Metallic glasses(MGs)exhibit exceptional mechanical properties,but their application is often limited by brittleness.At elevated temperatures near the glass transition(T_(g)),they undergo homogeneous viscoplastic defo...Metallic glasses(MGs)exhibit exceptional mechanical properties,but their application is often limited by brittleness.At elevated temperatures near the glass transition(T_(g)),they undergo homogeneous viscoplastic deformation,a regime commonly described using free volume(FV)theory.Despite its prevalence,the quantitative accuracy and applicability of FV models,particularly for transient behaviors,remain under investigation.This study examines the homogeneous rheology of a LaCeYNiAl high-entropy MG(HEMG)between 475 K and 490 K,and critically assesses the relevance of two prominent FV model formulations.Experimental characterization includes dynamic mechanical analysis and uniaxial tensile tests across various strain rates.The tensile data are subsequently analyzed using two elasto-viscoplastic constitutive frameworks incorporating distinct FV evolution kinetics:Spaepen's original formulation(model 1),and the bimolecular annihilation kinetics proposed by Van den Beukel/Sietsma(model 2).Our analysis reveals that model 1,when applied to steady-state flow,yields physically inconsistent negative parameters,calling its validity for homogeneous deformation into question.Model 2 demonstrates better qualitative agreement with the experimental stress–strain curves but still fails to accurately reproduce the stress overshoot features.Moreover,fitting model 2 requires unphysically low Young's modulus values and produces unusual negative apparent activation energies for key kinetic parameters,suggesting limitations in the model structure(e.g.,neglecting explicit viscoelasticity)or possibly unique behavior in HEMGs.These findings highlight significant shortcomings of standard FV models in quantitatively capturing the homogeneous deformation of this HEMG,particularly its transient characteristics,and underscore the need for more refined constitutive descriptions.展开更多
A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery.Despite being less conductive than standa rd aqueous electrolytes,it is thermally...A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery.Despite being less conductive than standa rd aqueous electrolytes,it is thermally stable on a 100 ℃ temperature window,chemically stable for at least 60 days,equally viscous and dense with typical aqueous solvents and most importantly able to solubilize to 6 mol L^(-1) vanadium sulfate,thus increasing the VRFB energy density by a factor of 2.5.Electrochemical measurements revealed quasi-reversible redox transitions for both catholyte and anolyte at 25 ℃ while a proof-of-concept redox flow cell with the proposed electrolyte was tested for a total of 150 cycles at 25 ℃,showing an open circuit potential of 1.39 V and energy and coulombic efficiencies of 65% and 93%,respectively.What’s more,the battery can be equally cycled at 45℃ showing good thermal stability.This study underlines a new route to improve the energy-to-volume ratio of energy storage system.展开更多
Prussian blue analogue(PBA)material is a promising cathode for applications in Na-ion and K-ion batteries which can support high c-rates for charge and discharge.In this study,the material of composition[K2 CuIIFeII(C...Prussian blue analogue(PBA)material is a promising cathode for applications in Na-ion and K-ion batteries which can support high c-rates for charge and discharge.In this study,the material of composition[K2 CuIIFeII(CN)6]was synthesized and its structural and electrochemical redox behavior was investigated with 5 different alkali insertion cations(Li^+,Na^+,K^+,Rb^+,Cs^+).Galvanostatic measurements indicate that the redox potential strongly depends on the ionic radius of the inserted cation.The redox potential varies by 400 m V between using Li^+(0.79A)or Cs^+(1.73A)in the electrolyte.The underlying modification of the Fe2^+/Fe3^+redox potential in PBA is proposed to be due to the weakening of the Fe–C bond in the material.This hypothesis is supported by XRD measurements which reveal that the lattice parameter of the de-intercalated host structure follows the same trend of monotonic increase with the cation size.The relatively minor volume changes accompanying the redox(1.2%–2.4%)allow the PBA to accommodate differently sized cations,although the structural hindrances are quite pronounced at high c-rates for the larger ones(Rb^+and Cs^+).Cycle aging studies indicate that the minimum capacity fade rate is observed in case of K^+ and Rb^+ containing electrolyte.The peak intensity corresponding to the[220]crystallographic plane varies depending on the state of charge of PBA,since this plane contains the insertion cations.Owing to the sensitivity of the redox potential to the insertion cation coupled with the observed fast ion-exchange ability,the PBA material may find additional analytical applications such as ion sensing or filtration devices.展开更多
