A closed-host bi-layer dense/porous solid electrolyte interphase for enhanced lithium-metal anode stability

Thanks to its high specific capacity and low electrochemical potential, lithium metal is an ideal anode for next-generation high-energy batteries. However, the unstable heterogeneous surface of lithium gives rise to safety and efficiency concerns that prevent it from being utilized in practical applications. In this work, the formation of a closed-host bi-layer solid electrolyte interphase (SEI) improves the stability of lithium metal anode. This is successfully realized by forming an interconnected porous LiF-rich artificial SEI in contact with Li metal, and a dense, stable in-situ formed upper layer SEI. The porous layer increases the number of Li/LiF interfaces, which reduces local volume fluctuations and improves Li⁺ diffusion along these interfaces. Additionally, the tortuous porous structure guides uniform Li⁺ flux distribution and mechanically suppresses dendrite propagation. The dense upper layer of the SEI accomplishes a closed-host design, preventing continuous consumption of active materials. The duality of a dense top layer with porous bottom layer led to extended cycle life and improved rate performance, evidenced with symmetric cell testing, as well as full cell testing paired with sulfur and LiFePO₄ (LFP) cathodes. This work is a good example of a rational design of the SEI, based on comprehensive consideration of various critical factors to improve Li-metal anode stability, and highlights a new pathway to improve cycling and rate performances of Li metal batteries.     

Microstructure evolution and bonding mechanisms of silica sol bonded coating at elevated temperatures

High emissivity coating plays a critical role in thermal protective system, which can radiate a large amount of aero-convective heat. Silica sol bonded MoSi₂-SiC-Al₂O₃ (S-MSA) coating was proved to be promising for mullite fibrous insulation. However, the bonding mechanisms of the coating at elevated temperatures are not clear. In this work, the S-MSA coatings were heat-treated at temperatures from 600 °C to 1500 °C to reveal the bonding mechanisms at elevated temperatures. The S-MSA coatings go through a relatively stable stage (600 °C–1000 °C), a crystallization stage (1100 °C–1200 °C), and a densification stage (1300 °C–1500 °C) at ever increasing temperatures. Results show that both the contact damage resistance and the bonding strength of the calcined coatings exhibit a decrease followed by an increase at elevated calcination temperatures, with the inflection point at 1200 °C, corresponding to the transition temperature of the bonding mechanisms from 600 °C to 1500 °C.     

Efficient PTB7-Th:Y6:PC71BM ternary organic solar cell with superior stability processed by chloroform

Blend morphology is crucial for the efficiency and stability of organic solar cells. Exploring and understanding the correlations between is meaningful and greatly desired. In this work, based on polymer donor (PTB7-Th), fullerene and non-fullerene acceptors (PC₇₁BM and Y6), we systematically study the influence of ternary strategy and solvent system on device performance and stability. It is found that insufficient and excessive phase separation of blend could result in the depressed performance of corresponding devices. Appropriate phase separation/blend morphology can be achieved by utilizing a ternary strategy or suitable solvent. Chloroform-processed ternary blend PTB7-Th:Y6:PC₇₁BM delivers efficiency of 9.55%, with dramatically enhanced J_SC of 24.68 mA cm⁻² due to optimized absorption, blend morphology and optoelectronic properties. More importantly, superior device stability is demonstrated for the optimal ternary device under both thermal stress and maximum power point operation, by maintaining 80% of initial efficiency at 85 °C for 880 h and presenting almost zero efficiency decay in 200 h under MPP operation.     

Soft and Self-Adhesive Thermal Interface Materials Based on Vertically Aligned,Covalently Bonded Graphene Nanowalls for Efficient Microelectronic Cooling

Urged by the increasing power and packing densities of integrated circuits and electronic devices, efficient dissipation of excess heat from hot spot to heat sink through thermal interface materials (TIMs) is a growing demand to maintain system reliability and performance. In recent years, graphene-based TIMs received considerable interest due to the ultrahigh intrinsic thermal conductivity of graphene. However, the cooling efficiency of such TIMs is still limited by some technical difficulties, such as production-induced defects of graphene, poor alignment of graphene in the matrix, and strong phonon scattering at graphene/graphene or graphene/matrix interfaces. In this study, a 120  µ m-thick freestanding film composed of vertically aligned, covalently bonded graphene nanowalls (GNWs) is grown by mesoplasma chemical vapor deposition. After filling GNWs with silicone, the fabricated adhesive TIMs exhibit a high through-plane thermal conductivity of 20.4 W m⁻¹ K⁻¹ at a low graphene loading of 5.6 wt%. In the TIM performance test, the cooling efficiency of GNW-based TIMs is ≈ 1.5 times higher than that of state-of-the-art commercial TIMs. The TIMs achieve the desired balance between high through-plane thermal conductivity and small bond line thickness, providing superior cooling performance for suppressing the degradation of luminous properties of high-power light-emitting diode chips.     

