A Facile Li_(2)TiO_(3) Surface Modification to Improve the Structure Stability and Electrochemical Performance of Full Concentration Gradient Li-Rich Oxides

Full concentration gradient lithium-rich layered oxides are catching lots of interest as the next generation cathode for lithium-ion batteries due to their high discharge voltage,reduced voltage decay and enhanced rate performance,whereas the high lithium residues on its surface impairs the structure stability and long-term cycle performance.Herein,a facile multifunctional surface modification method is implemented to eliminate surface lithium residues of full concentration gradient lithium-rich layered oxides by a wet chemistry reaction with tetrabutyl titanate and the post-annealing process.It realizes not only a stable Li_(2)TiO_(3)coating layer with 3D diffusion channels for fast Li^(+)ions transfer,but also dopes partial Ti^(4+)ions into the sub-surface region of full concentration gradient lithium-rich layered oxides to further strengthen its crystal structure.Consequently,the modified full concentration gradient lithium-rich layered oxides exhibit improved structure stability,elevated thermal stability with decomposition temperature from 289.57℃to 321.72℃,and enhanced cycle performance(205.1 mAh g^(-1)after 150 cycles)with slowed voltage drop(1.67 mV per cycle).This work proposes a facile and integrated modification method to enhance the comprehensive performance of full concentration gradient lithium-rich layered oxides,which can facilitate its practical application for developing higher energy density lithium-ion batteries.

Bottom-up lithium growth guided by Ag concentration gradient in 3D PVDF framework towards stable lithium metal anode

Three-dimensional(3 D)frameworks have received much attention as an effective modification strategy for next-generation high-energy-density lithium metal batteries.However,the top-growth mode of lithium(Li)on the 3 D framework remains a tough challenge.To achieve a uniform bottom-up Li growth,a scheme involving Ag concentration gradient in 3 D PVDF framework(C-Ag/PVDF)is proposed.Ag nanoparticles with a concentration gradient induce an interface activity gradient in the 3 D framework,and this gradient feature is still maintained during the cycle.As a result,the C-Ag/PVDF framework delivers a long lifespan over 1800 h at a current density of 1 mA cm^(-2) with a capacity of 1 mAh cm^(-2),and shows an ultra-long life(>1300 h)even at a high current density of 4 mA cm^(-2) with a capacity of 4 mAh cm^(-2).The advantage of concentration gradient provides further insights into the optimal design of the 3 D framework for stable Li metal anode.

Effect of transversal concentration gradient on H2–O2 cellular detonation

A two-dimensional detonation in H2–O2 system is simulated by a high-resolution code based on the fifth-order weighted essentially non-oscillatory(WENO)scheme in the spatial discretization and the 3th-order additive Runge–Kutta schemes in the time discretization,by using a detailed chemical model.The effect of a concentration gradient on cellular detonation is investigated.The results show that with the increase of the concentration gradient,the cell instability of detonation increases and gives rise to the oscillation of average detonation velocity.After a long time,for the case of the lower gradient the detonation can be sustained,with the multi-head mode and single-head mode alternating,while for the higher gradient it propagates with a single-head mode.

Numerical Investigation of the Influence of Fuel Concentration Gradient on Propane/Oxygen Detonation Propagation

In this paper,one-and two-dimensional numerical simulations are carried out to study the effects of fuel concentration gradients(such as steep,intermediate and shallow)on the detonation wave behavior.The equivalent ratio range of detonation propagation,the quenching mechanism and the change of cell size are discussed in detail.The simulation results show,as the fuel concentration gradient increases,the detonation wavefront decays faster and decouples into a leading shock and a following flame at equivalence ratios of 0.68,0.64 and 0.62,respectively.Moreover,there are two modes of the quenching mechanism.One occurs in the steep gradient that the detonation wave fails rapidly.The O_(2)in front of the detonation wave passes through the detonation wave and forms some unburned O_(2)pockets.The unburned pockets are affected by the marginal walls and reduce the heat release.The other occurs in the intermediate and shallow gradients that more triple points will survive in the flow field,which leads to a difference in the propagation speed of the detonation wavefront.This makes the detonation wavefront bent and deformed.The unburned O_(2)pockets are affected by the strong instability near the triple points and show different distribution characteristics compared with the steep gradient,which may be helpful to the detonation propagation.In addition,as the fuel concentration gradient increases,the triple points moving toward the wall gradually disappear while the triple points that move toward the center can continue to survive,which leads to the gradual increase in cell size and irregularity of the cell structure.