Herein,a comprehensive study of electrochemical performances of the combined effect of fluorinated additives;fluoroethylene carbonate(FEC);and tris(2,2,2-trifluoroethyl) phosphite(TTFP) or the 2,2,2-trifluoroethyl met...Herein,a comprehensive study of electrochemical performances of the combined effect of fluorinated additives;fluoroethylene carbonate(FEC);and tris(2,2,2-trifluoroethyl) phosphite(TTFP) or the 2,2,2-trifluoroethyl methyl carbonate(TFEMC) as co-solvent,on Graphite//LiMn2O4 cells cycled at high potential is reported.On one side,each additive has a specific function,the FEC is dedicated to the negative electrode and the TTFP to the opposite one.The electrolyte mixture with(4% FEC+1% TTFP) additive has shown the best ability to reduce fading of the LiMn2O4 electrode,especially at high rates.On the other side,by studying the comparative thermal and transport properties of the formulated electrolytes with different proportions of TFEMC,we demonstrate that the difference in charge distribution of EMC and TFEMC molecules induced by the presence of fluorine atoms,modifies the solvation model of the Li+cation,and changes its behavior at the CEI interface and impact strongly the electrochemical performances.Finally,the EIS investigation of the LMO/electrolyte interfaces in the presence of TFEMC demonstrates that despite a spontaneous chemical reactivity of the TFEMC at the cathode interface over time,the conductive and good quality CEI is formed,which positively impact the cyclability.This study shows that against LMO surface phenomena,the combination in adequate proportions of fluorinated additives or solvent can be a solution not only to avoid the oxidative reactivity of LMO-cathode,but also to prevent its harmful consequences on the Li-metal or graphite-anode by controlling the solvation of lithium-ion.展开更多
To gain better insight into the influence of the anion size and symmetry on the transport properties and thermal stability of an electrolyte based on lithium(fluorosulfonyl)(trifluoromethanesulfonyl)-imide(FTFSI)salt,...To gain better insight into the influence of the anion size and symmetry on the transport properties and thermal stability of an electrolyte based on lithium(fluorosulfonyl)(trifluoromethanesulfonyl)-imide(FTFSI)salt,we performed the physical and electrochemical characterization of an electrolyte based on FTFSI incorporated in standard binary(3 EC/7 EMC)and ternary(EC/PC/3 DMC)alkylcarbonate mixtures.By applying the Jones-Dole-Kaminsky(JDK),Eyring and Arrhenius empirical models to the electrolyte viscosity we show that the activation enthalpy and entropy energy barriers(ΔH≠,ΔS≠)for viscous flow are between 12 and 15 kJ·mol^(-1).They are strongly dependent on the solvent nature and are significantly lower than their symmetric anions LiFSI and LiTFSI(19-20 kJ·mol^(-1))in the binary mixture.Furthermore,the hydrodynamic radius,rs,calculated by JDK,and the ionicity behavior illustrated by the Walden role,showed that the FTFSI anion is outside the solvation sphere(rs>0.6 nm)which is smaller in the case of an EC/EMC solvent base.In the 3 EC/7 EMC solvent mixture,LiFTFSI is less conductive than in the ternary mixture i.e.,σ_(max)=8.9 mS cm^(-1) at C_(max)=1.1 mol L^(-1) for 3 EC/7 EMC and,σ_(max)=10.5 mS cm^(-1) at max=0.7 mol L^(-1) for EC/PC/3 DMC,due to a strong solvation and a greater association of FTFSI ions in the binary solvent mixture.The thermal stability of FTFSI based electrolytes was determined by the shift of the evaporation temperature of the volatile solvents(DMC,EMC)in the presence of salt,towards the higher temperatures.This feature is visible on the thermograms obtained by DSC both with the liquid electrolyte and with charged LMO cathodes in presence of electrolytes.The consequences of these properties on the electrochemical behavior of a graphite(Gr)half-cell,a lithium metal(Li)anode and a manganese lithium oxide(LMO)cathode demonstrated on the one hand the formation of a thick solid electrolyte interphase(SEI)on graphite that