Journal of The Electrochemical Society

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), LiNi_xCo_yAl_1−x−yO₂ (NCA), and LiNi_xMn_yCo_1−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.

Lithium-ion batteries can last many years but sometimes exhibit rapid, nonlinear degradation that severely limits battery lifetime. In this work, we review prior work on “knees” in lithium-ion battery aging trajectories. We first review definitions for knees and three classes of “internal state trajectories” (termed snowball, hidden, and threshold trajectories) that can cause a knee. We then discuss six knee “pathways”, including lithium plating, electrode saturation, resistance growth, electrolyte and additive depletion, percolation-limited connectivity, and mechanical deformation—some of which have internal state trajectories with signals that are electrochemically undetectable. We also identify key design and usage sensitivities for knees. Finally, we discuss challenges and opportunities for knee modeling and prediction. Our findings illustrate the complexity and subtlety of lithium-ion battery degradation and can aid both academic and industrial efforts to improve battery lifetime.

Capacity measurements and related quantities are the first layer of information acquired during testing of Li-ion cells. It is generally considered that elevated values of coulombic efficiency and capacity retention are absolute indicators of the existence of a stable solid electrolyte interphase (SEI). Here, we challenge this notion by analyzing how the effect of side reactions on cell capacity depends on the choice of electrodes. More specifically, we demonstrate that the extent of measurable capacity fade due to SEI growth is modulated by the shape of the voltage profile of the cathode and anode at the end of charge and discharge half-cycles. This shape-dependency creates a mismatch between SEI growth and cell capacity loss, which is relatively small for graphite anodes but sizable for silicon-containing electrodes. We illustrate this point by showing that, at the same coulombic efficiency and capacity retention, cells containing silicon-based materials could actually exhibit rates of SEI growth that are as much as ≥ 40% higher than graphite cells. The main implication of this behavior is that, for certain systems, capacity measurements may be an unreliable source of information about the extent of reactions at the SEI, allowing other consequences of these side reactions (such as electrolyte depletion) to proceed unchecked while the cell appears to be stable.

Single crystal Li[Ni_0.5Mn_0.3Co_0.2]O₂//graphite (NMC532) pouch cells with only sufficient graphite for operation to 3.80 V (rather than ≥4.2 V) were cycled with charging to either 3.65 V or 3.80 V to facilitate comparison with LiFePO₄//graphite (LFP) pouch cells on the grounds of similar maximum charging potential and similar negative electrode utilization. The NMC532 cells, when constructed with only sufficient graphite to be charged to 3.80 V, have an energy density that exceeds that of the LFP cells and a cycle-life that greatly exceeds that of the LFP cells at 40 °C, 55 °C and 70 °C. Excellent lifetime at high temperature is demonstrated with electrolytes that contain lithium bis(fluorosulfonyl)imide (LiFSI) salt, well beyond those provided by conventional LiPF₆ electrolytes. Ultra-high precision coulometry and electrochemical impedance spectroscopy are used to complement cycling results and investigate the reasons for the improved performance of the NMC cells. NMC cells, particularly those balanced and charged to 3.8 V, show better coulombic efficiency, less capacity fade and higher energy density compared to LFP cells and are projected to yield lifetimes approaching a century at 25 °C.

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.

Reduced-order battery lifetime models, which consist of algebraic expressions for various aging modes, are widely utilized for extrapolating degradation trends from accelerated aging tests to real-world aging scenarios. Identifying models with high accuracy and low uncertainty is crucial for ensuring that model extrapolations are believable, however, it is difficult to compose expressions that accurately predict multivariate data trends; a review of cycling degradation models from literature reveals a wide variety of functional relationships. Here, a machine-learning assisted model identification method is utilized to fit degradation in a stand-out LFP-Gr aging data set, with uncertainty quantified by bootstrap resampling. The model identified in this work results in approximately half the mean absolute error of a human expert model. Models are validated by converting to a state-equation form and comparing predictions against cells aging under varying loads. Parameter uncertainty is carried forward into an energy storage system simulation to estimate the impact of aging model uncertainty on system lifetime. The new model identification method used here reduces life-prediction uncertainty by more than a factor of three (86% ± 5% relative capacity at 10 years for human-expert model, 88.5% ± 1.5% for machine-learning assisted model), empowering more confident estimates of energy storage system lifetime.

