Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
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Synthesis and Characterization of MgCr2S4 Thiospinel as a Potential Magnesium Cathode Allison Wustrow,†,‡ Baris Key,†,§ Patrick J. Phillips,†,∥ Niya Sa,†,§ Andrew S. Lipton,⊥ Robert F. Klie,†,∥ John T. Vaughey,†,§ and Kenneth R. Poeppelmeier*,†,‡
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†
Joint Center for Energy Storage Research (JCESR) and ‡Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States § Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States ∥ Department of Physics, University of Illinois at Chicago, Chicago, Illinois 60607, United States ⊥ Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States S Supporting Information *
ABSTRACT: Magnesium-ion batteries are a promising energy storage technology because of their higher theoretical energy density and lower cost of raw materials. Among the major challenges has been the identification of cathode materials that demonstrate capacities and voltages similar to lithium-ion systems. Thiospinels represent an attractive choice for new Mg-ion cathode materials owing to their interconnected diffusion pathways and demonstrated high cation mobility in numerous systems. Reported magnesium thiospinels, however, contain redox inactive metals such as scandium or indium, or have low voltages, such as MgTi2S4. This article describes the direct synthesis and structural and electrochemical characterization of MgCr2S4, a new thiospinel containing the redox active metal chromium and discusses its physical properties and potential as a magnesium battery cathode. However, as chromium(III) is quite stable against oxidation in sulfides, removing magnesium from the material remains a significant challenge. Early attempts at both chemical and electrochemical demagnesiation are discussed.
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insertion intercalation.9 In 2016, Incorvati et al. showed that by inhibiting the disproportionation of the charged cathode to oxide loss (e.g., formation of MgO) and increasing the conductivity of the lattice using fluoride doping, magnesium transport and electrochemical capacity of layered α-MoO3 increased significantly.10 Three dimensional lattices have attracted significant attention because they may have higher intrinsic electronic conductivity and have higher dimensional stability. Spinels, notably LiMn 2O 4 (LMO)11 and LiNi0.5Mn1.5O4,12 have been used as cathodes in commercial Li-ion battery systems. These materials have the general formula AB2O4 in the space group Fd3̅m (227), where A is a tetrahedrally coordinated metal sitting in a three-dimensional network of channels created by a framework of octahedrally coordinated B cations. Oxide spinels have been investigated for Mg systems; however, challenges in finding compatible electrolyte systems,13 coupled with poor mobility in many of the spinels, 14 have limited development in this field. Thiospinels are compatible with a wider range of electrolytes making them an attractive target for Mg battery cathodes. In addition, computational studies have shown that the softer
INTRODUCTION Multivalent batteries have gained attention in recent years as high energy density alternatives to lithium-ion batteries.1,2 Using Mg metal directly as the anode has several advantages, notably battery safety and lifetime may be enhanced as magnesium electrodeposition tends to occur without the formation of dendrites, which is a common problem associated with zinc or lithium metal anodes.3,4 Identifying a suitable cathode for magnesium intercalation, however, remains a significant challenge. Extrapolating from known lithium-ion systems to multivalent systems has been done with limited success as the higher charged cation typically exists as a stable multinuclear cluster solution species in common solvents, leading to sluggish interfacial kinetics associated with solvation sphere stability. Additionally, cation mobility within the solid host electrode ((e.g., V2O5,5,6 TiS27) is under study and several approaches have been used to circumvent the problem. In 2000, Aurbach et al. reported reversible electrochemical magnesium intercalation into the Chevrel phase Mo6S8, made possible by the large channels and weak interactions of magnesium cations with the lattice.8 Extrapolation of these concepts to oxides, notably Toyota’s study of α-MnO2 materials, indicated that oxide abstraction to irreversibly form MgO was the predominate magnesiation reaction, rather than © XXXX American Chemical Society
Received: May 23, 2018
A
DOI: 10.1021/acs.inorgchem.8b01417 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry anion lattice lowers the diffusion barrier for Mg2+ ions.15 Chemical insertion studies on spinel materials have found magnesium inserts into thiospinel lattices to a greater extent than oxide spinel lattices.16 In addition, MgSc2S4 and MgIn2S4 have been studied as solid electrolytes and show that the high mobility can be experimentally achieved.17 Recent work by the Nazar group has shown that Mg can reversibly intercalate into a titanium thiospinel both at room temperature and at 60 °C18 using the Ti3+/4+ couple, indicating the lattice is stable to electrochemical cycling. However, the limited number of magnesium thiospinels requires that additional synthetic studies be performed to test other materials in this class. This work focuses on the synthesis of MgCr2S4 to harness the high voltage Cr3+/4+ couple. Although no successful synthetic pathways have been reported, the thiospinel MgCr2S4 has been predicted to be a stable compound19 and have a normal cation distribution. This work presents the synthesis and structural and electrochemical characterizations of a new ternary thiospinel, MgCr2S4.