Directional growth behavior of a(Al) dendrites during concentration-gradientcontrolled solidification process in static magnetic field

The large and small sized Cu（solid）/Al（liquid） couples were prepared to investigate the directional growth behavior of primary a（Al） phase during a concentration-gradient-controlled solidification process under various static magnetic fields（SMFs）.The results show that in the large couples,the α（Al） dendrites reveal a directional growth character whether without or with the SMF.However,the 12 T magnetic field induces regular growth,consistent deflection and the decrease of secondary arm spacing of the dendrites.In the small couples,the α（Al） dendrites still reveal a directional growth character to some extent with a SMF of ≤5 T.However,an 8.8 T SMF destroys the directional growth and induces severe random deflections of the dendrites.When the SMF increases to 12 T,the a（Al） dendrites become quite regular despite of the consistent deflection.The directional growth arises from the continuous long-range concentration gradient field built in the melt.The morphological modification is mainly related to the suppression of natural convections and the induction of thermoelectric magnetic convection by the SMF.

Enhancing Li NiO_(2) cathode materials by concentration-gradient yttrium modification for rechargeable lithium-ion batteries

Lithium nickel oxide(LiNiO_(2)) cathode materials are featured with high capacity and low cost for rechargeable lithium-ion batteries but suffer from severe interface and structure instability.Here we report that rationally designed LiNiO_(2) via concentration-gradient yttrium modification exhibits alleviative side reactions and improved electrochemical performance.The LiNiO_(2) cathode with LiYO_(2)-Y_(2) O_(3) coating layer delivers a discharge capacity of 225 mAh g^(-1) with a high initial Coulombic efficiency of 93.4%.These improvements can be attributed to the formation of in-situ modified hybrid LiYO_(2)-Y_(2 O3) coating layer,which suppresses phase transformation,electrolyte oxidation and salt dissociation due to the formation of protective cathode electrolyte interface.The results indicate promising application of concentration-gradient yttrium coating as a facile approach to stabilize nickel-rich cathode materials.

Microfluidic chip of concentration gradient and fluid shear stress on a single cell level

Concentration gradient and fluid shear stress(FSS)for cell microenvironment were investigated through microfluidic technology.The Darcy–Weisbach equation combined with computational fluid dynamics modeling was exploited to design the microfluidic chip,and the FSS distribution on the cell model with varying micro-channels(triangular,conical,and elliptical).The diffusion with the incompressible laminar flow model by solving the time-dependent diffusion–convection equation was applied to simulate the gradient profiles of concentration in the micro-channels.For the study of single cell in-depth,the FSS was investigated by the usage of polystyrene particles and the concentration diffusion distribution was studied by the usage of different colors of dyes.A successful agreement between model simulations and experimental data was obtained.Finally,based on the established method,the communication between individual cells was envisaged and modeled.The developed method provides valuable insights and allows to continuously improve the design of microfluidic devices for the study of single cell,the occurrence and development of tumors,and therapeutic applications.

Generation of Linear and Parabolic Concentration Gradients by Using a Christmas Tree-Shaped Microfluidic Network

This paper describes a simple method of generating concentration gradients with linear and parabolic profiles by using a Christmas tree-shaped microfluidic network.The microfluidic gradient generator consists of two parts：a Christmas tree-shaped network for gradient generation and a broad microchannel for detection.A two-dimensional model was built to analyze the flow field and the mass transfer in the microfluidic network.The simulating results show that a series of linear and parabolic gradient profiles were generated via adjusting relative flow rate ratios of the two source solutions（R_L^2≥0.995 and _PR^2≥0.999）,which could match well with the experimental results（R_L^2≥0.987 and _PR^2≥0.996）.The proposed method is promising for the generation of linear and parabolic concentration gradient profiles,with the potential in chemical and biological applications such as combinatorial chemistry synthesis,stem cell differentiation or cytotoxicity assays.

