Electrolyte Distribution Research Articles

Local potential measurement through reference electrodes in vanadium redox flow batteries: Evaluation of overpotentials and electrolytes imbalance

Vanadium redox flow battery performance is actually hindered by increased overpotentials at high current, due to poor electrochemical activity of the most commonly used carbon electrodes and to electrolyte distribution, implying local mass transport limiting conditions. Moreover, vanadium cross-contamination leads to coulombic efficiency reduction and uncontrolled electrolytes imbalance. This work presents the application of through-plate reference electrodes at inlet and outlet of both positive and negative electrodes. The utility of the electrodes potential measurement is firstly demonstrated in the identification of a relation between electrolytes potential and the corresponding state of charge. Subsequently, local overpotentials and impedance spectra at both electrodes are evaluated, evidencing that the negative electrode is kinetically dominated and presents high overpotential even at low current, while the positive exhibits mass transport effects at high current, especially at cell outlet. Finally, during cycling operation with fixed capacity reference electrode measurements permit to monitor electrolytes imbalance induced by cross-contamination, that mainly affects negative electrolyte. Moreover, additional insights into electrodes potential loss during cycling are provided.

Estimating and Identifying Parameters from Discharge Curves of Lithium-Ion Batteries

In order to improve the performance of Lithium ion secondary batteries (LiBs) for electric vehicles and hybrid electric vehicles, it is very important to understanding the internal transport phenomena and resistance under high rate condition to increase power density. In our previous studies, we focused on the actual porous electrode structure, and the Li ion and electron conductivity was evaluated by the effective conductive path with the actual reconstruction electrode structure [1]. In addition, the charge-discharge performance was simulated with the model of reaction and mass transfer in heterogeneous porous electrode structure [2]. In this simulation, as assumptions, Li concentration and potential distribution in active material (AM) and electrolyte (EL) were calculated with mass transport simulation and Butler-Volmer equation as the boundary condition of the interface between AM and EL. From these calculation results, the effect of heterogeneous porous structure, which consist of active material, conductive material and binder, on the cell performance could be evaluated. Then, the values of parameters in this model are essential to accuracy of it. However, some parameters cannot be measured precisely in the experiment, especially, reaction rate constant, tortuosity of separator, Li+ diffusion coefficient, and transport number in electrolyte are treated as literature value or ex-situ results. In this paper, we established the method of identifying these parameters by using experimental data in various condition and complex method [3]. We conducted fitting on experimental data of some SOC and some discharge rate condition. We adopted RMSE (Root Mean Square Error) to judge this fitting. Figure1 shows the overview of complex method. it is non-linear optimization method. Figure2 indicate transition of RMSE. From this, we can understand RMSE decreasing, and then, the value finally settle at 0.021. Thus the parameters can be identified. In addition, we will present the results of electrode structure optimization with complex method for high output power density cell.

Stable Metal Anode enabled by Porous Lithium Foam with Superior Ion Accessibility.

Lithium (Li) metal anodes have attracted much interest recently for high-energy battery applications. However, low coulombic efficiency, infinite volume change, and severe dendrite formation limit their reliable implementation over a wide range. Here, an outstanding stability for a Li metal anode is revealed by designing a highly porous and hollow Li foam. This unique structure is capable of tackling many Li metal problems simultaneously: first, it assures uniform electrolyte distribution over the inner and outer electrode's surface; second, it reduces the local current density by providing a larger electroactive surface area; third, it can accommodate volume expansion and dissipate heat efficiently. Moreover, the structure shows superior stability compared to fully Li covered foam with low porosity, and bulky Li foil electrode counterparts. This Li foam exhibits small overpotential (≈25 mV at 4 mA cm-2 ) and high cycling stability for 160 cycles at 4 mA cm-2 . Furthermore, when assembled, the porous Li metal as the anode with LiFePO4 as the cathode for a full cell, the battery has a high-rate performance of 138 mAh g-1 at 0.2 C. The beneficial structure of the Li hollow foam is further studied through density functional theory simulations, which confirms that the porous structure has better charge mobility and more uniform Li deposition.

