Electrolyte reactivity at the charged Ni-rich cathode interface and degradation in Li-ion batteries

The chemical and electrochemical reactions at the positive electrode-electrolyte interface in Li-ion batteries are hugely influential on cycle life and safety. Ni-rich layered transition metal oxides exhibit higher interfacial reactivity than their lower Ni-content analogues, reacting via poorly understood mechanisms. Here, we study the role of the electrolyte solvent, specifically cyclic ethylene carbonate (EC) and linear ethyl methyl carbonate (EMC), in determining the interfacial reactivity at LiNi0.33Mn0.33Co0.33O2 (NMC111) and LiNi0.8Mn0.1Co0.1O2 (NMC811). Parasitic currents are measured during high voltage holds in NMC/Li4Ti5O12 (LTO) cells, LTO avoiding parasitic currents related to anode-cathode reduction species cross-over, and are found to be higher for EC-containing vs. EC-free electrolytes with NMC811. No difference between electrolytes are observed with NMC111. On-line gas analysis reveals this to be related to lattice oxygen release, and accompanying electrolyte decomposition, which increases substantially with greater Ni content, and for EC-containing electrolytes with NMC811. This is corroborated by electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM) of NMC811 after the voltage hold, which show a higher interfacial impedance and a thicker oxygen-deficient rock-salt surface reconstruction layer, respectively. Combined findings from solution NMR, ICP (of electrolytes) and XPS analysis (of electrodes) reveal that higher lattice oxygen release from NMC811 in EC-containing electrolytes is coupled with more electrolyte breakdown and higher amounts of transition metal dissolution compared to EC-free electrolyte. Finally, new mechanistic insights for the chemical oxidation pathways of electrolyte solvents and, critically, the knock-on chemical and electrochemical reactions that further degrade the electrolyte and electrodes curtailing battery lifetime are provided.

Comparison of Two Solvers for Simulation of Single Bubble Rising Dynamics: COMSOL vs. Fluent

Multiphase flows are a part of many industrial processes, where the bubble motion influences the hydrodynamic behavior of the batch. The current trend is to use numerical solvers that can simulate the movement and mutual interactions of bubbles. The aim of this work was to study how two commercial CFD solvers, COMSOL Multiphysics and Ansys Fluent, can simulate the motion of a single rising bubble in a stagnant liquid. Simulations were performed for spherical or slightly deformed bubbles (Db = 0.6, 0.8, and 1.5 mm) rising in water or in propanol. A simple 2D axisymmetric approach was used. Calculated bubble terminal velocities and bubble shape deformations were compared to both experimental data and theoretical estimations. Solver Comsol Multiphysics was able to precisely calculate the movement of smaller and larger bubbles; due to the 2D rotational symmetry, better results were obtained for small spherical bubbles. The deformation of larger bubbles was calculated sufficiently. Solver Ansys Fluent, in the setting used, failed to simulate the motion of small bubbles due to parasitic currents but allowed for modeling of the motion of larger bubbles. However, the description of the bubble velocity and shape was worse in comparison with experimental values.

Initial designing a dual-band antenna baced on end-fed dipole-like radiators for digital antenna arrays

The paper deals with the designing of the initial arrangement for dual-band antennas comprising two parallel dipole-like radiators as the drivers for the mentioned antenna. The excitation of the drivers is provided by the source of the induced electromotive forces (EMF), whose outputs are attached to the remote terminals of the radiators. The paper also provides the key electrodynamic characteristics of the structure under research for the following procedure of multi-parametric nonlinear optimization. In addition, on the basis of the induced EMF method, has been obtained the expressions for the far-field zone (Fraunhofer zone) characteristics with taking into account the parasitic currents on the radiating bodies of the dipole, which allows more accurate design of the initial topology of the antenna.

Ways to Improve the Reliability of Bearings in Traction Induction Machines

The problem of electric rolling stock traction machinery failures caused by electrical erosion of bearings is addressed. Damages inflicted to traction machinery bearings as a result of electric current flowing through them have been known since long ago. In recent time, however, damages of this kind have become more frequent, because frequency and voltage converters for control of three-phase inductor motors are widely used in the electric rolling stock. An overview of factors causing the occurrence of stray currents generated in frequency converter driven traction motors and sources of these currents is presented. Electric current flows through rolling bearings in the area of the contact between the rolling elements with inner and outer rings, thus causing damage to the bearing metal components' rolling surfaces and degrading the quality of lubricants. To study and analyze the currents through bearings, the stray capacitances existing in traction machines are determined, and their calculation methods are defined, the necessity of which is stemming from the fact that these capacitances influence the generation of parasitic currents. The stray capacitances in traction machines include the capacitance between the stator windings and the stator core pack, the capacitance between the stator windings and the rotor, the capacitance between the rotor and the stator core pack, and the capacitances of the bearings. From the electrical point of view, bearings may also be regarded as capacitances. As long as there is a continuous lubricant film between the inner ring and outer rings and the rolling elements, the bearings behave as capacitors. A difference of potentials across the bearing elements may lead to electrostatic discharges and, hence, to discharge currents through the bearings. One of possible ways to enhance the reliability of traction machine bearing units is to use insulated bearings. The change in the impedance of bearings with ceramic coating and hybrid rolling elements depending on the applied voltage frequency and operating temperature is calculated and analyzed. Conclusions regarding the expediency of using hybrid bearings having rings made of bearing steel and rolling elements made of bearing silicon nitride (Si3N4) are drawn.

