以五氧化二钒干凝胶、碳酸锰、磷酸二氢铵、碳酸锂、乙炔黑为原料,采用固相法在相对较低的温度条件下合成了x Li Mn PO4·y Li3V2(PO4)3锂离子电池复合正极材料。采用X射线衍射(XRD)、扫描电镜(SEM)对其晶体结构和表面形貌进行表征...以五氧化二钒干凝胶、碳酸锰、磷酸二氢铵、碳酸锂、乙炔黑为原料,采用固相法在相对较低的温度条件下合成了x Li Mn PO4·y Li3V2(PO4)3锂离子电池复合正极材料。采用X射线衍射(XRD)、扫描电镜(SEM)对其晶体结构和表面形貌进行表征。结果表明,750℃下烧结15 h合成的3Li Mn PO4·Li3V2(PO4)3为结晶良好的两相结构,颗粒粒径较小且分布比较均匀,其在室温、0.2 C倍率下首次充放电容量分别为144.8 m Ah/g和139.8 m Ah/g,循环50次后容量为130.5 m Ah/g。展开更多
Na_(3)V_(2)(PO_(4))_(3)(NVP)has garnered great attentions as a prospective cathode material for sodium-ion batteries(SIBs)by virtue of its decent theoretical capacity,superior ion conductivity and high structural stab...Na_(3)V_(2)(PO_(4))_(3)(NVP)has garnered great attentions as a prospective cathode material for sodium-ion batteries(SIBs)by virtue of its decent theoretical capacity,superior ion conductivity and high structural stability.However,the inherently poor electronic conductivity and sluggish sodium-ion diffusion kinetics of NVP material give rise to inferior rate performance and unsatisfactory energy density,which strictly confine its further application in SIBs.Thus,it is of significance to boost the sodium storage performance of NVP cathode material.Up to now,many methods have been developed to optimize the electrochemical performance of NVP cathode material.In this review,the latest advances in optimization strategies for improving the electrochemical performance of NVP cathode material are well summarized and discussed,including carbon coating or modification,foreign-ion doping or substitution and nanostructure and morphology design.The foreign-ion doping or substitution is highlighted,involving Na,V,and PO_(4)^(3−)sites,which include single-site doping,multiple-site doping,single-ion doping,multiple-ion doping and so on.Furthermore,the challenges and prospects of high-performance NVP cathode material are also put forward.It is believed that this review can provide a useful reference for designing and developing high-performance NVP cathode material toward the large-scale application in SIBs.展开更多
Sodium ion batteries （SIBs） are very promising for large-scale energy storage in virtue of its high energy density, abundant sodium resources and low environmental impact, etc. However, it is still a big chal- lenge...Sodium ion batteries （SIBs） are very promising for large-scale energy storage in virtue of its high energy density, abundant sodium resources and low environmental impact, etc. However, it is still a big chal- lenge to develop high-performance and durable cathode materials for SIBs. Among different candidate materials, Na_3V_2（PO_4）_3 has attracted great attentions due to its high theoretical capacity （117 mAh/g）, stable framework structure and excellent ionic conductivity. However, Na_3V_2（PO_4）_3 delivers inferior rate capability and cycling stability due to its poor electronic conductivity. In this work, free-standing Na_3V_2（PO_4）_3/carbon nanofiber membranes are synthesized by an electrospinning-sintering mute. The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250 cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C, which is superior to many state-of- the-art SIB cathode materials. This can be attributed to the hierarchically distributed Na_3V_2（PO_4）_3 crystals in carbon nanofiber network, which possesses outstanding electronicfionic conductivity and thus leads to an ultrahigh rate capabilitY.展开更多
