A new kind of nano-crysta cellulose (NCC) prepared from natural cotton fiber has been obtained by the method ofacid hydrolysis. Compared to most other nanophase materials that derive from inorganic materials, our prod...A new kind of nano-crysta cellulose (NCC) prepared from natural cotton fiber has been obtained by the method ofacid hydrolysis. Compared to most other nanophase materials that derive from inorganic materials, our products are preparedfrom natural cotton fibers. The products are of spherical shape with mixed crystal forms of cellulose I and II. The preparationconditions determine the properties of the products. Prior treatment is a critical procedure. The properties of the products arealso strongly affected by such conditions as the kinds of acids used, the ratio of the acid mixture, the acid concentration, theultrasonic agitation time and hydrolysis temperature. The number average molecular weight of NCC is determined by gelpermeation chromatography (GPC). The particle size and shape were determined by transmission electron microscopy(TEM). X-ray diffraction was used to detect the crystallinity and average crystallite size of the panicle.展开更多
Mixed mode Ⅰ/Ⅱ fracture erperiments of LC4-CS aluminum alloy were conductedby using tension--shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracturemechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture ...Mixed mode Ⅰ/Ⅱ fracture erperiments of LC4-CS aluminum alloy were conductedby using tension--shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracturemechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture were first examined fromfracture surface morphology to correlate with the macroscopic fracture behavior andstress state. It is found that specimen thickness has a strong influence on mixed modefracture. As thickness varies from thin to thick the macroscopic fracture surfacesappear the characteristics of plane stress state (2mm, 4mm--thick specimen), three--dimensional stress state (8mm--thick specimens), and plane strain state (14mm--thickspecimens), respectively. The specimens of all kinds of thicknesses are typical of ten-sile type failure under mode Ⅰ loading condition and shear type failure under mode Ⅱloading condition. Two distinct features coexist on the fracture surfaces under mixedmode loading conditions, and the corresponding proportion varies with loading mix-ity. Void--growth processes are the failure mechanism in both predominately tensile-and shears--type fractures. The size and depth of dimples on the fracture surface varygreatly with thickness. Therefore, it is extraordinary necessary to take into accountthe thickness effect when a mixed mode fracture criterion is being established.展开更多
Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability.However,adverse impact also accompanies the mixed cation system simultaneously.It brings the compositional instabilit...Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability.However,adverse impact also accompanies the mixed cation system simultaneously.It brings the compositional instability,wherein the homogeneous film is likely to segregate into multi-phases during the fabrication and ageing process,thus resulting in the efficiency reduction of perovskite solar cells(PSCs)devices.This review focuses on the cation induced phase segregation,and elucidates the segregation mechanisms from the perspectives of film formation and ageing process,respectively.Furthermore,the influence of cation segregation on device performance and operational stability are discussed.And based on these understandings,viable strategies are proposed for the design of phase-stable mixed composition halide perovskites and for suppressing segregation to benefit its development towards commercial applications.展开更多
Hydrogen induced cracking(HIC)of 0.3% C,1% Cr,1% Mn,1% Si high strength steel has been studied under simple mode Ⅰ,mode Ⅱ and(Ⅰ+Ⅱ)mixed mode loading conditions.Af- ter being hydrogen-charged in IN H_2SO_4 solution...Hydrogen induced cracking(HIC)of 0.3% C,1% Cr,1% Mn,1% Si high strength steel has been studied under simple mode Ⅰ,mode Ⅱ and(Ⅰ+Ⅱ)mixed mode loading conditions.Af- ter being hydrogen-charged in IN H_2SO_4 solution,the material behaved hydrogen embrittlement in all the cases studied.The threshold K_(ⅡH)/K_(ⅡX) of HIC under mode Ⅱ load- ing was 0.27,which was nearly the same as that K(ⅠH)/K_(ⅠX)=0.29 under mode Ⅰ loading. While the thresholds of-HIC under(Ⅰ+Ⅱ)mixed mode loading were 0.36,0.41 and 0.37 cor- responding to the K_Ⅱ/K_Ⅰ ratio of 0.27,0.4 and O.81.The results show that simple mode Ⅰ or mode Ⅱ loading is more susceptible to hydrogen embrittlement than(Ⅰ+Ⅱ)mixed mode. For explaining the experimental results,the effects of triaxial stress as well as plastic deformation ahead of crack tip has been discussed.展开更多
