Silicon-based carbon composites are believed as promising anodes in the near future due to their outstanding specific capacity and relatively lower volume effect compared to pure silicon anodes.Herein,a multilayer sph...Silicon-based carbon composites are believed as promising anodes in the near future due to their outstanding specific capacity and relatively lower volume effect compared to pure silicon anodes.Herein,a multilayer spherical core-shell(M-SCS)electrode with a graphite framework prepared with Si@O-MCMB/C nanoparticles is developed,which aims to realize chemically/mechanically stability during the lithiation/delithiation process with high specific capacity.An electrochemical-/mechanical-coupling model for the M-SCS structure is established with various chemical/mechanical boundary conditions.The simulation of finite difference method(FDM)has been conducted based on the proposed coupling model,by which the diffusion-induced stress along both the radial and the circumferential directions is determined.Moreover,factors that influence the diffusion-induced stress of the M-SCS structure have been discussed and analyzed in detail.展开更多
By incorporating the contribution of solute atoms to the Helmholtz free energy of solid solution,a linear relation is derived between Young's modulus and the concentration of solute atoms.The solute atoms can eith...By incorporating the contribution of solute atoms to the Helmholtz free energy of solid solution,a linear relation is derived between Young's modulus and the concentration of solute atoms.The solute atoms can either increase or decrease Young's modulus of solid solution,depending on the first-order derivative of the Helmholtz free energy with respect to the concentration of solute atoms.Using this relation,a closed-form solution of the chemical stress in an elastic plate is obtained when the diffusion behavior in the plate can be described by the classical Fick's second law with convection boundary condition on one surface and zero flux on the other surface.The plate experiences tensile stress after short diffusion time due to asymmetrical diffusion,which will likely cause surface microcracking.The results show that the effect of the concentration dependence of Young's modulus on the evolution of chemical stress in elastic plates is negligible if the change of Young's modulus due to the diffusive motion of solute atomsis is not compatible in magnitude with Young's modulus of the pure material.Also,a new diffusion equation is developed for strictly regular binary solid solution.The effective diffusivity is a nonlinear function of the concentration of solute atoms.展开更多
In the current work,the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy(nc-HEA)with ultrahigh hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite.First,a dual-phase Al/CoCrFeN...In the current work,the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy(nc-HEA)with ultrahigh hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite.First,a dual-phase Al/CoCrFeNi nanocrystalline high-entropy alloy composite(nc-HEAC)was prepared by a laser source inert gas condensation equipment(laser-IGC).The as-prepared nc-HEAC is composed of well-mixed FCC-Al and FCC-CoCrFeNi nanocrystals.Then,the heat treatment was used to trigger the interdiffusion between Al and CoCrFeNi nanocrystals and form an FCC-AlCoCrFeNi phase.With the increase of the annealing temperature,element diffusion intensifies,and the Al Co Cr Fe Ni phase undergoes a phase transition from FCC to BCC structure.Finally,the BCC-AlCoCrFe Ni bulk nc-HEA with high Al content(up to 50 at.%)was obtained for the first time.Excitingly,the nc-HEAC(Al-40%)sample exhibits an unprecedented ultra-high hardness of 1124 HV after annealing at 500℃ for 1 h.We present a systematic investigation of the relationship between the microstructure evolution and mechanical properties during annealing,and the corresponding micro-mechanisms in different annealing stages are revealed.The enhanced nanoscale thermal diffusion-induced phase transition process dominates the mechanical performance evolution of the nc-HEACs,which opens a new pathway for the design of high-performance nanocrystalline alloy materials.展开更多