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V. Several solution based chemical oxidation methods were undertaken to demagnesiate MgCr2S4. Formal chromium oxidation was attempted chemically using solutions of Br2 (1.5 M) and NO2BF4 (0.6 M) in acetonitrile. MgCr2S4 was allowed to stir in both solutions over the course of a week at 45 °C, after which it was separated from the solution with vacuum filtration.
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RESULTS AND DISCUSSION Thiospinels and similar compounds have been studied for many applications related to their complex magnetic, electronic, and ionic conductivity properties. Compared to their oxide counterparts, however, only a limited number of these materials have been made. Recent work by Zunger et al. has identified several previously unreported thiospinels, which have been computationally shown to be stable.19 From the list we have selected the compound MgCr2S4 as a target owing to its ordered structure24 and the presence of the electroactive metal chromium, and its high predicted voltage as a Mg battery cathode.15 Previously reported synthesis attempts directed at MgCr2S4 resulted in the binary sulfides, MgS and Cr2S3, and it was concluded that the ternary sulfide was not stable.25,26 However, this work will show that the synthesis of MgCr2S4 from the elements is favorable, but far longer synthesis times are required than for similar systems such as ZnCr2S4 and CuCr2S4.27 This observation is attributed to poor diffusion of both magnesium and chromium during the synthesis. Starting from the elements, sulfur quickly reacts with the metal powders to form MgS and Cr2S3 compounds, and then these intermediates slowly react to form MgCr2S4. Heating to temperatures above 900 °C to increase the reaction kinetics was found to decompose MgCr2S4 to MgS and Cr2S3 (see Figure S.1). This may have played a role in the lack of success in previous reports attempting to synthesize this material, as the dwelling temperatures used were too high, preventing formation of the ternary phase. As higher temperatures did not decrease the synthesis times, an excess of magnesium and sulfur was added to the starting material to increase the amount of Cr2S3 in direct contact with MgS. This allowed the Cr2S3 to react more readily when heated to 800 °C. Figure 1 shows that the intensity of the spinel (511) peak relative to the Cr2S3 (116̅) peak increased as excess magnesium and sulfur were added to the reaction mixture, and the Cr2S3 was more
METHODS
Synthesis. MgCr2S4 was synthesized from the elemental powders in the molar ratio of 2Mg/2Cr/5S (MgCr2S4·MgS). The reagents were added to a carbon coated fused silica tube, which was sealed under a 10−4 Torr atmosphere. The reaction was heated to 800 °C over the course of 2 weeks with frequent grinding. This reaction produced a mixture of MgCr2S4 and MgS. The excess MgS was dissolved in a 2 M aqueous H2SO4 solution to recover a MgCr2S4 sample. Structural Characterization. Powder X-ray diffraction measurements were taken on a powdered sample using an Ultima IV X-ray diffractometer (Rigaku) with Cu radiation from 10° to 55°. Synchrotron powder data was also gathered at 11-BM on the Advanced Photon Source at Argonne National Laboratory with a wavelength of 0.414 Å. A Rietveld refinement was performed on this data using the General Structure Analysis System (GSAS) via EXPGUI using structural data from ZnCr2S4 as a starting point.20,21 Scanning transmission electron microscopy (STEM) analysis was performed using an aberration-corrected JEOL JEM-ARM200CF operated at 200 kV at the University of Illinois at Chicago. The JEOLARM200CF is equipped with a high-angle annular dark-field (HAADF) detector that allows for atomic-resolution imaging using an electron-probe convergence angle of 22 mrad and a detector range of 75−200 mrad. The electron probe size at 200 kV can be as small as 68 pm using these conditions.22 Solid state 25Mg Magic Angle Spinning (MAS) NMR experiments were performed at 19.89 T (850 MHz) on a Varian Direct Drive (VNMRS) Spectrometer operating at a Larmor frequency of 52.22 MHz using a 4 mm MAS probe. A calibrated π/2 (actual π/6) pulse width of 2 μs was used with pulse recycle delays of 0.2 s with rotor synchronized spin−echo experiments. All chemical shifts were referenced to 5 M MgCl2 (aq.) at 0 ppm. Demagnesiation. Initially, removing magnesium from the lattice (charging) and oxidizing Cr(III) to Cr(IV) were attempted electrochemically. In a typical test, MgCr2S4 was laminated onto a steel foil current collector as a slurry containing 80% active material, 10% polyvinylidene fluoride, and 10% Timcal C45 carbon by mass. BP2000 carbon (capacitive) was used as the counter electrode, while the electrolytes utilized were either a 1 M magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) in diglyme (DG), 0.5 M Mg(TFSI)2 in propylene carbonate (PC), or a 0.4 M all phenyl complex (APC) Grignard-type electrolytes in tetrahydrofuran typically employed for Chevrel phase studies.23 The material was also cycled against a Mg metal anode using the APC electrolyte. The results are displayed in the Supporting Information. 2032-type coin cells were galvanically cycled in a MACCOR cycler at constant current mode at 10 μA with the potential window set from −1.5 to 0.5
