Novel high-voltage cathode for aqueous zinc ion batteries:Porous K_(0.5)VOPO_(4)·1.5H_(2)O with reversible solid-solution intercalation and conversion storage mechanism

Cathode materials that possess high output voltage,as well as those that can be mass-produced using facile techniques,are crucial for the advancement of aqueous zinc-ion battery(ZIBs)applications,Herein,we present for the first time a new porous K_(0.5)VOPO_(4)·1.5H_(2)O polyanionic cathode(P-KIVP)with high output voltage(above 1.2 V)that can be manufactured at room temperature using straightforward coprecipitation and etching techniques.The P-KVP cathode experiences anisotropic crystal plane expansion via a sequential solid-solution intercalation and phase co nversion pathway throughout the Zn^(2+)storage process,as confirmed by in-situ synchrotron X-ray diffraction and ex-situ X-ray photoelectron spectroscopy.Similar to other layered vanadium-based polyanionic materials,the P-KVP cathode experiences a progressive decline in voltage during the cycle,which is demonstrated to be caused by the irreversible conversion into amorphous VO_(x).By introducing a new electrolyte containing Zn(OTF)_(2) to a mixed triethyl phosphate and water solution,it is possible to impede this irreversible conversion and obtain a high output voltage and longer cycle life by forming a P-rich cathode electrolyte interface layer.As a proof-of-concept,the flexible fiber-shaped ZIBs based on modified electrolyte woven into a fabric watch band can power an electronic watch,highlighting the application potential of P-KVP cathode.

Operando X-ray diffraction analysis of the degradation mechanisms of a spinel LiMn2O4 cathode in different voltage windows

The understanding of reaction mechanisms of electrode materials is of significant importance for the development of advanced batteries.The LiMn2O4 cathode has a voltage plateau around 2.8 V(vs.Li^+/Li),which can provide an additional capacity for Li storage,but it suffers from a severe capacity degradation.In this study,operando X-ray diffraction is carried out to investigate the structural evolutions and degradation mechanisms of LiMn2O4 in different voltage ranges.In the range of 3.0-4.3 V(vs.Li^+/Li),the LiMn2O4 cathode exhibits a low capacity but good cycling stability with cycles up to 100 cycles and the charge/discharge processes are associated with the reversible extraction/insertion of Li^+from/into LixMn2O4(0≤x≤1).In the range of 1.4-4.4 V(vs.Li^+/Li),a capacity higher than 200 mAh/g is achieved,but it rapidly decays during the cycling.The voltage plateau around 2.8 V(vs.Li^+/Li)is related to the transformation of the cubic LiMn2O4 phase to the tetragonal Li2Mn2O4 phase,which leads to the formation of cracks as well as the performance degradation.

Clarification of underneath capacity loss for O3-type Ni, co free layered cathodes at high voltage for sodium ion batteries

Earth abundant O3-type NaFe_(0.5)Mn_(0.5)O_(2)layered oxide is regarded as one of the most promising cathodes for sodium ion batteries due to its low cost and high energy density.However,its poor structural stability and cycle life strongly impede the practical application.Herein,the dynamic phase evolution as well as charge compensation mechanism of O3-type NaFe_(0.5)Mn_(0.5)O_(2)cathode during sodiation/desodiation are revealed by a systemic study with operando X-ray diffraction and X-ray absorption spectroscopy,high resolution neutron powder diffraction and neutron pair distribution functions.The layered structure experiences a phase transition of O3→P3→OP2→ramsdellite during the desodiation,and a new O3’phase is observed at the end of the discharge state(1.5 V).The density functional theory(DFT)calculations and nPDF results suggest that depletion of Na^(+)ions induces the movement of Fe into Na layer resulting the formation of an inert ramsdellite phase thus causing the loss of capacity and structural integrity.Meanwhile,the operando XAS clarified the voltage regions for active Mn^(3+)/Mn^(4+)and Fe^(3+)/Fe^(4+)redox couples.This work points out the universal underneath problem for Fe-based layered oxide cathodes when cycled at high voltage and highlights the importance to suppress Fe migration regarding the design of high energy O3-type cathodes for sodium ion batteries.

