With great superiorities in energy density,rate capability and structural stability,Na_(3)V_(2)(PO_(4))_(2) F_(3)(NVPF)has attracted much attentions as cathode of sodium ion battery(SIB),but it also faces challenges o...With great superiorities in energy density,rate capability and structural stability,Na_(3)V_(2)(PO_(4))_(2) F_(3)(NVPF)has attracted much attentions as cathode of sodium ion battery(SIB),but it also faces challenges on its poor intrinsic electronic conductivity and the controversial de/sodiation mechanism.Herein,a series of Zr-doped NVPF coated by N-doped carbon layer(~5 nm in thickness,homogenously)materials are fabricated by a sol-gel method,and the optimized heteroatom-doping amounts of Zr and N doping improve intrinsic properties on enlarging lattice distance and enhancing electronic conductivity,respectively.Specifically,among all samples of Na_(3) V_(2-x)Zr_(x)(PO_(4))_(2) F_(3)/NC(NVPF-Zr-x/NC,x=0,0.01,0.02,0.05,and 0.1),the optimized electrode of NVPF-Zr-0.02/NC delivers high reversible capacities(119.2 mAh g^(-1) at0.5 C),superior rate capability(98.1 mA h g^(-1) at 20 C)and excellent cycling performance.The structural evolution of NVPF-Zr-0.02/NC electrode,in-situ monitored by X-ray diffractometer,follows a step-wise Na-extraction/intercalation mechanism with reversible multi-phase changes,not just a solid-solutionreaction one.Full cells of NVPF-Zr-0.02/NC//hard carbon demonstrate high capacity(99.8 mA h g^(-1) at 0.5 C),high out-put voltage(3.5 V)and good cycling stability.This work is favorable to accelerate the development of high-performance cathode materials and explore possible redox reaction mechanisms of SIBs.展开更多
As a promising cathode material,Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)has attracted wide attention for sodium-ion batteries(SIBs)because of its high operating voltage and high structural stability.However,the low intrinsi...As a promising cathode material,Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)has attracted wide attention for sodium-ion batteries(SIBs)because of its high operating voltage and high structural stability.However,the low intrinsic electronic conductivity and insufficient Na ion mobility of NVPF limit its development.Herein,K-doping NVPF is prepared through a facile ball-milling combined calcination method.The effects of K-doping on the crystal structure,kinetic properties and electrochemical performance are investigated.The results demonstrate that the Na_(2.90)K_(0.10)V_(2)(PO_(4))_(3)F_(3)(K0.10-NVPF)exhibits a high capacity(120.8 mAh g^(-1) at 0.1 C),high rate capability(66 mAh g^(-1) at 30 C)and excellent cycling performance(a capacity retention of 97.5%at 1 C over 500 cycles).Also,the occupation site of K ions in the lattice,electronic band structure and Na-ion transport kinetic property in K-doped NVPF are investigated by density functional theory(DFT)calculations,which reveals that the K-doped NVPF exhibits improved electronic and ionic conductivities,and located K^(+) ions in the lattice to contribute to high reversible capacity,rate capability and cycling stability.Therefore,the K-doped NVPF serves as a promising cathode material for high-energy and high-power SIBs.展开更多
The dynamics of negative surface discharges in c-C_(4)F_(8)/CF_(3)I/CO_(2) gas mixture is investigated here with a 2D fuid model.The distributions of ion concentration,electric field strength and photon flux during th...The dynamics of negative surface discharges in c-C_(4)F_(8)/CF_(3)I/CO_(2) gas mixture is investigated here with a 2D fuid model.The distributions of ion concentration,electric field strength and photon flux during the propagation of the streamer are obtained by solving the drift-diffusion equations of particles and Poisson's equation,and the photon flux variation function during the propagation is also fitted.It is found that the streamer branches occur when the streamer transitions from the upper surface of the insulator to the side surface,and then when the streamer approaches the plane electrode,the photon flux will increase significantly.On this basis,the positive and negative surface discharge models are compared in terms of streamer characteristics,particle characteristics and streamer branches.It is found that the streamer has a higher electron concentration and electric field in the positive model.The streamer develops“floating”in the positive surface discharge,while it is close to the surface of the insulator in the negative model.In addition,the negative streamer branch has a wider width and develops further.展开更多