The photoluminescence of Dy^(3+) doped and Dy^(3+), Ce^(3+) codoped in Ba_3La(BO_3)_3 were studied. The dependence of the charge-to-radius ratio (z/r) for RE^(3+)(RE=La, Ce), the Ce^(3+), Dy^(3+) content on the emissi...The photoluminescence of Dy^(3+) doped and Dy^(3+), Ce^(3+) codoped in Ba_3La(BO_3)_3 were studied. The dependence of the charge-to-radius ratio (z/r) for RE^(3+)(RE=La, Ce), the Ce^(3+), Dy^(3+) content on the emission intensity and the yellow to blue intensity ratio (Y/B) of Dy^(3+) were investigated too. The results obtained indicate that Ce^(3+) can sensitize the luminescence of Dy^(3+). The optimum concentration of Dy^(3+) in Ba_3La(BO_3)_3 is x_(Dy)=0.06. According to the dependence of the concentration of Dy^(3+) in Ba_3La(BO_3)_3 under the excitation of 350 nm, it is confirmed that the mechanism of concentration selfquenching of Dy^(3+) () (()~4F_(9/2)→()~6H_(15/2),) (()~6H_(13/2)) transition is electric dipole-quadrupole interaction.展开更多
Ce_x(CoFe)_(3-x)O_4 ferrites with different contents of Ce have been prepared by wetchemical method. The phases, morphologies and magnetic properties of the products were studied.It has been found that the products we...Ce_x(CoFe)_(3-x)O_4 ferrites with different contents of Ce have been prepared by wetchemical method. The phases, morphologies and magnetic properties of the products were studied.It has been found that the products were a single phase with spinel structure and consisted of granular particles in most cases.The coercive force of the products increased with the increase of concentration of Ce￣(4+) in the reaction solution.On the other hand,if Ce￣(3+) and Ce(OH)_4 were present in the reaction solution,some rod-shape crystals in the products were observed, which causes a great increase in coercive force,and the optimum value was obtained when[Ce￣(3+)] was about 5% of the total([Ce￣(3+)]+[Ce￣(4+)]).展开更多
Europium (Eu￣(3+)) doped polycrystalline (LaO)_3BO_3 has been synthesized by solid state reaction with Li_2CO_3 as flux at 1200℃ for 10 h in air. X- ray powder diffraction shows that ( LaO)_3BO_3 crystallizes in a...Europium (Eu￣(3+)) doped polycrystalline (LaO)_3BO_3 has been synthesized by solid state reaction with Li_2CO_3 as flux at 1200℃ for 10 h in air. X- ray powder diffraction shows that ( LaO)_3BO_3 crystallizes in a monoclinic cell [a= 0. 69214 (9)nm , b=1. 2929(3) nm , c=1. 4590 (3 ) nm . β= 99. 35 (2)°,V= 1. 2882(4 ) nm￣3 and Z= 8] with a possible space group of P2_1/m or P2_1. The predominance of electric-dipole transition ￣5D_0→ ￣7F_2 in the fluorescence spectrum , as well as the splitting of the￣7F_j ground states of Eu￣(3+) reveals that the lanthanum atoms distribute in the sites with C_1 or C_s symmetry in this structure.展开更多
Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol (PEG) as the dispersing media, micro crystalline phosphors Zn_3(PO_4)_2∶Eu 3+ a...Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol (PEG) as the dispersing media, micro crystalline phosphors Zn_3(PO_4)_2∶Eu 3+ and LaPO_4∶Eu 3+ were synthesized by in-situ co-precipitation method. X-ray diffraction and scanning electronic micrograph were used to characterize the resultant samples, whose particle size are in the range of micrometer. The emission spectra of Zn_3(PO_4)_2∶Eu 3+ (λ_ ex=245 nm) and LaPO_4∶Eu 3+ (λ_ ex=390 nm) shows that the emission for Eu 3+ in Zn_3(PO_4)_2 is dominated by the 5D_0→7F_1 (592 nm) magnetic-dipole transition,While the dominant emission for Eu 3+ in LaPO_4 is the typical hypersensitive transition 5D_0→7F_2 (618 nm).展开更多
