Na_(2)SiF_(6) was used as surface activating flux for laser welding of TC4 titanium alloy. The effect of Na_(2)SiF_(6) on TC4 titanium alloy laser welding was determined by observing the weld surface. The morphologica...Na_(2)SiF_(6) was used as surface activating flux for laser welding of TC4 titanium alloy. The effect of Na_(2)SiF_(6) on TC4 titanium alloy laser welding was determined by observing the weld surface. The morphological characteristics of the high temperature plasma above the workpiece was observed and analyzed by using high-speed digital camera system. The variation of weld depth,width and microstructure were analyzed by optical microscope. The experimental results show that laser weld of TC4 titanium alloy has good appearance with activating flux of Na_(2)SiF_(6), weld penetration increases by about 0.8%–12%, while weld surface width decrease by about 10%–29%, the depth to width ratio is effectively improved. The inhomogeneity of weld microstructure was improved, and the crystallization direction of β columnar crystals on the upper part of the weld was changed, the grain size and microstructure of the weld were refined by Na_(2)SiF_(6).展开更多
Air-stable layered structured cathodes with high voltage and good cycling stability are highly desired for the practical application of Na-ion batteries.Herein,we report a P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2) cathode that...Air-stable layered structured cathodes with high voltage and good cycling stability are highly desired for the practical application of Na-ion batteries.Herein,we report a P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2) cathode that is stable in ambient air with an average operating voltage of~3.8 V,demonstrating excellent cycling stability with a capacity retention of more than 92.7%after 500 cycles at 20 mA g^(-1) and good rate capability with 91.9%capacity utilization at 500 mA g^(-1) with respect to capacity at 5 mA g^(-1) between 2.0 and 4.0 V.When the upper cutoff voltage is increased to 4.4 V,P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2) delivers a reversible capacity of 71.9 mAh g^(-1) and retains 91.8%of the capacity after 100 cycles at 20 mA g^(-1).The charge compensation during charge/discharge is mainly due to the redox couple of Ni^(2+)/Ni^(3+)in the host with a small amount of contribution from oxygen.The stable structure of the material without phase transformation and with small volume change during charge-discharge allows it to give excellent cycle performance especially when the upper cutoff voltage is not higher than 4.2 V.展开更多
Multiple regression equations of liquidus temperature, electrical conductivity and bath density of the Na_3AlF_6-AlF_3-BaC1_2-NaCl system were obtained from experiments by using orthogonal regression method. The exper...Multiple regression equations of liquidus temperature, electrical conductivity and bath density of the Na_3AlF_6-AlF_3-BaC1_2-NaCl system were obtained from experiments by using orthogonal regression method. The experiments were carried out in 100A cell with low melting point electrolyte, the influences of cathodic current density, electrolytic temperature, density differences of bath and liquid aluminum on current efficiency (CE) were studied; when the electrolyte cryolite ratio was 2.5, w(BaC1_2) and w(NaCl) were 48% and 10%, respectively, CE reached 90% and specific energy consumption was 10.97k Wb/kg/kg. Because of the fact that aluminum metal obtained floated on the surface of molten electrolyte, this electrolysis method was then defined as low temperature aluminum floating electrolysis. The results showed that the new low temperature aluminum electrolysis process in the Na_3AlF_6-AlF_3-BaC1_2-NaCl bath system was practical and promising.展开更多
Full-spectrum phosphor-converted white-light-emitting diodes(pc-WLED)are emerging as a mainstream technology in semiconductor lighting.Nevertheless,high-performance blue phosphor which can be excited efficiently by a ...Full-spectrum phosphor-converted white-light-emitting diodes(pc-WLED)are emerging as a mainstream technology in semiconductor lighting.Nevertheless,high-performance blue phosphor which can be excited efficiently by a 400 nm NUV diode chip is still lacking.Herein,we present a blue-emitting Na_(3)KMg_(7)(PO_(4))6:Eu^(2+)phosphor synthesized by the solid-reaction method.Particularly,we find that the using of Li_(2)CO_(3)as flux can significantly improve the crystal quality and thus the emission efficiency of the phosphor.Meanwhile,the excitation peak of the phosphor shifts from 365 to 400 nm,which is pivotal for efficient NUV(400 nm)diode chip excitation.The