Hydrogen diffusion in the wall of hydrogenation reactor for three situations, i.e. operating, normal shutdown and abnormal shutdown, was numerically simulated based on the finite element program-ABAQUS. The formula of...Hydrogen diffusion in the wall of hydrogenation reactor for three situations, i.e. operating, normal shutdown and abnormal shutdown, was numerically simulated based on the finite element program-ABAQUS. The formula of diffusion-induced stress was deduced for model of the thin walled cylinder. Distribution of diffusion-induced stress in the wall of hydrogenation reactor was studied. The results showed that the maximum stress was at the fusion surface between welding overlay and base metal and which would increase with cooling rate. The crack will initiate and propagate from fusion surface to welding overlay when the diffusion-induced stress is higher than yield stress, but it will not propagate to the base metal. Diffusion-induced stress is one of the important factors for crack initiation and propagation of welding overlay of hydrogenation reactor.展开更多
Diffusion-induced deformation during electrochemical cycling plays an important role in determining structural durability of the electrodes in lithium-ion batteries. In this work, we investigate the coupling between d...Diffusion-induced deformation during electrochemical cycling plays an important role in determining structural durability of the electrodes in lithium-ion batteries. In this work, we investigate the coupling between diffusion and stress in the boundary conditions of a bilayer electrode, and analyze the evolution of the lithium concentration and stress. Numerical simulations are performed under four different combinations of the boundary conditions between diffusion and mechanical deformation. The stress distributes uniformly in the bilayer electrode for all four cases. The concentration of lithium at the interface is discontinuous for the cases with fixed boundary conditions and is continuous for the cases with a surface at stress-free state. For the bilayer electrode fixed at both surfaces, the magnitude of the stress in the bilayer electrode increases with the increase of the diffusion time. This study reveals the importance of incorporating the coupling between diffusion and stress in the boundary condition in the analysis of the structural durability of lithium-ion batteries and in the design of multilayered and/or gradient electrodes.展开更多
Electrode is a key component to remain durability and safety of lithium-ion（Li-ion） batteries. Li-ion insertion/removal and thermal expansion mismatch may induce high stress in electrode during charging and discharg...Electrode is a key component to remain durability and safety of lithium-ion（Li-ion） batteries. Li-ion insertion/removal and thermal expansion mismatch may induce high stress in electrode during charging and discharging processes. In this paper, we present a continuum model based on COMSOL Multiphysics software, which involves thermal, chemical and mechanical behaviors of electrodes. The results show that,because of diffusion-induced stress and thermal mismatch, the electrode geometry plays an important role in diffusion kinetics of Li-ions. A higher local compressive stress results in a lower Li-ion concentration and thus a lower capacity when a particle is embedded another, which is in agreement with experimental observations.展开更多
A systematic microstructure-oriented magnetic property investigation for Al/CoCrFeNi nanocrystalline high-entropy alloys composite(nc-HEAC)is presented.In the initial state,the Al/CoCrFeNi nc-HEAC is composed of face-...A systematic microstructure-oriented magnetic property investigation for Al/CoCrFeNi nanocrystalline high-entropy alloys composite(nc-HEAC)is presented.In the initial state,the Al/CoCrFeNi nc-HEAC is composed of face-centered cubic(FCC)-Al,FCC-CoCrFeNi and hexagonal close-packed(HCP)-CoNi phases.High energy synchrotron radiation X-ray diffraction and high-resolution transmission electron microscopy were used to reveal the relationship between microstructure evolution and mag-netic mechanism of Al/CoCrFeNi nc-HEAC during heat treatment.At low-temperature annealing stage,the mag-netic properties are mainly contributed by the HCP-CoNi phase.With the increase of temperature,the diffusion-in-duced phase transition process including the transformation of AlCoCrFeNi HEA from FCC to BCC structure and the growth of B2 phase plays a dominant role in the magnetic properties.It was found that the magnetic properties can be effectively regulated through the control of the thermal diffusion process.The nano dual-phase thermal diffusion-induced phase transition behavior of nanocomposites pre-pared based on laser-IGC technology provides guidance for the diffusion process and microstructure evolution of two phases in composites.展开更多
