Diffusion Coefficients Of Electrolytes Research Articles

Analysis of Pressure Characteristics of Ultra-High Specific Energy Lithium Metal Battery for Flying Electric Vehicles

The lithium metal battery is likely to become the main power source for the future development of flying electric vehicles for its ultra-high theoretical specific capacity. In an attempt to study macroscopic battery performance and microscopic lithium deposition under different pressure conditions, we first conduct a pressure cycling test proving that amplifying the initial preload can delay the battery failure stage, and the scanning electron microscope (SEM) shows that the pressure is effective in improving the electrode’s surface structure. Secondly, we analyze how differing pressure conditions affect the topography of lithium deposits by coupling the nonlinear phase-field model with the force model. The results show that the gradual increase in the external pressure is accompanied by a drop in the length of the dendrite and the migration curvature in the diaphragm, and the deposition morphology is gradually geared towards smooth and thick development, which can significantly reduce the specific surface area of lithium dendrite. However, as cyclic charging and discharging continue, the decrease in the electrolyte diffusion coefficient results in higher internal stress inside the battery, and thus the external pressure must be increased so as to achieve marked inhibitory effects on the growth of the lithium dendrite.

Determination of Ionic Diffusion Coefficients in Ion‐Exchange Membranes: Strong Electrolytes and Sulfates with Dissociation Equilibria

AbstractIonic diffusion coefficients in the membrane are needed for the modelling of ion transport in ion‐exchange membranes (IEMs) with the Nernst‐Planck equation. We have determined the ionic diffusion coefficients of Na+, OH−, H+, Cl−, SO42−, NaSO4−, and HSO4− from the diffusion experiments of dilute NaCl, NaOH, HCl, Na2SO4, and H2SO4 solutions through IEMs and the membrane conductivity measured in these solutions, using electrochemical impedance spectroscopy. The order of diffusion fluxes across the anion‐exchange membrane is found to be as H2SO4>HCl>NaCl>Na2SO4>NaOH, whereas for the cation‐exchange membrane it was NaOH>NaCl>Na2SO4≥H2SO4. Special attention is given to sulfates because of the partial dissociation of bisulfate and NaSO4−, which makes the use of the Nernst‐Hartley equation, that is, splitting the electrolyte diffusion coefficient into its ionic contributions, impossible. The expression of the diffusion coefficient of sulfates taking into account the dissociation equilibrium has been derived and the corresponding Fick equation has been integrated. In addition, for sulfates, finite element simulations with COMSOL Multiphysics, applying a homogeneous membrane model, were done to give estimates of their ionic diffusion coefficients. This work offers a convenient approach to finding diffusion coefficients of various ions inside IEMs.

MATHEMATICAL MODEL OF TWO-CHAMBER ELECTROLYSER DYNAMICS FOR STUDYING PROPERTIES OF ION EXCHANGE MEMBRANES BASED ON PROTON IONIC LIQUIDS

A mathematical model of mass transfer processes in the electrolysis of one-component solutions of 1,1 symmetric strong electrolytes NaOH and NaCl in a two-chamber electrochemical reactor with mesh electrodes based on platinum titanium is formulated. Experimental modeling of processes is performed was carried out under conditions of continuous precise monitoring of the system (NaOH concentration and volume of solution in the chambers).The electrolysis system was designed to balance the flow of components through the membrane to study its properties and to determine five unknown parameters of mathematical modeling of the process. The mathematical model is a system of equations, which includes the unknown transfer numbers of counterions through the membrane, the electrolyte diffusion coefficient, the electroosmotic flux constant, and the empirical parameters of the approximating expressions.

A Comparative Study of Aqueous and Non-Aqueous Solvents to Be Used in Low-Temperature Serial Molecular–Electronic Sensors

This paper presents the experimental results of studying the samples of the electrochemical sensors of motion parameters on the base of Molecular Electronics Technology (MET). The sensors with microelectromechanical (MEMS) electrode assembly use electrolytes based on aqueous and non-aqueous solutions of potassium and lithium iodides. Electrolyte solutions contain impurities of ionic liquids and alcohols to achieve stable low-temperature operation and acceptable technical parameters of serial devices. The dependence of the general sensitivity and the shape of the amplitude-frequency characteristic on temperature have been studied. For the marginally acceptable samples, which had an acceptable temperature dependence of the conversion coefficient and low activation energies for the diffusion coefficient, the level of self-noise was found. The activation energy of the electrolyte diffusion coefficient was determined based on the analysis of the dependence of the background current on temperature. A conclusion was made regarding the possible prospects for using the studied solutions and components for operation in serial devices.

