The rapid development of the information era has led to in-creased power consumption,which generates more heat.This requires more efficient thermal management systems,with the most direct ap-proach being the developme...The rapid development of the information era has led to in-creased power consumption,which generates more heat.This requires more efficient thermal management systems,with the most direct ap-proach being the development of su-perior thermal interface materials(TIMs).Mesocarbon microbeads(MCMBs)have several desirable properties for this purpose,includ-ing high thermal conductivity and excellent thermal stability.Although their thermal conductivity(K)may not be exceptional among all carbon materials,their ease of production and low cost make them ideal filler materials for developing a new generation of carbon-based TIMs.We report the fabrication of high-performance TIMs by incorporating MCMBs in a polyimide(PI)framework,producing highly graphitized PI/MCMB(PM)foams and anisotropic polydimethylsiloxane/PM(PDMS/PM)composites with a high thermal conductivity using directional freezing and high-temperature thermal annealing.The resulting materials had a high through-plane(TP)K of 15.926 W·m^(−1)·K^(−1),4.83 times that of conventional thermally conductive silicone pads and 88.5 times higher than that of pure PDMS.The composites had excellent mechanical properties and thermal stability,meeting the de-mands of modern electronic products for integration,multi-functionality,and miniaturization.展开更多
Bimetallic Ni–Co sulfides are outstanding pseudocapacitive materials with high electrochemical activity and excellent energy storage performance as electrodes for high-performance supercapacitors.In this study,a nove...Bimetallic Ni–Co sulfides are outstanding pseudocapacitive materials with high electrochemical activity and excellent energy storage performance as electrodes for high-performance supercapacitors.In this study,a novel urchin-like NiCo2S4@mesocarbon microbead(NCS@MCMB) composite with a core–shell structure was prepared by a facile two-step hydrothermal method.The highly conductive MCMBs offered abundant adsorption sites for the growth of NCS nanoneedles,which allowed each nanoneedle to fully unfold without aggregation,resulting in improved NCS utilization and efficient electron/ion transferin the electrolyte.When applied as an electrode material for supercapacitors,the composite exhibited a maximum specific capacitance of 936 Fg-1 at 1 Ag-1 and a capacitance retention of 94% after 3000 cycles at 5 Ag-1,because of the synergistic effect of MCMB and NCS.Moreover,we fabricated an asymmetric supercapacitor based on the NCS@MCMB composite,which exhibited enlarged voltage windows and could power a light-emitting diode device for several minutes,further demonstrating the exceptional electrochemical performance of the NCS@MCMB composite.展开更多
DCLR-P was prepared by direct coal liquefaction residue (DCLR) with ash removal.In the present experiments,mesocarbon microbeads (MCMBs) were prepared by co-carbonization of coal tar pitch (CTP) and DCLR-P.With the in...DCLR-P was prepared by direct coal liquefaction residue (DCLR) with ash removal.In the present experiments,mesocarbon microbeads (MCMBs) were prepared by co-carbonization of coal tar pitch (CTP) and DCLR-P.With the increase of DCLR-P content,the yield of MCMBs increased from 47.8% to 56.8%.At the same time,the particle sizes distribution of MCMBs was narrowed,resulting in the decrease of D9o/D10 ratio from 154.88 to 6.53.The results showed that DCLR-P had a positive effect on the preparation of MCMBs.1H-NMR,FTIR,SEM and XRD were used to analyze the mechanisms and characteristics of MCMBs prepared by co-carbonization of CTP and DCLR-P.The results showed that the Proton Donor Quality Index (PDQI) of DCLR-P was 13.32,significantly higher than that of CTP (0.83).This indicated that DCLR-P had more naphthenic structure than CTP,which leads to hydrogen transferring in polycondensation reaction.The aliphatic structure of DCLR-P can improve the solubility and fusibility of mesophase,thereby making the structure of MCMBs more structured.The microstructure of the graphitized MCMBs had a substantially parallel carbon layer useful for its electrical performance.The performance of graphitized MCMBs as a negative electrode material for Li-ion batteries was tested.The particle sizes,tap density,specific surface area and initial charge-discharge efficiency of graphitized MCMBs met the requirements of CMB-I in GB/T-24533-2009.However,the initial discharge capacity of graphitized MCMB was only 296.3 mA h g-1 due to the low degree of graphitization of MCMBs.展开更多
