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
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.
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.
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.
Yuriy V. Tolmachev 2023 J. Electrochem. Soc. 170 030505
We present a quantitative bibliometric study of flow battery technology from the first zinc-bromine cells in the 1870's to megawatt vanadium RFB installations in the 2020's. We emphasize, that the cost advantage of RFBs in multi-hour charge-discharge cycles is compromised by an inferior energy efficiency of these systems, and that there are limits on the efficiency improvement due to internal cross-over and the cost of power (at low current densities) and due to an acceptable pressure drop (at high current densities). Differences between lithium-ion and vanadium redox flow batteries (VRFBs) are discussed from the end-user perspective. We conclude, that the area-specific resistance, cross-over current and durability of contemporaneous VRFBs are appropriate for commercialization in multi-hour stationary energy storage markets, and the most import direction in the VRFB development today is the reduction of stack materials and manufacturing costs. Chromium-iron RFBs should be given a renewed attention, since it seems to be the most promising durable low-energy-cost chemistry.
Kenneth Tuul et al 2024 J. Electrochem. Soc. 171 040510
Single crystal NMC640/artificial graphite cells balanced for low voltage operation (≤4.1 V) and using electrolyte salts rich in lithium bis(fluorosulfonyl)imide are demonstrated to have exceptional lifetime during continuous operation at 100 °C. Cells tested to an upper cutoff voltage of 4.0 V retained >80% of their original capacity for 600 cycles and 4300 h at 100 °C and 1200 cycles and 1 year cycling to 3.9 V at 85 °C. The cells exhibited minimal gassing, no transition metal dissolution from the positive electrode, and no detectable corrosion of the aluminum current collector. Ultra-high precision coulometry measurements from 20 to 100 °C suggest an Arrhenius-type relationship for the coulombic inefficiency and capacity fade of these cells. The possibility of exploiting this relationship to project ambient temperature lifetime from high-temperature measurements is suggested. However, cell performance at the highest temperatures is most likely reduced by the permeation of electrolyte through the seals of the pouch cell.
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.
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.
Latest articles
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Masaki Deguchi et al 2024 J. Electrochem. Soc. 171 040536
The electrolyte in current automotive lithium-ion batteries is a mixture of ethylene carbonate (EC), which has a high dielectric constant, and ethyl methyl carbonate or dimethyl carbonate, which have a low viscosity. However, the flash point of these mixed solvents is as low as 25 °C, so safety precautions must be taken. On the other hand, if only EC or propylene carbonate with a high flash point is used, the flash point will be 120 °C or higher. However, the high dielectric constant solvent cannot wet the hydrophobic separator whose material is polyethylene and/or polypropylene. Therefore, there is a problem that the battery does not work. In 1999, we proposed a "functional electrolyte" in which a small amount of an additive with a new function is added to the electrolyte, and many additives have since been commercialized. In recent work, we focused on a low viscosity linear carboxylic acid esters, designed an electrolyte with a flash point above 120 °C that provides wettability to the separator even in an electrolyte with a high dielectric constant solvent.
Ziwei Ye et al 2024 J. Electrochem. Soc. 171 040522
This study examines the influence of electrolyte salts and solvents on the performance of O3 layered oxide NaMn0.39Fe0.31Ni0.22Zn0.08O2/hard carbon sodium-ion pouch cells with polyethylene terephthalate (PET) jellyroll tape. A significant enhancement in cell performance between 2.0 and 3.8 V was observed across various temperatures (20, 40, and 55 °C) by substituting NaPF6 with NaFSI, including reduced impedance growth, minimized gas generation, and supressed jellyroll tape decomposition. Ultra-high precision coulometry revealed that the use of NaPF6 resulted in increased unwanted parasitic reactions associated with tape decomposition, e.g., capacity fade and charge endpoint capacity slippage. Teardown of sodium-ion pouch cells after cycling in DMC-based electrolytes revealed a severe decomposition of the PET tape with NaPF6 but not with NaFSI. Gas chromatography shows significantly more electrolyte decomposition products with NaPF6 as opposed to NaFSI. DEC-based electrolyte showed less capacity fade, less electrolyte decomposition products, and less tape decomposition after cycling than DMC-based electrolyte. The electrolyte additive DTD can prevent parasitic reactions in DMC- and NaPF6-based electrolyte. Overall, the choice of salts and linear carbonates in alkyl carbonate electrolytes plays a crucial role in determining the overall cycling performance of the layered oxide/hard carbon sodium-ion cells with PET jellyroll tape.
