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Conflat Two and Three Electrode Electrochemical Cells

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Abstract

Two and three-electrode electrochemical test cells based on low cost and readily available Conflat vacuum fittings are described. Two-electrode Conflat cells were found to have the same performance as two-electrode coin cells at room temperature, while three-electrode Conflat cells are much easier to assemble than three-electrode coin cells. Such cells maintain good stack pressure, tolerate high vapor pressure solvents and can operate at temperatures up to 200 degrees C. Conflat cells are especially useful for high temperature and magnesium battery research, where the need for three-electrode cells operated at elevated temperatures with volatile solvents makes the use of coin cell hardware impractical.

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... 80 • C for most electrolyte solvents, or lower with volatile solvents such as tetrahydrofuran. 6 Alternative gasket materials may offer slight sealing improvements at higher temperatures. 7 Other approaches include embedding coin cells within a high-temperature compatible epoxy. ...
... 7 Other approaches include embedding coin cells within a high-temperature compatible epoxy. 8 However, coin cells can deform with high internal pressure 6 and can be challenging to use with in-situ techniques 9 and in three-electrode designs. 10 Swagelok cells offer more experimental flexibility as the sealing ferrules and cell body are available in a variety of materials (e.g. ...
... However, electrical isolation between electrodes requires either a plastic cell body or plastic-coated plungers, and higher temperature testing is limited to 55 • C. 12,14 PTFE also reacts with lithium at low voltages, a major issue when investigating negative electrode materials. 6 Swagelok cells incorporating metal plungers embedded in alumina 15 were successfully cycled at 100 and 150 • C. 16,17 However, mismatched thermal expansion coefficients between the metal body, alumina sleeves, and metal plungers can limit cell sealing performance at higher temperatures. ...
... Several groups have already detected these errors and some possible solutions have been proposed to minimize measurement artifacts in three-electrode setups. [5][6][7][8][9][10] Approaches with different materials, such as pure lithium metal 7,8 or lithium iron phosphate, 11 as well as with different geometries, mostly point-5 or ring-shaped, 8 have previously been reported in literature. La Mantia et al. 12 very recently presented a promising novel setup using an LFP-coated stainless steel mesh. ...
... Several groups have already detected these errors and some possible solutions have been proposed to minimize measurement artifacts in three-electrode setups. [5][6][7][8][9][10] Approaches with different materials, such as pure lithium metal 7,8 or lithium iron phosphate, 11 as well as with different geometries, mostly point-5 or ring-shaped, 8 have previously been reported in literature. La Mantia et al. 12 very recently presented a promising novel setup using an LFP-coated stainless steel mesh. ...
... Several groups have already detected these errors and some possible solutions have been proposed to minimize measurement artifacts in three-electrode setups. [5][6][7][8][9][10] Approaches with different materials, such as pure lithium metal 7,8 or lithium iron phosphate, 11 as well as with different geometries, mostly point-5 or ring-shaped, 8 have previously been reported in literature. La Mantia et al. 12 very recently presented a promising novel setup using an LFP-coated stainless steel mesh. ...
Article
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Electrochemical Impedance Spectroscopy (EIS) is a well-established technique for investigating the loss processes that take place in lithium-ion batteries with different characteristic time constants. Three-electrode setups are needed to separate the contributions of working electrode (WE) and counter electrode (CE), but often suffer from measurement artifacts. This paper is the second part of a two-part paper dealing with the roots of these distortions: (I) electrochemical and (II) geometric asymmetry. The first part presents a theoretical examination by FEM simulation and the second part details the corresponding real-world measurements. The simulation results were confirmed: electrochemical and geometric asymmetry lead to artifacts for point-like reference electrodes but not for mesh reference electrodes. The geometric characteristics of the mesh reference electrode are crucial (thin wire and an open weave are essential). Furthermore, a possible realization of a mesh reference electrode setup is presented, using an aluminum mesh coated with Li4Ti5O12 powder as reference electrode. This combination was then validated by additional measurements in symmetric cells. Additionally, the benefits of using the proposed setup for recording quasi-equilibrium potential curves and for performing rate capability experiments are demonstrated.
... The magnesium reference electrode was polished with carbide paper (Mastercraft, 180 grit SiC) and cleaned with a Kimwipe inside an Ar-filled glovebox before use. The voltage profile for the nonaqueous system was studied in three-electrode cells obtained from DPM Solutions Inc. 38 The cell has a cylindrical geometry. A Mg ring, sandwiched in-between the positive and negative electrodes, is used as the reference electrode. ...