Validity of solid-state Li[formula omitted] diffusion coefficient estimation by electrochemical approaches for lithium-ion batteries

The solid-state diffusion coefficient of the electrode active material is one of the key parameters in lithium-ion battery modelling. Conventionally, this diffusion coefficient is estimated through the galvanostatic intermittent titration technique (GITT). In this work, the validity of GITT and a faster alternative technique, intermittent current interruption (ICI), are investigated regarding their effectiveness through a black-box testing approach. A Doyle-Fuller-Newman model with parameters for a LiNi0.8Mn0.1Co0.1O2 electrode is used as a fairly faithful representation as a real battery system, and the GITT and ICI experiments are simulated to extract the diffusion coefficient. With the parameters used in this work, the results show that both the GITT and ICI methods can identify the solid-state diffusion coefficient very well compared to the value used as input into the simulation model. The ICI method allows more frequent measurement but the experiment time is 85% less than what takes to perform a GITT test. Different fitting approaches and fitting length affected the estimation accuracy, however not significantly. Moreover, a thinner electrode, a higher C-rate and a greater electrolyte diffusion coefficient will lead to an estimation of a higher solid-state diffusion coefficient, generally closer to the target value.

Effect of current-induced coion transfer on the shape of chronopotentiograms of cation-exchange membranes

Chronopotentiometry using pulses of a constant current of density j is a powerful method for characterizing ion-exchange membranes (IEMs). We report on the influence of coion transport on the shape of chronopotentiogram (ChP) and the consequent new possibility of quantifying coion transport based on ChP analysis. We show that in the case where the bathing solution contains Ca2+ or Mg2+ ions, the ChPs of the homogeneous (CMX) and heterogeneous (MK-40) cation-exchange membranes at overlimiting current densities have a maximum (a peak), which appears a few seconds after the transition time. The time required to reach a stationary state is of the order of d2/D‾2 (where d is the membrane thickness and D‾2 is the coion diffusion coefficient in the membrane); this time under our experiment conditions is about 300–400 s. We show that the cause of the maximum is the increase in coion transfer caused by the current-induced concentration polarization of the bathing solution. This increase in coion transfer results in increasing the limiting current density jlim, which at j = const leads to a reduction in the resistance of the depleted diffusion layer over time and the appearance of a maximum on the ChP. 1D mathematical modeling is based on the Nernst-Planck-Poisson equations. The main assumption inspired by the works of Levich and Amatore is that the apparent electrolyte diffusion coefficient in the depleted solution increases with increasing electroconvection. The stationary value of this diffusion coefficient is found from the I–V curve. The only fitting parameter is the critical potential difference, which refers to the onset of intensive electroconvection.

Determination of the Transport Properties of Liquid Electrolytes Using a Multi-Electrode Cell