In this paper,a microscopic phase-field model was used to investigate the effect of the oriented diffusion channel and the phases' effect mechanism for the Ni75Al6.0V19.0 alloy during a phase transformation proces...In this paper,a microscopic phase-field model was used to investigate the effect of the oriented diffusion channel and the phases' effect mechanism for the Ni75Al6.0V19.0 alloy during a phase transformation process.A diffusion channel of V was formed in the [100] direction.The oriented growth of DO22 in this direction,when an elastic misfit stress field existed,forced Al to form a diffusion channel next to DO22,resulting in L12-oriented growth.With an increase in stress,the oriented growth increased initially and then decreased.At a higher stress,the average values of the occupation probability for V atoms became constant later while Al atoms earlier.展开更多
Nanostructured electrodes with surface effect show a distinct advantage in prolonging the lifetime of lithium-ion(Li-ion)battery.In order to characterize the surface and chemical diffusion effects in a cylindrical nan...Nanostructured electrodes with surface effect show a distinct advantage in prolonging the lifetime of lithium-ion(Li-ion)battery.In order to characterize the surface and chemical diffusion effects in a cylindrical nanowire electrode,a new theoretical model is proposed based on a combination of the diffusion theory and a surface energy density-based elastic theory.With the reformulation of the stress boundary condition in terms of a surface-induced traction,the bulk surface energy density and surface relaxation parameter are introduced as two simple parameters characterizing the surface effect in nanowire electrodes,instead of the surface elastic constants always used in existing models.Closed-form solutions of the diffusion-induced elastic fields under potentiostatic operation are derived.It is found that the radial expansion and tensile stress in nanowire electrodes become smaller than the classical predictions without surface effect and decrease monotonically with a decreasing nanowire radius when the surface effect is considered.Such phenomena can be basically attributed to the action of surface-induced traction on the nanowire surface.These results demonstrate the convenience and effectiveness of the present model in predicting the chemo-mechanical behavior of nanowire electrodes,which should be of guidance value for the optimal design of durable electrodes.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12072229 and 11602167).
文摘Silicon-based carbon composites are believed as promising anodes in the near future due to their outstanding specific capacity and relatively lower volume effect compared to pure silicon anodes.Herein,a multilayer spherical core-shell(M-SCS)electrode with a graphite framework prepared with Si@O-MCMB/C nanoparticles is developed,which aims to realize chemically/mechanically stability during the lithiation/delithiation process with high specific capacity.An electrochemical-/mechanical-coupling model for the M-SCS structure is established with various chemical/mechanical boundary conditions.The simulation of finite difference method(FDM)has been conducted based on the proposed coupling model,by which the diffusion-induced stress along both the radial and the circumferential directions is determined.Moreover,factors that influence the diffusion-induced stress of the M-SCS structure have been discussed and analyzed in detail.
文摘By incorporating the contribution of solute atoms to the Helmholtz free energy of solid solution,a linear relation is derived between Young's modulus and the concentration of solute atoms.The solute atoms can either increase or decrease Young's modulus of solid solution,depending on the first-order derivative of the Helmholtz free energy with respect to the concentration of solute atoms.Using this relation,a closed-form solution of the chemical stress in an elastic plate is obtained when the diffusion behavior in the plate can be described by the classical Fick's second law with convection boundary condition on one surface and zero flux on the other surface.The plate experiences tensile stress after short diffusion time due to asymmetrical diffusion,which will likely cause surface microcracking.The results show that the effect of the concentration dependence of Young's modulus on the evolution of chemical stress in elastic plates is negligible if the change of Young's modulus due to the diffusive motion of solute atomsis is not compatible in magnitude with Young's modulus of the pure material.Also,a new diffusion equation is developed for strictly regular binary solid solution.The effective diffusivity is a nonlinear function of the concentration of solute atoms.
