Journal of The Electrochemical Society

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.

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.

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.

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.

The maximum energy that lithium-ion batteries can store decreases as they are used because of various irreversible degradation mechanisms. Many models of degradation have been proposed in the literature, sometimes with a small experimental data set for validation. However, a comprehensive comparison between different model predictions is lacking, making it difficult to select modelling approaches which can explain the degradation trends actually observed from data. Here, various degradation models from literature are implemented within a single particle model framework and their behavior is compared. It is shown that many different models can be fitted to a small experimental data set. The interactions between different models are simulated, showing how some of the models accelerate degradation in other models, altering the overall degradation trend. The effects of operating conditions on the various degradation models is simulated. This identifies which models are enhanced by which operating conditions and might therefore explain specific degradation trends observed in data. Finally, it is shown how a combination of different models is needed to capture different degradation trends observed in a large experimental data set. Vice versa, only a large data set enables to properly select the models which best explain the observed degradation.

Reversible extraction of lithium from ${\mathrm{LiFePO}}_4$ (triphylite) and insertion of lithium into ${\mathrm{FePO}}_4$ 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, ${\mathrm{FePO}}_4$, isostructural with heterosite, ${\mathrm{Fe}}_{0.65}{\mathrm{Mn}}_{0.35}{PO}_4$. The ${\mathrm{FePO}}_4$ framework of the ordered olivine ${\mathrm{LiFePO}}_4$ 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 ${\mathrm{LiMPO}}_4$ (M = Mn, Co, or Ni) with an ${\mathrm{LiClO}}_4$ electrolyte was not possible; but successful extraction of lithium from ${\mathrm{LiFe}}_{1-x}{\mathrm{Mn}}_x{PO}_4$ was accomplished with maximum oxidation of the ${\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{2+}$ occurring at x = 0.5. The ${\mathrm{Fe}}^{3+}/{\mathrm{Fe}}^{2+}$ couple was oxidized first at 3.5 V followed by oxidation of the ${\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{2+}$ couple at 4.1 V vs. lithium. The ${\mathrm{Fe}}^{3+}‐O‐{\mathrm{Mn}}^{2+}$ interactions appear to destabilize the ${\mathrm{Mn}}^{2+}$ level and stabilize the ${\mathrm{Fe}}^{3+}$ level so as to make the ${\mathrm{Mn}}^{3+}/{\mathrm{Mn}}^{2+}$ energy accessible.

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.

Whilst extensive research has been conducted on the effects of temperature in lithium-ion batteries, mechanical effects have not received as much attention despite their importance. In this work, the stress response in electrode particles is investigated through a pseudo-2D model with mechanically coupled diffusion physics. This model can predict the voltage, temperature and thickness change for a lithium cobalt oxide-graphite pouch cell agreeing well with experimental results. Simulations show that the stress level is overestimated by up to 50% using the standard pseudo-2D model (without stress enhanced diffusion), and stresses can accelerate the diffusion in solid phases and increase the discharge cell capacity by 5.4%. The evolution of stresses inside electrode particles and the stress inhomogeneity through the battery electrode have been illustrated. The stress level is determined by the gradients of lithium concentration, and large stresses are generated at the electrode-separator interface when high C-rates are applied, e.g. fast charging. The results can explain the experimental results of particle fragmentation close to the separator and provide novel insights to understand the local aging behaviors of battery cells and to inform improved battery control algorithms for longer lifetimes.

A general energy balance for battery systems has been developed. This equation is useful for estimating cell thermal characteristics. Reliable predictions of cell temperature and heat‐generation rate are required for the design and thermal management of battery systems. The temperature of a cell changes as a result of electrochemical reactions, phase changes, mixing effects, and joule heating. The equation developed incorporates these effects in a complete and general manner. Simplifications and special cases are discussed. The results of applying the energy balance to a mathematical model of the $\mathrm{LiAl}/\mathrm{FeS}$ cell discharged through two different reaction mechanisms are given as examples. The examples illustrate how the energy equation may be applied to a specific system to examine the relative contributions corresponding to the terms in the equation. The examples show that the processes involved in cell heat generation may be complex and that the application of a sufficiently general energy equation is advantageous.

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.

SAF 2205 duplex stainless steel (DSS) is frequently used in hydrometallurgical environments where it is exposed to aggressive mixed-anion solutions. This study explores the mechanistic role of sulfate (SO₄²⁻) in inhibiting the localized corrosion of 2205 DSS in chloride-containing media. Using potentiodynamic polarization and critical temperature measurements (CPT and CCT), it is shown that increasing the SO₄²⁻/Cl⁻ ratio linearly enhances resistance to both pitting and crevice corrosion, shifting pitting potential and crevice repassivation potential to more noble values. To determine the mechanism of this inhibition, the lead-in pencil electrode technique was employed. It was found that SO₄²⁻ alters the pit solution chemistry by reducing the product of diffusion coefficient of the dissolving metal cations and the critical concentration for repassivation (D.C^*), along with the corresponding saturation product (D.C_S), thereby increasing the ratio D.C^*/D.C_S. This reduction in D.C^* and increase in D.C^*/D.C_S increases the ratio of repassivation tendency to dissolution driving force, thereby stabilizing the salt film and facilitating repassivation at shallower pit depths. These findings provide qualitative and quantitative explanations for the inhibitory effect of sulfate against localized corrosion of stainless steel.

figure placeholder

Highlights

• CPT and CCT of 2205 DSS were measured in different SO₄^2-/Cl⁻ ratios.

• For 2205 DSS, increasing SO₄²⁻/Cl⁻ ratio raised both CPT and CCT across 0.01-1.0 M NaCl.

• Sulfate shifted E_pit and E_rep to more noble values, enhancing resistance to localized corrosion initiation and repassivation.

