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.

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.

Reversible extraction of lithium from (triphylite) and insertion of lithium into at 3.5 V vs. lithium at 0.05 mA/cm² shows this material to be an excellent candidate for the cathode of a low‐power, rechargeable lithium battery that is inexpensive, nontoxic, and environmentally benign. Electrochemical extraction was limited to ∼0.6 Li/formula unit; but even with this restriction the specific capacity is 100 to 110 mAh/g. Complete extraction of lithium was performed chemically; it gave a new phase, , isostructural with heterosite, . The framework of the ordered olivine is retained with minor displacive adjustments. Nevertheless the insertion/extraction reaction proceeds via a two‐phase process, and a reversible loss in capacity with increasing current density appears to be associated with a diffusion‐limited transfer of lithium across the two‐phase interface. Electrochemical extraction of lithium from isostructural (M = Mn, Co, or Ni) with an electrolyte was not possible; but successful extraction of lithium from was accomplished with maximum oxidation of the occurring at x = 0.5. The couple was oxidized first at 3.5 V followed by oxidation of the couple at 4.1 V vs. lithium. The interactions appear to destabilize the level and stabilize the level so as to make the energy accessible.

As a promising low-cost solar energy conversion technology, dye-sensitized solar cells have attracted widespread attention from researchers due to their low cost, simple preparation method, low toxicity, and easy production. Improving the functional conversion efficiency of batteries has always been an important research direction in this field to obtain more commercial application prospects. Compared to a single photosensitive molecule, the combined action of multiple photosensitizers sometimes exhibits superior photovoltaic performance. In order to provide people with a better understanding of the extraordinary changes brought about by co-sensitization, this article introduces the research results of co-sensitization of various photosensitive dyes with N719 in the past 10 years from different perspectives according to the types of anchoring groups (cyanoacrylic acid, carboxyl group, rhodanine acetic acid, pyridine, and cyanoethylene benzoic acid), hoping to assist with further research on co sensitization mechanisms in the future.

Novel alpha-substituted mononuclear ball-type precursor and binuclear ball-type metallo (Cu, Mn, and Ni) phthalocyanines were synthesized by using 3,3'-((thiobis(naphthalene-1,2-diyl))bis(oxy))diphthalonitrile, characterized with UV–vis, FT-IR and MALDI-TOF mass spectroscopy. The rich electron transfers through ring and/or metal-based reductions/oxidations, accompanied by distinct spectral and color changes, had been recorded for the complexes, highlighting their potential applicability in various technological applications. Hydrodynamic voltammetry studies were conducted under conditions similar to polymer electrolyte membranes and direct methanol fuel cells to test the electrocatalytic performances of catalyst inks prepared with the complexes. The positive effect of the studied substituents on catalytic activity was revealed for mononuclear complexes, and the relative changes in activity for the ball-type structures are discussed. Furthermore, by using Mn complexes as co-catalysts, the oxidative activity of the Pt particles was effectively suppressed, and their performance was exceptionally preserved in the presence of methanol, demonstrating the applicability of the prepared catalyst mixtures in direct methanol fuel cell applications.

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Solid oxide fuel cells (SOFCs) are becoming increasingly important due to their high electrical efficiency, the flexible choice of fuels and relatively low emissions of pollutants. However, the increasingly growing demands for electrochemical devices require further performance improvements as for example by reducing degradation effects. Since it is well known that the 3D electrode morphology, which is significantly influenced by the underlying manufacturing process, has a profound impact on the resulting performance, a deeper understanding for the structural changes caused by modifications of the manufacturing process or degradation phenomena is desirable. In the present paper, we investigate the influence of the annealing time and the operating temperature on the 3D morphology of SOFC anodes using 3D image data obtained by focused-ion beam scanning electron microscopy, which is segmented into gadolinium-doped ceria, nickel and pore space. In addition, structural differences caused by manufacturing the anode via infiltration or powder technology, respectively, are analyzed quantitatively by means of various geometrical descriptors such as specific surface area, mean geodesic tortuosity, and constrictivity. The computation of these descriptors from 3D image data is carried out both globally as well as locally to quantify the heterogeneity of the anode structure.

The demand for a strong discharge capacity in lithium-ion batteries is increasing. However, there are few models and correlation analysis for special lithium-ion batteries with ultra-high discharge capacity in the existing research, and the existing conventional discharge rate model prediction is not satisfactory. Based on the single particle theory, a simplified lumped semi-empirical model containing multiple classes of overpotential and heat generation terms was established. The lithium-ion battery with high discharge rate capability was tested at large currents. The reliability and accuracy of the model were verified. The root mean square errors for the discharge current and temperature were respectively less than 30 mV and 2.8 °C at discharge rates above 30 C. The maximum relative error of the voltage was only 2.4%, which was the highest level of prediction accuracy known to the authors. Based on the model, the contribution from the various heat generation sources during the discharge process was analyzed. This model could be easily applied to the analysis and design of battery modules without the detailed information of cell materials.

