Battery research depends upon up-to-date information on the cell characteristics found in current electric vehicles, which is exacerbated by the deployment of novel formats and architectures. This necessitates open access to cell characterization data. Therefore, this study examines the architecture and performance of first-generation Tesla 4680 cells in detail, both by electrical characterization and thermal investigations at cell-level and by disassembling one cell down to the material level including a three-electrode analysis. The cell teardown reveals the complex cell architecture with electrode disks of hexagonal symmetry as well as an electrode winding consisting of a double-sided and homogeneously coated cathode and anode, two separators and no mandrel. A solvent-free anode fabrication and coating process can be derived. Energy-dispersive X-ray spectroscopy as well as differential voltage, incremental capacity and three-electrode analysis confirm a NMC811 cathode and a pure graphite anode without silicon. On cell-level, energy densities of 622.4 Wh/L and 232.5 Wh/kg were determined while characteristic state-of-charge dependencies regarding resistance and impedance behavior are revealed using hybrid pulse power characterization and electrochemical impedance spectroscopy. A comparatively high surface temperature of ∼70 °C is observed when charging at 2C without active cooling. All measurement data of this characterization study are provided as open source.
The Electrochemical Society (ECS) was founded in 1902 to advance the theory and practice at the forefront of electrochemical and solid state science and technology, and allied subjects.
ISSN: 1945-7111
JES is the flagship journal of The Electrochemical Society. Published continuously from 1902 to the present, JES remains one of the most highly-cited journals in electrochemistry and solid-state science and technology.
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Manuel Ank et al 2023 J. Electrochem. Soc. 170 120536
Yuliya Preger et al 2020 J. Electrochem. Soc. 167 120532
Energy storage systems with Li-ion batteries are increasingly deployed to maintain a robust and resilient grid and facilitate the integration of renewable energy resources. However, appropriate selection of cells for different applications is difficult due to limited public data comparing the most commonly used off-the-shelf Li-ion chemistries under the same operating conditions. This article details a multi-year cycling study of commercial LiFePO4 (LFP), LiNixCoyAl1−x−yO2 (NCA), and LiNixMnyCo1−x−yO2 (NMC) cells, varying the discharge rate, depth of discharge (DOD), and environment temperature. The capacity and discharge energy retention, as well as the round-trip efficiency, were compared. Even when operated within manufacturer specifications, the range of cycling conditions had a profound effect on cell degradation, with time to reach 80% capacity varying by thousands of hours and cycle counts among cells of each chemistry. The degradation of cells in this study was compared to that of similar cells in previous studies to identify universal trends and to provide a standard deviation for performance. All cycling files have been made publicly available at batteryarchive.org, a recently developed repository for visualization and comparison of battery data, to facilitate future experimental and modeling efforts.
George E. Blomgren 2017 J. Electrochem. Soc. 164 A5019
This year, the battery industry celebrates the 25th anniversary of the introduction of the lithium ion rechargeable battery by Sony Corporation. The discovery of the system dates back to earlier work by Asahi Kasei in Japan, which used a combination of lower temperature carbons for the negative electrode to prevent solvent degradation and lithium cobalt dioxide modified somewhat from Goodenough's earlier work. The development by Sony was carried out within a few years by bringing together technology in film coating from their magnetic tape division and electrochemical technology from their battery division. The past 25 years has shown rapid growth in the sales and in the benefits of lithium ion in comparison to all the earlier rechargeable battery systems. Recent work on new materials shows that there is a good likelihood that the lithium ion battery will continue to improve in cost, energy, safety and power capability and will be a formidable competitor for some years to come.
Peter Keil et al 2016 J. Electrochem. Soc. 163 A1872
In this study, the calendar aging of lithium-ion batteries is investigated at different temperatures for 16 states of charge (SoCs) from 0 to 100%. Three types of 18650 lithium-ion cells, containing different cathode materials, have been examined. Our study demonstrates that calendar aging does not increase steadily with the SoC. Instead, plateau regions, covering SoC intervals of more than 20%–30% of the cell capacity, are observed wherein the capacity fade is similar. Differential voltage analyses confirm that the capacity fade is mainly caused by a shift in the electrode balancing. Furthermore, our study reveals the high impact of the graphite electrode on calendar aging. Lower anode potentials, which aggravate electrolyte reduction and thus promote solid electrolyte interphase growth, have been identified as the main driver of capacity fade during storage. In the high SoC regime where the graphite anode is lithiated more than 50%, the low anode potential accelerates the loss of cyclable lithium, which in turn distorts the electrode balancing. Aging mechanisms induced by high cell potential, such as electrolyte oxidation or transition-metal dissolution, seem to play only a minor role. To maximize battery life, high storage SoCs corresponding to low anode potential should be avoided.
Loraine Torres-Castro et al 2024 J. Electrochem. Soc. 171 020520
The rate of electric vehicle (EV) adoption, powered by the Li-ion battery, has grown exponentially; largely driven by technological advancements, consumer demand, and global initiatives to reduce carbon emissions. As a result, it is imperative to understand the state of stability (SoS) of the cells inside an EV battery pack. That understanding will enable the warning of or prevention against catastrophic failures that can lead to serious injury or even, loss of life. The present work explores rapid electrochemical impedance spectroscopy (EIS) coupled with gas sensing technology as diagnostics to monitor cells and packs for failure markers. These failure markers can then be used for onboard assessment of SoS. Experimental results explore key changes in single cells and packs undergoing thermal or electrical abuse. Rapid EIS showed longer warning times, followed by VOC sensors, and then H2 sensors. While rapid EIS gives the longest warning time, with the failure marker often appearing before the cell vents, the reliability of identifying impedance changes in single cells within a pack decreases as the pack complexity increases. This provides empirical evidence to support the significant role that cell packaging and battery engineering intricacies play in monitoring the SoS.