• Lead-in pencil electrode studies showed that sulfate alters the pit chemistry, promoting repassivation.

Ether-based electrolytes have attracted considerable interest in the development of potassium-ion batteries (PIBs) owing to their superior compatibility with potassium metal anodes. Nevertheless, their inherently limited electrochemical stability windows, particularly with respect to inadequate oxidative stability, pose significant challenges for the practical implementation of high-voltage cathodes exceeding 4 V. Traditional ether electrolytes tend to undergo rapid decomposition at elevated potentials, leading to the deterioration of the cathode-electrolyte interphase and severe capacity degradation. In this study, we present a solvation chemistry engineering approach by incorporating Bis(2-fluoroethyl) carbonate (BFC) into a 1,3-dioxane electrolyte. The addition of BFC modifies the solvation sheath structure, enhances the desolvation kinetics of potassium ions (K⁺), and simultaneously broadens the electrochemical stability window. As a result, the optimized electrolyte facilitates stable cycling of high-voltage cathodes operating at approximately 4.5 V in PIBs, achieving a remarkable capacity retention of 92.2% after 1800 cycles under high current densities, alongside an outstanding Coulombic efficiency of 99.95%. This work establishes a framework for the deliberate manipulation of solvation chemistry in the design of high-voltage electrolytes and provides a viable strategy to overcome the voltage limitations inherent to ether-based electrolyte systems.

figure placeholder

Highlights

• BFC additive regulates solvation structure in 1,3-dioxane electrolyte for PIBs.

• Enhanced K⁺ desolvation kinetics achieved via solvation sheath modification.

• Electrochemical window broadened to enable 4.5 V high-voltage operation.

• 92.2% capacity retention after 1800 cycles at 4.5 V with 99.95% CE.

• Strategy overcomes voltage limitations of ether-based electrolytes.

Efficient and cost-effective catalysts are essential to drive the oxygen evolution reaction (OER) in sustainable hydrogen production through water splitting, especially in seawater electrolyte. Here, Ce and S co-doped FeOOH nanosheets grown on nickel foam (CeS-FeOOH) are fabricated. Benefiting from the co-doping of Ce and S, the CeS-FeOOH catalyst has efficient charge redistribution and sufficient solid-liquid-gas interfaces. As expected, the CeS-FeOOH catalyst exhibits excellent OER activity, requiring overpotentials of 248 and 273 mV to achieve a current density of 10 mA cm⁻² in alkaline water and alkaline seawater electrolytes outperforming the commercial IrO₂ catalyst, as well as superior stability. Meanwhile, the Faradaic efficiency of the CeS-FeOOH catalyst is still greater than 96.3% in alkaline seawater electrolyte. This work provides a new approach for the exploration of highly activity, efficient, and stable OER electrocatalyst for electrolysis of alkaline seawater.

figure placeholder

Highlights

• Ce and S co-doping induces charge redistribution in FeOOH for boosted OER

• Low overpotentials of 248 mV and 273 mV at 10 mA cm⁻² in alkaline water/seawater

• Maintains >96% Faradaic efficiency and high activity in alkaline seawater

• The nanosheet architecture remains stable after OER durability test

• Superhydrophilic and superaerophobic surface enhances mass transfer and stability

Phase change materials (PCMs) are passive cooling media for lithium-ion battery thermal management owing to their high latent heat capacity and operational reliability. However, their practical implementation remains hindered by low thermal conductivity and leakage during phase transition. Herein, we report a lightweight and low-cost shape-stabilized composite PCM fabricated by impregnating paraffin into a porous carbon foam scaffold derived from commercial melamine foam. The interconnected carbon framework provides structural confinement to suppress paraffin leakage while establishing continuous heat-transfer pathways that markedly enhance thermal transport. The optimized composite (PCM-800) exhibits a low density of 0.89 g cm⁻³ and an ultralow material cost of ~0.0097 USD g⁻¹, substantially lower than those of conventional metallic-foam-based composites. Benefiting from the conductive carbon network, PCM-800 achieves a thermal conductivity of 0.52 Wm⁻¹K⁻¹, representing a 2.3-fold enhancement over pristine paraffin, while maintaining a high melting latent heat of 234.61 J g⁻¹ and a phase transition temperature of 47.78 °C. Battery module tests demonstrate that PCM-800 maintains the cell temperature below 60 °C for 3750 s at 18 V, 1200 s at 22 V, and 550 s at 26.8 V, extending the safe operating time by 20% and 71% relative to pure paraffin and natural air cooling, respectively.

figure placeholder

Highlights

• A scalable pyrolysis–impregnation strategy was developed to fabricate shape-stabilized carbon foam/paraffin composite

• The optimized composite achieved an enhanced thermal conductivity of ~0.52 W m⁻¹K⁻¹

• Exhibited ultralow material cost of ~0.0097 USD g⁻¹ and density of ~0.89 g cm⁻³