Frendi Maulana et al 2024 J. Electrochem. Soc. 171 046505
This work investigates the potential of N, Ni, and N-Ni-doped ZnO as photocatalysts for hydrogen production through water splitting. Sonochemical techniques were used to synthesize these materials. In contrast to undoped or singly-doped ZnO, N-Ni-double-doped ZnO demonstrated a significantly narrower band gap (2.89 eV) and smaller crystallites (21.60 nm). This led to a remarkable doubling in the hydrogen production rate under UV-visible light irradiation. The combined effect of N and Ni doping effectively promotes efficient charge separation and enhanced light absorption, resulting in significantly increased photocatalytic activity. Furthermore, N-Ni-ZnO demonstrates exceptional stability, retaining over 95% of its initial activity after five cycles. This work paves the way for the development of cost-effective and scalable photocatalysts for sustainable solar hydrogen production.
Maria Escamilla et al 2024 J. Electrochem. Soc. 171 040533
In this paper, we describe the synthesis and characterization of alkoxylated TEMPO, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, radicals with potential application in organic non-aqueous redox flow batteries. The behavior of a series of TEMPO derivatives with varying lengths of alkoxy chain is analyzed in acetonitrile solutions using electrochemical techniques, electron paramagnetic resonance (EPR) spectroscopy, and measurements of permeability through three different membranes. Electrochemical redox potentials are only weakly dependent on the substituent, but, in contrast, exchange current densities derived from the data do depend on the substitution. EPR lends further insight into these properties via the determination of hyperfine splitting constant and rotational correlation time. There is a negligible effect of the substituents on those parameters among the modified TEMPO radicals. Finally, permeation rates of modified TEMPO derivatives through membranes depend significantly on both the membrane and the substitution of TEMPO, providing insights into capacity fade measurements in the literature.
Ido Ben-Barak and M. N. Obrovac 2024 J. Electrochem. Soc. 171 040535
Oxides in the NixMn0.5-x/2Co0.5-x/2-O system were investigated as precursors in the all-dry synthesis of NMC622 (LiNi0.6Mn0.2Co0.2O2). Single-phase spinel precursors in this system were found to have the highest compositional homogeneity. To synthesize NMC, NixMn0.5-x/2Co0.5-x/2-O precursors were heated with Li2CO3 and NiO (to attain the correct NMC stoichiometry) in air or oxygen. This represents a different strategy in NMC synthesis compared to conventional hydroxide precursors that have the same composition as the final NMC. The most homogeneous and best performing NMC (171.9 mAh g−1 with 90% after 183 cycles) were obtained by using precursors that were essentially single-phase cubic spinel (0.070 ≤ x ≤ 0.091 in NixMn0.5-x/2Co0.5-x/2-O) even though such precursors had compositions that had significantly less Ni content than the target NMC622 composition. These findings demonstrate an alternate route for obtaining compositional homogeneity in NMC all-dry synthesis.
Review articles
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Jiashuai Wang et al 2024 J. Electrochem. Soc. 171 040527
The growing demand for energy storage application has facilitated the development of Li-ion rechargeable batteries (LIBs). As such, there is an urgent need to design electrodes with a high specific energy and long cycle life. The evolution of conventional LIBs cathode materials in past 30 years has arrived at a bottleneck. Fortunately, the finding of the lithium-rich cation disordered rocksalt (DRXs) has largely broadened the element ranges of the promising cathode in the past several years. Compared with the classical cation-ordered oxides, the DRXs display a large charge storage capacity based on both transition metal and oxygen redox capacity. In addition, their wide compositional space and cobalt-free characteristic would greatly reduce production costs in promoting the commercialization process. Herein, we make an overview of the recent progress for DRXs materials, in terms of their compositions and structure, Li diffusion, charge storage mechanisms, and different redox centra-based system. The key challenges to practical application are also discussed. Last but not least, in order to design high-performance DRXs, we outlined perspectives in developing DRXs for the next generation of LIB cathodes.
