The voltage decay of lithium-rich layered oxides(LLOs)is still one of the key challenges for their application in commercial battery although these materials possess the advantages of high specific capacity and low co...The voltage decay of lithium-rich layered oxides(LLOs)is still one of the key challenges for their application in commercial battery although these materials possess the advantages of high specific capacity and low cost.In this work,the relationship between voltage decay and tap density of LLOs has been focused.The voltage decay can be significantly suppressed with the increasing tap density as well as the homogenization of the primary or secondary particle size of agglomerated spherical LLOs.Experimental results have shown that an extreme small voltage decay of 0.98 m V cycle^(-1)can be obtained through adjusting the tap density of agglomerated spherical LLOs to 1.99 g cm^(-3),in which the size of primary and secondary particles are uniform.Our work offers a new insight towards the voltage decay and capacity fading of LLOs through precursor preparation process,promoting their application in the real battery in the future.展开更多
Spherical cobalt carbonate with high tap density, good crystallization and uniform particle size was prepared by controlled chemical crystal method using cobalt chloride and ammonium bicarbonate as cobalt source and p...Spherical cobalt carbonate with high tap density, good crystallization and uniform particle size was prepared by controlled chemical crystal method using cobalt chloride and ammonium bicarbonate as cobalt source and precipitator. The effects of pH value and reaction time on crystallization and physical properties of cobalt carbonate were studied. The results show that the key factors influencing the preparation process of spherical cobalt carbonate with high tap density and good crystallization are how to control pH value (7.25±0.05) and keep some reaction time (about 10 h). Co4O3 was prepared by sintering spherical morphology CoCO3 samples at varied temperatures. The results show that as the decomposition temperature increases, the as-obtained Co4O3 products with porous structure transform into polyhedral structure with glazed surface, and simultaneously the cobalt content and tap density increase. However, the specific surface area shows a trend of decrease.展开更多
The Li Ni1/3Co1/3Mn1/3O2 is first obtained by the controlled crystallization method and then coated with Ni3(PO4)2particles. The effects of the coating on rate capability and cycle life at high cut-off voltage are inv...The Li Ni1/3Co1/3Mn1/3O2 is first obtained by the controlled crystallization method and then coated with Ni3(PO4)2particles. The effects of the coating on rate capability and cycle life at high cut-off voltage are investigated by electrochemical impedance spectroscopy and galvanostatic measurements. The element ratio of Ni:Mn:Co is tested by inductively-coupled plasma spectrometer(ICP) analysis and it testified to be 1:1:1. It is indicated that Ni3(PO4)2-coated Li Ni1/3Co1/3Mn1/3O2 has an outstanding capacity retention, where 99% capacity retention is maintained after 10 cycles at 5C discharge rate between 2.7 V and 4.6 V. The electrochemical impedance spectroscopy(EIS) results show that the current exchange density i0 of the coated sample is higher than that of Li Ni1/3Co1/3Mn1/3O2, which is beneficial to its electrochemical performances. All the conclusions show that the Ni3(PO4)2coating can prominently enhance the high rate performance of the Li Ni1/3Co1/3Mn1/3O2, especially at high cut-off voltage.展开更多
The soaring demand for smart portable electronics and electric vehicles is propelling the advancements in high-energy–density lithium-ion batteries.Lithium manganese iron phosphate(LiMn_(x)Fe_(1-x)PO_(4))has garnered...The soaring demand for smart portable electronics and electric vehicles is propelling the advancements in high-energy–density lithium-ion batteries.Lithium manganese iron phosphate(LiMn_(x)Fe_(1-x)PO_(4))has garnered significant attention as a promising positive electrode material for lithium-ion batteries due to its advantages of low cost,high safety,long cycle life,high voltage,good high-temperature performance,and high energy density.Although LiMn_(x)Fe_(1-x)PO_(4)has made significant breakthroughs in the past few decades,there are still facing great challenges in poor electronic conductivity and Li-ion diffusion,manganese dissolution affecting battery