Theoretical research on electron beam modulation in a field-emission cold cathode electron gun

In order to develop miniaturized and integrated electron vacuum devices, the electron beam modulation in a field- emission （FE） electron gun based on carbon nanotubes is researched. By feeding a high-frequency field between the cathode and the anode, the steady FE electron beam can be modulated in the electron gun. The optimal structure of the electron gun is discovered using 3D electromagnetism simulation software, and the FE electron gun is simulated by PIC simulation software. The results show that a broadband （74-114 GHz） modulation can be achieved by the electron gun with a rhombus channel, and the modulation amplitude of the beam current increases with the increases in the input power and the electrostatic field.

Fabrication Research and Property of Enhanced Petaling Cold Cathode with Carbon Nanotube

With high effective screen-printing technique, a new triode field emission display (FED)with enhanced petaling cold cathode was fabricated. For enhancing the field emission performance,a series of improved measures was adopted in the fabrication course. Seen from the fabrication structure of enhanced petaling cold cathode,the bar conducting electrode and the petaling bottom electrode were fabricated with the sintered silver slurry on cathode glass faceplate. The luminescence image with green phosphor was displayed for the sealed enhanced petaling cold cathode FED. The measured results showed that the enhanced petaling cold cathode had good field emission performance. The enhanced petaling cold cathode FED possessed low turn-on electric-field of 1. 95 V /μm,large emission current of 1 389. 6 μA,and high luminance brightness of 1 520 cd /m2 .

Thin film micro-scaled cold cathode structures of undoped and Si-doped AlN grown on SiC substrate with low turn-on voltage

The field emission characteristics of the AlN thin films with micro-scaled cold cathode structures are tested in the high vacuum system. The aluminum nitride （A1N） thin films with a thickness of about 100 nm are prepared on the n-type 6H-SiC （0001） substrate at 1100℃ by metal organic chemical vapor deposition （MOCVD） under low pressure. The I-V curves and surface micro-images of undoped and Si-doped AlN films are investigated. From the I-V and Fowler-Nordheim plots, it can be seen that the Si-doped AlN shows better field emission characteristics compared with the undoped AlN sample. The obtained turn-on field is 6.7 V/μm and the maximum emission current density is 154 mA/cm2 at 69.3 V for the Si- doped AlN film cathode after proper surface treatment. It is proposed that the relatively low electric resistivity of Si-doped AlN films is significant for electron migration to the surface region, and their rougher surface morphology is beneficial to a higher local electric field enhancement for the field emission.

Insight into the structural evolution and thermal behavior of LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2) cathode under deep charge

By virtue of the crucial effect of the crystal structure and transition metal(TM)redox evolution on the performance of LiNi_(x)Co_(y)Mn_(z)O_(2)(NCM)cathode,systematical investigation is carried out to better understand the charge mechanism upon deep charging.Based on the results of X-ray diffraction and highresolution transmission electron microscope,phase transformations existing on particle surface are promoted by high potential because of the deeper lithium vacancies,accompanied by more substantial structure instability.Soft X-ray absorption spectroscopy indicates that Ni acts as the major contributor to charge compensation while Co displays a remarkable redox activity over the deep charge range.The elevated integrated intensity of pre-edge in O K-edge spectra reveals the extensive amount of holes formed in O 2 p orbitals and the enhanced hybridization of TM 3 d-O 2 p orbitals.Considering the close relationship between thermal behavior and structural evolution,the tendency of phase transitions and O_(2) release upon heating is accelerated by voltage rise,demonstrating the aggravated instability due to deeper Li utilization.Remaining Li contents in NCM are employed to estimate the amount of oxygen released in structural transformation and its detrimental effect on stability declares Li contentdependent characteristics.Furthermore,the extended Li vacancies,higher proportion of Ni4+and stronger orbital hybridization are considered as three factors impeding the thermal stability of the highlydelithiated NCM.

