Positive Electrode Potentials Research Articles

Layer‑by‑layer assembled binder-free hydrated vanadium oxide-acetylene black electrode for flexible aqueous zinc ion battery

Vanadium oxides are potential positive electrode materials for aqueous zinc ion batteries (ZIBs) owing to their advantages of high theoretical capacity, low cost, and so on. Developments of methods for preparing binder-free vanadium oxide electrodes on a large scale and further investigation of their Zn2+ storage mechanisms are essential for expanding their uses in large-scale energy storage systems and wearable electronics. In this work, binder-free electrodes with hydrated vanadium oxide (V2O5·nH2O, denoted as VOH)-acetylene black (AB) on carbon cloth (VOH-AB/CC) are fabricated by a simple and scalable method which combined low-temperature hydrothermal treatment with layer-by-layer drop/spray-coating process. The AB can greatly improve the electrical conductivity of VOH, thereby enhancing the electrochemical performance. The as-prepared electrode with 20 wt% of AB (VOH-AB2/CC) delivers a high capacity of 280 mA h g−1 at 1 A/g and a good rate capability of 205 mA h g−1 at 4 A/g, which is better than many of the reported binder-free vanadium base electrodes. Besides, excellent cycling performance with 89 % retention rate after 3000 cycles at 4 A/g is achieved on the VOH-AB2/CC electrode. Furthermore, a storage mechanism of Zn2+/H+/H2O insertion accompanied by the formation of basic zinc salt precipitate during the discharging process is proposed by the aid of ex-situ XRD and XPS techniques. Additionally, the flexible Quasi-Solid-State ZIB constructed using VOH-AB/CC as positive electrode can work well at different bending states and two ZIBs connected in series can lighten a light-emitting diode even under bending state. This work provides a low-cost, time-saving, environmental-friendly and scalable method to fabricate binder-free hydrated vanadium oxide electrodes for flexible aqueous ZIBs.

Downsizing and coating effects on the electrochemical performance of Mn-doped iron fluorophosphate as cathode material for sodium-ion batteries

Sodium Mn-doped iron fluorophosphate Na2Fe0·5Mn0·5PO4F is a potential positive electrode material for lithium-ion and sodium-ion batteries. This study outlines the synthesis of Na2Fe0·5Mn0·5PO4F powder through a simplified and more accessible production method. The X-rays diffraction (XRD) technique showed a pure phase with monoclinic symmetry (S.G. P21/n). The resulting uncoated material (labeled as NFeMPF) was ball-milled with dopamine hydrochloride (mentioned as dopamine hereafter) as a carbon source to enhance the specific surface and improve its electronic conductivity. Raman spectra confirmed the presence of residual carbon after the pyrolysis process. Thermogravimetric analysis (TGA) demonstrated the stability of Mn-doped iron fluorophosphate up to 1000 °C. Additionally, Mössbauer spectroscopy disclosed structural improvements in the material, indicating the reduction of all Fe(III) when coated with dopamine. The uncoated material discharge capacity when cycled against sodium exhibits reversible capacities of only 80, 67, and 38 mAh/g during the first cycle at C/20, C/16, and C/5, respectively. The coated NFeMPF@D delivered improved capacities of 272 and 202 mAh/g at C/20 and C/16, respectively. This highlights the considerable promise of the investigated phosphate-based electrode material as a cathode composite for the next generation of sodium-ion batteries.

Investigation of work function and quantum capacitance of OH-terminated MXenes as supercapacitor electrodes: A theoretical perspective

MXene has shown promise in supercapacitor electrodes for energy storage devices. As key parameters to develop new electronic devices, the quantum capacitance and work function (WF) of OH-terminated MXenes with 3d, 4d, d transitional metals are investigated by density functional theory. The most stable configurations of 13 M2C(OH)2 MXenes are found, which are further confirmed by negative formation energies. The low WFs of M2C(OH)2 make them become potential candidates as thermionic electron emitters, especially for Sc2C(OH)2 and Lu2C(OH)2 with extra low WFs. Sc2C(OH)2, Cr2C(OH)2, Y2C(OH)2, and Lu2C(OH)2 are considered as negative electrodes, Other nine systems are potential positive electrodes for larger |Qp|/|Qn| than 1, especially for V2C(OH)2, Nb2C(OH)2, and Mo2C(OH)2. Th wide voltage maintains the electrode types of all systems unchanged, but drastically increases the |Qp|/|Qn| of V2C(OH)2. The quantum capacitance of M2CT2 with different terminations is further explored.

