Mo（CO）6 adsorption on the clean, oxygen-precovered and deeply oxidized Si（lll） surfaces was comparatively investigated by high-resolution electron energy loss spectroscopy. The downward vibrational frequency shift...Mo（CO）6 adsorption on the clean, oxygen-precovered and deeply oxidized Si（lll） surfaces was comparatively investigated by high-resolution electron energy loss spectroscopy. The downward vibrational frequency shift of the C-O stretching mode in adsorbed Mo（CO）6 illustrates that different interactions of adsorbed Mo（CO）6 occur on clean Si（111） and SiO2/Si（111） surfaces, weak on the former and strong on the latter. The strong interaction on SiO2/Si（111） might lead to the partial dissociation of Mo（CO）6, consequently the formation of molybdenum subcarbonyls. Therefore, employing Mo（CO）6 as the precursor, metallic molybdenum could be successfully deposited on the SiO2/Si（111） surface but not on the clean Si（111） surface. A portion of the deposited metallic molybdenum is transformed into the MoOa on the SiO2/Si（111） surface upon heating, and the evolved MoO3 finally desorbs from the substrate upon annealing at elevated temperatures.展开更多
A HeHPC （Helium high pressure chamber） filled up with pure gaseous helium at initial pressure about 1.1 bar was irradiated by braking γ-rays of 10 MeV threshold energy during 1.0 × 10^5 s at the electron beam ...A HeHPC （Helium high pressure chamber） filled up with pure gaseous helium at initial pressure about 1.1 bar was irradiated by braking γ-rays of 10 MeV threshold energy during 1.0 × 10^5 s at the electron beam current 22 - 24 μA. After irradiation, the residual pressure inside was equal to 430 bar. Synthesized foils of black color and other multiple objects were found inside the HeHPC mainly at the entrance window for γ-rays made from beryllium bronze as a plug of beryllium bronze HPC, at the inner surfaces of the reaction chamber made of high purity copper and at the copper collector. The element analysis, using SEM （Scanning electron microscopy） and MPRA （Microprobe roentgen analysis）, allowed us to establish that the foils consist predominantly of carbon and the smaller quantities of other elements from carbon to iron. An explanation for the observed elements is suggested on the basis of helium fusion reactions under the action of y-rays with the reactions taking place in giant stars （thermally activated）. The possible mechanism after 3α reaction is nα reactions and under barrier reactions. A second experiment with initial pressure of 3.05 kbar （with pressure drop by about 65 bar - after almost the same procedure of y-rays irradiation and with fully beryl bronze environment） suggests another possible nuclear reactions - He（Be, p）C, He（C, γ）O, and so on. The developed approach agrees well with a series of studies carried out by the authors where dense hydrogen and deuterium gases are acted on by γ-rays in the presence or absence of metals in the reaction chambers.展开更多
The elevated-temperature mechanical properties and thermal stability of Al-Cu-Mg-Ag heat-resistant alloy were studied by tensile test, transmission electron microscopy(TEM) and scanning electron microscopy(SEM), respe...The elevated-temperature mechanical properties and thermal stability of Al-Cu-Mg-Ag heat-resistant alloy were studied by tensile test, transmission electron microscopy(TEM) and scanning electron microscopy(SEM), respectively. The results show that with the increase of Ag content, the tensile strength and yield strength increase, which is attributed to the increase of the precipitations number and the decrease of the size. The same conclusions are drawn in the study of increasing Mg content. The alloy possesses excellent thermal stability. At 100-150 °C, the strength of the under-aged alloy increases at the initial stage, and after reaching the peak strength, it remains the same. The secondary precipitation of the under-aged alloy occurs in the process of exposure at 150℃, and it distributes diffusely after thermal exposed for 20 h. Then, the tensile strength decreases gradually with increasing the thermal exposure time at 200-250 °C. The strength of the peak-aged alloy decreases gradually, and the precipitation grows up, but the number decreases gradually with prolonging the exposure time at 100-250 °C. The strength of two kinds of alloys decreases with elevating of exposure temperature.展开更多
