No abstract

No abstract

The widely used QUICKEST method with ULTIMATE flux limiter is not capable of solving the charge transport problems with a very steep wavefront accurately, due to the wide stencil adopted. Furthermore, the splitting process of separating the convection and the reaction terms in the method introduces additional errors. To solve such problems accurately, a novel numerical method based on the Runge–Kutta discontinuous Galerkin (RKDG) method is introduced in this paper, which has high-order resolution and weak correlation between cells. The bipolar charge transport under dc voltage in solid dielectrics with trapping and recombination is simulated using this new method. The results of charge profiles provided by the method are obviously different from the simulation results in the existing literature. The method was verified by problems with analytical solution and experimental observations.

Developing advanced carbon nanomaterials with reasonable pore distribution and interconnection and matching the chargestorage capacities and electrode kinetics between the capacitive electrode and the battery-type electrode are two of the biggest challenges in lithium-ion capacitors (LICs). In this work, a sustainable strategy to fabricate N/S dual-doped hierarchical porous carbon nanofibers (N/S-CNF) is developed via electrospinning and thiourea treatment, and the N/S-CNF is employed as both the capacitor-type cathode and the battery-type anode for LICs. With rational design, N/S-CNF can not only offer a large specific surface area with a hierarchical pore structure but also be uniformly doped with heteroatoms, which is desirable for improving the electrochemical performance of both the cathode and the anode for LICs and alleviating the mismatch between the two electrodes. LICs assembled with the designed N/S-CNF electrodes can deliver a high energy density of 154 Wh kg −1 with a stable capacitance retention of 92% after 6000 cycles. Our work is expected to open up new avenues for developing heteroatom-doped porous carbon nanomaterials applied in other energy conversion and storage devices.

In this paper, gliding discharges with a point-to-point electrode geometry were produced by a repetitively pulsed power supply with a rise time of ∼100 ns and a full-width at half-maximum of ∼200 ns. The characteristics of such discharges were investigated by measuring their voltage-current waveforms and taking photographs of their discharge images. Experimental results showed that once the breakdown occurred, the nanosecond-pulse gliding discharges went into a stable stage at all air gaps, behaving in a mode of repetitive sparks. Under certain conditions, a non-stable stage would appear some time after the discharge went into the stable stage, in which the gliding discharges transitioned from repetitive sparks to diffuse discharges. Furthermore, several factors (gap spacing, pulse repetition frequency (PRF) and gas flow rate) influencing the discharge characteristics were investigated. It was observed that both the breakdown voltage and ignition voltage increased with the gap spacing, and a diffuse discharge was absent when the gap spacing was less than 6 mm. The breakdown voltage decreased with the increase in the PRF and its decrease ratio was larger in large gap spacing than in small gap spacing. Discharges would transit from repetitive sparks to diffuse discharges as the flow rate increased. Furthermore, a comparison of nanosecond-pulse and ac gliding discharges was conducted with respect to the power supply. The consumption and energy, the relationship between the power supply and the load, and the time interval between two pulses were three main factors which could lead to different characteristics between the nanosecond-pulse and ac gliding discharges.

This paper focuses on the effect of nanoparticle surface modification on the charge transport characteristics in XLPE/SiO 2 nanocomposites. A titanate coupling agent (TC9) and a 3-(Methacryloyloxy)propyltrimethoxysilane (KH570) were used for the surface modification of SiO 2 nanoparticles. It was found that both KH570 and TC9 coupling agents improve the nanoparticle dispersion compared with unmodified SiO 2 nanoparticles. The improvement in dispersion was found to be due to increased surface hydrophobicity of the treated SiO 2 nanoparticles. In addition, it was found that the surface modification improved the DC conductivity, dielectric characteristics, and space charge properties as compared to XLPE or XLPE/SiO 2 nanocomposites without surface modification. The results of the TSC measurements showed that the introduction of SiO 2 nanoparticles into XLPE increased the trap density and produced more trap energy levels. Improving the nanoparticle dispersion was found to further increase the corresponding trap depth and trap density. The trapped homocharge formed an independent electric field and reduced the effective electric field, which reduced charge injection and increased the charge injection barrier height. Therefore, the space charge formation in the material bulk was suppressed.

No abstract

No abstract