Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_(2) has been surface-modified by the lithium-ion conductor Li_(1.4)Al_(0.4)Ti_(1.6)(PO4)_(3) via a facile mechanical fusion method.The annealing temperature during coating process shows a...Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_(2) has been surface-modified by the lithium-ion conductor Li_(1.4)Al_(0.4)Ti_(1.6)(PO4)_(3) via a facile mechanical fusion method.The annealing temperature during coating process shows a strong impact on the surface morphology and chemical composition of Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_(2).The 600-℃ annealed material exhibits the best cyclic stability at high charging cut-off voltage of 4.5 V(versus Li^(+)/Li)with the capacity retention of 90.9%after 100 cycles,which is much higher than that of bare material(79%).Moreover,the rate capability and thermal stability are also improved by Li_(1.4)Al_(0.4)Ti_(1.6)(PO_(4))_(3) coating.The enhanced performance can be attributed to the improved stability of interface between Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_(2) and electrolyte by Li_(1.4)Al_(0.4)Ti_(1.6)(PO_(4))_(3) modification.The results of this work provide a possible method to design reliable cathode materials to achieve high energy density and long cycle life.展开更多
The study of how to “control forming and performance” during the thermal deformation of metal materials has always been a central theme in academic research, particularly in addressing the processing challenges asso...The study of how to “control forming and performance” during the thermal deformation of metal materials has always been a central theme in academic research, particularly in addressing the processing challenges associated with difficult-to-form alloys that possess unique functionalities. However, neither the currently commonly used phenomenological constitutive model, physical constitutive model, Dynamic Material Model (DMM) thermal processing theoretical model, and Ruano-Wadsworth-Sherby (R-W-S) deformation mechanism map model incorporating dislocation density nor the reported machine learning method has established a universal model that can achieve a quantitative description of the process-microstructure-formability of thermal processing. It is only possible first to use modeling research to obtain the law of thermal deformation behavior of alloys and then use the results of microscopic characterization to verify the theory. The research methods lack the characteristics of diagnosis and prediction optimization. This study proposes a machine learning framework for optimizing the random forest (RF) model based on a multivariate decision tree, including microstructure images and hot working process parameter information. It predicts the critical performance parameters, energy dissipation behavior, optimal processing window, and softening mechanism of ternary shape memory alloy Ni_(47)Ti_(33)Hf_(20) in the hot working process. This model has a certain universality. It enables coupled analysis of image information and process parameter data and introduces the calculation and ranking of feature importance, reflecting the applicability of feature values in model construction. Finally, the visualization technique Grad-CAM describes the correlation between the input microscopic image and the output, generating critical hotspots in the heat map. The model of accuracy in predicting the power dissipation rate is confirmed by the grain misorientation angles, thus realizing the establishment of a mechanism-driven model based on the evolution of critical microscopic structures during the thermal deformation of the alloy, which dramatically improves the interpretability of the machine learning model. This machine learning framework provides valuable guidance for quantitatively predicting the thermal deformation processing-microstructure-formability relationship of the Ni_(47)Ti_(33)Hf_(20) shape memory alloy and can potentially be applied to other alloys.展开更多
Hot compression tests were conducted on a Gleeble-1500D thermal simulating tester. Based on the deformation behavior and microstructural evolution of superalloy GH4742, different types of instability criteria of Prasa...Hot compression tests were conducted on a Gleeble-1500D thermal simulating tester. Based on the deformation behavior and microstructural evolution of superalloy GH4742, different types of instability criteria of Prasad, Gegel, Malas, Murty and Semiatin were compared, and the physical significance of parameters was analyzed. Meanwhile, the processing maps with different instability criteria were obtained. It was shown that instability did not occur when average power dissipation rate was larger than 50% in the temperature range of 1020- 1130℃, corresponding to the strain rate range of 5 × 10-4-3.2 × 10-3 s-1. The domain is appropriate for the processing deformation of superalloy GH4742.展开更多