... However, magnesium metal can still be used as a reference electrode owing to the extremely low current passed in this case. We first investigated the electrochemistry in a three-electrode cell, 38 with a magnesium reference electrode and a capacitive-carbon counter electrode. 44 Figure 5, panels a and b show the representative voltage profiles for the eighth cycle at a current density of C/10. ...
Article
Magnesium batteries are an energy storage system that potentially offers high energy density, but development of new high voltage cathode materials and understanding of their electrochemical mechanism are critical to realize its benefits. Herein, we synthesize the layered MnO2 polymorph (the birnessite phase) as a nanostructured phase supported on conductive carbon cloth and compare its electrochemistry and structural changes when it is cycled as a positive electrode material in a Mg-ion battery under nonaqueous or aqueous conditions. X-ray photoelectron spectroscopy and transmission electron microscopy studies show that a conversion mechanism takes place during cycling in a nonaqueous electrolyte, with the formation of MnOOH, MnO, and Mg(OH)2 upon discharge. In aqueous cells, on the other hand, intercalation of Mg2+ ions takes place, accompanied by expulsion of interlayer water and transformation to a spinel-like phase as evidenced by X-ray diffraction. Both systems are structurally quasireversible. The sharp contrast in behavior in the two electrolytes points to the important role of the desolvation energy of the Mg2+ cation in nonaqueous systems.
... Similar to APC, the dual salt electrolyte also shows reversible metal stripping/plating at the Mg anode and an anodic stability up to 3.2 V with an Mo cathode current collector ( Figure S3, Supporting Information). A series of Mg Li dual salt electrolytes with fi xed 0.2 M APC concentration and different LiCl concentrations were examined with both PBA materials in three-electrode cells [ 44 ] at a current density of 10 mA g −1 (≈C/10, where 1C corresponds to a 1 e − transfer per PBA formula). As the LiCl concentration increases up to 0.5 M , the capacity also increases until it reaches the maximum value achieved in this study of 125 mAh g −1 for both 23-PBA ( . ...
... Magnesium metal was polished with carbide paper (Mastercraft, 180 grit SiC) and cleaned prior to use. The 2325 type coin cells or three-electrode cells (DPM Solutions Inc.) [ 44 ] were assembled in an Ar-fi lled glovebox, with the cathode side protected by an Mo disc. Galvanostatic studies of all cells were performed on a VMP3 cycler (Biologic) at room temperature. ...
Article
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The major advantage of Mg batteries relies on their promise of employing an Mg metal negative electrode, which offers much higher energy density compared to graphitic carbon. However, the strong coulombic interaction of Mg²⁺ions with anions leads to their sluggish diffusion in the solid state, which along with a high desolvation energy, hinders the development of positive electrode materials. To circumvent this limitation, Mg metal negative electrodes can be used in hybrid systems by coupling an Li⁺insertion cathode through a dual salt electrolyte. Two “high voltage” Prussian blue analogues (average 2.3 V vs Mg/Mg²⁺; 3.0 V vs Li/Li⁺) are investigated as cathode materials and the influence of structural water is shown. Their electrochemical profiles, presenting two voltage plateaus, are explained based on the two unique Fe bonding environments. Structural water has a beneficial impact on the cell voltage. Capacities of 125 mAh g⁻¹are obtained at a current density of 10 mA g⁻¹(≈C/10), while stable performance up to 300 cycles is demonstrated at 200 mA g⁻¹(≈2C). The hybrid cell design is a step toward building a safe and high density energy storage system. © 2016 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
... After a long exposure, the carbon formed may even produce short circuits. 14,54,55 In contact with sodium metal, the reaction is highly dependent on the solvent used: no evidence of PTFE decomposition is observed in carbonates, whereas it is important with diglyme. 40 PTFE decomposition has also been proposed to be at the origin of capacity loss with graphite anodes when used as binder. ...
... Note, however, that the fluorocarbon resin is similar to PTFE and PVDF and its instability in lithium batteries at low potential has been reported. 14 Polyolefins (polypropylene, high-density polyethylene, etc.) form a very versatile family of polymers with higher stability at low potentials than the PTFE. However, they might be less resistant to dissolution and solvent uptake and could present low thermal stability depending on the polymer. ...