consumed a significant amount of lithium i.e.,18%of total capacity of the first charge.Furthermore,LiFTFSI delivered 95%of the initial capacity C=360 mAh g^(-1) at C/10 with EC/PC/3 DMC versus 91%when it was combined with 3 EC/7 EMC C=348 mAh g^(-1),while the capacities obtained for LiTFSI in EC/PC/3 DMC were the lowest(C=275 mAh g^(-1))compared to those of the other salts.After 10 cycles,the capacity loss at C/20 is<2%for LiFSI and LiFTFSI with the two solvent mixtures.On the other hand,manganese dissolution from LMO as well as current collector corrosion were confirmed by post-mortem examination of opened coin cells.The incompatibility of the LMO cathode with an electrolyte based on FTFSI was confirmed by the position of the decomposition peak of charged LMO in contact with this electrolyte observed by DSC These results demonstrate that the nature of the anion as well as the composition of the solvent considerably influence the performance of imide-based lithium salts both on the anode,but especially on the high voltage cathode.展开更多
This work has two main purposes： （i） introducing the basic concepts of molecular dynamics analysis to material scientists and engineers, and （ii） providing a better understanding of instrumented indentation measu...This work has two main purposes： （i） introducing the basic concepts of molecular dynamics analysis to material scientists and engineers, and （ii） providing a better understanding of instrumented indentation measurements, presenting an example of nanoindentation and scratch test simulations. To reach these purposes, three-dimensional molecular dynamics （MD） simulations of nanoindentation and scratch test technique were carried out for generic thin films that present BCC crystalline structures. Structures were oriented in the plane （100） and placed on FCC diamond substrates. A pair wise potential was employed to simulate the interaction between atoms of each layer and a repulsive radial potential was used to represent a spherical tip indenting the sample. Mechanical properties of this generic material were obtained by varying the indentation depth and dissociation energy. The load-unload curves and coefficient of friction were found for each test; on the other hand, dissociation energy was varied showing a better mechanical response for films that present grater dissociation energy. Structural change evolution was observed presenting vacancies and slips as the depth was varied.展开更多
The electrolyte is an essential component of a battery system since it is responsible for the conduction of ions between the electrodes.In the quest for cheaper alternatives to common organic electrolytes for lithium-...The electrolyte is an essential component of a battery system since it is responsible for the conduction of ions between the electrodes.In the quest for cheaper alternatives to common organic electrolytes for lithium-ion batteries(LIB),we formulated hybrid electrolytes comprising a mixture of Na,K,and Li alkaline salts with ethylene carbonate(EC),ethyl methyl carbonate(EMC),and lithium hexafluorophosphate(LiPF_(6)),giving a total salt concentration of 1.5 M;we determined their physicochemical properties and investigated their electrochemical behavior on a nickel cobalt aluminum oxide(NCA)cathode and graphite(Gr)anode.The electrolytes demonstrated a melting transition peak(T_(m)).eutectic behavior,and ionic conductivities(-13 mS cm^(-1))close to those of a commercial LIB electrolyte(SE,EC/EMC+1 M LiPF_(6))and activation energies of ca.3 kJ mol^(-1).The half-cell coin cells revealed high coulombic efficiency(99%),specific capacity(175 mAh g^(-1) at C/10),and capacity retention(92% for NaCF_(3)SO_(3))for the NCA cathode and a moderate performance(coulombic efficiency of 98%for 20 cycles)on the graphite anode after the formation of the SEI layer.The hybrid electrolytes were cycled at 25℃ in a Gr//NCA cell yielding specific capacities of ca.225 mAh g^(-1) at a C/5 rate,corroborating that the anion plays a key role and highlighting their potential for energy storage applications.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52271153 and 12472069)the Natural Science Basic Research Plan for Distinguished Young Scholars in Shaanxi Province(Grant No.2021JC-12)。