Improved thermal conductivity of sintered reaction-bonded silicon nitride using a BN/graphite powder bed

Sintered reaction-bonded silicon nitride (SRBSN) with improved thermal conductivity was achieved after the green compact of submicron Si powder containing 4.22 wt% impurity oxygen and Y₂O₃-MgO additives was nitrided at 1400 °C for 6 h and then post-sintered at 1900 °C for 12 h using a BN/graphite powder bed. During nitridation, the BN/10 wt% C powder bed altered the chemistry of secondary phase by promoting the removal of SiO₂, which led to the formation of larger, purer and more elongated Si₃N₄ grains in RBSN sample. Moreover, it also enhanced the elimination of SiO₂ and residual Y₂Si₃O₃N₄ secondary phase during post-sintering, and thus induced larger elongated grains, decreased lattice oxygen content and increased Si₃N₄-Si₃N₄ contiguity in final SRBSN product. These characteristics enabled SRBSN to obtain significant increase (∼40.7%) in thermal conductivity from 86 to 121 W ∙ m⁻¹ ∙ K⁻¹ without obvious decrease in electrical resistivity after the use of BN/graphite instead of BN as powder bed.     

Magnetic properties enhancement of hot-deformed NdFeB magnets by two different methods of CeNdCu diffusion

Two different ways were used to control the distribution of cerium for the enhancement of coercivity. One was by coating CeNdCu in the prepared magnet and annealing to make CeNdCu diffuse into the grain boundary to increase the coercivity, the other was by mixing CeNdCu with initial magnetic powders and then preparing the hot-deformed magnet. The SEM-EDS result indicates that cerium diffuses more easily into the main phase by the mixing way, while cerium is mainly distributed in the grain boundary via the coating way. The heat-treatment process may be one of the dominant influencing factors for the distribution of Ce. Multi-steps heat treatment in the mixing way, consisting of hot-pressing, hot-deforming and post heat process, easily introduces Ce into the main phase Nd₂Fe₁₄B, which forms the Ce₂Fe₁₄B shell resulting in the decrease of H_A. But the coating way can ensure uniform dispersion of Ce in the grain boundary, which leads to the high coercivity.     

Multi-component high aspect ratio turbulent jets issuing from non-planar nozzles

Fundamental insight into the physics of buoyant gas dispersion from realistic flow geometries is necessary to accurately predict flow structures associated with hydrogen outflow from accidental leaks and the associated flammability envelope. Using helium as an experimental proxy, turbulent buoyant jets issuing from high-aspect-ratio slots on the side wall of a circular tube were studied experimentally applying simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques. Two slots with an aspect ratio of 10 were considered in this study. The effects of buoyancy, asymmetry, jet densities and Reynolds numbers on the resulting flow structure were studied in both vertical and horizontal orientations. Significant discrepancies were found between the evolution of current realistic jets issuing from curved surfaces and conventional high-aspect-ratio jets originating from flat surfaces. These realistic pipeline leak-representative jets were found to deflect along the jet streamwise axis. It was found that increases in aspect ratio caused a reduction in the angle of deflection, jet centreline decay rates and the lateral growth of both velocity and scalar fields compared to their non-planar round jet counterparts, most notably in the far field.     

Experimental investigation of the biaxial strength of thermal barrier coating system

A piston-on-three-ball assembly is employed to evaluate the biaxial strength of the ceramic top-coat in thermal barrier coating system (TBCs). The design of bi-axial experiment is presented, in which the effects of the specimen geometric parameters, the contact between the specimen and the support, and the plastic deformation of substrate are numerically analyzed. Then, the piston-on-three-ball tests and Scanning Electron Microscopy (SEM) observations are carried out to measure the bi-axial strength and the failure patterns of the ceramic top-coat in TBCs, respectively. We experimentally obtained the bi-axial fracture strength of the ceramic top-coat in thermal barrier coating system, which obeys Weibull distribution function. The fracture patterns of the ceramic top-coat under bi-axial loading exhibit a typical channel network.     

Microstructure,mechanical and electrochemical properties of Ti3AlC2 coatings prepared by filtered cathode vacuum arc technology

Ti₃AlC₂ MAX phases have attracted increasing attention due to their unique properties. However, high synthesis temperatures of Ti₃AlC₂ bulk materials limit their further development. In this work, Ti₃AlC₂ coatings were prepared by a two-step method with filtered cathode vacuum arc (FCVA) deposition at room temperature and annealing at 800 °C for 1 h. The structure and properties of coatings were investigated. The results showed that the formation of Ti₃AlC₂ phase in the annealed coating depended on the C₂H₂ flow rate during deposition. At low C₂H₂ flow rates (≤ 9 sccm), almost no Ti₃AlC₂ phase was formed. As the C₂H₂ flow rate increased, the annealed coatings mainly exhibited Ti₃AlC₂ phases, the texture of which transformed from (104) to (105) planes. Meantime, the hardness of Ti₃AlC₂ coatings continuously increased to a maximum of 20.7 GPa, and the corrosion resistance first increased and then decreased with the increase of C₂H₂ flow rate.     

Application of Co3O4-based materials in electrocatalytic hydrogen evolution reaction: A review

Environmental pollution and energy shortage make the development of clean energy more and more urgent. As a kind of clean renewable energy, hydrogen have attracted great attentions in recent years. Recently, Co₃O₄-based materials have emerged as promising candidates for electrocatalytic hydrogen evolution reaction (HER), due to their attractive electrocatalytic activity, low cost as well as the electrochemical durability, which make it attract widely attentions. In this review, we summarize the application of Co₃O₄-based materials in electrocatalytic HER, including pure Co₃O₄, the doped Co₃O₄ and the Co₃O₄-based composite materials. Furthermore, the strategies to enhance their electrocatalytic performance are summarized and discussed, such as morphological engineering, doping, as well as compositing with other materials. Finally, the limitation and challenges of Co₃O₄-based materials for HER, as well as their prospects for future research, are proposed. We believe that this review will be helpful for scientists to seek promising HER electrocatalytic materials.