Using the model of the inverse Compton scattering between high-energy electrons and heat-radiation photons, the influence of heat-radiating photons on multi-photon Compton scattering high-energy electrons is studied ....Using the model of the inverse Compton scattering between high-energy electrons and heat-radiation photons, the influence of heat-radiating photons on multi-photon Compton scattering high-energy electrons is studied . The results show that the energy loss, power loss, light resistance and light pressure of the high-energy electron formed by heat radiating are all proportional to the temperature T4 of the vacuum cavity of the electron,the Lorentz factor γ2 of the high-energy electrons, the scattering section of the electron and the number of photons acting at the same time with high-energy electrons. A good method for lessening the energy loss of the high-energy electron by using the one-photon Compton scattering between high-energy electrons and heat radiation photons is proposed.展开更多
We present analytical studies of electron acceleration in the low-density preplasma of a thin solid target byan intense femtosecond laser pulse.Electrons in the preplasma are trapped and accelerated by the ponderomoti...We present analytical studies of electron acceleration in the low-density preplasma of a thin solid target byan intense femtosecond laser pulse.Electrons in the preplasma are trapped and accelerated by the ponderomotive forceas well as the wake field.Two-dimensional particle-in-cell simulations show that when the laser pulse is stopped by thetarget,electrons trapped in the laser pules can be extracted and move forward inertially.The energetic electron bunchin the bubble is unaffected by the reflected pulse and passes through the target with small energy spread and emittance.There is an optimal preplasma density for the generation of the monoenergetic electron bunch if a laser pulse is given.The maximum electron energy is inverse proportion to the preplasma density.展开更多
The evolution of energetic outer zone electron fluxes during the strong magnetic storm on September 28, 2002 is investigated based on the observations of SAMPEX and GOES-10 satellites. The observations of both satelli...The evolution of energetic outer zone electron fluxes during the strong magnetic storm on September 28, 2002 is investigated based on the observations of SAMPEX and GOES-10 satellites. The observations of both satellites showed that energetic electron fluxes increased significantly during the storm recovery phase, and reached the maximum on October 6. The 1.5–14 MeV and 2.5–14 MeV electron fluxes observed by SAMPEX peaked around L=3.5 with values of 6×10 2 cm -2 s -1 sr -1 keV -1 and 5×10 3 cm -2 s -1 sr -1 keV -1 , which were about 10 and 8 times the pre-storm values. At the geostationary orbit, the >0.6 MeV and >2 MeV electron fluxes observed by GOES-10 showed enhancement up to 50 and 30 times. The plasma parameters and whistler-mode chorus waves in the outer radiation belt are also analyzed based on the data from Cluster C3 satellite. Cluster C3 satellite went through the outer radiation belt twice from 1 October to 4 October, and observed whistler-mode chorus waves with high intensity (10 -5 –10 -4 nT 2 Hz -1 ). Numerical calculations indicated that the observed chorus waves were in gyro-resonance with the radiation belt electrons. The current observations and calculations provide new evidence for that the gyro-resonance with chorus waves contribute significantly to the buildup of energetic outer zone electron fluxes during storms.展开更多
Based on the magnetospheric kinetic theory, a model is developed to specify the flux of energetic electrons in the inner and middle magnetosphere. Under the assumption of adiabatic motion and isotropic particle distri...Based on the magnetospheric kinetic theory, a model is developed to specify the flux of energetic electrons in the inner and middle magnetosphere. Under the assumption of adiabatic motion and isotropic particle distribution maintained by pitch-angle scattering, the model calculates the electron flux by following bounce-averaged electric field, gradient, and curvature drift in the time dependent electric and magnetic field, meanwhile it counts the electron loss caused by pitch angle scattering. Using the model, the clectron flux distribution during a magnetic storm was calculated and compared with the observation data from the geosynchronous orbit. It is shown that the model can successfully reproduce most of the major electron flux enhancements observed at the geosynchronous orbit and generally tracks the satellite data well. The rms errors of the modeled logarithm of flux are between 0.5-1.0.展开更多
