Journal of The Electrochemical Society

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.

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.

Lithium iron phosphate (LFP) battery cells are ubiquitous in electric vehicles and stationary energy storage because they are cheap and have a long lifetime. This work compares LFP/graphite pouch cells undergoing charge-discharge cycles over five state of charge (SOC) windows (0%–25%, 0%–60%, 0%–80%, 0%–100%, and 75%–100%). Cycling LFP cells across a lower average SOC results in less capacity fade than cycling across a higher average SOC, regardless of depth of discharge. The primary capacity fade mechanism is lithium inventory loss due to: lithiated graphite reactivity with electrolyte, which increases incrementally with SOC, and lithium alkoxide species causing iron dissolution and deposition on the negative electrode at high SOC which further accelerates lithium inventory loss. Our results show that even low voltage LFP systems (3.65 V) have a tradeoff between average SOC and lifetime. Operating LFP cells at lower average SOC can extend their lifetime substantially in both EV and grid storage applications.

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.

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.

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-SiO_x 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.

The Solid-Electrolyte-Interphase (SEI) model for non-aqueous alkali-metal batteries constitutes a paradigm change in the understanding of lithium batteries and has thus enabled the development of safer, durable, higher-power and lower-cost lithium batteries for portable and EV applications. Prior to the publication of the SEI model (1979), researchers used the Butler-Volmer equation, in which a direct electron transfer from the electrode to lithium cations in the solution is assumed. The SEI model proved that this is a mistaken concept and that, in practice, the transfer of electrons from the electrode to the solution in a lithium battery, must be prevented, since it will result in fast self-discharge of the active materials and poor battery performance. This model provides [E. Peled, in "Lithium Batteries," J.P. Gabano (ed), Academic Press, (1983), E. Peled, J. Electrochem. Soc., 126, 2047 (1979).] new equations for: electrode kinetics (i_o and b), anode corrosion, SEI resistivity and growth rate and irreversible capacity loss of lithium-ion batteries. This model became a cornerstone in the science and technology of lithium batteries. This paper reviews the past, present and the future of SEI batteries.

Layered LiNi_xMn_yCo_zO₂ (NMC) is a widely used class of cathode materials with LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) being the most common representative. However, Ni-rich NMCs are more and more in the focus of current research due to their higher specific capacity and energy. In this work we will compare LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111), LiNi_0.6Mn_0.2Co_0.2O₂ (NMC622), and LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) with respect to their cycling stability in NMC-graphite full-cells at different end-of-charge potentials. It will be shown that stable cycling is possible up to 4.4 V for NMC111 and NMC622 and only up to 4.0 V for NMC811. At higher potentials, significant capacity fading was observed, which was traced back to an increase in the polarization of the NMC electrode, contrary to the nearly constant polarization of the graphite electrode. Furthermore, we show that the increase in the polarization occurs when the NMC materials are cycled up to a high-voltage feature in the dq/dV plot, which occurs at ∼4.7 V vs. Li/Li⁺ for NMC111 and NMC622 and at ∼4.3 V vs. Li/Li⁺ for NMC811. For the latter material, this feature corresponds to the H2 → H3 phase transition. Contrary to the common understanding that the electrochemical oxidation of carbonate electrolytes causes the CO₂ and CO evolution at potentials above 4.7 V vs. Li/Li⁺, we believe that the observed CO₂ and CO are mainly due to the chemical reaction of reactive lattice oxygen with the electrolyte. This hypothesis is based on gas analysis using On-line Electrochemical Mass Spectrometry (OEMS), by which we prove that all three materials release oxygen from the particle surface and that the oxygen evolution coincides with the onset of CO₂ and CO evolution. Interestingly, the onsets of oxygen evolution for the different NMCs correlate well with the high-voltage redox feature at ∼4.7 V vs. Li/Li⁺ for NMC111 and NMC622 as well as at ∼4.3 V vs. Li/Li⁺ for NMC811. To support this hypothesis, we show that no CO₂ or CO is evolved for the LiNi_0.43Mn_1.57O₄ (LNMO) spinel up to 5 V vs. Li/Li⁺, consistent with the absence of oxygen release. Lastly, we demonstrate by the use of ¹³C labeled conductive carbon that it is the electrolyte rather than the conductive carbon which is oxidized by the released lattice oxygen. Taking these findings into consideration, a mechanism is proposed for the reaction of released lattice oxygen with ethylene carbonate yielding CO₂, CO, and H₂O.

