Phase Diagram of Mg Insertion into Chevrel Phases, MgxMo6T8 (T = S, Se). 1. Crystal Structure of the Sulfides

Levi, Elena; Lancry, Eli; Mitelman, A.; Aurbach, Doron; Ceder, Gerbrand; Morgan, Dane; Isnard, O.

doi:10.1021/cm061656f

Cited by 119 publications

(192 citation statements)

References 44 publications

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“…This charge trapping is attributed to circular motion of Mg 2+ in the inner ring, since Mo-Mg interactions create a large energy barrier to escape the low-potential inner ring sites [117]. Levi et al [138] found that the improved mobility of Mg during the second reaction is a consequence of increased repulsion between Mg 2+ ions. Apart from the charge trapping, the high mobility is related to the nature of CPs, where the 3D channels of closely spaced vacant sites prevent Mg 2+ ions from occupying adjacent sites.…”

Section: Cathode Materialsmentioning

confidence: 99%

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

2015

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to develop and install renewable energy harvesting technologies [3]. However, their successful implementation will be dependent on reliable and robust storage devices since harvesting solar and wind energy is inherently intermittent and the majority of consumption targets cannot be readily tethered to the grid.As energy storage devices, batteries possess high portability, high energy density, high Coulombic efficiency, and long cycle life. They are ideal power sources for portable devices, automobiles, and backup power supplies; accordingly, batteries power nearly all of our mobile electronics and are used to improve the efficiency of hybrid electric vehicles [4,5]. Unfortunately, considerable improvements in performance are still required in order to meet the demands of advanced portable devices and achieve energy sustainability (e.g., through smart grid and electric vehicle technologies) [6]. These enduring needs have driven intensive research investments. While efforts have been successful, there is still significant room for improvement regarding the development and understanding of electrode materials [7]. The overall capacity and potential cycling window of many electrode materials are limited to prevent degradation over long term cycling. In addition to exploring new electrode materials, there have been strong efforts to improve those that are already utilized. Expense reduction is a priority as approximately 23% and 8% of the overall battery pack costs stem from the respective cathode and anode active materials alone [8].An alkali-ion battery consists of several electrochemical cells connected in parallel and/or in series to provide a designated current or voltage. Each electrochemical cell has two electrodes separated by an electrolyte that is electrically insulating but ionically conductive. During discharge, when the alkali-ion battery operates as a galvanic cell, alkali ions exit the negative electrode (typically carbon) and insert themselves into the positive electrode while electronsThe need for economical and sustainable energy storage drives battery research today. While Li-ion batteries are the most mature technology, scalable electrochemical energy storage applications benefit from reductions in cost and improved safety. Sodium-and magnesium-ion batteries are two technologies that may prove to be viable alternatives. Both metals are cheaper and more abundant than Li, and have better safety characteristics, while divalent magnesium has the added bonus of passing twice as much charge per atom. On the other hand, both are still emerging fields of research with challenges to overcome. For example, electrodes incorporating Na + are often pulverized under the repeated strain of shuttling the relatively large ion, while insertion and transport of Mg 2+ is often kinetically slow, which stems from larger electrostatic forces. This review provides an overview of cathode and anode materials for sodium-ion batteries, and a comprehensive summary of research on cathodes for magnesium-ion batteries. In additi...

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Section: Cathode Materialsmentioning

confidence: 99%

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

2015

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“…Therefore, the two reactions exhibit different activation-energy barriers. 28,29 The characteristic structure of Mg 2 Mo 6 S 8 also appears to affect the ion mobility in the solid. In 2005, Levi et al used the classical potentiostatic intermittent titration technique (PITT) to measure the solid diffusivity of Mg x Mo 6 S 8 as a function of Mg content, x.…”

Section: Rate Behavior Of Chevrel Phasementioning

confidence: 99%

“…Levi et al measured D s,fast using the PITT method; however, as mentioned above, they could not measure the lower diffusivity, D s,slow , because the value was too small, caused by Mg ions trapping. 28,29,38 For the exchangecurrent density, i 0 , no reported value of Mg x Mo 6 S 8 in APC/THF (Eq. 4) was found in the literature; therefore, we used i 0,fast , i 0,slow , and D s,slow as fitting parameters in the model.…”