practical Eu^(2+)concentration is also enhanced by using Li_(2)CO_(3)as flux,and the absorption efficiency is greatly increased.This phosphor exhibits superior PL thermal stability,namely retains 94%integrated photoluminescence intensity at 150℃of that at 25℃.As a result,the optimized phosphor shows an emission band peaked at 437 nm with a bandwidth of 40 nm and a high external photoluminescence quantum yield of 51.7%.Finally,a pc-WLED was fabricated by using NKMPO:Eu^(2+)blue,Sr_(2)SiO_(4):Eu^(2+)green,CaAlSiN_(3):Eu^(2+)red phosphors,and a 400 nm NUV diode chip.It shows a high color rendering index of R_(a)=96.4 and a correlated color temperature of 4358 K.These results prove that NKMPO:Eu^(2+)is a promising blue phosphor for full-spectrum WLED based on NUV diode chips.展开更多
Sodium-ion batteries(SIBs)are regarded as the ideal low-cost choice for next-generation large-scale energy storage system.Carbonyl-based organic salt-disodium rhodizonate(Na_(2)C_(6)O_(6))with high theoretical specifi...Sodium-ion batteries(SIBs)are regarded as the ideal low-cost choice for next-generation large-scale energy storage system.Carbonyl-based organic salt-disodium rhodizonate(Na_(2)C_(6)O_(6))with high theoretical specific capacity(501 mAh·g−1)is considered as a promising cathode material for SIBs.However,the dissolution of active material in electrolyte and low electronic conductivity lead to rapidly capacity decay and poor rate performance.Herein,a simple method is designed to construct free-standing and flexible Ti3C2Tx Na2C6O6/MXene paper via vacuum-assisted filtration and antisolvent approach.The MXene can form an electronic conductive network,adsorb the active materials,and offer additional active sites for Na storage.The binder-free Na_(2)C_(6)O_(6)/MXene paper delivers excellent electrochemical property with a high rate performance of 231 mAh·g−1 at 1,000 mA·g−1 and a high capacity of 215 mAh·g−1 after 100 cycles.This work provides an attractive strategy for designing high-performance organic electrode materials of SIBs.展开更多
A new P2-structured oxide Na0.8Ni0.4Mn0.6O2was synthesized using a solid reaction method in which Na2CO3, MnO2and NiO were used as starting materials.This oxide has a high amount of electrochemically active Ni and exh...A new P2-structured oxide Na0.8Ni0.4Mn0.6O2was synthesized using a solid reaction method in which Na2CO3, MnO2and NiO were used as starting materials.This oxide has a high amount of electrochemically active Ni and exhibits good electrochemical intercalation behavior of Na ions, including good rate capability and good cycle performance at both room temperature and elevated temperature. It displays two apparent voltage plateaus at about 3.6 and 3.3 V, and its discharge capacity reaches92 mAh·g-1at 0.1 C in the voltage range of 2.0-4.0 V. At1.0 C, its discharge capacity reaches 85.3 mAh·g-1. After80 cycles at different current rates, the as-prepared sample exhibits good capacity retention. At elevated temperature of 55 ℃, the discharge capacity remains the same at low current rate of 0.1 C, but at high current rate of 1.0 C, the discharge capacity is a little lower than that at room temperature.展开更多
In this work,we construct Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(NLTO-L)composites by a simple ball milled process and post-calcination in air atmosphere to improve the electrochemical performance.The thickness of the LiA...In this work,we construct Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(NLTO-L)composites by a simple ball milled process and post-calcination in air atmosphere to improve the electrochemical performance.The thickness of the LiAlO_(2)coating layer is approximate2 nm.The morphology and particle size of Na_(2)Li_(2)Ti_(6)O_(14)are not dramatically altered after LiAlO_(2)coating.All samples display similar particles with a size range from 150 to 500 nm.The LiAlO_(2)coating can supply fast charge transmission paths with good insertion/extraction dynamics of lithium ions and provide an excellent rate performance and cycle performance of as-prepared Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)anodes.Therefore,LiAlO_(2)coating efficiently enhances the rate performance and cycle performance of Na_(2)Li_(2)Ti_(6)O_(14)anode,even at large current densities.As a result,Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(5 wt%)reveals remarkable rate properties with reversible charge capacity of 238.7,214.7,185.8,168.5 and 139.8 mAh g^(-1)at 50,100,200,300 and 500 mA g^(-1),respectively.Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(5 wt%)also possesses a good cycle performance with a de-lithiation capacity of 166.5 mAh g-1 at 500 mA g^(-1)after 200 cycles.Nonetheless,the corresponding de-lithiation capacity of pure Na_(2)Li_(2)Ti_(6)O_(14)is only 140.1 mAh g^(-1).Consequently,LiAlO_(2)coating is efficeient approach to enhance the electrochemical performances of Na_(2)Li_(2)Ti_(6)O_(14).展开更多
