Electrolyte Polarization Research Articles

Self‐healable Mn‐doped PVA‐borax hydrogel electrodes for supercapacitor applications

AbstractThis study aims to investigate the effect of Mn doping on the performance of polyvinyl alcohol/borax‐structured (PMB) supercapacitor electrodes for high‐capacity, flexible, and self‐healing supercapacitor electrodes. The PMB electrodes were characterized by x‐ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). Electrochemical characterization was conducted using cyclic voltammetry (CV), which revealed that redox reactions, which are evident at low scan rates, enhance capacitive performance. However, high scan rates introduce limitations owing to the increased vibrations of the PVA chains and incomplete electrolyte polarization. The PMB electrodes exhibited remarkable electrochemical properties and capacitive performances, which were significantly affected by the MnO₂ structure. The electrodes exhibited self‐healing properties and demonstrated flexibility to stretch by up to 40%. In addition, the results indicate that the electrode capacity of the PVA/borax system increased by 2.03 times after 1000 cycles with manganese doping. The solid electrolyte interface (SEI) layer formed on the electrode surface plays a critical role in stabilizing the capacity loss during prolonged charge–discharge cycles. The study concluded that PMB supercapacitors offer higher capacitance in 0‐2 V applications compared to other PVA/borax combination hydrogels. Moreover, the incorporation of metal‐based additives, particularly manganese, enhanced the capacitive performance, and operating voltage levels.

One-step preparation of large-size 1.5-μm-thick robust YSZ electrolyte for high CH4 conversion SOFCs at 600 °C

Ultrathin electrolytes can lower the operating temperature of yttria-stabilized zirconia (YSZ)-based solid oxide fuel cells (SOFCs) to below 600 °C, accelerating their commercialization. However, current technologies for fabricating robust electrolytes with large areas and a thickness of a few microns for SOFCs suffer from substantial practical limitations, including high manufacturing costs, intricate technical demands, and multistep fabrication processes. This study introduces a low-cost, high-yield, and facile one-step phase inversion technology to fabricate large-area and shape-variable ultrathin YSZ electrolyte-based SOFCs (disc diameter >12 cm and area of 10 cm × 10 cm). An integrated form of SOFCs with dendritic YSZ microchannels supporting a 1.5-μm-thick dense YSZ thin film was fabricated. The ultrathin electrolyte layer lowered ohmic and polarization losses, enhancing SOFC electrochemical performance. The integrated anode/electrolyte structure overcame the interfacial thermal mismatch, resulting in more than 210 h of long-term stability even with cells operating in rapidly changing environments. The single cell also exhibited a high CH4 conversion efficiency (55%), which was attributed to the fast gas diffusion and excellent catalytic activity within the integrated anode. In addition, our 4 cm × 4 cm flat SOFCs exhibited a high power output (5.1 W) at 600 °C, paving the way for the mass production of ultrathin and robust YSZ electrolytes.

Analysis of the influence of local electrodeposition conditions on the accuracy of electrochemical 3D-printing

