi10Mg powder. The microstructure, composition distribution and phase structure of the graded Ti Al intermetallic coating were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), electron probe microanalysis (EPMA) and micro-area X-ray diffraction analysis (XRD). In order to evaluate the wear resistance of the graded Ti Al intermetallic coating, the sliding wear test was performed. Besides, the morphologies of the worn surface were analyzed by SEM and confocal microscope. The results show that the coating had a crack-free and well-graded compositional microstructure. Intermetallic Ti3Al, TiAl, TiAl3 and Ti5Si3 hard phase were the dominant constructive phases of the graded Ti Al intermetallic coating. These phases enhanced the micro-hardness of the graded coating and consequently improved its wear resistance. The average friction coefficient and the wear rate of the graded Ti Al intermetallic coating were 0.3704 and 1.989 × 10−4 mm3/Nm, respectively, which were significantly lower than those of the substrate (0.5667 and 8.384 × 10−4 mm3/Nm). The wear mechanism of the coating was mainly abrasive wear. Based on our finding, the graded Ti Al intermetallic coating is a promising wear resistant coating for Ti6Al4V alloy.