Plasma assisted synthesis of LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2) cathode materials with good cyclic stability at subzero temperatures

Layered Ni-rich cathode materials,LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2)(NCM622),are synthesized via solid reaction assisted with a plasma milling pretreatment,which is resulted in lowering sintering temperatures for solid precursors.The plasma milling pretreated NCM622 cathode material sintered at 780℃(named as PM-780)demonstrates good cycling stability at both room and subzero temperatures.Specifically,the PM-780 cathode delivers an initial discharge capacity of 171.2 mAh g^(-1) and a high capacity retention of 99.7%after 300 cycles with current rate of 90 mA g^(-1) at 30℃,while stable capacities of 120.3 and 94.0 m Ah g^(-1) can be remained at-10℃and-20℃in propylene carbonate contained electrolyte,respectively.In-situ XRD together with XPS and SEM reveal that the NCM622 cycled at-10℃presented better structural stability and more intact interface than that of cathodes cycled at 30℃.It is also found that subzero temperatures only limit the discharge potential of NCM622 without destroying its structure during cycling since it still exhibits high discharge capacity at 30℃after cycled at subzero temperatures.This work may expand the knowledge about the low-temperature characteristics of layered cathode materials for Li-ion batteries and lay the foundation for its further applications.

Modulation of lattice oxygen boosts the electrochemical activity and stability of Co-free Li-rich cathodes

Co-free Li-rich layered oxide cathodes have drawn much attention owing to their low cost and high energy density.Nevertheless,anion oxidation of oxygen leads to oxygen peroxidation during the first charging process,which leads to co-migration of transition metal ions and oxygen vacancies,causing structural instability.In this work,we propose a pre-activation strategy driven by chemical impregnation to modulate the chemical state of surface lattice oxygen,thus regulating the structural and electrochemical properties of the cathodes.In-situ X-ray diffraction confirms that materials based on activated oxygen configuration have higher structural stability.More importantly,this novel efficient strategy endows the cathodes having a lower surface charge transfer barrier and higher Li+transfer kinetics characteristic and ameliorates its inherent issues.The optimized cathode exhibits excellent electrochemical performance:after 300 cycles,high capacity(from 238 m Ah g^(-1)to 193 m Ah g^(-1)at 1 C)and low voltage attenuation(168 mV)are obtained.Overall,this modulated surface lattice oxygen strategy improves the electrochemical activity and structural stability,providing an innovative idea to obtain high-capacity Co-free Li-rich cathodes for next-generation Li-ion batteries.

Plasma characterization on carbon fiber cathode by spectroscopic diagnostics

This paper mainly investigates plasma characterization on carbon fiber cathodes with and without cesium iodide （CsI） coating powered by a - 300 ns, - 200 kV accelerating pulse. It was found that the CsI layers can not only improve the diode voltage, but also maintain a stable perveance. This indicates a slowly changed diode gap or a low cathode plasma expansion velocity. By spectroscopic diagnostics, in the vicinity of the cathode surface the average plasma density and temperature were found to be -3×10^14 cm^-3 and - 5 eV, respectively, for an electron current density of - 40 A/cm^2. Furthermore, there exists a multicomponent plasma expansion toward the anode. The plasma expansion velocity, corresponding to the carbon and hydrogen ions, is estimated to be - 1.5 cm/μs. Most notably, Cs spectroscopic line was obtained only at the distance - 0.5 mm from the cathode surface. Carbon and hydrogen ions are obtained up to the distance of 2.5 mm from the cathode surface. Cs ions almost remain at the vicinity of the cathode surface. These results show that the addition of CsI enables a slow cathode plasma expansion toward the anode, providing a positive prospect for developing long-pulse electron beam sources.