The practical application of silica-based composites as an alternative to commercial graphite anode materials is hampered by their large volumetric expansion,poor conductivity,and low Coulombic efficiency.In this work...The practical application of silica-based composites as an alternative to commercial graphite anode materials is hampered by their large volumetric expansion,poor conductivity,and low Coulombic efficiency.In this work,a novel silica/oxidized mesocarbon microbead/amorphous carbon(SiO2/O’MCMB/C)hierarchical structure in which SiO2 is sandwiched between spherical graphite and amorphous carbon shell was succes sfully fabricated through hydrogen bonding-assisted self-assembly and post-carbon coating method.The obtained three-layer hierarchical structure effectively accommodates the volumetric expansion of SiO2 and significantly enhances the electronic conductivity of composite materials.Moreover,the outer layer of amorphous carbon effectively increases the diffusion rate of lithium ions and promotes the formation of stable SEI film.As a result,the SiO2/O’MCMB/C composite exhibits superior electrochemical performance with a reversible capacity of 459.5 mA h/g in the first cycle,and the corresponding Coulombic efficiency is 62.8%.After 300 cycles,the capacity climbs to around 600 mA h/g.This synthetic route provides an efficient method for preparing SiO2 supported on graphite with excellent electrochemical performance,which is likely to promote its commercial applications.展开更多
Dual-ion batteries(DIBs)have attracted tremendous attention owing to their high operating voltage and are considered promising candidates for low-cost clean energy storage devices.However,the decomposition of electrol...Dual-ion batteries(DIBs)have attracted tremendous attention owing to their high operating voltage and are considered promising candidates for low-cost clean energy storage devices.However,the decomposition of electrolytes and collapse of the cathode structure may lead to low Coulombic efficiency(CE)and low cycling stability of DIBs.Wide-layered electrode materials can accommodate the intercalation/deintercalation of large anions,which is believed to overcome these issues.Herein,expanded mesocarbon microbeads(200HRO-MCMB)possessing an enlarged interlayer spacing(0.405 nm)were prepared via modified Hummers and subcritical hydrothermal reduction methods.After the indispensable electrochemical activation,200HRO-MCMB(hydrothermal reduction at 200℃)exhibited a high specific capacity(120 mAh·g^(-1)at50 mA·g^(-1))when used as a cathode for a sodium-based DIB,and the CE significantly improved within the 2.0-4.5 V voltage range.Additionally,the cycling stability exceeded over 600 cycles.Remarkably,this cathode possessed enlarged interlayers that decreased the barrier of PF6^(-)transport,and the battery storage mechanism corresponded to a transitioning state between double-layer capacitance and Faradaic intercalation.Undoubtedly,this work will expand the scope of the practical application of low-cost sodium-based DIBs.展开更多
The graphene/mesocarbon microbead(MCMB)composite is assessed as an anode material with a high capacity for lithium-ion batteries.The composite electrode exhibits improved cycling stability and rate capability,deliveri...The graphene/mesocarbon microbead(MCMB)composite is assessed as an anode material with a high capacity for lithium-ion batteries.The composite electrode exhibits improved cycling stability and rate capability,delivering a high initial charge/discharge capacity of 421.4 mA·h/g/494.8 mA·h/g as well as an excellent capacity retention over 500 cycles at a current density of 40 mA/g.At a higher current density of 800 mA/g,the electrode still retains 35%of its initial capacity which exceeds the capacity retention of pure graphene or MCMB reference electrodes.Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the composite electrode favors electrochemical kinetics as compared with graphene and MCMB separately.Superior electrochemical properties suggest a strong synergetic effect between highly conductive graphene and MCMB.展开更多
