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.
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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Jorn M. Reniers et al 2019 J. Electrochem. Soc. 166 A3189
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.
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.
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.
Manuel Ank et al 2023 J. Electrochem. Soc. 170 120536
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.
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.
Sarah F. Zaccarine et al 2022 J. Electrochem. Soc. 169 064502
Polymer electrolyte membrane water electrolyzers (PEMWEs) are devices of paramount importance, enabling the large-scale storage of hydrogen from intermittent renewable energy sources such as wind and solar. But a transition towards lower noble metal catalyst loadings and intermittent operation is needed for the widespread utilization of this technology. Although kinetic losses tend to dominate in membrane electrode assembly (MEA) results, it has been suggested that morphological changes and interfaces between the catalyst, ionomer, and membrane will also contribute to overall degradation. Moreover, the combination of degradation to the catalyst layer (CL) constituents will further lead to structural changes that have not been widely explored. The multitude and complexity of degradation mechanisms, which likely occur simultaneously, require a characterization approach that can explore surfaces and interfaces at a range of length-scales to probe chemical, morphological, and structural changes of constituents within the catalyst later. This paper presents a comprehensive characterization approach that features scanning electron microscopy (SEM), scanning transmission electron microscopy with energy-dispersive X-Ray spectroscopy (STEM/EDS), X-Ray photoelectron spectroscopy (XPS), X-Ray absorption spectroscopy (XAS), and transmission X-Ray microscopy (TXM) with X-Ray absorption near-edge structure (XANES) chemical mapping to study degradation of the catalyst layer with a focus on MEAs after intermittent and steady-state operation. Catalyst changes including dissolution, oxidation, and agglomeration were observed, as well as redistribution and dissociation of the ionomer. These smaller-scale changes were found to have a large influence on overall stability of the electrodes: they caused the formation of voids and segregation of constituents within regions of the film. Delamination and collapse of the overall catalyst layer were observed in some instances. Greater changes were observed after an extended 2 V hold compared to IV cycling, but similar degradation mechanisms were detected, which suggests the larger issues would likely also be experienced during intermittent PEMWE operation. These findings would not be possible without such a systematic, multi-scale, multi-technique characterization approach, which highlights the critical importance of detailed analysis of catalyst layer degradation to propose mitigation strategies and improve long-term PEM water electrolyzer performance.
John G. Petrovick et al 2023 J. Electrochem. Soc. 170 114519
Anion-exchange membranes (AEMs) are a possible replacement for perfluorosulfonic-acid membranes in energy-conversion devices, primarily due to the hydroxide mobile ion allowing the devices to operate in alkaline conditions with less expensive electrocatalysts. However, the transport properties of AEMs remain understudied, especially electro-osmosis. In this work, an electrochemical technique, where the open-circuit voltage is measured between two ends of a membrane maintained at different relative humidities, is used to determine the water transport number of various ionomers, including Versogen and Sustainion AEMs and Nafion cation-exchange membrane (CEM), as a function of water content and temperature. In addition, the CEMs and AEMs are examined in differing single-ion forms, specifically proton and sodium (CEM) and hydroxide and carbonate (AEM). Carbonate-form AEMs have the highest transport number (∼11), followed by sodium-form CEMs (∼8), hydroxide-form AEMs (∼6), and proton-form CEMs (∼3). Finally, a multicomponent transport model based on the Stefan-Maxwell-Onsager framework of binary interactions is used to develop a link between water transport number and water-transport properties, extracting a range for the unmeasured membrane water permeability of Versogen as a function of water content.
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.
Konosuke Watanabe et al 2022 J. Electrochem. Soc. 169 044515
The anode mass transport loss is one of the issues to expand the practical application scope of proton exchange membrane water electrolyzers (PEMWEs). However, there are few reports concerning the oxygen transport inside and near the anode catalyst layer (CL). Although especially near the anode CL, there are two transport mechanisms: gaseous oxygen and dissolved oxygen, there are no reports, as far as we could find, that experimentally examined the existence of dissolved oxygen in PEMWE. Herein, the bubble growth behavior near the anode catalyst was observed using a high-speed camera, and the bubble radius change was investigated. The radii of the bubbles continued to increase after they left the anode catalyst layer surface, and the existence of dissolved oxygen and the formation of an oxygen supersaturated region were confirmed. The existence of dissolved oxygen is an important factor in the future evaluation of anode mass transport loss in PEMWE and a good revelation for the future development of the anode porous structure to reduce the anode mass transport loss.
