Stabilizing High-Nickel Cathodes via Interfacial Hydrogen Bonding Effects Using a Hydrofluoric Acid-Scavenging Separator

Nickel-rich layered Li transition metal oxides are the most promising cathode materials for high-energydensity Li-ion batteries.However,they exhibit rapid capacity degradation induced by transition metal dissolution and structural reconstruction,which are associated with hydrofluoric acid(HF)generation from lithium hexafluorophosphate decomposition.The potential for thermal runaway during the working process poses another challenge.Separators are promising components to alleviate the aforementioned obstacles.Herein,an ultrathin double-layered separator with a 10 lm polyimide(PI)basement and a 2 lm polyvinylidene difluoride(PVDF)coating layer is designed and fabricated by combining a nonsolvent induced phase inversion process and coating method.The PI skeleton provides good stability against potential thermal shrinkage,and the strong PI-PVDF bonding endows the composite separator with robust structural integrity;these characteristics jointly contribute to the extraordinary mechanical tolerance of the separator at elevated temperatures.Additionally,unique HF-scavenging effects are achieved with the formation of-CO…H-F hydrogen bonds for the abundant HF coordination sites provided by the imide ring;hence,the layered Ni-rich cathodes are protected from HF attack,which ultimately reduces transition metal dissolution and facilitates long-term cyclability of the Ni-rich cathodes.Li||NCM811 batteries(where“NCM”indicates LiNi_(x)Co_(y)Mn_(1-x-y)O_(2))with the proposed composite separator exhibit a 90.6%capacity retention after 400 cycles at room temperature and remain sustainable at 60℃with a 91.4%capacity retention after 200 cycles.By adopting a new perspective on separators,this study presents a feasible and promising strategy for suppressing capacity degradation and enabling the safe operation of Ni-rich cathode materials.

A Single-Layer Piezoelectric Composite Separator for Durable Operation of Li Metal Anode at High Rates

Piezoelectric ceramic and polymeric separators have been proposed to effectively regulate Li deposition and suppress dendrite growth,but such separators still fail to satisfactorily support durable operation of lithium metal batteries owing to the fragile ceramic layer or low-piezoelectricity polymer as employed.Herein,by combining PVDF-HFP and ferroelectric BaTiO_(3),we develop a homogeneous,single-layer composite separator with strong piezoelectric effects to inhibit dendrite growth while maintaining high mechanical strength.As squeezed by local protrusion,the polarized PVDF-HFP/BaTiO_(3)composite separator generates a local voltage to suppress the local-intensified electric field and further deconcentrate regional lithium-ion flux to retard lithium deposition on the protrusion,hence enabling a smoother and more compact lithium deposition morphology than the unpoled composite separator and the pure PVDF-HFP separator,especially at high rates.Remarkably,the homogeneous incorporation of BaTiO_(3)highly improves the piezoelectric performances of the separator with residual polarization of 0.086 pC cm^(-2)after polarization treatment,four times that of the pure PVDF-HFP separator,and simultaneously increases the transference number of lithium-ion from 0.45 to 0.57.Beneficial from the prominent piezoelectric mechanism,the polarized PVDF-HFP/BaTiO_(3)composite separator enables stable cyclic performances of Li||LiFePO_(4)cells for 400 cycles at 2 C(1 C=170 mA g^(-1))with a capacity retention above 99%,and for 600 cycles at 5 C with a capacity retention over 85%.

A surfactant-modified composite separator for high safe lithium ion battery

Separators have been gaining increasing attention to improve the performance of lithium ion batteries(LIBs),especially for high safe and long cycle life.However,commercial polyolefin separators still face the problems of rapid capacity decay and safety issues due to the poor wettability with electrolytes and low thermal stability.Herein,a novel composite separator is proposed by introducing a surfactant of sodium dodecyl thiosulfate(SDS)into the polytetrafluoroethylene(PTFE)substrate with the binder of polyacrylic acid(PAA)through the suction filtration method.The introduction of PAA/SDS enhances the adsorption energy between PTFE substrate and electrolyte through density functional theory calculations,which improves wettability and electrolyte uptake of the separator significantly.The asachieved composite separator enables the LIBs to own high Li^(+)conductivity(0.64×10^(-3)S cm^(-1))and Li^(+)transference number(0.63),further leading to a high capacity retention of 93.50%after 500 cycles at 1 C.In addition,the uniform and smooth surface morphology of Li metal employed the composite separator after cycling indicates that the lithium dendrites can be successfully inhibited.This work indicates a promising route for the preparation of a novel composite separator for high safe LIBs.