The development of new positive electrode materials is on route to increase the energy density of lithium-ion batteries (LIBs) for electric vehicle and grid storage applications. The performance of new materials is typically evaluated using hand-made half coin cells with the new material as the positive electrode and a piece of lithium foil for the negative. Whereas half coin cells are easy to make and can give reproducible data, they can fail to accurately predict how a material would perform in a full cell. The present work develops methods to prepare full coin cells, using graphite as the negative electrode material. Detailed instructions are provided to enable researchers to prepare their own high quality full coin cells with good reproducibility between cells. The precision of the hand-made full coin cells is compared with and found to approach the quality of machine-made, commercially produced full cells.

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.

Many modern, commercially relevant Li-ion batteries use insertion materials that exhibit lithiation-induced phase change (e.g. lithium iron phosphate, LFP). However, the standard physics-based model—the Newman model—uses a microscopic description of particle lithiation (based on diffusion) that is incapable of describing phase-change behavior and the physical origins of the voltage hysteresis exhibited by such phase-change electrodes. In this work a simple and rational model of hysteretic lithiation (in an electrode comprised of an ensemble of phase-change nanoparticles) is derived using an approach based on minimisation of the Gibbs energy. Voltage hysteresis arises naturally as a prediction of the model. Initially, equations that model the phase-change dynamics in a single particle of active material are considered. These are generalised to a model, termed the composite phase-change model, of a coupled ensemble of particles in a thin electrode. The composite phase-change model is then incorporated into the framework of a classical Newman model, allowing for the inclusion of transport effects in the electrolyte and electrode conductivity. The resulting modified Newman model is used to predict voltage hysteresis in a graphite/LFP cell. A simulation tool that allows readers to replicate, and extend, the results presented here is provided via the DandeLiion simulator at www.dandeliion.com.

Parallel connections of lithium-ion cells in battery systems lead to current distributions between the cells, which impacts fast charging capabilities. This study examines the influence of interconnection resistance, format, electrode design, cell-to-cell variations, and temperature differences on system inhomogeneity and identifies anode potential safety margins that ensure safe charging without lithium plating. To this end, a physico-chemical parameterization of the Molicel INR21700-P45B is presented. An optimized fast-charging profile enables charging from 10%–80% cell capacity in under 10 minutes. The experimental application of the fast-charging profile yielded a result of over 300 equivalent full cycles before reaching 90% state of health. Furthermore, the cell model is scaled to different parallel-connected systems in an extensive simulation study. The interconnection resistance, and analogously the internal-to-interconnection resistance ratio, was found to be the primary factor influencing inhomogeneity in high parallel configurations, whereas cell-to-cell resistance variations are the most significant determinant in low parallel configurations. Variations in cooling were found to be more impactful than initial temperature disparities.

Electrochemical impedance spectroscopy is a non-destructive technique that provides useful information on the status of a lithium-ion battery, including its state-of-health. However, conventional harmonic perturbation methods are too sophisticated for applications in operating environments. This study systematically investigates the system requirements for reconstructing impedance via the Fourier transform of voltage and current signals obtained upon current interruption. Using a calibrated equivalent circuit model, key parameters such as the minimum sampling interval $\unicode{x02206}{t}_{s}$, the initial time collected during relaxation ${t}_{i}$, and the current removal duration ${t}_{f}$, are correlated with the frequency range [${{f}_{\min },\,f}_{\max }$] in which impedance is reconstructed within 1% error. A Gaussian window, whose width is modulated with frequency, effectively mitigates noise up to 0.1 mV. The resulting general relations, ${f}_{\min }\,=\,4/{t}_{f}$ and ${f}_{\max }\,=\,0.07/\unicode{x02206}{t}_{s}$ (or ${f}_{\max }\,=\,0.07/{t}_{i}$ for ${t}_{i}\gt \unicode{x02206}{t}_{s}$), are valid within 10⁻²–10⁴ Hz, that is sufficient to cover ohmic, polarisation, and diffusion impedance features. Experimental tests on a commercial lithium-ion cell corroborate the generality of these system requirements. With a sampling interval of 70 μs for ${f}_{\max }\,=\,{10}^{3}$ Hz and a waiting time of 40 s for ${f}_{\min }\,=\,{10}^{-1}$ Hz, the current interruption technique appears compatible with commercial instrumentation, making it potentially applicable for real-time impedance monitoring in operating lithium-ion batteries.