In situ prepared mesocarbon microbead/carbon nanotube(MCMB/CNT) composites are potential precursors of high density carbon materials for various applications. Integrated MCMB/CNT composites were successfully fabricate...In situ prepared mesocarbon microbead/carbon nanotube(MCMB/CNT) composites are potential precursors of high density carbon materials for various applications. Integrated MCMB/CNT composites were successfully fabricated by hot-press sintering at 550 ℃ under 30 MPa. After further calcination at 900 ℃, the hot-press sintering fabricated MCMB block has an apparent density of 1.77 g/cm3 and the open porosity 5.1%. With the addition of 5%(mass fraction) CNTs, the density of the composite block is elevated to 1.84 g/cm3, and its open porosity is reduced to 3.5%. The flexural strength of composite block with 5% CNTs is elevated to 116 MPa. Through the hot-press sintering, pores of 10-50 nm in the calcinated bulks are remarkably eliminated. The interstice between microbeads in the composite blocks is filled up by CNTs together with β-resin and quinoline-insoluble spheres, which can further contribute to the densification.展开更多
Mesocarbon microbeads (MCMB) with narrow size distribution, excellent sphericity and no obvious conglu-tination have been prepared with a coal tar pitch containing quinoline insolubles (QI) as the raw material. Optica...Mesocarbon microbeads (MCMB) with narrow size distribution, excellent sphericity and no obvious conglu-tination have been prepared with a coal tar pitch containing quinoline insolubles (QI) as the raw material. Optical mi-croscopy and scanning electron microscopy (SEM) are used to examine the structure of the MCMB. It has been found that SEM technique shows the structural information of MCMB clearly in the form of micrographs even when the structure of MCMB is complex, while the optical technique is useful for analysis of the regular structure of the mesophase spheres but cannot be effectively used to analyze either the complex structure of the green MCMB or the structures of the further heat-treated ones at different temperatures. Ac-cording to the characteristics of the carbon layers, the struc-tures of the as-prepared MCMB in the present experiment could be classified as (1) Parallel Layer type structure and (2) Bent Layer type structure with the carbon layers gathering at one or two points in the MCMB. In the experiments, SEM is also utilized to investigate the structures of MCMB that are heat-treated at different temperatures. It has been found that the MCMB without any further heat-treatment show no layered-carbons, while the ones heat-treated at temperature higher than 1000℃ exhibit obvious layered carbons across their sections. When increasing the heat-treatment tempera-ture, the carbon layers become thinner and flatter.展开更多
The influence of nitrogen-containing polycyclic aromatic hydrocarbons(NC-PAH)on the formation of carbonaceous mesophase remains enigmatic,despite extensive research on the production of carbonaceous materials from aro...The influence of nitrogen-containing polycyclic aromatic hydrocarbons(NC-PAH)on the formation of carbonaceous mesophase remains enigmatic,despite extensive research on the production of carbonaceous materials from aromatic-rich oils.Molecular dynamics simulation was used to investigate the variations in pyrolysis behavior between PAH and NC-PAH based on the composition analysis.Through adjusting the content of NC-PAH,the influence of NC-PAH on the thermal stability of slurry oils(SOs)was evaluated by thermogravimetry,viscosity,coke value,and quinoline insoluble(QI).The morphology and structure of mesocarbon microbeads(MCMBs)prepared with SOs were measured by a polarized-light microscope,SEM,XRD,and Raman.Simulation results indicate that NC-PAH possesses much higher reactivity and tends to produce highly condensed solid and coke products.It corresponds to the QI and high viscosity in thermal stability experiments.Therefore,high concentrations of NC-PAH result in nonuniform morphology and disordered structures.In a system with low viscosity and few QIs,SO,which has a low nitrogen content(475 ppm),reacts gently to produce MCMBs with a uniform particle size(10-40μm)and an excellent spherical shape.As NC-PAH content decreases,the crystalline size of graphitization elevates,as evidenced by parallel layers(10.472-11.764)and stack height(3.269-3.701 nm).The graphitization degree becomes worse and nonuniform with the increase of the content of NC-PAH,and the best is 20.58%evaluated by Raman spectra area ratio(AG/Aall).Overall,this work suggests a nitrogen content reference and a controlling technology of nitrogen for the preparation of superior MCMB.展开更多