Highlights

• A simplified semi-empirical lumped model based on single particle theory is established for lithium-ion battery with high discharge rate in the absence of additional internal battery information.

• The model has a high accuracy in predicting the battery's behavior under high discharge rate. The predicted error of the battery at more than 30 C discharge is not more than 30 mV and 2.8 °C.

• In the future, the model can provide a basis for accelerating the design iteration efficiency of battery modules' thermal management system.

To enhance the accuracy of lithium-ion battery state-of-charge (SOC) prediction, this study develops an improved deep learning model optimized by the novel improved dung beetle optimizer (NIDBO). The NIDBO algorithm is derived from traditional dung beetle optimizer by introducing an optimal value guidance strategy and a reverse learning strategy. The deep learning model integrates convolutional neural networks (CNN), bidirectional gated recurrent units (BIGRU), and a self-attention mechanism to form the CNN-BIGRU-SA model. Subsequently, the NIDBO algorithm is employed to optimize the hyperparameters of the model, aiming to improve prediction performance. Discharge data from ternary lithium batteries and lithium iron phosphate batteries were collected. Each type of battery was subjected to 12 operating conditions, totaling 24 sets of battery operating condition data, which were used to test and validate the effectiveness of the model. The results demonstrate that the proposed model exhibits exceptional accuracy in SOC prediction, offering significant advantages over traditional methods and unoptimized models. At the same time, the model was tested under dynamic stress test and federal urban driving schedule conditions. Additionally, the generalization capability of the model is verified by cross-validating the discharge data of the two types of batteries.

As a promising low-cost solar energy conversion technology, dye-sensitized solar cells have attracted widespread attention from researchers due to their low cost, simple preparation method, low toxicity, and easy production. Improving the functional conversion efficiency of batteries has always been an important research direction in this field to obtain more commercial application prospects. Compared to a single photosensitive molecule, the combined action of multiple photosensitizers sometimes exhibits superior photovoltaic performance. In order to provide people with a better understanding of the extraordinary changes brought about by co-sensitization, this article introduces the research results of co-sensitization of various photosensitive dyes with N719 in the past 10 years from different perspectives according to the types of anchoring groups (cyanoacrylic acid, carboxyl group, rhodanine acetic acid, pyridine, and cyanoethylene benzoic acid), hoping to assist with further research on co sensitization mechanisms in the future.

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.

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.

An in situ double probe beam deflection (PBD) technique has been developed using two laser beams to map the concentration profile of the diffusion layer in an electrochemical cell. A microscale moving upper probe and a fixed position secondary beam offer real-time concentration gradients to be profiled throughout the depth of the diffusion layer. The double PBD technique was used to plot concentration profiles for 0.1 mol/kg CuSO4 and ZnSO4 within a range of applied currents, showing increased magnitudes of gradients for higher currents. Both single and double beam PBD were explored, demonstrating the distance and time dependence of the developing concentration gradient. While CuSO4 showed a systematic trend of increased response delay and decreased deflection with increased distance from the electrode, ZnSO4 experienced some additional phenomena affecting the refractive index within the diffusion layer. The in situ double probe beam deflection was shown to be highly sensitive and offers future work in quantifying charge migration within this important region of the electrochemical cell.

The passage of current through a battery results in the development of concentration gradients in the electrolytic phase. For a fully characterized binary electrolyte, where the conductivity, salt diffusion coefficient, cation transference number, and the thermodynamic factor are known, concentration and potential gradients in the electrolytic phase can be modeled using Newman’s concentrated solution theory. We report two methods for measuring the transference number: the standard method based on electrochemical measurements (t_(+,echem)^0) and electrophoretic NMR (t_(+,eNMR)^0). The electrochemical approach requires combining measurements from multiple experiments; the equations used to determine the cation transference number and the thermodynamic factor are coupled, nonlinear algebraic equations. In the electrophoretic-NMR-based approach, however, the equations used to determine the cation transference number and the thermodynamic factor are decoupled. We find for a liquid electrolyte comprised of a lithium salt dissolved in tetraglyme, the values of the transference numbers obtained by these two methods are distinct. For example, at 30C, t_(+,echem)^0 = -1.02±1.11 and t_(+,eNMR)^0 = 0.25±0.04. The corresponding thermodynamic factors are also different. While the magnitude of the predicted concentration gradients based on the two sets of parameters are different, the predicted current-voltage relationships are similar.