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Highlights

• Modelling provides requirements for impedance reconstruction via current interruption

• A Gaussian window must be introduced in Fourier transform to damp measurement noise

• Sampling at 70 μs for 40 s enables reconstruction at 1% accuracy within 10⁻¹–10³ Hz

• The technique may be integrated for on-line state-of-health evaluation of batteries

The dissolution of transition metals (TM) from the cathode and their subsequent deposition on the anode represent significant degradation mechanisms in lithium-ion batteries, particularly as the industry seeks to transition towards more sustainable and cost-efficient materials. In this work, the impacts of Mn, Fe, Ni, and Co depositions on the lithiated graphite anode were investigated using pouch storage experiments to simulate the migration-deposition process and compare it to electrodes from real cells. The morphology, chemical distribution, and oxidation states of deposited TMs were investigated by scanning electron microscopy, X-ray absorption spectroscopy, and scanning transmission X-ray microscopy. X-ray diffraction and half-cell studies for post-storage electrodes determined the lithium loss and impedance growth due to TM deposition. The impact of each TM on the lithiated graphite was found to be significantly different. Deposited Mn and Fe were fully metallic, preferred to accumulate on electrode surface, and caused severe delithiation of the graphite, while Ni and Co deposition were rather harmless. The results obtained from simulated TM-containing graphite electrodes closely corresponded with those extracted from cycled cells. This alignment enhances our understanding of the behavior of dissolved TM and paves the way for solutions aimed at mitigating capacity fade in commercial lithium-ion batteries.

Steam oxidation behavior of four general-purpose stainless steels, SUS430, SUS430LX, SUS430J1L, and SUS445J1, under humidified H₂ was investigated for application in solid oxide fuel cells (SOFCs). A Cr-rich surface oxide layer, preliminarily formed via pre-oxidation, effectively mitigated steam oxidation and suppressed elemental diffusion and oxide growth. After pre-oxidation at 900 °C for 2 h in air, the oxidation rate was less dependent on the gas composition, which was varied from 10%H₂O–90%H₂ to 50%H₂O–50%H₂, whereas it was strongly dependent on temperature. The structure of the surface oxide layer and direction of oxide growth differed depending on the alloy composition. The oxidation rate of SUS430J1L was similar to that of ZMG232G10 and relatively lower than those of three other stainless steels The Cr-rich oxide layer contained few defects, and its structure suppressed the diffusion of metal ions. Although a Si-rich oxide layer grew on the alloy side during the durability test performed at 727 °C for 1500 h, it had a lesser impact on the area specific resistance than that in SUS430. The microstructure of the Si-rich oxide layer, which featured other elements such as Cr, Mn, and Fe, maintained the electrical conduction path.

Electrolysis serves as an effective technique for metal preparation, with the electrolytic cell being the fundamental apparatus. The design of the electrolytic cell significantly influences the mass transfer process. Therefore, it is crucial to create an appropriate structure for the electrolytic cell to minimize energy consumption during electrolysis. Given the unique characteristics of the metals involved, the configurations of electrolytic cells vary accordingly. This article examines primary metals produced through electrolysis, such as aluminum and alkali metals, and discusses advancements in research and design principles related to electrolytic cell structures. It also compares various types of electrolytic cells and suggests strategies for structural optimization. Additionally, the role of simulation in the design of electrolytic cells is emphasized. Finally, the article addresses the challenges encountered by electrolytic cells in industrial settings and offers recommendations for structural improvements.

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The opioid crisis has emerged as a critical public health issue, characterized by the widespread misuse, addiction, and adverse societal impacts of opioid substances. Addressing this multifaceted crisis demands innovative approaches, and the field of forensic science has increasingly turned to electrochemical methods as a powerful tool in the battle against opioids. Here we provide an overview of the significant role played by electrochemical techniques in the detection, analysis, and monitoring of opioids. By harnessing the capabilities of electrochemical sensors, nanomaterial-based platforms, and microfluidic devices, forensic scientists have achieved breakthroughs in opioid detection, offering higher sensitivity, specificity, and rapidity than traditional methods. We explore the latest advancements and applications of electrochemical techniques in forensic opioid analysis, highlighting their potential to revolutionize not only the investigative process but also the management of opioid-related crises. With an emphasis on real-time, on-site, and non-invasive detection, we underscore the importance of electrochemical techniques as a vital component in combating the opioid epidemic and contributing to public safety and well-being.

For many years since Gurney introduced quantum mechanics to electrochemistry, models and calculations assumed bonding and other properties at the electrochemical interface may be calculated with adequate accuracy at the potential of zero charge (PZC) and that the effect of potential lies solely in controlling the energy of the electron involved in the transfer, which comes from or goes to an external energy level. The energy of the electron is assigned to the Fermi energy, E_f, of the electrode for the particular potential being modeled. This is done in the Butler-Volmer theory as well as in several quantum mechanical modeling procedures that are introduced here. Though the PZC in fact changes as the identity, amount, and structures of molecules chemically bonded to the electrode are varied during calculations using these models, there is no control of the electrode potential in the calculations. The past two decades have seen the development of computer codes that can incorporate controlled incremental surface charging with polarizable electrolyte models that compensate it, resulting in zero net interface charge. Calculations using these codes provide accurate predictions of the potential-dependent energies of reactants and products, reversible potentials, and electron transfer activation energies.

