Maximizing Energy Storage of Flexible Aqueous Batteries through Decoupling Charge Carriers
Chunlong DaiXuting JinHongyun MaLinyu HuGuoqiang SunHao ChenQiuju YangMaowen XuQianwen LiuYukun XiaoXinqun ZhangHongsheng YangQiang GuoZhipan ZhangLiangti Qu
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Abstract Flexible aqueous rechargeable batteries that integrate excellent mechanical flexibility and reliable safety hold a great promise for next‐generation wearable electronics. Unfortunately, currently available options are unsatisfactory due to their low specific capacity, limited energy density, and unstable voltage output. Herein, to overcome these challenges, high theoretical specific capacity zinc and sulfur as the anode and cathode are selected, respectively. Furthermore, a strategy is proposed, that decoupling charge carriers in anolyte and catholyte to simultaneously endow the zinc anode and sulfur cathode with optimal redox chemistry, maximizes the energy storage of flexible aqueous batteries. The new zinc–sulfur hybrid battery possesses merits of ultrahigh theoretical specific capacity (3350 mAh g S −1 ) and volumetric energy density (3868 Wh L −1 ), low cost, ecofriendliness, and ease of fabrication and is a promising next‐generation aqueous energy storage system. The fabricated flexible aqueous zinc–sulfur hybrid battery delivers a stable output voltage (release 92% of its full capacity within a small voltage drop of 0.15 V) and an ultrahigh reversible capacity of 2063 mAh g S −1 at 100 mA g S −1 , thus setting a new benchmark for flexible aqueous batteries and is promising to play a part in future flexible electronics.Keywords:
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A semitransparent cathode is proposed for an efficient operation of the relativistic magnetron (RM) with axial extraction. The semitransparent cathode is a kind of shaped cathode. It is achieved using a cylindrical cathode with longitudinal strips removed. The cross section of each removed strip is fan-shaped and all the emit strips are connected in the central area of the cathode. Results of the 3-D particle-in-cell simulations show that the using a semitransparent cathode yields similar performance benefits compared with that using the transparent cathode proposed by the University of New Mexico. Simulation results also show that output characteristics of the RM using the semitransparent cathode are insensitive to the depth and width of each cathode slot. Thus, the semitransparent cathode might be more robust for practical applications.
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Mixed metal matrix cathodes (MM-cathodes) were optimized and their life behavior was tested in different test vehicles. In two separate life test programs, 57 MM-cathodes with a W/Os matrix were investigated in test vehicle (tetrodes) where the cathode environment was similar to that of a tube. In parallel, a further 100 MM-cathodes in other types of test vehicles were operated for supplementary investigations and cathode design optimization. The operational temperatures were between 880 degrees C/sub B/ and 1200 degrees C/sub B/ (brightness). One group of cathodes was operated at constant anode voltage with an initial current density of 0.75 A/cm/sup 2/, and the other group was operated with a loading of 2 A/cm/sup 2/ for as long as the anode voltage could be adjusted. The cathodes at lower temperatures (>
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In a dispenser cathode the surface is composed of many small regions having different and individual values of work functions called "patches". The non-uniform emission results in a gradual transition from space-charge (SC) region to temperature limited (TL) region. The emission of a planar cathode is modeled using a 'top-hat' model. In practice, the convergent guns are incorporated with a spherical cathode. The above model is applied to a spherical cathode-anode system. This model can also be extended to a gun geometry provided that the field distribution across the cathode cross section is uniform. In this paper the performance of three types of cathode, viz. B-Type, Alloy-coated, and Scandate cathodes are studied. In the present model the real cathode is replaced by a fictitious cathode, having a maximum current density at θ = 0° and a minimum at the rim. The analysis shows that there exists an analogy between a planar cathode and a spherical cathode, enabling the emission current to be modeled in a manner similar to a planar cathode.