Upscaling perovskite solar cell fabrication is one of the key challenges in the pathway for commercialization.The slow evaporation of frequently used solvents(DMF or DMSO) limits the fast perovskite layer crystallizat...Upscaling perovskite solar cell fabrication is one of the key challenges in the pathway for commercialization.The slow evaporation of frequently used solvents(DMF or DMSO) limits the fast perovskite layer crystallization,hindering their implementation in large scale deposition methods.Alternatively,methylamine-based precursors have demonstrated rapid crystallization,leading to uniform and specular films.Nonetheless,their application has been limited to MAPbI3 perovskites with limited efficiency and stability.In this work,we report the requirements for stabilizing α-phase of mixed cation perovskites with high amount of formamidinium by using a methylamine-based precursor.We found that even though,there are many methods for incorporating the methylamine(MA) in precursors or films;the MA content determines stabilization of the α-phase and therefore the viscous-solution route is the only method to incorporate high amounts of MA.At low amounts of MA,perovskite tend to crystallize in 1D dimensional FA_(3)(MA)PbI5 phases due to the incomplete solvation of the PbI6-clusters.In contrast,high MA ratio induces a full solvation of the clusters,leading to a rapid crystallization and a full stabilization of the active 3D α-phase.These results open a window in the development and understanding of new precursors for the fabrication of high efficient,stable and scalable perovskite devices.展开更多
Natural gas hydrate contains a specific amount of heavy hydrocarbons, such as ethane, propane, etc., aside from the primary guest gas of methane. Although the coexistence of two or even three hydrate structures has be...Natural gas hydrate contains a specific amount of heavy hydrocarbons, such as ethane, propane, etc., aside from the primary guest gas of methane. Although the coexistence of two or even three hydrate structures has been discovered at several hydrate sites, the requisite formation mechanism is still not well understood. In-situ observation of the formation process of mixed methane-propane hydrate in a confined space was conducted using confocal Raman imaging microscopy. The Raman imaging results reveal that sI methane hydrate and sII mixed methane-propane hydrate are formed and coexist in the reaction system. In the confined space, the sI hydrate originates from the dissolved gas in water, while the sII hydrate is formed from free gas. The results obtained can help explain the coexistence of sI and sII hydrates found in natural hydrate samples, as well as providing insights into a possible dynamic scenario of hydrate reservoirs in geological history.展开更多
The mixed-cation lead halide perovskites have emerged as a new class of promising light harvesting materials for solar cells. The formamidinium(FA), methylammonium(MA) and Cs cations are widely studied in the fiel...The mixed-cation lead halide perovskites have emerged as a new class of promising light harvesting materials for solar cells. The formamidinium(FA), methylammonium(MA) and Cs cations are widely studied in the field of mixed-cation perovskites. Here, we have investigated ethylammonium(EA) as an alternative cation to fabricate a mixed-cation perovskite of MA_(1-x)EA_xPbI_3. We have characterized the materials using the X-ray diffraction(XRD), scanning electron microscope(SEM), and UV–vis spectrum. Our results have confirmed the successful incorporation of EA cations into MAPbI_3. Interestingly, the optimal amount of EA to achieve the best performance is quite low. This is different from the FA–MA mixed-cation perovskites although EA and FA have similar radii. In short, the EA–MA mixed-cation perovskite has some material and device properties highly distinguishable from the FA–MA one.展开更多