Due to the advantages of environmental friendliness and high energy density, fuel cells have broad application prospects in many fields, such as automobiles, ships, aerospace, etc However, commercial applications of fuel cells also face challenges of durability and reliability, especially in shock and vibration environments. Here, the electrochemical and mechanical behaviours of fuel cells under vibration environments are described, and the effects of vibration and shock conditions on the electrochemical, mechanical, water and gas transport, and durability performance of fuel cells are systematically reviewed, involving the variation laws of assembly torque, sealing, relative slippage between cells, water and gas transport, electrical resistance, and membrane electrodes. In addition, the methods that can mitigate the effects of vibration on fuel cells in existing studies are summarised. Finally, discussions and perspectives on the research methods of fuel cell performance under vibration are presented. It is hoped that the review can provide a systematic comprehension and direction for vibration protection of fuel cells.

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Highlights

• Vibration and shock have a negative impact on fuel cell performance in most cases.

• Fuel cell performance degradation is affected by the coupling of multiple phenomena.

• Specific vibration levels improve cell performance by facilitating water management.

• Monitoring and vibration isolation/damping enable vibration protection of fuel cells.

Renewable energy systems will need large-scale energy storage to ensure reliability and provide power when and where it is needed. Even though lithium-ion batteries are increasingly used for large-scale storage, their costs and competition in terms of materials needed for electric vehicles are driving the need for alternative batteries for stationary energy storage systems. Molten sodium-ion batteries that operate at intermediate temperatures, approximately 150 °C or less, offer an abundant and cost-effective solution to our energy storage issues. This review paper highlights the materials, enhancements, and performance of molten Na–ion batteries that operate at temperatures at or below 150 °C for use in energy storage systems as well as an outlook on future improvements for this energy storage system.

This study explores chloride molten salt electrolysis (CMSE) as a promising route for energy-efficient iron metal (Fe) production. Moderate temperature (500 °C) LiCl-KCl molten salts offer excellent thermodynamic stability, high ionic conductivity and diffusivity, and high solubility for FeCl₃, thereby enabling efficient Fe metal extraction at high electrowinning rates. Here, we demonstrate the two essential steps for converting taconite ore into Fe metal. First, Fe₂O₃ from taconite pellets was selectively leached in HCl yielding a high-purity FeCl₃ aqueous solution, while the gangue components settled at the bottom. Then, anhydrous FeCl₃ was electrolyzed in a LiCl-KCl eutectic molten salt at 500 °C at high current density (1 A cm⁻²) and at high Coulombic efficiency (>85%). Analysis of the electrowon Fe deposits revealed dendritic structures with purity of >99 wt%, which could be further improved to nearly 100 wt% through arc re-melting. CMSE offers low specific energy consumption (3.7 kWhr kg⁻¹), competitive with H₂-DRI and other electrolytic approaches being pursued globally. Our findings underscore the potential of CMSE as an energy-efficient route for electrosynthesis of Fe metal.

Cathode-electrolyte interphase (CEI) is critical for inhibiting the cathode degradation to maintain cell life. However, the evolution of the CEI is still unclear due to its complex and slow dynamic process. Here we used scanning electrochemical microscopy (SECM) for in situ investigation of CEI formation process on LiFePO₄ cathode. Feedback images and probe scan curves showed a heterogeneous passivation that was gently generated on the LiFePO₄ particles during both charging and discharging. Besides, a LiFePO₄ composited electrode was also used to investigate the CEI formation to simulate the condition of real battery system. The composited cathode does not show obvious CEI formation within first two cycles. The SECM results between the pristine LiFePO₄ particles and the composited LiFePO₄ indicated the dynamic accumulation of CEI, which is influenced by the ability to charge transfer kinetics of cathode materials. This approach provided a feasible consideration for the connections between the dynamic evolution of the CEI and changes in charge transfer capability of cathode during cycling.

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Highlights

• In-situ investigation of cathode-electrolyte interphase formation.

• The evolution of native active material and composite slurry were compared.

• The electrochemical activity change upon cathode cycling are analysed in situ.

• The influence of the charge transfer capability upon CEI generation is revealed.

