The 50 most-cited articles in Journal of The Electrochemical Society, 2022

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

Lithium ion batteries (LIBs) have dominated the energy industry due to their unmatchable properties that include a high energy density, a compact design, and an ability to meet a number of required performance characteristics in comparison to other rechargeable systems. Both government agencies and industries are performing intensive research on Li-ion batteries for building an energy-sustainable economy. LIBs are single entities that consist of both organic and inorganic materials with features covering multiple length scales. Two vital parameters for LIBs are their stable and safe operation. Critical insights should be made for understanding the structure to property relationships and the behavior of components under the working condition of LIBs. Since, the cathode serves as a central component of LIBs, the overall cell performance is significantly affected by the chemical and physical properties of the cathode. Cathodes tend to react with the electrolytes and, hence, to undergo surface modifications accompanied by degradation. These side-reactions result in an erosion of battery…

Lowering the iridium loading at the anode of proton exchange membrane (PEM) water electrolyzers is crucial for the envisaged GW-scale deployment of PEM water electrolysis. Here, the durability of a novel iridium catalyst with a low iridium packing density, allowing for low iridium loadings without decreasing the electrode thickness, is being investigated in a 10-cell PEM water electrolyzer short stack. The anodes of the membrane electrode assemblies (MEAs) of the first five cells utilize a conventional iridium catalyst, at loadings that serve as benchmark for today's industry standard (2 mgIr cm−2). The last five cells utilize the novel catalyst at 8-fold lower loadings (0.25 mgIr cm−2). The MEAs are based on Nafion® 117 and are tested for 3700 h by load cycling between 0.2 and 2.0 A cm−2, with weekly polarization curves and impedance diagnostics. For both catalysts, the performance degradation at low current densities is dominated by an increase of the overpotential for the oxygen evolution reaction (OER), whereby the OER mass activity of the novel catalyst remains ≈4-fold higher…

Gas sensors are frequently used for detecting toxic gases and vapors for environmental control, industrial monitoring and household safety. Semiconductor conductivity can be modified by doping or fine-tuned by applying an electric or magnetic field in an ultra-wide range (10 −7 S cm −1 to 10 2 S cm −1 ). The conduction of semiconductor is significantly raised or reduced upon the exposure to external conditions, such as temperature variation, light, heat, mechanical stress or chemicals. Thus, semiconductors are excellent materials for sensors and the device structures are critical for sensing performance. The commonly used semiconductors materials include Si, Ge, III–V, and metal oxide semiconductors. Recently carbon-based materials gain signification attention due to their unique electrical, optical and mechanical properties. There are two major semiconductor gas sensors: resistor-based and FET-based sensors. In this review, the semiconductor materials, sensor device structure as well as gas sensing mechanisms will be systematically categorized, described and explored, with the…

Abstract Lithium-ion cells testing under different state of charge ranges, C-rates and cycling temperature have different degrees of lithium inventory loss, impedance growth and active mass loss. Here, a large matrix of polycrystalline NMC622/natural graphite Li-ion pouch cells were tested with seven different state of charge ranges (0-25, 0-50, 0-75, 0-100, 75-100, 50-100 and 25-100%), three different C-rates and at two temperatures. First, capacity fade was compared to a model developed by Deshpande and Bernardi. Second, after 2.5 years of cycling, detailed analysis by dV/dQ analysis, lithium-ion differential thermal analysis, volume expansion by Archimedes’ principle, electrode stack growth, ultrasonic transmissivity and x-ray computed tomography were undertaken. These measurements enabled us to develop a complete picture of cell aging for these cells. This then led to an empirical predictive model for cell capacity loss versus SOC range and calendar age. Although these particular cells exhibited substantial positive electrode active mass loss, this did not play a role in…

System durability is crucially important for the successful commercialization of fuel cell electric vehicles (FCEVs). Conventional accelerated durability testing protocols employ relatively high voltage to hasten carbon corrosion and/or platinum catalyst degradation. However, high voltages are strictly avoided in commercialized FCEVs such as the Toyota MIRAI to minimize these degradation modes. As such, conventional durability tests are not representative of real-world FCEV driving conditions. Here, modified start-stop and load cycle durability tests are conducted on prototype fuel cell stacks intended for incorporation into commercial FCEVs. Polarization curves are evaluated at beginning of test (BOT) and end of test (EOT), and the degradation mechanisms are elucidated by separating the overvoltages at both 0.2 and 2.2 A cm −2 . Using our modified durability protocols with a maximum cell voltage of 0.9 V, the prototype fuel cell stacks easily meet durability targets for automotive applications, corresponding to 15-year operation and 200,000 km driving range. These findings have…

Hydrogen crossover poses a critical issue in terms of the safe and efficient operation in polymer electrolyte membrane water electrolysis (PEMWE). The impact of key operating parameters such as temperature and pressure on crossover was investigated in the past. However, many recent studies suggest that the relation between the hydrogen crossover flux and the current density is not fully resolved. This study investigates the hydrogen crossover of PEMWE cells using a thin Nafion 212 membrane at current densities up to 10 A cm −2 and cathode pressures up to 10 bar, by analysing the anode product gas with gas chromatography. The results show that the hydrogen crossover flux generally increases over the entire current density range. However, the fluxes pass through regions with varying slopes and flatten in the high current regime. Only considering hydrogen diffusion as the single transport mechanism is insufficient to explain these data. Under the prevailing conditions, it is concluded that the electro-osmotic drag of water containing dissolved hydrogen should be considered additionally…