Analytical Model for Predicting the Discharge Performance of Thick Battery Electrodes

There is an increasing interest in using thick electrodes in Li-ion batteries to improve the energy density and lower the cost by reducing the amount of inactive components. However, increasing electrode thickness usually leads to inferior rate performance. Currently there lacks a quantitative understanding of the trade-off between the power and energy density for thick electrodes, which is essential for optimizing electrode structures for specific applications and developing novel thick electrode designs. Addressing this deficiency, here we present a simple and yet accurate analytical model for predicting the discharge performance of battery cells containing thick electrodes. Compared to the traditional porous electrode simulations, this model offers a more transparent understanding of the kinetic limitations of thick electrode configurations and the effects of various cell-level structural parameters on battery performance. Computation-wise, the model is substantially more efficient than the numerical pseudo-2D discharge simulation, and provides a powerful tool for performing the optimization of thick electrodes within the multi-dimensional design space. Our model is motivated by two important observations from numerical simulations and experiments, namely, the capacity utilization of thick electrodes is limited by electrolyte transport and a pseudo-steady state of electrolyte transport is established during discharge. Accordingly, we derived analytical expressions for the electrolyte distribution across the electrode and the discharge capacity at termination based on the steady state assumption. As shown in Figure 1a, the predicted distribution of Li ion concentration in electrolyte agrees well with the numerical simulation. The depth of discharge (DoD) calculated from the analytical model provides excellent approximations to the simulation results for various electrode thickness and cell configurations (half vs full cells) without any adjustable parameters, Figure 1b. This model is generally applicable to electrodes that display solid-solution intercalation behavior such as the layer oxide cathodes paired with the graphite anode at low to moderately high discharge rates. An important insight we obtained from the analytical model is that the discharge capacity of half and full cells exhibit qualitatively different scaling relation with electrode thickness and discharge current. As such, the half cell configuration with Li metal anode exhibits markedly improved DoD at large electrode thickness over full cells containing the graphite anode. This finding explains the seemingly scattered results from various thick electrode experiments reported in literature. It cautions against the practice of using the half cell testing as an indicator of the rate performance of full cells with thick electrodes. On the other hand, it suggests that the combination of a thick cathode with a high capacity anode such as Li metal, silicon and tin is an effective strategy to enable thick electrode designs with higher capacity utilization. Figure 1: a) Li ion concentration distribution in electrolyte during discharge calculated from the porous electrode simulation (solid lines) and steady-state analytical model (dashed line). Figure 1

Deciphering the Oxygen Reduction Reaction on Platinum: A Theoretical Framework

The conversion of oxygen into water is crucial to the operation of polymer electrolyte fuel cells and other emerging electrochemical energy technologies. Chemisorbed oxygen species play a central role in this reaction, since they necessarily act as intermediates but also as site-blockers. Any attempt to decipher the oxygen reduction reaction must relate the formation of oxygen intermediates to basic electronic and electrostatic properties of the catalyst surface and, on the other hand, link it to effective parameters of the electrode activity. An approach that accomplishes this feat will be of great utility in guiding design and development of catalyst materials and developing predictive models of electrode operation. Here, we present a theoretical framework for the multiple interrelated surface phenomena and processes involved. It correlates the formation of chemisorbed oxygen intermediates, metal surface charging phenomena, ion density and potential distribution in electrolyte, field-dependent ordering of interfacial water molecules, and effective kinetic parameters of the ORR. Parameterized with density functional theory results and rotating disk electrode data, the model sheds light on the double-edged roles of oxygen intermediates; it produces as output the Tafel slope and exchange current density as continuous functions of electrode potential and presents a new perspective on the volcano relation the ORR. The optimal oxide coverage is a result of two oppositely-headed trends upon increasing coverage by oxygen intermediates, viz, the intuitive site-blocking effect and the increasing protophilicity of the surface.