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Shuang Chen et al 2024 J. Electrochem. Soc. 171 060510
The development and application of polyethylene oxide (PEO) based solid polymer electrolyte (SPE) is severely constrained by its low ionic conductivity and poor tensile resistance. To improve the electrochemical performance of SPE without losing its mechanical properties, a benzene sulfonate-based additive is adopted into crosslinking system composed of -CH2-CH2-O- segments to obtain a membrane with a high ionic conductivity of 1.47 × 10−4 S cm−1 and an ionic transference number of 0.70 at room temperature. The activation energy value of 0.128 eV gives evidence for a favorable migration mechanism of PTH-SPE. Anti-dendrite growth and contact optimization can be realized by molecular structure design with a tensile elongation of 490%. The reversible overpotential of Li||Li symmetric cell within 1000 h demonstrates that the compact PTH-SPE can inhibit the growth of lithium dendrite. This work provides a new strategy for designing high-performance solid electrolytes for room temperature via a green solvent-free method.
Highlights
Attempt of adding toluene sulfonate-based additives into PEO matrix.
A high lithium transference number of 0.70.
High ionic conductivity of 1.47 × 10−4 S cm−1 at room temperature.
Soft form and large elongation of 490% for electrolyte membrane.
Claudia Triolo et al 2024 J. Electrochem. Soc. 171 060509
High-entropy oxides with spinel structure (SHEOs) are promising anode materials for next-generation lithium-ion batteries (LIBs). In this work, electrospun (Mn,Fe,Co,Ni,Zn) SHEO nanofibers produced under different conditions are evaluated as anode materials in LIBs and thoroughly characterised by a combination of analytical techniques. The variation of metal load (19.23 or 38.46 wt% relative to the polymer) in the precursor solution and of calcination conditions (700 °C/0.5 h, or 700 °C/2 h followed by 900 °C/2 h) affects the morphology, microstructure, crystalline phase, and surface composition of the pristine SHEO nanofibers and the resulting electrochemical performance, whereas mechanism of Li+ storage does not substantially change. Causes of long-term (≥650 cycles) capacity fading are elucidated via ex situ synchrotron X-ray absorption spectroscopy. The results evidence that the larger amounts of Fe, Co, and Ni cations irreversibly reduced to the metallic form during cycling are responsible for faster capacity fading in nanofibers calcined under milder conditions. The microstructure of the active material plays a key role. Nanofibers composed by larger and better-crystallized grains, where a stable solid/electrolyte interphase forms, exhibit superior long-term stability (453 mAh g−1 after 550 cycles at 0.5 A g−1) and rate-capability (210 mAh g−1 at 2 A g−1).
Highlights
High-entropy (Mn,Fe,Co,Ni,Zn) oxide nanofibers (NFs) are evaluated as LIB anodes.
The existence of a microstructure-performance relationship is demonstrated.
NFs with larger and less defective grains show superior stability and rate-capability.
Best anodes deliver 453 mAh g−1 after 550 cycles at 0.5 A g−1, and 210 mAh g−1 at 2 A g−1.
Long-term (≥650 cycles) capacity fading is due to the formation of Fe°, Co°, and Ni°.
Qiongde Zhang et al 2024 J. Electrochem. Soc. 171 063501
The structural design of the flow channel of a redox flow battery directly affects ion transport efficiency, electrode overpotential, and stack performance during charge-discharge cycles. A tapered hierarchical interdigitated flow field design that has independent flow channel structures for different levels of flow was developed in this work. Especially, the secondary branch channels are the tapered type and the corresponding cross-sections are gradually reduced along the flow direction, which is beneficial for improving the flow rate at the end of channels and enhancing mass transfer. The performances of a vanadium redox flow battery with interdigitated flow field, hierarchical interdigitated flow field, and tapered hierarchical interdigitated flow field were evaluated through 3D numerical model. The results showed that at 240 mA cm−2 and 6 ml s−1, the pump-based efficiency of the hierarchical interdigitated flow field increased by 4%-7% compared with the interdigitated flow field. Furthermore, the pump-based efficiency with tapered hierarchical interdigitated flow field increased by 1.6%-3% compared with the hierarchical interdigitated flow field. This indicates that the tapered hierarchical interdigitated flow field shows further advantages in redox flow battery applications.