Li-ion batteries have played a key role in the portable electronics and electrification of transport in modern society. Nevertheless,the limited highest energy density of Li-ion batteries is not sufficient for the lon...Li-ion batteries have played a key role in the portable electronics and electrification of transport in modern society. Nevertheless,the limited highest energy density of Li-ion batteries is not sufficient for the long-term needs of society. Since lithium is the lightest metal among all metallic elements and possesses the lowest redox potential of.3.04 V vs. standard hydrogen electrode, it delivers the highest theoretical specific capacity of 3860 mA h g^(-1) and a high working voltage of full batteries which causes a great interest in electrochemical energy storage systems. Lithium-sulfur, lithium-oxygen and corresponding all solid state batteries based on metal lithium anode have received widely attention owing to their high energy densities. However, the problems in the cathode,electrolyte and anode of these three systems restrict their practical application. In this review, the research status and problems of these three energy storage systems are summarized and the challenges and future perspectives are also outlined.展开更多
The variation of the flux of energetic electrons in the magnetosphere has been proven to be strongly related to the solar wind speed. Observations of GEO orbit show that the flux of low-energy electrons is not only mo...The variation of the flux of energetic electrons in the magnetosphere has been proven to be strongly related to the solar wind speed. Observations of GEO orbit show that the flux of low-energy electrons is not only modulated by the solar wind speed, but, if a time delay is added, is also positively correlated to the flux of high-energy electrons. This feature provides a possible method to forecast the flux of high-energy electrons in GEO orbit. In this study, the correlations of the fluxes between the high-energy electrons and low-middle-energy electrons obtained at different L values and in different orbits are investigated to develop the application of this feature. Based on the analysis of long–term data observed by NOAA POES and GOES, the correlations between the fluxes of high-energy electrons and low–middle–energy electrons are good enough at different L values and in different orbits in quiet time, but this correlation is strongly affected by CME–driven geomagnetic storms.展开更多
Lithium ion batteries （LIBs） represent one of the most promising solutions for environmentally friendly transportation such as electric vehicles. The demand for high energy density, low cost and environmentally frie...Lithium ion batteries （LIBs） represent one of the most promising solutions for environmentally friendly transportation such as electric vehicles. The demand for high energy density, low cost and environmentally friendly batteries makes high-capacity cathode materials very attractive for future LIBs. Layered LiNixCoyMn2O2 （x＋y＋z=1）, Li-rich oxides and Li-V-O compounds have attracted much attention due to their high capacities in recent years. In this review, we focus on the state-of-the-art research activities related to LiNixCoyMn2O2, Li-rich oxides and Li-V-O compounds, including their structures, reaction mechanisms during cycling, challenges and strategies that have been studied to improve their electrochemical performances.展开更多
Large specific surface area is critical for Li4Ti5O12 to achieve good rate capacity and cycling stability, since it can increase the contact area between electrolyte/ electrode and shorten the transport paths for elec...Large specific surface area is critical for Li4Ti5O12 to achieve good rate capacity and cycling stability, since it can increase the contact area between electrolyte/ electrode and shorten the transport paths for electrons and lithium ions. In this study, hierarchical hollow Li4Ti5O12 urchin-like microspheres with ultra-high specific surface area of over 140 m2·g^-1 and diameter more than 500 nm have been successfully synthesized by combining the versatile sol-gel process and a hydrothermal reaction, and exhibit excellent electrochemical performance with a high specific capacity of 120 mA-h.g-1 at 20 C and long cycling stability of 〈 2% decay after 100 cycles. Ex situ electron energy loss spectroscopy （EELS） analysis of Li4Ti5O12 microspheres at different charge-discharge stages indicates that only a fraction of the TP＊ ions are reduced to Ti3＋ and a phase transformation occurs whereby the spinel phase Li4TisO12 is converted into the rock-salt phase Li7Ti5O12. Even after 100 cycles, the oxidation-reduction reaction between Ti3＋ and Ti4＋ can be carried out much more effectively on the surface of Li4Ti5O12 nanosheets than on commercially available Li4Ti5O12 particles. All the results suggest that these Li4Ti5O12 microspheres may be attractive candidate anode materials for lithium ion batteries.展开更多
