The 50 most-cited articles in Journal of The Electrochemical Society, 2019

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.…

We present a wide range of testing results on an excellent moderate-energy-density lithium-ion pouch cell chemistry to serve as benchmarks for academics and companies developing advanced lithium-ion and other "beyond lithium-ion" cell chemistries to (hopefully) exceed. These results are far superior to those that have been used by researchers modelling cell failure mechanisms and as such, these results are more representative of modern Li-ion cells and should be adopted by modellers. Up to three years of testing has been completed for some of the tests. Tests include long-term charge-discharge cycling at 20, 40 and 55°C, long-term storage at 20, 40 and 55°C, and high precision coulometry at 40°C. Several different electrolytes are considered in this LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite chemistry, including those that can promote fast charging. The reasons for cell performance degradation and impedance growth are examined using several methods. We conclude that cells of this type should be able to power an electric vehicle for over 1.6 million kilometers (1 million miles) and last at…

The aim of this study is to provide a better understanding of performance degrading mechanisms occurring when a proton exchange membrane water electrolyzer (PEM-WE) is coupled with renewable energies, where times of operation and idle periods alternate. An accelerated stress test (AST) is proposed, mimicking a fluctuating power supply by operating the electrolyzer cell between high (3 A cm −2 geo ) and low current densities (0.1 A cm −2 geo ), alternating with idle periods during which no current is supplied and the cell rests at open circuit voltage (OCV). Polarization curves, periodically recorded during the OCV-AST, reveal an initial increase in activity (≈50 mV after 10 cycles) followed by a significant decrease in performance during prolonged OCV cycling due to an increasing high frequency resistance (HFR) (≈1.6-fold after 718 cycles). These performance changes can clearly be related to the OCV periods, since they are not observed in a reference experiment where the OCV period is replaced by a potential hold at 1.3 V. The origin of the phenomena, which are responsible for the…

Transition metal dissolution from the cathode active material and its deposition on the anode causes significant cell aging, studied most intensively for manganese. Owing to their higher specific energy, the current focus is shifting towards nickel-rich layered LiNi x Mn y Co z O 2 (NMC, x + y + z = 1) with x > 0.5, so that the effect of Ni dissolution on cell degradation needs to be understood. This study investigates the dissolution of transition metals from a NMC622 cathode and their subsequent deposition on a graphite anode using operando X-ray absorption spectroscopy. We show that in NMC622-graphite cells transition metals dissolve nearly stoichiometrically at potentials >4.6 V, highlighting the significance of investigating Ni dissolution/deposition. Using NMC622-graphite full-cells with electrolyte containing the bis(trifluoromethane)sulfonimide (TFSI) salts of either Ni, Mn, or Co, we compare the detrimental impact of these metals on cell performance. Using in-situ and ex-situ XRD, we show that the aging mechanism induced by all three metals is the loss of cycleable lithium…

As a derivative of LiNiO 2 , NCA (LiNi 1-x-y Co x Al y O 2 ) is widely used in the electric vehicle industry because of its high energy density. It is thought that Co and Al both play important roles in enhancing NCA material properties. However, there is no solid evidence in the literature that clearly shows that Co is required in NCA with high nickel (e.g. when 1-x-y > 0.9) content. Therefore, a systematic study on the roles of different cation substituents in a series of LiNi 1-n M n O 2 (M = Al, Mn, Mg, or Co) materials was made. In-situ X-ray diffraction (XRD) and differential capacity versus voltage (dQ/dV vs. V) studies showed that the multiple phase transitions in Li x NiO 2 during charge and discharge, thought to cause poor charge-discharge capacity retention, were suppressed in Li x Ni 0.95 M 0.05 O 2 (M = Al, Mn, or Mg), while 5% Co failed to suppress the phase transitions. First principles calculations were made to understand the function of each substituent. Accelerating rate calorimetry shows that unlike Al, Mn, or Mg, Co has no contribution to safety improvement.…

The lack of a reliable rechargeable lithium metal (Li-metal) anode is a critical bottleneck for next-generation batteries. The unique mechanical properties of lithium influence the dynamic evolution of Li-metal anodes during cycling. While recent models have aimed at understanding the coupled electrochemical-mechanical behavior of Li-metal anodes, there is a lack of rigorous experimental data on the bulk mechanical properties of Li. This work provides comprehensive mechanical measurements of Li using a combination of digital-image correlation and tensile testing in inert gas environments. The deformation of Li was measured over a wide range of strain rates and temperatures, and it was fitted to a power-law creep model. Strain hardening was only observed at high strain rates and low temperatures, and creep was the dominant deformation mechanism over a wide range of battery-relevant conditions. To contextualize the role of creep on Li-metal anode behavior, examples are discussed for solid-state batteries, "dead" Li, and protective coatings on Li anodes. This work suggests new research…