Emre B. Boz et al 2024 J. Electrochem. Soc. 171 053509
Carbon-based porous electrodes are commonly employed in electrochemical technologies as they provide a high surface area for reactions, an open structure for fluid transport, and enable compact reactor architectures. In electrochemical cells that sustain liquid electrolytes (e.g., redox flow batteries, CO2 electrolyzers, capacitive deionization), the nature of the interaction between the three phases - solid, liquid and gas - determines the accessible surface area for reactions, which fundamentally determines device performance. Thus, it is critical to understand the correlation between the electrolyte infiltration in the porous electrode and the resulting accessible surface area in realistic reactor architectures. To tackle this question, here we simultaneously perform neutron radiography with electrochemical measurements to correlate macroscopic electrode saturation/wetting with accessible surface area. We find that for untreated electrodes featuring neutral wettability with water, the electrode area remains underutilized even at elevated flow rates, both for interdigitated and parallel flow fields. Conversely, increasing the electrode hydrophilicity results in an order-of-magnitude increase in accessible surface area at comparable electrode saturation, and is less influenced by the electrolyte flow rate. Ultimately, we reveal useful correlations between reactor architectures and electrode utilization and provide a method that is broadly applicable to flow electrochemical reactors.
Zhina Wang et al 2024 J. Electrochem. Soc. 171 064502
The adaptability of fuel cell vehicles in low-temperature environments remains challenging for their commercialization owing to the propensity of water within the fuel cell to freeze during a cold start, which impedes gas transmission and subsequent reactions. Consequently, the initial water content before cold start and the heat and water generated during this process are crucial for achieving a successful cold start. In this study, current- and voltage-controlled starting strategies are analyzed using a stack comprising 20 cells with an area of 285 cm2. Furthermore, key parameters related to shut down purging and cold start are optimized using starting time and reverse polarity cell count as optimization objectives. The optimal conditions for cold start include a current density of 0.5 A cm−2, voltage of 0.45 V, purging time of 180 s, and stack temperature (during purging) of 60 °C. Furthermore, the ambient temperature boundary is determined as −25 °C–−30 °C for a successful cold start without auxiliary heating in the stack.
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Li Yang et al 2024 J. Electrochem. Soc. 171 060504
Lithium metal battery (LMB) technology is very attractive as it has the potential to offer energy densities greater than 1000 Wh L−1. A thorough investigation of cell performance against various vehicle operational requirements is required for the successful deployment of this technology in practical electric vehicle applications. For instance, there have been several reports on the high reactivity of Li metal with electrolyte leading to continuous electrolyte consumption in LMB. Due to these parasitic reactions, electrolyte dries out and Li metal morphological changes occur leading to reduced cycle life of lithium metal batteries. In contrast, there are also claims of stable and long cycle life of LMB in several publications, although most of the results were obtained in coin cells. In this report we will take a closer look at the LMB cell to understand its performance and manufacturability. Our goal is to investigate and provide a thorough report on advances and challenges starting from the cell level down to component design of LMB.
Lena V. Bühre et al 2024 J. Electrochem. Soc. 171 054519
The commercialization of proton exchange membrane water electrolysis cells (PEMWEs), which are essential for a greener and more sustainable future, is hindered by the high costs of noble metal catalysts, as well as the degradation of the catalysts and membranes. Examining the electrodes' characteristics with reference electrodes (REs) yields insights into their individual performance and can, e.g., help assess new catalyst layer designs, their interplay with the adjacent porous transport layer, or understand the complex and multi-faceted degradation mechanisms. This review provides an overview of previous approaches and the evolution of RE designs in PEMWE. By discussing the strengths and limitations of different RE setups, readers are enabled to make more informed decisions about their experiments' design and choose the best RE setup for their specific research question.
Kokilavani R et al 2024 J. Electrochem. Soc. 171 057516
Immunosensors have emerged as vital tools in cancer diagnostics, providing simplified and rapid detection of biomarkers that are necessary for timely diagnosis. The objective of using an electrochemical immunosensor is to detect cancers at early stages, so that obtained biological information can be analyzed using artificial intelligence (AI) for deciding an appropriate treatment, avoiding false diagnosis, and preventing patient fatalities. The focus of this article is on four major reproductive cancers—breast, ovarian, cervical, and prostate cancers. Specifically, it explores the identification and optimization of biomarkers crucial for the precise detection of these cancers. Examining a decade of research, the review delves into nanotechnology-assisted electrochemical immunosensors (affinity biosensors), outlining advancements and emphasizing their potential in reproductive cancer diagnostics. Furthermore, the review contemplates avenues for enhancing sensor characteristics to pave the way for their application in field diagnosis, with a forward-looking perspective on AI-assisted diagnostics for the next generation of personalized healthcare. In navigating the landscape of reproductive cancer diagnostics, the integration of advanced technologies promises to transform our approach, offering improved accuracy and outcomes for patients.