The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithi...The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO2 nanotubes （NTs） branched onto a carbon nanofiber （CNF） ＂tree＂ that provide a low resistance current path between the current collector and the TiO2 NTs. Compared to a TiO2 NT array grown directly on the current collector, the branched TiO2 NTs tree, coupled with the CNF electrode, exhibited -10 times higher areal energy density and excellent rate capability （discharge capacity of -150 mA.h.g-1 at a current density of 1,000 mA·g-1）. Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity （mA·h·cm-2） as well as excellent rate capability.展开更多
Fiber-shaped energy storage devices are indispensable parts of wearable and portable electronics.Aqueous rechargeable Ni/Fe battery is a very appropriate energy storage device due to their good safety without organic ...Fiber-shaped energy storage devices are indispensable parts of wearable and portable electronics.Aqueous rechargeable Ni/Fe battery is a very appropriate energy storage device due to their good safety without organic electrolytes, high ionic conductivity, and low cost. Unfortunately, the low energy density,poor power density and cycling performance hinder its further practical applications. In this study, in order to obtain high performance negative iron-based material, we first synthesized a-iron oxide(α-Fe2O3) nanorods(NRs) with superstructures on the surface of highly conductive carbon nanotube fibers(CNTFs), then electrically conductive polypyrrole(PPy) was coated to enhance the electron, ion diffusion and cycle stability. The as-prepared α-Fe2O3@PPy NRs/CNTF electrode shows a high specific capacity of 0.62 Ah cm-3 at the current density of 1 A cm-3. Furthermore, the Ni/Fe battery that was assembled by the above negative electrode shows a maximum volumetric energy density of 15.47 mWh cm-3 with228.2 mW cm-3 at a current density of 1 A cm-3. The cycling durability and mechanical flexibility of the Ni/Fe battery were tested, which show good prospect for practical application. In summary, these merits make it possible for our Ni/Fe battery to have practical applications in next generation flexible energy storage devices.展开更多
As promising,low-cost alternatives of lithiumion batteries for large-scale electric energy storage,sodiumion batteries(SIBs)have been studied by many researchers.However,the relatively large size of Na+leads to sluggi...As promising,low-cost alternatives of lithiumion batteries for large-scale electric energy storage,sodiumion batteries(SIBs)have been studied by many researchers.However,the relatively large size of Na+leads to sluggish diffusion kinetics and poor cycling stability in most cathode materials,restricting their further applications.In this work,we demonstrated a novel K+-intercalated Mn/Ni-based layered oxide material(K0.7Mn0.7Ni0.3O2,denoted as KMNO)with stabilized and enlarged diffusion channels for high energy density SIBs.A spontaneous ion exchange behavior in forming K0.1Na0.7Mn0.7Ni0.3O2between the KMNO electrode and the sodium ion electrolyte was clearly revealed by in situ X-ray diffraction and ex situ inductively coupled plasma analysis.The interlayer space varied from 6.90 to 5.76?,larger than that of Na0.7Mn0.7Ni0.3O2(5.63?).The enlarged ionic diffusion channels can effectively increase the ionic diffusion coefficient and simultaneously provide more K+storage sites in the product framework.As a proof-of-concept application,the SIBs with the as-prepared KMNO as a cathode display a high reversible discharge capacity(161.8 mA h g-1at0.1 A g-1),high energy density(459 W h kg-1)and superior rate capability of 71.1 mA h g-1at 5 A g-1.Our work demonstrates that the K+pre-intercalation strategy endows the layered metal oxides with excellent sodium storage performance,which provides new directions for the design of cathode materials for various batteries.展开更多