Pooja Saxena and Prashant Shukla 2024 J. Electrochem. Soc. 171 047504
Wearable sensors offer a non-invasive, continuous, and personalized approach to monitor various physiological and environmental parameters. Among the various materials used in the fabrication of wearable sensors, polymers have gained significant attention due to their versatile properties, low cost, and ease of integration. We present a comprehensive review of recent advances and challenges in the development of polymer-based wearable sensors. We begin by highlighting the key characteristics of wearable sensors, emphasizing their potential applications and advantages. Subsequently, we delve into the various types of polymers employed for sensor fabrication, such as conductive polymers, elastomers, and hydrogels. The unique properties of each polymer and its suitability for specific sensing applications are discussed in detail. We also address the challenges faced in the development of polymer-based wearable sensors and describes the mechanism of action in these kinds of wearable sensor-capable smart polymer systems. Contact lens-based, textile-based, patch-based, and tattoo-like designs are taken into consideration. Additionally, we paper discuss the performance of polymer-based sensors in real-world scenarios, highlighting their accuracy, sensitivity, and reliability when applied to healthcare monitoring, motion tracking, and environmental sensing. In conclusion, we provide valuable insights into the current state of polymer-based wearable sensors, their fabrication techniques, challenges, and potential applications.
Bianca-Maria Tuchiu et al 2024 J. Electrochem. Soc. 171 047502
Topical treatments rely on drugs that play a crucial role in addressing skin and mucous membrane disorders. Therefore, it is highly needed to utilize accurate analytical techniques that can determine the concentration of these chemicals in various sample matrices, including pharmaceuticals, food, and water. Currently, electrochemical sensors are predominantly used in specific fields such as biomedical, industrial, and environmental monitoring, while they have not yet been incorporated into the pharmaceutical manufacturing industry. However, electrochemical methods employing an expanding range of sensors provide a reliable, cost-effective, and efficient substitute for classical analytical methods. Their potential is highly favorable, offering possibilities for simultaneous determination, miniaturization, and real-time on-site monitoring. This work covers numerous sensors designed between 2020 and 2023 for the determination of topical drugs, highlighting their respective benefits and drawbacks while illuminating emerging trends. Moreover, it discusses the correlation between the used materials and the ease of manufacturing, to the achieved results, including dynamic range, detection limit, sensitivity, and selectivity. This work aims to serve as a valuable resource for researchers, engineers, and policymakers in the evolving field of electrochemical sensing by providing guidance and facilitating decision-making, which could lead to significant innovations in sensor technology.
Richard Bertram Church and A. John Hart 2024 J. Electrochem. Soc. 171 040512
Three-dimensional (3D) battery architectures have been envisioned to enable high energy density electrodes without the associated power drop experienced by planar cells. However, the development of 3D cells is hampered by difficulties producing conformal solid-state electrolytes (SSE), solid polymer electrolytes (SPE) and gel polymer electrolytes (GPE) that are pinhole-free and have adequate ionic conductivities. Fortunately, electrolytes in 3D cells are often utilized at lower thickness, which may compensate the decreased ionic conductivity. Here, we comprehensively review potential 3D SSE, SPE and GPE electrolyte materials by compiling their thickness and room temperature ionic conductivity. We use area specific resistance (ASR) as a metric to compare 3D electrolytes with one another and conventional electrolytes. We find that certain process-material combinations, such as atomic layer deposition of SSEs, electrodeposition of SPEs and GPEs, and initiated chemical vapor deposition of SPEs demonstrate ASRs beneath the interfacial impedances of Li-based systems and approach state-of-the-art electrolytes. We also comment on additional factors, such as electrochemical stability, that should be evaluated when determining 3D electrolyte suitability. Future research should focus on adapting known materials chemistries for conformal deposition techniques to further improve the ionic conductivity, as these techniques are capable of producing the necessary thicknesses and conformality.
Raphaël Gass et al 2024 J. Electrochem. Soc. 171 034511
Technologies based on the use of hydrogen are promising for future energy requirements in a more sustainable world. Consequently, modelling fuel cells is crucial, for instance, to optimize their control to achieve excellent performance, to test new materials and configurations on a limited budget, or to consider their degradation for improved lifespan. To develop such models, a comprehensive study is required, encompassing both well-established and the latest governing laws on matter transport and voltage polarization for Proton Exchange Membrane Fuel Cells (PEMFCs). Recent articles often rely on outdated or inappropriate equations, lacking clear explanations regarding their background. Indeed, inconsistent understanding of theoretical and experimental choices or model requirements hinders comprehension and contributes to the misuse of these equations. Additionally, specific researches are needed to construct more accurate models. This study aims to offer a comprehensive understanding of the current state-of-the-art in PEMFC modeling. It clarifies the corresponding governing equations, their usage conditions, and assumptions, thus serving as a foundation for future developments. The presented laws and equations are applicable in most multi-dimensional, dynamic, and two-phase PEMFC models.