Jorn M. Reniers et al 2019 J. Electrochem. Soc. 166 A3189
The maximum energy that lithium-ion batteries can store decreases as they are used because of various irreversible degradation mechanisms. Many models of degradation have been proposed in the literature, sometimes with a small experimental data set for validation. However, a comprehensive comparison between different model predictions is lacking, making it difficult to select modelling approaches which can explain the degradation trends actually observed from data. Here, various degradation models from literature are implemented within a single particle model framework and their behavior is compared. It is shown that many different models can be fitted to a small experimental data set. The interactions between different models are simulated, showing how some of the models accelerate degradation in other models, altering the overall degradation trend. The effects of operating conditions on the various degradation models is simulated. This identifies which models are enhanced by which operating conditions and might therefore explain specific degradation trends observed in data. Finally, it is shown how a combination of different models is needed to capture different degradation trends observed in a large experimental data set. Vice versa, only a large data set enables to properly select the models which best explain the observed degradation.
Weilong Ai et al 2020 J. Electrochem. Soc. 167 013512
Whilst extensive research has been conducted on the effects of temperature in lithium-ion batteries, mechanical effects have not received as much attention despite their importance. In this work, the stress response in electrode particles is investigated through a pseudo-2D model with mechanically coupled diffusion physics. This model can predict the voltage, temperature and thickness change for a lithium cobalt oxide-graphite pouch cell agreeing well with experimental results. Simulations show that the stress level is overestimated by up to 50% using the standard pseudo-2D model (without stress enhanced diffusion), and stresses can accelerate the diffusion in solid phases and increase the discharge cell capacity by 5.4%. The evolution of stresses inside electrode particles and the stress inhomogeneity through the battery electrode have been illustrated. The stress level is determined by the gradients of lithium concentration, and large stresses are generated at the electrode-separator interface when high C-rates are applied, e.g. fast charging. The results can explain the experimental results of particle fragmentation close to the separator and provide novel insights to understand the local aging behaviors of battery cells and to inform improved battery control algorithms for longer lifetimes.
Xia Cao et al 2021 J. Electrochem. Soc. 168 010522
The conventional LiPF6/carbonate-based electrolytes have been widely used in graphite (Gr)-based lithium (Li) ion batteries (LIBs) for more than 30 years because a stable solid electrolyte interphase (SEI) layer forms on the graphite surface and enables its long-term cycling stability. However, few of these electrolytes are stable under the more stringent conditions needed with a Li metal anode (LMA) and other anodes, such as silicon (Si), which exhibit large volume changes during charge/discharge processes. Many different approaches have been developed lately to stabilize Li metal batteries (LMBs) and Si-based LIBs. From this aspect, localized high-concentration electrolytes (LHCEs) have unique advantages: not only are they stable in a wide electrochemical window, they can also form stable SEI layers on LMA and Si anode surfaces to enable their long-term cycling stability. The ultrathin SEI layer formed on a Gr anode can also improve the safety and high-rate operation of conventional LIBs. In this paper, we give a brief summary of our recent work on LHCEs, including their design principle and applications in both LMBs and LIBs. A perspective on the future development of LHCEs is also discussed.
E. Peled and S. Menkin 2017 J. Electrochem. Soc. 164 A1703
The Solid-Electrolyte-Interphase (SEI) model for non-aqueous alkali-metal batteries constitutes a paradigm change in the understanding of lithium batteries and has thus enabled the development of safer, durable, higher-power and lower-cost lithium batteries for portable and EV applications. Prior to the publication of the SEI model (1979), researchers used the Butler-Volmer equation, in which a direct electron transfer from the electrode to lithium cations in the solution is assumed. The SEI model proved that this is a mistaken concept and that, in practice, the transfer of electrons from the electrode to the solution in a lithium battery, must be prevented, since it will result in fast self-discharge of the active materials and poor battery performance. This model provides [E. Peled, in "Lithium Batteries," J.P. Gabano (ed), Academic Press, (1983), E. Peled, J. Electrochem. Soc., 126, 2047 (1979).] new equations for: electrode kinetics (io and b), anode corrosion, SEI resistivity and growth rate and irreversible capacity loss of lithium-ion batteries. This model became a cornerstone in the science and technology of lithium batteries. This paper reviews the past, present and the future of SEI batteries.
Chang-Hui Chen et al 2020 J. Electrochem. Soc. 167 080534
Presented here, is an extensive 35 parameter experimental data set of a cylindrical 21700 commercial cell (LGM50), for an electrochemical pseudo-two-dimensional (P2D) model. The experimental methodologies for tear-down and subsequent chemical, physical, electrochemical kinetics and thermodynamic analysis, and their accuracy and validity are discussed. Chemical analysis of the LGM50 cell shows that it is comprised of a NMC 811 positive electrode and bi-component Graphite-SiOx negative electrode. The thermodynamic open circuit voltages (OCV) and lithium stoichiometry in the electrode are obtained using galvanostatic intermittent titration technique (GITT) in half cell and three-electrode full cell configurations. The activation energy and exchange current coefficient through electrochemical impedance spectroscopy (EIS) measurements. Apparent diffusion coefficients are estimated using the Sand equation on the voltage transient during the current pulse; an expansion factor was applied to the bi-component negative electrode data to reflect the average change in effective surface area during lithiation. The 35 parameters are applied within a P2D model to show the fit to experimental validation LGM50 cell discharge and relaxation voltage profiles at room temperature. The accuracy and validity of the processes and the techniques in the determination of these parameters are discussed, including opportunities for further modelling and data analysis improvements.
