Search

The research of borate materials as sodium-ion batteries (SIBs) anode is still in the early stages, but the boron polyoxoanions are attracting intense interest due to their low atomic weight and high electronegative features. In this work, FeBO3 was prepared with low-cost raw materials and evaluated as SIBs anode. The FeBO3 shows a high reversible capacity of 328 mAh/g at the current density of 0.4 A/g. In addition, the electrochemical performance of FeBO3 can be improved by carbon coating. The prepared carbon-coated FeBO3 composite has a reversible capacity of 426 mAh/g (at 0.4 A/g) and an outstanding rate capability of 272 mAh/g (at 1.6 A/g). Furthermore, the sodium storage mechanism of FeBO3 was studied by in-situ XRD and ex-situ XPS.

Rechargeable aqueous zinc ion batteries (ZIBs) are considered as one of the most promising candidates for large-scale energy storage due to their high safety, environmental benignity, and low cost. Developing cathode materials with high specific capacity and long cycle performance is the key to the commercialization of ZIBs. In this work, a perovskite structured bimetallic oxide (NiMnO3) was synthesized and firstly used as cathode for ZIBs. Electrochemical tests show that the NiMnO3 exhibits a high capacity (280 mA h g−1 at 300 mA g−1), good cycling stability, and rate performance (152 mA h g−1 at 1000 mA g−1). The fast ion transportation and the significant capacitance contribution should be the reasons for remarkable rate performance. The zinc storage mechanism of NiMnO3 is the insertion and extraction reaction and the formation/dissolution of ZHS (ZnSO4·3Zn(OH)2·5H2O). The results suggest that the bimetallic oxide with perovskite structure could be a promising cathode material for ZIBs.

In this work, a flake-structured Co2B2O5 material was obtained by a simple sol–gel method and researched for use in sodium ion batteries firstly. When serving as anode material for sodium ion batteries, it exhibits the high initial reversible capacity of 466 mAh·g−1 at a current density of 100 mA·g−1. Through the recombination of carbon nanotubes (CNTs), the composite Co2B2O5/CNTs delivers the initial reversible capacity of 464 mAh·g−1, and 324 mAh·g−1 is obtained after 60 cycles under the current density of 100 mA·g−1. When under the current density of 1000 mA·g−1, a capacity of 236 mAh·g−1 is obtained for Co2B2O5/CNTs while 160 mAh·g−1 for Co2B2O5. Moreover, the sodium storage behavior of Co2B2O5 is identified by kinetic analysis. The higher Na+ capacitive contribution of Co2B2O5/CNTs could account for the enhanced rate performance. The results indicate that Co2B2O5 is a promising anode material for sodium ion batteries.

Silicon is considered the most promising candidate for anode material in lithium-ion batteries due to the high theoretical capacity. Unfortunately, the vast volume change and low electric conductivity have limited the application of silicon anodes. In the silicon anode system, the binders are essential for mechanical and conductive integrity. However, there are few reviews to comprehensively introduce binders from the perspective of factors affecting performance and modification methods, which are crucial to the development of binders. In this review, several key factors that have great impact on binders' performance are summarized, including molecular weight, interfacial bonding, and molecular structure. Moreover, some commonly used modification methods for binders are also provided to control these influencing factors and obtain the binders with better performance. Finally, to overcome the existing problems and challenges about binders, several possible development directions of binders are suggested.

This paper describes the application of a microscopic defocusing image system to track 3D particle motions in microflow around a microcubic array near a microchannel wall surface. The measurement principle and calibration method were evaluated to provide accurate 3D microparticle location. Particle trajectories were measured in two microchannels. Measured velocity profiles of Hele–Shaw flows for two Reynolds numbers agreed well with theoretical profiles. Three-dimensional particle tracking in fluid flow around a microcubic array exhibited quasi-periodic and non-periodic trajectory modes. The experimental results indicated that 3D particle motions are spatially and time dependent even when the flow rate is constant, and microparticle trajectories may deviate from steady flow streamlines.