Experimentation of a Membrane-based Concentration Gradient Energy Storage of Liquid Desiccant Solutions Driven by Solar Energy

Solar energy storage is an indispensable and sustainable utilization mode of renewable energy;environment friendly,large-capacity,low heat loss,and long-term storage are critical to improving the integration of solar energy supply.Traditional thermal energy storage mode cannot achieve long-term storage due to the heat loss even under the excellent thermal insulation measures.In this work,a solar-powered membrane-based concentration gradient energy storage of liquid desiccant solutions is presented.In the membrane distillation process driven by solar energy under the right solar radiation conditions,the liquid desiccant solution is concentrated gradually and long-term stored as the concentration gradient energy.To this end,the measured temperature of solar hot water is in the range of 40°C to 90°C from May to September,2018,in Xi’an,China.And then,the LiBr solution(50 wt%),the LiCl solution(35 wt%),and the CaCl_(2)solution(40 wt%)were membrane-based concentrated in the temperature range of 42°C to 63°C,separately.The results showed that the water vapor pressure difference decides the water vapor transferred across the membrane pores from the liquid desiccant side to the air side.The energy storage density of liquid desiccant solutions increases along with the increases in temperature and the membrane area.Consequently,when the LiBr,LiCl,and CaCl_(2)solutions are concentrated from 50%to 55%,from 35%to 40%,and from 40%to 45%,separately,the concentration energy storage density is 245 kJ/kg,350 kJ/kg,and 306 kJ/kg,which is equivalent to or even higher than ice storage capacity.Due to the two independent closed cycle of the liquid desiccant solution and air,the liquid desiccant solution’s concentration gradient energy storage can be long-term stored environment-friendly without any insulation measures.

Modulating ion current rectification generating high energy output in a single glass conical nanopore channel by concentration gradient

Inspired by biological systems that have the inherent skill to generate considerable bioelectricity from the salt content in fluids with highly selective ion channels and pumps on cell membranes, herein, a fully abiotic, single glass conical nanopores energy-harvesting is demonstrated. Ion current rectification （ICR） in negatively charged glass conical nanopores is shown to be controlled by the electrolyte concentration gradient depending on the direction of ion diffusion. The degree of ICR is enhanced with the increasing forward concentration difference. An unusual rectification inversion is observed when the concentration gradient is reversely applied. The maximum power output with the individual nanopore approaches 10^4pW. This facile and cost-efficient energy-harvesting system has the potential to power tiny biomedical devices or construct future clean-energy recovery plants.

Flame Propagation Through Concentration Gradient

The experiment was carried out in homogeneous propane-air mixture and in several concentration gradient of mixture. Igniter is put on the upper side of the combustion chamber In concentration gradient experiment, fixture was ignited from lean side. An experimental study was conducted in a combustion chamber. The combustion chamber has glass windows for optical measurements at any side. For the measurement of distribution of fuel concentration, infrared absorption method using 3.39μm He-Ne laser was used, and for the observation of propagating flame, Schlieren method was employed. As a measurement result of flame propagation velocity and flammable limit, for a mixture of an identical local equivalence ratio, flame propagation velocity in concentration gradient is faster than that in homogeneous mixture, and rich flammable limit in concentration gradient shows a tendency to be higher than that in homogeneous mixture.

Concentration-and flux-based dose-responses of isoprene emission from poplar leaves and plants exposed to an ozone concentration gradient

Supported by the National Key Research and Development Program of China,Key Research Program of Frontier Sciences,CAS,the Hundred Talents Program,Chinese Academy of Sciences(CAS),and National Natural Science Foundation of China,a cooperative study by the research groups led by Prof.