Silicon monoxide(SiO)has been considered as one of the most promising anode materials for next generation highenergy-density Li-ion batteries(LiBs)thanks to its high theoretical capacity.However,the poor intrinsic ele...Silicon monoxide(SiO)has been considered as one of the most promising anode materials for next generation highenergy-density Li-ion batteries(LiBs)thanks to its high theoretical capacity.However,the poor intrinsic electronic conductivity and large volume change during lithium intercalation/de-intercalation restrict its practical applications.Fabrication of SiO/C composites is an effective way to overcome these problems.Herein,a series of micro-sized SiO@C/graphite(Si0@C/G)composite anode materials,with designed capacity of 600 mAh·g-1,are successfully prepared through a pitch pyrolysis reaction method.The electrochemical performance of SiO@C/G composite anodes with different carbon coating contents of 5 wt%,10 wt%,15 wt%,and 35 wt%is investigated.The results show that the SiO@C/G composite with15-wt%carbon coating content exhibits the best cycle performance,with a high capacity retention of 90.7%at 25℃and90.1%at 450 C after 100 cycles in full cells with LiNi0.5Co0.2Mn0.3O2 as cathodes.The scanning electron microscope(SEM)and electrochemistry impedance spectroscopy(EIS)results suggest that a moderate carbon coating layer can promote the formation of stable SEI film,which is favorable for maintaining good interfacial conductivity and thus enhancing the cycling stability of SiO electrode.展开更多
The oxidation behavior of the Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy at 900℃ was investigated at different oxidation times(5,20,60 and 100 h).The results show that the total weight gain of the alloy after 100 h at 900℃ ox...The oxidation behavior of the Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy at 900℃ was investigated at different oxidation times(5,20,60 and 100 h).The results show that the total weight gain of the alloy after 100 h at 900℃ oxidation is 9.1 g·m^(-2),and the oxidation rate decreases with oxidation time.The oxides on the alloy surface are mainly TiO_(2) and Al_(2)O_(3).At the beginning of oxidation(5 h),the oxide film is relatively complete,thin,and the interface between the oxide layer and the matrix is virtually flat.At the end of oxidation(100 h),the thickness of the oxide film is expanded,cracking and spalling occur,and the spalling form is intra-film spalling.At the same time,oxygen is mainly distributed in the oxide film and the oxygen content in the alloy substrate is reduced,confirming that the TiAl alloy has a certain oxidation stability at 900℃.From the outer surface of the oxide layer to the matrix,the TiO_(2) content increases and the Al_(2)O_(3) content decreases.Oxidation proceeds to completion in this system via the dissolution and diffusion of O atom.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2017YFB0102004)the National Natural Science Foundation of China(Grant No.51822211)the State Grid Technology Project,China(Grant No.DG71-17-010)
文摘Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_(2) has been surface-modified by the lithium-ion conductor Li_(1.4)Al_(0.4)Ti_(1.6)(PO4)_(3) via a facile mechanical fusion method.The annealing temperature during coating process shows a strong impact on the surface morphology and chemical composition of Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_(2).The 600-℃ annealed material exhibits the best cyclic stability at high charging cut-off voltage of 4.5 V(versus Li^(+)/Li)with the capacity retention of 90.9%after 100 cycles,which is much higher than that of bare material(79%).Moreover,the rate capability and thermal stability are also improved by Li_(1.4)Al_(0.4)Ti_(1.6)(PO_(4))_(3) coating.The enhanced performance can be attributed to the improved stability of interface between Li(Ni_(0.6)Co_(0.2)Mn_(0.2))O_(2) and electrolyte by Li_(1.4)Al_(0.4)Ti_(1.6)(PO_(4))_(3) modification.The results of this work provide a possible method to design reliable cathode materials to achieve high energy density and long cycle life.