基金the Equipment Advance Research field Fund(Nos.80922010401)the National Key R&D Program of China(Nos.2021YFB3802800)+5 种基金the Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scat-tering Science and Technology,the Fundamental Research Funds for the Central Universities(Nos.30919011404 and 30919011107)the National Natural Science Foundation of China(Nos.51871120 and 51571119)the Natural Science Foundation of Jiangsu Province(No.BK20200019)the support from the Qing Lan project and the distinguished professor project of Jiangsu provincethe support by Shenzhen Science and Technology Innovation Committee(No.JCYJ20170413140446951)the Research Grants Council of Hong Kong(No.City U 11215917)。
文摘In the current work,the BCC-AlCoCrFeNi bulk nanocrystalline high-entropy alloy(nc-HEA)with ultrahigh hardness was formed by nanoscale diffusion-induced phase transition in a nanocomposite.First,a dual-phase Al/CoCrFeNi nanocrystalline high-entropy alloy composite(nc-HEAC)was prepared by a laser source inert gas condensation equipment(laser-IGC).The as-prepared nc-HEAC is composed of well-mixed FCC-Al and FCC-CoCrFeNi nanocrystals.Then,the heat treatment was used to trigger the interdiffusion between Al and CoCrFeNi nanocrystals and form an FCC-AlCoCrFeNi phase.With the increase of the annealing temperature,element diffusion intensifies,and the Al Co Cr Fe Ni phase undergoes a phase transition from FCC to BCC structure.Finally,the BCC-AlCoCrFe Ni bulk nc-HEA with high Al content(up to 50 at.%)was obtained for the first time.Excitingly,the nc-HEAC(Al-40%)sample exhibits an unprecedented ultra-high hardness of 1124 HV after annealing at 500℃ for 1 h.We present a systematic investigation of the relationship between the microstructure evolution and mechanical properties during annealing,and the corresponding micro-mechanisms in different annealing stages are revealed.The enhanced nanoscale thermal diffusion-induced phase transition process dominates the mechanical performance evolution of the nc-HEACs,which opens a new pathway for the design of high-performance nanocrystalline alloy materials.
基金supported by Graduate Student Scientific Innovation Project of Jiangsu Province (No.CX09B 131Z)
文摘Hydrogen diffusion in the wall of hydrogenation reactor for three situations, i.e. operating, normal shutdown and abnormal shutdown, was numerically simulated based on the finite element program-ABAQUS. The formula of diffusion-induced stress was deduced for model of the thin walled cylinder. Distribution of diffusion-induced stress in the wall of hydrogenation reactor was studied. The results showed that the maximum stress was at the fusion surface between welding overlay and base metal and which would increase with cooling rate. The crack will initiate and propagate from fusion surface to welding overlay when the diffusion-induced stress is higher than yield stress, but it will not propagate to the base metal. Diffusion-induced stress is one of the important factors for crack initiation and propagation of welding overlay of hydrogenation reactor.
基金the National Natural Science Foundation of China (Grant 11402054), the Natural Science Foundation of Fujian Provincial (Grant 2018J01663)2016 Open Projects of Key Laboratory for Strength and Vibration of Mechanical Structures (Grant SV2016-KF-18)the National Science Foundation (Grant CMMI-1634540, monitored by Dr. Khershed Cooper).
文摘Diffusion-induced deformation during electrochemical cycling plays an important role in determining structural durability of the electrodes in lithium-ion batteries. In this work, we investigate the coupling between diffusion and stress in the boundary conditions of a bilayer electrode, and analyze the evolution of the lithium concentration and stress. Numerical simulations are performed under four different combinations of the boundary conditions between diffusion and mechanical deformation. The stress distributes uniformly in the bilayer electrode for all four cases. The concentration of lithium at the interface is discontinuous for the cases with fixed boundary conditions and is continuous for the cases with a surface at stress-free state. For the bilayer electrode fixed at both surfaces, the magnitude of the stress in the bilayer electrode increases with the increase of the diffusion time. This study reveals the importance of incorporating the coupling between diffusion and stress in the boundary condition in the analysis of the structural durability of lithium-ion batteries and in the design of multilayered and/or gradient electrodes.
基金supported by the National Natural Science Foundation of China (11702234 and 11602213)
文摘Electrode is a key component to remain durability and safety of lithium-ion（Li-ion） batteries. Li-ion insertion/removal and thermal expansion mismatch may induce high stress in electrode during charging and discharging processes. In this paper, we present a continuum model based on COMSOL Multiphysics software, which involves thermal, chemical and mechanical behaviors of electrodes. The results show that,because of diffusion-induced stress and thermal mismatch, the electrode geometry plays an important role in diffusion kinetics of Li-ions. A higher local compressive stress results in a lower Li-ion concentration and thus a lower capacity when a particle is embedded another, which is in agreement with experimental observations.