Editor's Choice
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Hong Zhang et al 2024 J. Electrochem. Soc. 171 047510
Ordered Pt/SnO2 composite porous thin films were prepared for fabrication of planar mixed-potential hydrogen sensors. Characterization of the Pt/SnO2 films revealed that Pt elements were primarily loaded in Pt° form on the SnO2 film surface and did not significantly change the morphology of the film electrodes. The potentiometric response of Pt/SnO2 thin films to hydrogen varied with the Pt loading contents. Compared to the pristine SnO2 film, the 1 at% and 2 at% Pt-loaded SnO2 composite films exhibited 1.6 and 2.0 times higher potentiometric response to 300 ppm hydrogen at 500 °C, with a similar response time of 6–10.5 s. By assembling an array of sensors composed of SnO2 films loaded with 1 at% and 2 at% Pt, and using principal component analysis, discrimination of hydrogen and four interfering gases (ammonia, carbon monoxide, nitrogen dioxide, and propane) in the concentration range of 100–300 ppm was achieved. The sensing behaviors of the Pt/SnO2 composite thin films were discussed in relation to the competitive promotion effects for the heterogeneous and electrochemical catalytic activities by Pt loading.
Highlights
Potentiometric hydrogen sensors based on Pt/SnO2 thin films were fabricated.
Hydrogen sensing response was enhanced by loading 1 at% and 2 at% Pt.
The sensing behavior was discussed by the Pt competitive promotion effects.
Discrimination of hydrogen and four interfering gases was achieved.
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.
Accepted manuscripts
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Li et al
A three-dimensional model of a methanol-fueled solid oxide fuel cell (SOFC) that sufficiently considers the rib structure to understand the effects of operating conditions on a methanol-fueled SOFC is developed. The model considers the coupling of electrochemical reactions, mass transport, heat transfer, and thermal stress. The overall performance of the methanol-fueled SOFC is investigated under the influence of operating voltage, steam-to-carbon ratio, and porosity. The results indicate that as the operating voltage increases, the overall anode switches from exothermic to endothermic, and the stress of the anode first decreases and then increases. As the steam-to-carbon ratio increases, the overall temperature of the anode decreases. However, when the steam-to-carbon ratio is less than 1, the temperature at the inlet is lower than the ambient temperature. Meanwhile, the first principal stress on the anode increases as the steam-to-carbon ratio increases. Increasing the porosity reduces the length of the three-phase boundary, thereby decreasing the current density and the overall temperature and thermal stress on the anode. This study revealed the effects of operating conditions on the methanol-fueled SOFC, especially on the rib, and contribute to controlling the operant conditions for SOFC fueled by a mixture of steam and methanol.
Böhm et al
The ethylene glycol (EG)/water mixture composition of an alkaline one-step polyol synthesis for Pt/C catalysts was systematically investigated and optimized for a low ethylene glycol content with regards to resulting Pt particle size and electrochemical performance of membrane electrode assemblies tested as proton exchange membrane (PEM) fuel cell cathode catalysts. Beginning test fuel cell data show a possible reduction of the required EG amount per gram of synthesized catalyst by up to 98% without significantly compromising the initial electrochemical performance. Taking catalyst durability into account, a Pt/C catalyst synthesized with 40 vol% H2O and 32 mM Pt precursor concentration showed a decent initial electrochemical performance (716 mV at 1 A cm-2) as well as an accelerated stress test-derived stability similar to an internal reference catalyst, obtained with 100 vol% EG. In summary, our study shows that optimizing the amount of water and platinum precursor in the synthesis process can lead to catalysts with excellent performance for PEM fuel cells while contributing significantly to cost reduction by using less EG during synthesis.