Latest articles
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Woo-Hyuk Lee et al 2024 J. Electrochem. Soc. 171 031504
L-cysteine as a corrosion inhibitor for ADC12 aluminum alloy in a modified coolant solution was investigated. Results reveal its effectiveness as a cathodic inhibitor, suppressing the oxygen reduction reaction. Immersion tests show efficient inhibition of localized corrosion at an optimized L-cysteine concentration of 1.0 mM. A favorable L-cysteine adsorption on θ-Al2Cu is confirmed, enhancing hydrophobicity, and leading to corrosion inhibition. This study proposes a tentative corrosion inhibition mechanism.
Cheng Jiang et al 2024 J. Electrochem. Soc. 171 037519
The lead (Pb) in the environment is harmful to human body, so it is of practical significance and application value to develop a method for detecting lead ions (Pb2+) in the environment. Herein, Zeolitic imidazolate framework/nickel foam (ZnCo ZIF-L/NF) was in situ grown on nickel foam (NF) substrate by hydrothermal method, and aged and hydrolyzed at room temperature to transform ZnCo ZIF-L into zinc cobalt layered double hydroxide/nickel foam (ZnCo ZLDH/NF). CeO2 nanospheres were synthesized and loaded onto ZnCo ZLDH/NF materials to prepare ZnCo ZLDH@CeO2/NF heterostructure composite electrodes. Finally, ZnCo ZLDH@CeO2/NF was used to detect divalent lead ion (Pb2+) by differential pulse anodic stripping voltammetry (DPASV). The electrochemical sensor constructed by the ZnCo ZLDH@CeO2/NF composite electrode exhibits the concentration linear range of 0.1 μM–30 μM with a limit of detection 9 nM (S/N = 3) and the sensitivity of 67 A/M. Meanwhile, the ZnCo ZLDH@CeO2/NF composite electrode has good repeatability and anti-interference stability.
Tobias Krenz et al 2024 J. Electrochem. Soc. 171 034509
It is common practice to characterize cells in polymer electrolyte membrane water electrolysis (PEMWE) using electrochemical impedance spectroscopy (EIS) and Tafel analysis, which require special equipment and operation procedures. Additionally, these techniques are not suitable for large industrial size cells with very low impedances. We present a simpler approach based on a novel evaluation of the current interrupt (CI) technique. The CI technique utilizes the voltage response after an instantaneous drop of electric current to identify the ohmic resistance RΩ, charge transfer resistance Rct and double-layer capacity Cdl in a simplified equivalent circuit (EC) of the cell. A direct link to results of typical EIS and Tafel analysis can be defined by using the improved CI method which considers a non-linear activation resistance instead of a constant charge transfer resistance. Thereby, access to equivalent information as the established standard method is granted, while being applicable to all cell and stack sizes without requiring special equipment (e.g. impedance spectrometer). The agreement with experimental data is significantly improved over the assumption of a constant charge transfer coefficient. Consistency of the proposed interpretation with explicit EIS and Tafel analysis is demonstrated and options for industrial application of the evaluation scheme are discussed.
R. A. Dressler and J. R. Dahn 2024 J. Electrochem. Soc. 171 030520
Lithium-ion batteries require a high energy density when being used in applications such as electric vehicles or portable electronics. This can be achieved on a large scale by improving packaging and implementation, or on a material scale by selecting more energy dense electrode active material. Silicon can be used as a replacement for graphite in negative electrodes if the detrimental volume expansions can be contained. These volume expansions cause continuous mechanical degradation capacity loss leading to short lifetimes that do not meet industry standards. These high-capacity high volume expansion materials such as silicon and SiO must be used in conjunction with more stable electrode materials like graphite to reduce the mechanical degradation caused by volume change. Single-walled carbon nanotubes are shown to be a simple yet effective drop in addition to improve electrical connectivity and increase capacity retention in these silicon-based composite negative electrodes. This added particle interconnectivity from the high tensile strength carbon nanotubes allows for the use of simple binders such as CMC/SBR to create composite electrodes with competitive performance without the use of expensive polymers or complex nanostructures.
Hidetaka Asoh et al 2024 J. Electrochem. Soc. 171 033502
Aluminum was anodized in a phosphoric acid solution containing glycerol. Anodization in high concentration and high temperature electrolytes typically faces challenges due to the chemical dissolution of the anodic film. However, we found that the maximum attainable film thickness could be doubled by incorporating glycerol into the electrolyte. This enhancement was more effective under conditions of high concentration and temperature than in environments with lower concentrations and temperatures.
Review articles
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Shirsendu Mitra et al 2024 J. Electrochem. Soc. 171 037511
Micro/-nano motors (MNMs) are deployed to perform cutting edge research and development activities that include biomedical engineering, environment monitoring, energy harvesting and more. MNMs progressively strives for miniaturization of MNMs, mightier self-propulsion, precision of motion, and smarter motion control. The last decade published several reports on biosensing applications of MNMs targeting enhanced specificity, selectivity. Among MNM mediated biosensors, the electrochemical biosensor is the most important stake holder. Motion of MNMs enable active transport, augmented reaction kinetics, and better selectivity causing smarter biosensing. This review article explores the most advanced development of electrochemical biosensing deploying MNMs that took place in recent past. Briefly, this article covers chronological development in the field of MNM mediated electrochemical biosensing with emphasis on, conventional working electrode based sensing, DNA walker modificaitons, MNM based real time electrochemical signal monitoring, and scope of MNM mediated electrochemical sensing for intracellular monitoring or drug delivery. Conclusively, the review considers the most recent development in the field of MNM mediated electrochemical sensing that includes both in vitro and in vivo electrochemical biosensing. Additionally, we discuss use of electorchemical redox reactions for imparting motion to the MNMs in physiological fluids for intracellular manipulation, targeted drug delivery, and more.