Na_(2)Li_(2)Ti_(6)O_(14) as a reliable anode material is becoming a hopeful candidate for Li-ion battery.Nevertheless,the pristine Na_(2)Li_(2)Ti_(6)O_(14) usually suffer from bad rate performance and poor cycling sta...Na_(2)Li_(2)Ti_(6)O_(14) as a reliable anode material is becoming a hopeful candidate for Li-ion battery.Nevertheless,the pristine Na_(2)Li_(2)Ti_(6)O_(14) usually suffer from bad rate performance and poor cycling stability under high current due to limited diffusion kinetics and poor electrical conductivity.Here,the PPy-coated Na_(2)Li_(2)Ti_(6)O_(14) composites are successfully obtained via the solid-state method and followed by chemical oxidation process in the first time.The results of tests prove that the Na_(2)Li_(2)Ti_(6)O_(14)@PPy composites have better electrochemical performance than the bare Na_(2)Li_(2)Ti_(6)O_(14) because of the excellent electrical conductivity and the special macromolecular architecture of PPy.In particular,the Na_(2) Li_(2) Ti_(6) O_(14) @PPy(4 wt%)exhibits excellent charge capacities of about 223.2,218.0,200.8,184.3 and 172.6 mAh g^(-1) at 50,100,200,300 and500 mA g^(-1),respectively,revealing the best rate capability of all electrode materials.The Na_(2)Li_(2)Ti_(6)O_(14)@PPy(4 wt%)not only has the highest charge capacity under 0.5 mA g^(-1),but also has the highest capacity retention of 85.12%among all samples after 100 loops.Hence,the PPy coating is known as a promising way to improve the electrochemical property of Na_(2)Li_(2)Ti_(6)O_(14).The PPy-coated Na_(2)Li_(2)Ti_(6)O_(14) demonstrates the great prospect as promising negative materials for Li-ion batteries.展开更多
Prussian blue analogues(PBAs)have gained significant popularity as cathode materials for sodium-ion batteries(SIBs)due to their remarkable features such as high capacity and convenient synthesis.However,PBAs usually s...Prussian blue analogues(PBAs)have gained significant popularity as cathode materials for sodium-ion batteries(SIBs)due to their remarkable features such as high capacity and convenient synthesis.However,PBAs usually suffer from kinetic problems during the electrochemical reactions due to sluggish Na~+diffusion in the large crystals,resulting in low-capacity utilization and inferior rate capability.In this study,we present a facile etching method aiming at activating the sodium storage sites and accelerating the Na~+transport of Na_2NiFe(CN)_6(denoted as NaNiHCF)by precisely controlling its morphologies.A progressive corner passivation phenomenon occurred in NaNiHCF during the etching process,which led to a substantial augmentation of the specific surface area as the morphology transitioned from a standard cube to a dice shape.Notably,by controlling the etching time,the obtained NaNiHCF-3 electrode exhibited boosted electrochemical performance with high reversible capacity of 83.5mAh g~(-1)(98.2%of its theoretical capacity),superior rate capability(71.2 mAh g~(-1)at 10 C),and stable cycling life-span at different temperatures.Both experimental and computational methods reveal the remarkably reversible structural evolution process and improved Na~+diffusion coefficient.We believe that this work can serve as an indispensable reference to tailor the structure of PBAs to obtain improved electrochemical performance.展开更多
基金National Natural Science Foundation of China (Grant No. 51165027)Inner Mongolia Natural Science Foundationt(2017MS(LH)0512)。
文摘Na_(2)SiF_(6) was used as surface activating flux for laser welding of TC4 titanium alloy. The effect of Na_(2)SiF_(6) on TC4 titanium alloy laser welding was determined by observing the weld surface. The morphological characteristics of the high temperature plasma above the workpiece was observed and analyzed by using high-speed digital camera system. The variation of weld depth,width and microstructure were analyzed by optical microscope. The experimental results show that laser weld of TC4 titanium alloy has good appearance with activating flux of Na_(2)SiF_(6), weld penetration increases by about 0.8%–12%, while weld surface width decrease by about 10%–29%, the depth to width ratio is effectively improved. The inhomogeneity of weld microstructure was improved, and the crystallization direction of β columnar crystals on the upper part of the weld was changed, the grain size and microstructure of the weld were refined by Na_(2)SiF_(6).