Accurately estimating the state of charge (SOC) of lithium-ion batteries is critical for developing more reliable and efficient operation of electric vehicles. However, the commonly used models cannot simultaneously extract effective spatial and temporal features from the original data, leading to an inefficient SOC estimation. This paper proposes a novel neural network method for accurate and robust battery SOC estimation, which incorporates the temporal convolutional network (TCN) and the long short-term memory (LSTM), namely TCN-LSTM model. Specifically, the TCN is employed to extract more advanced spatial features among multivariate variables, and the LSTM captures long-term dependencies from time-series data and maps battery temporal information into current SOC and historical inputs. The proposed model performs well in various estimation conditions. The average value of mean absolute error, root mean square error, and maximum error of SOC estimation achieve 0.48%, 0.60%, and 2.3% at multiple temperature conditions, respectively, and reach 0.70%, 0.81%, and 2.7% for a different…

A large-format pouch cell with a nominal capacity of 78 Ah from the Volkswagen ID.3 was disassembled and analyzed to characterize the state of the art of industrial-scale cells in automotive applications. The cell components were separated from each other, geometrically measured, and weighed to quantify the volume and weight fractions from electrode to cell level. Material samples from the electrodes were characterized by scanning electron microscopy (SEM), elemental analysis, and mercury porosimetry. Half cells were built post mortem and assessed in electrochemical tests. The results revealed a stacked cell of laminated electrode layers. The cathode showed a bi-modal particle distribution and its active material ranged with LiNi 0.65 Mn 0.2 Co 0.15 O 2 in between NMC622 and NMC811. Silicon-free graphite was used as the anode active material. Over 75% of the cell mass and over 81% of the cell volume directly contribute with its active material to the specific energy of 268 Wh kg −1 and energy density of 674 Wh L −1 at cell level. 91% of the anode and 93% of the cathode were utilized…

The efficient and sustainable use of energy is highly imperative to satisfy the escalating energy demands arising from the rapid commercialization of technologies. The development of novel electrochemical energy technologies is an essential aspect in the present-day scenario of rapid depletion of existing sources of energy. Conducting polymers are promising psuedocapacitive materials with an extended delocalisation network of π electrons, flexibility to functional modifications and facile intercalation and de-intercalation of electrolyte ions. These factors enable them to possess capacitances comparable with those of metal oxides. The use of copolymers in this context is noteworthy due to their diversity of combining different types of monomer units and facile integration. Carbon based materials have also been extensively employed on account of their high power densities and large number of charge-discharge cycles. The synergism of the non-faradaic double-layer capacitance with the faradaic charge transfer has the ability to provide impressive supercapacitor properties. Different…

Single crystal Li[Ni0.5Mn0.3Co0.2]O2//graphite (NMC532) pouch cells with only sufficient graphite for operation to 3.80 V (rather than ≥4.2 V) were cycled with charging to either 3.65 V or 3.80 V to facilitate comparison with LiFePO4//graphite (LFP) pouch cells on the grounds of similar maximum charging potential and similar negative electrode utilization. The NMC532 cells, when constructed with only sufficient graphite to be charged to 3.80 V, have an energy density that exceeds that of the LFP cells and a cycle-life that greatly exceeds that of the LFP cells at 40 °C, 55 °C and 70 °C. Excellent lifetime at high temperature is demonstrated with electrolytes that contain lithium bis(fluorosulfonyl)imide (LiFSI) salt, well beyond those provided by conventional LiPF6 electrolytes. Ultra-high precision coulometry and electrochemical impedance spectroscopy are used to complement cycling results and investigate the reasons for the improved performance of the NMC cells. NMC cells, particularly those balanced and charged to 3.8 V, show better coulombic efficiency, less capacity fade and…

The nucleation overpotential has been used by many researchers as an indicator of the energy required to form the Li nuclei during plating. Typically, a two-electrode system is used to measure the nucleation overpotential; this method, however, fails to show the contribution of working and counter electrodes separately. In this study, we have used a three-electrode configuration (three-dimensional nickel foam as working electrode, lithium foil as both reference and counter electrode) to deconvolute the potential associated with each electrode during the galvanostatic Li electrodeposition to obtain a clear picture of nucleation overpotential. The results indicate that, in such a system, the main source of overpotential is the sudden drop in the potential of the counter electrode, which can be attributed to the extraction of Li from the surface of lithium metal. Moreover, unlike the first half-cycle, the nuclear overpotential is dominated by the working electrode in the second half-discharge cycle, which should account for a true nucleation overpotential of the system. This finding…

Today, hydrogen (H 2 ) is overwhelmingly produced through steam methane reforming (SMR) of natural gas, which emits about 12 kg of carbon dioxide (CO 2 ) for 1 kg of H 2 (∼12 kg-CO 2 /kg-H 2 ). Water electrolysis offers an alternative for H 2 production, but today’s electrolyzers consume over 55 kWh of electricity for 1 kg of H 2 (>55 kWh/kg-H 2 ). Electric grid-powered water electrolysis would emit less CO 2 than the SMR process when the carbon intensity for grid power falls below 0.22 kg-CO 2 /kWh. Solar- and wind-powered electrolytic H 2 production promises over 80% CO 2 reduction over the SMR process, but large-scale (megawatt to gigawatt) direct solar- or wind-powered water electrolysis has yet to be demonstrated. In this paper, several approaches for solar-powered electrolysis are analyzed: (1) coupling a photovoltaic (PV) array with an electrolyzer through alternating current; (2) direct-current (DC) to DC coupling; and (3) direct DC-DC coupling without a power converter. Co-locating a solar or wind farm with an electrolyzer provides a lower power loss and a lower upfront…

