Search

Organic radical batteries (ORBs) represent a viable pathway to a more sustainable energy storage technology compared to conventional Li-ion batteries. For further materials and cell development towards competitive energy and power densities, a deeper understanding of electron transport and conductivity in organic radical polymer cathodes is required. Such electron transport is characterised by electron hopping processes, which depend on the presence of closely spaced hopping sites. Using a combination of electrochemical, electron paramagnetic resonance (EPR) spectroscopic, and theoretical molecular dynamics as well as density functional theory modelling techniques, we explored how compositional characteristics of cross-linked poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymers govern electron hopping and rationalise their impact on ORB performance. Electrochemistry and EPR spectroscopy not only show a correlation between capacity and the total number of radicals in an ORB using a PTMA cathode, but also indicates that the state-of-health degrades about twice as fast if the amount of radical is reduced by 15%. The presence of up to 3% free monomer radicals did not improve fast charging capabilities. Pulsed EPR indicated that these radicals readily dissolve into the electrolyte but a direct effect on battery degradation could not be shown. However, a qualitative impact cannot be excluded either. The work further illustrates that nitroxide units have a high affinity to the carbon black conductive additive, indicating the possibility of its participation in electron hopping. At the same time, the polymers attempt to adopt a compact conformation to increase radical-radical contact. Hence, a kinetic competition exists, which might gradually be altered towards a thermodynamically more stable configuration by repeated cycling, yet further investigations are required for its characterisation., (© 2023. The Author(s).)

Choline-based electrolytes have been proposed as environmentally friendly and low-cost alternatives for secondary zinc air batteries. Choline acetate [Ch] + [OAc] - in protic (D 2 O) and aprotic (DMSO-d 6 ) solvents has been studied by means of concentration-dependent 1 H NMR, viscosity, and density measurements. The viscosities have been calculated on the basis of the Jones-Dole equation and showed that the dominant contribution originates from short-range ion-solvent interactions. Site-specific association affinities were assigned from NMR chemical shift titrations. In DMSO-d 6 , the hydroxyl group of choline was found to have the smallest dissociation constant followed by the methyl group of acetate. The corresponding Gibbs energies at low concentration were found to be in agreement with a solvent-separated ion pair (2SIP) configuration, whereas at concentrations above 300 mM, a solvent-shared ion pair (SIP) configuration was assigned. For [Ch] + [OAc] - in D 2 O, association effects were found to be weaker, attributed to the high dielectric constant of the solvent. On time scales on the order of 100 ms, NMR linewidth perturbations indicated a change in the local rotational dynamics of the ions, attributed to short-range cation-solvent interactions and not to solvent viscosity. At 184 mM, ∼ 40 % of the cations in DMSO-d 6 and ∼ 10 % in D 2 O were found to exhibit short-range interactions, as indicated by the linewidth perturbations. It was found that at about 300 mM, the ions in DMSO-d 6 exhibit a transition from free to collective translational dynamics on time scales on the order of 400 ms. In DMSO-d 6 , both ions were found to be almost equally solvated, whereas in D 2 O solvation of acetate was stronger, as indicated by the obtained effective hydrodynamic radii. For [Ch] + [OAc] - in DMSO-d 6 , the results suggest a solvent-shared ion association with weak H-bonding interactions for concentrations between 0.3-1 M. Overall, the extent of ion association in solvents such as DMSO is not expected to significantly limit charge transport and hinder the performance of choline-based electrolytes., (© 2021 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Research in CO2 electro-reduction with the aim of providing green chemical feedstock (e.g., CO) has been driven towards optimization of individual components such as CO2-reducing gas diffusion electrodes (GDEs) to achieve stable electrolysis processes. Moving forward, investigation into the performance of electrodes at a cell- and system-level is needed to identify key operational parameters that enhance electrode efficiency. In this study, we characterize self-regulated steady-states within an electrolytic cell. Additionally, we explore the circumstances under which the current density passing through the cell becomes self-limiting. GDE-relevant system parameters and their impact on the overall electrode durability during electrolysis at high current densities up to -1.2 A cm-2 were analyzed on an intermediate time scale. Integration of inline sensors to the electrolysis test setup enabled close monitoring of changes in the electrolyte temperature and electrolyte pH, as well as the detection of pressure changes around the cathode. In the presented study, the GDE did not appear to be the bottleneck to achieving high current density CO2-electrolysis. Instead, electrolyte heating and gas evolution within the electrolyte gap limited the maximum current densities that could be applied to a GDE flow cell. Our results suggest that electrode performance (selectivity, durability) can sometimes be underestimated when electrolysis cells and their periphery are not optimally suited for operation with GDEs yet, thus preventing performance windows from being reached. [ABSTRACT FROM AUTHOR]