cycling performance,as well as low tap density.This review systematically summarizes the reaction mechanisms,various synthesis methods,and electrochemical properties of LiMn_(x)Fe_(1-x)PO_(4)to analyze reaction processes accurately and guide material preparation.Later,the main challenges currently faced are concluded,and the corresponding various modification strategies are discussed to enhance the reaction kinetics and electrochemical performance of LiMn_(x)Fe_(1-x)PO_(4),including multi-scale particle regulation,heteroatom doping,surface coating,as well as microscopic morphology design.Finally,in view of the current research challenges faced by intrinsic reaction processes,kinetics,and energy storage applications,the promising research directions are anticipated.More importantly,it is expected to provide key insights into the development of high-performance and stable LiMn_(x)Fe_(1-x)PO_(4)materials,to achieve practical energy storage requirements.展开更多
Despite advancements in silicon-based anodes for high-capacity lithium-ion batteries,their widespread commercial adoption is still hindered by significant volume expansion during cycling,especially at high active mass...Despite advancements in silicon-based anodes for high-capacity lithium-ion batteries,their widespread commercial adoption is still hindered by significant volume expansion during cycling,especially at high active mass loadings crucial for practical use.The root of these challenges lies in the mechanical instability of the material,which subsequently leads to the structural failure of the electrode.Here,we present a novel synthesis of a composite combining expanded graphite and silicon nanoparticles.This composite features a unique interlayer-bonded graphite structure,achieved through the application of a modified spark plasma sintering method.Notably,this innovative structure not only facilitates efficient ion and electron transport but also provides exceptional mechanical strength(Vickers hardness:up to658 MPa,Young's modulus:11.6 GPa).This strength effectively accommodates silicon expansion,resulting in an impressive areal capacity of 2.9 mA h cm^(-2)(736 mA h g^(-1)) and a steady cycle life(93% after 100cycles).Such outsta nding performance is paired with features appropriate for large-scale industrial production of silicon batteries,such as active mass loading of at least 3.9 mg cm^(-2),a high-tap density electrode material of 1.68 g cm^(-3)(secondary clusters:1.12 g cm^(-3)),and a production yield of up to 1 kg per day.展开更多
The ultrafine silver powders were prepared by liquid reduction method using Arabic gum as dispersant.The effects of different dispersants,pH values,and temperature on the morphology and particle size of silver powders...The ultrafine silver powders were prepared by liquid reduction method using Arabic gum as dispersant.The effects of different dispersants,pH values,and temperature on the morphology and particle size of silver powders were investigated.It is found that Arabic gum can better adsorb on silver particles via chemical adsorption,and it shows the best dispersive effect among all the selected dispersants.The particle size of silver powders can be finely tuned from 0.34 to 4.09μm by adjusting pH values,while the morphology of silver powders can be tuned by changing the temperature.The silver powders with high tap density higher than 4.0 g/cm3 were successfully prepared in a wide temperature range of 21.8-70°C.Especially,the tap density is higher than 5.0 g/cm3 when the temperature is optimized to be 50°C.The facile process and high silver concentration of this method make it a promising way to prepare high quality silver powders for electronic paste.展开更多
Nanoparticles reinforced steels have many advantaged mechanical properties.Additive manufacturing offers a new method for fabricating nanoparticles reinforced high performance metal components.In this work,we report t...Nanoparticles reinforced steels have many advantaged mechanical properties.Additive manufacturing offers a new method for fabricating nanoparticles reinforced high performance metal components.In this work,we report the application of low energy ball milling in mixing nanoparticles and micron 316 L powder.With this method,0.3 and 1.0 wt% Y2 O3 nanoparticles can be uniformly distributed on the surface of 316 L powder with the parameters of ball-to-powder ratio at 1:1,speed at 90 rpm and 7 h of mixing.The matrix 316 L powders remain spherical in