Endao Zhang and Wei Song 2024 J. Electrochem. Soc. 171 052503
Hydrogen is a prime candidate for replacing fossil fuels. Electrolyzing water to produce hydrogen stands out as a particularly clean method, garnering significant attention from researchers in recent years. Among the various techniques for electrolyzing water to produce hydrogen, alkaline electrolysis holds the most promise for large-scale industrialization. The key to advancing this technology lies in the development of durable and cost-effective electrocatalysts for the hydrogen evolution reaction (HER). Self-supporting electrode is an electrode structure in which a catalyst layer is formed directly on a substrate (such as carbon cloth, nickel foam, stainless steel, etc) without using a binder and with good structural stability. In contrast to traditional nanocatalysts, self-supporting electrocatalysts offer significant advantages, including reduced resistance, enhanced stability, and prolonged usability under high currents. This paper reviews recent advancements in HER electrochemical catalysts for alkaline water electrolysis, focusing on the utilization of hydrogen-evolving catalysts such as metal sulfides, phosphides, selenides, oxides, and hydroxides. With self-supported electrocatalysts as the focal point, the paper delves into progress made in their preparation techniques, structural design, understanding of reaction mechanisms, and strategies for performance enhancement. Ultimately, the future development direction of promoting hydrogen evolution by self-supported electrocatalysts in alkaline water electrolysis is summarized.
Vinh Van Tran et al 2024 J. Electrochem. Soc. 171 056509
The quest for economical and sustainable electrocatalysts to facilitate the hydrogen evolution reaction (HER) is paramount in addressing the pressing challenges associated with carbon dioxide emissions. Molybdenum carbide-based nanomaterials have emerged as highly promising electrocatalysts for HER due to their Pt-like catalytic proficiency, exceptional stability, and the versatility of their crystal phases. Within this comprehensive review, we explore the diverse methodologies for synthesizing molybdenum carbides, including solid-gas, solid-solid, and solid-liquid phase reactions. In addition, a thorough elucidation of the hydrogen generation process through water electrolysis is provided. Furthermore, a spectrum of innovative strategies aimed at augmenting the performance of molybdenum carbides in the HER milieu is introduced, encompassing cutting-edge techniques such as phase-transition engineering, the construction of heterostructures, hetero-atom doping, the integration of hybrid structures with carbon materials, defect engineering, and meticulous surface modification. The review culminates by underscoring the current challenges and the promising prospects in the advancement of electrocatalysts for hydrogen production, with a dedicated focus on molybdenum carbide-based catalysts.
Highlights
Outstanding properties of molybdenum carbides were presented.
Various approaches for the fabrication of molybdenum carbides.
Different strategies on molybdenum carbides-based electrocatalyst for water electrolysis were discussed.
Current difficulties and possible solutions on molybdenum carbides-based electrocatalyst for water electrolysis have been introduced.
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S. Friedrich et al 2024 J. Electrochem. Soc. 171 050540
The impact of mechanical pressure on electrode stability in full-cells comprising microscale silicon-dominant anodes and NCA cathodes was investigated. We applied different mechanical pressures using spring-compressed T-cells with metallic lithium reference electrodes enabling us to analyze the electrode-specific characteristics. Our investigation covers a wide pressure range from 0.02 MPa (low pressure - LP) to 2.00 MPa (ultra high pressure - UHP) to determine the optimal pressure for cyclic lifetime and energy density. We introduce an experimental methodology considering single-component compression to adjust the cell setup precisely. We characterize the cells using impedance spectroscopy and age them at C/2. In the post-mortem analysis, cross-sections of the aged anodes are measured with scanning electron microscopy. The images are analyzed with regard to electrochemical milling, thickness gain, and porosity decrease by comparing them to the pristine state. The results indicate that cycling at UHP has a detrimental effect on cycle life, being almost two-fold shorter when compared to cycling at normal pressure (NP, 0.20 MPa). Scanning electron microscopy showed a dependency of the thickness and the porosity of the aged silicon anodes on the applied pressure, with coating thickness increasing and porosity decreasing for all pressure settings, and a correlation between thickness and porosity.