This year, the battery industry celebrates the 25^th 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.

Recently, the field of CO₂ electrolysis has experienced rapid scientific and technological progress. This review focuses specifically on the electrochemical conversion of CO₂ into carbon monoxide (CO), an important “building block” for the chemicals industry. CO₂ electrolysis technologies offer potentially carbon-neutral routes for the production of specialty and commodity chemicals. Many different technologies are actively being pursued. Electrochemical CO₂ reduction from aqueous solutions stems from the success of alkaline and polymer electrolyte membrane electrolyzers for water electrolysis and uses performance metrics established within the field of aqueous electrochemistry. High-temperature CO₂ electrolysis systems rely heavily on experience gained from developing molten carbonate and solid oxide fuel cells, where device performance is evaluated using very different parameters, commonly employed in solid-state electrochemistry. In this review, state-of-the-art low-temperature, molten carbonate, and solid oxide electrolyzers for the production of CO are reviewed, followed by a direct comparison of the three technologies using some of the most common figures of merit from each field. Based on the comparison, high-temperature electrolysis of CO₂ in solid oxide electrolysis cells seems to be a particularly attractive method for electrochemical CO production, owing to its high efficiency and proven durability, even at commercially relevant current densities.

Mechanical degradation of electrode materials is an important failure mode in lithium-ion batteries. High-energy-density cathode materials like nickel-rich NMC (LiNi_xMn_yCo_zO₂) undergo significant anisotropic volume expansion during cycling that applies mechanical stress to the material. Computed tomography (CT) of cells can be used to image cell-level and electrode-level changes that result from long-term cycling, without the need for cell disassembly or destructive sampling. Previous work by our group has used synchrotron CT to show cathode thickness growth and depletion of liquid electrolyte after long-term (>2 years) cycling of polycrystalline NMC622/graphite cells. These phenomena were attributed to cathode microcracking, but direct evidence of this was not available at the time. In this study, we present in-situ, sub-micron CT of these unmodified pouch cells, providing new insights into the morphological changes occurring at the particle level. These results confirm that extensive microcracking and dramatic morphological changes are occurring in the cathode that were not previously observed. Combined with the cell-level and electrode-level scans presented previously, this study provides a complete, multi-scale picture of cathode microcracking and how its effects propagate throughout the cell.

Various modeling techniques are used to predict the capacity fade of Li-ion batteries. Algebraic reduced-order models, which are inherently interpretable and computationally fast, are ideal for use in battery controllers, technoeconomic models, and multi-objective optimizations. For Li-ion batteries with graphite anodes, solid-electrolyte-interphase (SEI) growth on the graphite surface dominates fade. This fade is often modeled using physically informed equations, such as square-root of time for predicting solvent-diffusion limited SEI growth, and Arrhenius and Tafel-like equations predicting the temperature and state-of-charge rate dependencies. In some cases, completely empirical relationships are proposed. However, statistical validation is rarely conducted to evaluate model optimality, and only a handful of possible models are usually investigated. This article demonstrates a novel procedure for automatically identifying reduced-order degradation models from millions of algorithmically generated equations via bi-level optimization and symbolic regression. Identified models are statistically validated using cross-validation, sensitivity analysis, and uncertainty quantification via bootstrapping. On a LiFePO₄/Graphite cell calendar aging data set, automatically identified models utilizing square-root, power law, stretched exponential, and sigmoidal functions result in greater accuracy and lower uncertainty than models identified by human experts, and demonstrate that previously known physical relationships can be empirically “rediscovered” using machine learning.