We revisit the classical derivation of the Butler-Volmer equation to include the effect of the electrode metal. If the metal is replaced by one with a different work function, keeping other conditions in the electrode constant, the chemical potential of electrons ${\mu }_{e}$ and the Galvani potential $\varphi$ change in a complementary manner. Changes in ${\mu }_{e}$ and $\varphi$ each impact the free energies of activation of the forward and backward electron transfer reactions, so we modify the classical expressions which relate them to applied voltage E by including also the effect of ${\mu }_{e}.$ Inserting these expressions in an Eyring-Polyani or Arrhenius type equation in the traditional way, we obtain a modified Butler-Volmer equation which expresses current density as a function of both $E$ and ${\rm{\Delta }}{\mu }_{e}.$ The exchange current density ${j}_{0}$ appears as an exponential function of ${\rm{\Delta }}{\mu }_{e}.$ For the work function ${\rm{\Phi }}$ of the metal, the approximation ${\rm{\Delta }}{\mu }_{e}\approx -F{\rm{\Delta }}{\rm{\Phi }}$ yields a linear relationship between $\mathrm{ln}{j}_{0}$ and ${\rm{\Phi }}.$ The linear increase in $\mathrm{ln}{j}_{0}$ with ${\rm{\Phi }}$ has long been reported. We show two experimental examples: the aqueous Fe²⁺/Fe³⁺ couple with positive slope and the hydrogen evolution reaction (HER) with parallel lines for the d and sp metals, both with positive slopes.

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The kinetics of composite cathodes for solid-state batteries (SSBs) relies heavily on their microstructure. Spatial distribution of the different phases, porosity, interface areas, and tortuosity factors are important descriptors that need accurate quantification for models to predict the electrochemistry and mechanics of SSBs. In this study, high-resolution focused ion beam-scanning electron microscopy tomography was used to investigate the microstructure of cathodes composed of a nickel-rich cathode active material (NCM) and a thiophosphate-based inorganic solid electrolyte (ISE). The influence of the ISE particle size on the microstructure of the cathode was visualized by 3D reconstruction and charge transport simulation. By comparison of experimentally determined and simulated conductivities of composite cathodes with different ISE particle sizes, the electrode charge transport kinetics is evaluated. Porosity is shown to have a major influence on the cell kinetics and the evaluation of the active mass of electrochemically active particles reveals a higher fraction of connected NCM particles in electrode composites utilizing smaller ISE particles. The results highlight the importance of homogeneous and optimized microstructures for high performance SSBs, securing fast ion and electron transport.

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.

Electrochemical oxidation of butylated hydroxytoluene (BHT) was revisited in acetonitrile (ACN) using cyclic voltammetry, numerical simulations, and density functional theory (DFT) calculations. BHT exhibited a single irreversible anodic peak at ~1 V vs. Ag/AgNO₃, corresponding to its oxidation to a cationic radical (BHT.+), which subsequently undergoes a deprotonation and second electron transfer to form BHT+. DFT calculations defined the possible oxidation pathways evaluated through experiments and simulations. In ACN, a two-electron ECEC mechanism dominates, where the second electron transfer occurs at a lower standard potential than the first, resulting in a single anodic peak. In contrast, previous studies in aqueous media have shown two distinct voltammetric peaks, due to the first electron transfer being at a lower standard potential than the second redox reaction. Addition of potassium t-butoxide shifted the BHT/BHT- equilibrium toward the formation of BHT-, resulting in an additional redox process at negative potentials; this redox reaction was predicted from DFT calculations. Numerical simulations of the current response aligned with experimental data revealed faster electron transfer kinetics in ACN compared to water. The dimeric oxidation products were elucidated by NMR experiments. These results provide detailed insights into BHT oxidation mechanisms, emphasizing solvent effects and the formation of reactive intermediates

Optimization of the formation process can be a major driver for cost reduction in lithium ion battery cell production. To further tune the formation process, a deeper understanding of the effect of the voltage window during operation is required. In this regard, formation processes based on micro-cycles, i.e. cycles within different voltage windows, were used with NMC811||graphite and NM811||graphite/10%SiOx 1 Ah pouch cells. Three different micro-cycle formation voltage windows were investigated: 3.0 V - 3.5 V (P1), 3.6 V 3.7 V (P2) and 4.0 V - 4.2 V (P3). The P1 formation process achieved on average 3% more discharge capacity after 300 cycles for the NMC811||graphite based cells. For the SiOx containing cells, a large voltage window (P3) formation process is the least suitable, leading to an average of 4% lower discharge capacity after 300 cycles. These differences in discharge capacity were attributable to capacity loss within the formation and the initial aging cycle, rather than capacity retention. Furthermore, gas evolution and VC electrolyte additive consumption during the formation process were notably lower for the SiOx containing cells.