Reliable electrochemical models are necessary for performing numerical battery-related studies. These models must be comprehended with a number of input parameters.Many literature papers deal with the determination of electrolyte transport properties [1- 4] but only a minority of them proposes an exhaustive characterization (namely the determination of the transference number, the conductivity, the diffusion coefficient and the thermodynamic factor, for the simplest case of a binary electrolyte). Furthermore, when comparison can be made[5], it is often the case that data gathered from different sources for a same electrolyte are not in good quantitative agreement with each other [1,6].The most commonly used experimental methods for a complete determination of the set of properties are: The Hittorf method [2,3] (for transference number), the restricted diffusion method [7] (for diffusion coefficient), the electrochemical impedance spectroscopy (for conductivity) and the concentration cell (for the activity coefficient).Back in 2016 [6], Farkhondeh and coworkers proposed to alleviate the tedious multi-experimental protocol by introducing a novel multi-electrode cell design, in which the potential between inner Li reference electrodes is measured during and after a current pulse applied between two outer Li working electrodes. The measured potential is free of any electrode polarization and can be fitted with a mathematical model of the electrolyte so that conductivity, salt diffusion coefficient, and lithium transference number are simultaneously determined in single experiment.Our current work builds on the prior art by Farkhondeh and coworkers. It deals with the use of a “multi-electrode electrochemical cell”. Different routes are being explored and will be discussed in the presentation, namely: Using more reference electrodes for the method to gain accuracy, and possibly to evaluate the composition dependence of parameters in a limited number of experiments (fig.1).Bypassing metallic-lithium-related problems by finding alternatives to be used as active electrodes. Theoretical and practical aspects will be discussed and LiPF6 dissolved in 1:1 weight proportions EC:DEC will be investigated as a benchmark electrolyte and compared with already-published data [1].Our work aims at (i) showing how the parameters evaluation process could be simplified, and (ii) reduce drastically the number of experiments needed for fully characterizing a liquid electrolyte. This is an essential step towards the elaboration of an electrolyte-property database, supplying valuable information for modeling, as well as formulation-engineering, purposes. Fig. 1 : Representation of voltage measured between reference electrodes (blue red and orange crosses), during a current-pulse (black dashed line) of 1.9 A/m² and following relaxation. These experimental data were used to fit the electrolyte transport parameters using a mathematical model (in purple, green and cyan). Determined parameters are the following : . D = 2.85×10-10 m²/s , t+ 0 = 0.217 and κ eff = 0.602 S/m. The gradient-colored strip at the bottom highlights the parts of the signal where the different transport parameters have the largest sensivity. The multi-reference cell is represented in inset: (dark-grey: Li metal reference electrodes, dark grey: polyethylene spacers).References :[1] H. Lundgren, M. Behm, and G. Lindbergh, “Electrochemical Characterization and Temperature Dependency of Mass-Transport Properties of LiPF6 in EC:DEC,” J. Electrochem. Soc., vol. 162, no. 3, pp. A413–A420, 2014.[2] L. O. Valo̸en and J. N. Reimers, “Transport Properties of LiPF[sub 6]-Based Li-Ion Battery Electrolytes,” J. Electrochem. Soc., vol. 152, no. 5, p. A882, 2005.[3] T. Hou and C. W. Monroe, “Composition-Dependent Thermodynamic and Mass-Transport Characterisation of Lithium Hexafluorophosphate in Propylene Carbonate,” Manuscr. Submitt. Publ., p. 135085, 2019.[4] Yanping Ma, Marc Doyle, Thomas F Fuller, Marca M. Doeff, Lutgard C. De Jonghe, and John Newman. The measurement of a complete set of transport properties of a concentrated solid polymer electrolyte solution. Journal of The Electrochemical Society, 142(6):1859–1868, 1995[5] A. Ehrl, J. Landesfeind, W. A. Wall, and H. A. Gasteiger, “Determination of Transport Parameters in Liquid Binary Electrolytes: Part II. Transference Number,” J. Electrochem. Soc., vol. 164, no. 12, pp. A2716–A2731, 2017.[6] FARKHONDEH, Mohammad, PRITZKER, Mark, FOWLER, Michael, et al. Transport property measurement of binary electrolytes using a four-electrode electrochemical cell. Electrochemistry Communications, 2016, vol. 67, p. 11-15.. [7] Herbert S. Harned and Douglas M. French. A conductance method for the determination of the diffusion coefficients of electrolytes. Annals of the New York Academy of Sciences, 46(1):267–284, 1945 Figure 1

A potentiometric sensor based on modified electrospun PVDF nanofibers - towards 2D ion-selective membranes.