The Influence of Electrode Microstructure on the Performance of Non-Aqueous Redox Flow Batteries

Redox flow batteries (RFBs) are promising rechargeable electrochemical devices for grid-scale energy storage but further cost reductions are needed for ubiquitous adoption of this technology [1]. While current state-of-the-art RFB systems employ aqueous chemistries, transitioning to nonaqueous electrolytes offer a new pathway to reduced cost through increased energy density. While research efforts have primarily focused on molecular discovery [2], there has been significantly less attention paid to the development of other critical system components. Of particular importance are the porous electrodes used in the RFB’s electrochemical stack. Today’s electrodes largely draw from the fuel cell material set, but, within a RFB, the porous electrode must perform a range of different roles including serving as active surfaces for electrochemical reactions, enabling excellent liquid electrolyte distribution, and maintaining low pressure drops [3]. Thus, to enable the development of advanced electrodes tailored for RFB applications, it is necessary to quantify the performance-limiting factors for the present materials set. However, unambiguous analysis is challenging in an operating RFB due to the complex coupling of transport and reactions which varies as a function of state of charge during cell cycling. Deconvoluting the role of electrode properties on flow battery performance requires the development of diagnostic techniques that enable electrode characterization under well-controlled but application-relevant conditions. To this end, we systematically compare the operando performance of RFBs containing selected carbon paper, felt, and cloth electrodes using the single-electrolyte cell configuration (Figure 1a) [4] and a model organic redox couple (TEMPO/TEMPO+) [5]. Using polarization and electrochemical impedance spectroscopy, we quantify the impact of electrode microstructure on battery performance (Figure 1b). We find that, depending on the electrode choice and flow conditions, current densities as high as 450 mA cm-2 can be achieved at an overpotential of 0.3 V with a cell area specific resistance as low as 0.7 Ω cm2. This result suggests that, through appropriate cell engineering and materials selection, high power performance is possible in nonaqueous flow batteries. Finally, a simple convection-diffusion mass transport model is developed to explain the observed experimental behavior and provide guidance for the bottom-up design of next generation RFB electrodes. Darlin et al., Energy Environ. Sci., 7, 3459 (2014).A. Kowalski et al., Curr. Op. Chem. En., 13, 45 (2016).Weber et al., J. Appl. Electrochem., 41(10), 1137 (2011).Darling et al., J. Electrochem. Soc., 161, A1381 (2014).D. Milshtein et al., J. Power Sources, 327, 151 (2016). Acknowledgments We gratefully acknowledge the financial support of the Swiss National Science Foundation (P2EZP2_172183) and the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the United States Department of Energy. Figure 1

Characterization of Spatial Distribution of Electrolyte in Molten Carbonate Fuel Cell Cathodes

High‐resolution computed X‐ray tomography (XCT) is applied in this study to characterize the microstructure of Molten Carbonate Fuel Cell (MCFC) cathodes after operation, where a “virgin cathode” formed by porous nickel has been in situ oxidized and infiltrated by liquid electrolyte. This technique extends state‐of‐the art methodology to characterize pores such as porosity analysis using Mercury porosimetry. XCT enables 3D imaging of the internal structure of the electrodes including all components present at the cathode side, particularly NiO, pores, and electrolyte. The quantitative 3D microstructure analysis based on high‐resolution XCT provides topological information for each component and their mutual spatial distribution, which is significant for the enhancement of the MCFC performance. In particular, volume fraction, specific surface area, continuity of each phase, as well as the Triple Phase Boundary (TPB) density are calculated from the experimental data. The results indicate that superior properties of the multi‐modal pore sized cathode, used in this study, can be attributed to the formation of three self‐interpenetrating networks of pathways for the transport of gasses, electrons, as well as ions throughout pores, NiO, and electrolyte, respectively.

Fragment Molecular Orbital Calculations with Implicit Solvent Based on the Poisson-Boltzmann Equation: Implementation and DNA Study.

In this study, an ab initio fragment molecular orbital (FMO) methodology was developed to evaluate the solvent effects on electrostatic interactions, which make a significant contribution to the physical and chemical processes occurring in biological systems. Here, a fully polarizable solute consisting of the FMO electron density was electrostatically coupled with an implicit solvent based on the Poisson-Boltzmann (PB) equation; in addition, the nonpolar contributions empirically obtained from the molecular surface area (SA) were added. Interaction analysis considering solvent-screening and dispersion effects is now available as a powerful tool to determine the local stabilities inside solvated biomolecules. This methodology is applied to a deoxyribonucleic acid (DNA) duplex known as the Dickerson dodecamer. We found that excessively large electrostatic interactions inside the duplex are effectively damped by the screening, and the frontier molecular orbital energies are also successfully lowered. These observations indicate the stability of highly charged DNA duplexes in solution. Moreover, the solvation free energies in the implicit model show fairly good agreement with those in the explicit model while avoiding the costly statistical sampling of the electrolyte distribution. Consequently, our FMO-PBSA approach could yield new insights into biological phenomena and pharmacological problems via this ab initio methodology.