Lithium-ion battery performance at low temperatures or fast charge/discharge rates is determined by the intrinsic electrolyte transport and the thermodynamic properties of the commonly used binary electrolytes. For the development of future electrolyte solutions, a quantification of the ionic conductivity, the binary diffusion coefficient, the transference number, and the thermodynamic factor over a large concentration and temperature range is mandatory. In this study, we apply previously discussed and established methods for the determination of ionic conductivities and binary diffusion coefficients to two commonly used electrolyte systems (EC:DMC (1:1 w:w) and EC:EMC (3:7 w:w)) as well as to one EC-free electrolyte (EMC:FEC (19:1 w:w)). To quantify transference numbers and thermodynamic factors, we introduce a novel analysis scheme, so that we are ultimately able to report temperature (−10°C–+50°C) and concentration (0.1 M–3.0 M) dependent values as well as approximate relationships for transport and thermodynamic properties required for numerical battery models. Comparison with…

What is the best approach for estimating standard electrochemical potentials, E (0) , from voltammograms that exhibit chemical irreversibility? The lifetimes of the oxidized or reduced forms of the majority of known redox species are considerably shorter than the voltammetry acquisition times, resulting in irreversibility and making the answer to this question of outmost importance. Half-wave potentials, E (1/2) , provide the best experimentally obtainable representation of E (0) . Due to irreversible oxidation or reduction, however, the lack of cathodic or anodic peaks in cyclic voltammograms renders E (1/2) unattainable. Therefore, we evaluate how closely alternative potentials, readily obtainable from irreversible voltammograms, estimate E (0) . Our analysis reveals that, when E (1/2) is not available, inflection-point potentials provide the best characterization of redox couples. While peak potentials are the most extensively used descriptor for irreversible systems, they deviate significantly from E (0) , especially at high scan rates. Even for partially irreversible systems,…

Detection of harmful gases is important to ensure human and environmental health. Industrial waste gases such as CO, NO 2 , H 2 S, and NH 3 are of typical focus among researchers over the years. Chemiresistive sensors are suitable for detecting these harmful gases. One suitable candidate material for this sensor is the conducting polymer, which offers the advantage of room-temperature operation. This review focuses on the overall development of conducting polymer as chemiresistive sensing materials. Effects of different parameters influencing sensor performance such as response, gas concentration, response time, and recovery time of conducting polymers are explored. Different conducting polymers are compared and their affinities to specific gases are determined. An understanding of pure conducting polymers assists further exploration of these polymers in composite form. A comprehensive understanding based on an overview of literature will facilitate researchers in selecting appropriate conducting polymers for different gas sensing applications and is expected to encourage further…

The use of sensors and the Internet of Things (IoT) is key to moving the world’s agriculture to a more productive and sustainable path. Recent advancements in IoT, Wireless Sensor Networks (WSN), and Information and Communication Technology (ICT) have the potential to address some of the environmental, economic, and technical challenges as well as opportunities in this sector. As the number of interconnected devices continues to grow, this generates more big data with multiple modalities and spatial and temporal variations. Intelligent processing and analysis of this big data are necessary to developing a higher level of knowledge base and insights that results in better decision making, forecasting, and reliable management of sensors. This paper is a comprehensive review of the application of different machine learning algorithms in sensor data analytics within the agricultural ecosystem. It further discusses a case study on an IoT based data-driven smart farm prototype as an integrated food, energy, and water (FEW) system.

In the pursuit of surpassing the energy density of conventional lithium ion cells, significant efforts have been made to develop lithium metal cells. However, many reports in the literature utilize Li-metal cells with significant excess lithium, resulting in a dramatically reduced practical energy density. In contrast, anode-free cells do not utilize excess lithium; instead, a lithium metal anode is formed in-situ from the stored lithium within the positive electrode during the first charge. Here, we evaluate anode-free lithium metal pouch cells (NMC532||Cu) with operando pressure measurements constrained to different stack pressures between 75–2205 kPa with two different electrolytes, 1M LiPF 6 FEC:DEC (1:2) and 1M LiPF 6 FEC:TFEC (1:2). Increasing the initial average pressure from 75–2200 kPa was found to generally improve cycle life, with the most significant benefits achieved up to 1200 kPa. Cells containing FEC:TFEC electrolyte exhibited a superior initial performance compared to FEC:DEC cells, as evidenced by cycling data and SEM analysis of the lithium morphology. Although…

Membrane electrode assembly durability is explored for polymer electrolyte membrane electrolyzers, focusing on catalyst (iridium, Ir) degradation at low loading and dynamic operation. Low catalyst loading and high cell potential are critical to observing durability losses over reasonably short experiments, regardless of test profile. While small losses are seen during steady operation, cycling greatly accelerates performance decreases. Ir dissolution mechanistically drives performance loss, thinning the anode catalyst layer and resulting in increasing kinetic losses during extended operation. While morphological changes to the catalyst layer are found, increasing polarization resistance suggests that degradation at the catalyst/ionomer/membrane interface may also contribute. Electrolyzer operation with model wind and solar profiles results in less severe performance losses compared to triangle- and square-wave potential cycling due to the lower cycling frequency of the renewable profiles. However, in both cases kinetics dominated the loss, indicating that higher cycling rates…