文摘The rapid development of the information era has led to in-creased power consumption,which generates more heat.This requires more efficient thermal management systems,with the most direct ap-proach being the development of su-perior thermal interface materials(TIMs).Mesocarbon microbeads(MCMBs)have several desirable properties for this purpose,includ-ing high thermal conductivity and excellent thermal stability.Although their thermal conductivity(K)may not be exceptional among all carbon materials,their ease of production and low cost make them ideal filler materials for developing a new generation of carbon-based TIMs.We report the fabrication of high-performance TIMs by incorporating MCMBs in a polyimide(PI)framework,producing highly graphitized PI/MCMB(PM)foams and anisotropic polydimethylsiloxane/PM(PDMS/PM)composites with a high thermal conductivity using directional freezing and high-temperature thermal annealing.The resulting materials had a high through-plane(TP)K of 15.926 W·m^(−1)·K^(−1),4.83 times that of conventional thermally conductive silicone pads and 88.5 times higher than that of pure PDMS.The composites had excellent mechanical properties and thermal stability,meeting the de-mands of modern electronic products for integration,multi-functionality,and miniaturization.
基金jointly supported by the National Natural Science Foundations of China(No.51572246)the Fundamental Research Funds for the Central Universities(Nos.2652017401 and 2652015425)
文摘Bimetallic Ni–Co sulfides are outstanding pseudocapacitive materials with high electrochemical activity and excellent energy storage performance as electrodes for high-performance supercapacitors.In this study,a novel urchin-like NiCo2S4@mesocarbon microbead(NCS@MCMB) composite with a core–shell structure was prepared by a facile two-step hydrothermal method.The highly conductive MCMBs offered abundant adsorption sites for the growth of NCS nanoneedles,which allowed each nanoneedle to fully unfold without aggregation,resulting in improved NCS utilization and efficient electron/ion transferin the electrolyte.When applied as an electrode material for supercapacitors,the composite exhibited a maximum specific capacitance of 936 Fg-1 at 1 Ag-1 and a capacitance retention of 94% after 3000 cycles at 5 Ag-1,because of the synergistic effect of MCMB and NCS.Moreover,we fabricated an asymmetric supercapacitor based on the NCS@MCMB composite,which exhibited enlarged voltage windows and could power a light-emitting diode device for several minutes,further demonstrating the exceptional electrochemical performance of the NCS@MCMB composite.
基金Supported by National Key Research and Development Program of China(2018YFB0604601)and the Technology Innovation Fund of China coal research institute(2016CX01).
文摘DCLR-P was prepared by direct coal liquefaction residue (DCLR) with ash removal.In the present experiments,mesocarbon microbeads (MCMBs) were prepared by co-carbonization of coal tar pitch (CTP) and DCLR-P.With the increase of DCLR-P content,the yield of MCMBs increased from 47.8% to 56.8%.At the same time,the particle sizes distribution of MCMBs was narrowed,resulting in the decrease of D9o/D10 ratio from 154.88 to 6.53.The results showed that DCLR-P had a positive effect on the preparation of MCMBs.1H-NMR,FTIR,SEM and XRD were used to analyze the mechanisms and characteristics of MCMBs prepared by co-carbonization of CTP and DCLR-P.The results showed that the Proton Donor Quality Index (PDQI) of DCLR-P was 13.32,significantly higher than that of CTP (0.83).This indicated that DCLR-P had more naphthenic structure than CTP,which leads to hydrogen transferring in polycondensation reaction.The aliphatic structure of DCLR-P can improve the solubility and fusibility of mesophase,thereby making the structure of MCMBs more structured.The microstructure of the graphitized MCMBs had a substantially parallel carbon layer useful for its electrical performance.The performance of graphitized MCMBs as a negative electrode material for Li-ion batteries was tested.The particle sizes,tap density,specific surface area and initial charge-discharge efficiency of graphitized MCMBs met the requirements of CMB-I in GB/T-24533-2009.However,the initial discharge capacity of graphitized MCMB was only 296.3 mA h g-1 due to the low degree of graphitization of MCMBs.