High voltage aqueous Li-ion batteries have the potential for sustainable large-scale energy storage due to their intrinsic advantages of safety, low cost, as well as environmental friendliness. “Water-in-salt” electrolytes have significantly enhanced the energy density of aqueous Li-ion batteries by extending the aqueous electrolyte stability window to 3.0 V. However, the cathodic limit and salt concentration need to be reduced, enabling to operate low cost LiMn 2 O 4 /Li 4 Ti 5 O 12 cells. In addition, gravimetric energy density of LiMn 2 O 4 /Li 4 Ti 5 O 12 , self-discharge rate, and operation temperature range remain rarely studied. This perspective aims to briefly summarize the opportunity and challenges of aqueous batteries for practical applications.

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

With a potential to deliver 60% greater energy density than conventional lithium-ion batteries, the simple design of anode-free lithium metal cells with liquid electrolytes has generated significant research interest. However, without excess lithium, the short lifetime and safety concerns for cells cycling lithium metal with liquid electrolytes make the development of anode-free cells particularly challenging. Herein, we investigate the effect of four different positive electrode materials on the performance of anode-free cells—LiNi0.5Mn0.3Co0.2O2 (NMC532), LiNi0.8Mn0.1Co0.1O2 (NMC811), LiCoO2 (LCO), and LiFePO4 (LFP). In-situ electrochemical impedance spectroscopy and electrolyte degradation measurements were performed on cells with dual-salt LiDFOB/LiBF4 electrolyte to elucidate cell failure. Additional state-of-the-art electrolyte systems as well as other testing conditions (temperature, pressure, depth of discharge) were also explored, along with nail safety tests and calendar aging cycle-hold experiments. We show that the rate of lithium inventory loss and impedance growth…

Lithium-ion batteries (LiBs) have been widely used in a variety of applications, however they still suffer from low capacity retention, large capacity fade ratio or inability to charge efficiently at low temperatures, especially below −20 °C. The reasons behind these drawbacks originate from the nature of active materials such as the anode and the cathode, along with the composition of electrolyte solutions. In particular, from the perspective of active materials, it has been reported that the most common problems arise from the dramatic increase in the resistances, especially charge transfer resistance, and the decrease of lithium-ion diffusivity, by more than one order of magnitude. In this report, we review the most recent strategies in the development of anode and cathode materials and composites, focusing on enhanced electronic and ionic conductivities for improved low-temperature electrochemical performance. Our overview aims to provide a comprehensive comparative study of the proposed methods to overcome the low-temperature challenges in order to develop high energy-density…

Effective diagnostic techniques for Li-ion batteries are vital to ensure that they operate in the required voltage and temperature window to prevent premature degradation and failure. Ultrasonic analysis has been gaining significant attention as a low cost, fast, non-destructive, operando technique for assessing the state-of-charge and state-of-health of Li-ion batteries. Thus far, the majority of studies have focused on a single C-rate at relatively low charge and discharge currents, and as such the relationship between the changing acoustic signal and C-rate is not well understood. In this work, the effect of cell temperature on the acoustic signal is studied and shown to have a strong correlation with the signal’s time-of-flight. This correlation allows for the cell temperature to be inferred using ultrasound and to compensate for these effects to accurately predict the state-of-charge regardless of the C-rate at which the cell is being cycled. Ultrasonic state-of-charge monitoring of a cell during a drive cycle illustrates the suitability of this technique to be applied in…

Anion exchange membrane water electrolyzers (AEMELs) have recently received significant attention due to their potential advantages over proton exchange membrane electrolyzers (PEMELs). However, some AEMELs feed an aqueous salt solution to the cell where PEMELs typically feed deionized (DI) water. DI water is preferred to keep the system and maintenance costs low. Because of this, many AEMEL researchers report performance both in the salt solution (typically KOH) and DI water. However, the methodology for switching between KOH and DI water is often poorly defined, and it is unclear what impact the residual salt has on cell performance after switching from salt to DI water. Having a fully deionized environment is important because the presence of salts in the water feed increase the effective electrochemical surface area of the catalyst in the three-dimensional electrode and residual salt remaining after switching to DI water feed can have a misleading transient effect on cell performance. This paper focuses on understanding the transition from KOH to DI water testing in AEMELs. It…

There has never been a more pressing need to develop sustainable energy systems as dramatic climate changes emerge across the World. Some of these effects can be alleviated by the development of efficient devices that are capable of producing hydrogen gas in an environmentally acceptable manner, which in turn can be employed as a clean fuel. In this context, the splitting of water is especially attractive. However, this technology requires the design of new cost-effective electrocatalytic materials. In this review, the progress made in the development of transition metal dichalcogenides (TMDs) and their composites as electrocatalysts for both acidic and alkaline electrolysis cells and as photocatalysts for the formation of hydrogen is described and discussed. Following a short introduction to the mechanisms of the electrochemical hydrogen and oxygen evolution reactions and the photoelectrochemical generation of hydrogen, an introduction to TMDs, their relevant general properties and the methods used in their synthesis are described. Then, the performance of various TMD-based…