基金supported by National Natural Science Foundation of China(Grant No.52100084)Shenzhen Natural Science Fund(the Stable Support Plan Program GXWD20201230155427003-20200824094017001).
文摘Air-stable layered structured cathodes with high voltage and good cycling stability are highly desired for the practical application of Na-ion batteries.Herein,we report a P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2) cathode that is stable in ambient air with an average operating voltage of~3.8 V,demonstrating excellent cycling stability with a capacity retention of more than 92.7%after 500 cycles at 20 mA g^(-1) and good rate capability with 91.9%capacity utilization at 500 mA g^(-1) with respect to capacity at 5 mA g^(-1) between 2.0 and 4.0 V.When the upper cutoff voltage is increased to 4.4 V,P2-Na_(2/3)Ni_(2/3)Te_(1/3)O_(2) delivers a reversible capacity of 71.9 mAh g^(-1) and retains 91.8%of the capacity after 100 cycles at 20 mA g^(-1).The charge compensation during charge/discharge is mainly due to the redox couple of Ni^(2+)/Ni^(3+)in the host with a small amount of contribution from oxygen.The stable structure of the material without phase transformation and with small volume change during charge-discharge allows it to give excellent cycle performance especially when the upper cutoff voltage is not higher than 4.2 V.
基金The project was financially supported by the National Natural Science Foundation of China! (Gmnt No.59574018)China Postdocto
文摘Multiple regression equations of liquidus temperature, electrical conductivity and bath density of the Na_3AlF_6-AlF_3-BaC1_2-NaCl system were obtained from experiments by using orthogonal regression method. The experiments were carried out in 100A cell with low melting point electrolyte, the influences of cathodic current density, electrolytic temperature, density differences of bath and liquid aluminum on current efficiency (CE) were studied; when the electrolyte cryolite ratio was 2.5, w(BaC1_2) and w(NaCl) were 48% and 10%, respectively, CE reached 90% and specific energy consumption was 10.97k Wb/kg/kg. Because of the fact that aluminum metal obtained floated on the surface of molten electrolyte, this electrolysis method was then defined as low temperature aluminum floating electrolysis. The results showed that the new low temperature aluminum electrolysis process in the Na_3AlF_6-AlF_3-BaC1_2-NaCl bath system was practical and promising.