We investigate the flux evolution of geostationary orbit energetic electrons during a strong storm on 24 August 2005(event A,the storm index Dst<200 nT,the average substorm index AE=436 nT)and a weak storm on 28 Oc...We investigate the flux evolution of geostationary orbit energetic electrons during a strong storm on 24 August 2005(event A,the storm index Dst<200 nT,the average substorm index AE=436 nT)and a weak storm on 28 October 2006(event B,Dst>50 nT,average AE=320 nT).Data collected by LANL and GOES-12 satellites show that energetic electron fluxes increase by a factor of 10 during the recovery phase compared to the prestorm level for both events A and B.As the substorm continued,the Cluster C4 satellite observed strong whistler-mode chorus waves(with spectral density approaching 10 5nT2/Hz).The wave amplitude correlates with the substorm AE index,but is less correlated with the storm Dst index.Using a Gaussian distribution fitting method,we solve the Fokker-Planck diffusion equation governing the wave-particle interaction.Numerical results demonstrate that chorus waves efficiently accelerate^1 MeV energetic electrons,particularly at high pitch angles.The calculated acceleration time scale and amplitude are comparable to observations.Our results provide new observational support for chorus-driven acceleration of radiation belt energetic electrons.展开更多
文摘Mo（CO）6 adsorption on the clean, oxygen-precovered and deeply oxidized Si（lll） surfaces was comparatively investigated by high-resolution electron energy loss spectroscopy. The downward vibrational frequency shift of the C-O stretching mode in adsorbed Mo（CO）6 illustrates that different interactions of adsorbed Mo（CO）6 occur on clean Si（111） and SiO2/Si（111） surfaces, weak on the former and strong on the latter. The strong interaction on SiO2/Si（111） might lead to the partial dissociation of Mo（CO）6, consequently the formation of molybdenum subcarbonyls. Therefore, employing Mo（CO）6 as the precursor, metallic molybdenum could be successfully deposited on the SiO2/Si（111） surface but not on the clean Si（111） surface. A portion of the deposited metallic molybdenum is transformed into the MoOa on the SiO2/Si（111） surface upon heating, and the evolved MoO3 finally desorbs from the substrate upon annealing at elevated temperatures.
文摘A HeHPC （Helium high pressure chamber） filled up with pure gaseous helium at initial pressure about 1.1 bar was irradiated by braking γ-rays of 10 MeV threshold energy during 1.0 × 10^5 s at the electron beam current 22 - 24 μA. After irradiation, the residual pressure inside was equal to 430 bar. Synthesized foils of black color and other multiple objects were found inside the HeHPC mainly at the entrance window for γ-rays made from beryllium bronze as a plug of beryllium bronze HPC, at the inner surfaces of the reaction chamber made of high purity copper and at the copper collector. The element analysis, using SEM （Scanning electron microscopy） and MPRA （Microprobe roentgen analysis）, allowed us to establish that the foils consist predominantly of carbon and the smaller quantities of other elements from carbon to iron. An explanation for the observed elements is suggested on the basis of helium fusion reactions under the action of y-rays with the reactions taking place in giant stars （thermally activated）. The possible mechanism after 3α reaction is nα reactions and under barrier reactions. A second experiment with initial pressure of 3.05 kbar （with pressure drop by about 65 bar - after almost the same procedure of y-rays irradiation and with fully beryl bronze environment） suggests another possible nuclear reactions - He（Be, p）C, He（C, γ）O, and so on. The developed approach agrees well with a series of studies carried out by the authors where dense hydrogen and deuterium gases are acted on by γ-rays in the presence or absence of metals in the reaction chambers.
基金Project(2012zzts067)supported by the Freedom Explore Program of Central South University,China
文摘The elevated-temperature mechanical properties and thermal stability of Al-Cu-Mg-Ag heat-resistant alloy were studied by tensile test, transmission electron microscopy(TEM) and scanning electron microscopy(SEM), respectively. The results show that with the increase of Ag content, the tensile strength and yield strength increase, which is attributed to the increase of the precipitations number and the decrease of the size. The same conclusions are drawn in the study of increasing Mg content. The alloy possesses excellent thermal stability. At 100-150 °C, the strength of the under-aged alloy increases at the initial stage, and after reaching the peak strength, it remains the same. The secondary precipitation of the under-aged alloy occurs in the process of exposure at 150℃, and it distributes diffusely after thermal exposed for 20 h. Then, the tensile strength decreases gradually with increasing the thermal exposure time at 200-250 °C. The strength of the peak-aged alloy decreases gradually, and the precipitation grows up, but the number decreases gradually with prolonging the exposure time at 100-250 °C. The strength of two kinds of alloys decreases with elevating of exposure temperature.