Figure 1. Diffraction peaks from the (511) of MgCr2S4 (blue star) and the (116̅) of Cr2S3 (orange circle) for materials synthesized with (a) a stoichiometric ratio of the elements, (b) a 50% excess of MgS, and (c) a 100% excess of MgS. As an excess of MgS was added to the material, a greater fraction of the Cr2S3 reacted to form the thiospinel. B
DOI: 10.1021/acs.inorgchem.8b01417 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
vary significantly even due to actual sample temperature differences at increasing spinning speeds due to increasing friction forces under MAS (see Figure 3b). No diamagnetic 25 Mg signal around 0 ppm (data not shown) was detected for any sample measured, which might indicate any MgS or MgO.31 Chromium(III) is remarkably resistant to oxidation in a sulfide environment. While this stability is beneficial for the voltage of MgCr2S4 as a cathode, it creates difficulties in obtaining the charged form of the material, Cr2S4. Attempts to remove magnesium cations from the lattice and oxidize the chromium(III) to chromium(IV), both chemically and electrochemically, resulted in no observable change in powder X-ray diffraction patterns (see Figures S.4 and S.5). Various electrolytes systems were used to try to remove magnesium by electrochemical charging including the chloride-based APC system and two more conventional systems based on Mg(TFSI)2 in both hybrid and full cells. At room temperature, no appreciable activity associated with MgCr2S4 was observed when the material was cycled against BP2000 (∼6 mAh/g), and any minimal capacity observed in the hybrid cells could be attributed to electrochemical processes happening at the carbon counter electrode. Cycling against Mg metal resulted in even lower capacities (∼1 mAh/g, see Figure S.9). Elevating the temperature slightly to 55 and 90 °C and cycling against BP2000 increased the observed capacity only slightly (Figure 4). Similarly, attempts to oxidize the structure with bromine and nitronium salts in acetonitrile showed no discernible reaction. The stability of MgCr2S4 against demagnesiation may stem from the instability of the chromium(IV) sulfide species that would result. Previous computations have shown that the 2p orbitals of S overlap energetically with the 3d orbitals of chromium, limiting the number of electrons that can be removed from chromium before oxidation occurs on the sulfur atoms instead of on the transition metal.32 Chromium sulfides with an oxidation state higher than III in the literature are limited to materials synthesized at high pressures33 or stabilized by a substrate.34,35 In order for MgCr2S4 to function as a magnesium cathode, alternative strategies to stabilize the charged phase will need to be considered.
rapidly consumed. The excess MgS readily dissolved in sulfuric acid, while the spinel and unreacted Cr2S3 remained. A Rietveld refinement was performed on synchrotron data to show the powder pattern was consistent with a normal spinel (space group Fd3̅m) with a = 10.14315(2)Å. Through this refinement, magnesium and chromium were both shown not to reside on the empty 16d and 8a sites, and no evidence of site mixing was observed. Relevant structural parameters are reported in Table 1. The high angle annular dark field images in Figure 2 further confirms that atomic positions within the lattice are consistent with a thiospinel structure. Table 1. Selected Crystallographic Parameters from the Refinement of MgCr2S4 formula weight (g/mol) temp (K) crystal system space group a = b = c (Å) α=β=γ volume (Å3) Z ρcalc (g/cm3) θ range # of reflections χ2 RF2 weight Fraction secondary Phase
256.56 300 cubic Fd3̅m (227) 10.14315(2) 90° 1043.5640(10) 8 3.266 0.5−50 49497 3.828 0.0459 93.10% Cr2S3
Solid state 25Mg MAS NMR measurements were performed to directly probe Mg environments in the spinel structure (see Figure 3). A single and relatively sharp resonance with an unusually large shift, about half an order of magnitude larger than oxide spinel structures,28,29 was observed. This is attributed to larger sulfur p-orbital overlap for the Fermi contact shift between Mg and paramagnetic Cr3+. The shift, centered at 11220 ppm (for the measurement at 20 °C) , is ascribed to tetrahedrally coordinated Mg in the spinel lattice. The large shifts, as expected,30 were highly temperature dependent (between −30 and 75 °C, Figure 3a) and found to
Figure 2. (a) Diffraction pattern of MgCr2S4. The pattern is indexed to a face-centered cubic lattice with a lattice parameter of a = 10.14315(2)Å. Peaks corresponding to Cr2S3 are marked with an asterisk. (b) STEM micrograph of MgCr2S4. The arrangement of atoms is consistent with a spinel structure. C
DOI: 10.1021/acs.inorgchem.8b01417 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
Figure 3. 25Mg MAS NMR of MgCr2S4 collected at 19.89 T: (a) variable temperature under constant spinning speed at 10 kHz and (b) variable spinning speed under constant nominal temperature at 20 °C.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
John T. Vaughey: 0000-0002-2556-6129 Kenneth R. Poeppelmeier: 0000-0003-1655-9127 Author Contributions
A.W. performed the synthesis, galvanostatic cycling experiments, and the powder X-ray diffraction experiments. B.K. and A.S.L. performed and analyzed the NMR experiments. P.J.P. and R.F.K. performed the electron imaging experiments. N.S. provided electrolytes for the electrochemistry experiments as well as guidance in analyzing the results. A.W. wrote the first draft of the manuscript under the supervision of J.T.V. and K.R.P with input and revision from all authors. All authors have given approval to the final version of the manuscript.