The luminescent enhancement effect of Na_5Eu(MoO_4)_4 by doping(WO_4)^(2-) has been studied. When the value x in Na_5Eu(Mo_(1-x)W_xO_4)_4 is in 0<x<0.21,its photoluminescent spectrum is near to that of Na_5Eu(Mo...The luminescent enhancement effect of Na_5Eu(MoO_4)_4 by doping(WO_4)^(2-) has been studied. When the value x in Na_5Eu(Mo_(1-x)W_xO_4)_4 is in 0<x<0.21,its photoluminescent spectrum is near to that of Na_5Eu(MoO_4)_4,but its luminescent intensity increases.When x=0.033,the intensity is increased by about 30%.According to the X-ray diffraction analysis,W ions get into the lattice and occupy the sites of the Mo ions.The change of crystal environment of Eu^(3+) may result in the luminescent enhancement.展开更多
The single crystal growth of stoichiometric host luminescent crystal Na_5Eu(WO_4)_4 has been investigated. Using Na_2WO_4 as a flux,the optimum conditions to grow a pure single crystal by flux-slow-cooling method have...The single crystal growth of stoichiometric host luminescent crystal Na_5Eu(WO_4)_4 has been investigated. Using Na_2WO_4 as a flux,the optimum conditions to grow a pure single crystal by flux-slow-cooling method have been determined.A high optical quality single crystal of dimention 4.5 mm has been grown,which is the largest one as we know so far.The micro-hardness of Na_5Eu(WO_4)_4 single crystal is 3.46×10~3 MPa.Its refractive index is 1.81 in white light wavelength region and the specific gravity is 5.65 g/cm^3.The fluorescent and excitation spectra have been determined and the reason of the fluorescent quench of ~5D_2 and ~5D_1 to ~7F_j of Eu^(3+)can be explained as multi-phonon non-radiation transition.展开更多
Objective To study the structural and anticorrosive property of microcrystalline α-Zn_3(PO_4)_2·4H_2O. Methods Zinc phosphate was prepared from zinc acetate and orthophosphate acid in aqueous solution. Structura...Objective To study the structural and anticorrosive property of microcrystalline α-Zn_3(PO_4)_2·4H_2O. Methods Zinc phosphate was prepared from zinc acetate and orthophosphate acid in aqueous solution. Structural characteristics of products were investigated by XRD, RAMAN, FTIR, TG-DTA, SEM, surface area, particle size distribution, and density measurements. Results The title compound, a highly crystalline, micronized and lamellar α-Zn_3(PO_4)_2·4H_2O, has an orthorhombic monoclinic system, space group a_0=10.597(),b_ 0 =18.308(), c_ 0 =5.0304(), V=975.86 3. Its specific area is 0.701m2/g, density 3.1612g/m3, and average size 4.75μm . Conclusion Comparing with commercial Zinc phosphate, the synthesized lamellar microcrystalline zinc phosphate had excellent anticorrosive property and dispersibility.展开更多
文摘以五氧化二钒干凝胶、碳酸锰、磷酸二氢铵、碳酸锂、乙炔黑为原料,采用固相法在相对较低的温度条件下合成了x Li Mn PO4·y Li3V2(PO4)3锂离子电池复合正极材料。采用X射线衍射(XRD)、扫描电镜(SEM)对其晶体结构和表面形貌进行表征。结果表明,750℃下烧结15 h合成的3Li Mn PO4·Li3V2(PO4)3为结晶良好的两相结构,颗粒粒径较小且分布比较均匀,其在室温、0.2 C倍率下首次充放电容量分别为144.8 m Ah/g和139.8 m Ah/g,循环50次后容量为130.5 m Ah/g。
基金partly supported by the National Natural Science Foundation of China(Grant No.52272225).