This study delves into the impact of substrate bias voltage on vanadium nitride thin films deposited via DC magnetron sputtering. By increasing the substrate bias voltage from 0 to -200 V, the microstructure of the films changes from crystalline and porous to amorphous and dense. This obvious change in microstructure is due to atomic peening effect, which is the sputtering of the film by energetic cations at high bias voltage during thin film growth. For capacitive storage devices, it is known that the microstructure of the electrode is key to achieve high capacitance, with the aim to maximize the electrode surface area and concomitantly the areal capacitance, while keeping a low characteristic time to achieve fast charge/discharge rates. In this study, we reveal that a trade-off must be found between areal capacitance and characteristic time. Samples sputtered with low substrate bias voltages present higher areal capacitance but also higher characteristic time compared to thin films sputtered with high substrate bias voltages. The evolution of the characteristic time associated with fast charge/discharge aligns with the electrical conductivity of VN films as determined by four-point probes measurement and indicates that the cycling rate is limited by electrical properties of the VN film.

Iron trifluoride (FeF3) is a promising cathode for high-powder thermal batteries because of higher discharge voltage (3.2 V vs. Li+/Li), high theoretical specific capacity (712 mAh⋅g-1), abundant resource, and low toxicity. Herein, single-phase FeF3 was prepared by fluorinating Fe(NO3)3 in concentrated ethanol solution followed by thermal calcination in inert atmosphere. The microstructure of FeF3 grains were modified by varying the ratio of ethanol to water (E/W) in the fluorinating process. The influence of FeF3 on the electrochemical performance was investigated. The discharging mechanism of FeF3 was discussed. The results showed that bigger FeF3 grain with a compact structure can be prepared at a moderate E/W value (3:1). The bigger FeF3 grains exhibits a specific capacity of 213 mAh·g-1 at 25 mA·cm-2 (cut-off voltage at 1.7 V), 34% higher than the capacity of commercial FeF3 powder. The discharge of the FeF3 is a two-step process employing Fe2+ as the intermediate.

LiMn0.8Fe0.2PO4 (LMFP) is projected to replace LiFePO4 cathode due to high voltage (4.1 V), long-term cyclability (> 90 % capacity retention after >1000 cycles), and safety for Lithium-ion batteries. The poor electronic conductivity (~ 10-10 S cm-1) and Li-ion diffusion (10-10-10-13 cm2 s-1), make it practically inferior. To address these challenges, a high surface area carbon (HSAC) and LMFP composite is developed in varying compositions, investigating the impact of HSAC content on the electrochemical performance of the LMFP composite. It demonstrates significant improvements (~2.43 times) in conductivity and Li-ion diffusion (~1 order) than pristine LMFP, leading to the enhanced overall performance of the cathode material. An optimum 6 wt.% HSAC composite delivers 140 mAh g-1 discharge capacity at 0.05 C and 118 mAh g-1 at 1 C with > 99% average coulombic efficiency and 93.7% retention after 1000 cycles. This work presents a promising approach for optimizing LMFP-based cathodes for Li-ion full cells with graphite anode, which delivers 119 mAh g-1 capacity at 0.1 C and 86 mAh g-1 at 1C rate (with respect to cathode active mass) with capacity retention of 65% and average coulombic efficiency of 99.5% over 200 cycles at 1 C rate.

Many modern, commercially relevant Li-ion batteries use insertion materials that exhibit lithiation-induced phase change (e.g. lithium iron phosphate, LFP). However, the standard physics-based model—the Newman model—uses a microscopic description of particle lithiation (based on diffusion) that is incapable of describing phase-change behavior and the physical origins of the voltage hysteresis exhibited by such phase-change electrodes. In this work a simple and rational model of hysteretic lithiation (in an electrode comprised of an ensemble of phase-change nanoparticles) is derived using an approach based on minimisation of the Gibbs energy. Voltage hysteresis arises naturally as a prediction of the model. Initially, equations that model the phase-change dynamics in a single particle of active material are considered. These are generalised to a model, termed the composite phase-change model, of a coupled ensemble of particles in a thin electrode. The composite phase-change model is then incorporated into the framework of a classical Newman model, allowing for the inclusion of transport effects in the electrolyte and electrode conductivity. The resulting modified Newman model is used to predict voltage hysteresis in a graphite/LFP cell. A simulation tool that allows readers to replicate, and extend, the results presented here is provided via the DandeLiion simulator at www.dandeliion.com.

Parallel connections of lithium-ion cells in battery systems lead to current distributions between the cells, which impacts fast charging capabilities. This study examines the influence of interconnection resistance, format, electrode design, cell-to-cell variations, and temperature differences on system inhomogeneity and identifies anode potential safety margins that ensure safe charging without lithium plating. To this end, a physico-chemical parameterization of the Molicel INR21700-P45B is presented. An optimized fast-charging profile enables charging from 10%–80% cell capacity in under 10 minutes. The experimental application of the fast-charging profile yielded a result of over 300 equivalent full cycles before reaching 90% state of health. Furthermore, the cell model is scaled to different parallel-connected systems in an extensive simulation study. The interconnection resistance, and analogously the internal-to-interconnection resistance ratio, was found to be the primary factor influencing inhomogeneity in high parallel configurations, whereas cell-to-cell resistance variations are the most significant determinant in low parallel configurations. Variations in cooling were found to be more impactful than initial temperature disparities.