Article
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While less mature than Li-ion battery, technologies based on Na, K, Mg and Ca are attracting more and more attention from the battery community. New material (cathode, anode or electrolyte) testing for these post Li systems commonly involves the use of an electrochemical setup called half-cell in which metal counter and reference electrodes are used. Here we firstly describe the different issues that become critical when moving away from Li with respect to the cell hardware (cell design, current collector, separator, insulator) and the nature of counter and reference electrodes. Workarounds are given and a versatile setup is proposed to run reliable electrochemical tests for post Li battery materials in general, in a broad range of electrolyte compositions.
... The average electrode loading was 2.4 mg/cm 2 . Conflat cells, as described in reference [10], were constructed using sputtered disc or composite lead electrodes and Mg foil (99.95%, 0.25 mm thick, Gallium Source, LLC, Scotts Valley, CA) counter/reference electrodes. All cells were constructed in an argon filled glovebox. ...
... 4,18 For simplicity, we omit the residual copper in the lattice from the formula and refer to this material as simply Ti 2 S 4 . To determine the equilibrium potential curves and diffusion coefficients of Mg 2+ and Li + as a function of ion concentration (x), we performed galvanic intermittent titration technique (GITT) experiments 19,20 using three-electrode Conflat cells 21 at 60°C. Figure 1 shows the quasi-equilibrium potential vs x curves for Li x Ti 2 S 4 (a) and Mg x Ti 2 S 4 (b). The first discharge profile of Li x Ti 2 S 4 shown in Figure 1a agrees with the results of Bruce and Saidi. ...
Article
Measurement of Li+ and Mg2+ diffusion in the same Ti2S4 thiospinel material in three electrode cells at elevated temperature negates factors of surface area and cell design, allowing the direct comparison of their diffusion coefficients (D). D values were measured using the Galvanic Intermittent Titration Technique (GITT) as a function of both ion concentration (x) and temperature. During discharge at 55 °C, DLi descends gradually from 2×10-8 cm2/s by an order of magnitude over the range 0 < xLi < 1.9 (i.e., DLi = 2×10-9 cm2/s at the maximum degree of intercalation; xLi = 1.9). In contrast, DMg starts at a similar value and decreases more steeply by two orders of magnitude to reach 1×10-10 cm2/s at xMg ≈ 0.65, but then declines sharply, reaching 1×10-12 cm2/s at xMg ≈ 0.8. This kinetic factor contributes to limiting the maximum practical discharge capacity of MgxTi2S4. The difference in behavior vis a vis Li+ implies that either increasing Mg2+ occupation of the tetrahedral site at xMg > 0.6 (which is not observed for Li+) and/or interactions between diffusing cations play a much larger role in mediating the diffusion of divalent compared to monovalent cations. Diffusion activation energies (Ea) extracted from the temperature-dependent data revealed that Ea,Mg (540 ± 80 meV) is about twice that of Ea,Li (260 ± 50 meV), explaining the poorer electrochemical performance of MgxTi2S4 at room temperature.
... In recent years, there has also been a tremendous increase in research devoted to investigating materials that may combine the high energy density of batteries and the long cycle life and short charging times of supercapacitors [15][16][17]. Vanadium oxides represent an attractive candidate as a cathode material due to their layered structure and high theoretical capacity [18][19][20][21][22][23][24]. As a result of their layered structure [25][26][27][28], it may be assumed that the total stored charge for vanadium oxide nanostructures in Li-ion battery applications is exclusively due to diffusion-based intercalation processes associated with well-defined phase changes in bulk crystalline V 2 O 5 . ...
Article
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Vanadium oxide nanostructures have been widely researched as a cathode material for Li-ion batteries due to their layered structure and shorter Li+ diffusion path lengths, compared to the bulk material. Some oxides exhibit charge storage due to capacitive charge compensation, and many materials with cation insertion regions and rich surface chemistry have complex responses to lithiation. Herein, detailed analysis by cyclic voltammetry was used to distinguish the charge stored due to lithium intercalation processes from extrinsic capacitive effects for micron-scale bulk V2O5 and synthesized nano-scale vanadium oxide polycrystalline nanorods (poly-NRs), designed to exhibit multivalent surface oxidation states. The results demonstrate that at fast scan rates (up to 500 mV/s), the contributions due to diffusion-controlled intercalation processes for micron-scale V2O5 and nanoscale V2O3 are found to dominate irrespective of size and multivalent surface chemistry. At slow potential scan rates, a greater portion of the redox events are capacitive in nature for the polycrystalline nanorods. Low dimensional vanadium oxide structures of V2O5 or V2O3, with greater surface area do not automatically increase their (redox) pseudocapacitive behaviour significantly at any scan rate, even with multivalent surface oxidation states.