Section: Mathematical Model Assumptions and Materials Propertiesmentioning

confidence: 99%

“…This issue manifests itself in the electrolyte phase, where the Mg ion is thought to form ion pairs, 26,27 and in typical cathode materials, where the diffusion of ions can be fairly slow. 28,29 Furthermore, although not clearly explored in the literature, the sluggish movement of Mg ions can also manifest itself at the interface during charge transfer. To date, it is unclear which of these limitations (bulk cathode vs. bulk electrolyte vs. interfaces) limits the rate capability of Mg-ion systems most.…”

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confidence: 99%

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Understanding Performance Limitations to Enable High Performance Magnesium-Ion Batteries

Kim

Perdue

Apblett

et al. 2016

J. Electrochem. Soc.

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A mathematical model was developed to investigate the performance limiting factors of Mg-ion battery with a Chevrel phase (Mg x Mo 6 S 8 ) cathode and a Mg metal anode. The model was validated using experimental data from the literature [Cheng et al., Chem. Mater., 26, 4904 (2014)]. Two electrochemical reactions of the Chevrel phase with significantly different kinetics and solid diffusion were included in the porous electrode model, which captured the physics sufficiently well to generate charge curves of five rates (0.1C-2C) for two different particle sizes. Limitation analysis indicated that the solid diffusion and kinetics in the highervoltage plateau limit the capacity and increase the overpotential in the Cheng et al. 's thin (20-μm) electrodes. The model reveals that the performance of the cells with reasonable thickness would also be subject to electrolyte-phase limitations. The simulation also suggested that the polarization losses on discharge will be lower than that on charge, because of the differences in the kinetics and solid diffusion between the two reactions of the Chevrel phase. During the past 30 years, Li-ion batteries have come to dominate the market for use in electric vehicles (EVs) and portable electronic devices. However, to extend the driving range of EVs and to make the portable electronic devices more compact and lighter, the energy density of the batteries must be increased. Significant effort has been devoted to finding new battery chemistries with the potential to exceed the energy density of Li-ion batteries. 1-4Among the novel approaches being studied, Mg-ion batteries are promising candidates, 5-24 partly because of the advantages of Mg metal anode. Although the reduction potential of Mg metal is similar to that of Li (-2.37 V vs. H + /H 2 for Mg compared with -3.0 V vs. H + /H 2 for Li), the volumetric capacity is significantly higher (3,833 mAh cm -3 for Mg compared with 2,046 mAh cm -3 for Li). In addition, Mg-ion batteries may be safer than Li-ion batteries, not only because Mg does not form hazardous dendrites when charged and discharged repeatedly 25 but also because a strong and stable oxide develops on the surface, protecting the battery if the metal is exposed to ambient conditions. Finally, the divalent charge on the Mg ion enables exploration of higher-capacity cathode materials that promise increases in the overall cell-energy density.Although multivalent systems are promising from an energydensity perspective, they are limited by the slow transport of the divalent cation. This issue manifests itself in the electrolyte phase, where the Mg ion is thought to form ion pairs, 26,27 and in typical cathode materials, where the diffusion of ions can be fairly slow. 28,29Furthermore, although not clearly explored in the literature, the sluggish movement of Mg ions can also manifest itself at the interface during charge transfer. To date, it is unclear which of these limitations (bulk cathode vs. bulk electrolyte vs. interfaces) limits the rate capability of Mg-ion systems ...

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“…13 Downloaded on 2018-05-12 to IP anisotropic channel character, would not allow filling of a larger part of the vacant sites although the number of them is high in o-Mo 9 Se 11 . 21 On the other hand, in the case of Chevrel compounds, Mo 6 X 8 (X = S, Se), with three-dimensional diffusion channel, 33 it is reported that both Li-and Mg-systems show the similar order capacity comparable with the theoretical capacity 11,12,[17][18][19][20]34,35 deduced from the molecular orbital model, 23 in which extra four electrons per formula unit form closed-shell configuration of bonding orbitals. The threedimensional diffusion channel could work effectively to reduce the energy increase by Coulomb repulsion between the inserted ions.…”