文摘Metallic glasses(MGs)exhibit exceptional mechanical properties,but their application is often limited by brittleness.At elevated temperatures near the glass transition(T_(g)),they undergo homogeneous viscoplastic deformation,a regime commonly described using free volume(FV)theory.Despite its prevalence,the quantitative accuracy and applicability of FV models,particularly for transient behaviors,remain under investigation.This study examines the homogeneous rheology of a LaCeYNiAl high-entropy MG(HEMG)between 475 K and 490 K,and critically assesses the relevance of two prominent FV model formulations.Experimental characterization includes dynamic mechanical analysis and uniaxial tensile tests across various strain rates.The tensile data are subsequently analyzed using two elasto-viscoplastic constitutive frameworks incorporating distinct FV evolution kinetics:Spaepen's original formulation(model 1),and the bimolecular annihilation kinetics proposed by Van den Beukel/Sietsma(model 2).Our analysis reveals that model 1,when applied to steady-state flow,yields physically inconsistent negative parameters,calling its validity for homogeneous deformation into question.Model 2 demonstrates better qualitative agreement with the experimental stress–strain curves but still fails to accurately reproduce the stress overshoot features.Moreover,fitting model 2 requires unphysically low Young's modulus values and produces unusual negative apparent activation energies for key kinetic parameters,suggesting limitations in the model structure(e.g.,neglecting explicit viscoelasticity)or possibly unique behavior in HEMGs.These findings highlight significant shortcomings of standard FV models in quantitatively capturing the homogeneous deformation of this HEMG,particularly its transient characteristics,and underscore the need for more refined constitutive descriptions.
基金"Le Studium Loire Valley Institute for Advanced Studies" and "Region Centre Val de Loire"through the "OBAMA" project under Lavoisier Ⅱ for financial support。
文摘A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery.Despite being less conductive than standa rd aqueous electrolytes,it is thermally stable on a 100 ℃ temperature window,chemically stable for at least 60 days,equally viscous and dense with typical aqueous solvents and most importantly able to solubilize to 6 mol L^(-1) vanadium sulfate,thus increasing the VRFB energy density by a factor of 2.5.Electrochemical measurements revealed quasi-reversible redox transitions for both catholyte and anolyte at 25 ℃ while a proof-of-concept redox flow cell with the proposed electrolyte was tested for a total of 150 cycles at 25 ℃,showing an open circuit potential of 1.39 V and energy and coulombic efficiencies of 65% and 93%,respectively.What’s more,the battery can be equally cycled at 45℃ showing good thermal stability.This study underlines a new route to improve the energy-to-volume ratio of energy storage system.
基金“Le Studium Loire Valley Institute for Advanced Studies” for financial and logistical support to the researchers involved in this study“Region Centre” for financial support under the “Lavoisier” program
文摘Prussian blue analogue(PBA)material is a promising cathode for applications in Na-ion and K-ion batteries which can support high c-rates for charge and discharge.In this study,the material of composition[K2 CuIIFeII(CN)6]was synthesized and its structural and electrochemical redox behavior was investigated with 5 different alkali insertion cations(Li^+,Na^+,K^+,Rb^+,Cs^+).Galvanostatic measurements indicate that the redox potential strongly depends on the ionic radius of the inserted cation.The redox potential varies by 400 m V between using Li^+(0.79A)or Cs^+(1.73A)in the electrolyte.The underlying modification of the Fe2^+/Fe3^+redox potential in PBA is proposed to be due to the weakening of the Fe–C bond in the material.This hypothesis is supported by XRD measurements which reveal that the lattice parameter of the de-intercalated host structure follows the same trend of monotonic increase with the cation size.The relatively minor volume changes accompanying the redox(1.2%–2.4%)allow the PBA to accommodate differently sized cations,although the structural hindrances are quite pronounced at high c-rates for the larger ones(Rb^+and Cs^+).Cycle aging studies indicate that the minimum capacity fade rate is observed in case of K^+ and Rb^+ containing electrolyte.The peak intensity corresponding to the[220]crystallographic plane varies depending on the state of charge of PBA,since this plane contains the insertion cations.Owing to the sensitivity of the redox potential to the insertion cation coupled with the observed fast ion-exchange ability,the PBA material may find additional analytical applications such as ion sensing or filtration devices.