基金Project supported by the National Natural Science Foundation of China(11974351)。
文摘Full-spectrum phosphor-converted white-light-emitting diodes(pc-WLED)are emerging as a mainstream technology in semiconductor lighting.Nevertheless,high-performance blue phosphor which can be excited efficiently by a 400 nm NUV diode chip is still lacking.Herein,we present a blue-emitting Na_(3)KMg_(7)(PO_(4))6:Eu^(2+)phosphor synthesized by the solid-reaction method.Particularly,we find that the using of Li_(2)CO_(3)as flux can significantly improve the crystal quality and thus the emission efficiency of the phosphor.Meanwhile,the excitation peak of the phosphor shifts from 365 to 400 nm,which is pivotal for efficient NUV(400 nm)diode chip excitation.The practical Eu^(2+)concentration is also enhanced by using Li_(2)CO_(3)as flux,and the absorption efficiency is greatly increased.This phosphor exhibits superior PL thermal stability,namely retains 94%integrated photoluminescence intensity at 150℃of that at 25℃.As a result,the optimized phosphor shows an emission band peaked at 437 nm with a bandwidth of 40 nm and a high external photoluminescence quantum yield of 51.7%.Finally,a pc-WLED was fabricated by using NKMPO:Eu^(2+)blue,Sr_(2)SiO_(4):Eu^(2+)green,CaAlSiN_(3):Eu^(2+)red phosphors,and a 400 nm NUV diode chip.It shows a high color rendering index of R_(a)=96.4 and a correlated color temperature of 4358 K.These results prove that NKMPO:Eu^(2+)is a promising blue phosphor for full-spectrum WLED based on NUV diode chips.
基金This work was supported by the Natural Science Foundation of Shandong Province(No.ZR2020JQ19)Taishan Scholars Program of Shandong Province(Nos.tsqn201812002,ts20190908,and ts201511004)+2 种基金the Young Scholars Program of Shandong University(No.2016WLJH03)Shenzhen Fundamental Research Program(No.JCYJ20190807093405503)the National Natural Science Foundation of China(Nos.51972198 and 61633015).
文摘Sodium-ion batteries(SIBs)are regarded as the ideal low-cost choice for next-generation large-scale energy storage system.Carbonyl-based organic salt-disodium rhodizonate(Na_(2)C_(6)O_(6))with high theoretical specific capacity(501 mAh·g−1)is considered as a promising cathode material for SIBs.However,the dissolution of active material in electrolyte and low electronic conductivity lead to rapidly capacity decay and poor rate performance.Herein,a simple method is designed to construct free-standing and flexible Ti3C2Tx Na2C6O6/MXene paper via vacuum-assisted filtration and antisolvent approach.The MXene can form an electronic conductive network,adsorb the active materials,and offer additional active sites for Na storage.The binder-free Na_(2)C_(6)O_(6)/MXene paper delivers excellent electrochemical property with a high rate performance of 231 mAh·g−1 at 1,000 mA·g−1 and a high capacity of 215 mAh·g−1 after 100 cycles.This work provides an attractive strategy for designing high-performance organic electrode materials of SIBs.
基金financially supported by the National Natural Science Foundation of China (No. 51574081)the Natural Science Foundation of Liaoning Province(No. 2014020035)
文摘A new P2-structured oxide Na0.8Ni0.4Mn0.6O2was synthesized using a solid reaction method in which Na2CO3, MnO2and NiO were used as starting materials.This oxide has a high amount of electrochemically active Ni and exhibits good electrochemical intercalation behavior of Na ions, including good rate capability and good cycle performance at both room temperature and elevated temperature. It displays two apparent voltage plateaus at about 3.6 and 3.3 V, and its discharge capacity reaches92 mAh·g-1at 0.1 C in the voltage range of 2.0-4.0 V. At1.0 C, its discharge capacity reaches 85.3 mAh·g-1. After80 cycles at different current rates, the as-prepared sample exhibits good capacity retention. At elevated temperature of 55 ℃, the discharge capacity remains the same at low current rate of 0.1 C, but at high current rate of 1.0 C, the discharge capacity is a little lower than that at room temperature.