• Extended battery safe operating time by 71% compared with air cooling

Pelitinib (PEL) is an irreversible tyrosine kinase inhibitor targeting the human epidermal growth factor receptor (HER) family and is generally utilized in the treatment of HER2-positive cancers. Despite its clinical significance, the electrochemical behavior of PEL has not been reported so far. In this research, the electrochemical features of PEL were systematically investigated for the first time at boron doped diamond electrode (BDDE) and pyrolytic graphite edge electrode (PGEE). Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and adsorptive stripping voltammetry (AdSV) were utilized to elucidate the oxidation mechanism and to develop sensitive electroanalytical methods for PEL determination. The oxidation of PEL was found to be irreversible at both electrodes. Scan rate studies revealed a diffusion-controlled process at BDDE, whereas a mixed diffusion–adsorption controlled behavior was observed at PGEE. The Ep–pH relationship indicated a proton-coupled electron transfer mechanism, and distinct breakpoints observed were associated with the pKa values of PEL. The effect of surfactants showed electrode-dependent behavior. Under optimized conditions, the DPV method at BDDE exhibited a linear response over the concentration range of 0.5–7.0 μM with a detection limit of 160.00 nM, whereas the AdSV method at PGEE provided a significantly improved sensitivity with a linear range of 0.003–0.3 μM and a remarkably low detection limit of 0.80 nM. In serum samples, the methods retained good analytical performance, with LOD values of 223.00 nM (BDDE) and 4.60 nM (PGEE), along with satisfactory recovery results. These findings demonstrate that the proposed electrochemical approaches offer simple, sensitive, and cost-effective alternatives for the determination of PEL in pharmaceutical and biological samples.

figure placeholder

Highlights

• Pelitinib was studied electrochemically at BDDE and PGEE.

• The pH dependence revealed a proton-coupled electron transfer.

• A breakpoint in Ep–pH were linked to pelitinib pKa values.

• Surfactants enhanced the signal at PGEE via adsorption effects.

• The method enabled reliable pelitinib determination in serum.

The transition to new energy resources is driving the need for efficient energy storage. Redox flow batteries (RFBs) are a promising solution due to their flexible design and safer materials, particularly for long-duration storage applications. Despite these advantages, RFB technologies still have considerable room for growth in terms of utilizing all of their available energy storage density. Herein, we assess RFB energy storage density utilization trends for multiple chemistries by accounting for their unique thermodynamic limits, energy efficiencies, and charge capacity constraints. Of the RFBs chemistries analyzed, most still use less than 60% of their theoretical energy storage capacity. The conventional all-vanadium RFB was the closest to its thermodynamic limit available. Moreover, the volumetric footprint and electrolyte cost analyses demonstrate the real-world implications of these inefficiencies. This analysis further indicates that future studies would benefit from clearer reporting of two key quantities: discharge efficiency, which is more directly tied to practically recoverable energy density than round-trip energy efficiency, and state-of-charge or capacity-utilization limits, which govern access to theoretical storage capacity. More consistent reporting of these factors would improve the accuracy and comparability of energy storage utilization analyses across RFB chemistries.

figure placeholder

Highlights

• Energy storage density values from energy efficiency and capacity constraints

• Redox flow batteries use less than 60% of their energy storage density limit

• Inefficiencies in redox flow batteries increase their volumetric footprint

• Cost effective electrolytes make up for underutilized energy storage density

Starting batteries are critical electrochemical energy storage systems that deliver high power pulses for engine ignition and auxiliary electrical functions. Their performance, durability, and safety are governed by complex electrochemical interactions involving electrode materials, electrolytes, interfacial processes, and operating conditions. This review provides a comprehensive electrochemical perspective on major starting battery technologies, including flooded lead–acid, absorbed glass mat, gel cell, lithium-ion, and nickel–cadmium batteries. Key electrochemical performance-limiting factors such as charge–discharge behavior, polarization losses, internal resistance, ion transport, and electrode–electrolyte interfacial stability are systematically analyzed. Further, the review emphasizes degradation and aging mechanisms such as sulfation, grid corrosion, gas evolution, lithium plating, and thermal runaway. It explains their electrochemical origins and how they affect long-term battery stability. The effects of temperature, charge rate, discharge rate, and material composition on electrochemical efficiency and cycle life are critically discussed. Recent advances in electrode materials, electrolyte systems (gel, polymer, ionic liquid, and deep eutectic electrolytes), and separator design are reviewed from an electrochemical perspective. These advances focus on strategies to enhance charge-transfer kinetics, suppress degradation, and improve thermal stability. Finally, key challenges and future research directions are outlined to guide the development of robust and sustainable next-generation starting batteries.

figure placeholder

Zirconium (Zr) possesses outstanding properties, including exceptional chemical resistance and a high melting point, and is therefore desirable for use in a wide variety of challenging environments, such as in nuclear reactors and the chemical processing industry. To minimize the amount of Zr required for any given application, developing methods for generating metallic Zr coatings is highly advantageous. Owing to Zr’s highly negative reduction potential, electrodeposition in traditional solvents at near ambient temperatures remains challenging and thus not well understood. Due to the extreme conditions required to deposit this metal, extensive work has been conducted in molten salt electrolytes, however the broad applicability of this methodology is limited due to its corrosivity. The primary focus of this article is to present an overview of Zr’s electrochemical behavior and to consolidate the efforts of researchers in exploring electrodeposition techniques for Zr involving aqueous, organic, ionic liquid, deep eutectic, and molten salt solvents. With this information, we highlight trends across solvent systems and opportunities for future research.

figure placeholder

This study presents a thorough analysis of machine learning techniques utilized for monitoring the health and predicting the remaining useful life (RUL) of lithium-ion batteries, which is essential for optimizing the performance of electric vehicles (EVs). Given the challenges faced by lithium-ion batteries, such as capacity fading and environmental factors, key indicators like State of Health (SOH) and RUL become vital. The paper reviews several adaptive machine learning methodologies, including Support Vector Regression (SVR), Gaussian Process Regression (GPR), and hybrid neural networks that integrate convolutional neural networks (CNNs) with long short-term memory (LSTM) algorithms. Special emphasis is placed on these models’ effectiveness in addressing the complex nonlinear behaviors associated with battery aging. Moreover, innovative approaches like fuzzy logic systems are examined, showcasing their potential to enhance SOH estimation via adaptable rule-based techniques. The manuscript stresses the necessity of integrating multiple methodologies to enhance predictive accuracy and reliability. By compiling empirical studies, the work aims to elucidate the capabilities of these algorithms, thereby enriching the knowledge base within battery management systems. Ultimately, this research aims to drive advancements in efficient energy storage solutions, which are crucial for the sustainable development of electric mobility.

figure placeholder

Highlights

• Machine learning techniques like CNN and DNN significantly enhance the prediction accuracy of battery health by modeling complex relationships.