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Both kinds of 10 cm diameter thermionic dispenser cathode have been fabricated at BVERI. One is impregnated scandate (I-Sc) cathode and the other is traditional Ir-coated "M" cathode with 411 impregnant. Figure 1 is the photograph of Φ10 cm cathode assembly. The scandate cathode can deliver the same density as "M" cathode but 80-100°C lower in temperature, though it needs higher vacuum than "M" cathode. Structure and heat designs are very important for the manufacture of the big-size cathode assembly. There are only four materials such as tungsten, molybdenum, tantalum, and stainless steel used in structure so as to enhance the structure reliability of the cathode assembly for their high melt point, low evaporation rate as well as excellent mechanical performance. Among them, molybdenum and stainless steel are adopted to support cathode button and heater assembly. Heat conduction and radiation are the major heat loss for the cathode in the vacuum. Yet, under the conditions of high temperature and big area, radiation is the dominant mechanism for heat loss. Some methods were introduced to decrease the heat loss. For instance, a series of slots which distribute in angle and vertical direction regularly are machined along the cathode support stem to reduce the heat conduction loss. Especially, a complicated and reliable thermal shield structure has been designed to reduce the radiation and ensure heat efficiency. More than 2 layers thermal shields surrounding the cathode are used, and 4 layers shields exist behind the cathode. The heater was made of six 20% ReW coiled filaments in parallel and the operation power is below 1500 W. Alumina ceramic insulators are employed between the cathode and heater. The total weight of the entire cathode assembly is 1.95 kilogram. There are some factors influencing on the cathode electron emission performance significantly such as outgas path, vacuum, temperature nonuniformity on cathode surface, air moisture and so forth. The vacuum of the injector test stand at IFP can be maintained in the range of (2~5) × 10 -5 Pa, but poor pumping conductance in the region behind the cathode will lead to poor local vacuum nearby the cathode surface. Although the dispenser cathode has the capability of resistance to poisoning, poor vacuum near the cathode surface will still low the emission current dramatically. That is the reason why sometimes the higher temperature is needed to produce the same beam current. Generally the higher temperature tends to decrease the reliability of heater. Thus, keeping good vacuum is very important for normal operating of big-size cathode. Both Ir-coated and I-Sc cathodes have been tested in injector test stand. The applied pulse voltage is not more than 2MV, and pulse width (FWHM) is about 90 ns. The accepted experimental data are as follows (Figure 2, 3). At the pressure of the 4.4 × 10 -5 Pa, the I-Sc cathode has the capability to give 1000 ampere in total during 1100~1120°C and the current density is about 12.7A/cm , whereas the total emission current of the "M" cathode is only 720 Ampere because of cathode exposing the poor vacuum during the testing. The optical pyrometer was utilized to monitor the temperature at cathode surface. On the basis of the Φ10 cm cathode assemblies development, the Φ15.5 cm planar cathode assembly has been designed (Figure 4) and fabrication is in process. 3 kinds of cathodes will be attempted for the larger structure. The first is the traditional "M" cathode and the objective is 12A/cm 2 ; the second is the I-Sc cathode with the objective of 15A/cm 2 ; the third is the sub-micron Sc 2 O 3 +W cathode which is expected to offer the current density of 20A/cm 2 .
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Hollow cathode discharge and micro-hollow cathode discharge have numerous applications in the fields of industry, medical treatment, environmental protection, and analytical chemistry. However, many of them lack the typical features of hollow cathode mode, especially the applications at atmospheric pressure. In order to investigate the underlying basic science of hollow cathode discharge, the hollow cathode discharge in argon was studied by experiments. The range for the operation of the hollow cathode mode in the argon–aluminum device was quantitatively determined to be from 0.8 to 4 Torr cm, no matter how small the cathode cavity is. The atmospheric pressure operation of the hollow cathode mode was realised with the aluminum cathode of a 50 μm cavity. The hollow cathode discharges were consistent with Townsend similarity law when the anode was very close to the cathode and the value of p·D was chosen at the lower limit of the range for hollow cathode mode. In contrast, if the anode was moved a little bit far from the cathode and the value of p D was significantly increased, the results followed Allis–White scaling law. The reason for the deviation of Allis–White scaling law from Townsend similarity law was given.
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