Riegraf et al
The currently ongoing scale-up of high-temperature solid oxide electrolysis (SOEL) requires an understanding of the underlying dominant degradation mechanisms to enable continuous progress in increasing stack durability. In the present study, the degradation behavior of SOEL stacks of the type ‘MK35x’ with chromium-iron-yttrium (CFY) interconnects and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS was investigated. For this purpose, the initial electrochemical performance of a 10-cell stack was characterized in various operating conditions in both fuel cell and electrolysis mode. Degradation was evaluated during galvanostatic steady-state steam electrolysis operation for more than 3000 h at an oxygen side outlet temperature of 816°C and a current density of -0.6 A cm-2 and showed an average voltage evolution rate of -0.3 %/kh demonstrating high stability. Initial and final characterization at the part load operating point at -0.39 A cm-2 and 800°C led to the determination of a positive overall degradation rate of 0.4 %/kh showing a considerable impact of the operating conditions on the degradation rate. By means of electrochemical impedance spectroscopy analysis it was shown that the stack’s ohmic resistance increased whereas the polarization resistance decreased most likely due to an enhancement in LSMM’/ScSZ oxygen electrode performance.
Sepe et al
Optimization of proton exchange membrane water electrolyzers (PEMWE) has become a focus of researchers looking for a reliable way to generate power. A vital component to PEMWE operation is the porous transport layer (PTL) on the anode side, which is where oxygen is produced. The PTL must allow water access to the catalyst layer and remove oxygen simultaneously. In this work, a previously developed imaging technique is used to generate bilayer PTL structures. A multiscale modeling approach was used to study the effect of a bilayer PTL on oxygen evolution and PEMWE performance. First, a micro scale model was used to predict oxygen transport pathways through different PTL structures. Results showed that the bilayer PTL results in higher oxygen saturation and faster oxygen transport through the PTL. Second, a macro scale model was used to predict performance using bilayer PTLs. Predictions showed potential values between 10 and 20 mV below single layer potential values. This points to the bilayer improving PEMWE operation. Findings from this work show how the addition of a mesoporous layer to a PTL substrate will improve oxygen transport and removal from the catalyst surface, which will improve PEMWE performance.
Newman et al
Free-standing conducting polymer films, polypyrrole doped with dodecylbenzene sulfonate, were obtained with electrochemical delamination by using redox cycling to delaminate electropolymerized film from the substrate. The use of electrochemical delamination to obtain thinner films than mechanical peeling and the effect of different electropolymerization substrates was investigated. The free-standing films were characterized with electrochemical filling efficiency and scanning electron microscopy. Electrochemical delamination allowed thin free-standing films <10 μm and <1 μm thick to be obtained from 304 stainless steel and gold substrates, respectively. The thinnest films obtainable from 304 stainless steel were limited by the electropolymerization charge density needed for complete film growth and not by electrochemical delamination. The filling efficiency of the films did not appear to be decreased by electrochemical delamination. These findings show the utility of electrochemical delamination to obtain thin free-standing films that also have the benefits of electropolymerization.
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Masaki Deguchi et al 2024 J. Electrochem. Soc. 171 040536
The electrolyte in current automotive lithium-ion batteries is a mixture of ethylene carbonate (EC), which has a high dielectric constant, and ethyl methyl carbonate or dimethyl carbonate, which have a low viscosity. However, the flash point of these mixed solvents is as low as 25 °C, so safety precautions must be taken. On the other hand, if only EC or propylene carbonate with a high flash point is used, the flash point will be 120 °C or higher. However, the high dielectric constant solvent cannot wet the hydrophobic separator whose material is polyethylene and/or polypropylene. Therefore, there is a problem that the battery does not work. In 1999, we proposed a “functional electrolyte” in which a small amount of an additive with a new function is added to the electrolyte, and many additives have since been commercialized. In recent work, we focused on a low viscosity linear carboxylic acid esters, designed an electrolyte with a flash point above 120 °C that provides wettability to the separator even in an electrolyte with a high dielectric constant solvent.
Ziwei Ye et al 2024 J. Electrochem. Soc. 171 040522
This study examines the influence of electrolyte salts and solvents on the performance of O3 layered oxide NaMn0.39Fe0.31Ni0.22Zn0.08O2/hard carbon sodium-ion pouch cells with polyethylene terephthalate (PET) jellyroll tape. A significant enhancement in cell performance between 2.0 and 3.8 V was observed across various temperatures (20, 40, and 55 °C) by substituting NaPF6 with NaFSI, including reduced impedance growth, minimized gas generation, and supressed jellyroll tape decomposition. Ultra-high precision coulometry revealed that the use of NaPF6 resulted in increased unwanted parasitic reactions associated with tape decomposition, e.g., capacity fade and charge endpoint capacity slippage. Teardown of sodium-ion pouch cells after cycling in DMC-based electrolytes revealed a severe decomposition of the PET tape with NaPF6 but not with NaFSI. Gas chromatography shows significantly more electrolyte decomposition products with NaPF6 as opposed to NaFSI. DEC-based electrolyte showed less capacity fade, less electrolyte decomposition products, and less tape decomposition after cycling than DMC-based electrolyte. The electrolyte additive DTD can prevent parasitic reactions in DMC- and NaPF6-based electrolyte. Overall, the choice of salts and linear carbonates in alkyl carbonate electrolytes plays a crucial role in determining the overall cycling performance of the layered oxide/hard carbon sodium-ion cells with PET jellyroll tape.