Ruijing Kong et al 2024 J. Electrochem. Soc. 171 032504
Molten salts play an important role in the electrolysis of solid metal compounds, especially oxides and sulfides, and have an impressive storage capacity and power, so they are now the electrolyte for many new types of rechargeable batteries. Unfortunately, due to the high viscosity and high surface tension of molten salt, the unsatisfactory wettability of electrode and molten salt restricts the development of molten salt electrochemistry. In the past half century, the research on interface phenomena has been devoted to establishing more accurate models for measuring surface tension and wetting angle, developing more scientific wetting angle measurement techniques, and exploring the influencing factors of wettability. Different from water solution interface, molten salt experiment is in high temperature and pressure environment, so it is difficult to test the wetting angle, and there are few researches on the interface phenomenon of molten salt. In this paper, on the basis of existing models and experimental data, the factors and mechanisms that lead to the difference of wettability between melt and solid matrix in molten salt systems are analyzed in detail. Finally, we put forward the prospects and suggestions for the study of the wettability of melt to solid substrate in molten salt.
Highlights
The research status of electrode wettability in molten salt is reviewed systematically, and the measuring method and mechanism of high-temperature interface wettability are introduced briefly.
To propose a priority scheme to improve the wettability of electrodes, the factors affecting the wettability of electrodes in molten salt were summarized and discussed in detail.
We put forward the prospects and suggestions for the study of the wettability of electrodes in molten salt.
Kaan Kececi and Ali Dinler 2024 J. Electrochem. Soc. 171 037505
This article reviews the recent advances and applications of resistive-pulse sensors of 2D nanopores, which are based on atomically thin materials such as graphene, MoS2, WS2, h-BN, and MXenes. Due to their thickness, they are superior to other materials (e.g., SiNx, SiO2) in terms of spatial resolution which is desired for DNA, RNA, and protein sequencing. They can be used for single-molecule detection and analysis as well as their nature. However, there are still some challenges that need to be addressed such as improving the stability, large-scale production, and size reproducibility of 2D nanopores. This review briefly discusses briefly the nanopore fabrication techniques, recent sensing applications in the last five years, and performance characteristics of 2D nanopore sensors, as well as their advantages and limitations over other types of nanopore sensors.
Highlights
Recent studies have shown advancements in stability and large-scale production of 2D materials which are the current bottleneck of 2D nanopores.
Due to their atomically thin nature, 2D nanopores will replace the present solid-state nanopore platforms.
2D nanopores can be potentially used for sequencing studies for both DNA and protein in the near future.
Manish Man Shrestha and Lin Wei 2024 J. Electrochem. Soc. 171 027526
Smart agriculture (SA) based on the framework of precision agriculture (PA) is a vital component of sustainable and efficient food production, with nitrogen (N) management playing a pivotal role. However, existing agricultural practices often suffer from low nitrogen use efficiency (NUE), posing a challenge to SA. To tackle this issue, real-time N sensing technologies offer farmers precise and timely information about soil N levels, enabling precise N fertilizer application. Integrating these technologies with the Internet of Things (IoT) can further augment their capabilities, creating a seamless platform for data collection, analysis, and decision-making for great opportunities to improve NUE. Nevertheless, the adoption of real-time N sensing and IoT integration also presents several challenges, including selecting appropriate sensing technologies, effective data mining and management, and acquiring specialized knowledge and training. This review paper provides a comprehensive analysis of the opportunities and challenges associated with real-time N sensing technologies and IoT integration in smart farming. By showcasing best practices and innovative solutions, the paper aims to foster widespread adoption of SA practices, ultimately elevating the sustainability and productivity of agricultural systems.
Qianjun Yin et al 2024 J. Electrochem. Soc. 171 027524
Electrostatic spinning technology is widely used in the manufacturing of flexible sensors. It is a mature and reliable method to fabricate nanofibers with tailorable fiber diameter surface microstructure like porosities and specific surface areas. Based on these properties, the electrically conductive composite nanofiber mats achieved by functionalizing nanofibers with active conductive nanomaterials are used as a sensitive layer for flexible sensors with tunable sensing performance. However, it is crucial to select suitable materials and optimal electrospinning technology, as well as design of the sensitive layer structure, for tuning the mechano-electrical performance of flexible sensors. This paper first reviews the current methods for the fabrication of flexible sensors with a focus on preparation method based electrospinning technology. Then, we introduce in detail the types and properties of common substrate materials and conductive fillers used to make sensor sensitive layers, with emphasis on the design of sensitive layer structures for the properties of the materials themselves. Finally, there is a summary of improvements and derivations based on the traditional electrospinning technologies that have been reported in recent years. It is hoped that this review will provide both references and inspiration for researchers in the field of flexible sensors.
Highlights
Electrospinning for fabricating substrate for flexible sensing sensitive layers.
Design methods for structures that depend on the properties of the material itself.
Ingenious sensitive layer structure improves the conductive flexibility of sensor.
New mode of electrospinning is being used to manufacture flexible sensors.