基金Natural Science Foundation of Zhumadian City(058002)
文摘Using the model of the inverse Compton scattering between high-energy electrons and heat-radiation photons, the influence of heat-radiating photons on multi-photon Compton scattering high-energy electrons is studied . The results show that the energy loss, power loss, light resistance and light pressure of the high-energy electron formed by heat radiating are all proportional to the temperature T4 of the vacuum cavity of the electron,the Lorentz factor γ2 of the high-energy electrons, the scattering section of the electron and the number of photons acting at the same time with high-energy electrons. A good method for lessening the energy loss of the high-energy electron by using the one-photon Compton scattering between high-energy electrons and heat radiation photons is proposed.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10875015,10834008,10963002the 973 Program under Grant No.2006CB806004Educational Commission of Jiangxi Province of China under Grant No.GJJ10052
文摘We present analytical studies of electron acceleration in the low-density preplasma of a thin solid target byan intense femtosecond laser pulse.Electrons in the preplasma are trapped and accelerated by the ponderomotive forceas well as the wake field.Two-dimensional particle-in-cell simulations show that when the laser pulse is stopped by thetarget,electrons trapped in the laser pules can be extracted and move forward inertially.The energetic electron bunchin the bubble is unaffected by the reflected pulse and passes through the target with small energy spread and emittance.There is an optimal preplasma density for the generation of the monoenergetic electron bunch if a laser pulse is given.The maximum electron energy is inverse proportion to the preplasma density.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40925014, 40874076)
文摘The evolution of energetic outer zone electron fluxes during the strong magnetic storm on September 28, 2002 is investigated based on the observations of SAMPEX and GOES-10 satellites. The observations of both satellites showed that energetic electron fluxes increased significantly during the storm recovery phase, and reached the maximum on October 6. The 1.5–14 MeV and 2.5–14 MeV electron fluxes observed by SAMPEX peaked around L=3.5 with values of 6×10 2 cm -2 s -1 sr -1 keV -1 and 5×10 3 cm -2 s -1 sr -1 keV -1 , which were about 10 and 8 times the pre-storm values. At the geostationary orbit, the >0.6 MeV and >2 MeV electron fluxes observed by GOES-10 showed enhancement up to 50 and 30 times. The plasma parameters and whistler-mode chorus waves in the outer radiation belt are also analyzed based on the data from Cluster C3 satellite. Cluster C3 satellite went through the outer radiation belt twice from 1 October to 4 October, and observed whistler-mode chorus waves with high intensity (10 -5 –10 -4 nT 2 Hz -1 ). Numerical calculations indicated that the observed chorus waves were in gyro-resonance with the radiation belt electrons. The current observations and calculations provide new evidence for that the gyro-resonance with chorus waves contribute significantly to the buildup of energetic outer zone electron fluxes during storms.
基金supported by the National Natural Science Foundation of China(Grant No.40704032)
文摘Based on the magnetospheric kinetic theory, a model is developed to specify the flux of energetic electrons in the inner and middle magnetosphere. Under the assumption of adiabatic motion and isotropic particle distribution maintained by pitch-angle scattering, the model calculates the electron flux by following bounce-averaged electric field, gradient, and curvature drift in the time dependent electric and magnetic field, meanwhile it counts the electron loss caused by pitch angle scattering. Using the model, the clectron flux distribution during a magnetic storm was calculated and compared with the observation data from the geosynchronous orbit. It is shown that the model can successfully reproduce most of the major electron flux enhancements observed at the geosynchronous orbit and generally tracks the satellite data well. The rms errors of the modeled logarithm of flux are between 0.5-1.0.