To improve electric vehicle market acceptance, the charge time of their batteries should be reduced to 10–15 minutes. However, achieving 4C to 6C charge rates with today's batteries is only possible for cells with thin electrodes coming at the expense of low energy density and high battery manufacturing cost. An electrochemical model is validated versus high rate charge data for cells with several loadings. The model elucidates that the main limitations for high energy density cells are poor electrolyte transport resulting in salt depletion within the anode and Li plating at the graphite/separator interface. Next, the model is used to understand what future electrode and electrolyte properties can help enable 4C and 6C charging. Ideally, future electrolytes would be identified with 2X conductivity, 3–4X diffusivity, and transference number of 0.5–0.6. Alternatively charging at elevated temperatures enhances electrolyte transport by 1.5X conductivity and 2–3X diffusivity with a negligible effect on transference number. Another effective strategy to enable 4C and 6C charging is…

Alkaline fuel cells and electrolyzers are of interest because they have potential advantages over their acid counterparts. High-conductivity anion conducting membranes were analyzed and used in alkaline hydrogen/oxygen fuel cells. The membranes were composed of reinforced block copolymers of poly(norbornenes) with pendant quaternary ammonium head-groups. It was found that membranes with light cross-linking provided excellent mechanical stability and allowed very high ion exchange capacity polymers to be used without penalty of excessive water uptake and swelling. The optimum membrane and fuel cell operating conditions were able to achieve a peak power density of 3.4 W/cm 2 using hydrogen and oxygen. The performance increase was greater than expected from minimizing ohmic losses. Mechanical deformations within the membrane due to excess water uptake can disrupt full cell operation. Cells were also run for over 500 h under load with no change in the membrane resistance and minimal loss of operating voltage.

In the first paper of this series the bulk and surface structural properties of Ti-fiber based porous transport layers (PTL) were characterized and described. In this second part the correlation of structure to the performance in polymer electrolyte water electrolysis cells is analyzed by determination of the three main overpotentials of ohmic, kinetics and mass transport losses. The strongest correlation between the PTL bulk transport properties and cell performance is obtained for heat transport. The current density dependent temperature gradients show good agreement with ex situ determined heat conductivity from part one. However, surface properties of the PTL materials, have a stronger influence on cell performance than the bulk properties. Catalyst layer utilization and ohmic interfacial resistances correlate with the interfacial contact areas reported in part one and performance increases with increasing contact area. This is due to a local mass transport resistance decreasing with increasing catalyst layer utilization.

The rotating disk electrode (RDE) technique was frequently used for investigating the stability of oxygen evolution reaction (OER) catalysts under galvanostatic conditions, where the increase in potential is reported to be due to catalyst degradation. The galvanostatic RDE stability test typically results in catalyst life-time of several hours, although the same catalyst can last for thousands of hours in a PEM electrolyzer under similar conditions, a discrepancy that is still unresolved. In this work, we present a careful examination of the use of the RDE technique as a tool for the investigation of the OER catalyst stability. Our findings provide a clear evidence that the change in potential during the stability test is not related at all to catalyst degradation, but is rather due to an experimental artifact caused by nano- and micro-bubbles formed within the pores of the catalyst layer during the OER, which cannot be removed by electrode rotation. Instead, they accumulate and shield the OER active sites from the electrolyte, resulting in an increase of the potential, which is…

Maintaining high performance after extensive use remains a key challenge for low-Pt proton exchange membrane fuel cells for transportation applications. Strategically improving catalyst durability requires better understanding of the relationship between degradation mechanisms and catalyst structure. To investigate the effects of the carbon support morphology, we compare the electrochemical performance and durability of membrane electrode assemblies (MEAs) using Pt and PtCo x catalysts with a range of porous, solid, and intermediate carbon supports (HSC, Vulcan, and acetylene black). We find that electrochemical surface area (ECSA) retention after a catalyst-targeted durability test tends to improve with increasing support porosity. Using electron microscopy, we investigate microstructural changes in the catalysts and reveal the underlying degradation mechanisms in MEA specimens. Pt migration to the membrane and catalyst coarsening, measured microscopically, together were quantitatively consistent with the ECSA loss, indicating that these were the only two significant degradation…

Ni-rich layered oxides, like NCM-811, are promising lithium-ion battery cathode materials for applications such as electric vehicles. However, pronounced capacity fading, especially at high voltages, still lead to a limited cycle life, whereby the underlying degradation mechanisms, e.g. whether they are detrimental reactions in the bulk or at the surface, are still controversially discussed. Here, we investigate the capacity fading of NCM-811/graphite full-cells over 1000 cycles by a combination of in situ synchrotron X-ray powder diffraction, impedance spectroscopy, and X-ray photoelectron spectroscopy. In order to focus on the NCM-811 material, we excluded Li loss at the anode by pre-lithiating the graphite. We were able to find a quantitative correlation between NCM-811 lattice parameters and capacity fading. Our results prove that there are no considerable changes in the bulk structure, which could be responsible for the observed ≈20% capacity loss over the 1000 cycles. However, we identified the formation of a resistive surface layer, which is responsible for (i) an…