Low-cost, high performance proton exchange membrane fuel cells (PEMFCs) have been difficult to develop due to limited understanding of coupled processes in the cathode catalyst layer (CCL). Low-Pt-loaded PEMFCs suffer losses beyond those predicted solely due to reduced catalyst area. Although consensus links these losses to thin ionomer films in the CCL, a precise mechanistic explanation remains elusive. In this publication, we present a physically based PEMFC model with novel structure-property relationships for thin-film Nafion, validated against PEMFC data with low Pt loading. Results suggest that flooding exacerbates kinetic limitations in low-loaded PEMFCs, shifting the Faradaic current distribution. As current density increases, protons travel further into the CCL, resulting in higher Ohmic overpotentials. We also present a parametric study of CCL design parameters. We find that graded Pt and ionomer loadings reduce Ohmic losses and flooding, but individually do not provide significant improvements. However, a dual-graded CCL (i.e., graded Pt and ionomer) is predicted to significantly improve the maximum power density and limiting current compared to uniformly loaded CCLs. This work highlights the importance of accurate transport parameters for thin-film Nafion and provides a pathway to low-cost PEMFCs via precise control of CCL microstructures.

We provide a simple and inexpensive manual DC-offset method for extending the accepted voltage range of a battery cycler to negative voltages, without interfering with the actual operation of the electrochemical cell under the test or exceeding the voltage specs of the battery cycler instrument. We describe the working principles of the method and validate the proposed setup by operating short-term and long-term redox flow battery cycling using compositionally symmetric cell, with open-circuit voltage of zero, and full cell configurations. The method can be used to extend the capability of battery cycler instrumentation to operate any electrochemical cell that requires the polarity to be reversed during operation. Applications include cycling of other symmetric cells (e.g., Li-ion cells), implementation of polarity reversal steps for rejuvenation of electroactive species or rebalancing electrochemical cells, and alternating polarity for electrochemical synthesis.

The lithium stripping process generates vacancies, which may accumulate as voids and lead to uneven current distribution and dendrite growth in the following plating cycles. A stack pressure is typically required during stripping, but how to optimize the stack pressure is not clear. In this work, extremely lithiophilic Li/Li₂O and lithiophobic Li/LiF interfaces were used to reveal the combining effect of interface interaction and stack pressure induced lithium creep on the stripping critical current density (CCD). A multiscale simulation scheme with Density Functional Theory (DFT), kinetic Monte Carlo (KMC) simulations, and an analytical model was developed. The analytical model predicted lithiophobic interfaces require a higher stack pressure than lithiophilic interfaces to reach the same CCD. The KMC simulations also showed higher stack pressure is needed at lithiophobic interfaces to accelerate Li vacancy diffusion into the bulk and maintain a flat surface. This stack pressure needs to be high enough to alter the Li forward-and-backward hopping barriers at the interface. This multiscale simulation scheme illustrates the importance to include the chemical-mechanical effects during Li stripping morphology evolution. It can be used to design ideal interlayer coating materials to maintain a flat Li surface during cycling.

Electrochemical formation of Pd-Co alloy nanoparticles, PdCoNPs, onto a glassy carbon electrode, GCE, from their metallic precursors dissolved in the reline deep eutectic solvent, is reported for the first time. Potentiodynamic and potentiostatic studies indicated that PdCoNPs were electrodeposited by multiple nucleation of 3D bimetallic centers with mass transferred-controlled growth. Potentiostatic current density transients, j–t, were adequately fitted by a theoretical model that describes the kinetics of nucleation and diffusion-controlled growth of bimetallic phases and the number density of active sites for PdCoNPs nucleation, N₀, and their nucleation frequency, A, was determined as a function of the applied potential. SEM image recorded on the GCE electrodeposited with PdCoNPs showed that sizes and particle number density of these PdCoNPs depend on both the applied potential and the deposition time considered. At −0.42 V and 10 s the PdCoNPs had (30 ± 4) nm as average size and a particle number density of (4.23 ± 0.33) x10¹⁰ PdCoNPs cm^–2. EDS, XRD and XPS observations indicated the presence of Pd and Co. forming a PdCo alloy as zero and bivalenced oxidation states. GCE/PdCoNPs depict higher mass activity towards FAOR than GCE/PdNPs and other modified electrodes reported in the literature where the electrocatalysts were synthesized by different means.