shape after the mixing process.In the meantime,the effect of low energy ball milling and the addition of Y2 O3 nanoparticles on the powder characteristics(flowability,apparent density and tap density) are also studied.Results show that the process of low energy ball milling itself can slightly decrease the flowability and apparent density of the 316 L powder.The addition of 0.3 and 1.0 wt% Y2 O3 nanoparticles can also decrease the flowability,the tap density and the apparent density compared with the original 316 L powder.All of these changes result from the rough surface of the mixed powder produced by ball milling and the addition of Y2 O3 nanoparticles.The powder’s rough surface can increase the coefficient of friction of powders.The mixture of 316 L powder and Y2 O3 nanoparticles can be successfully used for selective laser melting(SLM).The relative density of SLM 316 L-Y2 O3 is measured at 99.5%.However,Y2 O3 agglomerations were observed which is due to the poor wettability between 316 L and Y2 O3.展开更多
Permeability is a key powder property for many industrial applications as it affects the flowability during powder handling and the quality of the final product.Indeed,the ability of air to pass through a powder bed,q...Permeability is a key powder property for many industrial applications as it affects the flowability during powder handling and the quality of the final product.Indeed,the ability of air to pass through a powder bed,quantified by permeability,is decisive for die or bag filling,dry powder inhalers,silo discharge,pneumatic transport,fluidized bed,etc.Usually,the permeability is measured on a powder bed subjected to high consolidation stresses and without the possibility to control the packing fraction of the powder.In the present study,we show how GranuPack measurement can be combined with a permeability measurement cell to measure the permeability at low consolidation and for various packing fractions,which correspond to many process conditions.A selection of usual powders(pharmaceutical excipients and abrasives)has been tested and the results highlight how the permeability can be used to obtain additional information about powder behavior.For that,a two levels analysis is proposed:an entry-level based on straightforward parameters like initial and final(after the tapping process)permeability and a more advanced level based on two new metrics.These metrics are the permeability ratio and the rate of variation of permeability.These parameters are directly related to the powder cohesiveness and hence can be used to complement the classical flowability indexes.展开更多
Densified products produced from pellet mill are commercially used as a commodity type product for energy applications that are transported nationally and internationally.The quality of the pelletized biomass produce...Densified products produced from pellet mill are commercially used as a commodity type product for energy applications that are transported nationally and internationally.The quality of the pelletized biomass produced depends on the process variables such as die diameter,length to diameter(L/D)ratio,die speed,preheating,and steam conditioning;and feedstock variables such as feedstock type,moisture content,and particle size and shape.In the present study,pelleting tests were conducted with both woody(i.e.,lodgepole pine and pinyon-juniper)and herbaceous(i.e.,corn stover,wheat straw,and energy sorghum)biomass.A high level of feedstock moisture content of 33%(w.b.)was selected,while the die speed and preheating temperature process variables were kept at 60 Hz(380 rpm)and 70C.Results indicated that during the pelleting and cooling process,an approximate 10–13%(w.b.)moisture loss in both the woody and herbaceous biomass was observed.The high moisture pellets produced were further dried in a laboratory oven at 70C for three hours to reduce the moisture content of the pellets to<10%(w.b).The dried pellets were then evaluated further for other quality attributes including unit,bulk,and tapped density;and durability.The pellets that resulted in the highest unit,bulk,and tapped densities following this process were the herbaceous biomass corn stover(e.g.,>1133,>580,>620 kg/m3)and the woody biomass lodgepole pine(e.g.,>1037,>568,>641 kg/m3),respectively.In the case of durability for the 8 mm diameter pellets,wheat straw and corn stover recorded a maximum of about 96%,respectively,while the lodgepole pine and pinion juniper recorded a maximum of>96%,respectively.展开更多