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.
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Lee et al
The imperative shift towards decarbonization necessitates the production of clean hydrogen through water electrolysis, powered by renewable energy sources. Among electrolyzer technologies, proton-exchange-membrane (PEM) systems emerge as a promising option for large-scale hydrogen generation due to their modular design and rapid response, aligning well with the intermittency of renewable energy. In this study, we employ a tape casting method to fabricate microporous layers (MPLs), both as a single layer and as a bilayer over commercial porous transport layers (PTLs), to further enhance performance of water electrolyzers. We demonstrate that microporous layers require adequate pore sizes to facilitate gas removal, preventing gas flooding and preserving electrolyzer performance. Our single layer microporous layers exhibit lower overpotentials compared to commercial sintered Ti PTLs by 142 mV at 4 A·cm⁻². Moreover, we show that having an effective microporous layer enhances electrolyzer performance irrespective of the substrate used, offering avenues for cost reduction. We also investigate novel PTL structures with reduced tortuosity and integrated MPL fabricated via phase inversion tape casting, resulting in a performance enhancement of 92 mV. Our findings unravel the critical role of microporous layer structures and their impact on electrolyzer performance.
Shakil et al
Acetylcholine (ACh) is a vital neurotransmitter in the peripheral and central nervous systems. Disturbances in its transmission are linked to serious diseases such as Parkinson’s and Alzheimer’s. Detecting ACh concentrations in biological samples is critical for understanding and managing these conditions. This review examines the latest advancements in electrochemical sensors for ACh detection, highlighting their principles, methodologies, and applications. Various sensor types, including enzymatic and non-enzymatic sensors, potentiometric and conductometric methods are discussed in detail. Emphasis is placed on the advantages of using electrochemical methods for ACh detection, such as high sensitivity, selectivity, and rapid response times. Further research needs to focus on innovative materials and techniques to overcome current challenges and improve the practical application of ACh detection in clinical settings.
Abrego Tello et al
The suitability of electrochemical methods for quantitative measurements at microdevices is influenced by the relatively large electrode-insulator interface-to-electrode area ratio, greatly impacting charging dynamics due to interactions among electrolyte and conductor/insulator materials. The resulting charging current can overwhelm the current from redox chemistry. The device studied here features a 70-µm×100-µm electroactive window, hosts gold coplanar microband electrodes, and is insulated by SU-8, which serves as both overlayer and substrate. The overlayer defines the electroactive length and isolates the leads of the electrodes from the sample solution. Cyclic voltammetry in 0.10 M KCl yields unexpected, nonlinear dependence of current on scan rate, which can be explained with two empirical approaches. The first employs an equivalent circuit, involving leakage resistance and double-layer capacitance in parallel, to address both background processes and electrode imperfections as a function of scan rate. The second associates the enhanced current to a changing-chargeable area resulting from interface irregularities. Prior publications on alternative conductor-insulator materials are benchmarked in this study. The comparison of the materials shows that charging dynamics for devices made with SU-8 lead to more favorable electrochemical performance than for those constructed with glass, epoxy, and silicon nitride, and under certain circumstances, polyimide and Tefzel.
Dickinson et al
Theoretical models used to describe the catalyst layers (CLs) in polymer electrolyte membrane fuel cells (PEMFCs) are reviewed, with a focus on continuum treatments as incorporated in device-scale models used to predict and optimise PEMFC operating performance. Consideration is given to the mathematical relationships between CL design properties (Pt/C mass ratio, catalyst loading, ionomer loading), and physical properties. Relevant physical models are summarised, considering couplings between the CL and the phenomena of charge transfer, reactant mass transfer, hydrogen oxidation, and oxygen reduction electrode kinetics, heat transfer, and water balance. The relevance of thin film methods (through-thickness homogenisation) is compared to those resolving the macroscopic depth of the CL. Specific continuum homogenisations of microstructural models incorporating CL transport limitations in a continuum treatment, such as the agglomerate model, are discussed.