Phase Engineering via Aluminum Doping Enhances the Electrochemical Stability of Lithium-Rich Cobalt-Free Layered Oxides for Lithium-Ion Batteries.

Lithium-rich, cobalt-free oxides are promising potential positive electrode materials for lithium-ion batteries because of their high energy density, lower cost, and reduced environmental and ethical concerns. However, their commercial breakthrough is hindered because of their subpar electrochemical stability. This work studies the effect of aluminum doping on Li1.26 Ni0.15 Mn0.61 O2 as a lithium-rich, cobalt-free layered oxide. Al doping suppresses voltage fade and improves the capacity retention from 46% for Li1.26 Ni0.15 Mn0.61 O2 to 67% for Li1.26 Ni0.15 Mn0.56 Al0.05 O2 after 250 cycles at 0.2C. The undoped material has a monoclinic Li2 MnO3 -type structure with spinel on the particle edges. In contrast, Al-doped materials (Li1.26 Ni0.15 Mn0.61-x Alx O2 ) consist of a more stable rhombohedral phase at the particle edges, with a monoclinic phase core. For this core-shell structure, the formation of Mn3+ is suppressed along with the material's decomposition to a disordered spinel, and the amount of the rhombohedral phase content increases during galvanostatic cycling. Whereas previous studies generally provided qualitative insight into the degradation mechanisms during electrochemical cycling, this work provides quantitative information on the stabilizing effect of the rhombohedral shell in the doped sample. As such, this study provides fundamental insight into the mechanisms through which Al doping increases the electrochemical stability of lithium-rich cobalt-free layered oxides.

Feeling the strain: Enhancing the electrochemical performance of olivine LiMnPO[formula omitted] as cathode materials for Li-ion batteries through strain effects

Currently, the improvement of Li-ion batteries (LIBs) is more important than ever, especially due to the increasing spread and rapid progress of electric vehicles and high-tech applications. Materials used for positive electrodes are one of the main constituents of batteries, which typically determine their electrochemical efficiency. Phospho-olivine LiMnPO4 (LMP) material has been regarded as a potential positive electrode material for LIBs due to its outstanding properties. However, it suffers from low electronic and ionic conductivity. Therefore, this work aims to overcome these drawbacks by applying a biaxial strain to LMP. In this regard, we used density functional theory calculations to investigate the effect of biaxial strain on the dynamic and thermal stabilities, structural, electronic, ionic diffusion, electrochemical potential, and defect properties of LiMnPO4 (LMP) structure, as well as on the Average (Mn–O, Li–O and P–O) bond lengths, electrical conductivity, and charge transfer. Moreover, the influence of anti-site defects on the ionic conductivity of LMP compound was evaluated. Our findings suggest that the biaxial tensile strain has a remarkable effect on the rate performance of LMP cathode material. A biaxial tensile strain of +2% reduces the band gap of LMP from 3.51 to 3.41 eV, and ameliorates the diffusion coefficient by 100 times. Furthermore, the migration barrier was calculated to be 0.37 eV for strained (+2%) defective MP, lower than 1.12 eV for unstrained defective MP, indicating that biaxial tensile strain can mitigate the negative effect of anti-site defects on Li-ion migration. These results can prompt us to suggest biaxial tensile strain as a good strategy for improving the electrochemical performance of LMP as cathode material for LIBs. Furthermore, this study may supply insights to cathode material designers and engineers on the importance of an appropriate biaxial strain value to improve the rate performance of LiMnPO4 as cathode materials for LIB batteries.

Evaluation of P3-Type Layered Oxides as K-Ion Battery Cathodes.

