Search

In our work, fluoroethylene carbonate (FEC) with higher ionic conductivity and oxidative stability has been used to replace ethylene carbonate along with 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluor...

Localized high-concentration electrolytes have attracted much attention of researchers due to their low viscosity, low cost, and relatively higher electrochemical performance than their low-concentration counterparts. In our work, 1.5 M (mol L-1) locally concentrated ether-based electrolyte has been obtained by adding 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) into a 4 M LiFSI concentrated dimethoxyethane (DME)-based electrolyte. The optimal ratio is determined by density functional theory (DFT) calculation and experimental combination, and finally, DH(3/5)-1.5M-LiFSI (DME/HFE = 3:5 by volume) is obtained. The electrolyte not only has relatively good physical properties such as low viscosity and high conductivity but also shows decent electrochemical performance. Li∥Cu half-cells can maintain a coulombic efficiency of no less than 99% after circulating for 250 cycles under the condition of 1 mA cm-2 current density and 1 mAh cm-2 lithium deposition for each cycle, and the stable battery polarization voltage was about 50 mV. Furthermore, 0.15 M lithium trifluoromethyl acetate (LiCO2CF3) has been added as an additive to enhance the oxidation stability. The new electrolyte DH(3/5)-1.65M-LiFC (LiFC/LiFSI + LiCO2CF3) makes Li||NCM523 batteries maintain about 83% capacity after cycling for 250 times with a 0.5 C charge current density and a 1 C discharge current density of 160 mAh g-1 when charged to 4.3 V. Furthermore, this new additive has a little negative effect on the Li||Cu half-cell performance under the same condition as before, indicating this new type of localized high-concentration DME-based electrolyte benefits both high-voltage cathode and lithium-metal anode.

Lithium sulfur batteries have been widely studied because of their high energy density. However, their commercialization has been impeded by several problems, such as the poor conductivity of the active material sulfur and its discharge products, the volume expansion and the shuttle effect caused by the polysulfide intermediates dissolving in organic electrolytes. To address these problems well, we have constructed high sulfur content spherical sulfur-carbon nanotube-polyethylene glycol-nickel nitrate hydroxide (SCNT-PEG-NNH) composite material by using a simple ball-milling method. The conductivity of the composite material gets improvement due to the spherical conductive frame constructed by CNT, while the shuttle effect of polysulfides is well inhibited by the wrapping of the PEG and the fixation of NNH. The results of electrochemical tests have shown that the performance of cathode made by the SCNT-PEG-NNH composite material is greatly improved. Therefore, the SCNT-PEG-NNH composite material can be a promising cathode material for lithium sulfur batteries.

Lithium-metal batteries have attracted extensive attention due to the increasing demand for storage devices with high energy density. For the modification of lithium-metal battery, how to effectively inhibit the growth of lithium dendrites has become a key challenge. Ether electrolytes have been widely used owing to their good compatibility with lithium metal. However, they are still difficult to be applied in high-voltage battery systems because of the poor cathodic stability. In this work, we have dissolved the lithium carboxylate, LiCO

Transition metal sulfides are widely used in energy storage and conversion due to their exclusive physical and chemical performance. In this work, FeSx/C/CNT composites have been prepared by spray drying assisted and then calcined in an Ar atmosphere. As lithium-ion battery anodes and electrode material for supercapacitor, the FeSx/C/CNT composites display the excellent reversible capacity, capacitance and cycle stabilities. Cyclic voltammetry at different scan rates indicate that the Faraday electrochemical reaction and surface capacitance behavior occur simultaneously when the FeSx/C/CNT composites act as anode material for lithium ion battery. Cycling under 200 mA g−1 current density for 100 times, the Coulomb efficiency is still about 99% while the capacity is about 630 mAh g−1. At the current density of 1, 2, 3 and 5 A g−1, the specific capacitances of the FeSx/C/CNT composites are 617.5, 508.0, 436.1 and 365.0 F g−1, respectively. Thus, as-prepared FeSx/C/CNT composites are expected to become anode materials for high-performance lithium-ion batteries and electrode materials for high-performance supercapacitors.

We have found that the formation of passivation film plays a major role in the negative shift of the decomposition voltage in the hydrogen-generating process. Both the hydrolysis of weak acid ions and the decarboxylation reaction of carboxylate can make the LiCO2CH3 produce a passivation film to inhibit the water decomposition to a certain extent. As for the LiCO2CF3 without hydrolysis of weak acid ion, it can be highly possible to facilitate the introduction of CO2 via its carboxylate specific decarboxylation reaction, and further produce lithium carbonate passivation film as well. However, the water decomposition voltage in the oxygen-producing process is more dependent on the properties of lithium salt anions. Those with strong electron-absorbing groups such as the trifluoromethyl are more likely to effectively endue the aqueous electrolyte with a high oxidative decomposition potential. Moreover, the concentration of LiCO2CF3 aqueous electrolyte can reach up to 28 mol kg−1, and hence the electrochemical stability window of this water-base electrolyte can be expanded to about 3.0 V. This work provides a new idea for the selection of high concentration lithium salt.

In this paper, a new approach for fault detection and location of open switch faults in the closed-loop inverter fed vector controlled drives of Electric Multiple Units is proposed. Spectral kurtosis (SK) based on Choi–Williams distribution (CWD) as a statistical tool can effectively indicate the presence of transients and locations in the frequency domain. Wavelet-packet energy Shannon entropy (WPESE) is appropriate for the transient changes detection of complex non-linear and non-stationary signals. Based on the analyses of currents in normal and fault conditions, SK based on CWD and WPESE are combined with the DC component method. SK based on CWD and WPESE are used for the fault detection, and the DC component method is used for the fault localization. This approach can diagnose the specific locations of faulty Insulated Gate Bipolar Transistors (IGBTs) with high accuracy, and it requires no additional devices. Experiments on the RT-LAB platform are carried out and the experimental results verify the feasibility and effectiveness of the diagnosis method.

In this paper, a diagnosis plan is proposed to settle the detection and isolation problem of open switch faults in high-speed railway traction system traction inverters. Five entropy forms are discussed and compared with the traditional fault detection methods, namely, discrete wavelet transform and discrete wavelet packet transform. The traditional fault detection methods cannot efficiently detect the open switch faults in traction inverters because of the low resolution or the sudden change of the current. The performances of Wavelet Packet Energy Shannon Entropy (WPESE), Wavelet Packet Energy Tsallis Entropy (WPETE) with different non-extensive parameters, Wavelet Packet Energy Shannon Entropy with a specific sub-band (WPESE3,6), Empirical Mode Decomposition Shannon Entropy (EMDESE), and Empirical Mode Decomposition Tsallis Entropy (EMDETE) with non-extensive parameters in detecting the open switch fault are evaluated by the evaluation parameter. Comparison experiments are carried out to select the best entropy form for the traction inverter open switch fault detection. In addition, the DC component is adopted to isolate the failure Isolated Gate Bipolar Transistor (IGBT). The simulation experiments show that the proposed plan can diagnose single and simultaneous open switch faults correctly and timely.