The electrodeposition behavior of Al nanoplatelets, which are two-dimensional Al metal thin layer deposits, was investigated in five types of Lewis acidic 60–x–(40−x) [0 ≤ x ≤ 40] mol% AlCl₃–1-ethyl-3-methylimidazolium chloride ([C₂mim]Cl)–urea room-temperature melts. Al nanoplatelets were obtained in 60–10–30 and 60–0–40 mol% AlCl₃–[C₂mim]Cl–urea melts. X-ray diffraction measurements revealed that these Al nanoplatelets were oriented in the 111 direction. The formation of this anomalous Al nanoplatelets was analyzed using the operando digital microscope observation technique with our original air-tight electrochemical cell. We succeeded in video recording of the entire formation of Al nanoplatelets in the 60–0–40 mol% AlCl₃–[C₂mim]Cl–urea melt. Considering these results and electrode reactions involved in the Al deposition process, the electrodeposition behavior of the Al nanoplatelet formation could be attributed to the adequate quantities of free urea molecules generated during the electrode reaction and their specific adsorption onto the (111) Al crystal plane. The applied current density was an important key factor for the electrodeposition of the Al nanoplatelets in the AlCl₃–[C₂mim]Cl–urea melt. Al nanoplatelets were produced at low applied current densities smaller than −5.0 mA cm⁻². The Al nanoplatelets became larger at lower applied current densities.

A review of experimental author’s works proving the existence of the phenomenon of the electrochemical phase formation in metals and alloys via a supercooled liquid state stage is presented. The research findings focused on the electrochemical formation of metastable structures and intermediate phases, as well as on the structural features accompanying them. Electrochemical amorphous phase formation in metals and alloys, electrochemical quasicrystalline phase formation in metals, and electrochemical polymorphic phase formation in metals are discussed. Electrochemical hydrogen-related structure formation in metals, electrochemical high-defect crystalline phase formation in metals, and electrochemical texture-inhomogeneous structure formation in metals are considered. Electrochemical formation of intermediate phases in metals and alloys, electrochemical formation of eutectics in metallic alloys, and electrochemical formation of chemical compounds at the metallic cathode/electrodepositing metal interface are analyzed. Electrochemical reduction of ions in metals and alloys at a liquid cathode versus a solid chemically identical one, electrochemical phase formation of metals at chemically identical solid or liquid cathode, and electrochemical phase formation of alloys at chemically identical solid or liquid cathode are discussed.

Lithium plating on the negative electrode of Li-ion batteries remains as a great concern for durability, reliability and safety in operation under low temperatures and fast charging conditions. High-accuracy detection of Li-plating is critically needed for field operations. To detect the lithium plating is to track its multiphysics footprint since lithium plating often is a localized event while the driving force from chemical, electrical, thermal and mechanical origins could vary with time and locality which makes the detection and characterization challenging. Here, we summarize the multiphysical footprints of lithium plating and the corresponding state-of-the-art detection methods. By assessing and comparing these methods, the combination of capacity/voltage differential, R–Q mapping and Arrhenius outlier tracking could be promising and effective for battery diagnosis, prognosis and management. We analyze the origins of quantitative error in sample preparation, overly simplified assumption and dynamic evolution of the plated Li, and recommend the in situ and quantitative chemical analysis method, such as in situ NMR, EPR, X-ray and neutron. In addition, we propose the four conjectures on the capacity plunge, lithium plating, pore clogging, electrolyte drainage and rapid SEI growth, can be aligned and unified to one scenario basically triggered by lithium plating.

Epitaxial electrodeposition of Co, Cu and Ru is compared and contrasted. The seed layer for electrodeposition of all three metals was an epitaxial Ru(0001) film that was deposited at an elevated temperature onto a sapphire(0001) substrate and annealed post deposition. The epitaxial orientation relationship of the electrodeposited film and the seed layer, the epitaxial misfit strain, the role of symmetry of the seed layer versus the electrodepositing layer is addressed. In addition, the impact of underpotential deposition on film nucleation, and the growth morphology of the films is discussed. It is shown that epitaxial electrodeposition of metallic films to thicknesses of tens of nanometers is readily achievable.

This paper 1189 was presented during the 241st Meeting of the Electrochemical Society, May 29–June 2, 2022.