Washing is a commonly used method to remove surface impurities of cathode materials for lithium-ion batteries. However, a clear mechanistic understanding of the washing process is missing in the literature. In this study, we will investigate the effect of washing and subsequent drying of nickel-rich NCM cathodes (85% nickel) with respect to gassing and impedance of the washed cathodes. By on-line electrochemical mass spectrometry (OEMS), we will show a drastic reduction of the O 2 release above 80% SOC for the NCM washed with deionized water, suggesting the formation of an oxygen-depleted surface layer on the NCM particle surface. The modification of the surface can be confirmed by a strong impedance buildup of cathodes composed of washed NCM (using a micro-reference electrode in a full-cell), revealing that the impedance increases strongly with increasing drying temperature after washing. Last, we will propose a comprehensive mechanism on the processes occurring during the washing/drying process of nickel-rich NCM materials and identify the drying temperature after washing as the…

High ionic conductivity membranes can be used to minimize ohmic losses in electrochemical devices such as fuel cells, flow batteries, and electrolyzers. Very high hydroxide conductivity was achieved through the synthesis of a norbornene-based tetrablock copolymer with an ion-exchange capacity of 3.88 meq/g. The membranes were cast with a thin polymer reinforcement layer and lightly cross-linked with N , N , N ', N '-tetramethyl-1,6-hexanediamine. The norbornene polymer had a hydroxide conductivity of 212 mS/cm at 80°C. Light cross-linking helped to control the water uptake and provide mechanical stability while balancing the bound (i.e. waters of hydration) vs. free water in the films. The films showed excellent chemical stability with <1.5% conductivity loss after soaking in 1 M NaOH for 1000 h at 80°C. The aged films were analyzed by FT-IR before and after aging to confirm their chemical stability. A H 2 /O 2 alkaline polymer electrolyte fuel cell was fabricated and was able to achieve a peak power density of 3.5 W/cm 2 with a maximum current density of 9.7 A/cm 2 at 0.15 V at…

The quality of metal oxide-based battery active materials is compromised by surface contamination from storage and handling at ambient conditions. We present a detailed analysis of the true nature and the quantity of the surface contaminants on two different cathode active materials, the widely used LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM111) and the Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). We process these materials in three distinct conditions "wet" (excessive exposure to moisture), "dry" (standard drying of as-received materials), and "calcined" (heat-treatment of cathode powders). Surface contaminants are then quantified by thermogravimetric analysis coupled with mass spectrometry (TGA-MS), and their reactivity with an ethylene carbonate-based electrolyte is evaluated using on-line mass spectrometry (OMS). We demonstrate that not only the commonly assumed LiOH and Li 2 CO 3 residues account for NCM performance deterioration upon storage in moisture and CO 2 containing atmosphere, but also basic transition metal hydroxides/carbonates formed on the material surface. Eventually, we…

Nitrite (NO 2 − ) has been extensively applied in agricultural and industrial products and is often found in various foodstuff, tap water, biological samples and environmental systems. However, NO 2 − as a toxic contaminant probably threaten the human health by producing highly carcinogenic N-nitrosamines. Compared with the traditional analytical techniques, electroanalytical method has considerable advantages such as cost-effective, rapidness, facile operation, and easy miniaturization. Graphene nanocomposites have significant synergistic electrocatalytic effect toward the nitrite redox, which could eventually amplify the electrochemical response signals, and improve the selectivity, sensitivity, and practicability for the nitrite detection in various real samples. The recent developments on graphene-based nitrite electrochemical sensors are reviewed from the view of sensing materials, including graphene, metal nanoparticle/graphene composites, nanostructured metal compound/graphene composites, polymer/graphene composites, MOF/graphene composites, enzyme/graphene composites,…

Fast charging of batteries is currently limited, particularly at low temperatures, due to difficulties in understanding lithium plating. Accurate, online quantification of lithium plating increases safety, enables charging at speeds closer to the electrochemical limit and accelerates charge profile development. This work uses different cell cooling strategies to expose how voltage plateaus arising from cell self-heating and concentration gradients during fast charging can falsely indicate plating, contrary to prevalent current assumptions. A solution is provided using Differential Voltage (DV) analysis, which confirms that lithium stripping is observable. However, scanning electron microscopy and energy-dispersive X-ray analysis are used to demonstrate the inability of the plateau technique to detect plating under certain conditions. The work highlights error in conventional plating quantification that leads to the dangerous underestimation of plated amounts. A novel method of using voltage plateau end-point gradients is proposed to extend the sensitivity of the technique, enabling…

In the first paper of this series, the bulk, surface and transport properties of porous transport layer materials (PTL) for polymer electrolyte water electrolysis cells (PEWE) are characterized. A systematic PTL matrix of Ti fiber materials with 3 fiber diameters and 2 nominal porosities as well as a state of the art sintered powder material are investigated to get a better understanding of the governing parameters in electrolysis cells. X-ray tomographic microscopy analysis of ex situ PTL structures and post operando membrane electrode assemblies is performed. On the tomographic structures, bulk (porosity, pore/solid size distributions, fiber orientation), mass transport (diffusivity, permeability, conductivities) and surface parameters (roughness, membrane deformation, PTL surface area and interfacial contact area) are determined. The second paper of this series will correlate the structural parameters with in-depth electrochemical analysis. The new insights into the effect of PTL properties on PEWE performance allow to isolate governing key parameters. From know-how obtained on…