Effects of metal foam properties on flow and water distribution in polymer electrolyte fuel cells (PEFCs)

Using a two-phase polymer electrolyte fuel cell (PEFC) model, we numerically investigated the influence of metal foam porous properties and wettability on key species and current distributions within a PEFC. Three-dimensional simulations were conducted under practical low humidity inlet hydrogen and air gases, and numerical comparisons were made for different metal foam design variables. These simulations were conducted to elucidate the detailed operating characteristics of PEFCs using metal foams as a flow distributor, and the simulation results showed that two-phase transport and the resulting flooding behavior in a PEFC are influenced by both the metal foam porous properties and the porous properties of an adjacent layer (e.g., the gas diffusion layer). This paper offers basic directions to design metal foams for optimal water management of PEFCs.

Replica Ornstein-Zernike Theory Applied for Studying the Equilibrium Distribution of Electrolytes across Model Membranes.

By means of replica Ornstein-Zernike theory (supplemented in a few cases by Monte Carlo simulations) we examined the distribution of an annealed primitive model +1:-1 electrolyte in a mixture with uncharged hard spheres, or another model +1:-1 or +2:-1 electrolyte inside and outside the quenched vesicles, decorated by a model membrane, and across the membrane phase. We explored the influence of the size and charge of the annealed fluid on the partition equilibrium, as well as the effect of the vesicle size and membrane interaction parameters (repulsive barrier height, attractive depth, and membrane width). A hydrophobic cation, present in the mixture with NaCl, slightly enhanced the concentration of sodium ions inside the model vesicle, compared to pure NaCl solution. The replica theory was in good agreement with computer simulations and as such adequate for studying partitioning of small and hydrophobic ions or hydrophobic solutes across model membranes.

Influence of Type 2 Diabetes on Serum Electrolytes and Renal Function Indices in Patients

Introduction: Type 2 diabetes, a disease condition characterised by hyperglycaemia can damage the kidney, an organ which regulates water and electrolytes. Also, high blood sugar can increase plasma osmolarity thereby, drifting water movement from the intracellular to the extracellular spaces and alter the distribution of electrolytes in the body. However, little is known on the relationship between serum electrolytes, renal function and Type 2 Diabetes (T2D). Aim: This study was aimed to assess the serum electrolyte level of diabetic patients in order to evaluate the relationship of these electrolytes with renal dysfunction indices as well as other diabetes risk factors in T2D patients. Materials and Methods: A case-control study involving 72 T2D and 75 Non-Diabetic (ND) outpatients was conducted at Enugu State University Teaching Hospital (ESUTH) Enugu, Nigeria. The patients’ demographic and anthropometric data was obtained and the serum electrolytes; potassium (K+), sodium (Na+) and chloride (Cl-) ions along with creatinine and urea as renal function indices were measured. Results: Serum K+ was significantly higher (p = 0.002) in T2D patients while Na+, Cl-, creatinine and urea were insignificantly higher in T2D patients compared to the ND patients. Serum K+ disorder were significantly greater (p<0.05) in T2D patients as 8.8% of T2D patients were hyperkalaemic compared to ND patients (2.7%). Creatinine level positively correlated with K+ (p = 0.004) while age, Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP) correlated with serum electrolytes. Conclusion: T2D was found to promote electrolyte imbalance particularly potassium ion derangement and may affect renal function. Risk factors of T2D such as old age and high blood pressure may also promote electrolyte disorders.