基金supported by the National Basic Research Program of China(2014CB932301)the National Natural Science Foundation of China(21473040)Science&Technology Commission of Shanghai Municipality(08DZ2270500)
文摘Li-ion batteries have played a key role in the portable electronics and electrification of transport in modern society. Nevertheless,the limited highest energy density of Li-ion batteries is not sufficient for the long-term needs of society. Since lithium is the lightest metal among all metallic elements and possesses the lowest redox potential of.3.04 V vs. standard hydrogen electrode, it delivers the highest theoretical specific capacity of 3860 mA h g^(-1) and a high working voltage of full batteries which causes a great interest in electrochemical energy storage systems. Lithium-sulfur, lithium-oxygen and corresponding all solid state batteries based on metal lithium anode have received widely attention owing to their high energy densities. However, the problems in the cathode,electrolyte and anode of these three systems restrict their practical application. In this review, the research status and problems of these three energy storage systems are summarized and the challenges and future perspectives are also outlined.
基金supported by the National Natural Science Foundation of China(Grant Nos.41374167,41074117&41374166)
文摘The variation of the flux of energetic electrons in the magnetosphere has been proven to be strongly related to the solar wind speed. Observations of GEO orbit show that the flux of low-energy electrons is not only modulated by the solar wind speed, but, if a time delay is added, is also positively correlated to the flux of high-energy electrons. This feature provides a possible method to forecast the flux of high-energy electrons in GEO orbit. In this study, the correlations of the fluxes between the high-energy electrons and low-middle-energy electrons obtained at different L values and in different orbits are investigated to develop the application of this feature. Based on the analysis of long–term data observed by NOAA POES and GOES, the correlations between the fluxes of high-energy electrons and low–middle–energy electrons are good enough at different L values and in different orbits in quiet time, but this correlation is strongly affected by CME–driven geomagnetic storms.
文摘Lithium ion batteries （LIBs） represent one of the most promising solutions for environmentally friendly transportation such as electric vehicles. The demand for high energy density, low cost and environmentally friendly batteries makes high-capacity cathode materials very attractive for future LIBs. Layered LiNixCoyMn2O2 （x＋y＋z=1）, Li-rich oxides and Li-V-O compounds have attracted much attention due to their high capacities in recent years. In this review, we focus on the state-of-the-art research activities related to LiNixCoyMn2O2, Li-rich oxides and Li-V-O compounds, including their structures, reaction mechanisms during cycling, challenges and strategies that have been studied to improve their electrochemical performances.
文摘Large specific surface area is critical for Li4Ti5O12 to achieve good rate capacity and cycling stability, since it can increase the contact area between electrolyte/ electrode and shorten the transport paths for electrons and lithium ions. In this study, hierarchical hollow Li4Ti5O12 urchin-like microspheres with ultra-high specific surface area of over 140 m2·g^-1 and diameter more than 500 nm have been successfully synthesized by combining the versatile sol-gel process and a hydrothermal reaction, and exhibit excellent electrochemical performance with a high specific capacity of 120 mA-h.g-1 at 20 C and long cycling stability of 〈 2% decay after 100 cycles. Ex situ electron energy loss spectroscopy （EELS） analysis of Li4Ti5O12 microspheres at different charge-discharge stages indicates that only a fraction of the TP＊ ions are reduced to Ti3＋ and a phase transformation occurs whereby the spinel phase Li4TisO12 is converted into the rock-salt phase Li7Ti5O12. Even after 100 cycles, the oxidation-reduction reaction between Ti3＋ and Ti4＋ can be carried out much more effectively on the surface of Li4Ti5O12 nanosheets than on commercially available Li4Ti5O12 particles. All the results suggest that these Li4Ti5O12 microspheres may be attractive candidate anode materials for lithium ion batteries.
文摘The inherently low electrical conductivity of TiO2-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO2 nanotubes （NTs） branched onto a carbon nanofiber （CNF） ＂tree＂ that provide a low resistance current path between the current collector and the TiO2 NTs. Compared to a TiO2 NT array grown directly on the current collector, the branched TiO2 NTs tree, coupled with the CNF electrode, exhibited -10 times higher areal energy density and excellent rate capability （discharge capacity of -150 mA.h.g-1 at a current density of 1,000 mA·g-1）. Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity （mA·h·cm-2） as well as excellent rate capability.