Low volumetric energy density is a bottleneck for the application of lithium-sulfur (Li-S)battery.The low- density sulfur cooperated with the light-weight carbon sub- strate realizes electrochemical cycle stability,bu...Low volumetric energy density is a bottleneck for the application of lithium-sulfur (Li-S)battery.The low- density sulfur cooperated with the light-weight carbon sub- strate realizes electrochemical cycle stability,but leads to worse volumetric energy density.Here,nickel ferrite (NiFe2O4)nanofibers as novel substrate for sulfur not only anchor lithium polysulfides to enhance the cycle stability of sulfur cathode,but also contribute to the high volumetric capacity of the S/nickel ferrite composite.Specifically,the S/ nickel ferrite composite presents an initial volumetric capacity of 1,281.7mA h cm^-3-composite at 0.1C rate,1.9times higher than that of S/carbon nanotubes,due to the high tap density of the S/nickel ferrite composite.展开更多
Solid and hollow microspheres of LiMn_(2)O_(4) have been synthesized by lithiating MnCO_(3) solid microspheres and MnO_(2) hollow microspheres,respectively.The LiMn_(2)O_(4) solid microspheres and hollow microspheres ...Solid and hollow microspheres of LiMn_(2)O_(4) have been synthesized by lithiating MnCO_(3) solid microspheres and MnO_(2) hollow microspheres,respectively.The LiMn_(2)O_(4) solid microspheres and hollow microspheres had a similar size of about 1.5μm,and the shell thickness of the hollow microspheres was only 100 nm.When used as a cathode material in lithium ion batteries,the hollow microspheres exhibited better rate capability than the solid microspheres.However,the tap density of the LiMn_(2)O_(4) solid microspheres(1.0 g/cm^(3))was about four times that of the hollow microspheres(0.27 g/cm^(3)).The results show that controlling the particle size of LiMn_(2)O_(4) is very important in terms of its practical application as a cathode material,and LiMn_(2)O_(4) with moderate particle size may afford acceptable values of both rate capability and tap density.展开更多
基金financially supported by the Beijing Natural Science Foundation(JQ19003)National Key R&D Program of China(grant no.2018YFB0104300)+4 种基金National Natural Science Foundation of China(grant no 51622202,21603009,and 21875007)Beijing Natural Science Foundation(B)(KZ201910005002)Beijing Natural Science Foundation(L182009)Project of Youth Talent Plan of Beijing Municipal Education Commission(CIT&TCD201804013)High-grade discipline construction of Beijing(PXM2019-014204-500031)。
文摘The voltage decay of lithium-rich layered oxides(LLOs)is still one of the key challenges for their application in commercial battery although these materials possess the advantages of high specific capacity and low cost.In this work,the relationship between voltage decay and tap density of LLOs has been focused.The voltage decay can be significantly suppressed with the increasing tap density as well as the homogenization of the primary or secondary particle size of agglomerated spherical LLOs.Experimental results have shown that an extreme small voltage decay of 0.98 m V cycle^(-1)can be obtained through adjusting the tap density of agglomerated spherical LLOs to 1.99 g cm^(-3),in which the size of primary and secondary particles are uniform.Our work offers a new insight towards the voltage decay and capacity fading of LLOs through precursor preparation process,promoting their application in the real battery in the future.
文摘Spherical cobalt carbonate with high tap density, good crystallization and uniform particle size was prepared by controlled chemical crystal method using cobalt chloride and ammonium bicarbonate as cobalt source and precipitator. The effects of pH value and reaction time on crystallization and physical properties of cobalt carbonate were studied. The results show that the key factors influencing the preparation process of spherical cobalt carbonate with high tap density and good crystallization are how to control pH value (7.25±0.05) and keep some reaction time (about 10 h). Co4O3 was prepared by sintering spherical morphology CoCO3 samples at varied temperatures. The results show that as the decomposition temperature increases, the as-obtained Co4O3 products with porous structure transform into polyhedral structure with glazed surface, and simultaneously the cobalt content and tap density increase. However, the specific surface area shows a trend of decrease.