文摘Na_(3)V_(2)(PO_(4))_(3)(NVP)has garnered great attentions as a prospective cathode material for sodium-ion batteries(SIBs)by virtue of its decent theoretical capacity,superior ion conductivity and high structural stability.However,the inherently poor electronic conductivity and sluggish sodium-ion diffusion kinetics of NVP material give rise to inferior rate performance and unsatisfactory energy density,which strictly confine its further application in SIBs.Thus,it is of significance to boost the sodium storage performance of NVP cathode material.Up to now,many methods have been developed to optimize the electrochemical performance of NVP cathode material.In this review,the latest advances in optimization strategies for improving the electrochemical performance of NVP cathode material are well summarized and discussed,including carbon coating or modification,foreign-ion doping or substitution and nanostructure and morphology design.The foreign-ion doping or substitution is highlighted,involving Na,V,and PO_(4)^(3−)sites,which include single-site doping,multiple-site doping,single-ion doping,multiple-ion doping and so on.Furthermore,the challenges and prospects of high-performance NVP cathode material are also put forward.It is believed that this review can provide a useful reference for designing and developing high-performance NVP cathode material toward the large-scale application in SIBs.
基金the financial support from the 973 program of China (Grant No. 2014CB932401, 2015CB932500)Beijing Nova Program (Grant No. Z161100004916099)the Tsinghua University Initiative Scientific Research Program (Grant Nos. 20173080001, 20151080367)
文摘Sodium ion batteries （SIBs） are very promising for large-scale energy storage in virtue of its high energy density, abundant sodium resources and low environmental impact, etc. However, it is still a big chal- lenge to develop high-performance and durable cathode materials for SIBs. Among different candidate materials, Na_3V_2（PO_4）_3 has attracted great attentions due to its high theoretical capacity （117 mAh/g）, stable framework structure and excellent ionic conductivity. However, Na_3V_2（PO_4）_3 delivers inferior rate capability and cycling stability due to its poor electronic conductivity. In this work, free-standing Na_3V_2（PO_4）_3/carbon nanofiber membranes are synthesized by an electrospinning-sintering mute. The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250 cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C, which is superior to many state-of- the-art SIB cathode materials. This can be attributed to the hierarchically distributed Na_3V_2（PO_4）_3 crystals in carbon nanofiber network, which possesses outstanding electronicfionic conductivity and thus leads to an ultrahigh rate capabilitY.
文摘The photoluminescence of Dy^(3+) doped and Dy^(3+), Ce^(3+) codoped in Ba_3La(BO_3)_3 were studied. The dependence of the charge-to-radius ratio (z/r) for RE^(3+)(RE=La, Ce), the Ce^(3+), Dy^(3+) content on the emission intensity and the yellow to blue intensity ratio (Y/B) of Dy^(3+) were investigated too. The results obtained indicate that Ce^(3+) can sensitize the luminescence of Dy^(3+). The optimum concentration of Dy^(3+) in Ba_3La(BO_3)_3 is x_(Dy)=0.06. According to the dependence of the concentration of Dy^(3+) in Ba_3La(BO_3)_3 under the excitation of 350 nm, it is confirmed that the mechanism of concentration selfquenching of Dy^(3+) () (()~4F_(9/2)→()~6H_(15/2),) (()~6H_(13/2)) transition is electric dipole-quadrupole interaction.
文摘Ce_x(CoFe)_(3-x)O_4 ferrites with different contents of Ce have been prepared by wetchemical method. The phases, morphologies and magnetic properties of the products were studied.It has been found that the products were a single phase with spinel structure and consisted of granular particles in most cases.The coercive force of the products increased with the increase of concentration of Ce￣(4+) in the reaction solution.On the other hand,if Ce￣(3+) and Ce(OH)_4 were present in the reaction solution,some rod-shape crystals in the products were observed, which causes a great increase in coercive force,and the optimum value was obtained when[Ce￣(3+)] was about 5% of the total([Ce￣(3+)]+[Ce￣(4+)]).