Problem. Additive manufacturing of metal parts by local electrodeposition is a new promising area with several unique features. The use of electrolysis makes it possible to manufacture metal parts at room temperature with high accuracy and low energy consumption. The accuracy and speed of electrochemical 3D printing are inversely related, and therefore it is important to find optimal electrodeposition conditions at maximum speed without degrading accuracy. The aim of the study. The purpose of this work was to analyse the influence of electrodeposition parameters (electrode distance, electrical conductivity and electrolyte polarization) on the accuracy of metal deposit formation in a computer model and to conduct experimental verification of optimal conditions for electroforming a real object from copper sulphate electrolyte. Methodology of implementation. To achieve the goals of the study, computer simulation of the electrochemical deposition process in the COMSOL Multiphysics software and electrochemical measurements of the characteristics of copper sulphate electrolytes were used. Research results. Computer simulation established optimal conditions: the distance between the edge of the capillary and the surface on which deposition occurs is not more than 0.5 mm, the electrolyte in which the inverse slope of the cathode polarization curve is not lower than 2000 mA/(V×cm2) and the electrical conductivity is not higher than 0.02 S/сm. The influence of the electrolyte composition on the inverse polarization of the cathode process and its electrical conductivity was investigated. The optimal composition of the electrolyte was selected, containing 200 g/L CuSO4, 60 g/L H2SO4, 0.2 g/L KCl and RUBIN T-200 additive. In the selected electrolyte, the value of the inverse slope of the cathode polarization curve is 2120 mA/(V×cm2). Verification of the process of local electrodeposition in the selected electrolyte during the electroformation of a cylindrical object with a diameter of 4 mm and a height of 100 μm was carried out. It was determined that no more than 5 % of metal was deposited outside the capillary of the working electrode. Conclusions. The results of the work can be used to create an electrochemical 3D printing system. Further research should be aimed at approbation of the obtained parameters of local electrodeposition in an installation that simulates the operation of a 3D printer and establish the accuracy and speed of printing of a three-dimensional object. Key words: additive manufacturing, electrical conductivity, electrolyte composition, polarization, local electrodeposition.

Simulating the charging mechanism of a realistic nanoporous carbon-based supercapacitor using a fully polarizable model

Nanoporous carbon-based supercapacitors are established energy storage devices, that complement Li-ion batteries in high-power applications. So far, the study of these systems through simulations required drastic simplification of the electrolyte and/or of the electrode. In this work, we use state-of-the-art constant potential classical molecular dynamics simulations, where both the electrode and the electrolyte are polarizable, to study complex carbide-derived carbons with 1-ethyl-3-methylimidazolium bis(trifluoromethane)sulfonyl imide ionic liquid electrolyte. We show that using this set-up allows to obtain integral capacitances (i.e. the main property to characterize supercapacitors) in quantitative agreement with experiments. The simulations, performed in a range of applied potentials of 1V to 4V, then provide microscopic details on the charging mechanism, revealing that it is not symmetrical between the positive and negative electrodes. A pure exchange of ions is observed on the positive electrode, while an ion exchange combined with cation adsorption takes place on the negative one. Our work shows that accounting for the coupling of electrode and electrolyte polarization improves the accuracy of the results, opening the way toward a more quantitative comparison with experiments.

Stabilization versus Penetration Dynamics Induced by Localized Concentration Polarization in Solid Polymer Electrolytes

While the onset of dendrites found inside solid polymer electrolytes was typically analyzed by the dilute solution theory, nonideal behaviors such as dendrites at underlimiting current densities were often reported. Here, we consider two critical factors that were often neglected in existing studies, the severe heterogeneous current distribution and the dynamic change of modulus during the polarization process. Polymers with different dynamic mechanical properties were assessed, exploiting the recently discovered mechanism of phase transformation inside low-salt-concentration polymers. Analyses of the operando images revealed two characteristic points on the potential curve, the local and total concentration depletion which each corresponded to the starting and stopping point of dendrites. We further assess these dynamics at different degrees of heterogeneity controlled by different electrode sizes. The penetration dynamics and Sand’s time scaling exponent were heavily affected by both the initial concentration and the electrode size, which stress the significance of interfacial dynamic heterogeneity in working batteries.

Reconciling electrolyte donicity and polarity for lithium carbon fluoride batteries

For nonaqueous electrolytes designed for carbon fluoride batteries, a higher donicity is beneficial for stabilizing positively charged carbon atoms, while a moderate polarity is favorable for detaching negatively charged fluorine atoms.