基金supported by the National Key Research and Development Program of China (No.2016YFB0100511)
文摘The practical application of silica-based composites as an alternative to commercial graphite anode materials is hampered by their large volumetric expansion,poor conductivity,and low Coulombic efficiency.In this work,a novel silica/oxidized mesocarbon microbead/amorphous carbon(SiO2/O’MCMB/C)hierarchical structure in which SiO2 is sandwiched between spherical graphite and amorphous carbon shell was succes sfully fabricated through hydrogen bonding-assisted self-assembly and post-carbon coating method.The obtained three-layer hierarchical structure effectively accommodates the volumetric expansion of SiO2 and significantly enhances the electronic conductivity of composite materials.Moreover,the outer layer of amorphous carbon effectively increases the diffusion rate of lithium ions and promotes the formation of stable SEI film.As a result,the SiO2/O’MCMB/C composite exhibits superior electrochemical performance with a reversible capacity of 459.5 mA h/g in the first cycle,and the corresponding Coulombic efficiency is 62.8%.After 300 cycles,the capacity climbs to around 600 mA h/g.This synthetic route provides an efficient method for preparing SiO2 supported on graphite with excellent electrochemical performance,which is likely to promote its commercial applications.
基金financially supported by the National Natural Science Foundation(NSFC)of China(No.22179094)。
文摘Dual-ion batteries(DIBs)have attracted tremendous attention owing to their high operating voltage and are considered promising candidates for low-cost clean energy storage devices.However,the decomposition of electrolytes and collapse of the cathode structure may lead to low Coulombic efficiency(CE)and low cycling stability of DIBs.Wide-layered electrode materials can accommodate the intercalation/deintercalation of large anions,which is believed to overcome these issues.Herein,expanded mesocarbon microbeads(200HRO-MCMB)possessing an enlarged interlayer spacing(0.405 nm)were prepared via modified Hummers and subcritical hydrothermal reduction methods.After the indispensable electrochemical activation,200HRO-MCMB(hydrothermal reduction at 200℃)exhibited a high specific capacity(120 mAh·g^(-1)at50 mA·g^(-1))when used as a cathode for a sodium-based DIB,and the CE significantly improved within the 2.0-4.5 V voltage range.Additionally,the cycling stability exceeded over 600 cycles.Remarkably,this cathode possessed enlarged interlayers that decreased the barrier of PF6^(-)transport,and the battery storage mechanism corresponded to a transitioning state between double-layer capacitance and Faradaic intercalation.Undoubtedly,this work will expand the scope of the practical application of low-cost sodium-based DIBs.
基金Project supported by the National Natural Science Foundation of China(No.21573239)the Guangdong Provincial Project for Science and Technology(Nos.2014TX01N14,2015B010135008,and 2016B010114003)+1 种基金the Guangzhou Municipal Project for Science and Technology(No.201509010018)the K.C.WONG Education Foundation,China。
文摘The graphene/mesocarbon microbead(MCMB)composite is assessed as an anode material with a high capacity for lithium-ion batteries.The composite electrode exhibits improved cycling stability and rate capability,delivering a high initial charge/discharge capacity of 421.4 mA·h/g/494.8 mA·h/g as well as an excellent capacity retention over 500 cycles at a current density of 40 mA/g.At a higher current density of 800 mA/g,the electrode still retains 35%of its initial capacity which exceeds the capacity retention of pure graphene or MCMB reference electrodes.Cyclic voltammetry and electrochemical impedance spectroscopy reveal that the composite electrode favors electrochemical kinetics as compared with graphene and MCMB separately.Superior electrochemical properties suggest a strong synergetic effect between highly conductive graphene and MCMB.