• Gaussian Process Regression (GPR) effectively addresses battery aging issues by flexibly modeling nonlinear relationships and estimating prediction uncertainty.

• Condition monitoring utilizes critical parameters such as voltage and temperature to improve state-of-health and remaining useful life assessments.

• Machine learning algorithms are essential for predicting battery failure signs and diagnosing degradation trends, thereby enhancing energy storage system reliability.

• Various methodologies for estimating state-of-health showcase a mixture of experimental and adaptive techniques aimed at refining battery health evaluation.

This narrative summarizes, in retrospect, the enormous and quietly-conducted contribution of Dr Johan Coetzer, a South African scientist and entrepreneur, to the discovery, development and implementation of the high temperature sodium—metal chloride “ZEBRA” battery (Na/β-Al₂O₃, NaAlCl₄/MCl₂ (M = Ni, Fe)). This research activity was initiated in the mid 1970’s at the Council for Scientific and Industrial Research (CSIR) in South Africa and subsequently developed primarily in partnership with the Atomic Energy Research Establishment (AERE, Harwell, UK), Beta R&D (Derby, UK) and Daimler Benz (Germany), before being transferred to industry worldwide for electric vehicle and energy storage applications, albeit at a relatively low production rate. Coetzer’s wide-ranging, innovative and, at times, unconventional scientific approach also laid the foundation for the discovery and implementation of manganese-based spinel and layered metal oxide cathode materials for the Li-ion battery industry.

figure placeholder

This study investigates aqueous electrolytes for efficient iron electrodeposition directly from Fe³⁺ at ambient temperature. Concentrated lithium chloride (LiCl) based electrolytes were found to stabilize the Fe³⁺ in the electrolyte, suppress parasitic hydrogen evolution and suppress redox shuttling of intermediate Fe²⁺, thus promoting efficient iron electrodeposition. These attributes collectively enabled high Coulombic efficiencies (>75%) at high current densities (>200 mA cm⁻²). Furthermore, detailed investigation revealed that increasing the LiCl concentration increased the electrolyte viscosity and decreased the Fe²⁺ out-diffusion rate while also suppressing the activity of water. Sufficiently high LiCl concentrations (>7 M) thus provide a window of current densities in which elevated Coulombic efficiencies can be achieved. Overall, this paper develops an understanding of the effects of electrolyte composition on the competition between Fe electrodeposition, hydrogen co-evolution, and intermediate Fe²⁺ out-diffusion for efficient Fe metal electrosynthesis.

figure placeholder

Production of volatile fatty acids (VFAs) from biomass fermentation is a promising pathway for sustainable chemical production. A central challenge is cost-effective recovery and fractionation of VFAs from fermentation broths. Redox-mediated electrodialysis (redox-ED) can be an energy efficient technique for VFA separation, replacing water splitting with redox-reactions. However, the low selectivity between VFAs of different lengths (separation factors <3) obtained using commercially-available anion-exchange membranes limits the final product purity for industrial use. Cascaded operation can overcome these material limitations and increase product purity, yet multistage redox-ED can be complex and has not been extensively explored for selective ion separations. Here, we developed a physics-based model of redox-ED using finite elements to simulate the separation of a ternary carboxylic acid feed (propionic, butyric, and hexanoic) and evaluated five different multistage architectures including series, parallel, co-current, and counter-current setups. The single-stage, two-dimensional steady-state model captured the effect of the flow-field, concentration, and potential gradients, yielding reasonable agreement with experimental data. We then investigated the tradeoff between number of stages, product purity, and productivity, and assessed the impact of membrane selectivity. In sum, cascaded redox-ED with reflux simultaneously improved product purity and productivity, while series or equivalent single-stage architectures presented a tradeoff between VFA purity and productivity.

figure placeholder

Voltammetric measurements of electrochemical CO₂ reduction reaction (CO₂RR) selectivity on rotating ring disk electrodes (RRDE) are a rapid and sensitive method for quantifying an electrocatalyst’s selectivity, i.e. faradaic efficiency (FE). This method has been applied to polycrystalline Au electrocatalysts where a Au disk electrode catalyzes both the CO₂RR and hydrogen evolution reaction while the concentric Au ring electrode selectively senses CO by oxidizing CO back to CO₂. Such measurements enabled fundamental mechanistic studies but suffer from poor inter-laboratory reproducibility. This work identifies causes of variability in RRDE selectivity measurements by comparing protocols with different electrochemical methods, reagent purities, and glassware cleaning procedures. We observed FE_CO decrease by 56% during 5 min chronoamperometry measurements, a phenomenon that is not readily apparent in voltammetric scans due to their dynamic nature. Electroplating of electrolyte impurities onto the disk and ring surfaces were identified as a major contributor to Au deactivation. Additionally, the oxygen reduction reaction may lead to higher disk currents in inadequately purged electrolytes, causing an apparent underestimation of FE_CO at low overpotentials. Lastly, we propose operational bounds for CO₂RR selectivity measurements on Au using the RRDE method and provide suggestions on steps for improving the accuracy of this technique.

figure placeholder

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.

figure placeholder

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.