Na3(VO)2(PO4)2F coated carbon nanotubes: A cathode material with high-specific capacity for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are one of the candidate technologies for large-scale energy storage systems due to their environmental friendliness, safety and resourcefulness. However, designing and synthesizing high-performance cathode materials with practical application value is currently a great challenge. Herein, we synthesize a carbon-nanotube-coated Na3(VO)2(PO4)2F (Na3(VO)2(PO4)2F@CNT) cathode material for AZIBs, which has a continuous and interconnected ion transport channel structure. A Zn2+/H+ co-intercalation mechanism is revealed by ex-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) characterizations. The Na3(VO)2(PO4)2F@CNT cathode material exhibits a high specific capacity of 143 mAh‧g Wan et al. (2019). at 0.2 C in the electrolyte of 3 M Zn(OTf)2 aqueous solution. In addition, Na3(VO)2(PO4)2F@CNT shows a good low-temperature electrochemical performance in the electrolyte of 2 M Zn(OTf)2 deionized water/ethylene glycol (DIW/EG) mixed solution with a different ion storage mechanism. This study provides a new polyanionic cathode material for AZIBs and an idea to modulate the electrolyte polarity to enhance the zinc storage capacity of the cathode material.

Controlled electrochemical hydridation of Ti surfaces – optimisation and electrochemical properties

Ti is used as a construction material in many applications including electrodes in various electrochemical technologies due to its high corrosion stability provided by the stable oxide layer on the surface. However, this oxide layer is also the reason for its resistivity causing high interfacial resistance between components and energy losses. This problem can be solved by various surface modifications such as acid etching or coating with a layer of precious metals. In this study, we present a novel method for controlled hydridation of Ti materials based on a combination of acid etching and cathodic hydridation aimed primarily for surface modification of Ti components for proton exchange membrane water electrolyser. Cathodic polarisation represents the means to increase the amount of Ti hydride and to tune its properties to obtain a Ti surface with low interfacial resistance and preserved corrosion stability. The study investigated the effects of concentration, temperature, time, and current density on cathodic polarization in H2SO4 electrolytes. The resulting samples were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, Kelvin probe and temperature-programmed desorption. This allowed finding interesting correlations between the surface composition of the Ti samples and their electrochemical properties.

Mitigating anode/electrolyte interfacial Ni diffusion by a microwave sintering method for proton-conducing solid oxide fuel cells

Although Ni-based anodes are commonly employed in proton-conducting solid oxide fuel cells (H-SOFCs), interfacial diffusion of Ni from the anode to the electrolyte is difficult to avoid, resulting in lower electrolyte and fuel cell performance. In this study, the electrolyte/anode half-cells are co-sintered using a microwave sintering process, providing a lower co-sintering temperature than the standard sintering approach. The lower co-sintering temperature minimizes Ba-evaporation at the electrolyte and mitigates anode/electrolyte interfacial Ni diffusion, resulting in decreased electrolyte and interfacial polarization resistance. The microwave-sintered cell outperforms the traditionally sintered cell in electrochemical performance, with higher fuel cell performance and lower cell resistances. Furthermore, the improved interfacial condition improves the fuel cell's long-term durability, allowing the cell to operate for 200 h without detectable degradation. This study presents an intriguing and simple way to reduce anode/electrolyte interfacial Ni diffusion, which improves fuel cell output and operational stability.

A fractional-order electrochemical lithium-ion batteries model considering electrolyte polarization and aging mechanism for state of health estimation

Accurate state of health (SOH) estimation of lithium-ion batteries is critical for the safe and reliable operation of battery power system. To achieve better SOH estimation with low computational complexity, a fractional-order model considering electrolyte polarization and aging mechanism (FOMeA) is proposed. The proposed model simplifies solid phase lithium-ion distribution with fractional-order Padé approximation and electrolyte phase lithium-ion distribution with a two-state system. The solid electrolyte interphase (SEI) layer formation and lithium plating side reactions, which lead to battery aging, are modeled to establish the relationship between the cycle number and the aging parameters in the proposed simplified electrochemical model. Finally, FOMeA is compared with the pseudo-2D (P2D) aging model. The result shows that FOMeA can achieve accurate voltage prediction and SOH estimation in whole battery cycle life, and greatly save computational time.

A Static Tin-Manganese Battery with 30000-Cycle Lifespan Based on Stabilized Mn3+/Mn2+ Redox Chemistry.