Increasing energy demand throughout the world produces great environmental issues, therefore, renewable and clean energy sources, such as tidal energy, wind energy, solar energy and geothermal energy, are desirable request. Meanwhile, developing a new critical energy storage technology to balance the instantaneous energy supply and demand of arranged electric energy is urgent. Rechargeable flow batteries are solutions for storing electricity in form of chemical energy, containing positive and negative electrodes reserved in two separate containers, which have the advantages of low self—discharge and independent scaling of power, therefore considered as promising energy storage technologies. Ionic liquids (ILs) have been widely studied and used in energy storage devices, such as lithium ion battery, for their unique prospective properties. Herein, the key role of ILs and their applications in supporting electrolytes, separators and additives in flow batteries are highlighted in this review. The approaches and challenges in developing ILs supported flow batteries are discussed, and a significative overview of the opportunities of ILs promote flow batteries are finally provided, which is expected to help achieving further improvements in flow batteries.

Pathogenic bacteria are a major public cause of foodborne and waterborne infections and are currently among the most serious public health threats. Conventional diagnostic techniques for bacteria, including plate culturing, the polymerase chain reaction, and the enzyme-linked immunosorbent assay, have many limitations, such as time consumption, high rates of false results, and complex instrument requirements. Aptamer-based electrochemical biosensors for bacteria address several of these issues and are promising for bacterial detection. This review discusses the current advances in electrochemical aptasensors for pathogenic bacteria with regard to the sensing performance with various specific aptamers for different types of bacteria. The advantages and disadvantages of these electrochemical aptasensors were investigated with the aim of promoting the development and commercialization of electrochemical aptasensors for the point-of-care detection of bacteria.

Lithium (Li) metal anodes are essential for developing next-generation high-energy-density batteries. However, Li dendrite/whisker formation caused short-circuiting issue and short cycle life have prevented lithium metal from being viably used in rechargeable batteries. Numerous works have been done to study how to regulate the Li growth in electrochemical cycling by using external stacking forces. While it is widely agreed that stack pressure positively affects the lithium plating/stripping process, the optimized pressure range provided by different works varies greatly because of the difference in the pressure control setup. In this work, a pressure control apparatus is designed for Li metal batteries with liquid and solid-state electrolytes (SSE). With considerations of minimizing cell to cell variation, a reusable split cell and pressure load cell are made for testing electrochemical cells with high precision pressure control. The capability of the designed setup is demonstrated by studying the pressure effect on the Li plating/stripping process.

Ternary metal halides A₃MX₆, (A = Li⁺, Na⁺; M = trivalent metal; X = halide) are a promising family of solid electrolytes for potential applications in all-solid-state batteries. Recent research efforts have demonstrated that chemical substitution at all three sites is an effective strategy to controlling battery-relevant material properties. The A₃MX₆ family exhibits a wide breadth of structure and anion sublattice types, making it worthwhile to comprehend how chemical substitutions manifest desirable functional properties including ion transport, electrochemical stability, and environmental tolerance. Yet, a cohesive understanding of the materials design principles for these substitutions have not yet been developed. Here, we bring together prior literature focused on chemical substitutions in the A₃MX₆ ternary metal halide solid electrolytes. Using materials chemistry perspectives and principles, we aim to provide insights into the relationships between crystal structure, choice of substituting ions and the extent of substitutions, ionic conductivity, and electrochemical stability. We further present targeted approaches to future substitution studies to enable transformative advances in A₃MX₆ solid electrolytes and all-solid-state batteries.

Active cathode material and graphite anode material are routinely mixed with conductor and binder to improve the electric conductivity and mechanical stability of electrodes. Despite its benefits, this carbon binder domain (CBD) impedes ionic transport and reduces the active surface area, thus impacting the battery performance. We consider a composite spherical particle, whose active-material core is coated with CBD, and its homogeneous counterpart, for which we derived equivalent electrical conductivity, ionic diffusivity, and reaction parameters in the Butler-Volmer equation. These equivalent characteristics are defined to ensure that the same mass and charge enter the composite and homogenized spheres. They are expressed in terms of the volume fraction of the active material and transport properties of the active material and CBD. In general, the equivalent effective diffusion coefficient and reaction parameters are time-dependent and exhibit two-stage behavior characterized by the reaction delay time. At later times, these characteristics are time-independent and given explicitly by closed-form formulae. The simplicity of these expressions facilitates their use in single- and multi-particle representations of Li-ion and Li-metal batteries.