A novel synthesis approach for Cu0.16VOPO4•2.5H2O material is reported, consisting of VOPO4 layers incorporating water molecules and Cu2+ ions within the interlayer space. The inclusion of Cu2+ ions leads to significant changes in the previously reported electrochemical properties of VOPO4•2H2O. Indeed, copper ion insertion leads to a reduced interlayer space, a higher surface area, and, consequently, to a higher specific charge. Moreover, the appearance of new fast faradaic reactions is depicted from the presence of new redox peaks in cyclic voltammograms. The capacity of this material is 93 Cg-1 in 3M LiOH, 114 Cg-1 in 3M NaOH, and 126 Cg-1 in 3M KOH at a scan rate of 5 mVs-1. It was determined that an intercalation process takes place across the entire operational range in all three electrolytes, even at scan rates as high as 500 mVs-1. Additionally, electrochemical impedance spectroscopy (EIS) was used for a more comprehensive understanding of the electrochemical role of the interlayer Cu2+ cations. EIS enables us to propose a new mechanism of electron transfer between VOPO4 layers and Cu2+ ion layers, which extends to neighboring layers, thus explaining the fast kinetic of the related faradaic reactions.

The polysulfide shuttle effect remains a fundamental challenge in lithium-sulfur batteries, particularly for high-energy-density applications where conventional mitigation strategies prove insufficient. Here, we introduce a state-resolved methodology for quantifying shuttle current by analyzing Coulombic efficiency across discretized charging blocks, addressing limitations in traditional voltage-dependent measurement techniques. Through systematic analysis of cells with and without LiNO₃ additive, we demonstrate that shuttle activity peaks at 60-70% state of charge (SOC), correlating with maximum Li₂S₄ concentration as confirmed by UV-vis spectroscopy. The block efficiency analysis reveals distinct patterns: cells without LiNO₃ show efficiency dropping to 60% in the mid-SOC region, while LiNO₃-containing cells maintain minimum efficiency around 80%, demonstrating approximately 70% suppression of peak shuttle current. Electrochemical impedance analysis further reveals how polysulfide evolution affects transport processes, with bulk resistance peaking at mid-SOC due to pore blockage, while interfacial resistance changes reflect the transition between different polysulfide species. By correlating block efficiency with polysulfide speciation, we establish that Li₂S₄ drives shuttle activity through its optimal balance of solubility and mobility, while larger Li₂S₈ species contribute less despite higher solubility. This work provides quantitative insights into shuttle current distribution across different SOC ranges while establishing a robust methodology for evaluating shuttle suppression strategies.

The physicochemical and electrochemical properties of an ionic liquid consisting of the dichlorocuprate anion, [CuCl2]–, were investigated. The equimolar mixture of CuCl and 1-butyl-1-methylpyrrolidinium chloride (BMPCl) was found to yield an ionic liquid at 298 K composed predominantly of BMP+ and [CuCl2]–. Fine deposits of metallic Cu were obtained on a glassy carbon electrode by potentiostatic and galvanostatic reduction of [CuCl2]– in CuCl-BMPCl (50.0-50.0 mol%). The overpotential for Cu nucleation was larger on a glassy carbon electrode than on a Pt electrode. The electrochemical deposition and dissolution of Cu were analyzed using an electrochemical quartz crystal microbalance. The local viscosity and density of the electrolyte near the electrode/electrolyte interface increased during both deposition and dissolution of Cu, probably reflecting the shift in the electrolyte composition to the local basic and acidic conditions, respectively.

Solid oxide fuel cells (SOFCs) are becoming increasingly important due to their high electrical efficiency, the flexible choice of fuels and relatively low emissions of pollutants. However, the increasingly growing demands for electrochemical devices require further performance improvements as for example by reducing degradation effects. Since it is well known that the 3D electrode morphology, which is significantly influenced by the underlying manufacturing process, has a profound impact on the resulting performance, a deeper understanding for the structural changes caused by modifications of the manufacturing process or degradation phenomena is desirable. In the present paper, we investigate the influence of the annealing time and the operating temperature on the 3D morphology of SOFC anodes using 3D image data obtained by focused-ion beam scanning electron microscopy, which is segmented into gadolinium-doped ceria, nickel and pore space. In addition, structural differences caused by manufacturing the anode via infiltration or powder technology, respectively, are analyzed quantitatively by means of various geometrical descriptors such as specific surface area, mean geodesic tortuosity, and constrictivity. The computation of these descriptors from 3D image data is carried out both globally as well as locally to quantify the heterogeneity of the anode structure.