基金This work was supported by the National Natural Science Foundation of China (51972162 and 51703241)the Postdoctoral Foundation of Jiangsu Province (2019Z203 and 2019K001)the Science and Technology Project of Nanchang (2017-SJSYS008)
文摘Fiber-shaped energy storage devices are indispensable parts of wearable and portable electronics.Aqueous rechargeable Ni/Fe battery is a very appropriate energy storage device due to their good safety without organic electrolytes, high ionic conductivity, and low cost. Unfortunately, the low energy density,poor power density and cycling performance hinder its further practical applications. In this study, in order to obtain high performance negative iron-based material, we first synthesized a-iron oxide(α-Fe2O3) nanorods(NRs) with superstructures on the surface of highly conductive carbon nanotube fibers(CNTFs), then electrically conductive polypyrrole(PPy) was coated to enhance the electron, ion diffusion and cycle stability. The as-prepared α-Fe2O3@PPy NRs/CNTF electrode shows a high specific capacity of 0.62 Ah cm-3 at the current density of 1 A cm-3. Furthermore, the Ni/Fe battery that was assembled by the above negative electrode shows a maximum volumetric energy density of 15.47 mWh cm-3 with228.2 mW cm-3 at a current density of 1 A cm-3. The cycling durability and mechanical flexibility of the Ni/Fe battery were tested, which show good prospect for practical application. In summary, these merits make it possible for our Ni/Fe battery to have practical applications in next generation flexible energy storage devices.
基金supported by the National Natural Science Foundation of China(51872218 and 51832004)the National Key R&D Program of China(2016YFA0202603)the Fundamental Research Funds for the Central Universities(WUT:2017III009)。
文摘As promising,low-cost alternatives of lithiumion batteries for large-scale electric energy storage,sodiumion batteries(SIBs)have been studied by many researchers.However,the relatively large size of Na+leads to sluggish diffusion kinetics and poor cycling stability in most cathode materials,restricting their further applications.In this work,we demonstrated a novel K+-intercalated Mn/Ni-based layered oxide material(K0.7Mn0.7Ni0.3O2,denoted as KMNO)with stabilized and enlarged diffusion channels for high energy density SIBs.A spontaneous ion exchange behavior in forming K0.1Na0.7Mn0.7Ni0.3O2between the KMNO electrode and the sodium ion electrolyte was clearly revealed by in situ X-ray diffraction and ex situ inductively coupled plasma analysis.The interlayer space varied from 6.90 to 5.76?,larger than that of Na0.7Mn0.7Ni0.3O2(5.63?).The enlarged ionic diffusion channels can effectively increase the ionic diffusion coefficient and simultaneously provide more K+storage sites in the product framework.As a proof-of-concept application,the SIBs with the as-prepared KMNO as a cathode display a high reversible discharge capacity(161.8 mA h g-1at0.1 A g-1),high energy density(459 W h kg-1)and superior rate capability of 71.1 mA h g-1at 5 A g-1.Our work demonstrates that the K+pre-intercalation strategy endows the layered metal oxides with excellent sodium storage performance,which provides new directions for the design of cathode materials for various batteries.
基金supported by the National Natural Science Foundation of China(Grant Nos.40925014&41274165)Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Provincethe Construct Program of the Key Discipline inHunan Province
文摘We investigate the flux evolution of geostationary orbit energetic electrons during a strong storm on 24 August 2005(event A,the storm index Dst<200 nT,the average substorm index AE=436 nT)and a weak storm on 28 October 2006(event B,Dst>50 nT,average AE=320 nT).Data collected by LANL and GOES-12 satellites show that energetic electron fluxes increase by a factor of 10 during the recovery phase compared to the prestorm level for both events A and B.As the substorm continued,the Cluster C4 satellite observed strong whistler-mode chorus waves(with spectral density approaching 10 5nT2/Hz).The wave amplitude correlates with the substorm AE index,but is less correlated with the storm Dst index.Using a Gaussian distribution fitting method,we solve the Fokker-Planck diffusion equation governing the wave-particle interaction.Numerical results demonstrate that chorus waves efficiently accelerate^1 MeV energetic electrons,particularly at high pitch angles.The calculated acceleration time scale and amplitude are comparable to observations.Our results provide new observational support for chorus-driven acceleration of radiation belt energetic electrons.