文摘Europium (Eu￣(3+)) doped polycrystalline (LaO)_3BO_3 has been synthesized by solid state reaction with Li_2CO_3 as flux at 1200℃ for 10 h in air. X- ray powder diffraction shows that ( LaO)_3BO_3 crystallizes in a monoclinic cell [a= 0. 69214 (9)nm , b=1. 2929(3) nm , c=1. 4590 (3 ) nm . β= 99. 35 (2)°,V= 1. 2882(4 ) nm￣3 and Z= 8] with a possible space group of P2_1/m or P2_1. The predominance of electric-dipole transition ￣5D_0→ ￣7F_2 in the fluorescence spectrum , as well as the splitting of the￣7F_j ground states of Eu￣(3+) reveals that the lanthanum atoms distribute in the sites with C_1 or C_s symmetry in this structure.
文摘Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol (PEG) as the dispersing media, micro crystalline phosphors Zn_3(PO_4)_2∶Eu 3+ and LaPO_4∶Eu 3+ were synthesized by in-situ co-precipitation method. X-ray diffraction and scanning electronic micrograph were used to characterize the resultant samples, whose particle size are in the range of micrometer. The emission spectra of Zn_3(PO_4)_2∶Eu 3+ (λ_ ex=245 nm) and LaPO_4∶Eu 3+ (λ_ ex=390 nm) shows that the emission for Eu 3+ in Zn_3(PO_4)_2 is dominated by the 5D_0→7F_1 (592 nm) magnetic-dipole transition,While the dominant emission for Eu 3+ in LaPO_4 is the typical hypersensitive transition 5D_0→7F_2 (618 nm).
文摘The luminescent enhancement effect of Na_5Eu(MoO_4)_4 by doping(WO_4)^(2-) has been studied. When the value x in Na_5Eu(Mo_(1-x)W_xO_4)_4 is in 0<x<0.21,its photoluminescent spectrum is near to that of Na_5Eu(MoO_4)_4,but its luminescent intensity increases.When x=0.033,the intensity is increased by about 30%.According to the X-ray diffraction analysis,W ions get into the lattice and occupy the sites of the Mo ions.The change of crystal environment of Eu^(3+) may result in the luminescent enhancement.
文摘The single crystal growth of stoichiometric host luminescent crystal Na_5Eu(WO_4)_4 has been investigated. Using Na_2WO_4 as a flux,the optimum conditions to grow a pure single crystal by flux-slow-cooling method have been determined.A high optical quality single crystal of dimention 4.5 mm has been grown,which is the largest one as we know so far.The micro-hardness of Na_5Eu(WO_4)_4 single crystal is 3.46×10~3 MPa.Its refractive index is 1.81 in white light wavelength region and the specific gravity is 5.65 g/cm^3.The fluorescent and excitation spectra have been determined and the reason of the fluorescent quench of ~5D_2 and ~5D_1 to ~7F_j of Eu^(3+)can be explained as multi-phonon non-radiation transition.
文摘Objective To study the structural and anticorrosive property of microcrystalline α-Zn_3(PO_4)_2·4H_2O. Methods Zinc phosphate was prepared from zinc acetate and orthophosphate acid in aqueous solution. Structural characteristics of products were investigated by XRD, RAMAN, FTIR, TG-DTA, SEM, surface area, particle size distribution, and density measurements. Results The title compound, a highly crystalline, micronized and lamellar α-Zn_3(PO_4)_2·4H_2O, has an orthorhombic monoclinic system, space group a_0=10.597(),b_ 0 =18.308(), c_ 0 =5.0304(), V=975.86 3. Its specific area is 0.701m2/g, density 3.1612g/m3, and average size 4.75μm . Conclusion Comparing with commercial Zinc phosphate, the synthesized lamellar microcrystalline zinc phosphate had excellent anticorrosive property and dispersibility.