For insertion-type lithium-ion batteries, the solid-state diffusion coefficient of Li⁺ in an active material is considered a key parameter within the research community. The capabilities and limits of related parameter extraction methods are usually well-established.However, there is a gap in understanding the influence of the applied measurement setup. In practice, many setups unintentionally violate the assumptions of the extraction method. We apply the galvanostatic intermittent titration technique (GITT) in virtual experiments using 3D microstructure-resolved simulations in varying model measurement setups. Diffusion coefficients are extracted by applying a state-of-the-art Bayesian optimization approach which is particularly suitable for non-uniquely solvable problems. The investigated parameters are within the typical literature range of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811). Because experimental boundary conditions are precisely known within the simulation setups, the influence of microstructural features on the extracted diffusion can be isolated and quantified. The investigation shows, that the applied monodisperse thin-electrode and single-particle setup are capable of extracting the actual diffusivity with up to 4 % and 17 % point-estimate deviation, respectively. Particle cracking proved to have the largest impact on extracted diffusion coefficients. Nevertheless, all predictions remained close to the correct order of magnitude, i.e.~point estimates deviated at most by factors in the range of 10^±0.88.

Structural health monitoring (SHM) using piezoelectric transducers has been widely explored for individual lithium-ion cells, yet its applicability at the module level remains largely unstudied. This work demonstrates the feasibility of SHM on a realistic battery module composed of four 60 Ah pouch cells and operated in a mechanically constrained setup similar to an electric-vehicle (EV) battery environment. In this configuration, breathing-induced stack pressure varies during cycling, and these pressure changes are captured simultaneously with the parameters of the propagating guided wave using a self-developed ultrasonic battery management system (UBMS). Measurements at two C-rates and two ambient temperatures show that the group velocity shifts by approximately 32ms−1 between 25°C and 10°C, while cycling-induced stack pressure variations, corresponding to measured forces of up to 250 N, are reflected in a decrease of the normalized amplitude to values as low as 0.5. These findings demonstrate that piezoelectric SHM operates reliably in a realistic module-level environment. Moreover, it shows sensitivity to pressure changes within the cell stack, providing a foundation for future diagnostic approaches that are able to identify safety-critical states through their impact on the cell’s mechanical behavior.

A through-glass, non-immersion observation platform was developed for real-time optical observation of localized corrosion with turret-based magnification switching during electrochemical measurement. The platform was applied to hypoeutectic high-chromium cast iron (HCCI; Fe–27Cr–2.8C, wt.%) in 3.5 wt.% NaCl aqueous solution. The microstructure consisted of primary and eutectic γ (austenite) and (Fe,Cr)7C3 carbide. Scanning Kelvin probe force microscopy (SKPFM) revealed that the eutectic γ phase had the lowest contact potential difference (CPD) among the constituent phases. Potentiodynamic polarization with in situ observation showed that localized corrosion initiated at the carbide–eutectic γ interfaces at the pitting potential and propagated into the eutectic γ regions. Naturally aerated immersion confirmed the same initiation behavior, with ring-shaped corrosion product deposits forming around the localized corrosion sites.

Electrolyte motion–induced salt inhomogeneity (EMSI) can limit fast-charging performance in lithium-ion cells, yet its underlying mechanisms remain insufficiently understood. Here, we investigate EMSI in multilayer pouch cells with 50 wt. % of a silicon:carbon composite (chemical Si:C) and 50 wt. % graphite in the negative electrode by varying electrolyte fill volume, electrolyte formulation, and mechanical constraints. Long-term fast-charging cycling shows how these factors affect EMSI-induced capacity fade and ultimately trigger cell failure. We show that electrolyte pumping occurs not only under rigid confinement but also under soft confinement, where it gives rise to a counterintuitive, reversed EMSI pattern characterized by edge-enriched and center-depleted salt distributions governed by confinement compliance and the applied state-of-charge window. Under rigid constraints regions of electrodes under high pressure, for example near tabs, show localized salt depletion. Overall, this study establishes EMSI as a multifaceted phenomenon arising from the coupled interplay of electrochemical, mechanical and cell format factors, rather than a simple consequence of anode-driven expulsion of low-concentration electrolyte during fast charging. These results offer actionable guidelines for improving fast-charging durability across Li-ion cell formats

Electrocatalytic reduction is a promising approach for removing toxic and refractory pollutants from water, but conventional catalysts often suffer from limited active sites, high resistance, and poor stability. In this study, an integrated S-Co3O4-TNAs/Ti electrode was fabricated by constructing TiO2 nanotube arrays (TNAs) on a Ti foil substrate, followed by electrodeposition and water-bath sulfidation of the Co-based catalytic layer. Characterization results indicated that the sulfur-doped Co3O4 nanosheets exhibited significantly enhanced electrochemical performance, with higher oxygen vacancy concentration and a more favorable Co2+/Co3+ redox couple. Under optimized conditions (current density of 30 mA·cm-2, sulfidation time of 6 hours, and initial p-nitrophenol (PNP) concentration of 100 mg·L-1), the S-Co3O4-TNAs/Ti electrode achieved removal efficiencies of 86.31% for PNP and 37.44% for chemical oxygen demand (COD). Water was used as the hydrogen source for the electrocatalytic reduction process, thereby avoiding secondary pollution. These results demonstrate the potential of the S-Co3O4-TNAs/Ti electrode for electrocatalytic environmental remediation and provide insight into active-hydrogen-assisted PNP reduction.