Abrego Tello et al
Optimization of redox-cycling currents was performed by adjusting the height (sidewalls, h), width (w) ,and length (l) of band electrodes and their spacing (wgap) in coplanar arrays restricted to a small-electroactive window of 70 × 100 µm. These arrays can function in µL-volumes for chemical analysis (e.g., in vivo dopamine detection using probes). Experiments were conducted with an array of five electrodes (NE = 5), w = 4.3 µm, wgap = 3.7 µm, h = 0.150 µm, and l = 99.2 µm. Reasons for disparities between currents from experiments and approximate equations were determined by high-density mesh simulations and were found to arise from sluggish heterogeneous electron transfer kinetics and diffusion at electrode ends, edges, and heights. Ferricyanide, with its moderately slow kinetics, exhibits redox-cycling currents that fall below predictions by the equations as wgap decreases and diffusional flux outpaces reaction rates. Simulations aid investigations of various array designs, achievable through conventional photolithography, by decreasing w and wgap and increasing NE to fit within the electroactive window. A coplanar array, NE = 58, w = wgap = 0.6 µm, h = 0.150 µm and l = 100 µm, yielded ferricyanide sensitivities of 0.266, 0.259 nA·µM−1, enhancements of 8× and 9× over w = wgap = 4 µm, and projected dopamine limits of quantification of 139 nM, 171 nM at generator and collector electrodes, respectively
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Claudia Triolo et al 2024 J. Electrochem. Soc. 171 060509
High-entropy oxides with spinel structure (SHEOs) are promising anode materials for next-generation lithium-ion batteries (LIBs). In this work, electrospun (Mn,Fe,Co,Ni,Zn) SHEO nanofibers produced under different conditions are evaluated as anode materials in LIBs and thoroughly characterised by a combination of analytical techniques. The variation of metal load (19.23 or 38.46 wt% relative to the polymer) in the precursor solution and of calcination conditions (700 °C/0.5 h, or 700 °C/2 h followed by 900 °C/2 h) affects the morphology, microstructure, crystalline phase, and surface composition of the pristine SHEO nanofibers and the resulting electrochemical performance, whereas mechanism of Li+ storage does not substantially change. Causes of long-term (≥650 cycles) capacity fading are elucidated via ex situ synchrotron X-ray absorption spectroscopy. The results evidence that the larger amounts of Fe, Co, and Ni cations irreversibly reduced to the metallic form during cycling are responsible for faster capacity fading in nanofibers calcined under milder conditions. The microstructure of the active material plays a key role. Nanofibers composed by larger and better-crystallized grains, where a stable solid/electrolyte interphase forms, exhibit superior long-term stability (453 mAh g−1 after 550 cycles at 0.5 A g−1) and rate-capability (210 mAh g−1 at 2 A g−1).
Highlights
High-entropy (Mn,Fe,Co,Ni,Zn) oxide nanofibers (NFs) are evaluated as LIB anodes.
The existence of a microstructure-performance relationship is demonstrated.
NFs with larger and less defective grains show superior stability and rate-capability.
Best anodes deliver 453 mAh g−1 after 550 cycles at 0.5 A g−1, and 210 mAh g−1 at 2 A g−1.
Long-term (≥650 cycles) capacity fading is due to the formation of Fe°, Co°, and Ni°.
Emre B. Boz et al 2024 J. Electrochem. Soc. 171 053509
Carbon-based porous electrodes are commonly employed in electrochemical technologies as they provide a high surface area for reactions, an open structure for fluid transport, and enable compact reactor architectures. In electrochemical cells that sustain liquid electrolytes (e.g., redox flow batteries, CO2 electrolyzers, capacitive deionization), the nature of the interaction between the three phases - solid, liquid and gas - determines the accessible surface area for reactions, which fundamentally determines device performance. Thus, it is critical to understand the correlation between the electrolyte infiltration in the porous electrode and the resulting accessible surface area in realistic reactor architectures. To tackle this question, here we simultaneously perform neutron radiography with electrochemical measurements to correlate macroscopic electrode saturation/wetting with accessible surface area. We find that for untreated electrodes featuring neutral wettability with water, the electrode area remains underutilized even at elevated flow rates, both for interdigitated and parallel flow fields. Conversely, increasing the electrode hydrophilicity results in an order-of-magnitude increase in accessible surface area at comparable electrode saturation, and is less influenced by the electrolyte flow rate. Ultimately, we reveal useful correlations between reactor architectures and electrode utilization and provide a method that is broadly applicable to flow electrochemical reactors.
Jason Keonhag Lee et al 2024 J. Electrochem. Soc.