Core-shell modified nanofiber mats were used as ion-selective membranes for the first time. Keeping the overall macroscopic size of the sensing element the same as for classical plasticized poly(vinyl chloride) membranes, herein the proposed nanofiber based systems resulted in ultrathin (<10 nm) recognition layers with the total area nearly 3 orders of magnitude larger and the surface to volume ratio close to 7.5 × 107. Thus, for the first time close to 2D potentiometric receptors were obtained. Formation of thin and continuous liquid recognition layers on nanofibers was confirmed by XPS studies. The nanofiber based ion-selective mats used in the classical internal-solution arrangement were characterized with analytical parameters - the slope and detection limit well comparable to those for classical plasticized poly(vinyl chloride) based membranes. Despite the novel arrangement of the ion-selective layer and its nanometric thickness, the reproducibility of the recorded potentials, studied for more than 30 days, was high. Using confocal microscopy it was shown that electrolyte transport through porous nanofibers' mat phase is the rate limiting step in conditioning of the receptor layer. The estimated electrolyte diffusion coefficients for the nanofiber phase are close to 10-10 cm2 s-1, and thus are orders of magnitude lower compared to values characterizing ion transport through classical poly(vinyl chloride) based membranes. The truly nanostructural character of nanofiber ion-selective mats is visible in chronoamperometric experiments. It was shown that a core-shell nanofiber mat behaves as an array of nanoelectrodes - individual nanofibers. Thus, the novel nanofiber based architecture of ion-selective mats brings also a new quality to the current based electrochemistry of ion-selective sensors.

Numerical Simulation of a Lead-Acid Battery Discharge Process using a Developed Framework on Graphic Processing Units

In the present work, a framework is developed for implementation of finite difference schemes on Graphic Processing Units (GPU). The framework is developed using the CUDA language and C++ template meta-programming techniques. The framework is also applicable for other numerical methods which can be represented similar to finite difference schemes such as finite volume methods on structured grids. The framework supports both linear and nonlinear finite difference stencils. Furthermore, the arithmetic operators and math functions are overloaded to ease the array-based computations on GPUs. The reduction algorithms are also efficiently included in the framework. The discharge process of a lead-acid battery cell is simulated using the facilities provided by the framework. The governing equations are unsteady and include two nonlinear diffusion equations for solid (electrode) and liquid (electrolyte) potentials and three transient equations for acid concentration, porosity and the state of charge. The equations are discretized using the finite volume method. The framework allows the user to develop the numerical solver with a few efforts. The numerical simulation results are reported for different relations for open circuit potential and the electrolyte diffusion coefficient

Transport Characteristics of Homogeneous and Heterogeneous Ion-Exchange Membranes in Sodium Chloride, Calcium Chloride, and Sodium Sulfate Solutions

Structural (volume fractions of the gel phase and the intergel solution) and transport (electrical conductivity, diffusion permeability, transport numbers of counterions and coions) characteristics of cation-exchange (CMX, MK-40) and anion-exchange (AMX, MA-41) membranes in NaCl, CaCl2, and Na2SO4 solutions have been studied. The investigated membranes have the same chemical nature of the ion-exchange matrix and similar values of ion-exchange capacity, but they differ in the degree of heterogeneity and chemical nature of the reinforcing materials. The difference in the properties between heterogeneous (MK-40 and MA-41) and (conventionally) homogeneous (CMX and AMX) membranes is due to the fact that the heterogeneous membranes have macropores, whereas the homogeneous membranes do not have such pores. It has been shown that the largest macropores, which basically determine the high diffusion permeability of heterogeneous membranes, are formed at the boundaries of reinforcing fabric threads and the composite material. Regarding the influence of the electrolyte nature, the sorption of coions of the membrane gel phase (not containing macropores) is of primary importance; the sorption of coions, as well as diffusion permeability and the transport number of coions, increase in the order: 1 : 2 < 1 : 1 < 2 : 1, where the first numeral is the charge of the counterion and the second one is that of the coion. An important role, especially in the case of heterogeneous membranes, is played by the electrolyte diffusion coefficients in the electroneutral solution that fills the central part of meso- and macropores.

Peridynamic Modeling of Intergranular Corrosion Damage

A new peridynamic (PD) model for Intergranular corrosion (IGC) damage is presented. The model can simulate conditions ranging from grain boundary-only corrosion to full grain dissolution. Compared with other models, we require minimal input data for calibration: Tafel kinetics and electrolyte diffusion coefficient. Once calibrated, the PD model predicts, quantitatively, the penetration depth of the corrosion front as well as the morphology of the corroded microstructure in AA2024-T3 exposed to NaCl solution. We note that, when grain dissolution is negligible over hours, the diffusion controlled assumption gives results that match well the experimental observations. Tests for anisotropic microstructures confirm the direction dependency of corrosion penetration in rolled AA2024-T3 sheets. Without any other changes to the model, increasing the applied potential leads to partial and full grain dissolution. The PD model introduced here can be applied to any polycrystalline alloy.