Measurements of velocity and pressure differences for flows in porous chip fabricated with micropost arrays arranged in square pattern were implemented by using micro-particle image velocimetry (micro-PIV) and high precision micromanometer. Based on the measurement results, the permeability was solved by Brinkman equation under the averaged velocities over the cross section, two-dimensional velocities on the center plane of the microchannels, and the averaged velocities on the center plane considering the effect of depth of correlation (DOC), respectively. The experimental results indicate that the nondimensional permeability based on different velocities satisfies the Kozeny–Carman (KC) equation. The Kozeny factor is taken as 40 for the averaged velocity over the cross section and 15 for two kinds of center velocities based on the micropost array of this study, respectively. The permeability calculated by the velocities on the center plane is greater than that by the averaged velocity over the cross section.

With the requests of medical, biological and chemical analyses, measurements for micro- and nano-liter flow rate of flow in microchannels have been the hot points, where great difficulties exist. In recent years, microfluidic particle image velocimetry (micro-PIV), a quantitative, non-intrusive technique for the full field measurement of velocity at microscales, has been developed, and it makes the highly accurate measurement for micro- and nano-liter flow rate realized. In this research, micro-PIV technique is suggested for use in flow rate measurements at microscales. Measurements for the square sectional microchannels with side lengths of 0.8 mm, 0.6 mm and 0.4 mm are presented after obtaining a group of visualized velocities under the conditions of the reference Reynolds number of 100 and 200. The analytical velocity solutions on median plane of square sectional duct are employed in flow rate calculations. Research shows that micro-PIV technique is a promising method for the flow rate measurement at microscales.

The regular perturbation method is introduced to investigate the influences of three-dimensional wall roughness on the laminar flow in microtube. Rough wall surface is modeled by two-dimensional simple harmonic function whose axial and azimuthal wavenumbers are alterable. Under this rough wall model, a set of coupled leading-order and first-order perturbation equations are obtained and computed iteratively. The numerical results show that flow in microtubes are more complex than those in macrotubes; pressure drops are about 0–65% higher than that of Hagen–Poiseuille flow on condition that the relative roughness increases from 0 to 0.05 and the wavenumbers of wall rough function range between 0 and 30; there exists apparent fluctuations in flow fields. Analysis shows that the effects of roughness on the flow pattern is distinct from those on the friction factor.

The regular perturbation method is introduced to investigate the influence of two-dimensional roughness on laminar flow in microchannels between two parallel plates. By superimposing a series of harmonic functions with identical dimensional amplitude as well as the same fundamental wave number, the wall roughness functions are obtained and the relative roughness can be determined as the maximal value of the product between the normalized roughness functions and a small parameter. Through modifying the fundamental wave number, the dimensionless roughness spacing is changed. Under this roughness model, the equations with respect to the disturbance stream function are obtained and analyzed numerically. The numerical results show that flowing in microchannels are more complex than that in macrochannels; there exist apparent fluctuations with streamlines and clear vortex structures in microchannels; the flow resistances are about 5–80% higher than the theoretical value under different wall-roughness parameters. Furthermore, analysis shows that the effect of roughness on the flow pattern is distinct from that on the friction factor.

Micro-particle image velocimetry was employed to measure the water flow rates for three types of T-shaped microchannels. From the two-dimensional velocities on multiple fluid planes along the out-of-plane directions of the microchannels, the quasi-three-dimensional velocity field was constructed and flow rates were calculated by taking the integral of the velocity distribution over the effective cross sections of the microchannels. The results indicate that the experimental flow rates have high precision for complex branching microchannels. For 24 standard flow rates from 2.619 to 11.693 µl min−1 input by a syringe pump, the ranges of the total relative errors of the measured flow rates were calculated as 0.056%–1.928% and 0.036%–1.824% when using interrogation window lengths of 64 and 32 pixels, respectively. Hence, the measured flow rates evaluated with the smaller window are more precise than those evaluated with the larger window, which indicates that the spatial resolution of the two-dimensional velocity determines the measurement accuracy.