基金“La region Centre Val de Loire” for financial support to the researchers involved in this study on OBAMA project under “Lavoisier Ⅱ” regional program。
文摘Herein,a comprehensive study of electrochemical performances of the combined effect of fluorinated additives;fluoroethylene carbonate(FEC);and tris(2,2,2-trifluoroethyl) phosphite(TTFP) or the 2,2,2-trifluoroethyl methyl carbonate(TFEMC) as co-solvent,on Graphite//LiMn2O4 cells cycled at high potential is reported.On one side,each additive has a specific function,the FEC is dedicated to the negative electrode and the TTFP to the opposite one.The electrolyte mixture with(4% FEC+1% TTFP) additive has shown the best ability to reduce fading of the LiMn2O4 electrode,especially at high rates.On the other side,by studying the comparative thermal and transport properties of the formulated electrolytes with different proportions of TFEMC,we demonstrate that the difference in charge distribution of EMC and TFEMC molecules induced by the presence of fluorine atoms,modifies the solvation model of the Li+cation,and changes its behavior at the CEI interface and impact strongly the electrochemical performances.Finally,the EIS investigation of the LMO/electrolyte interfaces in the presence of TFEMC demonstrates that despite a spontaneous chemical reactivity of the TFEMC at the cathode interface over time,the conductive and good quality CEI is formed,which positively impact the cyclability.This study shows that against LMO surface phenomena,the combination in adequate proportions of fluorinated additives or solvent can be a solution not only to avoid the oxidative reactivity of LMO-cathode,but also to prevent its harmful consequences on the Li-metal or graphite-anode by controlling the solvation of lithium-ion.
基金“La Région Centre Val de Loire” for financial support。
文摘To gain better insight into the influence of the anion size and symmetry on the transport properties and thermal stability of an electrolyte based on lithium(fluorosulfonyl)(trifluoromethanesulfonyl)-imide(FTFSI)salt,we performed the physical and electrochemical characterization of an electrolyte based on FTFSI incorporated in standard binary(3 EC/7 EMC)and ternary(EC/PC/3 DMC)alkylcarbonate mixtures.By applying the Jones-Dole-Kaminsky(JDK),Eyring and Arrhenius empirical models to the electrolyte viscosity we show that the activation enthalpy and entropy energy barriers(ΔH≠,ΔS≠)for viscous flow are between 12 and 15 kJ·mol^(-1).They are strongly dependent on the solvent nature and are significantly lower than their symmetric anions LiFSI and LiTFSI(19-20 kJ·mol^(-1))in the binary mixture.Furthermore,the hydrodynamic radius,rs,calculated by JDK,and the ionicity behavior illustrated by the Walden role,showed that the FTFSI anion is outside the solvation sphere(rs>0.6 nm)which is smaller in the case of an EC/EMC solvent base.In the 3 EC/7 EMC solvent mixture,LiFTFSI is less conductive than in the ternary mixture i.e.,σ_(max)=8.9 mS cm^(-1) at C_(max)=1.1 mol L^(-1) for 3 EC/7 EMC and,σ_(max)=10.5 mS cm^(-1) at max=0.7 mol L^(-1) for EC/PC/3 DMC,due to a strong solvation and a greater association of FTFSI ions in the binary solvent mixture.The thermal stability of FTFSI based electrolytes was determined by the shift of the evaporation temperature of the volatile solvents(DMC,EMC)in the presence of salt,towards the higher temperatures.This feature is visible on the thermograms obtained by DSC both with the liquid electrolyte and with charged LMO cathodes in presence of electrolytes.The consequences of these properties on the electrochemical behavior of a graphite(Gr)half-cell,a lithium metal(Li)anode and a manganese lithium oxide(LMO)cathode demonstrated on the one hand the formation of a thick solid electrolyte interphase(SEI)on graphite that consumed a significant