Time-and-space resolved measurements of the emission uniformity of carbon fibre cathode in high-current pulsed discharge

The remaining challenges, confronting high-power microwave （HPM） sources and pulsed power generators, stim- ulate the developments of robust relativistic electron beam sources. This paper presents a carbon fibre cathode which is tested in a single pulsed power generator. The distribution and the development of cathode plasma are observed by time-and-space resolved diagnostics, and the uniformity of electron beam density is checked by taking x-ray images. A quasistationary behaviour of cathode plasma expansion is observed. It is found that the uniformity of the extracted electron beam is satisfactory in spite of individual plasma jets on the cathode surface. These results show that carbon fibre cathodes can provide a positive prospect for developing a high-quality electron beam.

Revealing the inhomogeneous surface chemistry on the spherical layered oxide polycrystalline cathode particles

The hierarchical structure of the composite cathodes brings in significant chemical complexity related to the interfaces,such as cathode electrolyte interphase.These interfaces account for only a small fraction of the volume and mass,they could,however,have profound impacts on the cell-level electrochemistry.As the investigation of these interfaces becomes a crucial topic in the battery research,there is a need to properly study the surface chemistry,particularly to eliminate the biased,incomplete characterization provided by techniques that assume the homogeneous surface chemistry.Herein,we utilize nano-resolution spatially-resolved x-ray spectroscopic tools to probe the heterogeneity of the surface chemistry on LiNi0.8Mn0.1Co0.1O2 layered cathode secondary particles.Informed by the nano-resolution mapping of the Ni valance state,which serves as a measurement of the local surface chemistry,we construct a conceptual model to elucidate the electrochemical consequence of the inhomogeneous local impedance over the particle surface.Going beyond the implication in battery science,our work highlights a balance between the high-resolution probing the local chemistry and the statistical representativeness,which is particularly vital in the study of the highly complex material systems.

Optimization of Synthesis Conditions of LiMn_2–xFe_xO₄Cathode Materials Based on Thermal Characterizations

We have synthesized LiMn2–xFexO4 (x = 0, 0.25, and 0.50) cathode materials for applications in Li ion rechargeable batteries via sol-gel method. We studied thermal characteristics of as synthesized materials using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In order to optimize the synthesis conditions, we studied X-ray diffraction (XRD) of synthesized cathode materials at various temperatures, based on the transitions obtained from DSC/TGA. The XRD results can be co-related to the thermal behavior of the synthesized cathode materials and the synthesis conditions optimized.

小型化冷阴极触发管的研究

冷阴极触发管是电子引信系统中的关键器件,具有开关电流大、使用电压范围宽、温度范围宽、可靠性高、抗干扰性强等特点。针对电子引信系统小型化、集成化、低成本、高可靠发展的需要,本文开展小型化冷阴极触发管的研究,设计并制得样管。通过仿真,给出静电场分布情况。对样管进行电参数和可靠性能测试,结果表明,其工作电压范围为1.2~1.8 kV,且可通过对工作寿命、振动、高低温工作和贮存、冲击等可靠性试验考核,主要参数基本满足现代电子引信的使用需求。

一种冷阴极电子枪的模拟研究

文章通过Computer Simulation Technology粒子工作室软件建立了一种电子通过率极高的微焦点冷阴极电子枪。重点研究了电子枪自身结构对焦点、电子通过率和阴极发射电流的影响。特别是仿照了皮尔斯电子枪的结构,采用了一种弧面阴极,并在此基础上增加了一个阴极凹槽,使电子通过率从75.21%提高到90.26%,同时将近500μm的焦点缩小到50μm以内。最终设计出的冷阴极电子枪在阳极电压为90 kV且栅极电压为1 kV的条件下,电子通过率可达95.41%,在阳极靶面得到的束斑有效焦点尺寸约为45μm。

核电冷源设备的阴极保护及腐蚀智能监测

核电冷源设备具有材质多样化、腐蚀环境苛刻等特点,其阴极保护系统的有效运行和预防性腐蚀管理至关重要,但受空间限制,在设备运行期间阴极保护系统参数无法有效采集,阴极保护系统运行管理存在盲区。基于此,从核电冷源设备的特殊工况和实际需求出发,提出了具有数据采集、存储、远程传输、远程控制、故障预警等功能的阴极保护及腐蚀智能监测方案,通过实际案例分析,验证了此方案可以实现核电冷源设备运行期间腐蚀与防护状态的整体评价和故障预警。