High-potential Mn3+/Mn2+ redox couple (>1.3 V vs SHE) in a static battery system is rarely reported due to the shuttle and disproportionation of Mn3+ in aqueous solutions. Herein, based on reversible stripping/plating of the Sn anode and stabilized Mn2+/Mn3+ redox couple in the cathode, an aqueous Sn-Mn full battery is established in acidic electrolytes. Sn anode exhibits high deposition efficiency, low polarization, and excellent stability in acidic electrolytes. With the help of H+ and a complexing agent, a reversible conversion between Mn2+ and Mn3+ ions takes place on the graphite surface. Pyrophosphate ligand is initially employed to form a protective layer through a complexation process with Sn4+ on the electrode surface, effectively preventing Mn3+ from disproportionation and hindering the uncontrollable diffusion of Mn3+ to electrolytes. Benefiting from the rational design, the full battery delivers satisfied electrochemical performance including a large capacity (0.45 mAh cm-2 at 5 mA cm-2), high discharge plateau voltage (>1.6 V), excellent rate capability (58% retention from 5 to 30 mA cm-2), and superior cycling stability (no decay after 30 000 cycles). The battery design strategy realizes a robustly stable Mn3+/Mn2+ redox reaction, which broadens research into ultrafast acidic battery systems.

Adjusting the Electrolyte Polarity to Address the Dissolution Issue of Organic Electrode

AbstractSmall organic molecules with carbonyl active site are a prominent member in the family of organic electrode material, due to the reversible reaction and more tunable electrochemical property. However, the dissolution loss is the biggest obstacle in its application. In this work, we tried to address the dissolution issue of 5,7,12,14‐pentacenetetrone (PT), a typical quinone‐based organic electrode. Highly concentrated electrolyte of 5 M LiTFSI DME was used and it significantly reduced the dissolution and well maintained the capacity after 500 cycles. Besides, through the investigation of the relationship between solvent/electrolyte property and dissolution, and the interaction between electrode and electrolyte, a guiding rule of the dependence of dissolution on polarity was proposed. With the rule, non‐polar solvent of hexane was further added as co‐solvent and its‐adding decreased the polarity and substantially eliminated the dissolution loss. The work supplies a common electrolyte strategy to address the dissolution issue of small organic molecules.

A fractional-order model of lithium-ion battery considering polarization in electrolyte and thermal effect

With the growing demand of safety and accurate control for electric vehicles, it is urgent to develop a physics-based electrochemical model of lithium-ion battery with simple calculation and high accuracy over wide temperature range for application in battery management system (BMS). However, traditional electrochemical models are too complex to be applied in real usage, and most of them fail to capture thermal characteristics of the cell. Therefore, a fractional-order model of lithium-ion battery considering polarization in electrolyte and thermal effect (FOMeT) is proposed in this paper. The fractional-order model (FOM) is improved by considering the polarization in electrolyte. The particle thermal model is proposed to describe the heat generation and absorption of the cell. Finally, the FOM considering electrolyte polarization and the particle thermal model are combined to form FOMeT by coupling the cell temperature and dynamics of lithium-ion. The results show that the proposed model performs high voltage accuracy and temperature accuracy over wide temperature range (273.15K∼318.15K) and wide current load range (0.5C∼2C).

Stabilizing lithium plating in polymer electrolytes by concentration-polarization-induced phase transformation

<h2>Summary</h2> It is widely accepted that concentration polarization in liquid electrolytes promotes whisker growth during metal deposition, and therefore, high salt concentration is favored. Here, we report unexpected opposite behaviors in solid polymer electrolytes: concentration polarization can induce phase transformation in a polyethylene oxide (PEO) electrolyte, forming a new PEO-rich but salt-/plasticizer-poor phase at the lithium/electrolyte interface, as unveiled by stimulated Raman scattering microscopy. The new phase has a significantly higher Young's modulus (∼1–3 GPa) than a bulk polymer electrolyte (<1 MPa). We hereby propose a design rule for PEO electrolytes: their compositions should be near the boundary between single-phase and two-phase regions in the phase diagram so that the applied current can induce the formation of a mechanically rigid PEO-rich phase to suppress lithium whiskers. LiFePO₄/PEO/Li cells with concentration-polarization-induced phase transformation can be reversibly cycled 100 times, while cells without such transformation fail within 10 cycles, demonstrating the effectiveness of this strategy.