基金Project(10332020) supported by the National Natural Science Foundation of China
文摘In situ prepared mesocarbon microbead/carbon nanotube(MCMB/CNT) composites are potential precursors of high density carbon materials for various applications. Integrated MCMB/CNT composites were successfully fabricated by hot-press sintering at 550 ℃ under 30 MPa. After further calcination at 900 ℃, the hot-press sintering fabricated MCMB block has an apparent density of 1.77 g/cm3 and the open porosity 5.1%. With the addition of 5%(mass fraction) CNTs, the density of the composite block is elevated to 1.84 g/cm3, and its open porosity is reduced to 3.5%. The flexural strength of composite block with 5% CNTs is elevated to 116 MPa. Through the hot-press sintering, pores of 10-50 nm in the calcinated bulks are remarkably eliminated. The interstice between microbeads in the composite blocks is filled up by CNTs together with β-resin and quinoline-insoluble spheres, which can further contribute to the densification.
文摘Mesocarbon microbeads (MCMB) with narrow size distribution, excellent sphericity and no obvious conglu-tination have been prepared with a coal tar pitch containing quinoline insolubles (QI) as the raw material. Optical mi-croscopy and scanning electron microscopy (SEM) are used to examine the structure of the MCMB. It has been found that SEM technique shows the structural information of MCMB clearly in the form of micrographs even when the structure of MCMB is complex, while the optical technique is useful for analysis of the regular structure of the mesophase spheres but cannot be effectively used to analyze either the complex structure of the green MCMB or the structures of the further heat-treated ones at different temperatures. Ac-cording to the characteristics of the carbon layers, the struc-tures of the as-prepared MCMB in the present experiment could be classified as (1) Parallel Layer type structure and (2) Bent Layer type structure with the carbon layers gathering at one or two points in the MCMB. In the experiments, SEM is also utilized to investigate the structures of MCMB that are heat-treated at different temperatures. It has been found that the MCMB without any further heat-treatment show no layered-carbons, while the ones heat-treated at temperature higher than 1000℃ exhibit obvious layered carbons across their sections. When increasing the heat-treatment tempera-ture, the carbon layers become thinner and flatter.
基金support of National Natural Science Foundation of P.R.China(22308104).
文摘The influence of nitrogen-containing polycyclic aromatic hydrocarbons(NC-PAH)on the formation of carbonaceous mesophase remains enigmatic,despite extensive research on the production of carbonaceous materials from aromatic-rich oils.Molecular dynamics simulation was used to investigate the variations in pyrolysis behavior between PAH and NC-PAH based on the composition analysis.Through adjusting the content of NC-PAH,the influence of NC-PAH on the thermal stability of slurry oils(SOs)was evaluated by thermogravimetry,viscosity,coke value,and quinoline insoluble(QI).The morphology and structure of mesocarbon microbeads(MCMBs)prepared with SOs were measured by a polarized-light microscope,SEM,XRD,and Raman.Simulation results indicate that NC-PAH possesses much higher reactivity and tends to produce highly condensed solid and coke products.It corresponds to the QI and high viscosity in thermal stability experiments.Therefore,high concentrations of NC-PAH result in nonuniform morphology and disordered structures.In a system with low viscosity and few QIs,SO,which has a low nitrogen content(475 ppm),reacts gently to produce MCMBs with a uniform particle size(10-40μm)and an excellent spherical shape.As NC-PAH content decreases,the crystalline size of graphitization elevates,as evidenced by parallel layers(10.472-11.764)and stack height(3.269-3.701 nm).The graphitization degree becomes worse and nonuniform with the increase of the content of NC-PAH,and the best is 20.58%evaluated by Raman spectra area ratio(AG/Aall).Overall,this work suggests a nitrogen content reference and a controlling technology of nitrogen for the preparation of superior MCMB.