A 3D-printed microfluidic gradient concentration chip for rapid antibiotic-susceptibility testing

The rise of antibiotic resistance as one of the most serious global public health threats has necessitated the timely clinical diagnosis and precise treatment of deadly bacterial infections.To identify which types and doses of antibiotics remain effective for fighting against multi-drug-resistant pathogens,the development of rapid and accurate antibiotic-susceptibility testing(AST)is of primary importance.Conventional methods for AST in well-plate formats with disk diffusion or broth dilution are both labor-intensive and operationally tedious.The microfluidic chip provides a versatile tool for evaluating bacterial AST and resistant behaviors.In this paper,we develop an operationally simple,3D-printed microfluidic chip for AST which automatically deploys antibiotic concentration gradients and fluorescence intensity-based reporting to ideally reduce the report time for AST to within 5 h.By harnessing a commercially available,digital light processing(DLP)3D printing method that offers a rapid,high-precision microfluidic chip-manufacturing capability,we design and realize the accurate generation of on-chip antibiotic concentration gradients based on flow resistance and diffusion mechanisms.We further demonstrate the employment of the microfluidic chip for the AST of E.coli to representative clinical antibiotics of three classes:ampicillin,chloramphenicol,and kanamycin.The determined minimum inhibitory concentration values are comparable to those reported by conventional well-plate methods.Our proposed method demonstrates a promising approach for realizing robust,convenient,and automatable AST of clinical bacterial pathogens.

Two Methods to Solve the Ionospheric Electron Concentration Horizontal Gradient at Chongqing

The electron concentration horizontal gradient vector of the ionosphere and its south-north and east-west components over Chongqing station are analyzed and calculated, using the first approximation, time correlation and space correlation and another approach introduced. And then, the validity of the two methods is analyzed and compared.

Cycling performance of layered oxide cathode materials for sodium-ion batteries

Layered oxide is a promising cathode material for sodium-ion batteries because of its high-capacity,high operating voltage,and simple synthesis.Cycling performance is an important criterion for evaluating the application prospects of batteries.However,facing challenges,including phase transitions,ambient stability,side reactions,and irreversible anionic oxygen activity,the cycling performance of layered oxide cathode materials still cannot meet the application requirements.Therefore,this review proposes several strategies to address these challenges.First,bulk doping is introduced from three aspects:cationic single doping,anionic single doping,and multi-ion doping.Second,homogeneous surface coating and concentration gradient modification are reviewed.In addition,methods such as mixed structure design,particle engineering,high-entropy material construction,and integrated modification are proposed.Finally,a summary and outlook provide a new horizon for developing and modifying layered oxide cathode materials.

Low-Enthalpy and High-Entropy Polymer Electrolytes for Li-Metal Battery

lonic-conductive solid-state polymer electrolytes are promising for the development of advanced lithium batteries yet a deeper understanding of their underlying ion-transfer mechanism is needed to improve performance.Here we demonstrate the low-enthalpy and high-entropy(LEHE)electrolytes can intrinsically generate remarkably free ions and high mobility,enabling them to efficiently drive lithium-ion storage.The LEHE electrolytes are constructed on the basis of introducing CsPbl_(3)perovskite quantum dots(PQDs)to strengthen PEO@LiTFSI complexes.An extremely stable cycling>1000 h at 0.3 mA cm^(-2)can be delivered by LEHE electrolytes.Also,the as-developed Li|LEHE|LiFePO_(4)cell retains 92.3%of the initial capacity(160.7 mAh g^(-1))after 200 cycles.This cycling stability is ascribed to the suppressed charge concentration gradient leading to free lithium dendrites.It is realized by a dramatic increment in lithium-ion transference number(0.57 vs 0.19)and a significant decline in ion-transfer activation energy(0.14 eV vs 0.22 eV)for LEHE electrolytes comparing with PEO@LiTFSI counterpart.The CsPbl_(3)PQDs promote highly structural disorder by inhibiting crystallization and hence endow polymer electrolytes with low melting enthalpy and high structural entropy,which in turn facilitate long-term cycling stability and excellent rate-capability of lithium-metal batteries.