The loss of electrochemically active surface area (ECSA) in the cathode during load cycling remains a major durability issue for proton exchange membrane fuel cells (PEMFCs). Here, the degradation of low-loaded cathodes (0.1 mg Pt cm MEA − 2 ) was investigated by accelerated stress tests (ASTs) in H2/N2 configuration, varying the upper potential limit (UPL, 0.85–1.0 V) and the hold time (1, 2, or 8 s) of the square wave voltage cycling profiles. A full voltage loss analysis was performed at beginning-of-life and after 100, 300, 1 k, 2 k, 5 k, 10 k, 20 k, 50 k, 100 k, 200 k, and 500 k cycles, determining: (i) the roughness factor (rf) via CO-stripping; (ii) the H2-crossover; (iii) the cathode electrode’s proton conduction resistance; (iv) the H2/O2 and H2/air performance; and, (v) the O2 transport resistance. It was found that the ECSA/rf deteriorates linearly vs the logarithm of the number of cycles or time at UPL, with higher slopes for harsher ASTs. The individual voltage losses were found to be either unaffected by the aging (H2-crossover and proton conduction resistance) or…

With the ongoing transformation to e-mobility, lithium all-solid-state batteries are promising candidates for advanced mobile energy storage. Other than in conventional lithium ion cells, the rigid solid electrolyte entails its own morphology and does not wet residual voids in composite electrodes, which can limit the cell performance. We therefore take a closer look at the influence of microstructural characteristics on different scales in composite cathodes by means of electrochemical simulation using the finite element method. Cathode active material particle arrangements are constructed to validate the model against experimental data. We highlight the significance of the active material particle size distribution and state-of-charge dependent input parameters, such as the lithium diffusion coefficient in NCM811 and the exchange current density at the interface of NCM811 and Li 6 PS 5 Cl. We zoom in on that interface under the presence of void space that can result from manufacturing or arise from inter-particle contact loss upon volume changes. In a 1-particle-void model, the…

Ternary metal halides A 3 MX 6 , ( A = Li + , Na + ; M = trivalent metal; X = halide) are a promising family of solid electrolytes for potential applications in all-solid-state batteries. Recent research efforts have demonstrated that chemical substitution at all three sites is an effective strategy to controlling battery-relevant material properties. The A 3 MX 6 family exhibits a wide breadth of structure and anion sublattice types, making it worthwhile to comprehend how chemical substitutions manifest desirable functional properties including ion transport, electrochemical stability, and environmental tolerance. Yet, a cohesive understanding of the materials design principles for these substitutions have not yet been developed. Here, we bring together prior literature focused on chemical substitutions in the A 3 MX 6 ternary metal halide solid electrolytes. Using materials chemistry perspectives and principles, we aim to provide insights into the relationships between crystal structure, choice of substituting ions and the extent of substitutions, ionic conductivity, and…

Dye-sensitized solar cells (DSSCs) are promising photovoltaic technology with diverse indoor and outdoor applications. DSSCs can be integrated with curtains and glasses to power various devices, including wireless sensors, computer network peripherals, internet-of-things (IoT) devices, and wearable electronics. DSSCs have the potential to become the future source of energy. However, their efficiency, stability, and industrial production still need to be scaled up. The present review encompasses these elements and the various changes that have occurred inside the DSSC over the last few years, including device structure, TiO 2 photoelectrode, novel electrolytes, new organic photosensitizers, efficient catalyst materials, and encapsulation strategies for sealing DSSC devices. We further discuss how the performance of each functional component of a DSSC has been enhanced as a result of the introduction of novel materials and manufacturing processes. In addition, we also briefly cover p-DSSCs and tandem DSSCs. Finally, the prospect of highly efficient and stable DSSCs is highlighted.

Microscale silicon particles in lithium-ion battery anodes undergo large volume changes during (de)lithiation, resulting in particle pulverization and surface area increase concomitant with a continuous growth of the solid-electrolyte-interphase. One approach to overcome these phenomena is to operate the silicon anode under capacity-limited conditions (i.e., with partial capacity utilization). Since crystalline silicon is irreversibly transformed into amorphous phases upon lithiation, the purpose of the partial capacity utilization is to maintain a crystalline phase and thus prevent particle disintegration. Here, we investigate the amorphization process of micro-sized silicon particles in a silicon-rich anode (70 wt% silicon) over extended charge/discharge cycling in half-cells with a lithium reference electrode, varying the lower cutoff potential of the Si electrode. While the capacity of Si electrodes after formation remain constant for lithiation cutoffs of ≥170 mV vs Li+/Li, their capacity continuously increases over cycling for cutoffs of <170 mV vs Li+/Li, implying an ongoing…

The Vanadium Flow Battery (VFB) was taken from the initial concept stage at UNSW in 1983 through the development and demonstration of several 1–5 kW prototypes in stationary and electric vehicle applications in the 1990s with on-going research activities continuing to the present day. As part of this 38 year R&D program, a wide range of research projects was undertaken in the areas of electrodes and membranes, electrolyte process development and characterisation, electrolyte additives and precipitation inhibitors, conducting plastic bipolar plate formulation and manufacturing trials, mathematical modelling of membrane transfer, shunt currents and pumping energy losses in bipolar stacks, thermal modelling of redox cells under a range of operating conditions, impedance spectroscopy and control system development, sensors and state-of-charge monitoring, chemical and electrochemical rebalancing, gelled electrolyte, vanadium bromide cell and V/O redox fuel cell. Several field trials of the VFB were conducted by UNSW in the mid-1990s with early licensing leading to large-scale…