Measuring electrochemical impedance spectra of lithium-ion symmetric cells at low temperatures allows for unambiguous separation of charge transfer impedance contributions from other cell impedance features. Electrodes from dry Li[Ni 0.5 Mn 0.3 Co 0.2 ]O 2 (NMC 532)/artificial graphite (AG) pouch cells were used to make blocking electrode configuration symmetric cells and blocking electrode full coin cells. NMC532/AG cells with 1.2M LiPF 6 in EC:DMC 3:7 (w:w) electrolyte also underwent the formation process before the electrodes were used to make non-blocking configuration symmetric and full coin cells. Through the use of temperature dependent measurements on blocking and non-blocking cells, the impedance contribution due to faradaic, charge transfer interactions can be distinguished from non-faradaic, high frequency impedance contributions. Fitting the EIS spectra allowed both the charge transfer resistances and the related capacitances to be determined for the solid electrolyte interphase layers on the negative and positive electrodes. The charge transfer resistances were strongly…

Single crystal positive electrode materials for lithium-ion batteries have superior properties compared to their polycrystalline counterparts as has been demonstrated by industry and academia. Single crystal LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532), NMC622 and now NMC811 have been successfully commercialized. However, single crystal LiNi 1-x-y Co x Al y O 2 (NCA) materials have not been reported yet. One simple method for producing single crystal NMC material requiring high temperature and excess lithium during synthesis creates Li 5 AlO 4 impurities if applied directly in attempts to synthesize single crystal NCA materials. This work introduces a two-step lithiation method for single crystal LiNi 0.88 Co 0.09 Al 0.03 O 2 synthesis, which can prevent the formation of Li 5 AlO 4 impurities. Powder X-ray diffraction, electron backscatter diffraction, and electrochemical measurements show the viability of the two-step lithiation method. Full coin cell cycling shows that the capacity retention of the single crystal NCA samples is at least as good as their polycrystalline counterparts. It is…

Anode-free batteries (AFBs) are impressive and recent phenomena in the era of energy storage devices due to their high energy density and relative ease of production compared to the traditional Lithium metal batteries (LMBs). However, dendrite formation during plating and stripping and low coulombic efficiency (CE) are the main challenges that impede practical implementation of these batteries. Here we report an extremely stable dual-salt electrolyte, 2M LiFSI+1M LiTFSI (2FSI+1TFSI)) in DME/DOL (1:1, v/v), system in comparison to the single salt 3M LiTFSI (3TFSI) in DME/DOL (1:1, v/v), to effectively stabilize AFB composed of LiFePO 4 cathode and bare Cu-foil anode for the first time. The electrolyte stabilized anode-free cell with the configuration Cu||LiFePO 4 via reductive decomposition of its anions and enabled the cell to be cycled with CE of 98.9% for 100 cycles. This results from the formation of stable, ion conductive and electrically insulating inorganic components rich Solid Electrolyte Interface (SEI) layer on the surface of in-situ deposited Li-metal that blocks the…

Cell designs for the electrochemical reduction of CO 2 from gas phase were developed and investigated, and the critical elements for an efficient process were identified. Various types of polymeric membrane were used to build membrane electrode assembly adapted for CO 2 reduction in gas phase: protonic and anion exchange membrane (AEM), bipolar membrane and a modified bipolar like membrane configuration. Configurations using anion exchange ionomer in the cathodic catalytic layer in contact with an AEM allow for a great enhancement of the cathode reaction selectivity toward CO. However, a severe problem was identified when co-electrolysis is performed using only an AEM: this type of membrane acts as a CO 2 "pump" meaning that for each molecule of CO 2 reduced at the cathode, one or two CO 2 molecules are produced at the anode by oxidation of the carbonate/bicarbonate anion transported in the membrane. A bipolar membrane system was shown to soften this problem, but only a newly developed cell design was able to fully prevent the parasitic CO 2 pumping. Using this new cell…

We offer an explanation for how dendrite growth can be inhibited when Li metal pouch cells are subjected to external loads, even for cells using soft, thin separators. We develop a contact mechanics model for tracking Li surface and sub-surface stresses where electrodes have realistically (micron-scale) rough surfaces. Existing models examine a single, micron-scale Li metal protrusion under a fixed local current density that presses more or less conformally against a separator or stiff electrolyte. At the larger, sub-mm scales studied here, contact between the Li metal and the separator is heterogeneous and far from conformal for surfaces with realistic roughness: the load is carried at just the tallest asperities, where stresses reach tens of MPa, while most of the Li surface feels no force at all. Yet, dendrite growth is suppressed over the entire Li surface. To explain this dendrite suppression, our electrochemical/mechanics model suggests that Li avoids plating at the tips of growing Li dendrites if there is sufficient local stress; that local contact stresses there may be high…

This paper studied the gases release of a graphite//NMC111(LiNi 1/3 Mn 1/3 Co 1/3 O 2 ) cell during cycle in the voltage ranges of 2.6-4.2V and 2.6-4.8V and the temperatures of at 25°C and 60°C.It was proved that the CO 2 , CO, and H 2 gases are released as a result of electrolyte decomposition.And it shows that the CO and H 2 gases evolution is a direct consequence of the electrochemical reaction of electrolyte decomposition, while the CO 2 generation is a consequence of the additional chemical reaction of interaction between the O 2 released from the cathode atomic lattice oxygen and CO released from the same place on the cathode (appearing because of the electrolyte decomposition).That is why at the same electrochemical reaction of electrolyte decomposition, the ratio CO 2 /CO varies in the wide range from 0.82 to 2.42 depending on cycling conditions (temperature and cutoff voltage).It was proved that a potential-independent H 2 evolution is a consequence of its adsorption in pores of powdered graphite on anode.There was proposed the mechanism of the electrolyte decomposition and…