Mechanism of oscillation of aqueous electrical double layer capacitance: Role of solvent

The present classical density functional theory (CDFT) study is focused on role of solvent in differential capacitance (Cd) behavior of aqueous electrolyte electric double-layer capacitor (EDLC). In the CDFT, water molecule is described by a solvent primitive model, which is constructed to give two experimentally measured aandb parameters in the van der Waals equation of state of water; Lennard-Jones parameters of both cation and anion are chosen to be reminiscent of properties of K+ andCl-1; a structureless and soft wall comprised of carbon atoms is considered to represent a graphene electrode. Main findings are summarized as follows. (i) The CdH (H is separation between two graphene electrodes) curve is always shifted up (at lower electrode voltage) or down (at higher electrode voltage) by increasing the electrolyte bulk concentrationc. The anomalous negative correlation between c and Cd at high voltage originates from the so-called charge inversion and one additional weak co-ion peak located closer to the electrode surface at higher voltage. (ii) Oscillation periods of CdH curves are basically fixed at 3 Å regardless of molecular characteristics of counter- and co-ions, c value, and electrode voltage; explicit consideration of the solvent granularity and polarity greatly reduces the attenuation rate of the oscillation with pore size. Increase of CdH with pore size reducing towards the ion size, does occur but only with moderate magnitude; a main CdH extreme value occurs approximately around H being two times ion diameter, which can be either a maximum or a minimum, depending on electrolyte bulk concentration, polarity and strength of the electrode. These oscillation features differ greatly from those observed in solvent-free ionic liquids and continuum solvent model. (iii) Potential of zero charge ψpzc for the case of small size of cation and weaker LJ interaction of the cation with solvent molecule in large number, is necessarily positive and its value is positively correlated with the c value; minimum point ψMin of the Cdψs curve is always larger than theψpzc, not consistent with the Gouy-Chapman theory, and both the ψpzcH curve and ψMinH curve change quasi periodically with the pore size H also in 3 Å cycle. (iv) Theoretical analysis shows that the capacitance behavior is mainly controlled by the number and position of solvent peaks and their changes with pore size, while distribution of ions is largely controlled by their LJ interaction with solvent. This shows the importance of the solvent in modulating the capacitance behavior.

Anion doping enabling SnO2 superior electrocatalytic performances for vanadium redox reactions

ABSTRACT SnO2 has been applied in various fields due to its high activity, low cost, variety, and tunable structure. However, the low electrical conductivity of SnO2 hinders its application in electrochemical catalysis. Both cationic and anionic doping can improve the electrical conductivity of SnO2. In this work, doping F was used to optimize the catalysis of SnO2 on the redox reactions for VO2+/VO2 + and V3+/V2+. O2- is replaced by F- with the production of a free electron in SnO2 structure, which increases the electronic conductivity of SnO2. Furthermore, F doping increases the concentration of structural defects in SnO2, such as oxygen vacancies. F doping increases the structural defect of SnO2, such as oxygen vacancy. Therefore, F doping can increase the electrochemical activity of SnO2 by increasing active sites, promoting vanadium ion adsorption and accelerating electron transport. The activity of the VO2+/VO2 + and V3+/V2+ reactions of F doped SnO2 is higher than that of undoped SnO2. The SnO2 at doping mass ratio of 10% (SnO2/F-10) exhibits the best electrochemical performance over 5% and 20%. After SnO2/F-10 modification, the reversibility and electrochemical kinetics of the graphite felt are improved. Cell adopting SnO2/F-10 has larger discharge capacity, higher utilization rate of electrolyte and lower polarization than blank cell. At 150 mA cm−2, the energy efficiency of cell is increased from 52.3% to 68.7% by using SnO2/F-10. At 50 mA cm−2, the modified cell also shows good stability during 50 cycles. Overall, this work promotes the application of metal oxides in vanadium redox flow battery.