Besides the performance of a lithium-ion battery cell, the manufacturing costs are crucial for the success of battery electric vehicles. To enable cost efficient yet well performing battery cells, an optimization of the manufacturing steps with respect to the cell properties is necessary. The slurry mixing process, being the initial step of the lithium-ion battery cell manufacturing process, is well known to affect the structure of the electrode coating (e.g. porosity, tortuosity or the distribution of the binder and conductive additive), which is further connected to its electrical and ionic resistances. Therefore, a variation of the formulation strategy or mixing device can affect the performance of the lithium-ion battery cell. In this study, several variations of the slurry mixing process are investigated with respect to its effect on the fast-charge capability of the lithium-ion battery cell. Properties of the slurry, the electrode and the resulting lithium-ion battery cell are characterized for each variation to detect interdependencies and derive process-structure-property…

Herein we report the electrochemical system for the detection of specific antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) proteins in blood serum patient samples after coronavirus disease 2019 (COVID-19). For this purpose, the recombinant SARS-CoV-2 spike protein (SCoV2-rS) was covalently immobilised on the surface of the gold electrode pre-modified with mixed self-assembled monolayer (SAMmix) consisting of 11-mercaptoundecanoic acid and 6-mercapto-1-hexanol. The affinity interaction of SCoV2-rS with specific antibodies against this protein (anti-rS) was detected using two electrochemical methods: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The anti-rS was detected with a detection limit of 2.53 nM and 1.99 nM using CV and EIS methods, respectively. The developed electrochemical immunosensor is suitable for the confirmation of COVID-19 infection or immune response in humans after vaccination.

Molybdenum diselenide (MoSe 2 ), an in-organic analog of graphene, is considered a rising star in the family of transition-metal dichalcogenides (TMDs) because of its stable covalent Mo–Se bond, good catalytic properties, huge specific surface area, higher electrical, multivalent oxidation states of transition metal ions, and its ability to be intercalated with suitably-sized metal atoms or organic molecules to modify their physical properties with a distinguishing layered structure. It is being projected as the next-generation 2D layered nano-material for many energy storage-conversion applications. This review covers the properties, functionalization of MoSe 2 , and their applications in supercapacitors, discussing the current developments of MoSe 2 and its nano-composites-based supercapacitors, providing emphasis to the capacitive performances which comprise of specific capacitance/ capacity, cyclic lifespan, energy density, power density, rate capability, and their practicality in the real environments. Fundamental charge-storage mechanisms are also discussed to provide better…

Graphite is, in principle, applicable as a high-power anode in lithium-ion batteries (LIBs) given its high intralayer lithium diffusivity at room temperature. However, such cells are known to exhibit poor capacity retention and/or undergo irreversible side reactions including lithium plating when charged at current rates above ∼2 C (∼740 mA g−1). To explore the inherent materials properties that limit graphite anodes in rapid-charge applications, a series of full-cells consisting of graphite as the anode and a standard Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) cathode was investigated. Instead of a conventional cathode-limited cell design, an anode-limited approach was used in this work to ensure that the overall cell capacity is only determined by the graphite electrode of interest. The optimized N:P capacity ratio was determined as N/P = 0.67, enabling stable cycling across a wide range of charging rates (4–20 C) without inhibition by the NMC811 cathode. The results show that unmodified, highly crystalline graphite can be an excellent anode for rapid-charge applications at up to 8 C, even…

Emphasis on clean energy has led to a widespread focus on lithium-ion batteries. However, a major obstacle is their degradation with several cycles or calendar aging. Battery Management System relies on an essential model-based algorithm to protect the battery from operating outside the safety limit. Thus, this work attempts to answer important research questions on battery models: (1) Are physics-based electrochemical models (EM) robust enough to identify internal cell degradation and abnormal battery behavior? (2) How are the structural simplifications and mathematical order reductions imposed on the EMs and what are their trade-offs? (3) How to apply simplified EM for safer and more efficient battery operation? (4) What are the prospects and obstacles of employing EM-based algorithms in the future? This paper presents a detailed analysis of EM from a modeling and application perspective. The paper introduces battery operating mechanisms, typical failures, and their effects. Followed by an analysis of full order EM (Pseudo 2-Dimensional), and further classification into simpler…

The formation of complexes between copper ions and biomolecules plays important roles in biological systems. In this work, the structures and electrochemical properties of copper-creatinine complexes were investigated by both experimental and computational approaches. DFT calculation revealed the possible structures of copper-creatinine complexes and provided the data of formation energies, bond lengths, and charge distribution. The properties of the complexes were further investigated by cyclic voltammetry, UV-visible spectrophotometry, X-ray absorption spectroscopy, and scanning electron microscopy. The combination of experimental and computational findings revealed that CuII binds with creatinine via the endocyclic nitrogen. In aqueous environment, the [Cu(creatinine)2(H2O)2]2+ complex is formed. The reduction of [Cu(creatinine)2(H2O)2]2+ formed a stable 1:4 complex between CuI and creatinine. Importantly, the understanding of the electrochemical behaviors of copper-creatinine complexes leads to the development of a novel sensor for the detection of creatinine, a biomarker for…

Cyclic and linear sweep voltammetry techniques substantially misjudge the performance of water splitting electrocatalysts due to their transient nature that forbids the interface from reaching a steady-state. This misjudgment leads to the potentially detrimental yet unwittingly falsified data accumulation in the literature that requires immediate attention. Alternatively, sampled-current voltammetry (SCV) constructed from steady-state responses is advised to be widely adopted for screening electrocatalysts that are actually destined for steady-state operations. To show that this exaggeration is universal, a well-characterized activated SS, coprecipitated Co(OH) 2 , and Pt foil electrodes are studied for OER and HER in 1.0 M KOH. The results urge that it is time to adopt a relatively more precise alternative technique such as SCV.