基金financially supported by the National Natural Science Foundation of China(No.U1960107)the“333”Talent Project of Hebei Province(No.A202005018)the Fundamental Research Funds for the Central Universities(No N2123001)。
文摘In this work,we construct Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(NLTO-L)composites by a simple ball milled process and post-calcination in air atmosphere to improve the electrochemical performance.The thickness of the LiAlO_(2)coating layer is approximate2 nm.The morphology and particle size of Na_(2)Li_(2)Ti_(6)O_(14)are not dramatically altered after LiAlO_(2)coating.All samples display similar particles with a size range from 150 to 500 nm.The LiAlO_(2)coating can supply fast charge transmission paths with good insertion/extraction dynamics of lithium ions and provide an excellent rate performance and cycle performance of as-prepared Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)anodes.Therefore,LiAlO_(2)coating efficiently enhances the rate performance and cycle performance of Na_(2)Li_(2)Ti_(6)O_(14)anode,even at large current densities.As a result,Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(5 wt%)reveals remarkable rate properties with reversible charge capacity of 238.7,214.7,185.8,168.5 and 139.8 mAh g^(-1)at 50,100,200,300 and 500 mA g^(-1),respectively.Na_(2)Li_(2)Ti_(6)O_(14)@LiAlO_(2)(5 wt%)also possesses a good cycle performance with a de-lithiation capacity of 166.5 mAh g-1 at 500 mA g^(-1)after 200 cycles.Nonetheless,the corresponding de-lithiation capacity of pure Na_(2)Li_(2)Ti_(6)O_(14)is only 140.1 mAh g^(-1).Consequently,LiAlO_(2)coating is efficeient approach to enhance the electrochemical performances of Na_(2)Li_(2)Ti_(6)O_(14).
基金financially supported by the National Natural Science Foundation of China(No.U1960107)the“333”Talent Project of Hebei Province(No.A202005018)the Fundamental Research Funds for the Central Universities(No.N2123001)。
文摘Na_(2)Li_(2)Ti_(6)O_(14) as a reliable anode material is becoming a hopeful candidate for Li-ion battery.Nevertheless,the pristine Na_(2)Li_(2)Ti_(6)O_(14) usually suffer from bad rate performance and poor cycling stability under high current due to limited diffusion kinetics and poor electrical conductivity.Here,the PPy-coated Na_(2)Li_(2)Ti_(6)O_(14) composites are successfully obtained via the solid-state method and followed by chemical oxidation process in the first time.The results of tests prove that the Na_(2)Li_(2)Ti_(6)O_(14)@PPy composites have better electrochemical performance than the bare Na_(2)Li_(2)Ti_(6)O_(14) because of the excellent electrical conductivity and the special macromolecular architecture of PPy.In particular,the Na_(2) Li_(2) Ti_(6) O_(14) @PPy(4 wt%)exhibits excellent charge capacities of about 223.2,218.0,200.8,184.3 and 172.6 mAh g^(-1) at 50,100,200,300 and500 mA g^(-1),respectively,revealing the best rate capability of all electrode materials.The Na_(2)Li_(2)Ti_(6)O_(14)@PPy(4 wt%)not only has the highest charge capacity under 0.5 mA g^(-1),but also has the highest capacity retention of 85.12%among all samples after 100 loops.Hence,the PPy coating is known as a promising way to improve the electrochemical property of Na_(2)Li_(2)Ti_(6)O_(14).The PPy-coated Na_(2)Li_(2)Ti_(6)O_(14) demonstrates the great prospect as promising negative materials for Li-ion batteries.
基金financially supported from the National Natural Science Foundation of China(U20A20249,21972108,and 22209125)。
文摘Prussian blue analogues(PBAs)have gained significant popularity as cathode materials for sodium-ion batteries(SIBs)due to their remarkable features such as high capacity and convenient synthesis.However,PBAs usually suffer from kinetic problems during the electrochemical reactions due to sluggish Na~+diffusion in the large crystals,resulting in low-capacity utilization and inferior rate capability.In this study,we present a facile etching method aiming at activating the sodium storage sites and accelerating the Na~+transport of Na_2NiFe(CN)_6(denoted as NaNiHCF)by precisely controlling its morphologies.A progressive corner passivation phenomenon occurred in NaNiHCF during the etching process,which led to a substantial augmentation of the specific surface area as the morphology transitioned from a standard cube to a dice shape.Notably,by controlling the etching time,the obtained NaNiHCF-3 electrode exhibited boosted electrochemical performance with high reversible capacity of 83.5mAh g~(-1)(98.2%of its theoretical capacity),superior rate capability(71.2 mAh g~(-1)at 10 C),and stable cycling life-span at different temperatures.Both experimental and computational methods reveal the remarkably reversible structural evolution process and improved Na~+diffusion coefficient.We believe that this work can serve as an indispensable reference to tailor the structure of PBAs to obtain improved electrochemical performance.