amount of lithium i.e.,18%of total capacity of the first charge.Furthermore,LiFTFSI delivered 95%of the initial capacity C=360 mAh g^(-1) at C/10 with EC/PC/3 DMC versus 91%when it was combined with 3 EC/7 EMC C=348 mAh g^(-1),while the capacities obtained for LiTFSI in EC/PC/3 DMC were the lowest(C=275 mAh g^(-1))compared to those of the other salts.After 10 cycles,the capacity loss at C/20 is<2%for LiFSI and LiFTFSI with the two solvent mixtures.On the other hand,manganese dissolution from LMO as well as current collector corrosion were confirmed by post-mortem examination of opened coin cells.The incompatibility of the LMO cathode with an electrolyte based on FTFSI was confirmed by the position of the decomposition peak of charged LMO in contact with this electrolyte observed by DSC These results demonstrate that the nature of the anion as well as the composition of the solvent considerably influence the performance of imide-based lithium salts both on the anode,but especially on the high voltage cathode.
基金supported by la Direcci o′n Nacional de Investigación of the Universidad Nacional de Colombia,“the Theoretical Study of Physical Properties of Hard Materials for Technological Applications”(Grant No.20101007903)
文摘This work has two main purposes： （i） introducing the basic concepts of molecular dynamics analysis to material scientists and engineers, and （ii） providing a better understanding of instrumented indentation measurements, presenting an example of nanoindentation and scratch test simulations. To reach these purposes, three-dimensional molecular dynamics （MD） simulations of nanoindentation and scratch test technique were carried out for generic thin films that present BCC crystalline structures. Structures were oriented in the plane （100） and placed on FCC diamond substrates. A pair wise potential was employed to simulate the interaction between atoms of each layer and a repulsive radial potential was used to represent a spherical tip indenting the sample. Mechanical properties of this generic material were obtained by varying the indentation depth and dissociation energy. The load-unload curves and coefficient of friction were found for each test; on the other hand, dissociation energy was varied showing a better mechanical response for films that present grater dissociation energy. Structural change evolution was observed presenting vacancies and slips as the depth was varied.
文摘The electrolyte is an essential component of a battery system since it is responsible for the conduction of ions between the electrodes.In the quest for cheaper alternatives to common organic electrolytes for lithium-ion batteries(LIB),we formulated hybrid electrolytes comprising a mixture of Na,K,and Li alkaline salts with ethylene carbonate(EC),ethyl methyl carbonate(EMC),and lithium hexafluorophosphate(LiPF_(6)),giving a total salt concentration of 1.5 M;we determined their physicochemical properties and investigated their electrochemical behavior on a nickel cobalt aluminum oxide(NCA)cathode and graphite(Gr)anode.The electrolytes demonstrated a melting transition peak(T_(m)).eutectic behavior,and ionic conductivities(-13 mS cm^(-1))close to those of a commercial LIB electrolyte(SE,EC/EMC+1 M LiPF_(6))and activation energies of ca.3 kJ mol^(-1).The half-cell coin cells revealed high coulombic efficiency(99%),specific capacity(175 mAh g^(-1) at C/10),and capacity retention(92% for NaCF_(3)SO_(3))for the NCA cathode and a moderate performance(coulombic efficiency of 98%for 20 cycles)on the graphite anode after the formation of the SEI layer.The hybrid electrolytes were cycled at 25℃ in a Gr//NCA cell yielding specific capacities of ca.225 mAh g^(-1) at a C/5 rate,corroborating that the anion plays a key role and highlighting their potential for energy storage applications.