Reaction of the ligand dmpt(dmpt=6,7-dimethylbenzo[f][1,10]phenanthroline)with CuCl2 afforded mixed valent Cu(Ⅰ)/Cu(Ⅱ) discrete tetranuclear complexes[Cu(Ⅱ)Cl2(dmpt)Cu(Ⅰ)Cl](1),while the reaction of ...Reaction of the ligand dmpt(dmpt=6,7-dimethylbenzo[f][1,10]phenanthroline)with CuCl2 afforded mixed valent Cu(Ⅰ)/Cu(Ⅱ) discrete tetranuclear complexes[Cu(Ⅱ)Cl2(dmpt)Cu(Ⅰ)Cl](1),while the reaction of ligand dppz(dppz = dipyrido[3,2-a:20,30-c]phenazine) with divalent halogen copper salt CuX2(X=Cl,Br) gave one-dimensional chain mixed valent Cu(Ⅰ)/Cu(Ⅱ) complexes [Cu(Ⅱ)Cl2(dppz)Cu(Ⅰ)Cl]n(2) and discrete mixed valent Cu(Ⅰ)/Cu(Ⅱ)complexes [Cu(Ⅱ)Br2(dppz)(DMF)Cu(Ⅰ)Br](3). Complex 2 consists of a one-dimensional chain-dppzC u(Ⅱ)-Clμ2-Cu(Ⅰ)-Cl-dppzC u(Ⅱ)-Clμ2-Cu(Ⅰ)-with Cu(Ⅱ) and Cu(Ⅰ) atoms linked together by chloride anion. Complex 3 is a discrete complex,which is the same as complexes 1 and 2 involving two different copper valent Cu(Ⅰ) and Cu(Ⅱ). The Cu(Ⅰ) ion presents a pseudo-trihedral geometry,while the Cu(Ⅱ) ion presents a slightly distorted square-pyramidal geometry. This fact proved that halogen ions play a vital role in the assembly procedure. Our research results demonstrate the structural diversification that can be achieved by halogen ions mediated. Moreover,halogen ions-mediated self-assembly may provide useful information for further design of compounds with novel structures and properties.展开更多
A novel mixed-valence copper (Ⅰ,Ⅱ) complex Cu3 [CH2=C(CH3) COO]5 (imH)3 (H2O)has been synthesized and characterized by XPS spectra and single crystal X-ray structural analysis.The title complex crystallized in monoc...A novel mixed-valence copper (Ⅰ,Ⅱ) complex Cu3 [CH2=C(CH3) COO]5 (imH)3 (H2O)has been synthesized and characterized by XPS spectra and single crystal X-ray structural analysis.The title complex crystallized in monoclinic space group P21/c, with α=11 .225 (3), b=13.9023 (12),c=24.559 (2), β=92.372 (10)°and Z=4. Final R=0.0495 for 5546 reflections [I>2σ (Ⅰ)].展开更多
High-performance lithium-ion batteries(LIB)are important in powering emerging technologies.Cathodes are regarded as the bottleneck of increasing battery energy density,among which layered oxides are the most promising...High-performance lithium-ion batteries(LIB)are important in powering emerging technologies.Cathodes are regarded as the bottleneck of increasing battery energy density,among which layered oxides are the most promising candidates for LIB.However,a limitation with layered oxides cathodes is the transition metal and Li site mixing,which significantly impacts battery capacity and cycling stability.Despite recent research on Li/Ni mixing,there is a lack of comprehensive understanding of the origin of cation mixing between the transition metal and Li;therefore,practical means to address it.Here,a critical review of cation mixing in layered cathodes has been provided,emphasising the understanding of cation mixing mechanisms and their impact on cathode material design.We list and compare advanced characterisation techniques to detect cation mixing in the material structure;examine methods to regulate the degree of cation mixing in layered oxides to boost battery capacity and cycling performance,and critically assess how these can be applied practically.An appraisal of future research directions,including superexchange interaction to stabilise structures and boost capacity retention has also been concluded.Findings will be of immediate benefit in the design of layered cathodes for high-performance rechargeable LIB and,therefore,of interest to researchers and manufacturers.展开更多
A closed-form solution for predicting the tangential stress of an inclusion located in mixed mode Ⅰ and Ⅱ crack tip field was developed based on the Eshelby equivalent inclusion theory. Then a mixed mode fracture cr...A closed-form solution for predicting the tangential stress of an inclusion located in mixed mode Ⅰ and Ⅱ crack tip field was developed based on the Eshelby equivalent inclusion theory. Then a mixed mode fracture criterion, including the fracture direction and the critical load, was established based on the maximum tangential stress in the inclusion for brittle inclusioninduced fracture materials. The proposed fracture criterion is a function of the inclusion fracture stress, its size and volume fraction, as well as the elastic constants of the inclusion and the matrix material. The present criterion will reduce to the conventional one as the inclusion having the same elastic behavior as the matrix material. The proposed solutions are in good agreement with detailed finite element analysis and measurement.展开更多