A model for impedance of a PEM fuel cell cathode taking into account oxygen transport in the cathode catalyst layer (CCL), gas–diffusion layer (GDL) and in channel is solved analytically. A formula for the cathode impedance is valid for the cell current densities below 100 mA cm⁻² and air flow stoichiometries exceeding 10. Least–squares fitting of experimental spectrum using the analytical result takes about 5 s on a standard PC. Fitting returns Tafel slope of the oxygen reduction reaction, double layer capacitance, CCL proton conductivity and oxygen diffusivities of the CCL and GDL. Analytical impedance can be coded as a user–defined function for a standard spectra fitting software supplied with EIS–meters.

While Li−carbon monofluoride (CF_x) is the current energy leader among primary batteries, the technology is maturing, motivating further fundamental study of Li battery chemistry based on C−F redox. This study examines the possibility to conduct multi-electron carbon reduction using a candidate class of liquid CF_x analogues, perfluoroalkyl iodides (C_nF_2n+1I, with F/C ratios of x > 2), in supporting electrolyte as catholytes for Li cells. The large, polarizable iodine supports electrochemical reduction with concerted F⁻ ligand expulsion, forming lithium fluoride (LiF) as the main solid discharge product. Under initial conditions (1 M reactant and 0.3 mA cm⁻² in dimethylsulfoxide), only limited defluorination (1.5 e⁻/molecule) is accessed. Governing factors for C−F bond redox are further investigated, including reactant concentration, discharge rate, temperature, and solvent properties (e.g. catholyte viscosity). A maximum of 8 e⁻/C₆F₁₃I, or 8/₁₃ available F, is accessible in the voltage range 2.8−1.9 V vs Li/Li⁺ with low reactant concentrations (0.1 M) and rates (20 μA cm⁻²). The data indicate that multiple handles exist to tailor extended C−F bond activation in these reactants. However, premature reaction termination caused by deactivation of intermediates, which is particularly exacerbated at higher concentrations and/or rates, is likely to be a persistent challenge for practical applications.

Desaturation of polymer electrolyte fuel cells (PEFCs) is a critical operation step for providing cell cold-start performance by minimizing residual water in the gas diffusion layers (GDLs), flow field (FF) channels, catalyst layers, and membrane after cell shutdown. In this work, transient liquid water removal processes in the FF channels and GDLs are visualized and quantified by subsecond in situ X-ray tomographic microscopy (XTM), and correlated to high frequency resistance (HFR) measurements of the cell. Time-resolved desaturation profiles are analyzed for three commercially available GDLs with representative substrate dimensions. The influence of different substrates on the GDL desaturation behavior is investigated with a cluster connectivity analysis and saturation-dependent effective diffusivities are determined by numerical simulations. Characteristic drying phases are identified for the HFR curves and confirmed with XTM imaging results, providing fundamental understanding of the desaturation dynamics in the PEFCs and enabling the optimization of GDL substrates and gas purge protocols accordingly.

The use of thinner membranes in polymer electrolyte water electrolysis increases the likelihood of forming an explosive H₂/O₂ mixture in the anode stream. Doping Pt nanoparticles into a Nafion membrane as recombination catalyst effectively lowers the hydrogen crossover. Here, we propose the additional co-doping of cerium-zirconium oxide as radical scavenger to mitigate membrane degradation. Our results show over 4-fold reduction of anodic hydrogen content compared to a non-doped membrane, and a nearly 3-fold decrease of fluoride release rate compared to the membrane with only Pt-doping at 80°C and differential pressure (p_c = 3 bar, p_a = 1 bar) operation.