Thermal Simulations of Polymer Electrolyte 3D Li-Microbatteries

High charge and discharge rates are desired properties for Li-ion batteries of both macro- and micro-scale (i.e. a footprint area of < 1mm2). Under these conditions, a rise of the cell temperature can take place, leading to performance limitations and safety issues. Investigations of thermal effects in battery cells provide possible explanations of the limiting factors of cell performance and can suggest improvements. We present here extensive simulations with a fully coupled 3D thermal-electrochemical model of 3D microbatteries (3D-MBs) using Finite Element Methodology (FEM). 3D-MB architectures comprising pillar shaped, plate shaped and concentric electrode arrangements are simulated, using LiCoO2 and graphite as electrodes and solid polymer electrolytes with LiTFSI salt. Sensitivity analysis of the electrolyte diffusion coefficient, depending on the C-rate, is used to benchmark the performance of these 3D-MB cells. FEM simulations of the 3D-MB during operation provide a complete 3D time-dependent description of the thermal behavior of the cells. Temperature gradients in the cell highlight critical regions which are likely causing performance bottlenecks and safety hazards. The simulations clearly demonstrate that the highest heat sources appear near the regions with most active charge transfer processes, thereby providing insights for optimization of the cell geometry in terms of both performance and safety.

Inclusion of the concentration dependence of the diffusion coefficient in the sand equation

The applications of the Sand equation in potentiometry of electrode and membrane systems for precise measurements of the transition time (τ) have been determined. An approach was suggested for choosing the diffusion coefficient of electrolyte (D) in the case when the concentration changes from its value in the agitated solution (where D = Db) to the nearly zero value at the surface (D = D0 corresponds to an infinitely dilute solution), Db and D0 being substantially different. The Nernst–Planck–Poisson nonstationary equations were numerically solved in a one-dimensional system including an ion-exchange membrane and two adjacent diffusion layers (for the electrode–solution system, the result is a particular case). An effective value Def was found, whose substitution in the Sand equation gave τ identical to that obtained by numerical solution. The neglect of the concentration dependence D(с) can lead to a nonadequate determination of the ion transport numbers in the membrane.

A New Technique for Measuring the Diffusion Coefficient of Electrolytes for Lithium-Ion Batteries

The electrolyte is a crucial component in modern Lithium-Ion batteries. It is responsible for the transport Lithium-Ions not only through the separator but also within the porous structure of the electrodes. A small diffusion coefficient of the electrolyte leads to an increased voltage drop due to depletion of Lithium-Ions and thus limits the performance of a battery for high currents. While the diffusion coefficient is mostly measured by potentiostatic or galvanostatic intermittent titration techniques (PITT or GITT), also an evaluation of the diffusion impedance of the electrolyte should yield according values. However, standard impedance measurement techniques like Electrochemical Impedance Spectroscopy (EIS) suffer severe disadvantages: Due to the sinusoidal excitation a current is permanently flowing and, in case of beneficially used metallic Lithium electrodes, Lithium is continuously being deposited and stripped. This causes a continuously changing surface area during the measurement and hence a time-variant and thus invalid impedance spectrum. Moreover, the diffusion impedance needs to be measured down to very low frequencies, which results in very long measurement times for regular Electrochemical Impedance Spectroscopy. As an adequate solution for both issues we suggest computing the diffusion impedance from time-domain measurements [1]: By choosing an appropriate excitation signal, changes within the system during measurement can be prevented and, as all frequencies are excited simultaneously, measurement time can be minimized. By experimentally shifting the diffusion process to lower frequencies we are further able to clearly separate it from other, surface reaction related processes and thus to isolate the diffusion impedance. For an example see Figure 1, where repeated measurements of the diffusion impedance of LiPF6 in EC/DMC (1:1) are shown. From the time constant of the diffusion impedance, the diffusion coefficient of the electrolyte is finally obtained. Caption Figure 1: Repeated measurement of the diffusion impedance of LiPF6 in EC/DMC (1:1), as it is commonly used in Lithium-Ion batteries (real-parts shifted to origin).