Design of an Automated System to Accelerate the Electrolyte Distribution in Lithium-Ion Batteries

Design of an Automated System to Accelerate the Electrolyte Distribution in Lithium-Ion Batteries

Influence of electrolyte distribution in PEDOT:PSS based flexible electrochromic devices

Two flexible electrochromic devices based on PEDOT:PSS were prepared by roll-to-roll method, these devices were built with the conventional layered geometry or using PEO:LiClO4 and charge balancing material mixed at the same layer. Analysis of the properties leads to the conclusion that the presence of the percolation channels of PEDOT:PSS inside the PEO/LiClO4 results in the performance improvement as monitored by impedance spectroscopy and the respective Randles equivalent circuits. From mixed electrochromic layer, ηd increases up to 834 C−1 cm2 after 1.5 s of switch time, while the corresponding layered device showed ηd of 472 C−1 cm2 at the same time interval.

Hydrogen Peroxide Generation in Divided-Cell Trickle Bed Electrochemical Reactor

A divided-cell trickle bed electrochemical reactor (TBER) with a porous cathode composed of carbon black and polytetrafluoroethylene was developed for generation of hydrogen peroxide. An important feature of the reactor is a divided cathode of different cells made with stainless steel mesh. This division into a sectional cathode resulted in a concentration of hydrogen peroxide that is more than twice that produced in an undivided cathode. The much improved performance was attributed to the even distribution of electrolyte and oxygen in the cathode bed, as well as an effective mass transport of oxygen from the gas phase to the electrolyte–cathode interface. Hydrogen peroxide generation was demonstrated from electrochemically reducing oxygen in concentrated alkaline electrolyte solutions using the TBER. Factors for the hydrogen peroxide electrosynthesis were systematically studied, including cell potential, electrolyte flow rates and concentrations, temperatures, and the number of cells.

SERS Analysis on Interfacial Reaction of Rechargeable Battery Electrode Using Plasmonic Sensor Element – SEI Formation at Graphite Electrode Surface

Surface enhanced Raman scattering (SERS) effect to magnificently intensify Raman signals, provided by nano-structured metal surface or plasmonic nano particles, is a powerful tool for analyzing interfacial phenomena on the electrodes [1,2]. To produce this SERS effect handily in practical analyses of solid-liquid interfacial reaction at the electrode, we have developed optical components made of transparent materials with nano particles of plasmon-active metals (Ag, Au, etc.), which we call as “SERS sensor” [3]. Just locating this sensor onto the electrode surface magnifies the Raman signals about chemicals at the electrode, providing the information to investigate the interfacial reaction phenomena. We employs this SERS measurement technique to reaction mechanism analyses for electrode surfaces. One of our present targets is the reaction behavior at electrodes in Li ion secondary battery (LIB), focusing on formation mechanism of solid-electrolyte interface (SEI) [4]. SEI formation is one of the critical factors to determine the performance of LIB [5,6], which could avoid farther decomposition of electrolyte, while permitting Li+ to penetrate. Such properties of SEI films strongly depend on the composition of the film itself, which is determined by unclear mechanism of SEI formation. To understand the SEI film formation mechanism in the LIB in detail, Raman spectroscopy including highly precise SERS measurements was performed. Here, Li2CO3 generation was particularly focused on, whose formation mechanism is not clear in spite of its critical roles in the SEI films. Two kinds of solvent were used as electrolytes: mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with 1:1 in volume, called as EC-EMC, and mixture of propylene carbonate (PC) and EMC with 1:1 (v/v), PC-EMC. This is because these two organic solvents, EC and PC, show clearly different performances on SEI formation. The graphite anode and the LiCoO2thin film cathode composed LIB model cell systems. SERS measurements using the SERS sensor revealed clear difference between EC-based and PC-based electrolytes for the SEI formation behavior. Formation of Li2CO3 in the SEI film was not detected in EC-EMC, while that appeared in the case of PC-EMC, which should be due to the difference in the electrolyte distribution; PC-based electrolytes locate relatively lower amount of PC at the graphite electrodes than the amount of EC at the electrode in the case of EC-EMC, which leads to 2-electron reduction mechanism of SEI formation, resulting in Li2CO3formation. Acknowledgements This research was partially supported by the “Development of Systems and Technology for Advanced Measurement and Analysis”, and the “Research & Development Initiative for Scientific Innovation of New Generation Batteries (RISING II)” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