基金Supported by the National Natural Science Foundation of China(51074096)
文摘The Li Ni1/3Co1/3Mn1/3O2 is first obtained by the controlled crystallization method and then coated with Ni3(PO4)2particles. The effects of the coating on rate capability and cycle life at high cut-off voltage are investigated by electrochemical impedance spectroscopy and galvanostatic measurements. The element ratio of Ni:Mn:Co is tested by inductively-coupled plasma spectrometer(ICP) analysis and it testified to be 1:1:1. It is indicated that Ni3(PO4)2-coated Li Ni1/3Co1/3Mn1/3O2 has an outstanding capacity retention, where 99% capacity retention is maintained after 10 cycles at 5C discharge rate between 2.7 V and 4.6 V. The electrochemical impedance spectroscopy(EIS) results show that the current exchange density i0 of the coated sample is higher than that of Li Ni1/3Co1/3Mn1/3O2, which is beneficial to its electrochemical performances. All the conclusions show that the Ni3(PO4)2coating can prominently enhance the high rate performance of the Li Ni1/3Co1/3Mn1/3O2, especially at high cut-off voltage.
基金National Natural Science Foundation of China(52104294)Fundamental Research Funds for the Central Universities(FRF-TP-19-079A1)。
文摘The soaring demand for smart portable electronics and electric vehicles is propelling the advancements in high-energy–density lithium-ion batteries.Lithium manganese iron phosphate(LiMn_(x)Fe_(1-x)PO_(4))has garnered significant attention as a promising positive electrode material for lithium-ion batteries due to its advantages of low cost,high safety,long cycle life,high voltage,good high-temperature performance,and high energy density.Although LiMn_(x)Fe_(1-x)PO_(4)has made significant breakthroughs in the past few decades,there are still facing great challenges in poor electronic conductivity and Li-ion diffusion,manganese dissolution affecting battery cycling performance,as well as low tap density.This review systematically summarizes the reaction mechanisms,various synthesis methods,and electrochemical properties of LiMn_(x)Fe_(1-x)PO_(4)to analyze reaction processes accurately and guide material preparation.Later,the main challenges currently faced are concluded,and the corresponding various modification strategies are discussed to enhance the reaction kinetics and electrochemical performance of LiMn_(x)Fe_(1-x)PO_(4),including multi-scale particle regulation,heteroatom doping,surface coating,as well as microscopic morphology design.Finally,in view of the current research challenges faced by intrinsic reaction processes,kinetics,and energy storage applications,the promising research directions are anticipated.More importantly,it is expected to provide key insights into the development of high-performance and stable LiMn_(x)Fe_(1-x)PO_(4)materials,to achieve practical energy storage requirements.
基金supported by the National Research Foundation, Prime Minister’s Office, Singapore, under its Competitive Research Programme (CRP award number NRF-CRP22-2019-008)Medium-Sized Centre Programme (CA2DM)+1 种基金the Ministry of Education of Singapore, under its Research Centre of Excellence award to the Institute for Functional Intelligent Materials (I-FIM, Project No. EDUNC-33-18-279-V12)by the EDB Singapore, under its Space Technology Development Programme (S2219013-STDP)。
文摘Despite advancements in silicon-based anodes for high-capacity lithium-ion batteries,their widespread commercial adoption is still hindered by significant volume expansion during cycling,especially at high active mass loadings crucial for practical use.The root of these challenges lies in the mechanical instability of the material,which subsequently leads to the structural failure of the electrode.Here,we present a novel synthesis of a composite combining expanded graphite and silicon nanoparticles.This composite features a unique interlayer-bonded graphite structure,achieved through the application of a modified spark plasma sintering method.Notably,this innovative structure not only facilitates efficient ion and electron transport but also provides exceptional mechanical strength(Vickers hardness:up to658 MPa,Young's modulus:11.6 GPa).This strength effectively accommodates silicon expansion,resulting in an impressive areal capacity of 2.9 mA h cm^(-2)(736 mA h g^(-1)) and a steady cycle life(93% after 100cycles).Such outsta nding performance is paired with features appropriate for large-scale industrial production of silicon batteries,such as active mass loading of at least 3.9 mg cm^(-2),a high-tap density electrode material of 1.68 g cm^(-3)(secondary clusters:1.12 g cm^(-3)),and a production yield of up to 1 kg per day.