The design of the microporous structure of solid oxide fuel cell (SOFC) anodes can significantly affect the overall cell efficiency. A novel pore-scale computational framework has been developed using Plurigaussian methods to create micorporous anode topologies at will. A multi-dimensional model describing the electrochemical phenomena occurring within the corresponding discretised domain of the active layer of the porous anode cermet has been constructed and solved using the finite volume method. Three different anode configurations have been computationally synthesized and analyzed with respect to their topological properties and electrochemical performance: A conventional Ni/YSZ configuration, and two novel designs, a fibrous and a lattice microstructure are synthesized and tested. Utilization of synthetically generated microstructures enables the direct study of microporous and image acquisition attributes. Our numerical investigations demonstrate that lattice and fibrous structures produce increased current densities by 4.8 and 1.4 times, respectively, compared to conventional configurations. In addition, gradient microstructures also have the capacity to enhance electrochemical performance when subjected to careful fabrication methodologies.

Molten salt electrochemistry has not been widely studied compared to aqueous and ionic liquids, and an experimental methodology to perform those experiments is crucial to the molten salt community. One of the main challenges in performing these experiments is the inability to visualize the position of the electrodes or the condition of the molten bath. In some cases, the placement of electrodes and the temperature of the molten bath can raise problems when the electrodes are not in contact with the molten salt or when the electrodes are in direct contact with each other. This methodology study investigates scenarios where a molten salt experiment can fail. This methodology study also provides new approaches to enhance and provide more accurate results when performing electrochemical analysis in molten salts to obtain prominent properties, such as the diffusion coefficient. Even though this paper does not involve determining those properties, it provides general guidelines and suggestions to improve the quality of electrochemical data and troubleshoot experimental setups.

Highlights

• A clear methodology improves molten salt electrochemical experiment reliability.

• Challenges with electrode placement and molten salt temperatures are addressed.

• iR compensation and surface roughness effects on accuracy are carefully examined.

• Insights into quasi-reference electrodes reveal their limits in molten salt systems.

• Practical advice enhances the quality and success of molten salt experiments.

An in situ double probe beam deflection (PBD) technique has been developed using two laser beams to map the concentration profile of the diffusion layer in an electrochemical cell. A microscale moving upper probe and a fixed position secondary beam offer real-time concentration gradients to be profiled throughout the depth of the diffusion layer. The double PBD technique was used to plot concentration profiles for 0.1 mol/kg CuSO4 and ZnSO4 within a range of applied currents, showing increased magnitudes of gradients for higher currents. Both single and double beam PBD were explored, demonstrating the distance and time dependence of the developing concentration gradient. While CuSO4 showed a systematic trend of increased response delay and decreased deflection with increased distance from the electrode, ZnSO4 experienced some additional phenomena affecting the refractive index within the diffusion layer. The in situ double probe beam deflection was shown to be highly sensitive and offers future work in quantifying charge migration within this important region of the electrochemical cell.

The passage of current through a battery results in the development of concentration gradients in the electrolytic phase. For a fully characterized binary electrolyte, where the conductivity, salt diffusion coefficient, cation transference number, and the thermodynamic factor are known, concentration and potential gradients in the electrolytic phase can be modeled using Newman’s concentrated solution theory. We report two methods for measuring the transference number: the standard method based on electrochemical measurements (t_(+,echem)^0) and electrophoretic NMR (t_(+,eNMR)^0). The electrochemical approach requires combining measurements from multiple experiments; the equations used to determine the cation transference number and the thermodynamic factor are coupled, nonlinear algebraic equations. In the electrophoretic-NMR-based approach, however, the equations used to determine the cation transference number and the thermodynamic factor are decoupled. We find for a liquid electrolyte comprised of a lithium salt dissolved in tetraglyme, the values of the transference numbers obtained by these two methods are distinct. For example, at 30C, t_(+,echem)^0 = -1.02±1.11 and t_(+,eNMR)^0 = 0.25±0.04. The corresponding thermodynamic factors are also different. While the magnitude of the predicted concentration gradients based on the two sets of parameters are different, the predicted current-voltage relationships are similar.

The physicochemical and electrochemical properties of an ionic liquid consisting of the dichlorocuprate anion, [CuCl2]–, were investigated. The equimolar mixture of CuCl and 1-butyl-1-methylpyrrolidinium chloride (BMPCl) was found to yield an ionic liquid at 298 K composed predominantly of BMP+ and [CuCl2]–. Fine deposits of metallic Cu were obtained on a glassy carbon electrode by potentiostatic and galvanostatic reduction of [CuCl2]– in CuCl-BMPCl (50.0-50.0 mol%). The overpotential for Cu nucleation was larger on a glassy carbon electrode than on a Pt electrode. The electrochemical deposition and dissolution of Cu were analyzed using an electrochemical quartz crystal microbalance. The local viscosity and density of the electrolyte near the electrode/electrolyte interface increased during both deposition and dissolution of Cu, probably reflecting the shift in the electrolyte composition to the local basic and acidic conditions, respectively.

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.