In order to ensure the effective analysis and reconstruction of forests,it is key to ensure the quantitative description of their spatial structure.In this paper,a distance model for the optimal stand spatial structur...In order to ensure the effective analysis and reconstruction of forests,it is key to ensure the quantitative description of their spatial structure.In this paper,a distance model for the optimal stand spatial structure based on weighted Voronoi diagrams is proposed.In particular,we provide a novel methodological model for the comprehensive evaluation of the spatial structure of forest stands in natural mixed conifer-broadleaved forests and the formulation of management decision plans.The applicability of the rank evaluation and the optimal solution distance model are compared and assessed for different standard sample plots of natural mixed conifer-broadleaved forests.The effect of crown width on the spatial structure unit of the trees is observed to be higher than that of the diameter at breast height.Moreover,the influence of crown length is greater than that of tree height.There are nine possible spatial structure units determined by the weighted Voronoi diagram for the number of neighboring trees in the central tree,with an average intersection of neighboring crowns reaching 80%.The rank rating of natural forest sample plots is correlated with the optimal solution distance model,and their results are generally consistent for natural forests.However,the rank rating is not able to provide a quantitative assessment.The optimal solution distance model is observed to be more comprehensive than traditional methods for the evaluation of the spatial structure of forest stands.It can effectively reflect the trends in realistic stand spatial structure factors close to or far from the ideal structure point,and accurately assesses the forest spatial structure.The proposed optimal solution distance model improves the integrated evaluation of the spatial structure of forest stands and provides solid theoretical and technical support for sustainable forest management.展开更多
We study the crystal structure of a triplite-structured (Li0.5Fe0.5)SO4F with full Li+/Fe2+ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li+/Li with a theor...We study the crystal structure of a triplite-structured (Li0.5Fe0.5)SO4F with full Li+/Fe2+ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li+/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li+ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO4 with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.展开更多
基金This work was supported by the Special Funds for Major State Basic Research Projects (95-12 and G1999064800).
文摘A new kind of nano-crysta cellulose (NCC) prepared from natural cotton fiber has been obtained by the method ofacid hydrolysis. Compared to most other nanophase materials that derive from inorganic materials, our products are preparedfrom natural cotton fibers. The products are of spherical shape with mixed crystal forms of cellulose I and II. The preparationconditions determine the properties of the products. Prior treatment is a critical procedure. The properties of the products arealso strongly affected by such conditions as the kinds of acids used, the ratio of the acid mixture, the acid concentration, theultrasonic agitation time and hydrolysis temperature. The number average molecular weight of NCC is determined by gelpermeation chromatography (GPC). The particle size and shape were determined by transmission electron microscopy(TEM). X-ray diffraction was used to detect the crystallinity and average crystallite size of the panicle.
文摘Mixed mode Ⅰ/Ⅱ fracture erperiments of LC4-CS aluminum alloy were conductedby using tension--shear specimens with thicknesses of 2, 4, 8 and 14mm. Fracturemechanisms of thickness effect on mixed mode Ⅰ/Ⅱ fracture were first examined fromfracture surface morphology to correlate with the macroscopic fracture behavior andstress state. It is found that specimen thickness has a strong influence on mixed modefracture. As thickness varies from thin to thick the macroscopic fracture surfacesappear the characteristics of plane stress state (2mm, 4mm--thick specimen), three--dimensional stress state (8mm--thick specimens), and plane strain state (14mm--thickspecimens), respectively. The specimens of all kinds of thicknesses are typical of ten-sile type failure under mode Ⅰ loading condition and shear type failure under mode Ⅱloading condition. Two distinct features coexist on the fracture surfaces under mixedmode loading conditions, and the corresponding proportion varies with loading mix-ity. Void--growth processes are the failure mechanism in both predominately tensile-and shears--type fractures. The size and depth of dimples on the fracture surface varygreatly with thickness. Therefore, it is extraordinary necessary to take into accountthe thickness effect when a mixed mode fracture criterion is being established.