Given the increasing energy storage demands and limited natural resources of Li, K-ion batteries (KIBs) could be promising next-generation systems having natural abundance, similar chemistry, and energy density. Here, we have investigated the P3-type K0.5TMO2 (where TM = Ti, V, Cr, Mn, Co, or Ni) systems using density functional theory calculations as potential positive intercalation electrodes (or cathodes) for KIBs. Specifically, we have identified ground-state configurations and calculated the average topotactic voltages, electronic structures, on-site magnetic moments, and thermodynamic stabilities of all P3-K0.5TMO2 compositions and their corresponding depotassiated P3-TMO2 frameworks. Additionally, we evaluated the dynamic stability and K-mobility in select P3 structures. We find that K adopts the honeycomb or zig-zag configuration within each K-layer of all P3 structures considered, irrespective of the transition-metal (TM). In terms of voltages, we find the Co- and Ti-based compositions to exhibit the highest (4.59 V vs. K) and lowest (2.24 V) voltages, respectively, with the TM contributing to the redox behavior upon K (de-)intercalation. We observe all P3-K0.5TMO2 to be (meta)stable and hence experimentally synthesizable according to our 0 K convex hull calculations, while all depotassiated P3-TMO2 configurations are unstable and may appear during electrochemical cycling. Also, we verified the stability of the prismatic coordination environment of K compared to octahedral coordination at the K0.5TMO2 compositions using Rouxel and cationic potential models. Finally, combining our voltage and stability calculations, we find P3-KxCoO2 to be the most promising cathode composition, while P3-KxNiO2 is worth exploring. We also find P3-KxMnO2 to be worth pursuing given its dynamic stability and facile migration of K+ at both potassiated and depotassiated compositions. Our work should contribute to the exploration of strategies and materials required to make practical KIBs.

Corrosion processes at the GGG40 steel–bentonite interface

Abstract. Spheroidal graphite cast iron (GGG40/0.7040) is used as an overpack material for the reference Pollux 10 container, a prototype for the storage of fuel elements in different types of host rocks (Hassel et al., 2019). Corrosion processes are expected to be triggered after some decades, as the contacting bentonite, which is used as fill material, becomes soggy because of the decay of the fission heat generation and the intrusion of pore water as the temperature decreases under the condensation point (King and Padovani, 2011). The distinct electrochemical reactivities of the graphite, ferrite, pearlite, and cementite phases exposed by this material introduce local galvanic elements which influence the topographic evolution of degradation (Spence, 2005). The aim of this work is to elucidate the corrosion dynamics of active and passive areas by following the chemical evolution at the interface of cast iron–bentonite during the first stages after its saturation with geological pore water. Polarization experiments and electrochemical impedance spectroscopy were applied to monitor the corrosion process in a bentonite cell, where GGG40 steel is put into contact with a light compacted Wyoming bentonite slurry 1 : 10 w/w of bentonite to Opalinus Clay pore water (Fig. 1a). Experiments were performed at 30 and 50 ∘C for longer than 3 months. The surface chemistry and morphological changes were investigated by local XPS, SEM-EDX, and TEM (X-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive X-ray, and transmission electron microscopy, respectively). These experiments were complemented with corrosion studies performed in pore water under different temperatures, hydrostatic pressures, and pH and with and without dissolved oxygen. The polarization curves indicate a constant corrosion rate of GGG40 steel in saturated bentonite after 30 d. SEM micrographs reveal a preferential dissolution of the ferrite phase around the graphite spheres and the ferrite lamellae contained in the pearlitic eutectic. A strong localized dissolution of ferrite along the graphite boundary can be also observed; this is a typical case of crevice corrosion caused by the unhindered access of oxygen to the graphitic cathodic areas (Wang et al., 2022). The surface chemical studies indicate the accumulation of iron oxides, which can be attributed to a hydrated magnetite and the formation of iron silicates (Zhang et al., 2021). TEM pictures of a cross-sectional lamella, including part of graphite sphere, show the formation of a silicate film covering the corroding surface with an irregular adherence (Fig. 1b). The initial relatively high corrosion rate of GGG40 steel can be attributed to the dissolution of the more active ferrite with the formation of poorly passivating iron oxides and silicates. The system is driven towards the dissolution of pearlite at more positive electrode potentials. The bentonite slurry limits the access of oxygen to the graphitic cathodic areas, reducing the corrosion rate by 1 order of magnitude in comparison with that in aerated pore water. A surface enrichment of cementite with superior passive properties and the neutralization of the local elements by approaching the corrosion potential of graphite (Kadowaki et al., 2019) is also expected. Thus, the consumption of oxygen and the transport limitation of the cathodic reaction by bentonite forecast a considerable reduction in the degradation of the container after a sacrificial corrosion phase.