The combination of Li-metal anode and high-voltage cathode is regarded as a solution for the next-generation high-energy-density secondary batteries. However, a traditional electrolyte is either incompatible with the Li-metal anode or vulnerable to high voltage. This work reports a 1 M dual-salts Localized-High-Concentration-Electrolyte with Fluoroethylene carbonate (FEC) additive. It enables stable cycling of Li||LiNi0.8Co0.1Mn0.1O2 (NMC811) battery, which shows 81.5% capacity retention after 300 cycles with a charge/discharge current density of 1 C and a voltage range of 2.7–4.4 V. Scanning electron microscopy (SEM) images show that this electrolyte not only largely reduced Li dendrites and 'dead' Li on anode surface but also well protected the microstructure of NMC811 cathode. Possible components of both solid-electrolyte interlayer (SEI) and cathode-electrolyte interlayer (CEI) were characterized by energy-dispersive X-ray spectroscopy (EDX). The result illustrates that FEC protected Li salts from decomposition on the anode side and suppressed the decomposition of solvents on the cathode side. [ABSTRACT FROM AUTHOR]

A direct current in an electrochemical cell with a diluted liquid electrolyte leads to the displacement of ions within the solvent, while diffusion works against the resulting concentration differences. This study aims to experimentally evaluate a physicochemical ion transport model (source code provided) that describes current‐driven concentration gradients in diluted electrolytes. Hereto, an aqueous 0.1 M CuSO4 electrolyte between metallic copper electrodes serves as an experimental test system. Spatially resolved optical measurements are used to monitor the evolution of the ion concentration gradient in the electrolyte. Moreover, measured limited currents are related to computationally modeled concentration gradients. A constant parameterization of the diffusion coefficient, molar conductivity and ion transport number lead to a slight overestimation of the cathodic ion depletion and cell resistance, whereas a literature data based concentration dependent parameterization matches better to the measured data. The limited current is considered under a computational parameter variation and thereby related to the physicochemical impact of different electrolyte properties on the ion transport. This approach highlights the differences between purely diffusion limited currents and the limited current resulting from the combined electric field and diffusion driven ion motion. A qualitative schematic sketch of the physical mechanisms of the ion movement is presented to illustrate the current driven ion displacement in liquid electrolytes. [ABSTRACT FROM AUTHOR]

The electrochemical carbon dioxide reduction on copper attracted considerable attention within the last decade, since Cu is the only elemental transition metal that catalyses the formation of short-chain hydrocarbons and alcohols. Research in this field is mainly focused on understanding the reaction mechanism in terms of adsorbates and intermediates. Furthermore, dynamic changes in the micro-environment of the catalyst, i.e. local pH and CO 2 concentration values, play an equivalently important role in the selectivity of product formation. In this study, we present an in operando 13 C nuclear magnetic resonance technique that enables the simultaneous measurement of pH and CO 2 concentration in electrode vicinity during electroreduction. The influence of applied potential and buffer capacity of the electrolyte on the formation of formate is demonstrated. Theoretical considerations are confirmed experimentally and the importance of the interplay between catalyst and electrolyte is emphasised. [ABSTRACT FROM AUTHOR]