Section: Resultsmentioning

confidence: 72%

Reversible Electrochemical Insertion/Extraction of Mg and Li Ions for Orthorhombic Mo₉Se₁₁with Cluster Structure

Taniguchi

Yoshino

et al. 2014

J. Electrochem. Soc.

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The reversible electrochemical insertion/extraction of Mg 2+ and Li + into/from a crystalline has been found in orthorhombic Mo 9 Se 11 (o-Mo 9 Se 11 ), the crystal structure of which is composed of molybdenum cluster units. The insertion/extraction reversibility of bivalent ion, Mg 2+ , could be ascribed to improvement of slow diffusion in the host lattice through the delocalization effect of electrons induced by cluster structure as supposed in Chevrel phase. The characteristic of Li/Mg-ion half-cell with o-Mo 9 Se 11 cathode, such as discharge curve and theoretical capacity, are discussed based on the electronic structure. A part of discharge curve in the insertion process of Li + was likely ascribed to the psuedogap structure in the density of state for the electronic band. The reversible capacity of o-Mg x Mo 9 Se 11 was below 40% of the theoretical capacity deduced from the molecular orbital model, whereas over 80% of that was observed in o-Li x Mo 9 Se 11 . The smaller reversible capacity for Mg 2+ could be ascribed to the Coulomb repulsion between bivalent Mg-ions confined in the one-dimensional channel of o-Mo 9 Se 11 , which highly prevents ion-insertion for bivalent Mg-ions compared with that for monovalent Li-ions. We suggest that both delocalized electronic structure and high dimensional ion-channel are necessary to realize reversible cathodes of Mg-ion battery with high capacity. Reversible electrochemical insertion/extraction of cations into/from materials is an important phenomenon from the view point of today's science and technology. In particular, reversible insertion/extraction of Li-ion is applied to secondary battery systems (Li-ion batteries) and has enabled realization of widely used portable devices such as cellular phones and lap-top computers.1-4 In recent years, an effort for developing new energy storage systems, which use ion-insertion mechanism, is being invested also in nonlithium-ion battery systems, such as sodium-ion, 5,6 potassium-ion 7,8 and multivalent-ion batteries. 9-16 Among them, Mg-ion battery is one of the fascinating battery systems due to its possible low cost and safety, which could be realized by rich resource and moderate reactivity of magnesium. [9][10][11][12] However, in most materials, the strong electrostatic interaction between introduced Mg 2+ and host lattice, which is due to bivalence of Mg 2+ , induces the slow solid state diffusion of Mg-ions within the crystal lattice and hampers reversible electrochemical insertion/extraction of Mg 2+ . 9,11,12 At present, the only family of insertion systems, into/from which reversible insertion/extraction of Mg-ions has been rigorously established, is Chevrel phases, Mo 6 X 8 (X = S, Se). These systems have demonstrated reversible insertion/extraction of Mg-ions over 1000 cycles and the capacity over 70 mAh/g, which is higher than those of other transition metal sulphides, as a cathode of Mg-ion battery at ambient temperature. 17,18 The successful performance of Chevrel phases as Mg-insertion materials is suggested...

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Phase Diagram of Mg Insertion into Chevrel Phases, Mg_xMo₆T₈ (T = S, Se). 1. Crystal Structure of the Sulfides

Cited by 119 publications

References 44 publications

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

Understanding Performance Limitations to Enable High Performance Magnesium-Ion Batteries

Reversible Electrochemical Insertion/Extraction of Mg and Li Ions for Orthorhombic Mo₉Se₁₁with Cluster Structure

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Phase Diagram of Mg Insertion into Chevrel Phases, MgxMo6T8 (T = S, Se). 1. Crystal Structure of the Sulfides

Cited by 119 publications

References 44 publications

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

Understanding Performance Limitations to Enable High Performance Magnesium-Ion Batteries

Reversible Electrochemical Insertion/Extraction of Mg and Li Ions for Orthorhombic Mo9Se11with Cluster Structure

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Product

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Phase Diagram of Mg Insertion into Chevrel Phases, Mg_xMo₆T₈ (T = S, Se). 1. Crystal Structure of the Sulfides

Reversible Electrochemical Insertion/Extraction of Mg and Li Ions for Orthorhombic Mo₉Se₁₁with Cluster Structure