Simulation of Lithium-Ion Battery with Effect of Volume Expansion of Active Materials

In order to improve the performance of Lithium ion secondary batteries (LiBs) for electric vehicles and hybrid electric vehicles, it is very important to understanding the internal transport phenomena under high rate condition to increase power density. In our previous studies, we focused on the actual porous electrode structure, and the Li ion and electron conductivity was evaluated by the effective conductive path with the actual reconstruction electrode structure [1]. In addition, the charge-discharge performance was simulated with the model of reaction and mass transfer in heterogeneous porous electrode structure [2]. This model was developed with the multi-block method which is the method of coarse graining to keep the information of heterogeneous structure [3]. Furthermore, in order to design high capacity anodes based on volumetrically expanding active materials for lithium-ion batteries, we investigated the effects of the expansion ratio of active materials on the charge capacity by carrying out numerical simulations based on the porous electrode theory [4]. In this simulation, as assumptions, Li concentration and potential distribution in active material (AM) and electrolyte (EL) were calculated with Butler-Volmer equation as the boundary condition of the interface between AM and EL. it was assumed that temperature is constant, the formation of SEI is ignored, binder phase inhibit ionic transfer. From these calculation results, the effect of heterogeneous porous structure, which consist of active material, conductive material and binder, on the cell performance could be evaluated. Especially, we focused on the dynamic effective parameter which means the ratio of the effective ionic conductivity in porous electrode between the local time and the initial condition. In the case of expansion ratios of 0.5, which means the 50 % enlargement of active material at the SOC=100%, this value becomes approximately 0.24. Thus, the effective ionic conductivity decrease about 0.2 times than that at initial condition. However, in order to examine then in detail, there are some subjects. In this study, the effect of various expansion ratio and the aggregate structure of active materials was examined. And also, the validity of this simulation was evaluated with some experimental charge-discharge curve and direct observation of volume expansion. Figure 2 shows the cross section view of cell under charge condition and the change of electrode layer thickness. In our presentation, we will discuss the effect of the micro-scale structure on cell performance with volume expansion and the validity of this simulation. Figure 1

Enhanced energy density and electrochemical performance of all-solid-state lithium batteries through microstructural distribution of solid electrolyte

Abstract Maximizing the proportion of active material in the composite cathode is a technical challenge for the All-Solid-State Lithium ion battery. Among viable solutions, employing a powder with minimized and uniform size distribution might be the most effective and practical solution. To address this issue, we carefully control the size of the high ionic conducting Li 2 S-P 2 S 5 solid electrolyte to a smaller and narrower size distribution than standard solid electrolyte. We show the milled electrolytes have significantly higher capacity than standard one in the composite cathode. Electrochemical impedance spectroscopy suggests that both the active material-solid electrolyte interfacial resistance and the solid electrolyte pathway resistance through the composite cathode are important. Moreover, at higher active material ratios, the resistance through ion conducting pathways becomes the most limiting factor for discharge rates. A preliminary model is suggested to guide future development of the microstructure in all-solid-state batteries.

Plasma Electrolyte Distributions in Humans—Normal or Skewed?

BackgroundIt is widely believed that plasma electrolyte levels are normally distributed. Statistical tests and calculations using plasma electrolyte data are often reported based on this assumption of normality. Examples include t tests, analysis of variance, correlations and confidence intervals. The purpose of our study was to determine whether plasma sodium (Na+), potassium (K+), chloride (Cl−) and bicarbonate (HCO3−) distributions are indeed normally distributed. MethodsWe analyzed plasma electrolyte data from 237 consecutive adults (137 women and 100 men) who had normal results on a standard basic metabolic panel which included plasma electrolyte measurements. The skewness of each distribution (as a measure of its asymmetry) was compared to the zero skewness of a normal (Gaussian) distribution. ResultsThe plasma Na+ distribution was skewed slightly to the right, but the skew was not significantly different from zero skew. The plasma Cl− distribution was skewed slightly to the left, but again the skew was not significantly different from zero skew. On the contrary, both the plasma K+ and HCO3− distributions were significantly skewed to the right (P < 0.01 zero skew). There was also a suggestion from examining frequency distribution curves that K+ and HCO3− distributions were bimodal. ConclusionsIn adults with a normal basic metabolic panel, plasma potassium and bicarbonate levels are not normally distributed and may be bimodal. Thus, statistical methods to evaluate these 2 plasma electrolytes should be nonparametric tests and not parametric ones that require a normal distribution.