Pencil is one of the most widely used electrode material in electrochemical sensing of various organic and inorganic species with significant lower detection limit. Due to their lower background currents, superior sensitivity, reproducibility, amendable electroactive surface area, cost effective and ease of disposability, pencil graphite electrode has gain considerable attention in recent years. It signifies a viable substitute to other expensive traditional electrodes such as Glassy carbon, Gold, Boron-doped-diamond, platinum etc. This review addresses a wide overview of the characteristics, preparations, pre-treatment and application of bare PGE and in combination with other modifier as electrochemical sensors for the quantification of organic pollutants specifically pharmaceuticals and pesticides.

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

Lithium-sulfur (Li-S) secondary batteries with sulfur cathodes and theoretical energy density of ∼2600 Wh/kg, are promising high energy-density system for next-generation electric-vehicles (EVs) potentially mitigating the gravimetric and volumetric energy density limitations of existing lithium-ion (Li-ion) batteries. Herein, a chemically synthesized sulfonic acid-based complex framework material (CFM) termed as (SCFM), was used as sulfur host (S-SCFM) to prevent polysulfide dissolution in Li-S batteries. The S-SCFM based CFM cathodes show an initial capacity of 1190 mAh/g and a capacity of 1044 mAh/g after 100 cycles. In addition, the S-SCFM based CFM cathodes exhibited good cycling stability with a minimal fade rate of ∼0.0012% per cycle. XPS analysis of the cycled separators with the S-SCFM electrodes shows complete absence of polysulfide species after 100 charge-discharge cycles. It was also identified that the SCFM based CFM chemically binds sulfur via -C-S- linkages thereby exhibiting an affinity for the polysulfide species formed during the charge-discharge cycles. As a…

In this review we shortly discuss about the graphene and graphene-based materials synthesis and present the recent year's research progress (2017−2019) in the enhancement of the analytical performance of sensors and biosensors. Particularly, we covered a very broad range of graphene-based electrochemical sensors and biosensors for the detection of glucose, cholesterol, dopamine (DA), ascorbic acid (AA), uric acid (UA), bisphenol A (BPA), cancer biomarkers and heavy metal ions. We believe that the discussed subjects are useful and may be used as an instruction guide for the future developments in the field of graphene and graphene-based materials for sensors and biosensors.

Prussian blue and its analogs (PBA) form an attractive family of materials for sensing and biosensing applications. Due to their open framework structure their electrochemical behavior is closely linked to the intercalation of alkaline ions. Moreover, these compounds show a clear peroxidase activity that makes them excellent transducers in biosensors based on H 2 O 2 quantification. In this review, we present in a progressive manner an overview of the structure, composition, and synthesis of PBA. Subsequently we approach the current trends in the use of PBA in the field of electrochemical sensors, providing a critical discussion on their electrochemical behavior and the electrocatalytic activity toward H 2 O 2 electrooxidation and electroreduction, along with the determination of toxic, hazardous compounds and drugs.

Time of Flight Secondary Ion Mass Spectroscopy, X-Ray Photoelectron Spectroscopy, in situ Photo-Current Spectroscopy and electrochemical analysis were combined to characterize the physicochemical alterations induced by electrochemical passivation of the surface oxide film providing corrosion resistance to 316L stainless steel. The as-prepared surface is covered by a ∼2 nm thick, mixed (Cr(III)-Fe(III)) and bi-layered hydroxylated oxide. The inner layer is highly enriched in Cr(III) and the outer layer less so. Molybdenum is concentrated, mostly as Mo(VI), in the outer layer. Nickel is only present at trace level. These inner and outer layers have bandgap values of 3.0 and 2.6−2.7 eV, respectively, and the oxide film would behave as an insulator. Electrochemical passivation in sulfuric acid solution causes the preferential dissolution of Fe(III) resulting in the thickness decrease of the outer layer and its increased enrichment in Cr(III) and Mo(IV-VI). The further Cr(III) enrichment of the inner layer causes loss of photoactivity and improved corrosion protection with the anodic…

Due to their extreme volume expansion, Si/C-composites suffer from fracture or delamination and consequent capacity fading during the Li-ion cell operation. One approach to reduce the electrical contact loss and improve the performance is the application of mechanical pressure on the cell. Therefore, a comprehensive aging study of Si/C|NMC811 pouch cells is conducted with cells in different compression configurations as uncompressed and under flexible and fixed compression at pressure levels in the range of 0.08 MPa, 0.42 MPa, and 0.84 MPa. In-situ swelling measurements by dilation as well as in-operando mapping of the pressure distribution on the cell surfaces reveal the positive influence of the low pressure fixed and the middle pressure flexible compression on the cycle life. For the heavily fixed compressed cells, an inhomogeneous pressure distribution and occurring pressure hot -spots close to the cell current collectors of up to 5.2 MPa are found. An extensive post-mortem analysis including SEM cross-sectioning and EIS measurements of the aged anodes and the separator confirms…