As power generated from renewables becomes more readily available, the need for power-efficient energy storage devices, such as redox flow batteries, becomes critical for successful integration of renewables into the electrical grid. An important aspect of a redox flow battery is the planar flow field, which is usually composed of two-dimensional channels etched into a backing plate. As reactant-laden electrolyte flows into the flow battery, the channels in the flow field distribute the fluid throughout the reactive porous electrode. We utilize topology optimization to design flow fields with full three-dimensional geometry variation, i.e., 3D flow fields. Specifically, we focus on vanadium redox flow batteries and use the optimization algorithm to generate 3D flow fields evolved from standard interdigitated flow fields by minimizing the electrical and flow pressure power losses. To understand how these 3D designs improve performance, we analyze the polarization of the reactant concentration and exchange current within the electrode to highlight how the designed flow fields mitigate…

Hydrogen permeation across the membrane is a critical safety hurdle within polymer electrolyte membrane (PEM) water electrolysis (WE). It is crucial to implement recombination catalysts into the membrane electrode assemblies (MEAs) for reducing hydrogen concentrations and allow the use of much thinner membrane architectures that allow high efficiency operation. Here we show how recombination catalyst layers can be fabricated into MEAs by using a scalable method. In subsequent slot-die coating steps, an electrically insulating and then a recombination layer (both 5 μ m thick) are applied directly to the anode. This three-layer system is then processed into a 5-layer MEA with a cathode and membrane using the decal process. The 5-layer MEA shows a reliable hydrogen reduction in the anode product gas for a wide-range of membrane thicknesses. The long-term stability of the recombination layer is shown for a 5-layer Nafion™ HP-MEA in comparison to a 3-layer MEA. Even after long-term operation, the MEA shows a safe hydrogen concentration reduction on the anode. Finally, the presented…

In this review, we summarize the latest research progress on Mo 2 C based materials for various electrochemical applications. It starts with discussing the different synthesis methods and the tactics for modifying the physicochemical characteristics of Mo 2 C. In addition, the variables that influence the morphology and electrochemical performance of Mo 2 C have been explored. The synthesis methods are examined based on their tricks, benefits, and drawbacks, including solid-gas, solid-solid, solid-liquid, and some other processes (chemical vapor deposition, Sonochemical, microwave-assisted, plasma, etc.). Methods that are safe, cost-effective, environmentally friendly, and suited for large-scale production of Mo 2 C are given special consideration. The solid-solid reaction is found to be a facile and cost-effective method to synthesize Mo 2 C structures having high surface area and small particle size. Also, the various electrochemical applications of Mo 2 C are reviewed. Mo 2 C is an extremely active and durable electrocatalyst mainly for hydrogen evolution reaction (HER). The…

Li-ion batteries will lose both capacity and power over time due to calendar aging caused by slow parasitic processes that consume Li+ ions. Studying and mitigating these processes is traditionally an equally slow venture, which is especially taxing for the validation of new active materials and electrolyte additives. Here, we evaluate whether potentiostatic holds can be used to accelerate the diagnosis of Li+ loss during calendar aging. The technique is based on the idea that, under the right conditions, the current measured as the cell voltage is held constant can be correlated with the instantaneous rate of side reactions. Thus, in principle, these measurements could capture the rate of capacity fade in real time. In practice, we show that this method is incapable of quantitatively forecasting calendar aging trends. Instead, our study demonstrates that potentiostatic holds can be applied for initial qualitative screening of systems that exhibit promising long-term stability, which can be useful to shrink the parameter space for calendar aging studies. By facilitating the…

Polymer electrolyte membrane water electrolyzers (PEMWEs) are devices of paramount importance, enabling the large-scale storage of hydrogen from intermittent renewable energy sources such as wind and solar. But a transition towards lower noble metal catalyst loadings and intermittent operation is needed for the widespread utilization of this technology. Although kinetic losses tend to dominate in membrane electrode assembly (MEA) results, it has been suggested that morphological changes and interfaces between the catalyst, ionomer, and membrane will also contribute to overall degradation. Moreover, the combination of degradation to the catalyst layer (CL) constituents will further lead to structural changes that have not been widely explored. The multitude and complexity of degradation mechanisms, which likely occur simultaneously, require a characterization approach that can explore surfaces and interfaces at a range of length-scales to probe chemical, morphological, and structural changes of constituents within the catalyst later. This paper presents a comprehensive…