Mesoscopic Ti2Nb10O29 cages comprised of nanorod units as high-rate lithium-ion battery anode

Benefiting from large tunnel structure, zero strain feature, and excellent pseudocapacitive performance, Ti2Nb10O29 was considered as a potential anode material for lithium-ion batteries (LIBs). Herein, Ti2Nb10O29 cages comprised of nanorod units were elaborately designed. The mesoscopic structure could effectively shorten the ion diffusion pathway, and the big central electrolyte reservoir relieves the concentration polarization of electrolyte. Moreover, the perforated pore feature guarantees competent contact between electrolyte and framework. As the anode of LIBs, the mesoscopic Ti2Nb10O29 cages deliver high reversible capacity (302.5 mAh/g) and rate capability (134.3 mAh/g at 30 A/g). This unique mesoscopic structure holds excellent potential for the electrode design of high-rate and long-life LIBs.

High performance thick cathodes enabled by gradient porosity

Thick electrode with high areal loading is considered to be the most valid and practical strategy to improve the energy density of lithium ion batteries, however, its application is limited by serious electrochemical performance deterioration due to the sluggish Li+transportation. Here, LiNi0.8Co0.15Al0.05O2 (NCA) electrodes with areal loading of about 28 mg/cm2 and gradient porosity are constructed by two preparation methods, doctor-blade coating (DC) and electrostatic spinning (ES). It is revealed that the double-layered electrode (DE), whose bottom layer (close to the current collector) is made by DC and upper layer (closes to the separator) by ES, shows a high specific capacity of more than 150mAh/g under 0.5C rate, meantime it demonstrates preferable cycling stability and rate property compared to the other electrodes fabricated by diverse approaches. Experimental and simulation results indicate that the lithium concentration distribution and reaction kinetics of DE is preferable due to the reasonable porosity distribution in favor of electrolyte infiltration and polarization diminution. This finding proposes that the optimization of electrode architecture can improve the property of thick electrodes effectively, which is worth well for more attention in state-of-the-art battery manufacturing processes.

Mathematical analysis of dynamic safe operation area of very large capacity lead-acid battery

Flooded lead-acid battery dominates the emergency power supply system of nuclear power plants. However, Valve-Regulated Lead-Acid (VRLA) battery occupies important parts in emergency power supply systems. Structure design for internal consistency of big capacity is a challenge. Electrical variables of battery fluctuate as hysteresis while aging. This paper decouples terminal voltage in deep discharge by concentration polarization of electrolyte. Voltages of both bulk electrolyte capacitance and internal resistance are constants. This principle presents a novel model of dynamic threshold of contacting resistance. The model is sensitive to the battery nonlinear hysteresis. The model alarms remaining useful capacity at the end of service life. Parallel experiments at 4200 (Ah) VRLA batteries verifies the model. A Microchip embedded management board runs the algorithm.

Lithography Processable Ta2O5 Barrier-Layered Chitosan Electric Double Layer Synaptic Transistors.

We proposed a synaptic transistor gated using a Ta2O5 barrier-layered organic chitosan electric double layer (EDL) applicable to a micro-neural architecture system. In most of the previous studies, a single layer of chitosan electrolyte was unable to perform lithography processes due to poor mechanical/chemical resistance. To overcome this limitation, we laminated a high-k Ta2O5 thin film on chitosan electrolyte to ensure high mechanical/chemical stability to perform a lithographic process for micropattern formation. Artificial synaptic behaviors were realized by protonic mobile ion polarization in chitosan electrolytes. In addition, neuroplasticity modulation in the amorphous In–Ga–Zn-oxide (a-IGZO) channel was implemented by presynaptic stimulation. We also demonstrated synaptic weight changes through proton polarization, excitatory postsynaptic current modulations, and paired-pulse facilitation. According to the presynaptic stimulations, the magnitude of mobile proton polarization and the amount of weight change were quantified. Subsequently, the stable conductance modulation through repetitive potential and depression pulse was confirmed. Finally, we consider that proposed synaptic transistor is suitable for advanced micro-neural architecture because it overcomes the instability caused when using a single organic chitosan layer.