基金National Natural Science Foundation of China(22109057,21805010,21975028,52172182,22011540377,22005035)Beijing Municipal Science and Technology Project(Z181100005118002)+2 种基金Beijing Municipal Natural Science Foundation(JQ19008)the China Postdoctoral Science Foundation(Grant No.2020TQ0043,2020M680012)Research Foundation of Jiangxi Educational Committee(GJJ200836).
文摘Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability.However,adverse impact also accompanies the mixed cation system simultaneously.It brings the compositional instability,wherein the homogeneous film is likely to segregate into multi-phases during the fabrication and ageing process,thus resulting in the efficiency reduction of perovskite solar cells(PSCs)devices.This review focuses on the cation induced phase segregation,and elucidates the segregation mechanisms from the perspectives of film formation and ageing process,respectively.Furthermore,the influence of cation segregation on device performance and operational stability are discussed.And based on these understandings,viable strategies are proposed for the design of phase-stable mixed composition halide perovskites and for suppressing segregation to benefit its development towards commercial applications.
文摘Hydrogen induced cracking(HIC)of 0.3% C,1% Cr,1% Mn,1% Si high strength steel has been studied under simple mode Ⅰ,mode Ⅱ and(Ⅰ+Ⅱ)mixed mode loading conditions.Af- ter being hydrogen-charged in IN H_2SO_4 solution,the material behaved hydrogen embrittlement in all the cases studied.The threshold K_(ⅡH)/K_(ⅡX) of HIC under mode Ⅱ load- ing was 0.27,which was nearly the same as that K(ⅠH)/K_(ⅠX)=0.29 under mode Ⅰ loading. While the thresholds of-HIC under(Ⅰ+Ⅱ)mixed mode loading were 0.36,0.41 and 0.37 cor- responding to the K_Ⅱ/K_Ⅰ ratio of 0.27,0.4 and O.81.The results show that simple mode Ⅰ or mode Ⅱ loading is more susceptible to hydrogen embrittlement than(Ⅰ+Ⅱ)mixed mode. For explaining the experimental results,the effects of triaxial stress as well as plastic deformation ahead of crack tip has been discussed.
基金financial support provided by the committee for the development of research(CODI) of the Universidad de Antioquia,in the framework of the project 2017-16000the financial support of the Colombia Scientific Program within the framework of the call Ecosistema Cientifíco(Contract FP44842-218-2018)。
文摘Upscaling perovskite solar cell fabrication is one of the key challenges in the pathway for commercialization.The slow evaporation of frequently used solvents(DMF or DMSO) limits the fast perovskite layer crystallization,hindering their implementation in large scale deposition methods.Alternatively,methylamine-based precursors have demonstrated rapid crystallization,leading to uniform and specular films.Nonetheless,their application has been limited to MAPbI3 perovskites with limited efficiency and stability.In this work,we report the requirements for stabilizing α-phase of mixed cation perovskites with high amount of formamidinium by using a methylamine-based precursor.We found that even though,there are many methods for incorporating the methylamine(MA) in precursors or films;the MA content determines stabilization of the α-phase and therefore the viscous-solution route is the only method to incorporate high amounts of MA.At low amounts of MA,perovskite tend to crystallize in 1D dimensional FA_(3)(MA)PbI5 phases due to the incomplete solvation of the PbI6-clusters.In contrast,high MA ratio induces a full solvation of the clusters,leading to a rapid crystallization and a full stabilization of the active 3D α-phase.These results open a window in the development and understanding of new precursors for the fabrication of high efficient,stable and scalable perovskite devices.