基金financially supported by National Key R&D Program of China (No.2021YFB3802800)the Equipment Advance Research field Fund (No.80922010401)+6 种基金equipment project of China (JZX7Y20210162400201)Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technologythe Fundamental Research Funds for the Central Universities (Nos.30919011404 and 30919011107)the National Natural Science Foundation of China (Nos.51871120 and 51571119)the Natural Science Foundation of Jiangsu Province (No. BK20200019)the support from Qing Lan projectthe distinguished professor project of Jiangsu province
文摘A systematic microstructure-oriented magnetic property investigation for Al/CoCrFeNi nanocrystalline high-entropy alloys composite(nc-HEAC)is presented.In the initial state,the Al/CoCrFeNi nc-HEAC is composed of face-centered cubic(FCC)-Al,FCC-CoCrFeNi and hexagonal close-packed(HCP)-CoNi phases.High energy synchrotron radiation X-ray diffraction and high-resolution transmission electron microscopy were used to reveal the relationship between microstructure evolution and mag-netic mechanism of Al/CoCrFeNi nc-HEAC during heat treatment.At low-temperature annealing stage,the mag-netic properties are mainly contributed by the HCP-CoNi phase.With the increase of temperature,the diffusion-in-duced phase transition process including the transformation of AlCoCrFeNi HEA from FCC to BCC structure and the growth of B2 phase plays a dominant role in the magnetic properties.It was found that the magnetic properties can be effectively regulated through the control of the thermal diffusion process.The nano dual-phase thermal diffusion-induced phase transition behavior of nanocomposites pre-pared based on laser-IGC technology provides guidance for the diffusion process and microstructure evolution of two phases in composites.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51075335, 10902086, 50875217)the NPU Foundation for Fundamental Research (Grant No. JC201005)the Doctorate Foundation of Northwestern Polytechnical University (Grant No.CX201007)
文摘In this paper,a microscopic phase-field model was used to investigate the effect of the oriented diffusion channel and the phases' effect mechanism for the Ni75Al6.0V19.0 alloy during a phase transformation process.A diffusion channel of V was formed in the [100] direction.The oriented growth of DO22 in this direction,when an elastic misfit stress field existed,forced Al to form a diffusion channel next to DO22,resulting in L12-oriented growth.With an increase in stress,the oriented growth increased initially and then decreased.At a higher stress,the average values of the occupation probability for V atoms became constant later while Al atoms earlier.
基金This work was supported by the National Natural Science Foundation of China(Grants Nos.11532013,11872114,11772333)and the Project of State Key Laboratory of Explosion Science and Technology(Grants No.ZDKT17-02).
文摘Nanostructured electrodes with surface effect show a distinct advantage in prolonging the lifetime of lithium-ion(Li-ion)battery.In order to characterize the surface and chemical diffusion effects in a cylindrical nanowire electrode,a new theoretical model is proposed based on a combination of the diffusion theory and a surface energy density-based elastic theory.With the reformulation of the stress boundary condition in terms of a surface-induced traction,the bulk surface energy density and surface relaxation parameter are introduced as two simple parameters characterizing the surface effect in nanowire electrodes,instead of the surface elastic constants always used in existing models.Closed-form solutions of the diffusion-induced elastic fields under potentiostatic operation are derived.It is found that the radial expansion and tensile stress in nanowire electrodes become smaller than the classical predictions without surface effect and decrease monotonically with a decreasing nanowire radius when the surface effect is considered.Such phenomena can be basically attributed to the action of surface-induced traction on the nanowire surface.These results demonstrate the convenience and effectiveness of the present model in predicting the chemo-mechanical behavior of nanowire electrodes,which should be of guidance value for the optimal design of durable electrodes.