Editor's Choice
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S. Yanev et al 2024 J. Electrochem. Soc. 171 020512
Li-In electrodes are widely applied as counter electrodes in fundamental research on Li-metal all-solid-state batteries. It is commonly assumed that the Li-In anode is not rate limiting, i.e. the measurement results are expected to be representative of the investigated electrode of interest. However, this assumption is rarely verified, and some counterexamples were recently demonstrated in literature. Herein, we fabricate Li-In anodes in three different ways and systematically evaluate the electrochemical properties in two- and three-electrode half-cells. The most common method of pressing Li and In metal sheets together during cell assembly resulted in poor homogeneity and low rate performance, which may result in data misinterpretation when applied for investigations on cathodic phenomena. The formation of a Li-poor region on the separator side of the anode is identified as a major kinetic bottleneck. An alternative fabrication of a Li-In powder anode resulted in no kinetic benefits. In contrast, preparing a composite from Li-In powder and sulfide electrolyte powder alleviated the kinetic limitation, resulted in superior rate performance, and minimized the impedance. The results emphasize the need to fabricate optimized Li-In anodes to ensure suitability as a counter electrode in solid-state cells.
Highlights
The fabrication of Li-In anodes needs to be optimized to ensure suitability as a counter electrode in sulfide all-solid-state batteries.
The Li-In counter electrode may often be the limiting factor of sulfide all-solid-state halfcells.
Pressing Li and In foil together results in a kinetically limited anode.
Composites from Li-In and sulfide electrolyte result in stable reference potential, superior rate performance and low impedance of the counter electrode.
Ramver Singh et al 2024 J. Electrochem. Soc. 171 013501
Electrical discharge micromachining (EDM) poses challenges to the fatigue-life performance of machined surfaces due to thermal damage, including recast layers, heat-affected zones, residual stress, micro-cracks, and pores. Existing literature proposes various ex situ post-processing techniques to mitigate these effects, albeit requiring separate facilities, leading to increased time and costs. This research involves an in situ sequential electrochemical post-processing (ECPP) technique to enhance the quality of EDMed micro-holes on titanium. The study develops an understanding of the evolution of overcutting during ECPP, conducting unique experiments that involve adjusting the initial radial interelectrode gap (utilizing in situ wire-electrical discharge grinding) and applied voltage. Additionally, an experimentally validated transient finite element method (FEM) model is developed, incorporating the passive film formation phenomenon for improved accuracy. Compared to EDM alone, the sequential EDM-ECPP approach produced micro-holes with superior surface integrity and form accuracy, completely eliminating thermal damage. Notably, surface roughness (Sa) was reduced by 80% after the ECPP. Increasing the voltage from 8 to 16 V or decreasing the gap from 60 to 20 μm rendered a larger overcut. This research's novelty lies in using a two-phase dielectric (water-air), effectively addressing dielectric and electrolyte cross-contamination issues, rendering it suitable for commercial applications.
Highlights
Better micro-hole quality through in situ sequential eco-friendly near-dry EDM & ECM
Successfully resolved dielectric-electrolyte cross-contamination in sequential processes
Unique experiments that adjust the initial radial IEG using in situ wire-EDG
Developed and validated a transient FEM model, incorporating passivation aspect
Achieved recast layer-free holes with Sa values approximately 80% lower than EDM holes
Yuefan Ji and Daniel T. Schwartz 2023 J. Electrochem. Soc. 170 123511
Analytical theory for second harmonic nonlinear electrochemical impedance spectroscopy (2nd-NLEIS) of planar and porous electrodes is developed for interfaces governed by Butler-Volmer kinetics, a Helmholtz (mainly) or Gouy-Chapman (introduced) double layer, and transport by ion migration and diffusion. A continuum of analytical EIS and 2nd-NLEIS models is presented, from nonlinear Randles circuits with or without diffusion impedances to nonlinear macrohomogeneous porous electrode theory that is shown to be analogous to a nonlinear transmission-line model. EIS and 2nd-NLEIS for planar electrodes share classic charge transfer RC and diffusion time-scales, whereas porous electrode EIS and 2nd-NLEIS share three characteristic time constants. In both cases, the magnitude of 2nd-NLEIS is proportional to nonlinear charge transfer asymmetry and thermodynamic curvature parameters. The phase behavior of 2nd-NLEIS is more complex and model-sensitive than in EIS, with half-cell NLEIS spectra potentially traversing all four quadrants of a Nyquist plot. We explore the power of simultaneously analyzing the linear EIS and 2nd-NLEIS spectra for two-electrode configurations, where the full-cell linear EIS signal arises from the sum of the half-cell spectra, while the 2nd-NLEIS signal arises from their difference.
Leonardo I. Astudillo and Hubert A. Gasteiger 2023 J. Electrochem. Soc. 170 124512
A major degradation mechanism of polymer electrolyte membrane fuel cells (PEMFCs) in transportation applications is the loss of the electrochemically active surface area (ECSA) of platinum cathode catalysts upon dynamic load cycling (resulting in cathode potential cycles). This is commonly investigated by accelerated stress tests (ASTs), cycling the cell voltage under H2/N2 (anode/cathode). Here we examine the degradation of membrane electrode assemblies with Vulcan carbon supported Pt catalysts over extended square-wave voltage cycles between 0.6-1.0 VRHE at 80 °C and 30%-100% RH under either H2/N2 or H2/Air; for the latter case, differential reactant flows were used, and the lower potential limit is controlled to correspond to the high-frequency resistance corrected cell voltage, assuring comparable aging conditions. Over the course of the ASTs, changes of the ECSA, the hydrogen crossover current, the proton conduction resistance and the oxygen transport resistance of the cathode electrode, as well as the differential-flow H2/O2 and H2/Air performance at 80 °C/100% RH were monitored. While the ECSA loss decreases with decreasing RH, it is independent of the gas feeds. Furthermore, the H2/Air performance loss only depends on the ECSA loss. ASTs under H2/N2 versus H2/Air only differ with regards to the chemical/mechanical degradation of the membrane.