Sodium-ion batteries(SIBs)have received significant attention in large-scale energy storage due to their low cost and abundant resources.To obtain high-performance SIBs,many intensive studies about electrode materials...Sodium-ion batteries(SIBs)have received significant attention in large-scale energy storage due to their low cost and abundant resources.To obtain high-performance SIBs,many intensive studies about electrode materials have been carried out,especially the cathode material.As various types of cathode material for SIBs,a 3D open framework structural Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)with Na superionic conductor(NASICON)structure is a promising cathode material owing to its high operating potential and high energy density.However,its electrochemical properties are severely limited by the poor electronic conductivity due to the insulated[PO_(4)]tetrahedral unit.In this review,the challenges and strategies for NVPF are presented,and the synthetic strategy for NVPF is also analyzed in detail.Furthermore,recent developments of modification research to enhance their electrochemical performance are discussed,including designing the crystal structure,adjusting the electrode structure,and optimizing the electrolyte components.Finally,further research and application for future development of NVPF are prospected.展开更多
Sc-based nanomaterials have attracted considerable attention due to their unique optical properties different from those of Ln/Y-based nanomaterials.However,studies on Sc-based nanomaterials are far from comprehensive...Sc-based nanomaterials have attracted considerable attention due to their unique optical properties different from those of Ln/Y-based nanomaterials.However,studies on Sc-based nanomaterials are far from comprehensive.Particularly,nanoscale alkaline(Ca,Sr and Ba)scandium fluorides were almost ignored for their stringent synthetic conditions.Herein,we synthesize high-quality tetragonal phase Ba_(3)Sc_(2)F_(12) nanocrystals with uniform morphology and good dispersibility by carefully tailoring the reaction conditions,such as the molar ratio of reactants,temperature and reaction time.Then,the upconversion(UC)luminescence property of Ba_(3)Sc_(2)F_(12):Yb/Er(Ho)samples is investigated in detail.The doping concentrations of sensitizer(Yb^(3+))and activator(Er^(3+)and Ho^(3+))are optimized for the strongest UC luminescence,of which the corresponding energy transfer processes are also discussed.Moreover,tetragonal Ba_(3)Sc_(2)F_(12) nanocrystals can gradually transform into hexagonal Ba_(4)Yb_(3)F_(17) nanocrystals with the increase in Yb^(3+)doping content.This work provides a novel type of Sc-based nanomaterials with strong red UC emissions which are promising in high-resolution 3-dimensional color displays,laser,bioimaging and biolabels.展开更多
基金the National Natural Science Foundation of China(21975154)the Shanghai Municipal Education Commission(Innovation Program(2019-01-07-00-09E00021)+2 种基金Innovative Research Team of High-level Local Universities in Shanghaisupported by The Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher LearningShanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power。
文摘With great superiorities in energy density,rate capability and structural stability,Na_(3)V_(2)(PO_(4))_(2) F_(3)(NVPF)has attracted much attentions as cathode of sodium ion battery(SIB),but it also faces challenges on its poor intrinsic electronic conductivity and the controversial de/sodiation mechanism.Herein,a series of Zr-doped NVPF coated by N-doped carbon layer(~5 nm in thickness,homogenously)materials are fabricated by a sol-gel method,and the optimized heteroatom-doping amounts of Zr and N doping improve intrinsic properties on enlarging lattice distance and enhancing electronic conductivity,respectively.Specifically,among all samples of Na_(3) V_(2-x)Zr_(x)(PO_(4))_(2) F_(3)/NC(NVPF-Zr-x/NC,x=0,0.01,0.02,0.05,and 0.1),the optimized electrode of NVPF-Zr-0.02/NC delivers high reversible capacities(119.2 mAh g^(-1) at0.5 C),superior rate capability(98.1 mA h g^(-1) at 20 C)and excellent cycling performance.The structural evolution of NVPF-Zr-0.02/NC electrode,in-situ monitored by X-ray diffractometer,follows a step-wise Na-extraction/intercalation mechanism with reversible multi-phase changes,not just a solid-solutionreaction one.Full cells of NVPF-Zr-0.02/NC//hard carbon demonstrate high capacity(99.8 mA h g^(-1) at 0.5 C),high out-put voltage(3.5 V)and good cycling stability.This work is favorable to accelerate the development of high-performance cathode materials and explore possible redox reaction mechanisms of SIBs.