SAF 2205 duplex stainless steel (DSS) is frequently used in hydrometallurgical environments where it is exposed to aggressive mixed-anion solutions. This study explores the mechanistic role of sulfate (SO₄²⁻) in inhibiting the localized corrosion of 2205 DSS in chloride-containing media. Using potentiodynamic polarization and critical temperature measurements (CPT and CCT), it is shown that increasing the SO₄²⁻/Cl⁻ ratio linearly enhances resistance to both pitting and crevice corrosion, shifting pitting potential and crevice repassivation potential to more noble values. To determine the mechanism of this inhibition, the lead-in pencil electrode technique was employed. It was found that SO₄²⁻ alters the pit solution chemistry by reducing the product of diffusion coefficient of the dissolving metal cations and the critical concentration for repassivation (D.C^*), along with the corresponding saturation product (D.C_S), thereby increasing the ratio D.C^*/D.C_S. This reduction in D.C^* and increase in D.C^*/D.C_S increases the ratio of repassivation tendency to dissolution driving force, thereby stabilizing the salt film and facilitating repassivation at shallower pit depths. These findings provide qualitative and quantitative explanations for the inhibitory effect of sulfate against localized corrosion of stainless steel.

figure placeholder

Highlights

• CPT and CCT of 2205 DSS were measured in different SO₄^2-/Cl⁻ ratios.

• For 2205 DSS, increasing SO₄²⁻/Cl⁻ ratio raised both CPT and CCT across 0.01-1.0 M NaCl.

• Sulfate shifted E_pit and E_rep to more noble values, enhancing resistance to localized corrosion initiation and repassivation.

• Lead-in pencil electrode studies showed that sulfate alters the pit chemistry, promoting repassivation.

Composite materials containing heterointerfaces composed of two or more metal oxides are functional materials with great potential for a wide range of applications in various fields. If methods for controlling the nanoscale structure of such metal oxide heterointerfaces can be established, it is expected to not only improve properties through an increased specific surface area but also enable the incorporation of new functions based on geometric structures. In this study, we fabricated ordered metal oxide nanohole arrays with heterointerfaces formed by anodization. To verify the fabrication process, we prepared a nanohole array with a heterointerface composed of Nb₂O₅ and WO₃. By mask-assisted sputtering, we formed a composite thin film composed of Nb and W on the surface of the template. The template was then removed to obtain a composite thin film with a regular dimple pattern on its surface. The anodization of the obtained sample resulted in pore growth originating from the dimples in both the Nb and W regions, enabling the formation of an ordered nanohole array with metal oxide heterointerfaces. This process is expected to enable the fabrication of ordered nanohole arrays with a heterointerface composed of various metal oxides.

figure placeholder

Highlights

• Preparation of ordered nanohole array with a heterointerface of metal oxides by anodization

• Formation of metal thin films with dimple patterns that act as the starting point for pore growth in the initial stage of anodization

• Optimization of anodization conditions to obtain an ordered anodic porous oxide

For insertion-type lithium-ion batteries, the solid-state diffusion coefficient of Li⁺ in an active material is considered a key parameter within the research community. The capabilities and limits of related parameter extraction methods are usually well-established.However, there is a gap in understanding the influence of the applied measurement setup. In practice, many setups unintentionally violate the assumptions of the extraction method. We apply the galvanostatic intermittent titration technique (GITT) in virtual experiments using 3D microstructure-resolved simulations in varying model measurement setups. Diffusion coefficients are extracted by applying a state-of-the-art Bayesian optimization approach which is particularly suitable for non-uniquely solvable problems. The investigated parameters are within the typical literature range of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811). Because experimental boundary conditions are precisely known within the simulation setups, the influence of microstructural features on the extracted diffusion can be isolated and quantified. The investigation shows, that the applied monodisperse thin-electrode and single-particle setup are capable of extracting the actual diffusivity with up to 4 % and 17 % point-estimate deviation, respectively. Particle cracking proved to have the largest impact on extracted diffusion coefficients. Nevertheless, all predictions remained close to the correct order of magnitude, i.e.~point estimates deviated at most by factors in the range of 10^±0.88.

Structural health monitoring (SHM) using piezoelectric transducers has been widely explored for individual lithium-ion cells, yet its applicability at the module level remains largely unstudied. This work demonstrates the feasibility of SHM on a realistic battery module composed of four 60 Ah pouch cells and operated in a mechanically constrained setup similar to an electric-vehicle (EV) battery environment. In this configuration, breathing-induced stack pressure varies during cycling, and these pressure changes are captured simultaneously with the parameters of the propagating guided wave using a self-developed ultrasonic battery management system (UBMS). Measurements at two C-rates and two ambient temperatures show that the group velocity shifts by approximately 32ms−1 between 25°C and 10°C, while cycling-induced stack pressure variations, corresponding to measured forces of up to 250 N, are reflected in a decrease of the normalized amplitude to values as low as 0.5. These findings demonstrate that piezoelectric SHM operates reliably in a realistic module-level environment. Moreover, it shows sensitivity to pressure changes within the cell stack, providing a foundation for future diagnostic approaches that are able to identify safety-critical states through their impact on the cell’s mechanical behavior.

Electrolyte motion–induced salt inhomogeneity (EMSI) can limit fast-charging performance in lithium-ion cells, yet its underlying mechanisms remain insufficiently understood. Here, we investigate EMSI in multilayer pouch cells with 50 wt. % of a silicon:carbon composite (chemical Si:C) and 50 wt. % graphite in the negative electrode by varying electrolyte fill volume, electrolyte formulation, and mechanical constraints. Long-term fast-charging cycling shows how these factors affect EMSI-induced capacity fade and ultimately trigger cell failure. We show that electrolyte pumping occurs not only under rigid confinement but also under soft confinement, where it gives rise to a counterintuitive, reversed EMSI pattern characterized by edge-enriched and center-depleted salt distributions governed by confinement compliance and the applied state-of-charge window. Under rigid constraints regions of electrodes under high pressure, for example near tabs, show localized salt depletion. Overall, this study establishes EMSI as a multifaceted phenomenon arising from the coupled interplay of electrochemical, mechanical and cell format factors, rather than a simple consequence of anode-driven expulsion of low-concentration electrolyte during fast charging. These results offer actionable guidelines for improving fast-charging durability across Li-ion cell formats