Additives such as vinylene carbonate (VC) and fluoroethylene carbonate (FEC) are commonly added to lithium-ion battery electrolytes in order to form a solid electrolyte interphase (SEI) on the anode, suppressing continuous solvent reduction. In this work, we directly compare VC and FEC by analyzing the SEI with FTIR and XPS, and the evolved gases with on-line electrochemical mass spectrometry (OEMS) in different model systems. Since both additives evolve mainly CO 2 during formation, the effect of CO 2 as an additive is compared to the addition of VC and FEC. While Li 2 CO 3 is as expected the main SEI compound found due to the added CO 2 , surprisingly no CO was detected in the gas phase of such cells. Based on FTIR, NMR and OEMS analyses of cells filled with 13 C labeled CO 2 , we suggest a mechanism explaining the beneficial effects of CO 2 and hence also of CO 2 evolving additives in lithium-ion battery cells. While the generation of polycarbonate from FEC or VC reduction is observed, the generation of Li 2 CO 3 may be as important as the generation of polycarbonate.

Infectious diseases commonly occur in contaminated water, food, and bodily fluids and spread rapidly, resulting in death of humans and animals worldwide. Among infectious agents, viruses pose a serious threat to public health and global economy because they are often difficult to detect and their infections are hard to treat. Since it is crucial to develop rapid, accurate, cost-effective, and in-situ methods for early detection viruses, a variety of sensors have been reported so far. This review provides an overview of the recent developments in electrochemical sensors and biosensors for detecting viruses and use of these sensors on environmental, clinical and food monitoring. Electrochemical biosensors for determining viruses are divided into four main groups including nucleic acid-based, antibody-based, aptamer-based and antigen-based electrochemical biosensors. Finally, the drawbacks and advantages of each type of sensors are identified and discussed.

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…

Redox flow batteries are an emerging technology for long-duration grid energy storage, but further cost reductions are needed to accelerate adoption. Improving electrode performance within the electrochemical stack offers a pathway to reduced system cost through decreased resistance and increased power density. To date, most research efforts have focused on modifying the surface chemistry of carbon electrodes to enhance reaction kinetics, electrochemically active surface area, and wettability. Less attention has been given to electrode microstructure, which has a significant impact on reactant distribution and pressure drop within the flow cell. Here, drawing from commonly used carbon-based diffusion media (paper, felt, cloth), we systematically investigate the influence of electrode microstructure on electrochemical performance. We employ a range of techniques to characterize the microstructure, pressure drop, and electrochemically active surface area in combination with in-operando diagnostics performed in a single electrolyte flow cell using a kinetically facile redox couple…

In the production process chain of lithium-ion battery cells, the filling process is eminent for the final product quality and costs. The filling consists of several dosing steps of electrolyte liquid into the cell and the subsequent (intermediate) wetting of the cell components. The quantity of electrolyte filled not only has an impact on the wetting rate of electrodes and separator but also limits the capacity of the cell and influences the battery lifetime. However, too much electrolyte is dead weight, results in a lower energy density and unnecessarily increases the costs of the battery. To ensure low costs in production and at the same time high quality of the cells, the optimal amount of electrolyte is studied in this paper. Based on experimental data from electrochemical impedance spectroscopy, the filling process, the formation process as well as a lifetime test, the interdependencies between electrolyte quantity, wetting rate, capacity, energy density and lifetime are presented for large-format cells.

Growth of the solid electrolyte interphase (SEI) is a primary driver of capacity fade in lithium-ion batteries. Despite its importance to this device and intense research interest, the fundamental mechanisms underpinning SEI growth remain unclear. In Part I of this work, we present an electroanalytical method to measure the dependence of SEI growth on potential, current magnitude, and current direction during galvanostatic cycling of carbon black/Li half cells. We find that SEI growth strongly depends on all three parameters; most notably, we find SEI growth rates increase with nominal C rate and are significantly higher on lithiation than on delithiation. We observe this directional effect in both galvanostatic and potentiostatic experiments and discuss hypotheses that could explain this observation. This work identifies a strong coupling between SEI growth and charge storage (e.g., intercalation and capacitance) in carbon negative electrodes.