Electrochemical impedance spectroscopy is a non-destructive technique that provides useful information on the status of a lithium-ion battery, including its state-of-health. However, conventional harmonic perturbation methods are too sophisticated for applications in operating environments. This study systematically investigates the system requirements for reconstructing impedance via the Fourier transform of voltage and current signals obtained upon current interruption. Using a calibrated equivalent circuit model, key parameters such as the minimum sampling interval $\unicode{x02206}{t}_{s}$, the initial time collected during relaxation ${t}_{i}$, and the current removal duration ${t}_{f}$, are correlated with the frequency range [${{f}_{\min },\,f}_{\max }$] in which impedance is reconstructed within 1% error. A Gaussian window, whose width is modulated with frequency, effectively mitigates noise up to 0.1 mV. The resulting general relations, ${f}_{\min }\,=\,4/{t}_{f}$ and ${f}_{\max }\,=\,0.07/\unicode{x02206}{t}_{s}$ (or ${f}_{\max }\,=\,0.07/{t}_{i}$ for ${t}_{i}\gt \unicode{x02206}{t}_{s}$), are valid within 10⁻²–10⁴ Hz, that is sufficient to cover ohmic, polarisation, and diffusion impedance features. Experimental tests on a commercial lithium-ion cell corroborate the generality of these system requirements. With a sampling interval of 70 μs for ${f}_{\max }\,=\,{10}^{3}$ Hz and a waiting time of 40 s for ${f}_{\min }\,=\,{10}^{-1}$ Hz, the current interruption technique appears compatible with commercial instrumentation, making it potentially applicable for real-time impedance monitoring in operating lithium-ion batteries.

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Highlights

• Modelling provides requirements for impedance reconstruction via current interruption

• A Gaussian window must be introduced in Fourier transform to damp measurement noise

• Sampling at 70 μs for 40 s enables reconstruction at 1% accuracy within 10⁻¹–10³ Hz

• The technique may be integrated for on-line state-of-health evaluation of batteries

The dissolution of transition metals (TM) from the cathode and their subsequent deposition on the anode represent significant degradation mechanisms in lithium-ion batteries, particularly as the industry seeks to transition towards more sustainable and cost-efficient materials. In this work, the impacts of Mn, Fe, Ni, and Co depositions on the lithiated graphite anode were investigated using pouch storage experiments to simulate the migration-deposition process and compare it to electrodes from real cells. The morphology, chemical distribution, and oxidation states of deposited TMs were investigated by scanning electron microscopy, X-ray absorption spectroscopy, and scanning transmission X-ray microscopy. X-ray diffraction and half-cell studies for post-storage electrodes determined the lithium loss and impedance growth due to TM deposition. The impact of each TM on the lithiated graphite was found to be significantly different. Deposited Mn and Fe were fully metallic, preferred to accumulate on electrode surface, and caused severe delithiation of the graphite, while Ni and Co deposition were rather harmless. The results obtained from simulated TM-containing graphite electrodes closely corresponded with those extracted from cycled cells. This alignment enhances our understanding of the behavior of dissolved TM and paves the way for solutions aimed at mitigating capacity fade in commercial lithium-ion batteries.

The abnormal expression of CYFRA21-1 is closely related to the development of non-small cell lung cancer (NSCLC), making its detection crucial for early diagnosis. In this study, we successfully constructed an electrochemical sensor based on nanopipettes and CRISPR/Cas12a for the detection of CYFRA21-1. We utilized an electrochemical three-electrode system to quantify the target by monitoring changes in electrochemical signals at the single-cell level. The small size of the nanopipettes, combined with the trans-cleavage activity of Cas12a, ensures reaction specificity while detecting CYFRA21-1 at the single-cell level. Experimental results demonstrated that the sensor exhibited a linear relationship with T-DNA concentration over the range of 1 fM to 1 μM, with a detection limit of 0.362 nM, indicating high sensitivity. The nanopipettes successfully detected CYFRA21-1 at the single-cell level, showing distinct signaling changes before and after the assay. Additionally, the sensor exhibited high specificity for CYFRA21-1 and was not affected by single-base or three-base mismatched DNA. In stability tests, the sensor demonstrated good reproducibility and stability. These properties render this electrochemical sensor a promising tool for important applications in disease diagnosis and monitoring.