The ionomer film and its transport resistance for oxygen are important aspects for polymer exchange membrane fuel cells (PEMFC) performance. Ionomer film sub-models are therefore frequently used in PEMFC modeling to account for this effect. Mathematically these are expressed by a non-linear equation for the oxygen concentration, which depending on the reaction order cannot be solved analytically. Typically, a numerical solution of this equation, e.g., using the Newton-method is needed. Here, we derive a highly accurate approximate analytical solution for the ionomer film model. This enables faster computation, which is particularly important for computationally demanding higher dimensional PEMFC.

Low-cost, high performance proton exchange membrane fuel cells (PEMFCs) have been difficult to develop due to limited understanding of coupled processes in the cathode catalyst layer (CCL). Low-Pt-loaded PEMFCs suffer losses beyond those predicted solely due to reduced catalyst area. Although consensus links these losses to thin ionomer films in the CCL, a precise mechanistic explanation remains elusive. In this publication, we present a physically based PEMFC model with novel structure-property relationships for thin-film Nafion, validated against PEMFC data with low Pt loading. Results suggest that flooding exacerbates kinetic limitations in low-loaded PEMFCs, shifting the Faradaic current distribution. As current density increases, protons travel further into the CCL, resulting in higher Ohmic overpotentials. We also present a parametric study of CCL design parameters. We find that graded Pt and ionomer loadings reduce Ohmic losses and flooding, but individually do not provide significant improvements. However, a dual-graded CCL (i.e., graded Pt and ionomer) is predicted to significantly improve the maximum power density and limiting current compared to uniformly loaded CCLs. This work highlights the importance of accurate transport parameters for thin-film Nafion and provides a pathway to low-cost PEMFCs via precise control of CCL microstructures.

We provide a simple and inexpensive manual DC-offset method for extending the accepted voltage range of a battery cycler to negative voltages, without interfering with the actual operation of the electrochemical cell under the test or exceeding the voltage specs of the battery cycler instrument. We describe the working principles of the method and validate the proposed setup by operating short-term and long-term redox flow battery cycling using compositionally symmetric cell, with open-circuit voltage of zero, and full cell configurations. The method can be used to extend the capability of battery cycler instrumentation to operate any electrochemical cell that requires the polarity to be reversed during operation. Applications include cycling of other symmetric cells (e.g., Li-ion cells), implementation of polarity reversal steps for rejuvenation of electroactive species or rebalancing electrochemical cells, and alternating polarity for electrochemical synthesis.

The lithium stripping process generates vacancies, which may accumulate as voids and lead to uneven current distribution and dendrite growth in the following plating cycles. A stack pressure is typically required during stripping, but how to optimize the stack pressure is not clear. In this work, extremely lithiophilic Li/Li₂O and lithiophobic Li/LiF interfaces were used to reveal the combining effect of interface interaction and stack pressure induced lithium creep on the stripping critical current density (CCD). A multiscale simulation scheme with Density Functional Theory (DFT), kinetic Monte Carlo (KMC) simulations, and an analytical model was developed. The analytical model predicted lithiophobic interfaces require a higher stack pressure than lithiophilic interfaces to reach the same CCD. The KMC simulations also showed higher stack pressure is needed at lithiophobic interfaces to accelerate Li vacancy diffusion into the bulk and maintain a flat surface. This stack pressure needs to be high enough to alter the Li forward-and-backward hopping barriers at the interface. This multiscale simulation scheme illustrates the importance to include the chemical-mechanical effects during Li stripping morphology evolution. It can be used to design ideal interlayer coating materials to maintain a flat Li surface during cycling.

Strongyloidiasis is an intestinal helminth infection caused by Strongyloides stercoralis. Early detection of this infection in immunocompromised patients is crucial to avoid severe complications and fatality. Herein, we present the potential application of electrodeposited AuNP-film in developing a label-free electrochemical immunosensor for strongyloidiasis using our synthesized monoclonal antibody. Layer-upon-layer attachment of Strongyloides monoclonal recombinant antibody protein (rMAb23) onto AuNP-film was constructed, utilizing a thiol linker via a self-assembly monolayer (SAM) technique. The modified electrode was utilized to detect S. stercoralis recombinant NIE (rNIE) protein. Each successful modification step was tested in a 10 mM [Fe(CN)6]3-/4- redox couple solution utilizing cyclic voltammetric (CV) and electrochemical impedance spectroscopic (EIS) techniques. The developed immunosensor required 20 minutes of incubation with an rNIE solution. Specificity study showed no cross-reaction with three other helminth recombinant proteins. Utilizing EIS measurements for a concentration series of rNIE protein in phosphate-buffered saline, ranging from 1 µg/mL to 10 µg/mL, we obtained a detection limit of 0.182 µg/mL. The electrochemical immunosensor was also successfully used to analyze serum samples of individuals with strongyloidiasis and healthy people. The results indicate that the immunosensor might offer an excellent diagnostic capability and a rapid and sensitive antigen detection of strongyloidiasis.