... A simple setup is obtained by immersing the three electrodes in a beaker cell. There are also other available three-electrode cell designs, such as the Conflat cell, 35 T-shaped Swagelok cell, 36 and modified coin cell, 37 where the cells are airtight and only a small amount of electrolyte is required. Note that special care needs to be taken for impedance measurements because the cell geometry has a significant influence on the results. ...
Article
We present an overview of the procedures and methods to prepare and evaluate materials for electrochemical cells in battery research in our laboratory, including cell fabrication, two and three electrode cell studies, and methodology for evaluating diffusion coefficients and impedance measurements. Informative characterization techniques employed to assess new materials for batteries are also described, including operando XRD, pair-distribution function analysis, X-ray photoelectron spectroscopy and operando X-ray absorption spectroscopy. Examples of insightful information that each technique has provided in the research areas of Li-S, Na-ion, and Mg batteries are presented along with excellent references for detailed description of the theory, experimental procedures, various designs, and data processing and analysis methods.
... Again they emphasize that accurate control of the electrode alignment is essential. Periyapperuma et al. 10 used Conflat vacuum fittings to build temperature resistant three-electrode cells. These feature a ring-shaped reference electrode which is supposed to be well suited for polymer electrolyte studies at elevated temperatures. ...
Article
Material and degradation effects in lithium-ion batteries are studied in three-electrode cells using electrochemical impedance spectroscopy. But half-cell impedance spectra are often superimposed by distortions caused by the individual cell arrangement. Finite Element Method simulations of the three-electrode cell were applied to identify and quantify these contributions. This study identified two basic mechanisms: (I) a radially inhomogeneous current distribution originating from geometric asymmetry of the electrodes; and (II) a frequency-dependent inhomogeneous current distribution in the electrolyte caused by an electrochemical asymmetry. Mechanism II is caused by different electrode materials, and enhanced when the electrolyte diameter exceeds those of both working and counter electrode. With the help of the FEM model, we evaluated three-electrode cells featuring different reference electrode geometries: (a) point-like, (b) wire and (c) mesh reference electrode. The results of these FEM simulations are shown as half-cell and full-cell impedance data, disclosing the magnitude of distortions and artifacts for each type of reference electrode geometry. The mesh reference electrode, proposed in literature but not widely adopted, showed the largest potential for error-free impedance spectra. The FEM simulations were supported by experiments, comparing a point-like with a mesh reference electrode in a three-electrode cell (see part II).
... This procedure facilitates measurement of WE and CE potential profiles without impacting battery performance, at least for the initial 20 cycles, although no EIS measurements were reported. Other configurations have also been explored, such as the Conflat cell (which is similar to a coin cell and where a ring-shaped RE is employed), where an electrode alignment chosen to enhance measurement reliability has been reported [158]. Some studies have also reported analyses of cells with cylindrical geometry, where the body of the cell is immersed in an electrolyte-containing vessel together with the RE, all in an inert atmosphere [97,159,160]. ...
Article
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Use of a reference electrode (RE) in Li-ion batteries (LIBs) aims to enable quantitative evaluation of various electrochemical aspects of operation such as: (i) the distinct contribution of each cell component to the overall battery performance, (ii) correct interpretation of current and voltage data with respect to the components, and (iii) the study of reaction mechanisms of individual electrodes. However, care needs to be taken to ensure the presence of the RE does not perturb the normal operation of the cell. Furthermore, if not properly controlled, geometrical and chemical features of the RE can have a significant influence on the measured response. Here, we present a comprehensive review of the range of RE types and configurations reported in the literature, with a focus on critical aspects such as electrochemical methods of analysis, cell geometry, and chemical composition of the RE and influence of the electrolyte. Some of the more controversial issues reported in the literature are highlighted and the benefits and drawbacks of the use of REs as an in situ diagnostic tool in LIBs are discussed.
... For instance, PTFE, which is used in Maxwell-type electrolytes, exhibits low stability with Li metal anodes. 121,122 The stability of PTFE at high voltages has not been clearly evaluated. On one hand, the decomposed binder will decrease the Coulombic efficiency due to the consumption of additional active lithium. ...