Development and Validation of a ROM Incorporated By a Semi-Empirical Aging Model for a Large-Format LiFePO4/Graphite Cell

Lithium iron phosphate (LFP) as cathode materials was firstly introduced by Padhi etc. in 1997. It has undergone remarkable developments and been widely used in commercial Li-ion batteries because of its good electrochemical and thermal stability. In order to overcome the low conductivity and high-current capability, carbon coating and nanoparticles are used to achieve a high rate capability with low cost. LFP as cathode materials has caused great interest in the field of electric and hybrid electric vehicles. The research aims to develop an online algorithms for LFP/Graphite cells to detailed describe lithiation and delithiation process during galvanostatic discharging and charging. The model is based on the electrochemical thermal principles. A reduced order model (ROM) has been developed for both fresh and aged lithium iron phosphate (LFP) based cells (nominal capacity: 20Ah), in which plateau and path dependence phenomena caused by two-phase transition during charging and discharging have been taken into consideration. Two-phase transition during lithium intercalation/deintercalation into/from LFP particles is approximately modeled by a shrinking core with a moving boundary at the interface between two phases, lithium-rich phase and lithium-deficiency phase. Moreover, it is also described by the modified diffusion equations with consideration of multiple layers that formed in cathode particles. Polynomial approach, state space approach and some other reduction assumptions, such as linearization of Bulter-Volmer equations, are used for solid concentration, electrolyte concentration and potentials, separately. For fresh cells, the physics-based ROM has been validated by experimental data obtained through galvanostatic charging and discharging at different C-rate (1C, 3C, 4C) and temperature (25, 45). Path dependence experiments are also conducted and then used to do comparable analysis with simulation results. The simulation results of single cycles, multiple cycles and pulse cycles show great consistent with experiment results. Furthermore, parameter sensitivity of ROM has also been analyzed. Therefore, the model is able to represent the characteristics of plateau and path dependence of LFP cells. For aged cells, a semi-empirical degradation model has been incorporated into the former ROM. By fitting the semi-empirical degradation model, three important parameters, resistance, electrolyte diffusion coefficient and volume fraction of anode active materials, are extracted from the experimental voltage curve. Five cells are stored in a thermal chamber at 25 for six months at different SOC (10%, 30%, 50%, 70%, 90%). Five cells are cycled under 4C/4C charging/discharging procedure at different temperature (25, 45), SOC cycling range (5%-75%, 25%-95%) and number of cycles. The capacity fade of these five cells are 5.81%, 10.95%, 12.17%, 14.17%, and 23.54%, separately. Experiment results illustrate that high temperature and SOC could accelerate the battery aging. EIS and capacity measurements are conducted every 30 cycles during cycling. EIS results show that the impedance curve shifts rightwards as the increase of ohmic resistance and SEI resistance caused by side reactions. Post-mortem analysis, XRD and SEM, are used to analyze the change of morphology and composition for aged cells The impedances are increased as the number of cycles on the rise. It shows that there is no structure change in both cathode and anode. The model with semi-empirical degradation model incorporated is validated against cycling experiments and shows good consistency.

Accounting for the concentration dependence of electrolyte diffusion coefficient in the Sand and the Peers equations

The equations for calculating the diffusion limiting current, ilim, in steady-state voltammetry (known as the Peers equation in membrane science) and the transition time, τ, in chronopotentiometry (the Sand equation) are broadly used in electrode and membrane electrochemistry. The applicability of these equations is limited because they are deduced under the assumption of a constant diffusion coefficient. However, within the diffusion boundary layer, the diffusion coefficient, D, varies between the values corresponding to the bulk solution (Db), and the infinitely dilute solution (D0) near the electrode or membrane surface. In this paper, we explore two models, which account for the concentration dependence D(c) in order to generalise the above fundamental equations. We show that the correct value of ilim can be found via solution of a 2D model, while to find τ, a 1D non-stationary model is sufficient. Generally, the dependence of ilim on the bulk concentration deviates from the proportionality. The similar situation occurs with the proportionality of τ to the squared concentration in the Sand equation. We show that the numerical solutions for ilim and τ can be presented in the forms analogous to the Peers and the Sand equations, respectively, but with an additional correction factor. In particular, an effective diffusion coefficient, Def (an average between Db and D0) has to be introduced in the case of Sand equation. Comparison of our theoretical prediction with experimental chronopotentiograms confirms the necessity of taking into account the D(с) dependence.