基金funded by a grant from the China Geological Survey(Grant No.DD20221703)。
文摘Natural gas hydrate contains a specific amount of heavy hydrocarbons, such as ethane, propane, etc., aside from the primary guest gas of methane. Although the coexistence of two or even three hydrate structures has been discovered at several hydrate sites, the requisite formation mechanism is still not well understood. In-situ observation of the formation process of mixed methane-propane hydrate in a confined space was conducted using confocal Raman imaging microscopy. The Raman imaging results reveal that sI methane hydrate and sII mixed methane-propane hydrate are formed and coexist in the reaction system. In the confined space, the sI hydrate originates from the dissolved gas in water, while the sII hydrate is formed from free gas. The results obtained can help explain the coexistence of sI and sII hydrates found in natural hydrate samples, as well as providing insights into a possible dynamic scenario of hydrate reservoirs in geological history.
基金the support of the NSFC(Grant 51372151 and21303103)Huoyingdong Grant(151046)
文摘The mixed-cation lead halide perovskites have emerged as a new class of promising light harvesting materials for solar cells. The formamidinium(FA), methylammonium(MA) and Cs cations are widely studied in the field of mixed-cation perovskites. Here, we have investigated ethylammonium(EA) as an alternative cation to fabricate a mixed-cation perovskite of MA_(1-x)EA_xPbI_3. We have characterized the materials using the X-ray diffraction(XRD), scanning electron microscope(SEM), and UV–vis spectrum. Our results have confirmed the successful incorporation of EA cations into MAPbI_3. Interestingly, the optimal amount of EA to achieve the best performance is quite low. This is different from the FA–MA mixed-cation perovskites although EA and FA have similar radii. In short, the EA–MA mixed-cation perovskite has some material and device properties highly distinguishable from the FA–MA one.
基金Supported by the Science and Technology Planning Project of Shengli College China University of Petroleum(No.13070316)
文摘Reaction of the ligand dmpt(dmpt=6,7-dimethylbenzo[f][1,10]phenanthroline)with CuCl2 afforded mixed valent Cu(Ⅰ)/Cu(Ⅱ) discrete tetranuclear complexes[Cu(Ⅱ)Cl2(dmpt)Cu(Ⅰ)Cl](1),while the reaction of ligand dppz(dppz = dipyrido[3,2-a:20,30-c]phenazine) with divalent halogen copper salt CuX2(X=Cl,Br) gave one-dimensional chain mixed valent Cu(Ⅰ)/Cu(Ⅱ) complexes [Cu(Ⅱ)Cl2(dppz)Cu(Ⅰ)Cl]n(2) and discrete mixed valent Cu(Ⅰ)/Cu(Ⅱ)complexes [Cu(Ⅱ)Br2(dppz)(DMF)Cu(Ⅰ)Br](3). Complex 2 consists of a one-dimensional chain-dppzC u(Ⅱ)-Clμ2-Cu(Ⅰ)-Cl-dppzC u(Ⅱ)-Clμ2-Cu(Ⅰ)-with Cu(Ⅱ) and Cu(Ⅰ) atoms linked together by chloride anion. Complex 3 is a discrete complex,which is the same as complexes 1 and 2 involving two different copper valent Cu(Ⅰ) and Cu(Ⅱ). The Cu(Ⅰ) ion presents a pseudo-trihedral geometry,while the Cu(Ⅱ) ion presents a slightly distorted square-pyramidal geometry. This fact proved that halogen ions play a vital role in the assembly procedure. Our research results demonstrate the structural diversification that can be achieved by halogen ions mediated. Moreover,halogen ions-mediated self-assembly may provide useful information for further design of compounds with novel structures and properties.
文摘A novel mixed-valence copper (Ⅰ,Ⅱ) complex Cu3 [CH2=C(CH3) COO]5 (imH)3 (H2O)has been synthesized and characterized by XPS spectra and single crystal X-ray structural analysis.The title complex crystallized in monoclinic space group P21/c, with α=11 .225 (3), b=13.9023 (12),c=24.559 (2), β=92.372 (10)°and Z=4. Final R=0.0495 for 5546 reflections [I>2σ (Ⅰ)].