Evans Leshinka Molel and Thomas F. Fuller 2023 J. Electrochem. Soc. 170 103501
Mathematical models of electrochemical systems are useful to refine our understanding of systems containing complex, coupled phenomena, to design and control electrochemical devices, and to help novices in developing intuition for the behavior of electrochemical systems. Regardless of the application, elucidating the relationship between current and potential is central to understanding how electrochemical systems behave. Here, we report on historical and future perspectives of simulating electrochemical systems with open-source, python-based tools. FEniCSx, a popular open-source computing platform for solving partial differential equations, is applied to the solution of primary and secondary current distributions for two- and three- dimensional geometries. FEniCSx is used on both desktop computers as well as within high performance computing environments, such as Georgia Tech's PACE. Simulations are known to increase interactions between instructors and students, and to help students visualize content. Recently, python tools have been applied to simple electrochemical systems. Because of the low barrier to entry and access to numerous computational packages, the Anaconda distribution of python is promoted. A series of dynamic simulations are designed to help students improve their understanding of electrochemical systems. These simulations feature animation and use of widgets that allow students to adjust parameters and immediately observe the results.
Accepted manuscripts
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Luo et al
With the increasing need for high power density of proton exchange membrane fuel cells, new composite membranes have been explored for superior proton transport and gas impermeability. These membranes’ physicochemical properties usually deviate from existing empirical formulas, which are poorly understood, especially when mechanical deformation occurs. This poor understanding hinders development of novelty membranes and their fuel cell applications. Here, using polytetrafluoroethylene reinforced ionomer membrane as an example, we conducted extensive water absorption experiments to determine hydration levels at different water activities. Molecular dynamics simulations and electrochemical impedance spectroscopy were used to investigate the impacts of hydration level, external electric field strength, and tensile deformation on proton transport and electroosmotic drag coefficient, as well as the impact of hydration level and free volume ratio on oxygen permeability. We proposed mathematical correlations for these impacts and incorporated them into a single-cell voltage model to analyze their effects on fuel cell performance. Results show that an increase in the electric field strength alters the proton transport pattern, but has minimal impact on the electro-osmosis coefficient. The oxygen permeability coefficient of a deformed membrane with a free volume ratio of 28.57% is more than two orders of magnitude higher than that of a non-deformed membrane. The electro-osmatic drag coefficient imposes a larger influence on fuel cell performance than oxygen permeability
Naito et al
Liquid water that accumulates inside GDL prevents oxygen transport and degrades the performance of PEFCs. Therefore, improving the drainage of GDL is neccesary. One factor that directly affects drainage is the wettability of GDLs. In this study, the relationship between wettability of GDL and drainage was investigated through a numerical simulation using the VOF method. The simulation incorporated condensation model to mimic the actual operation of a PEFC. As a result of the simulation, it was found that condensation occurs near the catalyst layer (CL), and that liquid water accumulation develops from the vicinity of the CL side to the channel side. Simulations for different contact angles of θ=60°, θ=90°, θ=110° and θ=150° were performed, and showed that the liquid water volume inside the GDL decreased in the case of higher contact angle. In addition, we found that the hydrophobicity of the GDL promotes the movement of liquid water and hastened liquid-water discharge from the GDL surface. In the case of higher contact angle, the proportion of the gas-liquid interface in the GDL and its curvature were found to increase. Furthermore, the liquid water was discharged from greater number of pores on the GDL surface.
Vanheusden et al
Electrochemically induced sol-gel depositions have become a widespread, versatile method for fabricating hybrid and nanostructured oxides on conductive substrates. The process is based on the buildup of electrochemically generated OH- in the diffusion layer near the electrode surface. For the electrodeposition of silica thin films, these OH- ions catalyze the gelation of a kinetically stable precursor solution, thereby resulting in an electrochemically controlled process. The control of the diffusion layer has proven pivotal to depositing thin films while preventing the formation of aggregated by-products deeper in the solution. In this work, the silica sol-gel reactions and electrochemical OH- generation were critically analyzed and described to gain insight into the deposition mechanism. A general model is proposed that predicts the pH profile during both stationary and rotating disk electrode depositions under different conditions (i.e., current densities, times, and rotation rates). This model provides insights into the reactive zones where gelation occurs, and explains typical phenomena observed during deposition such as the dependence of film growth rates and aggregate formation on the deposition conditions. The insights and expressions obtained in this work are invaluable when designing future experiments using novel chemistries or setups.
Ma et al
The interface design between anode catalyst layer (ACL) and porous transport layer (PTL) significantly influences the performance of proton exchange membrane water electrolyzers. Lately, the influence of the ACL/PTL interface on performance is more intensively investigated, including modeling approaches. Contrary to other models that apply through-plane resolved modeling, in-plane models better characterize the ACL/PTL interface. These models separate the interface into three domains: in an open pore area (P), under a contacted solid of the PTL (S), and the interfacial point between the pore and solid (S│P). In our work, we focused on the behavior of the model in the kinetic region, in which no two-phase behavior is to be expected. Consequently, we apply a one-phase model as the main model and a simple two-phase model for comparison. We find that for most reference samples, the one-phase model well describes polarization behavior. However, for samples with larger interfacial contact area, a two-phase model might explain the found effect better even for very low current densities. Finally, we show that the one-phase model and the simple two-phase model can be used to study the general behavior of different solid to pore ratios to guide electrode development in the future.