基金financially funded by the Regional Innovation and Development Joint Fund,National Natural Science Foundation of China(No.U20A20249)National Key Research Program of China(No.2016YFB0901500)。
文摘As a promising cathode material,Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)has attracted wide attention for sodium-ion batteries(SIBs)because of its high operating voltage and high structural stability.However,the low intrinsic electronic conductivity and insufficient Na ion mobility of NVPF limit its development.Herein,K-doping NVPF is prepared through a facile ball-milling combined calcination method.The effects of K-doping on the crystal structure,kinetic properties and electrochemical performance are investigated.The results demonstrate that the Na_(2.90)K_(0.10)V_(2)(PO_(4))_(3)F_(3)(K0.10-NVPF)exhibits a high capacity(120.8 mAh g^(-1) at 0.1 C),high rate capability(66 mAh g^(-1) at 30 C)and excellent cycling performance(a capacity retention of 97.5%at 1 C over 500 cycles).Also,the occupation site of K ions in the lattice,electronic band structure and Na-ion transport kinetic property in K-doped NVPF are investigated by density functional theory(DFT)calculations,which reveals that the K-doped NVPF exhibits improved electronic and ionic conductivities,and located K^(+) ions in the lattice to contribute to high reversible capacity,rate capability and cycling stability.Therefore,the K-doped NVPF serves as a promising cathode material for high-energy and high-power SIBs.
基金the National Natural Science Foundation of China(No.62075045)。
文摘The dynamics of negative surface discharges in c-C_(4)F_(8)/CF_(3)I/CO_(2) gas mixture is investigated here with a 2D fuid model.The distributions of ion concentration,electric field strength and photon flux during the propagation of the streamer are obtained by solving the drift-diffusion equations of particles and Poisson's equation,and the photon flux variation function during the propagation is also fitted.It is found that the streamer branches occur when the streamer transitions from the upper surface of the insulator to the side surface,and then when the streamer approaches the plane electrode,the photon flux will increase significantly.On this basis,the positive and negative surface discharge models are compared in terms of streamer characteristics,particle characteristics and streamer branches.It is found that the streamer has a higher electron concentration and electric field in the positive model.The streamer develops“floating”in the positive surface discharge,while it is close to the surface of the insulator in the negative model.In addition,the negative streamer branch has a wider width and develops further.
基金the National Natural Science Foundation of China(No.91961126)Jiangsu Development&Reform CommissionChangzhou Development and Reform Commission for their support。
文摘Sodium-ion batteries(SIBs)have received significant attention in large-scale energy storage due to their low cost and abundant resources.To obtain high-performance SIBs,many intensive studies about electrode materials have been carried out,especially the cathode material.As various types of cathode material for SIBs,a 3D open framework structural Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)with Na superionic conductor(NASICON)structure is a promising cathode material owing to its high operating potential and high energy density.However,its electrochemical properties are severely limited by the poor electronic conductivity due to the insulated[PO_(4)]tetrahedral unit.In this review,the challenges and strategies for NVPF are presented,and the synthetic strategy for NVPF is also analyzed in detail.Furthermore,recent developments of modification research to enhance their electrochemical performance are discussed,including designing the crystal structure,adjusting the electrode structure,and optimizing the electrolyte components.Finally,further research and application for future development of NVPF are prospected.
基金financially supported by the National Natural Science Foundation of China(Nos.11904323,11874328 and 211902148)the Certificate of Postdoctoral Research Grant in Henan Province(No.1902014)。
文摘Sc-based nanomaterials have attracted considerable attention due to their unique optical properties different from those of Ln/Y-based nanomaterials.However,studies on Sc-based nanomaterials are far from comprehensive.Particularly,nanoscale alkaline(Ca,Sr and Ba)scandium fluorides were almost ignored for their stringent synthetic conditions.Herein,we synthesize high-quality tetragonal phase Ba_(3)Sc_(2)F_(12) nanocrystals with uniform morphology and good dispersibility by carefully tailoring the reaction conditions,such as the molar ratio of reactants,temperature and reaction time.Then,the upconversion(UC)luminescence property of Ba_(3)Sc_(2)F_(12):Yb/Er(Ho)samples is investigated in detail.The doping concentrations of sensitizer(Yb^(3+))and activator(Er^(3+)and Ho^(3+))are optimized for the strongest UC luminescence,of which the corresponding energy transfer processes are also discussed.Moreover,tetragonal Ba_(3)Sc_(2)F_(12) nanocrystals can gradually transform into hexagonal Ba_(4)Yb_(3)F_(17) nanocrystals with the increase in Yb^(3+)doping content.This work provides a novel type of Sc-based nanomaterials with strong red UC emissions which are promising in high-resolution 3-dimensional color displays,laser,bioimaging and biolabels.