基金the Australian Institute of Nuclear Science and Engineering (AINSE) Limited for providing financial assistance in the form of a Post Graduate Research Award (PGRA) to carry out this worksupported by the Australian Research Council under grants DP200101862, DP210101486, and FL210100050
文摘High-performance lithium-ion batteries(LIB)are important in powering emerging technologies.Cathodes are regarded as the bottleneck of increasing battery energy density,among which layered oxides are the most promising candidates for LIB.However,a limitation with layered oxides cathodes is the transition metal and Li site mixing,which significantly impacts battery capacity and cycling stability.Despite recent research on Li/Ni mixing,there is a lack of comprehensive understanding of the origin of cation mixing between the transition metal and Li;therefore,practical means to address it.Here,a critical review of cation mixing in layered cathodes has been provided,emphasising the understanding of cation mixing mechanisms and their impact on cathode material design.We list and compare advanced characterisation techniques to detect cation mixing in the material structure;examine methods to regulate the degree of cation mixing in layered oxides to boost battery capacity and cycling performance,and critically assess how these can be applied practically.An appraisal of future research directions,including superexchange interaction to stabilise structures and boost capacity retention has also been concluded.Findings will be of immediate benefit in the design of layered cathodes for high-performance rechargeable LIB and,therefore,of interest to researchers and manufacturers.
基金Project supported by the National Basic Research Program of China (No. 2004CB619303).
文摘A closed-form solution for predicting the tangential stress of an inclusion located in mixed mode Ⅰ and Ⅱ crack tip field was developed based on the Eshelby equivalent inclusion theory. Then a mixed mode fracture criterion, including the fracture direction and the critical load, was established based on the maximum tangential stress in the inclusion for brittle inclusioninduced fracture materials. The proposed fracture criterion is a function of the inclusion fracture stress, its size and volume fraction, as well as the elastic constants of the inclusion and the matrix material. The present criterion will reduce to the conventional one as the inclusion having the same elastic behavior as the matrix material. The proposed solutions are in good agreement with detailed finite element analysis and measurement.
基金funded by National Key Research and development project(2022YFD2201001)。
文摘In order to ensure the effective analysis and reconstruction of forests,it is key to ensure the quantitative description of their spatial structure.In this paper,a distance model for the optimal stand spatial structure based on weighted Voronoi diagrams is proposed.In particular,we provide a novel methodological model for the comprehensive evaluation of the spatial structure of forest stands in natural mixed conifer-broadleaved forests and the formulation of management decision plans.The applicability of the rank evaluation and the optimal solution distance model are compared and assessed for different standard sample plots of natural mixed conifer-broadleaved forests.The effect of crown width on the spatial structure unit of the trees is observed to be higher than that of the diameter at breast height.Moreover,the influence of crown length is greater than that of tree height.There are nine possible spatial structure units determined by the weighted Voronoi diagram for the number of neighboring trees in the central tree,with an average intersection of neighboring crowns reaching 80%.The rank rating of natural forest sample plots is correlated with the optimal solution distance model,and their results are generally consistent for natural forests.However,the rank rating is not able to provide a quantitative assessment.The optimal solution distance model is observed to be more comprehensive than traditional methods for the evaluation of the spatial structure of forest stands.It can effectively reflect the trends in realistic stand spatial structure factors close to or far from the ideal structure point,and accurately assesses the forest spatial structure.The proposed optimal solution distance model improves the integrated evaluation of the spatial structure of forest stands and provides solid theoretical and technical support for sustainable forest management.
基金supported by the National High Technology Research and Development Program of China (Grant No. 2009AA033101)
文摘We study the crystal structure of a triplite-structured (Li0.5Fe0.5)SO4F with full Li+/Fe2+ mixing. This promising polyanion cathode material for lithium-ion batteries operates at 3.9 V versus Li+/Li with a theoretical capacity of 151 mAh/g. Its unique cation mixing structure does not block the Li+ diffusion and results in a small lattice volume change during the charge/discharge process. The calculations show that it has a three-dimensional network for Li-ion migration with an activation energy ranging from 0.53 eV to 0.68 eV, which is comparable with that in LiFePO4 with only one-dimensional channels. This work suggests that further exploring cathode materials with full cation mixing for Li-ion batteries will be valuable.