Application of high energy X-ray diffraction and Rietveld refinement in layered lithium transition metal oxide cathode materials

Layered lithium transition metal oxide(LTMO)cathode materials have attracted much attention for lithium-ion batteries and are shining in the current market.Establishing a clear structure-performance relationship is necessary for the performance improvement of LTMO cathode materials.The combination of synchrotron X-ray diffraction(XRD)with high intensity and XRD Rietveld refinement is powerful for revealing the structural characteristics of LTMO cathode materials.This review summarizes the application of high energy XRD and Rietveld refinement in LTMO cathode materials,including the brief introduction of synchrotron XRD and Rietveld refinement and their applications in understanding the structural evolution related to the synthetic,thermal runaway,cycling,and high-rate charge/discharge process of LTMO cathode materials.Synchrotron XRD can provide insights into the intermediates and reaction paths in the synthesis process,the origin of thermal runaway,the mechanism of structural decay during cycles,and the structural evolution during high-rate charging/discharging.Future works should focus on the development of higher intensity X-rays to gain more in-depth insights into the intrinsic relationship between their structural characteristics and properties.

Transition-metal redox evolution and its effect on thermal stability of LiNixCoyMnzO_(2) based on synchrotron soft X-ray absorption spectroscopy

Based on the synchrotron soft X-ray absorption spectroscopy experiments,the fundamental electronic structures of layered Li NixCoyMnzO_(2)(NCM)are investigated systematically and the data of transitionmetal(TM)L-and O K-edges spectra are collected.Distribution of Ni ions under different oxidation states is evaluated according to linear combination fit.It is found that the ratio of Ni^(4+)expands with the increase of Ni since it dominates in charge compensation during charging,and that the existence of Ni^(3+)is nearly negligible in delithiated NCM.The valence state of Co also strongly depends on Ni content,the perceptible position shift of Co L_(3)-edge absorption peak towards higher energy in Ni-rich material agrees well with the small voltage plateau at around 4.2 V.The stability of Mn is verified as no obvious spectral change with the Mn L-edge is observed.Moreover,as Ni content rises,the O 2p holes near the Femi level increases with higher oxidation state of Ni,indicating the enhanced hybridization of O 2p-TM 3 d.Delithiated NCMs with higher Ni content are prior to lose electron existing in highly hybridized Ni3 dO 2 p bands upon heating,which accounts for the pronounced O_(2)release in phase transitions and the deterioration in thermal stability.These detailed observation of the electronic structure evolution is one of the key ingredients to improving the electrochemical and thermal performance of NCM.

Influence of Bias on the Properties of Carbon Nitride Films Prepared by Vacuum Cathodic Arc Method

Carbon nitride films have been synthesized in a wide range of biases from 0 to -900 V by vacuum cathodic arc method. The N content was about 12.0-22.0 at. pct. Upon increasing the biases from 0 to -100 V, the N content increased from 15.0 to 22.0 at. pct which could be attributed to the knot-on effect. While the further increasing biases led to the gradual falling of the N content to 12.0 at. pct at -900 V due to the enhancement of the sputtering effect. Below -200 V, with the increasing biases the sp2C fraction in the films decreased, as a result of vvhich the I(D)/I(G) fell in the Raman spectra and the sp peaks also showed the decreasing tendency relative to the s peaks in the VBXPS (valence band X-ray photoelectron spectroscopy). While above -200 V, the sp2C fraction increased and the films became graphitinized gradually, accompanying which the I(D)/I(G) rose from -200 V to -300 V and the Raman spectra even shovved the graphite characteristic above -300 V and the sp peaks rose again relative to the s peak. The carbon nitride films mainly consist of three types of bonding: CC, sp2CN and sp3CN bonds. In the first stage the sp3CN relative ratio rises and falls in the second stage, which corresponded well with the variation of the sp2C in the films. The subpiantation mechanism resulting from the effect of ion energy played an important role in deciding'the variation of the microstructure of the carbon nitride films.