Modification strategies for non-aqueous, highly proton-conductive benzimidazole-based high-temperature proton exchange membranes

High-temperature proton exchange membranes(HT-PEMs) possess excellent thermal and outstanding electrochemical stability, providing an avenue to realize high-temperature proton exchange membranes fuel cells(HT-PEMFCs) with both superior power density and long-term durability. Unfortunately, polybenzimidazole(PBI), a typical material for conventional HT-PEMs, fails to compromise the high nonaqueous proton conductivity and high mechanical properties, thus hindering their practical applications.Achieving efficient nonaqueous proton conduction is crucial for HT-PEMFC, and many insightful research works have been done in this area. However, there still lacks a report that integrates the host-guest interactions of phosphoric acid doping and the structural stability of polymers to systematically illustrate modification strategies. Here, we summarize recent advancements in enhancing the nonaqueous proton conduction of HT-PEMs. Various polymer structure modification strategies, including main chain and side group modification, cross-linking, blocking, and branching, are reviewed. Composite approaches of polymer, including compounding with organic porous polymers, filling the inorganic components and modifying with ionic liquids, etc., are also covered in this work. These strategies endow the HT-PEMs with more free volume, nanophase-separated structure, and multi-stage proton transfer channels, which can facilitate the proton transportation and improve their performance. Finally, current challenges and future directions for further enhancements are also outlined.

Nanodiamond reinforced self-healing and transparent poly(urethane-urea)protective coating for scratch resistance

With increasing demand for scratch-resistant flexible electro-nics,the development of transparent coatings with good scratch resistance and self-healing properties has emerged as a key research topic.In this study,a high-strength self-healing poly(urethane-urea)(PUU)-based nanocomposite coating was prepared by introducing functionalized nanodiamond(ND)into a PUU matrix via solution blending.The PUU matrix had hard-segment repeating units and was constructed using iso-phorone diamine and isophorone isocyanate.The ND particles were modifed using a silane coupling agent,3-aminopropyl-triethoxysilane,to obtain well-dispersed KH-ND nanoparticles.KH-ND promoted microphase separation in the PU matrix,inducing the formation of dense and homogeneous hard domains that dissipated stress,prevented further crack devel-opment,and improved the mechanical properties and scratch resistance of the coating.In addition,the coating exhibited excellent self-healing properties.Fourier-transform infrared spectroscopy,scanning electron microscopy,and atomic force microscopy were used to characterize the self-healing and hardening mechanisms of the coating.The environmentally friendly PUU/KH-ND coating is easy to prepare and has broad application prospects in transparent and anti-scratch coatings for flexible electronics,automobiles,and home appliances.

SiCp/Al Composites Fabricated by Modified Squeeze Casting Technique

A cost effective method was introduced to fabricate pure aluminum matrix composites reinforced with 20% volume fraction of 3.5 μm SiC particles by squeeze casting followed by hot extrusion. In order to lower volume fraction of the composites, a mixed preform containing pure aluminum powder and the SiC particles was used. The suitable processing parameters for the infiltration of pure aluminum melt into the mixed preform are： melt temperature 800℃, preform temperature 500℃, infiltration pressure 5 MPa, and solidification pressure 50 MPa. Microstructure and properties of the composites in both as-cast and hot extruded states were investigated. The results indicate that hot extrusion can obviously improve the mechanical properties of the composite.

Theoretical Analysis of Solidly Mounted Film Bulk Acoustic Resonator with Nanocrystalline Diamond as High Impedance Material of Bragg Reflector

In this paper,a solidly mounted resonator(SMR)was designed with nanocrystalline diamond(NCD)as the high acoustic impedance material of Bragg reflector to improve the quality.We used Mathcad to investigate the effect of the Bragg reflector on the performance of the SMR,as well as the influence of different materials and the number of layers of Bragg reflector on the quality factor Q.Results show that the Bragg reflector could reduce energy loss effectively,and the higher the impedance of the high acoustic impedance layer,the better the SMR.The parasitic factors of the SMR using two high acoustic impedance materials,tungsten(W)and NCD,were also simulated by an Advanced Design System(ADS)using the Mason model.It was found that the parasitic effect caused by metal would significantly decrease the Q factor of the SMR.In the frequency range below 6 GHz,within which the SMR works normally,NCD performed better than W.Therefore,NCD is a better choice of high acoustic impedance material in the design of the SMR,with improved quality at high frequency and low loss.The optimum number of layers of Bragg reflector is 6.