Chakrabarti et al
Density functional theory simulation has been performed to illuminate the mechanism of lithiation and sodiation in Sb2S3 and Sb2Se3 anodes which is accompanied by anionic S/Se redox. The lithiation and sodiation of Sb2S3 and Sb2Se3 is comprised of two steps, (a) conversion and (b) alloying -dealloying. During conversion Sb and alkaline (Li/Na) chalcogenides are formed. Voltages during the conversion reaction of lithiation and sodiation were ~1.6 and ~1.25 V, respectively, for both Sb2S3 and Sb2Se3. Comparison of X-ray absorption near edge spectroscopy imaging of S/Se as present in pristine chalcogenides and A2S/Se with A=Li/Na reflects the presence of S/Se redox, which is further confirmed by electronic charge density analysis. Sb acts as an active center for the second step alloying-dealloying reaction. The formation of alloy mainly occurs via formation of Li3Sb and Na3Sb, which exhibits redox peaks at 1.025 V for lithiation and 0.686 V for sodiation. As reported in earlier reports, the redox peak, at 0.95 V is found to appear due to the formation of alloy NaSb.
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Tobias Krenz et al 2024 J. Electrochem. Soc. 171 034509
It is common practice to characterize cells in polymer electrolyte membrane water electrolysis (PEMWE) using electrochemical impedance spectroscopy (EIS) and Tafel analysis, which require special equipment and operation procedures. Additionally, these techniques are not suitable for large industrial size cells with very low impedances. We present a simpler approach based on a novel evaluation of the current interrupt (CI) technique. The CI technique utilizes the voltage response after an instantaneous drop of electric current to identify the ohmic resistance RΩ, charge transfer resistance Rct and double-layer capacity Cdl in a simplified equivalent circuit (EC) of the cell. A direct link to results of typical EIS and Tafel analysis can be defined by using the improved CI method which considers a non-linear activation resistance instead of a constant charge transfer resistance. Thereby, access to equivalent information as the established standard method is granted, while being applicable to all cell and stack sizes without requiring special equipment (e.g. impedance spectrometer). The agreement with experimental data is significantly improved over the assumption of a constant charge transfer coefficient. Consistency of the proposed interpretation with explicit EIS and Tafel analysis is demonstrated and options for industrial application of the evaluation scheme are discussed.
R. A. Dressler and J. R. Dahn 2024 J. Electrochem. Soc. 171 030520
Lithium-ion batteries require a high energy density when being used in applications such as electric vehicles or portable electronics. This can be achieved on a large scale by improving packaging and implementation, or on a material scale by selecting more energy dense electrode active material. Silicon can be used as a replacement for graphite in negative electrodes if the detrimental volume expansions can be contained. These volume expansions cause continuous mechanical degradation capacity loss leading to short lifetimes that do not meet industry standards. These high-capacity high volume expansion materials such as silicon and SiO must be used in conjunction with more stable electrode materials like graphite to reduce the mechanical degradation caused by volume change. Single-walled carbon nanotubes are shown to be a simple yet effective drop in addition to improve electrical connectivity and increase capacity retention in these silicon-based composite negative electrodes. This added particle interconnectivity from the high tensile strength carbon nanotubes allows for the use of simple binders such as CMC/SBR to create composite electrodes with competitive performance without the use of expensive polymers or complex nanostructures.
Hidetaka Asoh et al 2024 J. Electrochem. Soc. 171 033502
Aluminum was anodized in a phosphoric acid solution containing glycerol. Anodization in high concentration and high temperature electrolytes typically faces challenges due to the chemical dissolution of the anodic film. However, we found that the maximum attainable film thickness could be doubled by incorporating glycerol into the electrolyte. This enhancement was more effective under conditions of high concentration and temperature than in environments with lower concentrations and temperatures.
Jiaqiang Huang et al 2024 J. Electrochem. Soc. 171 030516
Batteries are essential for the electrification of transport and the replacement of internal combustion engines. Thermodynamics was largely established with the development of the engines, and this knowledge has been applied to batteries for years. In particular, entropy profiles are sensitive to structural changes and are useful for diagnosing and understanding battery ageing. However, entropy profiling of aged batteries is mainly limited to the potentiometric method, which makes the technique in situ and time-consuming. Herein, we rely on optical fiber calorimetry to perform operando entropy profiling of commercial sodium-ion cells. Firstly, we directly compare the entropy profile of sodium-ion Na3V2(PO4)2F3/hard carbon (NVPF/HC) chemistry against those of commercialized lithium-ion chemistries, highlighting the uniqueness of NVPF/HC chemistry in battery thermal management. Operando entropy profiling of NVPF/HC chemistry further elucidates the structural degradations that take place during cycling and provide features that can be important indicators of the battery’s state of health. This work reintroduces thermodynamic analyses as a valuable tool for batteries and spotlights the new horizons offered by the convergence of battery sensing, thermodynamics, and other disciplines.
Anita Li et al 2024 J. Electrochem. Soc. 171 030515
Operando cell expansion measurements on Si-NMC622 coin cells using a magnetic dilatometer were performed to understand the effects of electrode binder content, electrode formulation, negative-to-positive electrode capacity ratio (N/P ratio), and electrolyte selection on reversible and irreversible cell expansions. Our experiments reveal a complex relationship between cell properties, imparted by the selected cell parameters, and cell expansion. Reversible cell expansions scaled with cell discharge capacity and electrode mechanical properties, while irreversible cell expansions were sensitive to capacity fade, silicon utilization, and electrolyte decomposition mechanisms. Additionally, volumetric cell energy densities were calculated using the measured capacities and irreversible expansions over the life of the cells. We show that judicious selection of cell parameters can improve volumetric energy density after 200 charge/discharge cycles by approximately two-fold. Our work provides valuable insight, at an early stage of cell development, towards minimizing the effects of cell expansion on battery cell, pack, and module designs.