This study investigates the influence of flow-through electrode length in redox flow batteries on mass transport and related changes in battery resistance and performance metrics. A modular test cell was used that accommodated electrodes between 3 to 20 cm long. Experiments were carried out at 10 and 50 % state of charge and with different electrolyte velocities. Parasitic effects such as varying pumping power and inductive distortions were accounted for, enabling fair comparison of electrochemical results. Electrochemical impedance spectroscopy and pulse tests revealed that for the 20 cm electrode, mass transport can be responsible for over 50 % of total cell resistance even with a low current density, and that its influence increases for higher currents and lower velocities. By reducing the electrode length to 3 cm, this value decreased to less than 12 % for the same operating conditions. Polarization curves and cycling tests demonstrated the resulting impact on system performance, specifically reaching 30 % more discharge capacity, higher discharge current densities up to 560 mA cm^-2, as well as a threefold increase in maximum discharge power density. As commercially available graphite felts were employed, this study suggests a scalable path to high-power flow-through redox flow stacks.

Engineering the complex transport electrodes within proton exchange membrane water electrolysis (PEMWE) is a complex task: the anode catalyst layer (ACL) properties such as activity, electrical and ionic conductivities, permeability, thickness, contact angle, and its interface with the porous transport layer (PTL) significantly influence the performance of PEMWEs. To enable better exploitation of this interplay, this study presents a two-dimensional, two-phase model to capture the ACL dependence on its PTL interface structure, quantifying catalyst utilization. The model is validated against reference polarization curves, literature-based tomographic data, and an in-house constructed digital twin of the ACL. Simulation results reveal that catalyst utilization decreases with increasing electrode potential due to pronounced product transport limitations, which can already provide impulses to future electrode engineering. To mitigate these effects, balanced and high electrical and ionic conductivities and optimal pore size at the interface are analyzed by the model. The simulation results suggest an optimal pore size of ∼3 μm at ACL/PTL interface under constrained electrical conductivity, while larger pores (∼6 μm) are favored when conductivity is moderate. With an improved interface, the model shows that cell performance can be improved by 11.7% and 3.2%, respectively.

figure placeholder

Highlights

• 2-D and two-phase model validated using tomography data

• Application of a tomography-based digital twin for anode catalyst layer optimization

• Prediction of anode catalyst utilization in water electrolysis at varied potentials

• The influence of anode catalyst layer/porous transport layer interface on performance

Improving energy density and cycle life of lithium-ion batteries (LiBs), while maintaining or improving safety is important. Introducing silicon-containing materials to graphite negative electrodes is a promising way to increase LiB energy density. This study focuses on the impact of varying concentrations (0–10 wt%) of fluoroethylene carbonate (FEC), on the performance of Li-ion pouch cells that include 20 wt% chemical silicon-carbon (chemical SiC) in their negative electrodes. Long-term cycling tests at 40 °C and 55 °C along with long-term storage experiments at 60 °C were carried out to evaluate the effect of FEC on cell lifetime. Upon reaching 90% capacity retention, post-mortem analyses were performed using electrochemical impedance spectroscopy (EIS), while gas chromatography-mass spectrometry (GC-MS) was performed to investigate electrolyte degradation products. Scanning electron microscopy (SEM) was utilized to examine changes in the negative electrode surface after cycling at 40 °C until 90% capacity. The results demonstrate that employing FEC as an additive, in the range of 0 to 4%, has little effect on capacity retention and voltage polarization during long-term cycling or storage for cells that contain chemical SiC (at least for the sample tested here) in the negative electrode, while cells with 8 and 10% FEC performed worse.

figure placeholder

In this work, a series of novel derivatives of ethylene sulfate, formally called 1,3,2-dioxathiolane-2,2-dioxide (DTD), were synthesized and evaluated. DTD itself is a very effective electrolyte additive but suffers from poor chemical stability during storage and transport of premixed electrolyte. Electrolyte storage experiments showed that DTD degraded by ~50% over 15 weeks at room temperature, whereas 4,4′-Bi-1,3,2-dioxathiolane, 2,2,2′,2′-tetraoxide (bis-DTD) in the same electrolytes remained chemically stable throughout the same period. Bis-DTD also demonstrated wide electrochemical applicability in NMC442/graphite, Ni65/graphite, and LFP/graphite cells. In particular, using bis-DTD as an additive in Ni65/graphite cells enabled long term cycling at 40 °C to an upper cutoff of 4.4 V with excellent capacity retention and minimal impedance growth reaching 2500 cycles to end of life. In addition, electrolytes for LFP/graphite cells including bis-DTD as an co-additive, enabled effective operation from room temperature to 70 °C while maintaining low charge transfer resistance which is important for fast charge. Some of the DTD derivatives also show effectiveness in Na-ion cells, most importantly reducing the rate of impedance growth. These and other results highlight bis-DTD as a high-performing additive that demonstrates effectiveness in different Li-ion and Na-ion chemistries, over wide temperature and voltage ranges.

figure placeholder

Layered-oxides are one of most used positive active material classes in lithium ion batteries (LIB), but they are responsible for the drawback of transition metal (TM) ion dissolution and subsequent deposition on the negative electrode. This can lead to capacity loss and safety risks due to decomposition reactions involving active lithium at the TM deposition site. This study presents a new operando method to analyze the influence of TMs and moisture on lithium ion batteries (LIB). With the addition of transition metal ions during a constant voltage (CV) step with a fully charged graphite electrode, the reaction of the TM with the electrode surface could be monitored via the current. To quantify the capacity consumed by the addition of TM ions, the resulting peaks were integrated and separated into two pathways: TM deposition and a catalytic reaction at which TM° acts as catalyst for electrolyte decomposition. Manganese was found to have a notable impact on capacity loss, primarily due catalytic reactions. Furthermore, the presence of moisture in combination with TM ions increased the catalytic reaction in terms of nickel and decreased TM deposition overall. Therefore, the presence of TM ions, both alone and in combination with moisture, demonstrates that the catalytic reaction is a dominant factor in capacity fading.