Development of lutetium oxide continuous fibers with excellent mechanical properties

The difficulty of reducing the diameter of lutetium oxide(Lu_(2)O_(3))continuous fibers below 50μm not only limits the flexibility of the sample but also seriously affects their application and development in high-energy lasers.In this work,a Lu-containing precursor with high ceramic yield was used as raw material,fiberized into precursor fibers by dry spinning.The pressure-assisted water vapor pretreatment(PAWVT)method was creatively proposed,and the effect of pretreatment temperature on the ceramization behavior of the precursor fibers was studied.By regulating the decomposition behavior of organic components in the precursor,the problem of fiber pulverization during heat treatment was effectively solved,and the Lu_(2)O_(3) continuous fibers with a diameter of 40μm were obtained.Compared with the current reported results,the diameter was reduced by about 50%,successfully breaking through the diameter limitation of Lu_(2)O_(3) continuous fibers.In addition,the tensile strength,elastic modulus,flexibility,and temperature resistance of Lu_(2)O_(3) continuous fibers were researched for the first time.The tensile strength and elastic modulus of Lu_(2)O_(3) continuous fibers were 373.23 MPa and 31.55 GPa,respectively.The as-obtained flexible Lu_(2)O_(3) continuous fibers with a limit radius of curvature of 3.5-4.5 mm had a temperature resistance of not lower than 1300℃,which established a solid foundation for the expansion of their application form in the field of high-energy lasers.

高熵纳米材料的电催化应用及研究进展

高熵纳米材料由于其独特的微观结构和理化特性,在电化学过程中呈现出优异的催化活性,使其有望成为理想的电催化材料.为进一步拓宽高熵材料的电化学应用场景,设计新型高熵纳米材料电催化剂并探究其催化作用机制是当前研究的重点.本文主要介绍了近年来高熵纳米材料在电催化领域的重要研究进展.重点讨论了包括碳热冲击法、移动床热解法、湿化学法等高熵纳米材料的合成策略,分析了高熵纳米材料作为催化剂在析氢反应、析氧反应、氧还原反应、醇氧化反应以及二氧化碳还原反应中的应用.最后,从实验和理论方面展望了高熵纳米材料的应用前景和未来的研究趋势.

Advanced liquid crystal-based switchable optical devices for light protection applications:principles and strategies

With the development of optical technologies,transparent materials that provide protection from light have received considerable attention from scholars.As important channels for external light,windows play a vital role in the regulation of light in buildings,vehicles,and aircrafts.There is a need for windows with switchable optical properties to prevent or attenuate damage or interference to the human eye and light-sensitive instruments by inappropriate optical radiation.In this context,liquid crystals(LCs),owing to their rich responsiveness and unique optical properties,have been considered among the best candidates for advanced light protection materials.In this review,we provide an overview of advances in research on LC-based methods for protection against light.First,we introduce the characteristics of different light sources and their protection requirements.Second,we introduce several classes of light modulation principles based on liquid crystal materials and demonstrate the feasibility of using them for light protection.In addition,we discuss current light protection strategies based on liquid crystal materials for different applications.Finally,we discuss the problems and shortcomings of current strategies.We propose several suggestions for the development of liquid crystal materials in the field of light protection.

Talcum-doped composite separator with superior wettability and heatproof properties for high-rate lithium metal batteries

Separator is supposed to own outstanding thermal stability,superior wettability and electrolyte uptake,which is essential for developing high-rate and safe lithium metal batteries(LMBs).However,commercial polyolefin separators possess poor wettability and limited electrolyte uptake.For addressing this issue,we put forward a composite separator to implement above functions by doping layered-silicate(talcum)into polyvinylidene fluoride(PVDF).With significant improvement of electrolyte absorption benefiting from the strong adsorption energy values(-1.64-1.70 eV)between talcum and the electrolyte in lithium metal batteries,PVDF/Talcum(PVDF/TM)composite separator owns a small contact angle and superior electrolyte uptake.PVDF/TM composite separator with 10 wt%talcum(T-10)owns a tiny contact angle of 8°,while those of polypropylene(PP)and PVDF are 48°and 20°with commercial electrolyte.Moreover,the addition of thermotolerant talcum endows the T-10 composite separator with great thermostability,whose thermal shrinkage is only 5.39%at 150°C for 0.5 h.The cell with LiFeO4cathode and the T-10 composite separator reaches 91.7 m Ah/g in discharge capacity at 4.8 m A/cm^(2)(10 C),far superior to that with pure PVDF separator(56.3 m Ah/g)and PP(51.4 m Ah/g).