Article
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The industrialization of solid-state batteries (SSBs) with high energy density and high safety is a growth point. The scale-up application toward using SSBs is mainly restrained by batch fabrication of large-sheet, high-energy electrodes (>4 mAh/cm²) and robust thin solid-state electrolytes (SSEs; <50 μm) to achieve the high-energy-density demand of >400 Wh/kg. Conventional slurry casting fabrications in SSBs suffer from fragility, solvent sensitivity, and blocked ionic transport. Dry battery electrode (DBE) is an emerging concept and technology in the battery industry that innovates electrode fabrication as a “powder to film” route. The DBE technique can significantly simplify the manufacturing process, reconstruct the electrode microstructures, and increase the material compatibilities. This perspective introduces the concept of DBE techniques and analyzes their superiorities, protocols, scientific principles, and potential attempts at improving the performances and production efficiency of SSBs, aiming to popularize the promising DBE toward the industrialization of SSBs.
... As for transference number measurement, we used an electrochemical method similar to previous reports [18,19]. In essence, a nonblocking cell was assembled using a revised conflat cell [20] with two stainless steel (SS) spacers as current collectors in close contact with two lithium metal disks sandwiching a high-density polyethylene cylinder. The cylinder was filled with the electrolytes, and the distance between the two lithium disks was 8 mm. ...
Article
Enabling fast charging capability of high energy density Li-ion cells could dramatically increase the widespread adoption of battery electric vehicles. However, fast charging is limited by Li ion depletion in the electrolyte and increasing Li ion transport from cathode to anode is essential. By evaluating different Li salts in the electrolyte, we find lithium bis(fluorosulfonyl)imide (LFSI) has both higher conductivity and higher Li ion transference number compared to the traditional LiPF6 salt. In a 12-minute charge, the electrolyte with LiPF6 salt reaches the cut-off voltage rapidly while the one with LiFSI exhibits a longer constant current charge with more capacity achieved. The LiFSI electrolyte also shows better cycling performance and less Li plating after repeated fast charging cycles. Keywords: Fast charging, NMC811, Electrolyte, LiFSI
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Mg electrodes were studied in a variety of polar aprotic electrolyte solutions, using cyclic voltammetry (CV), impedance spectroscopy (EIS), surface sensitive FTIR spectroscopy, element analysis by dispersive X-rays (EDAX), scanning electron microscopy (SEM), and electrochemical quartz crystal microbalance (EQCM) studies. The solutions included Mg, Li, Na, K and Bu4N+ salt solutions in acetonitrile (AN), propylene carbonate (PC) and tetrahydrofuran (THF). In addition, THF+RMgX (R=alkyl, X=Cl, Br) solutions were studied. This paper aims at providing a general description of the electrochemical behavior of Mg electrodes in different types of polar aprotic systems. It appears that Mg electrodes are spontaneously covered by surface films in most of the solutions studied. In AN and PC, solvent reduction seems to dominate surface film formation, while in THF, the solvent is inactive and, thus, reduction of salt anions such as ClO4− and BF4− leads to the precipitation of surface films. The impedance of Mg electrodes is very high, due to these surface films (several orders of magnitude higher than that of Li electrodes in the same solutions). However, the above difference in the surface chemistry is clearly reflected by the electrode’s impedance. Consequently, Mg dissolution in these solutions occurs via a breakdown of the surface films. However, it is possible to reduce the overpotential of Mg dissolution considerably by the presence of acidic species in solutions, which remove part of the surface films chemically. Reversible Mg deposition and dissolution are obtained in THF+RMgX solution due to the fact that in these solutions, irreversible formation of stable surface films on the Mg electrodes is avoided largely. However, EQCM studies showed that these processes are not just a simple two-electron transfer to Mg ions and are complicated by adsorption–desorption processes of the solution species.
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Electrochemical techniques have been used to study the reversible insertion of sodium into hard-carbon host structures at room temperature. In this paper the authors compare these results with those for lithium insertion in the same materials and demonstrate the presence of similar alkali metal insertion mechanisms in both cases. Despite the gravimetric capacities being lower for sodium than lithium insertion, the authors achieved a reversible sodium capacity of 300 mAh/g, close to that for lithium insertion in graphitic carbon anode materials. Such materials may therefore be useful as anodes in rechargeable sodium-ion batteries.