Frendi Maulana et al 2024 J. Electrochem. Soc. 171 046505
This work investigates the potential of N, Ni, and N-Ni-doped ZnO as photocatalysts for hydrogen production through water splitting. Sonochemical techniques were used to synthesize these materials. In contrast to undoped or singly-doped ZnO, N-Ni-double-doped ZnO demonstrated a significantly narrower band gap (2.89 eV) and smaller crystallites (21.60 nm). This led to a remarkable doubling in the hydrogen production rate under UV-visible light irradiation. The combined effect of N and Ni doping effectively promotes efficient charge separation and enhanced light absorption, resulting in significantly increased photocatalytic activity. Furthermore, N-Ni-ZnO demonstrates exceptional stability, retaining over 95% of its initial activity after five cycles. This work paves the way for the development of cost-effective and scalable photocatalysts for sustainable solar hydrogen production.
Maria Escamilla et al 2024 J. Electrochem. Soc. 171 040533
In this paper, we describe the synthesis and characterization of alkoxylated TEMPO, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl, radicals with potential application in organic non-aqueous redox flow batteries. The behavior of a series of TEMPO derivatives with varying lengths of alkoxy chain is analyzed in acetonitrile solutions using electrochemical techniques, electron paramagnetic resonance (EPR) spectroscopy, and measurements of permeability through three different membranes. Electrochemical redox potentials are only weakly dependent on the substituent, but, in contrast, exchange current densities derived from the data do depend on the substitution. EPR lends further insight into these properties via the determination of hyperfine splitting constant and rotational correlation time. There is a negligible effect of the substituents on those parameters among the modified TEMPO radicals. Finally, permeation rates of modified TEMPO derivatives through membranes depend significantly on both the membrane and the substitution of TEMPO, providing insights into capacity fade measurements in the literature.
Ido Ben-Barak and M. N. Obrovac 2024 J. Electrochem. Soc. 171 040535
Oxides in the NixMn0.5-x/2Co0.5-x/2-O system were investigated as precursors in the all-dry synthesis of NMC622 (LiNi0.6Mn0.2Co0.2O2). Single-phase spinel precursors in this system were found to have the highest compositional homogeneity. To synthesize NMC, NixMn0.5-x/2Co0.5-x/2-O precursors were heated with Li2CO3 and NiO (to attain the correct NMC stoichiometry) in air or oxygen. This represents a different strategy in NMC synthesis compared to conventional hydroxide precursors that have the same composition as the final NMC. The most homogeneous and best performing NMC (171.9 mAh g−1 with 90% after 183 cycles) were obtained by using precursors that were essentially single-phase cubic spinel (0.070 ≤ x ≤ 0.091 in NixMn0.5-x/2Co0.5-x/2-O) even though such precursors had compositions that had significantly less Ni content than the target NMC622 composition. These findings demonstrate an alternate route for obtaining compositional homogeneity in NMC all-dry synthesis.
Martins Sarma et al 2024 J. Electrochem. Soc. 171 040531
This paper presents the cycling of a novel low-cost Na-Zn liquid metal battery. Its 600 °C operating temperature presents multiple challenges that must be overcome to achieve commercial viability, both from a structural and electrochemical perspective. To enable long-term cycling of the Na-Zn battery in a realistic environment, we have developed a reusable, hermetically sealed, high temperature and sufficiently corrosion resistant cell concept. The design as well as various approaches for assembling and filling the cell are presented. The factors considered when selecting specific components are documented and explained. The active volume of the cell design can be up to 40 ml, corresponding to a nominal capacity of 1 A h, while the entire cell body weighs around 800 g and costs approximately €200 ($215). The performance of the cell is demonstrated in terms of longevity (1000 h) and high discharge current density (100 mA cm-2). The manuscript not only presents the first long-term cycling performance of the novel Na-Zn chemistry achieving Coulombic efficiency of up to 80%, but also demonstrates the design’s versatility with in situ dynamic neutron radiography of the cell.