Proton exchange membrane water electrolyzers (PEMWEs) have demonstrated enormous potential as the next generation hydrogen production technology. The main challenges that the state-of-the-art PEMWEs are currently facing are excessive cost and poor durability. Understanding the failure modes in PEMWEs is a key factor for improving their durability, lowering the precious metal loading, and hence cost reduction. In this work, reactive spray deposition technology (RSDT) has been used to fabricate a membrane electrode assembly (MEA) with one order of magnitude lower Pt and Ir catalyst loadings (0.2–0.3 mg PGM cm −2 ) in comparison to the precious metal loadings in the stat-of-the-art commercial MEAs (2–3 mg PGM cm −2 ). As fabricated MEA with an active area of 86 cm 2 , has been tested for over 5000 h at steady-state conditions that are typical for an industrial hydrogen production system. Herein, we present and discuss the results from a comprehensive post-test analysis of the MEA of interest. The main degradation mechanisms, governing the performance loss in the RSDT fabricated MEA…

Most metal AM technologies are rapidly approaching, and in some cases even exceeding the Technology Readiness Level 8, indicating that they are widely available and capable of completing a wide range of projects despite identified process restrictions. Thanks to significant technological progress made in the last decade, more industries are incorporating metal additive manufacturing in their production process to obtain highly customized parts with complex geometries. However, the poor surface finish of AM parts is a major drawback to their aesthetics and functionality. Over the years, different approaches were proposed to enhance their surface quality, each bearing its limitations. Among the proposed technologies, electropolishing is a strong candidate for improving the surface finish of AM parts. This study aims to review the literature on electropolishing of AM parts. However, to provide a comprehensive study of the different aspects involved, a brief review is also presented on the origin and consequences of the surface properties of AM parts as well as an evaluation of other…

Improving the intrinsic catalytic activity of NiFe layered double hydroxide (LDH), which is a benchmark electrocatalyst for oxygen evolution reaction (OER), is a significant challenge. In the present study, we doped ruthenium ions into NiFe LDH (Ru-NiFe LDH) to accelerate the OER kinetics. Electrochemical measurements of NiFe LDH and Ru-NiFe LDH at similar mass loadings showed that Ru-NiFe LDH demonstrated a higher OER activity than that of NiFe LDH. Ru-NiFe LDH only requires an overpotential of 246 mV at 10 mA cm −2 in alkaline media. This attributes to ruthenium doping primarily, which can promote the catalytic activity of Fe sites and boost the electronic interaction among the Ni, Fe, and Ru metals according to the theoretical calculations. Ru-NiFe LDH is stable during OER stability measurements, which was confirmed by structure and elemental analysis. These findings will provide a useful approach for promoting the intrinsic activity of multi-metallic (oxy) hydroxide electrocatalysts toward the OER.

A better understanding of the cathode active material (CAM) plays a crucial role in the improvement of lithium-ion batteries. We have previously reported the structural properties of the model cathode material LiNiO2 (LNO) in dependence of its calcination conditions and found that the deviation from the ideal stoichiometry in LiNiO2 (Ni excess) shows no correlation to the 1st cycle capacity loss. Rather, the morphology of LNO appears to be decisive. As CAM secondary agglomerates fracture during battery operation, the surface area in contact with the electrolyte changes during cycle life. Thus, particle morphology and especially the primary particle size become critical and are analyzed in detail in this report for LNO, using an automated SEM image segmentation method. It is shown that the accessible surface area of the pristine CAM powder measured by physisorption is close to the secondary particle geometric surface area. The interface area between CAM and electrolyte is measured by an in situ capacitance method and approaches a value proportional to the estimated primary particle…

The oxygen reduction reaction (ORR) is a critical, but sluggish reaction used for various applications, including fuel cells and metal-oxygen batteries. Currently, the benchmark catalysts for ORR are Pt-based catalysts. However, due to these catalysts being scarce and very expensive, alternative catalysts that are more abundant and less expensive are urgently in demand. MXenes, a new two-dimensional (2D) material based on transition metal carbides and nitrides, have advanced the performance of many existing technologies, including batteries, supercapacitors, sensors, etc. Owing to their unique electronic structure, physical and chemical properties, and tunable morphology, MXenes are expected to thrive in the ORR electro- and photo-catalytic systems. Recent studies reported better-performing ORR catalysts with MXenes as supports, which holds promise in the significant reduction of Pt loading for efficient catalysts. Furthermore, MXenes exhibit wide applicability and stability in a range of pH values, from acidic to basic. In this work, we carefully review the most pertinent works on…

This paper presents a simplified thermal runaway model (FEM) used to guide the design of a novel battery pack designed to resist thermal runaway propagation passively. The model is based on the heat equation for a 2D geometry with a heat generation term based on the maximum amount of energy measured using a custom-made calorimeter. The model was validated against experimental data using a 48-cell subscale of a full-scale battery pack for three different runs with three trigger cells with Internal Short Circuit Devices (ISCD) implanted in the separators. One trigger cell was placed at the edge, one placed in the middle, surrounded by six cells, and one placed in one corner of the subscale pack. It was shown that by simplifying the geometry and looking at the complex thermal runaway propagation mechanism only from a thermal perspective (no electrochemical reactions or fluid flow), the model predicted the experimental data with good precision. Furthermore, such a model was used to validate some experimental observations, which indicated the practicality of such a simplified design tool.