figure placeholder

A density functional theory database of hydrogen chemisorption energies on close packed surfaces of a number of transition and noble metals is presented. The bond energies are used to understand the trends in the exchange current for hydrogen evolution. A volcano curve is obtained when measured exchange currents are plotted as a function of the calculated hydrogen adsorption energies and a simple kinetic model is developed to understand the origin of the volcano. The volcano curve is also consistent with Pt being the most efficient electrocatalyst for hydrogen evolution. © 2005 The Electrochemical Society. All rights reserved.

We compare the adsorption energies calculated by Nørskov et al. with data derived from experimental values; except for Ni and Co, which absorb hydrogen strongly, there is a linear relation. We discuss the model proposed by these authors in the light of extensive previous work and of experimental data and find it overly simplistic.

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.

Electrochemical techniques have been used to study the reversible insertion of sodium into hard‐carbon host structures at room temperature. In this paper we compare these results with those for lithium insertion in the same materials and demonstrate the presence of similar alkali metal insertion mechanisms in both cases. Despite the gravimetric capacities being lower for sodium than lithium insertion, we have achieved a reversible sodium capacity of 300 mAh/g, close to that for lithium insertion in graphitic carbon anode materials. Such materials may therefore be useful as anodes in rechargeable sodium‐ion batteries. © 2000 The Electrochemical Society. All rights reserved.

Lithium-ion batteries are well-suited for fully electric and hybrid electric vehicles due to their high specific energy and energy density relative to other rechargeable cell chemistries. However, these batteries have not been widely deployed commercially in these vehicles yet due to safety, cost, and poor low temperature performance, which are all challenges related to battery thermal management. In this paper, a critical review of the available literature on the major thermal issues for lithium-ion batteries is presented. Specific attention is paid to the effects of temperature and thermal management on capacity/power fade, thermal runaway, and pack electrical imbalance and to the performance of lithium-ion cells at cold temperatures. Furthermore, insights gained from previous experimental and modeling investigations are elucidated. These include the need for more accurate heat generation measurements, improved modeling of the heat generation rate, and clarity in the relative magnitudes of the various thermal effects observed at high charge and discharge rates seen in electric vehicle applications. From an analysis of the literature, the requirements for lithium-ion thermal management systems for optimal performance in these applications are suggested, and it is clear that no existing thermal management strategy or technology meets all these requirements.

In this paper, we compare the interactions of lithium and sodium with a range of carbon materials in electrochemical cells. Through wide angle in situ X-ray scattering studies, we demonstrate that both lithium and sodium can be inserted into the interlayer space in disordered carbon materials. This insertion process is accompanied by an increase in the interlayer spacing in these materials. Small-angle in situ scattering studies are presented to clearly show the insertion of lithium and sodium into nanopores within disordered hard carbons. We also show that very little, if any, sodium can be inserted into graphitic materials in contrast to the large capacity seen for lithium insertion. © 2001 The Electrochemical Society. All rights reserved.

Past theories of electrode stability assume that the surface tension resists the amplification of surface roughness at cathodes and show that instability at lithium/liquid interfaces cannot be prevented by surface forces alone [Electrochim. Acta, 40, 599 (1995)]. This work treats interfacial stability in lithium/polymer systems where the electrolyte is solid. Linear elasticity theory is employed to compute the additional effect of bulk mechanical forces on electrode stability. The lithium and polymer are treated as Hookean elastic materials, characterized by their shear moduli and Poisson’s ratios. Two-dimensional displacement distributions that satisfy force balances across a periodically deforming interface are derived; these allow computation of the stress and surface-tension forces. The incorporation of elastic effects into a kinetic model demonstrates regimes of electrolyte mechanical properties where amplification of surface roughness can be inhibited. For a polymer material with Poisson’s ratio similar to poly(ethylene oxide), interfacial roughening is mechanically suppressed when the separator shear modulus is about twice that of lithium. © 2005 The Electrochemical Society. All rights reserved.

The kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) on polycrystalline platinum [Pt(pc)] and high surface area carbon-supported platinum nanoparticles (Pt/C) were studied in 0.1 M KOH using rotating disk electrode (RDE) measurements. After corrections of noncompensated solution resistance from ac impedance spectroscopy and of hydrogen mass transport in the HOR branch, the kinetic current densities were fitted to the Butler–Volmer equation using a transfer coefficient of $\alpha =0.5$, from which HOR/HER exchange current densities on Pt(pc) and Pt/C were obtained, and the HOR/HER mechanisms in alkaline solution were discussed. Unlike the HOR/HER rates on Pt electrodes in alkaline solution, the HOR/HER rates on a Pt electrode in 0.1 M ${\text{HClO}}_4$ were limited entirely by hydrogen diffusion, which renders the quantification of the HOR/HER kinetics impossible by conventional RDE measurements. The simulation of the hydrogen anode performance based on the specific exchange current densities of the HOR/HER at $80°C$ illustrates that in addition to the oxygen reduction reaction cell voltage loss on the cathode, the slow HOR kinetics are projected to cause significant anode potential losses in alkaline fuel cells for low platinum loadings ($130\text{mV}$ at $0.05{\text{mg}}_{\text{Pt}}/{\text{cm}}_{\text{anode}}^2$ and $1.5A/{\text{cm}}_{\text{anode}}^2$), contrary to what is reported for proton exchange membrane fuel cells.

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.