A Reduced Order Modeling Approach to Capture Transport within a Three-Electrode System Towards Fast Charge Applications

In support of GM's traction battery efforts, we derive and implement a reduced order modeling method to describe the electrochemical performance of a battery cell through the combination of a modified Newman Pseudo-2-Dimensional model and a three-electrode experimental apparatus. To assess the capability of the method, we compare the modeling results with experimental data for a lithiated graphite electrode and a lithiated nickel rich electrode system. The model is applied to simulate the electrochemical and transport processes within the battery cell to predict the negative electrode potential and positive electrode potential with respect to a lithium iron phosphate reference electrode, as well as the terminal voltage.The manufacture and set up of the three electrode system, model development and reduction approaches, as well as a discussion of applicability to fast charge considerations to avoid lithium plating at the anode during a charging event will be presented.

Using Reference Electrodes to Validate Parameterization of Individual Electrode Soh in the Single Particle Model with Electrolyte

Most model parametrization techniques for reduced order physics-based Lithium-ion battery models like the single particle model rely on minimizing the error in the measured and predicted cell terminal voltage. The battery terminal voltage is the difference between the voltages of the positive and negative electrode solid phase potentials. If the individual contribution of each electrode overpotential to the terminal voltage, is not measured, there could be multiple combinations of parameters that provide similar RMSE for voltage prediction, yielding non-unique solutions and local minima. Misattributing the parameters for kinetics and diffusion in each electrode could result in increased plating or over-conservative designs at higher operating currents.Adding a reference electrode to the battery allows us to measure the individual electrode potentials experimentally. Using this extra measurement, we can parametrize the kinetic and diffusion reactions in positive and negative electrodes with better confidence [1], and validate the electrode-specific state of health parameterization, specifically the increased resistances due to SEI growth and shift in the stoichiometric window as the cell ages [2,3]. In our experiments, we used a pouch cell manufactured in the U of M Battery Lab with Targray NMC 622 Single Crystal cathode powder, Superior SLC 1520-T anode powder, and a custom fabricated Lithium Iron Phosphate (LFP) reference electrode deposited on a porous electrode layer. Further details of the reference electrode are given in [4]. The model was parametrized using discharge data at different C-rates and a modified Hybrid Pulse Power Characterization test. Finally, the RMSE for both the modeled negative and positive electrode potentials are calculated for the validation data set which uses the US06 Drive cycle.

Enhancement of the stability window of PEO for high voltage all-solid-state lithium batteries

Polyethylene oxide (PEO), one of the leading polymer electrolytes recommended against the safety concerns of liquid electrolytes, is unsuitable for high potential positive electrodes (e.g. LiNixMnyCozO2) needed to meet the increasing energy demand. Herein PEO main chain has been stabilized by modifying its (-OH) reactive terminal group. Modification of the reactive (-OH) group with (-OCH3) and (−CN) terminal groups exhibit a remarkable increase in the ionic conductivity at ambient temperature (4.52 × 10−4 S cm−1). In addition, electrochemical stability window (ESW) has been expanded (>4.18 V). The modified gel polymer electrolyte (GPE) has exhibited 150 mAh g−1 discharge capacity and has retained 92% of its capacity for 50 cycles in charge-discharge tests. Instead of increasing the ESW with inorganic additives, modification of PEO's (-OH) reactive terminal groups and making the PEO main chain a stable matrix can be a more permanent solution/strategy in the first instance. Moreover, developed solid electrolyte promise stability, safety and flexibility, making their utilization possible even with complex geometry batteries with high energy density.