Article
The first discharge of a nanostructured FeSn2 based negative electrode for Li-ion batteries has been studied by combining operando 119Sn Mössbauer spectroscopy and ex situ magnetic measurements. A modified Swagelok-type cell has been designed to perform in situ Mössbauer measurements, which allowed us to quantitatively follow the first discharge. The electrochemical mechanism consists in a conversion reaction that transforms FeSn2 into Li7Sn2. The Mössbauer spectrum at the end of the first discharge has been analysed from first principles calculations of the Mössbauer parameters. The observed differences with bulk Li7Sn2 have been explained by the small size of the electrochemically formed particles. The magnetic measurements of the electrode material at the end of the discharge show the existence of rather pure superparamagnetic iron nanoparticles with an average diameter in the range 2-3 nm as evaluated from three different methods. The electrode saturation magnetization increases during the discharge, due to the increasing number of formed iron nanoparticles, but unexpected two-step variations were observed. They are interpreted by changes in the FeSn2 magnetization caused by interactions with iron nanoparticles.
Article
The potential distribution through plastic Li‐ion cells during electrochemical testing was monitored by means of three‐ or four‐electrode measurements in order to determine the origin of the poor electrochemical performance (namely, premature cell failure, poor storage performance in the discharged state) of /C Li‐ion cells encountered at 55°C. Several approaches to insert reliably one or two reference electrodes that can be either metallic lithium or an insertion compound such as into plastic Li‐ion batteries are reported. Using a reference electrode, information regarding the evolution of (i) the state of charge of each electrode within a Li‐ion cell, (ii) their polarization, and (iii) their rate capability can be obtained. From these three‐electrode electrochemical measurements, coupled with chemical analyses, X‐ray diffraction, and microscopy studies, one unambiguously concludes that the poor 55°C performance is mainly due to the instability of the phase toward Mn dissolution in ‐type electrolytes. A mechanism, based on Mn dissolution, is proposed to account for the poor storage performance of /C Li‐ion cells.
Article
Research leading to the construction of an ambient temperature rechargeable magnesium battery based on organic electrolytes and positive electrodes capable of reversible intercalation of Mg+2 ions is discussed. The number of combinations of solvent, solute, and intercalation cathode which give reasonable battery performance is much more limited for Mg than for alkali metals. The only electrolytes which allowed Mg dissolution and deposition were solutions of organomagnesium compounds in ethers or tertiary amines; many of these were unstable in the presence of transition metal oxides or sulfides which were found to function acceptably as intercalation electrodes. Possible directions for future research which could solve these problems are discussed, as well as theoretical aspects of magnesium compound behavior in nonaqueous solvents.
Article
An active metal that should be considered as an anode material in high energy density batteries is definitely magnesium. It is relatively cheap, much safer to use and handle than lithium, and its compounds are usually non-toxic.Similar to lithium, magnesium is covered by surface films in any ‘inert’ atmosphere that contains atmospheric contaminants, and in most of the relevant electrolyte solutions for batteries. In contrast to lithium where the surface films covering the active metal are Li-ion conductors, surface films formed similarly on magnesium cannot conduct the bivalent Mg2+ ions. We developed new electrolyte solutions based on ethers of the ‘glyme’ family and magnesium aluminates whose electrochemical window is 2.5 V wide. The efficiency of Mg deposition–dissolution cycles in these solutions is higher than 99%. We also showed that it is possible to construct rechargeable Mg batteries using these electrolyte solutions and cathodes of the MgxMoSy type (chevrel phase), which operate at 1–1.5 V, and can deliver more than 1000 charge–discharge cycles. Some technical details of these battery systems are discussed.
Article
In the present study, we explored how milling Mo6S8 Chevrel phase in inert or air atmosphere affects their electrochemical behavior as a Mg-ion insertion material for rechargeable Mg batteries. Electrochemical tools such as slow scan rate cyclic voltammograms and potentiostatic intermittent titration technique have been used in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. In contrast to the deterioration observed for milling Mo6S8 in air, its milling under Ar results in specific capacity increase due to improved Mg-ion diffusion kinetics. It was shown that in spite of the conservation of the bulk crystallographic structure, both for air and the Ar-milled materials, they differ significantly in the average particle sizes and the degree of surface oxidation state.
Article
The influence of geometric and electrochemical asymmetries on the impedance spectra recorded in three-electrode test cells for lithium ion batteries was investigated. These asymmetries lead to distortions such as e.g. scaling effects which appear in common Swagelok cells. Moving the reference electrode to a coaxial position in combination with a precise alignment of the electrode stack optimized the geometry of current lines, leading to reliable impedance spectra up to frequencies of 50 kHz regardless of the electrode configuration.
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