Tien-Ching Ma et al 2024 J. Electrochem. Soc.
The interface design between anode catalyst layer (ACL) and porous transport layer (PTL) significantly influences the performance of proton exchange membrane water electrolyzers. Lately, the influence of the ACL/PTL interface on performance is more intensively investigated, including modeling approaches. Contrary to other models that apply through-plane resolved modeling, in-plane models better characterize the ACL/PTL interface. These models separate the interface into three domains: in an open pore area (P), under a contacted solid of the PTL (S), and the interfacial point between the pore and solid (S│P). In our work, we focused on the behavior of the model in the kinetic region, in which no two-phase behavior is to be expected. Consequently, we apply a one-phase model as the main model and a simple two-phase model for comparison. We find that for most reference samples, the one-phase model well describes polarization behavior. However, for samples with larger interfacial contact area, a two-phase model might explain the found effect better even for very low current densities. Finally, we show that the one-phase model and the simple two-phase model can be used to study the general behavior of different solid to pore ratios to guide electrode development in the future.
Yeting Wen and Kevin Huang 2024 J. Electrochem. Soc.
One of the leading causes for the performance degradation in H2-producing solid oxide electrolytic cells (SOECs) is the gradual delamination of oxygen electrode (OE) from the electrolyte under a strong anodic polarization. Identification of the key factor that controls the rate of OE delamination is of paramount importance to achieve long-term stable operation of SOECs. Here we show from thousands of hours of testing data that the exchange current density (io) of OE can be leveraged as a predictor for the rate of delamination. To obtain io, we apply DC-biased electrochemical impedance spectroscopy on a three-electrode symmetrical cell to measure polarization resistance (Rp) of OE as a function of current density (i) and time (t). The collected Rp-i-t raw data are then converted to overpotential ()-i-t, from which io is extracted from the “low-field” approximation. An analytical relationship between io and time-to-delamination (TTD) is further established from the established io-i-t relationship. We show that under a constant anodic polarization current density i, the greater the ratio i/io, the faster the delamination. Therefore, we conclude that the exchange current density of an OE, io, can be used to predict the rate of OE degradation in solid oxide-ion electrolyzers.
Dawei Xia et al 2024 J. Electrochem. Soc.
Earth-abundant, cost-effective electrode materials are essential for sustainable rechargeable batteries and global decarbonization. Manganese dioxide (MnO2) and hard carbon both exhibit high structural and chemical tunability, making them excellent electrode candidates for batteries. Herein, we elucidate the impact of electrolytes on the cycling performance of commercial electrolytic manganese dioxide in Li chemistry. We leverage synchrotron X-ray analysis to discern the chemical state and local structural characteristics of Mn during cycling, as well as to quantify the Mn deposition on the counter electrode. By using an ether-based electrolyte instead of conventional carbonate electrolytes, we circumvent the formation of a surface Mn(II)-layer and Mn dissolution from LixMnO2. Consequently, we achieved an impressive ~100% capacity retention for MnO2 after 300 cycles at C/3. To create a lithium metal-lean full cell, we introduce hard carbon as the anode which is compatible with ether-based electrolytes. Commercial hard carbon delivers a specific capacity of ~230 mAh/g at 0.1 A/g without plateau, indicating a surface-adsorption mechanism. The resulting manganese dioxide||hard carbon full cell exhibits stable cycling and high Coulombic efficiency. Our research provides a promising solution to develop cost-effective, scalable, and safe energy storage solutions using widely available manganese oxide and hard carbon materials.
Youngju Lee and Peng Bai 2024 J. Electrochem. Soc.
While the onset of dendrites found inside solid polymer electrolytes was typically analyzed by the dilute solution theory, nonideal behaviors such as dendrites at underlimiting current densities were often reported. Here, we consider two critical factors that were often neglected in existing studies, the severe heterogeneous current distribution and the dynamic change of modulus during the polarization process. Polymers with different dynamic mechanical properties were assessed, exploiting the recently discovered mechanism of phase transformation inside low-salt-concentration polymers. Analyses of the operando images revealed two characteristic points on the potential curve, the local and total concentration depletion which each corresponded to the starting and stopping point of dendrites. We further assess these dynamics at different degrees of heterogeneity controlled by different electrode sizes. The penetration dynamics and Sand’s time scaling exponent were heavily affected by both the initial concentration and the electrode size, which stress the significance of interfacial dynamic heterogeneity in working batteries.
Izaak Cohen et al 2024 J. Electrochem. Soc.
In previous work, we introduced an elegant approach for bromide recovery from water by the introduction of a hybrid physical adsorption and capacitive deionization processes for selective removal and recovery of boron from water. In this paper, we show that the harsh environment of water contaminated with bromine-moieties adversely affects the longevity of relevant electrodes, with close to 100 consecutive work hours of bromides removal without noticeable degradation. To extend the lifespan of electrodes, we used an asymmetric CDI cell with a 1:5 positive/negative electrodes ratio in which a polarity switch between electrodes is applied every six adsorption-desorption cycles in a way that in each adsorption-desorption cycle, a different electrode of the six electrodes, functions as the positive electrode. We deduce that the polarity switch reduces oxidation and subsequent degradation of the positive electrodes, resulting in an extended lifecycle. After examining nine different carbonaceous materials, carbon cloth was chosen to be incorporated in the bromide- recovery cells because of its favorable kinetics and its physical and mechanical properties. We show that with a combination between endurance of the electrodes and asymmetric mode of operation, it is possible to overcome the main barrier that holds the technology from being practical.