Optimization of the formation process can be a major driver for cost reduction in lithium ion battery cell production. To further tune the formation process, a deeper understanding of the effect of the voltage window during operation is required. In this regard, formation processes based on micro-cycles, i.e. cycles within different voltage windows, were used with NMC811||graphite and NM811||graphite/10%SiOx 1 Ah pouch cells. Three different micro-cycle formation voltage windows were investigated: 3.0 V - 3.5 V (P1), 3.6 V 3.7 V (P2) and 4.0 V - 4.2 V (P3). The P1 formation process achieved on average 3% more discharge capacity after 300 cycles for the NMC811||graphite based cells. For the SiOx containing cells, a large voltage window (P3) formation process is the least suitable, leading to an average of 4% lower discharge capacity after 300 cycles. These differences in discharge capacity were attributable to capacity loss within the formation and the initial aging cycle, rather than capacity retention. Furthermore, gas evolution and VC electrolyte additive consumption during the formation process were notably lower for the SiOx containing cells.

This study delves into the impact of substrate bias voltage on vanadium nitride thin films deposited via DC magnetron sputtering. By increasing the substrate bias voltage from 0 to -200 V, the microstructure of the films changes from crystalline and porous to amorphous and dense. This obvious change in microstructure is due to atomic peening effect, which is the sputtering of the film by energetic cations at high bias voltage during thin film growth. For capacitive storage devices, it is known that the microstructure of the electrode is key to achieve high capacitance, with the aim to maximize the electrode surface area and concomitantly the areal capacitance, while keeping a low characteristic time to achieve fast charge/discharge rates. In this study, we reveal that a trade-off must be found between areal capacitance and characteristic time. Samples sputtered with low substrate bias voltages present higher areal capacitance but also higher characteristic time compared to thin films sputtered with high substrate bias voltages. The evolution of the characteristic time associated with fast charge/discharge aligns with the electrical conductivity of VN films as determined by four-point probes measurement and indicates that the cycling rate is limited by electrical properties of the VN film.

This paper discusses factors controlling electrochemistry-induced deposition of a zeolitic imidazolate framework-8 (ZIF-8) film on a planar substrate that is placed under an electrode. This method, which was recently demonstrated by us [T. Ito, et al. Cryst. Growth Des., 23, 6369 (2023)], provides a simple means to form a ZIF-8 film having lateral dimensions replicating those of a working electrode on an underlying substrate. We reported the effects of applied cathodic potential, electrode–substrate distance, and deposition time on the film formation, and proposed a mechanism involving cathodic base generation at a working electrode that promoted ligand deprotonation to form intermediate species, followed by their diffusion toward an underlying substrate. Here, we discuss details on the deposition mechanism by investigating the influences of other factors on the film deposition. We have investigated the effects of precursor concentration on film formation, and clarified that O₂ is a probase, rather than H₂O. We have also shown the influences of substrate surface properties controlled by self-assembled monolayers on film thickness and morphology. Most notably, we successfully demonstrated the formation of microscale ZIF-8 films using an ultramicroelectrode, revealing the applicability of the electrochemistry-induced method for micropatterned film deposition on an underlying substrate.

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Fire and deflagration that might occur in high-energy content/high-power lithium ion (Li-ion) batteries are due to propagation of thermal runaway (TR) from just a single failing “trigger” cell to the remaining fully-functional cells. Here we describe iterative housing designs of a multi-cell Li-ion battery module with the goal of preventing cell-to-cell TR propagation from a trigger cell to the remaining cells in the module. After series of experimental tests and iterations, we demonstrate a battery module, containing eight fully charged 18650 cells connected in series, that prevents TR propagation from one externally-heated trigger cell. We demonstrate further that even after TR of an individual cell in that module, all remaining cells continue to maintain nameplate cell voltage and cell capacity after the event.

Anion-exchange membrane water electrolyzers (AEM-WE) have been identified as a promising solution to deliver green hydrogen at a lower cost than alkaline water electrolyzers (AWEs) and proton-exchange membrane water electrolyzers (PEM-WEs). However, scaling AEM-WE is limited by high voltage degradation rates which can become amplified and more complicated during operation as components within the membrane electrode assembly (MEA) evolve and interact with one another. These phenomena necessitate testing protocols that capture the degradation of individual MEA components in-situ. Herein, an edge-type reference electrode and a novel flow plate design enabled decoupling of anode and cathode degradation over stability tests >200 hours. A critical assessment of the overpotential measurements is provided, utilizing half-cell impedance measurements to highlight the effects of electrode misalignment. 3-electrode cyclic voltammetry is presented as an effective in-situ tool to evaluate electrode degradation. These findings demonstrate the utility of edge-type reference electrode configurations in stability tests for the development of commercial scale AEM-WE.