文摘The study of how to “control forming and performance” during the thermal deformation of metal materials has always been a central theme in academic research, particularly in addressing the processing challenges associated with difficult-to-form alloys that possess unique functionalities. However, neither the currently commonly used phenomenological constitutive model, physical constitutive model, Dynamic Material Model (DMM) thermal processing theoretical model, and Ruano-Wadsworth-Sherby (R-W-S) deformation mechanism map model incorporating dislocation density nor the reported machine learning method has established a universal model that can achieve a quantitative description of the process-microstructure-formability of thermal processing. It is only possible first to use modeling research to obtain the law of thermal deformation behavior of alloys and then use the results of microscopic characterization to verify the theory. The research methods lack the characteristics of diagnosis and prediction optimization. This study proposes a machine learning framework for optimizing the random forest (RF) model based on a multivariate decision tree, including microstructure images and hot working process parameter information. It predicts the critical performance parameters, energy dissipation behavior, optimal processing window, and softening mechanism of ternary shape memory alloy Ni_(47)Ti_(33)Hf_(20) in the hot working process. This model has a certain universality. It enables coupled analysis of image information and process parameter data and introduces the calculation and ranking of feature importance, reflecting the applicability of feature values in model construction. Finally, the visualization technique Grad-CAM describes the correlation between the input microscopic image and the output, generating critical hotspots in the heat map. The model of accuracy in predicting the power dissipation rate is confirmed by the grain misorientation angles, thus realizing the establishment of a mechanism-driven model based on the evolution of critical microscopic structures during the thermal deformation of the alloy, which dramatically improves the interpretability of the machine learning model. This machine learning framework provides valuable guidance for quantitatively predicting the thermal deformation processing-microstructure-formability relationship of the Ni_(47)Ti_(33)Hf_(20) shape memory alloy and can potentially be applied to other alloys.
基金supported by the National Key Basic Research Program of China (No. 2010CB631203)
文摘Hot compression tests were conducted on a Gleeble-1500D thermal simulating tester. Based on the deformation behavior and microstructural evolution of superalloy GH4742, different types of instability criteria of Prasad, Gegel, Malas, Murty and Semiatin were compared, and the physical significance of parameters was analyzed. Meanwhile, the processing maps with different instability criteria were obtained. It was shown that instability did not occur when average power dissipation rate was larger than 50% in the temperature range of 1020- 1130℃, corresponding to the strain rate range of 5 × 10-4-3.2 × 10-3 s-1. The domain is appropriate for the processing deformation of superalloy GH4742.
基金Project supported by the State Grid Technology Project,China(study on the mechanism and characterization of lithium dendrite growth in lithium ion batteries,Project No.DG71-17-010)the National Key Research and Development Program of China(Grant No.2017YFB0102004)the National Natural Science Foundation of China(Grant No.51822211)
文摘Silicon monoxide(SiO)has been considered as one of the most promising anode materials for next generation highenergy-density Li-ion batteries(LiBs)thanks to its high theoretical capacity.However,the poor intrinsic electronic conductivity and large volume change during lithium intercalation/de-intercalation restrict its practical applications.Fabrication of SiO/C composites is an effective way to overcome these problems.Herein,a series of micro-sized SiO@C/graphite(Si0@C/G)composite anode materials,with designed capacity of 600 mAh·g-1,are successfully prepared through a pitch pyrolysis reaction method.The electrochemical performance of SiO@C/G composite anodes with different carbon coating contents of 5 wt%,10 wt%,15 wt%,and 35 wt%is investigated.The results show that the SiO@C/G composite with15-wt%carbon coating content exhibits the best cycle performance,with a high capacity retention of 90.7%at 25℃and90.1%at 450 C after 100 cycles in full cells with LiNi0.5Co0.2Mn0.3O2 as cathodes.The scanning electron microscope(SEM)and electrochemistry impedance spectroscopy(EIS)results suggest that a moderate carbon coating layer can promote the formation of stable SEI film,which is favorable for maintaining good interfacial conductivity and thus enhancing the cycling stability of SiO electrode.
基金financially supported by the National Natural Science Foundation of China (51805335)
文摘The oxidation behavior of the Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy at 900℃ was investigated at different oxidation times(5,20,60 and 100 h).The results show that the total weight gain of the alloy after 100 h at 900℃ oxidation is 9.1 g·m^(-2),and the oxidation rate decreases with oxidation time.The oxides on the alloy surface are mainly TiO_(2) and Al_(2)O_(3).At the beginning of oxidation(5 h),the oxide film is relatively complete,thin,and the interface between the oxide layer and the matrix is virtually flat.At the end of oxidation(100 h),the thickness of the oxide film is expanded,cracking and spalling occur,and the spalling form is intra-film spalling.At the same time,oxygen is mainly distributed in the oxide film and the oxygen content in the alloy substrate is reduced,confirming that the TiAl alloy has a certain oxidation stability at 900℃.From the outer surface of the oxide layer to the matrix,the TiO_(2) content increases and the Al_(2)O_(3) content decreases.Oxidation proceeds to completion in this system via the dissolution and diffusion of O atom.