The imperative shift towards decarbonization necessitates the production of clean hydrogen through water electrolysis, powered by renewable energy sources. Among electrolyzer technologies, proton-exchange-membrane (PEM) systems emerge as a promising option for large-scale hydrogen generation due to their modular design and rapid response, aligning well with the intermittency of renewable energy. In this study, we employ a tape casting method to fabricate microporous layers (MPLs), both as a single layer and as a bilayer over commercial porous transport layers (PTLs), to further enhance performance of water electrolyzers. We demonstrate that microporous layers require adequate pore sizes to facilitate gas removal, preventing gas flooding and preserving electrolyzer performance. Our single layer microporous layers exhibit lower overpotentials compared to commercial sintered Ti PTLs by 142 mV at 4 A·cm⁻². Moreover, we show that having an effective microporous layer enhances electrolyzer performance irrespective of the substrate used, offering avenues for cost reduction. We also investigate novel PTL structures with reduced tortuosity and integrated MPL fabricated via phase inversion tape casting, resulting in a performance enhancement of 92 mV. Our findings unravel the critical role of microporous layer structures and their impact on electrolyzer performance.
Louis Hartmann et al 2024 J. Electrochem. Soc. 171 060506
The trend for increased nickel content in layered transition metal oxide cathode active materials and increasing charging cut-off voltages aggravates aging of lithium-ion battery cells at high state of charge (SOC). We investigate the calendaric aging behavior of large-format automotive prototype cells and laboratory single-layer pouch cells at high but realistic cell voltages/SOCs and demonstrate that electrolyte oxidation in combination with follow-up reactions can cause a significant loss of the LiPF6 salt in the electrolyte. For this, we analyze the LiPF6 concentration in aged cells, the generation of H2 upon storage, and the cell resistance for different aging conditions. We show that the LiPF6 loss is a critical aging phenomenon, as it cannot readily be detected by capacity fading measurements at low/medium C-rates or by cell resistance measurements, while it severely reduces rate and fast-charging capability. Under certain circumstances, LiPF6 loss can even lead to a temporary capacity increase due to conversion of the conducting salt in the electrolyte to cyclable lithium in the active material. Finally, we suggest a possible reaction mechanism and a simple accounting model to keep track of how different side reactions involved in LiPF6 loss change the cyclable lithium inventory of a lithium-ion cell.
Li Yang et al 2024 J. Electrochem. Soc. 171 060504
Lithium metal battery (LMB) technology is very attractive as it has the potential to offer energy densities greater than 1000 Wh L−1. A thorough investigation of cell performance against various vehicle operational requirements is required for the successful deployment of this technology in practical electric vehicle applications. For instance, there have been several reports on the high reactivity of Li metal with electrolyte leading to continuous electrolyte consumption in LMB. Due to these parasitic reactions, electrolyte dries out and Li metal morphological changes occur leading to reduced cycle life of lithium metal batteries. In contrast, there are also claims of stable and long cycle life of LMB in several publications, although most of the results were obtained in coin cells. In this report we will take a closer look at the LMB cell to understand its performance and manufacturability. Our goal is to investigate and provide a thorough report on advances and challenges starting from the cell level down to component design of LMB.
Miguel Angel Abrego Tello et al 2024 J. Electrochem. Soc.
The suitability of electrochemical methods for quantitative measurements at microdevices is influenced by the relatively large electrode-insulator interface-to-electrode area ratio, greatly impacting charging dynamics due to interactions among electrolyte and conductor/insulator materials. The resulting charging current can overwhelm the current from redox chemistry. The device studied here features a 70-µm×100-µm electroactive window, hosts gold coplanar microband electrodes, and is insulated by SU-8, which serves as both overlayer and substrate. The overlayer defines the electroactive length and isolates the leads of the electrodes from the sample solution. Cyclic voltammetry in 0.10 M KCl yields unexpected, nonlinear dependence of current on scan rate, which can be explained with two empirical approaches. The first employs an equivalent circuit, involving leakage resistance and double-layer capacitance in parallel, to address both background processes and electrode imperfections as a function of scan rate. The second associates the enhanced current to a changing-chargeable area resulting from interface irregularities. Prior publications on alternative conductor-insulator materials are benchmarked in this study. The comparison of the materials shows that charging dynamics for devices made with SU-8 lead to more favorable electrochemical performance than for those constructed with glass, epoxy, and silicon nitride, and under certain circumstances, polyimide and Tefzel.