基金Project(2014DFA90520)supported by the International Cooperation Program of Ministry of Science and Technology of ChinaProject(2013A090100003)supported by the Production,Teaching and Research Program of Guangdong Province,ChinaProject(2013DY048)supported by the Science and Technology Cooperation Program of Daye Nonferrous Metals Group,China
文摘The ultrafine silver powders were prepared by liquid reduction method using Arabic gum as dispersant.The effects of different dispersants,pH values,and temperature on the morphology and particle size of silver powders were investigated.It is found that Arabic gum can better adsorb on silver particles via chemical adsorption,and it shows the best dispersive effect among all the selected dispersants.The particle size of silver powders can be finely tuned from 0.34 to 4.09μm by adjusting pH values,while the morphology of silver powders can be tuned by changing the temperature.The silver powders with high tap density higher than 4.0 g/cm3 were successfully prepared in a wide temperature range of 21.8-70°C.Especially,the tap density is higher than 5.0 g/cm3 when the temperature is optimized to be 50°C.The facile process and high silver concentration of this method make it a promising way to prepare high quality silver powders for electronic paste.
基金supported by A*STAR Industrial Additive Manufacturing Program:The A*STAR Additive Manufacturing Centre(AMC)Initiative:Work Package 1(High Temperature Mate-rials Development for 3D Additive Manufacturing,Grant No.1426800088)financial support from Nanyang Technological University。
文摘Nanoparticles reinforced steels have many advantaged mechanical properties.Additive manufacturing offers a new method for fabricating nanoparticles reinforced high performance metal components.In this work,we report the application of low energy ball milling in mixing nanoparticles and micron 316 L powder.With this method,0.3 and 1.0 wt% Y2 O3 nanoparticles can be uniformly distributed on the surface of 316 L powder with the parameters of ball-to-powder ratio at 1:1,speed at 90 rpm and 7 h of mixing.The matrix 316 L powders remain spherical in shape after the mixing process.In the meantime,the effect of low energy ball milling and the addition of Y2 O3 nanoparticles on the powder characteristics(flowability,apparent density and tap density) are also studied.Results show that the process of low energy ball milling itself can slightly decrease the flowability and apparent density of the 316 L powder.The addition of 0.3 and 1.0 wt% Y2 O3 nanoparticles can also decrease the flowability,the tap density and the apparent density compared with the original 316 L powder.All of these changes result from the rough surface of the mixed powder produced by ball milling and the addition of Y2 O3 nanoparticles.The powder’s rough surface can increase the coefficient of friction of powders.The mixture of 316 L powder and Y2 O3 nanoparticles can be successfully used for selective laser melting(SLM).The relative density of SLM 316 L-Y2 O3 is measured at 99.5%.However,Y2 O3 agglomerations were observed which is due to the poor wettability between 316 L and Y2 O3.
文摘Permeability is a key powder property for many industrial applications as it affects the flowability during powder handling and the quality of the final product.Indeed,the ability of air to pass through a powder bed,quantified by permeability,is decisive for die or bag filling,dry powder inhalers,silo discharge,pneumatic transport,fluidized bed,etc.Usually,the permeability is measured on a powder bed subjected to high consolidation stresses and without the possibility to control the packing fraction of the powder.In the present study,we show how GranuPack measurement can be combined with a permeability measurement cell to measure the permeability at low consolidation and for various packing fractions,which correspond to many process conditions.A selection of usual powders(pharmaceutical excipients and abrasives)has been tested and the results highlight how the permeability can be used to obtain additional information about powder behavior.For that,a two levels analysis is proposed:an entry-level based on straightforward parameters like initial and final(after the tapping process)permeability and a more advanced level based on two new metrics.These metrics are the permeability ratio and the rate of variation of permeability.These parameters are directly related to the powder cohesiveness and hence can be used to complement the classical flowability indexes.