Energy Harvesting by Waste Acid/Base Neutralization via Bipolar Membrane Reverse Electrodialysis

Bipolar Membrane Reverse Electrodialysis (BMRED) can be used to produce electricity exploiting acid-base neutralization, thus representing a valuable route in reusing waste streams. The present work investigates the performance of a lab-scale BMRED module under several operating conditions. By feeding the stack with 1 M HCl and NaOH streams, a maximum power density of ~17 W m−2 was obtained at 100 A m−2 with a 10-triplet stack with a flow velocity of 1 cm s−1, while an energy density of ~10 kWh m−3 acid could be extracted by a complete neutralization. Parasitic currents along feed and drain manifolds significantly affected the performance of the stack when equipped with a higher number of triplets. The apparent permselectivity at 1 M acid and base decreased from 93% with the five-triplet stack to 54% with the 38-triplet stack, which exhibited lower values (~35% less) of power density. An important role may be played also by the presence of NaCl in the acidic and alkaline solutions. With a low number of triplets, the added salt had almost negligible effects. However, with a higher number of triplets it led to a reduction of 23.4–45.7% in power density. The risk of membrane delamination is another aspect that can limit the process performance. However, overall, the present results highlight the high potential of BMRED systems as a productive way of neutralizing waste solutions for energy harvesting.

SIMULATION OF PARASITIC TUNNEL CURRENTS IN FLASH-MEMORY ELEMENTS BASED ON SHORT-CHANNEL MOS-TRANSISTORS

Simulation of parasitic currents in Flash-memory cells based on short-channel MOSFET. In present paper the distributions of parasitic tunneling current as well as mean electron energy and mobility along the channel are calculated for short-channel MOSFETs by using Monte Carlo simulation of electron drift in such devices. The effect of drain bias in Flash-memory cells on these distributions is investigated for reading information regime. It is shown that the value of parasitic current is very small at considered conditions. But long storage can be change the charge in a floating gate of short-channel MOSFETs.

NEUTRALIZATION OF CIRCULATING CURRENT IN THE DIRECT CYCLONE

Parasitic currents, their occurrence and measures to eliminate the circulation current.

Ground Leakage Current Caused by Common-Mode Voltage of PWM inverter

In railway tractive vehicles, three-phase PWM (Pulse Width Modulation) inverters generate parasitic Differential-Mode Voltages (DMV) and Common-Mode Voltages (CMV). Parasitic voltages are a side effect of using the width modulation to shape the phase-to-phase inverter’s voltage. In this article, the authors present a mathematical description of the DM and CM voltages and carry out their spectral analysis. Based on the spectral harmonics analysis, the authors present a method for filtration of harmonics of DM and CM voltages aimed at limiting the capacitance parasitic currents: due to DM voltage – phase-to-phase parasitic current and CM voltage – ground parasitic currents. As the final result of the tests, almost complete elimination of leakage parasitic current form PE shock protection system was achieved.

AN ENERGY DISSIPATIVE SPATIAL DISCRETIZATION FOR THE REGULARIZED COMPRESSIBLE NAVIER-STOKES-CAHN-HILLIARD SYSTEM OF EQUATIONS

We consider the regularized 3D Navier-Stokes-Cahn-Hilliard equations describing isothermal flows of viscous compressible two-component fluids with interphase effects. We construct for them a new energy dissipative finite-difference discretization in space, i.e., with the non-increasing total energy in time. This property is preserved in the absence of a regularization. In addition, the discretization is well-balanced for equilibrium flows and the potential body force. The sought total density, mixture velocity and concentration of one of the components are defined at nodes of one and the same grid. The results of computer simulation of several 2D test problems are presented. They demonstrate advantages of the constructed discretization including the absence of the so-called parasitic currents.

THE STUDY OF THE ELECTROPHYSICAL PROPERTIES OF A COMPOSITE MEMRISTOR-DIODE CROSSBAR AS A BASIS OF THE NEUROPROCESSOR HARDWARE IMPLEMENTATION

The aim of this article lies in checking the efficiency of memory and logic matrices. Achieving this has required producing a composite memristor-diode crossbar and studying its electrophysical properties. For these purposes, the authors have made a measuring bench, which consists of a composite memristor-diode crossbar, control peripheral circuitry, based on discrete elements with CMOS logic, and Keithley SourceMeter 2400. The silicon junction p-Si/n-Si has been chosen because its electrical properties better suit the Zenner diode’s requirements compared to the p-Si/ZnO junction. The memristor-diode crossbar with the TiN/Ti0,93Al0,07Ox/p-Si/n-Si/W structure was made with implementation of a new diode. The results show that the crossbar cell with a p-Si/n-Si diode has better rectifying properties in comparison with a p-Si/ZnOx diode, because the current in the crossbar cell with positive voltage bias is much higher than with negative voltage bias. Strong rectifying properties of the cell are necessary for the functioning of diode logic in the logic matrix and for memristor state recording in the logic and memory matrices. The study of electrophysical properties of the composite memristor-diode crossbar, measurement of current-voltage characteristics of the diode and composite memristor-diode crossbar cell and signal processing were performed. The signal processing was performed in the following modes: addition of output impulses of neurons and their routing to synapses of other neurons; multiplication of number matrix by vector, performed in the memory matrix with weighing and totalling of signals; and associative self-learning. For the first time, the generation of a new association (new knowledge) in the composite memristor-diode crossbar has been shown, as opposed to associative self-learning in existing hardware neural networks with discrete-memristors-based synapses. The change of crossbar cell’s output current caused by parasitic currents through adjacent cells has been determined. The results show that the control over Zenner diode characteristics allows reducing the power consumption of the composite crossbar. Obtained electrophysical characteristics prove the efficiency of the composite memristor-diode crossbar, intended for production of the memory and logic matrices.