CO_2 CONCENTRATION AND FLUX NEAR GROUND IN MARSH OF THE SANJIANG PLAIN OF NORTHEAST CHINA

There is limited information available on CO2 concentration and flux over marsh. The objective of this work was to characterize CO2 concentration and flux within and above marsh plant (Cares lasiocarpa Ehrh. and C. pseudoucuaica F. Schm) canopy at heights 0. 5, 1. 0 and 1. 5 m.CO2 concentration was measured sequentially every 3 bars by using an infrared gas analyzer. Soil and air temperature, wind speed, net radiation and soil heat flux were also measured simultaneously. Extremely drily minimum and maximum CO2 concentration rangal from 250 to 754 μmd/mol for the 4-year work. The typical minimum and maximum values ranged from 314 to 464 μmol/mol at the height of marsh plant (about 0. 5 m) during the fruiting perioed and mature date. The seasonal changes in CO2 concentration show that the minimum CO2 concentration occurred in the fruiting period and mature date, and both of their minimum values were 314 μmol/mol. This illustrates that CO2 consumed by photosynthesis was stable during the period. The flux of CO2 can be thought as a turbulent diffusion phenomenon. By micrometeorological methods, the diurnal CO2 fluxes were measured in the flowering peried, fruiting period, early mature date, late mature date and yellow-ripe stage. Their values were -0. 18, 38. 15,24. 13, 10. 9 and 4. 91 μmol/mol respectively.

Low-strain Co-free Li-rich layered cathode with excellent voltage and capacity stability

Owing to the inherent advantages of low cost and high capacity,cobalt(Co)-free lithium(Li)-rich layered oxides have become one of the most promising cathodes for next-generation high-energy lithium-ion batteries.However,these familial cathodes suffer from serious voltage decay due to many reasons,such as oxygen release and transition metal(TM)migration,which are closely related to nanoscale strain evolution.Here,by combining the synergistic effects of surface integration,bulk doping,and concentration gradient,we successfully construct a Co-free Li-rich layered cathode with a very small volumetric strain(1.05%)between 2.0 and 4.8 V,approaching the critical value of zero strain.Various characterizations indicate that the constructed zero-strain cathode can significantly suppress the TM migration,interfacial reactions,and structural degradation including cracks,lattice defects,phase evolution,and nanovoids,leading to improved voltage stability of Co-free Li-rich layered oxides during the prolonged cycles.This work provides a strategy to eliminate the lattice strain of Li-rich layered cathodes and facilitates the up-scaled application of the as-prepared cathode materials.

A Hydrogen Iron Flow Battery with High Current Density and Long Cyclability Enabled Through Circular Water Management

The hydrogen-iron(HyFe)flow cell has great potential for long-duration energy storage by capitalizing on the advantages of both electrolyzers and flow batteries.However,its operation at high current density(high power)and over continuous cycling testing has yet to be demonstrated.In this article,we discuss our design and demonstration of a water-management strategy that supports high current and long-cycling performance of a HyFe flow cell.Water molecules associated with the movement of protons from the iron electrode to the hydrogen electrode are sufficient to hydrate the membrane and electrode at a low current density of 100 mA cm^(-2)during the charge process.At higher charge current density,more aggressive measures must be taken to counter back-diffusion driven by the acid concentration gradient between the iron and hydrogen electrodes.Our water-management approach is based on water vapor feeding in the hydrogen electrode and water evaporation in the iron electrode,thus enabling high current density operation of 300 mA cm^(-2).

Effect of one-step and two-step homogenization treatments on distribution of Al_3Zr dispersoids in commercial AA7150 aluminium alloy

Semi-quantitative electron probe microanalysis （EPMA） mapping, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） were employed to study the effect of one-step and two-step treatments on the Zr distribution and Al3Zr dispersoid characteristics in as-cast commercial AA7150 aluminum alloy. It is shown that the Zr concentration in the dendrite centre regions is higher than that near the dendrite edges in the as-cast condition, and that homogenization at 460 °C for 20 h is insufficient to remove these concentration gradients. After homogenizing at 460-480 °C, a high number density of larger dispersoids can be observed in dendrite centre regions but not near dendrite edges. Furthermore, the dispersoid size increases with increasing the temperature during both one-step and two-step homogenization treatments.