Carbon felt-polypyrrole-silver chloride composite as a rechargeable positive electrode for the seawater magnesium cell

In the paper, for the first time, the new concept of rechargeable cathode for Mg-based seawater cells is demonstrated. The pristine carbon felt (CF) is functionalized with electrodeposited polypyrrole (PPy), and the composite with silver chloride (AgCl) is prepared by the modified successive ion layer adsorption and reaction (SILAR) method. Pristine carbon felt – polypyrrole (CF/PPy) and carbon felt - polypyrrole - silver chloride (CF/PPy-AgCl) are investigated as potential rechargeable positive electrodes for the magnesium seawater cell. During charge, which can be accomplished with small photovoltaic cells, polypyrrole, and silver are oxidized while on Mg hydrogen is evolved. During discharge dissolution of Mg alloy, and reduction of doped polypyrrole and silver chloride occurred. The specific capacity, energy, and power of the cell, as well as cyclic stability, are estimated. The possible application of the cell is also proposed.

Electrochemical capacitance properties of pre-sodiated manganese oxide for aqueous Na-ion supercapacitors.

Mn-based oxides are widely investigated as electrode materials for electrochemical supercapacitors, because of their high specific capacitance in addition to the high abundance, low cost, and environmental friendliness of Mn. The pre-insertion of alkali metal ions is found to improve the capacitance properties of MnO2. While the capacitance properties of MnO2, Mn2O3, P2-Na0.5MnO2, and O3-NaMnO2etc. are reported, there is no report yet on the capacitive performance of P2-Na2/3MnO2, which has already been studied as a potential positive electrode material for Na-ion batteries. In this work, we have synthesized sodiated manganese oxide, P2-Na2/3MnO2 by a hydrothermal method followed by annealing at a high temperature of about 900 °C for 12 h. For comparison, manganese oxide Mn2O3 (without pre-sodiation) is synthesized by following the same method, but annealing at 400 °C. While P2-Na2/3MnO2 exhibits a high specific capacitance of 234 F g-1, Mn2O3 can deliver only 115 F g-1 when cycled at 0.4 A g-1 in an aqueous electrolyte of 1.0 M Na2SO4 in a three-electrode cell. An asymmetric supercapacitor Na2/3MnO2‖AC is assembled, which can exhibit a SC of 37.7 F g-1 at 0.1 A g-1 with an energy density of 20.9 W h kg-1, based on the total weight of Na2/3MnO2 and AC with an operational voltage of 2.0 V and possesses excellent cycling stability. This asymmetric Na2/3MnO2‖AC supercapacitor can be cost-effective considering the high abundance, low-cost and environmental friendliness of Mn-based oxides and aqueous Na2SO4 electrolyte.

Modeling Electrochemical Transport within a Three-Electrode System Towards Fast Charge Applications

In support of GM's traction battery efforts, we derive and implement a method to describe the electrochemical performance of a battery cell through the combination of a modified Newman Pseudo 2-Dimensional model and a three-electrode experimental apparatus. To assess the capability of the method, we compare model results with experimental data for a lithiated graphite and lithium nickel manganese cobalt oxide system. The model is applied to simulate the electrochemical and transport processes within the battery cell to predict the negative electrode potential and positive electrode potential with respect to a lithium iron phosphate reference electrode, as well as the terminal voltage. We extend this discussion to cover applicability to fast charge considerations to avoid lithium plating at the anode during a fast charge event.

Zero volt storage of Na-ion batteries: Performance dependence on cell chemistry!

Sodium-ion batteries (NIBs) are regaining their importance in recent years as a sustainable complementary energy storage device for Li-ion batteries. Although, they cannot compete in terms of energy density with respect to Li-ion, they present a few advantages, namely the 0 V stability that makes them safe during external short and/or over-discharge. When the cell is discharged to 0 V, the negative electrode potential shoots up high during which the copper current collector in use for Li-ion cells could oxidize, dissolve and leads to internal short. In contrast, Na-ion cells utilize an aluminium current collector that is strongly resistant against oxidation, hence enabling their 0 V stability. However, apart from the current collector stability, the negative electrode potential rise could cause interphase instability which is not well elucidated. Hence, herein, we explored two different Na-ion chemistries, namely polyanionic Na3V2(PO4)2F3-hard carbon and sodium layered oxide-hard carbon using different electrolyte formulations. Combined impedance analyses, ex-situ X-ray photoelectron spectroscopy (XPS) and operando optical sensing indicate the 0 V discharge involves SEI degradation thereby deteriorating the cell performance, the extent of which depends on the positive electrode potential and the electrolyte in use. Overall, the 0 V stability is not an in-built property of Na-ion cells and a careful selection of cell chemistry is mandatory to achieve 0 V stable Na-ion cells.