Erno Kemppainen et al 2024 J. Electrochem. Soc. 171 044507
Understanding the physical and chemical basis of device operation is important for their development. While hydrogen fuel cells are a widely studied topic, direct ammonia fuel cells (DAFCs) are a smaller field with fewer studies. Although the theoretical voltage of a DAFC is approximately equal to that of a hydrogen fuel cell, the slow kinetics of the ammonia oxidation reaction hamper cell performance. Therefore, development of anode catalysts is especially needed for practical viability of the DAFCs. To study DAFC operation, specifically interactions between reaction kinetics and different transport phenomena, we developed a one-dimensional model of a DAFC and performed a sensitivity analysis for several parameters related to the cell operating conditions (e.g., temperature, relative humidity) and properties (e.g., catalyst loading). As expected, temperature and relative humidity were very important for cell power. However, while faster reaction kinetics improved the cell performance, simply increasing the catalyst loading did not always produce a comparable enhancement. These and other observations about the relative importance of the operating parameters should help to prioritize and guide future development of and research on DAFCs. Further studies are needed to understand and optimize e.g. humidity management in different scenarios.
Matthias Riegraf et al 2024 J. Electrochem. Soc.
The currently ongoing scale-up of high-temperature solid oxide electrolysis (SOEL) requires an understanding of the underlying dominant degradation mechanisms to enable continuous progress in increasing stack durability. In the present study, the degradation behavior of SOEL stacks of the type ‘MK35x’ with chromium-iron-yttrium (CFY) interconnects and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS was investigated. For this purpose, the initial electrochemical performance of a 10-cell stack was characterized in various operating conditions in both fuel cell and electrolysis mode. Degradation was evaluated during galvanostatic steady-state steam electrolysis operation for more than 3000 h at an oxygen side outlet temperature of 816°C and a current density of -0.6 A cm-2 and showed an average voltage evolution rate of -0.3 %/kh demonstrating high stability. Initial and final characterization at the part load operating point at -0.39 A cm-2 and 800°C led to the determination of a positive overall degradation rate of 0.4 %/kh showing a considerable impact of the operating conditions on the degradation rate. By means of electrochemical impedance spectroscopy analysis it was shown that the stack’s ohmic resistance increased whereas the polarization resistance decreased most likely due to an enhancement in LSMM’/ScSZ oxygen electrode performance.
Mitchell Sepe et al 2024 J. Electrochem. Soc.
Optimization of proton exchange membrane water electrolyzers (PEMWE) has become a focus of researchers looking for a reliable way to generate power. A vital component to PEMWE operation is the porous transport layer (PTL) on the anode side, which is where oxygen is produced. The PTL must allow water access to the catalyst layer and remove oxygen simultaneously. In this work, a previously developed imaging technique is used to generate bilayer PTL structures. A multiscale modeling approach was used to study the effect of a bilayer PTL on oxygen evolution and PEMWE performance. First, a micro scale model was used to predict oxygen transport pathways through different PTL structures. Results showed that the bilayer PTL results in higher oxygen saturation and faster oxygen transport through the PTL. Second, a macro scale model was used to predict performance using bilayer PTLs. Predictions showed potential values between 10 and 20 mV below single layer potential values. This points to the bilayer improving PEMWE operation. Findings from this work show how the addition of a mesoporous layer to a PTL substrate will improve oxygen transport and removal from the catalyst surface, which will improve PEMWE performance.
Matthew James Newman and Vicky Doan-Nguyen 2024 J. Electrochem. Soc.
Free-standing conducting polymer films, polypyrrole doped with dodecylbenzene sulfonate, were obtained with electrochemical delamination by using redox cycling to delaminate electropolymerized film from the substrate. The use of electrochemical delamination to obtain thinner films than mechanical peeling and the effect of different electropolymerization substrates was investigated. The free-standing films were characterized with electrochemical filling efficiency and scanning electron microscopy. Electrochemical delamination allowed thin free-standing films <10 μm and <1 μm thick to be obtained from 304 stainless steel and gold substrates, respectively. The thinnest films obtainable from 304 stainless steel were limited by the electropolymerization charge density needed for complete film growth and not by electrochemical delamination. The filling efficiency of the films did not appear to be decreased by electrochemical delamination. These findings show the utility of electrochemical delamination to obtain thin free-standing films that also have the benefits of electropolymerization.