Unified throughout-pore microstructure enables ultrahigh separator porosity for robust high-flux lithium batteries

With small thickness,commercial polyolefin separators own low porosity to ensure sufficient thermomechanical properties,resulting in tortuous and enlarged Li+diffusion pathways that induce large overpotentials and detrimental dendrite growth.As a dilemma,the exploration of highly porous separators has been challenged by their large thickness,impairing the applicability of such pursuits.Herein,an ultraporous architecture is designed to shorten Li+transfer pathways by impregnating electrolyteaffinitive poly(vinylidene fluoride-co-hexafluoropropylene)into ultralight~3μm 3D-polytetrafluoroethylene scaffold(abbreviated as UP3D).The UP3D separator with a porosity of 74%gives rise to 70%enhancement in Li+transference and 77%reduction in Li+transfer resistance(2.67 mΩmm^(−1))and thus enables an ultrahigh Li+flux of 22.7 mA cm^(−2),effectively alleviating Li+concentration gradient across the separator.With the separator,the LiFePO4 half cell delivers a capacity of 118 mAh g^(−1) with an unparalleled capacity retention of 90%after 1000 cycles at 2 C,and a graphite||LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)pouch full cell delivers an areal energy density of 6.8 mWh cm^(−2)at 8.848 mA(1.4 mA cm^(−2))with a high cathode loading of 134.9 mg.Such results,together with the scalable production of the separator,reflect its promising potential in high-flux battery applications of separators that require both ultrahigh porosity and reliability.

Energizing the future:Empowering sustainability with Electron

The advent of industrial civilization has brought about enormous materials advancements;yet it has also caused a rapid depletion of natural resources,leading to global energy crisis and environmental pollution.Facing human civilization,one fundamental issue stands at its core:how can we achieve a harmonious coexistence between humanity and nature?This question has become the key challenge of our time,demanding our utmost attention and concerted efforts.

Advances in ultra-high temperature ceramics,composites,and coatings

Ultra-high temperature ceramics(UHTCs)are generally referred to the carbides,nitrides,and borides of the transition metals,with the Group IVB compounds(Zr&Hf)and TaC as the main focus.The UHTCs are endowed with ultra-high melting points,excellent mechanical properties,and ablation resistance at elevated temperatures.These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles,particularly nozzles,leading edges,and engine components,etc.In addition to bulk UHTCs,UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics.Recently,high-entropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials.This review presents the state of the art of processing approaches,microstructure design and properties of UHTCs from bulk materials to composites and coatings,as well as the future directions.

Thermal response, oxidation and ablation of ultra–high temperature ceramics, C/SiC, C/C, graphite and graphite–ceramics

Various thermal protection materials exhibit obviously different and complicated thermal response,oxidation and ablation behavior,which are very important for the appropriate design and selection.However,the relative researches are very few currently.In this work,the thermal response,oxidation and ablation behavior of representative thermal protection materials including ultra-high temperature ceramics,C/SiC,C/C, graphite and graphite-ceramic were investigated systematically in strong heat flux,high enthalpy and low-pressure environments.Thermal response of these materials was analyzed based on experimental results and thermal energy balance that accounts for all of the heat transfer processes transporting energy into and out of the surface.Many factors were playing important roles in the thermal response including thermal conductivity,volumetric heat capacity,catalytic efficiency,emissivity and oxidation characteristics of the materials.The importance of each factor not only depends on the material characteristics such as material composition and phase content but also environment parameters including heat flux,enthalpy,pressure and testing time.The comparisons and relationships of oxidation and ablation behaviors for these materials under extreme environments were also illustrated in detail.Furthermore,thermal response and ablation behaviors of pre-oxidized material or repeated tests were also performed to evaluate the effect of pre-treatment on the performance and reusability of thermal protection materials.This work offers guiding significance for the appropriate design and selection of thermal protection materials.

Au nanospheres modified boron-doped diamond microelectrode grown via hydrogen plasma etching solid doping source for dopamine detection

Boron doped diamond(BDD)electrode is a promising electrochemical material for detecting dopamine level in the human’s body.In this work,we developed a new doping source-graphite and solid boron oxide powders to synthesize BDD film with microwave plasma chemical vapor deposition,so as to avoid using toxic or corrosive dopants,such as boroethane and trimethylborate.The synthesized BDD film is pinhole free and with high doping density of 8.44×10^20 cm^-3 calculated from the Raman spectroscopy.Subsequently,Au nanospheres were decorated on the surface of BDD film to improve electrochemical performance of the BDD film.The Au nanoparticles modified BDD electrode demonstrates an excellent electrochemical response,a high sensitivity(in the range of 5μM-1 m M),and a low detection limit(~0.8μM)for detecting dopamine.