Dealloying of Ni- and Fe-Based Alloys in Boiling Caustic Environments and the Parameters Influencing the Geometry of a Dealloyed Layer

Nickel alloys and stainless have been the material of choice for a wide range of industrial applications like power and petrochemical plants that involve exposure to corrosive environments. For instance, Alloy 800 (Fe-30Ni-20Cr) has been used as the tubing material in CANDU and Siemens steam generators (SGs) for decades with excellent in-service performance. However, despite their good resistance to general to localize corrosion, Ni- and Fe-based alloys are susceptible to environmentally assisted cracking (EAC) in certain environments, such as hot caustic aqueous solutions. Laboratory experiments have shown that these materials are susceptible to dealloying in hot caustic environments due to the selective removal of Fe, Cr and Mo (less noble elements). As a result of dealloying, a brittle nanoporous film forms on the surface that is enriched in Ni (the more noble element). This film has been proposed to act as a precursor to stress corrosion cracking (SCC) by a film-induced cleavage (FIC) mechanism, where the brittle film injects a high speed/energy crack to the substrate material.The fast kinetics of dealloying requires a connected percolating pathway of less noble element atoms to exist within the alloy that extends from the surface into the material. The presence of this pathway depends on the composition of the alloy. The parting limit defines the minimum amount of the more reactive element(s) in a particular alloy system that makes it susceptible to dealloying. Below the parting limit composition, dealloying will be suppressed by surface diffusion of the more noble element, even at very oxidizing potentials, and the surface of the material will show a passive-like behavior (general dissolution would eventually occur at high anodic overpotentials). Besides the alloy composition, dealloying highly depends on the electrode potential. Below a threshold potential (dealloying critical potential), surface diffusion of the more noble element will overcome the dissolution of the less noble element(s) and suppress dealloying.In this study, we examine different factors that affect dealloying and the geometry of a dealloyed layer through electrochemical measurements and nano-scale characterization techniques. Several engineering Ni- and Fe-based alloys were tested in deaerated boiling caustic solutions to understand the effect of alloy composition on the susceptibility to dealloying. Results indicate that an increase in Ni content will shift the dealloying critical potential to more positive potentials and subsequently the resistance to dealloying. Although Ni is the alloying element that provides nobility and resistance in hot caustic environments, our results show that the thermodynamic and kinetic behaviour, and the content of the less noble elements play an important role in these environments. A comparison between different alloys with similar Ni-content but different Cr and Mo contents shows the beneficial and detrimental role of Cr and Mo in dealloying, respectively. The air-formed chromia-based oxide on the surface of alloys with high Cr-content slowly dissolves in the caustic environment, delays the dissolution of less noble elements, and increases the resistance to dealloying.Changes in electrode potential and time of exposure to the caustic environments, alter the geometry of the dealloyed layer. Results show an increase in the diameter and coarsening of ligaments with increasing time of exposure to the caustic environment. Coarsening of ligaments is believed to impair the ability of a dealloyed layer to inject a micro-crack to the underlying material and initiate SCC. Also, results show that an increase in anodic overpotential of only a few millivolts in the vicinity of dealloying critical potential would change the geometry of the dealloyed layer significantly. The surface diffusion of the more noble element (i.e. Ni) cannot keep up with the fast removal of atoms of the less noble elements (i.e. Cr, Mo, and Fe) at more positive electrode potentials compared to the dealloying critical potential which results in a weak bonding at the film/metal interface. The weak bonding may not be able to support the transmission of a high-speed crack to the substrate material, reducing the likelihood of SCC initiation. Figure 1

In Situ Synthesis of AgCl@Ag Plates as Binder-Free Cathodes in a Magnesium Seawater-Activated Battery