The hydrogen evolution reaction (HER) on iron is a parasitic side reaction for the reduction of iron (hydr)oxide in alkaline electrolyte, which lowers the Coulombic efficiency of iron‐based batteries. Tackling this issue, here we investigate the HER on iron electrodes by in situ gas chromatography, allowing for a quantitative correlation of the applied electrode potential and the resulting hydrogen evolution. As a result, it is shown that the HER follows a distinctive profile corresponding to the electrode potential and changes depending on the state of the iron electrode formation. Moreover, it is shown that the charging efficiency of the iron electrode can be increased by an alteration of the charging procedure, i. e., a more negative cut‐off potential for the discharge and a potential limitation for the recharge. In this study, a charging efficiency of 96.7 % is achieved, using an optimized charging procedure for a formed carbonyl iron electrode containing 8.5 wt.% of Bi2S3. [ABSTRACT FROM AUTHOR]

Supporting electrolytes contain inert dissolved salts to increase the conductivity, to change microenvironments near the electrodes and to assist in electrochemical reactions. This combined experimental and computational study examines the impact of supporting salts on the ion transport and related limited currents in electrochemical cells. A physical model that describes the multi-ion transport in liquid electrolytes and the resulting concentration gradients is presented. This model and its parameterization are evaluated by the measured limited current of the copper deposition in a CuSO4 electrolyte under a gradually increasing amount of Na2SO4 that acts as a supporting salt. A computational sensibility analysis of the transport model reveals that the shared conductance between the ions lowers the limited currents with larger supporting salt concentrations. When the supporting salt supplies most of the conductance, the electric-field-driven transport of the electrochemically active ions becomes negligible so that the limited current drops to the diffusion-limited current that is described by Fick's first law. The transition from diluted supporting electrolyte to the case of ionic liquids is elucidated with the transport model, highlighting the different physical transport mechanisms in a non-conducting (polar) and a conducting (ionic) solvent. [ABSTRACT FROM AUTHOR]

Rapid deactivation presently limits a wide spread use of high‐temperature solid oxide cells (SOCs) as otherwise highly efficient chemical energy converters. With deactivation triggered by the ongoing conversion reactions, an atomic‐scale understanding of the active triple‐phase boundary between electrolyte, electrode, and gas phase is essential to increase cell performance. Here, a multi‐method approach is used comprising transmission electron microscopy and first‐principles calculations and molecular simulations to untangle the atomic arrangement of the prototypical SOC interface between a lanthanum strontium manganite (LSM) anode and a yttria‐stabilized zirconia (YSZ) electrolyte in the as‐prepared state after sintering. An interlayer of self‐limited width with partial amorphization and strong compositional gradient is identified, thus exhibiting the characteristics of a complexion that is stabilized by the confinement between two bulk phases. This offers a new perspective to understand the function of SOCs at the atomic scale. Moreover, it opens up a hitherto unrealized design space to tune the conversion efficiency. [ABSTRACT FROM AUTHOR]

Keywords: metal-air batteries; iron electrodes; hydrogen evolution reaction; in situ gas chromatography; quantitative analysis EN metal-air batteries iron electrodes hydrogen evolution reaction in situ gas chromatography quantitative analysis 1 1 1 05/10/22 20220501 NES 220501 B The Front Cover b illustrates the hydrogen evolution on carbonyl iron electrodes with the latter being a resource-efficient option to store renewable electricity for stationary applications. Metal-air batteries, iron electrodes, hydrogen evolution reaction, in situ gas chromatography, quantitative analysis Cover Picture: In Situ Hydrogen Evolution Monitoring During the Electrochemical Formation and Cycling of Pressed-Plate Carbonyl Iron Electrodes in Alkaline Electrolyte (Batteries & Supercaps 5/2022). [Extracted from the article]