Direct observation of chaotic resonances in optical microcavities

Optical microcavities play a significant role in the study of classical and quantum chaos.To date,most experimental explorations of their internal wave dynamics have focused on the properties of their inputs and outputs,without directly interrogating the dynamics and the associated mode patterns inside.As a result,this key information is rarely retrieved with certainty,which significantly restricts the verification and understanding of the actual chaotic motion.Here we demonstrate a simple and robust approach to directly and rapidly map the internal mode patterns in chaotic microcavities.By introducing a local index perturbation through a pump laser,we report a spectral response of optical microcavities that is proportional to the internal field distribution.With this technique,chaotic modes with staggered mode spacings can be distinguished.Consequently,a complete chaos assisted tunneling(CAT)and its time-reversed process are experimentally verified in the optical domain with unprecedented certainty.

Evolution of microstructures and optical properties of gadolinium oxide with oxygen flow rate and annealing temperature

In this study, the effects of oxygen flow rate and annealing temperature on Gd_2 O_3 structures and optical properties were systematically analyzed. Gd_2 O_3 films were deposited on both quartz and ZnS substrates by magnetron sputtering and then annealed under vacuum at 700, 800 and 900℃, Restructure and phase transformation from cubic to monoclinic occur at different temperatures depending on the oxygen flow rate. The optical band gap, which is more sensitive to the annealing temperature than oxygen flow rate changes from 5.32 to 5.65 eV. The refractive index is approximately 1.75 at 550 nm and is adjustable by the oxygen flow rate. The transmittance of the ZnS substrate with Gd_2 O_3 film exceeds 80% and reaches82% at the 7.5-9.5 μm range. When ZnS is coated on both sides, the transmittance is increased to approximately 90%. Our results indicate that Gd_2 O_3 films are promising new candidates for anti-reflective coatings in the infrared region.

Investigation of thermal radiation effect on optical dome of sapphire coated yttrium oxide

Compared to traditional optical domes, domes of sapphire coated with films can effectively reduce emissivity and increase transmittance. The purpose of this work is to investigate the thermal radiation effect on sapphire optical dome coated with yttrium oxide by a radio frequency mag- netron sputtering method. The emissivity of sapphire coated with Y203 films is studied by both numerical and experi- mental methods. The results indicate that the emissivity of sapphire substrate is reduced effectively with increasing the thickness of the Y203 film. In addition, a finite element model is developed to simulate the radiation intensity of the optical dome. The thermal responses indicate that the max- imum temperature is reduced apparently compared with the uncoated sapphire as Y203 film thicknesses increase. The average irradiance distribution at different film thicknesses with time shows that the self-thermal radiation disturbance of sapphire optical dome delays 0.93 s when the thickness of Y203 film is 200μm, which can guarantee the dome works properly and effectively even in a harsh environment.

Electrolyte Engineering for High-Voltage Lithium Metal Batteries

High-voltage lithium metal batteries(HVLMBs)have been arguably regarded as the most prospective solution to ultrahigh-density energy storage devices beyond the reach of current technologies.Electrolyte,the only component inside the HVLMBs in contact with both aggressive cathode and Li anode,is expected to maintain stable electrode/electrolyte interfaces(EEIs)and facilitate reversible Li+transference.Unfortunately,traditional electrolytes with narrow electrochemical windows fail to compromise the catalysis of high-voltage cathodes and infamous reactivity of the Li metal anode,which serves as a major contributor to detrimental electrochemical performance fading and thus impedes their practical applications.Developing stable electrolytes is vital for the further development of HVLMBs.However,optimization principles,design strategies,and future perspectives for the electrolytes of the HVLMBs have not been summarized in detail.This review first gives a systematical overview of recent progress in the improvement of traditional electrolytes and the design of novel electrolytes for the HVLMBs.Different strategies of conventional electrolyte modification,including high concentration electrolytes and CEI and SEI formation with additives,are covered.Novel electrolytes including fluorinated,ionic-liquid,sulfone,nitrile,and solid-state electrolytes are also outlined.In addition,theoretical studies and advanced characterization methods based on the electrolytes of the HVLMBs are probed to study the internal mechanism for ultrahigh stability at an extreme potential.It also foresees future research directions and perspectives for further development of electrolytes in the HVLMBs.