A binder-free AgCl@Ag (SPL-A) cathode was prepared via a facile one-step synthesis by the in situ growth of AgCl active material on the surface of Ag foil substrate. Compared with the AgCl cathode (SPL-B) prepared by the traditional smelting-rolling method, the coarse-grained particulates of AgCl in AgCl@Ag cathode facilitated the permeation of the electrolyte. In addition, it exhibited a preferred growth orientation of the (111), (222), and (311) crystal planes to reduce the charge transfer resistance. The electrochemical behaviors of the optimized SPL-A-24 cathode (prepared with reaction time of 24 h) and the SPL-B cathode were also compared. The galvanostatic discharge results showed that SPL-A-24 cathode had a more positive electrode potential than SPL-B cathode (−0.06 V vs −0.19 V at 50 mA cm−2). Moreover, SPL-A cathode exhibited a stable discharge process that SPL-B cathode could not achieve at 100 mA cm−2 and 250 mA cm−2. The magnesium seawater-activated battery assembled with SPL-A-24 cathode displayed a shorter time to reach the voltage plateau (0.2 s), a higher maximum discharge voltage (1.69 V), a larger specific power (255.5 mWh g−1), and higher specific capacity (167.7 mAh g−1) at the discharge current density of 50 mA cm−2.

Overoxidation of Intrinsically Conducting Polymers.

Intrinsically conducting polymers may undergo significant changes of molecular structure and material properties when exposed to highly oxidizing conditions or very positive electrode potentials, commonly called overoxidation. The type and extent of the changes depend on the experimental conditions and chemical environment. They may proceed already at much lower rates at lower electrode potentials because some of the processes associated with overoxidation are closely related to more or less reversible redox processes employed in electrochemical energy conversion and electrochromism. These changes may be welcome for some applications of these polymers in sensors, extraction, and surface functionalization, but in many cases, the change of properties affects the performance of the material negatively, contributing to material and device degradation. This report presents published examples, experimental observations, and their interpretations in terms of both structural and of material property changes. Options to limit and suppress overoxidation are presented, and useful applications are described extensively.

Influence of heat treatment on tribocorrosion properties of Ni-B composite coatings

Various surface protection technologies, in particular, electrochemical, are used to increase the wear and corrosion resistance of steels and alloys. Composite electrochemical coatings (CEC) technology is more promising than "pure" galvanic coatings. Application of CEC increases the wear, corrosion and fatigue failure resistance of metals. Nickel often is chosen as a CEC matrix because it easily forms uniformly filled defect-free composite structures with many particles of the dispersed phase (DP).
 Physical and mechanical properties of metal coatings determine practical application of such composition. The characteristics of nickel-based CEC are: high hardness and strength, significant corrosion resistance in atmospheric environment, as well as in alkali and mild acidy environments. An effective composition coating with tribological designation can be CEC Ni-B, received in the process of electrolysis from suspension of amorphous boron in nickel electrolyte. A new composite structure of matrix filled type Ni-Ni3B is formed after heat treatment. Composition and structure of coating is determined by regimes of diffusion annealing. Ni-B coatings increase wear resistance of steel in chlorine-based environments. The influence of low-temperature thermal treatment of Ni-B CEC on steel 09Mn2Si on their tribocorrosion behavior is investigated. It is shown that the structural factor has a decisive influence on the efficiency of such friction pairs. The CEC has the least wear and the most positive compromise electrode potential after vacuum annealing at 450°C, when the initial stage of solid-phase interaction of coating components with the formation of Ni-Ni3B occurs.

Rate-controlling element in the self-discharge process in electrochemical double-layer capacitors

Suppression of self-discharge is crucial in the development of electrochemical double-layer capacitors (EDLCs). In this study, the rate-controlling element of the self-discharge process in EDLCs was explored without any new additives, and the anion was found to play a critical role in this process. The thickness ratio between the positive and negative electrodes (P/N ratio) was the primary factor used to control the self-discharge rate. As the P/N ratio increased, the anion density in the positive electrode decreased. The P/N ratio was increased to retain the anions for a longer period in the cell, which caused self-discharge suppression and led to a slow change in the positive electrode potential when held at an open-circuit status. Cells with a P/N ratio of 1.37 showed 26 to 32% reduced voltage decay than did those with a P/N ratio of 1.00 after 70 h.

Towards reliable three-electrode cells for lithium-sulfur batteries.

Three-electrode measurements are valuable to the understanding of the electrochemical processes in a battery system. However, their application in lithium-sulfur chemistry is difficult due to the complexity of the system and thus rarely reported. Here, we present a simple three-electrode cell format with relatively good life time and minimum interference with the cell operation.