基金the U.S.Department of Energy Office of Energy Efficiency and Renewable Energy under DOE Idaho Operations Office Contract DE-AC07-05ID14517。
文摘Densified products produced from pellet mill are commercially used as a commodity type product for energy applications that are transported nationally and internationally.The quality of the pelletized biomass produced depends on the process variables such as die diameter,length to diameter(L/D)ratio,die speed,preheating,and steam conditioning;and feedstock variables such as feedstock type,moisture content,and particle size and shape.In the present study,pelleting tests were conducted with both woody(i.e.,lodgepole pine and pinyon-juniper)and herbaceous(i.e.,corn stover,wheat straw,and energy sorghum)biomass.A high level of feedstock moisture content of 33%(w.b.)was selected,while the die speed and preheating temperature process variables were kept at 60 Hz(380 rpm)and 70C.Results indicated that during the pelleting and cooling process,an approximate 10–13%(w.b.)moisture loss in both the woody and herbaceous biomass was observed.The high moisture pellets produced were further dried in a laboratory oven at 70C for three hours to reduce the moisture content of the pellets to<10%(w.b).The dried pellets were then evaluated further for other quality attributes including unit,bulk,and tapped density;and durability.The pellets that resulted in the highest unit,bulk,and tapped densities following this process were the herbaceous biomass corn stover(e.g.,>1133,>580,>620 kg/m3)and the woody biomass lodgepole pine(e.g.,>1037,>568,>641 kg/m3),respectively.In the case of durability for the 8 mm diameter pellets,wheat straw and corn stover recorded a maximum of about 96%,respectively,while the lodgepole pine and pinion juniper recorded a maximum of>96%,respectively.
基金supported by the New Energy Project for Electric Vehicles in National Key Research and Development Program (2016YFB0100200)the National Natural Science Foundation of China (21573114 and 51502145)
文摘Low volumetric energy density is a bottleneck for the application of lithium-sulfur (Li-S)battery.The low- density sulfur cooperated with the light-weight carbon sub- strate realizes electrochemical cycle stability,but leads to worse volumetric energy density.Here,nickel ferrite (NiFe2O4)nanofibers as novel substrate for sulfur not only anchor lithium polysulfides to enhance the cycle stability of sulfur cathode,but also contribute to the high volumetric capacity of the S/nickel ferrite composite.Specifically,the S/ nickel ferrite composite presents an initial volumetric capacity of 1,281.7mA h cm^-3-composite at 0.1C rate,1.9times higher than that of S/carbon nanotubes,due to the high tap density of the S/nickel ferrite composite.
基金This work was supported by the National Nature Science Foundation of China(NSFC)(Nos.20921001 and 90606006)the Tsinghua University Initiative Scientific Research Program(No.2009HTZ08).
文摘Solid and hollow microspheres of LiMn_(2)O_(4) have been synthesized by lithiating MnCO_(3) solid microspheres and MnO_(2) hollow microspheres,respectively.The LiMn_(2)O_(4) solid microspheres and hollow microspheres had a similar size of about 1.5μm,and the shell thickness of the hollow microspheres was only 100 nm.When used as a cathode material in lithium ion batteries,the hollow microspheres exhibited better rate capability than the solid microspheres.However,the tap density of the LiMn_(2)O_(4) solid microspheres(1.0 g/cm^(3))was about four times that of the hollow microspheres(0.27 g/cm^(3)).The results show that controlling the particle size of LiMn_(2)O_(4) is very important in terms of its practical application as a cathode material,and LiMn_(2)O_(4) with moderate particle size may afford acceptable values of both rate capability and tap density.