The development of high performance polymer electrolyte fuel cells increasingly relies on modeling to optimally tune cathode catalyst layers (CCL) to desired properties. This includes models to rationalize the role of water as promoter and asphyxiant to the oxygen reduction reaction. Existing models are able to reproduce or predict, using assumed parameters, the performance of the cell. However, consideration of the wetting properties of the composite has remained elusive. Experiments to characterize these properties are difficult to perform. There is thus a gap in theory for relating material choices with wetting properties. This article elaborates on this gap and presents a novel conceptual approach to close it. Fundamental modeling approaches, molecular dynamics studies and experimental works have shown that the interaction of ionomer with the Pt/C surface exerts a major impact on wetting behavior and water sorption properties of the porous CCL composite. In our approach, the state of molecular alignment of ionomer sidechains and backbones is linked to the structural…

Liquid electrolyte engineering plays a critical role in modern lithium-ion batteries. However, the existing electrolytes fall short when used with some trending battery chemistries such as high-voltage and high-energy-density electrodes. Fluorination of electrolyte solvents has been identified as an effective approach for improved cyclability, but few works systematically studied the effects of fluorination extent of carbonate solvents on battery performance. Here we design and synthesize a family of fluorinated ethyl methyl carbonates. Different numbers of F atoms are finely tuned to yield monofluoroethyl methyl carbonate (F1EMC), difluoroethyl methyl carbonate (F2EMC) and trifluoroethyl methyl carbonate (F3EMC). The cycling behavior of several types of lithium-ion pouch cells, including graphite (Gr)/single-crystalline LiNi 0.8 Mn 0.1 Co 0.1 O 2 (SC-NMC811), Gr-SiO x /LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622), high-voltage Gr/LiNi 0.5 Mn 1.5 O 4 (LNMO), Gr/layered Li-rich Mn-based oxide (LLMO) and fast-charging Gr/NMC622, were systematically investigated to understand the impact of…

High-capacity Ni-rich cathode such as LiNi0.8Mn0.1Co0.1O2 (NMC811) has a great potential to enable high energy lithium-ion batteries (LIBs) for long-range electrical vehicles. However, the utilization of NMC 811 in large-scale application is still challenging. While many published papers on NMC811 focus on materials modification, the moisture sensitivity of NMC811 and its implications in storage and large-scale electrode coating are not well explored, not to mention how to overcome those challenges for industry application. This work discusses the key parameters impacting the rheological properties of NMC811 slurries and their correlations to the properties of dried electrodes. Effective solutions are proposed to address the gelation issue of NMC811 slurry during large-scale coating to hopefully inspire more effective and practical approaches to tackle the grand challenges in electrochemical energy storage.

The manufacture, characterisation and application of carbon cloth (CC) are reviewed and its use as an electrode in fundamental electrochemical studies and technological applications over the last fifty-five years is considered. The most widely used precursors to produce commercial CC are polyacrylonitrile (PAN) fibres manufactured by heat treatment at 1500–2000 o C. Carbon cloth has good electrical conductivity, high mechanical strength and high chemical resistance. CC is a versatile electrode material that can operate over a wide potential range in aqueous electrolytes and molten salts. Chemical and thermal methods can enhance the surface area and help control CC surfaces’ wettability. Electrodes can be decorated by nanostructured carbons, precious metal nanoparticles or enzyme immobilisation to modify surface functionality, improve activity and widen applications. The doping of CC with polymers, metals and metal oxides has enabled its use in sensors, electrosynthesis of chemicals, environmental remediation and water treatment, as well as energy storage and conversion.…

The introduction of Manganese (Mn) ions (2+ ⇋ 3+ ⇋ 4+) to transition metal oxides proved to be a potential strategy to tailor the redox behavior of these materials for energy storage. We fabricate a lower electronegative element (i.e., Mn) doped copper cobaltite and copper oxide (CuCo 2 O 4 /CuO; CCO) heterostructures electrodes through the hydrothermal synthesis route. The ensued electrodes have a more than 2-fold improvement in specific capacity (382.9 C g −1 ) than the undoped CCO electrode (120.8 C g −1 ) at 1 A g −1 . The all-solid-state asymmetric supercapacitor (ASC) practical device is constructed with higher Mn-doped CCO heterostructures as the positive electrode and activated carbon (AC) as the negative electrode. With a voltage window of 1.5 V, the fabricated ASC device has a high specific energy of 52.6 Wh kg −1 and specific power of 774.3 W kg −1 . The long-term cyclic stability of 92% capacity retention after 5000 cycles at the current density of 4 A g −1 . Additionally, two ASC devices are series-connected that can power up a red light-emitting diode (LED) display for…

Raman spectroscopy is widely used to evaluate the ionic interactions and solvates present in electrolytes. As shown here, however, Raman spectra for crystalline solvates containing the lithium bis(trifluoromethanesulfonyl)imide (or amide) (i.e., LiN(SO 2 CF 3 ) 2 , LiTFSI, LiTFSA, LiNTf 2 or LiTf 2 N) salt indicate that the commonly used vibrational band analyses are likely to be inaccurate and thus result in misleading conclusions about the ion interactions in liquid electrolytes with this salt. In particular, it is found by examining the Raman spectrum of a known crystalline solvate with the CIP-I- C 2 coordination mode (i.e., a TFSI − anion with a C 2 conformation coordinated to a single Li + cation via a single oxygen atom), that the vibrational band for this mode of coordination overlaps (or is closely positioned beside) that for the uncoordinated (i.e., SSIP) TFSI − anion. This realization further complicates the assessment of Raman data for LiTFSI-based electrolytes.