The interface between ceramic particles and a polymer matrix in a hybrid electrolyte is studied with high spatial resolution by means of Electrochemical Strain Microscopy (ESM), an Atomic Force Microscope (AFM)-based technique. The electrolyte consists of polyethylene oxide with lithium bis(trifluoromethanesulfonyl)imide (PEO6–LiTFSI) and Li6.5La3Zr1.5Ta0.5O12 (LLZO:Ta). The individual components are differentiated by their respective contact resonance, ESM amplitude and friction signals. The ESM signal shows increased amplitudes and higher contact resonance frequencies on the ceramic particles, while lower amplitudes and lower contact resonance frequencies are present on the bulk polymer phase. The amplitude distribution of the hybrid electrolyte shows a broader distribution in comparison to pure PEO6–LiTFSI. In the direct vicinity of the particles, an interfacial area with enhanced amplitude signals is found. These results are an important contribution to elucidate the influence of the ceramic–polymer interaction on the conductivity of hybrid electrolytes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • In operando EPR spectroscopy is utilized to monitor redox processes in LCO. • In the pristine battery, Co2+ due to electrolyte decomposition was found. • A pure oxygen redox mechanism is found for standard battery cycling. • Cobalt remains redox inactive during charging and discharging. Abstract Electron paramagnetic resonance (EPR) spectroscopy was utilized in operando to analyze redox mechanisms in lithium cobalt oxide (LCO) cathode material during battery cycling. In the pristine battery, a considerable amount of paramagnetic Co2+ was detected that was formed during initial contact of the electrolyte with the LCO. The Co2+ got oxidized during the formation cycle. The absence of an EPR signal during subsequent battery cycles, irrespective of the state-of-charge, indicates that no EPR active Co4+ is formed. This suggests the presence of an anionic oxygen redox mechanism in the active material. [ABSTRACT FROM AUTHOR]

• The fracture behavior of LATP electrolyte was investigated. • Micro-pillar splitting method was adopted to determine the fracture toughness. • K IC obtained via pillar splitting agrees well with that via Vickers indentation. • Grain orientation shows no distinct effect on intrinsic fracture toughness. • The effect of pre-existing defects on fracture behavior needs to be considered. The NASICON type solid electrolyte LATP is a promising candidate for all-solid-state Li-ion batteries considering energy density and safety aspects. To ensure the performance and reliability of batteries, crack initiation and propagation within the electrolyte need to be suppressed, which requires knowledge of the fracture characteristics. In the current work, micro-pillar splitting was applied to determine the fracture toughness of LATP material for different grain orientations. The results are compared with data obtained using a conventional Vickers indentation fracture (VIF) approach. The fracture toughness obtained via micro-pillar splitting test is 0.89 ± 0.13 MPa∙m1/2, which is comparable to the VIF result, and grain orientation has no significant effect on the intrinsic fracture toughness. Being a brittle ceramic material, the effect of pre-existing defects on the toughness needs to be considered. [ABSTRACT FROM AUTHOR]

Si–air batteries, unlike other resource efficient metal–air batteries that were subject of investigations for quite a long time, came to the focus of research only recently. When operated with alkaline electrolyte, severe limitations of the discharge capacities were reported, which were attributed to a passivation layer on the anode. As a consequence, only small fractions of the surface from Si-anodes could be used for discharge. The objective of the present work is to reconsider the discharge behavior of Si–air cells with KOH electrolyte and to point out how a discharge process can be put forward until the complete anode is exhausted. Operating Si–air cells with alkaline electrolyte causes substantial corrosion, which produces also hydrogen gas as a reaction product. Moreover, along with the dissolution of Si in KOH, condensation of silicate structures in the electrolyte has been observed. Both effects accelerate electrolyte loss in the cell. Therefore, appropriately balancing the electrolyte supply of the Si–air cell is a precondition for ongoing discharge. Specifically, cells with As-doped Si-wafer anodes with 0.6 mm and 3.0 mm thickness were discharged in 5 M KOH electrolyte at current densities up to 0.05 mA/cm 2 for 260 and 1100 hours, respectively. The drawback is that a minimum amount of electrolyte is required in order not to exceed 4 M Si content, which otherwise leads to a gelation of the electrolyte. Although a considerable fraction of the anode material is not transformed to electrical energy owing to corrosion, specific energies up to 140 Wh/kg (for 1100 h) related to the total anode mass loss were realized. [ABSTRACT FROM AUTHOR]