Cells containing LiNi x Co y Mn 1-x-y O 2 (NCM) materials with very high nickel content suffer from cathode material degradation upon cycling, especially when operating these cells at higher voltage. While the cathode particle degradation is a problem other issues contribute to electrochemical performance loss. Graphite/LiNi 0.8 Co 0.1 Mn 0.1 O 2 cells have been cycled to different upper cutoff voltages and investigated with electrochemical impedance spectroscopy (EIS), gas analysis with online electrochemical mass spectroscopy (OEMS), nuclear magnetic resonance (NMR) spectroscopy, gas chromatography with MS (GCMS) and inductively coupled plasma MS (ICP-MS). Increased gas evolution was observed when the upper cutoff voltage was increased from 4.2 to 4.6 V. An increase in O 2 evolution upon cycling as well as an increase of CO 2 upon increasing the voltage, have been observed. More electrolyte decomposition products are observed on the anode for cells cycled to higher voltage. An increased amount of nickel has been detected on the graphite electrode in accordance with an increased…

Two types of solid oxide cells with different Ni-YSZ cermet microstructures have been aged in electrolysis and fuel cell modes for operating times ranging from 1000 to 15000 hours.The pristine and aged cermets have been reconstructed by synchrotron X-ray holotomography.Nickel agglomeration has been observed in the bulk of the operated samples inducing a significant loss of triple phase boundary lengths.The inspection of the microstructural properties has confirmed the stabilizing role of YSZ on Ni coarsening.Furthermore, the gradients of properties quantified at the electrolyte interface have revealed a depletion of Ni only in the electrochemically active region of the electrode.The process is strongly promoted for a coarse cermet microstructure when operated under electrolysis current.The evolution of the microstructural properties has been implemented in an in-house multiscale model.The simulations have shown that the loss of performance is dominated by the depletion of Ni in case of a coarse microstructure.Thanks to the computations, it has been shown that the Ni depletion is…

Recently, because of their cost effectiveness, high safety and environmental friendliness, zinc-ion batteries (ZIBs) are receiving enormous attention. Until now, aqueous-based ZIBs have been the focus of attention. However, the issues regarding hydrogen evolution, and zinc electrode passivation as well as dendrite formation limit their practical application. In this work, a biocompatible, stable and low-cost choline chloride/ urea (ChCl/urea) deep eutectic solvent is reported as an alternative electrolyte for rechargeable ZIBs based on delta-type manganese oxide (δ-MnO 2 ) intercalation electrode. The behavior of the zinc electrode on stripping and deposition in ChCl/urea electrolyte was examined. Besides, the charge storage and charge-transfer characteristics of the battery was studied. The results showed that there was no sign of dendrite formation on the zinc electrode during long-term cycling. Consequently, the fabricated battery exhibited good electrochemical performance with the maximum specific capacity of 170 mAh/g and good cyclability. In addition, the system showed…

Extreme Fast Charge Challenges for Lithium-Ion Battery: Variability and Positive Electrode Issues, Tanim, Tanvir R., Dufek, Eric J., Evans, Michael, Dickerson, Charles, Jansen, Andrew N., Polzin, Bryant J., Dunlop, Alison R., Trask, Stephen E., Jackman, Ryan, Bloom, Ira, Yang, Zhenzhen, Lee, Eungje

Significant mass-transport resistances in polymer-electrolyte-fuel-cell catalyst layers (CLs) impose a lower limit on Pt-loading levels, hindering wide-spread fuel-cell commercialization. The origin of this resistance remains unclear. Minimization of CL mass-transport resistance is imperative to achieve better CL design and performance. In this paper, an operando method based on H 2 limiting current is used to characterize and quantify CL resistance in traditional porous Pt/carbon-based electrodes. CL sub-resistances are isolated using continuum multiscale modeling and experiments, investigating the effects of reactant molecular weight, pressure, and ionomer to carbon weight ratio. The results expose CL resistance including both interfacial and transport components, although the majority of the CL resistance is ascribed to a local resistance close to the Pt reaction sites, which includes interfacial resistance and local transport resistance. Variations in temperature, humidity, and primary particle loading (Pt:C ratio) highlight the impact of operating conditions and CL design…

Heavy duty Li-ion batteries in the electric vehicles suffer from serious safety issues due to their operation in abuse conditions.The worst consequence of these conditions is the thermal runaway, which causes a dramatic rise in temperature and pressure leading to a catastrophic failure of the battery.Therefore, precise determination of thermal runaway behavior of the battery under different abusive scenarios holds critical importance.This paper reviews the understanding of the thermal runaway behavior of Li-ion batteries through experimental routes.The impact of initial conditions (SoC, overcharge and ageing) and design (geometry, material and capacity) of the battery on the severity of thermal runaway is extensively discussed.It is observed that the thermal runaway becomes more severe in high SoC, overcharged and aged batteries, and the mechanism of thermal runaway primarily depends on the battery design.The quantification of the fire-induced hazards is presented in terms of the heat release rate.Further, we observe that the electrical and mechanical abuse conditions induce an…

A new "hot formation" protocol is proposed to improve lower temperature cycling of lithium metal batteries. The cycling stability of anode-free pouch cells under low pressure (75 kPa) is shown to decline significantly as the cycling temperature is decreased from 40°C to 20°C. At low pressure and 40°C the initial morphology of the lithium anode is dense and columnar, far superior to that plated at 20°C. For "hot formation" two initial 40°C cycles (C/10 charge C/2 discharge) are conducted prior to extended low temperature (20°C) cycling. These two initial cycles have a surprisingly large impact; capacity retention to 80% is increased from only 18 cycles without hot formation to 60 cycles with hot formation at low pressure. When the applied pressure is increased to 1200 kPa, the hot formation (20°C cycling) cells show 85% capacity retention at 100 cycles. The benefits established during these two initial formation cycles are apparently carried forward to improve the longer term performance of lithium metal cells tested at room temperature.