Electrochemical drilling of multiple small holes with optimized electrolyte dividing manifolds

Structures with multiple small holes have been widely used to aid cooling in aeronautical engine components. Electrochemical drilling uses a side-insulated tube as the tool cathode and removes anodic material via controlled electrochemical reactions in a cell. The flexibility for simultaneous drilling makes electrochemical drilling a feasible technique for producing multiple small holes. In multiple hole electrochemical drilling, uneven electrolyte volume divided to each tube electrode would cause each hole machining status different. This paper addresses the design of an electrolyte dividing manifold for use in electrochemical drilling of multiple holes. Structural parameters such as the distance from the manifold inlet to the first tube electrode, the manifold inlet diameter and the tube electrode length have obvious effects on the electrolyte distribution along the electrode array. Experiments illustrate an optimized manifold structure is feasible for practical fabrication. Finally, two types of hole arrays are successfully fabricated.

Bending Stress Analysis of All Solid State Flexible Lithium Battery

Wearable electronic devices like smart watches and smart bracelets are promising products in the market. Batteries that are implanted to these devices are required to be thin-layered, light, powerful, and the most importantly, safe. It will also be more convenient for users to wear if the devices are bendable. All solid state lithium battery (ASSLB) can play a good role as the power source of wearable devices due to its high energy density, noninflammability and flexibility. Along with the growing applications of ASSLB, it is important to fully understand its characteristics. With the help of a physical model of ASSLB, this study attempts to establish a relationship between the performance of battery and the bending stress. In the past, several studies constructing a mathematical model for ASSLB have been reported. Danilov et al. 1 first presented an ASSLB model in 2011. Even this model provides a good agreement between simulation and experiment, several parameters used in this model are still questionable or undetermined. For example, the charge transfer number is not the unity and the diffusion coefficient of anion cannot be determined. Fabre et al.2proposed a simpler model with good accuracy, which however ignored the variation of cation’s concentration in electrolyte, which then fails to show what is actually happening in the electrolyte and results in inaccuracy of discharge curves at high C-rate. Although the two models provide a description of several physical mechanisms of ASSLB, its stress analysis is lacking. In this work, we establish a comprehensive physical model for ASSLB and discuss the behavior of the battery when it is under bending. Similar to the work in [3], we derive the concentration and potential distribution in electrolyte by Nernst-Plank equation(1) and Poisson equation(2). In addition, we obtain the boundary conditions of the electrolyte potential, which are derived from Butler-Volmer equation rather from the theory of Stern layer. In this way, the diffusion coefficient of anion is not needed and the dielectric constant can be easily yielded. Figure 1 demonstrates a good match between our electrochemical model and the experiment data for different C-rates. Regarding the bending stress analysis, it is noted in [4] that external force may influence the diffusion process in the electrode. This motivates us to empirically set the diffusion coefficient in positive electrode as a function of deformation angle. The simulation of the performance of flexible battery under different bending conditions is shown in Fig. 2. The relationship between the bending stress and the battery performance can be of help in finding a more appropriate design and range of use for flexible thin film battery. Further development of related analyses and experiments is now under way. REFERENCES [1] D. Danilov, R. Niessen, and P. Notten, J. Electrochem. Soc. 158, 215 (2011). [2] S. D. Fabre, D. Guy-Bouyssou, P. Bouillon, F. Le Cras, and C. Delacourt, J. Electrochem. Soc. 159,104 (2012) [3] K. Becker-Steinberger, S. Funken, M. Landstorfer, and K. Urban, ECS Trans. 25(36), 285 (2010). [4] Han JN, Pyun SI J Korean Electrochem Soc.4, 70 (2001). [5] Koo, M. Park, K.I. Lee, S.H. Suh, M. Jeon, D.Y. Choi, J.W. Kang, K. Lee, K.J. Nano Lett. 12, 4810 (2012). Figure 1