Photovoltaic and Impedance Characteristics of Quasi Solid-State Dye-Sensitized Solar Cell Using Polymer Gel Electrolytes

In order to overwhelm the electrolyte leakage problem and improve the stability in extreme climate conditions, we have studied the fabrication and characteristics of dye sensitized solar cell (DSSC) using polymer gel electrolyte (PGE), which is developed from siloxane based polymer gel blended with imidazolium ionic liquid. In many cases, the use of PGE often reduces its photovoltaic performance due to the decrease in its ionic mobility. However, such influence was not observed in our present work. In this work, the fabricated DSSC do not exhibit significant degradation in its working performance. The best overall energy conversion efficiency is about 5.25%, as indicated by short circuit photocurrent (Jsc) larger than 12 mA/cm2, which is comparable to performance of reference cell made by using ionic liquid only. We found from the impedance spectroscopy measurements that the electrolyte diffusion coefficient in the DSSC using this PGE is comparable to that in DSSC using ionic liquid electrolyte.

Numerical modeling of passive layer formation and stabilization in electrochemical polishing process

The electrochemical polishing generates surface finish in micro-/nano-scale. The process, primarily works on the principle of preferential anodic dissolution owing to the passive layer formation. The current–voltage characteristics curve of the process shows that stable passive layer by anodic dissolution is obtained in plateau region that is a favorable condition for the electrochemical polishing process. This work presents numerical simulations of effect of main process parameters: inlet velocity, diffusion coefficient of electrolyte, inter-electrode gap and roughness of anode surface on uniformity and time to obtain steady passive layer. It is observed that all the above parameters govern uniformity of the passive layer. The inlet velocity and diffusion coefficient of electrolyte mainly govern the time required for stabilization of the passive layer followed by the inter-electrode gap; however, surface roughness at anode has a negligible effect. Further, the process gives better performance when the inlet velocity is 0.007–0.008m/s, diffusion coefficient is 10−8 to 10−9m2/s and inter-electrode gap is greater than 6mm.

Modeling of degradation effects considering side reactions for a pouch type Li-ion polymer battery with carbon anode

When a lithium ion polymer battery (LiPB) is being cycled, one major cause for degradations is the irreversible side reactions between ions and solvent of electrolyte taking place at the surface of anode particles. SEM analysis of cycled battery cells has revealed that the deposits from the side reactions are dispersed not only on particles, but also between the composite anode and the separator. Thus, the solid electrolyte interface (SEI) becomes thicker and extra deposit layers are formed between composite anode and separator. Also, XPS analysis showed that the deposits are composed of Li2CO3, which is ionic conductive and electronic nonconductive. Based on the mechanisms and findings, we identified four degradation parameters, including volume fraction of accessible active anode, SEI resistance, resistance of deposit layer and diffusion coefficient of electrolyte, to describe capacity and power fade caused by the side reactions. These degradation parameters have been incorporated into an electrochemical thermal model that has been previously developed. The terminal voltage and capacity of the integrated model are compared with experimental data obtained for up to 300 cycles. Finally, the resistance of the deposit layer calculated by the model is validated against the thickness of the deposit layer measured by SEM.

A Novel Method for Limiting Current Calculation in Electrodialysis Modules

The purpose of this work was to develop a novel semi-empirical method for calculation of limiting currents in electrodialysis modules. Experiments were carried out at pilot-scale module with five electrolytes. Current-voltage curves were measured and limiting currents were determined. Subsequently, dependence of the mass transfer coefficient on linear flow velocity was evaluated and its parameters a, b were estimated. The main advance of this work is that comparison of electrolytes showed the clear relationship between parameter a, electrolyte diffusion coefficient and the difference of cation transport numbers in membrane and solution. The semi-empirical relationship between the mass transfer coefficient and linear flow velocity was set up, and the limiting current calculation run was proposed. At the same time, dependence of the diffusion layer thickness on linear flow velocity was examined and the way of its calculation was established. The proposed method is unique thanks to its applicability in a broad range of experimental conditions; its use is not limited neither by electrolyte type nor electrodialysis module size.