Steven H. Stradley et al 2024 J. Electrochem. Soc. 171 060501
Mg batteries are a promising alternative to Li-based chemistries due to the high abundance, low cost, and high volumetric capacity of Mg relative to Li. Mg is also less prone to dendritic plating morphologies, promising safer operation. Mg plating and stripping is highly efficient in chloride-containing electrolytes; however, chloride is incompatible with many candidate cathode materials. In this work, we capitalize on the positive effect of chloride by using transition metal chloride cathodes with a focus on low cost, Earth-abundant metals. Both soluble and sparingly soluble chlorides show capacity fade upon cycling. Active material dissolution and subsequent crossover to the Mg anode are the primary drivers of capacity fade in highly soluble metal chloride cathodes. We hypothesize that incomplete conversion and chemical reduction by the Grignard-based electrolyte are major promoters of capacity fade in sparingly soluble metal chlorides. Modifications to the electrolyte can improve capacity retention, suggesting that future work in this system may yield low cost, high retention Mg-MClx batteries.
Edmund J.F. Dickinson and Oliver Rodríguez 2024 J. Electrochem. Soc.
Theoretical models used to describe the catalyst layers (CLs) in polymer electrolyte membrane fuel cells (PEMFCs) are reviewed, with a focus on continuum treatments as incorporated in device-scale models used to predict and optimise PEMFC operating performance. Consideration is given to the mathematical relationships between CL design properties (Pt/C mass ratio, catalyst loading, ionomer loading), and physical properties. Relevant physical models are summarised, considering couplings between the CL and the phenomena of charge transfer, reactant mass transfer, hydrogen oxidation, and oxygen reduction electrode kinetics, heat transfer, and water balance. The relevance of thin film methods (through-thickness homogenisation) is compared to those resolving the macroscopic depth of the CL. Specific continuum homogenisations of microstructural models incorporating CL transport limitations in a continuum treatment, such as the agglomerate model, are discussed.
Miguel Angel Abrego Tello et al 2024 J. Electrochem. Soc.
Optimization of redox-cycling currents was performed by adjusting the height (sidewalls, h), width (w) ,and length (l) of band electrodes and their spacing (wgap) in coplanar arrays restricted to a small-electroactive window of 70 × 100 µm. These arrays can function in µL-volumes for chemical analysis (e.g., in vivo dopamine detection using probes). Experiments were conducted with an array of five electrodes (NE = 5), w = 4.3 µm, wgap = 3.7 µm, h = 0.150 µm, and l = 99.2 µm. Reasons for disparities between currents from experiments and approximate equations were determined by high-density mesh simulations and were found to arise from sluggish heterogeneous electron transfer kinetics and diffusion at electrode ends, edges, and heights. Ferricyanide, with its moderately slow kinetics, exhibits redox-cycling currents that fall below predictions by the equations as wgap decreases and diffusional flux outpaces reaction rates. Simulations aid investigations of various array designs, achievable through conventional photolithography, by decreasing w and wgap and increasing NE to fit within the electroactive window. A coplanar array, NE = 58, w = wgap = 0.6 µm, h = 0.150 µm and l = 100 µm, yielded ferricyanide sensitivities of 0.266, 0.259 nA·µM−1, enhancements of 8× and 9× over w = wgap = 4 µm, and projected dopamine limits of quantification of 139 nM, 171 nM at generator and collector electrodes, respectively
Rachel N. Gaines et al 2024 J. Electrochem. Soc.
Many studies have investigated the conversion of biomass derivatives to value-added products. However, the influence of different factors on the reaction outcomes of these often-complex systems is not well understood. Herein, a statistical design of experiments – specifically, response surface methodology – is applied to the glycerol electrooxidation reaction in a flow electrolyzer. Four operational variables (glycerol concentration, NaOH concentration, flow rate, and catalyst loading) were investigated for their effects on measurable responses of the electrochemical reaction: current density and Faradaic efficiency to a given product. Independent optimizations of current density and Faradaic efficiency, as well as simultaneous optimization of both, were investigated. Each optimization was evaluated using response surface coefficients to analyze sensitivity and simulated runs to visualize the parameter space. These evaluations revealed contradictions in operating conditions required to simultaneously maximize current density and Faradaic efficiency to C3 products glycerate and lactate, leading to low current densities and Faradaic efficiencies. However, simultaneously maximizing current density and Faradaic efficiency to C1 product formate led to high current densities and Faradaic efficiencies. These insights guide tuning GEOR production to maximize overall reactor performance. Furthermore, this study outlines a framework for experimental evaluation and optimization of other electrolysis chemistries.