For galvanostatic metal electrodeposition under diffusion-limited conditions, the Sand’s equation provides the time at which the concentration of the cation being reduced reaches zero at the electrode-electrolyte interface. Such a condition causes amplification of the electrodeposit roughness and triggers dendritic growth during electrodeposition. In this perspective article, the question of whether the classical Sand equation reliably predicts the onset of morphological evolution in lithium electrodeposition is addressed and answered in the negative. A comparison of Sand’s times () with experimentally observed lithium dendrite onset times reveals significant discrepancies over a wide range of Li electrodeposition current densities. Specifically, it is shown that morphology evolution in lithium electrodeposition from organic liquid electrolytes commences at time-scales that are at least 1–2 orders of magnitude lower than Sand’s time. To explain this discrepancy, we present a modified Sand’s approach in which transient multi-phase diffusion through the liquid electrolyte as well as through the solid-electrolyte-interphase (SEI) layer is considered. The proposed approach leads to increased accuracy in the prediction of the morphology onset time in lithium electrodeposition. We hope that this perspective helps researchers circumvent the erroneous application of the classical Sand’s equation for lithium electrodeposition, and stimulates experimental and theoretical research into the complex multi-phase transport processes relevant to morphology evolution in lithium electrodeposition.

Lithium-ion batteries will contribute to the energy storage needs that will enable the widespread implementation of renewable energy alternatives to fossil fuels. Here the role of cell lifetime in achieving sufficient battery deployment to satisfy these needs is discussed in the context of battery manufacturing limitations and the necessity of developing cells with lifetimes beyond those found in contemporary cells. A cell design, and usage scheme reliant on this design, that demonstrates vastly improved lifetime capability is presented, including usage beyond traditional definitions of end-of-life. Specifically, Li[Ni_0.5Mn_0.3Co_0.2]O₂//graphite cells, a technology that is neither exotic nor innovative, can be built to operate to a low charge voltage limit (3.8 V) and hence contain excess positive electrode capacity. Charging to low voltage naturally reduces the rate of capacity loss and the excess positive electrode capacity functions as a lithium reservoir that can be accessed to counteract capacity loss, both of which combine to yield an incredible lifetime. Specifically, the use of the positive electrode lithium reservoir projects to extend high temperature lifetime at 70 °C by an additional factor of between 1.5 and 10 compared to the lifetime achieved by conventional cycling without accessing this reservoir.

In water electrolyzers, polymer electrolyte membranes (PEMs) such as Nafion can accumulate cations stemming from salt impurities in the water supply, which leads to severe cell voltage increases. This combined experimental and computational study discusses the influence of sodium ion poisoning on the ionic conductivity of Nafion membranes and the ion transport in a thereon based water electrolysis cell. Conductivities of Nafion and aqueous solutions with the same amount of dissolved cations are measured with impedance spectroscopy and compared with respect to Nafion’s microstructure. The dynamic behavior of the voltage of a water electrolysis cell is characterized as a function of the sodium ion content and current density, showing the differences of the ion transport at alternating and direct currents. These experimental results are elucidated with a physical ion transport model for sodium ion poisoned Nafion membranes, which describes a proton depletion and sodium ion accumulation at the cathode. During proton depletion, the cathodic hydrogen evolution is maintained by the water reduction that forms hydroxide ions. Together with sodium ions from the membrane, the formed hydroxide ions can diffuse pairwise into the water supply, so that the membrane’s sodium ions can be at least partly be replaced with anodically formed protons.