Figure 4. Charge cycles of MgCr2S4 against a carbon counter electrode with a variety of electrolyte systems. The low capacity was consistent with the lack of magnesium removal seen in these tests.
Notes
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The authors declare no competing financial interest.
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CONCLUSION Thiospinels have been identified as a promising class of magnesium battery cathodes. MgCr2S4, a material with a structure analogous to a number of other materials with high magnesium mobility, was synthesized for the first time. However, using various chemical and electrochemical methods proved unsuccessful in removing magnesium from the lattice. This is attributed to the high stability of the material relative to the Cr2S4 material that would result. While the Cr3+/4+ couple would lead to a cathode with a high voltage for a sulfide, further study is required to stabilize the charged cathode material.
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ACKNOWLEDGMENTS
This work was supported as a part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. This work made use of the J.B.Cohen X-Ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-1720139) at the Materials Research Center of Northwestern University and the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205). Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. High field solid state NMR experiments were performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the DOE Office of Science, Office of Biological and Environmental Research, and Physical Science Laboratory both located at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle Memorial Institute under Contract No. DE-AC05-76RL01830
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01417. Complete diffraction patterns showing the effects of temperature and excess MgS on synthesis. Galvanostatic cycling of MgCr2S4 under various conditions. Diffraction patterns of cycled cathodes (PDF) D
DOI: 10.1021/acs.inorgchem.8b01417 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
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Principles Thermodynamics. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 86, 014109. (20) Larson, A.; Von Dreele, R. GSAS-General Structure Analysis System; Los Alamos National Laboratory: Los Alamos, NM, 1994. (21) Toby, B. H. EXPGUI, a Graphical User Interface for GSAS. J. Appl. Crystallogr. 2001, 34, 210−213. (22) Klie, R.; Gulec, A.; Guo, Z.; Paulauskas, T.; Qiao, Q.; Tao, R.; Wang, C.; Low, K.; Nicholls, A.; Phillips, P. The New JEOL JEMARM200CF at the University of Illinois at Chicago. Cryst. Res. Technol. 2014, 49, 653−662. (23) Aurbach, D.; Gizbar, H.; Schechter, A.; Chusid, O.; Gottlieb, H. E.; Gofer, Y.; Goldberg, I. Electrolyte Solutions for Rechargeable Magnesium Batteries Based on Organomagnesium Chloroaluminate Complexes. J. Electrochem. Soc. 2002, 149, A115−A121. (24) Verwey, E.; Heilmann, E. Physical Properties and Cation Arrangement of Oxides with Spinel Structures I. Cation Arrangement in Spinels. J. Chem. Phys. 1947, 15, 174−180. (25) Hahn, H. Untersuchungen über Ternäre Chalkogenide. II. Ü ber Die Struktur Einiger Chromthiospinelle. Z. Anorg. Allg. Chem. 1951, 264, 184−187. (26) Omloo, W.; Bommerson, J.; Heikens, H.; Risselada, H.; Vellinga, M.; Van Bruggen, C.; Haas, C.; Jellinek, F. Europium Chromium Sulfide, EuCr2S4, and Some Isotypic Compounds. Phys. Status Solidi (A) 1971, 5, 349−357. (27) Bouchard, R.; Russo, P.; Wold, A. Preparation and Electrical Properties of Some Thiospinels. Inorg. Chem. 1965, 4, 685−688. (28) Kim, C.; Phillips, P. J.; Key, B.; Yi, T.; Nordlund, D.; Yu, Y.-S.; Bayliss, R. D.; Han, S.-D.; He, M.; Zhang, Z.; Burrell, A. K.; Klie, R. F.; Cabana, J. Direct Observation of Reversible Magnesium Ion Intercalation into a Spinel Oxide Host. Adv. Mater. 2015, 27, 3377− 3384. (29) Lee, J.; Seymour, I. D.; Pell, A. J.; Dutton, S. E.; Grey, C. P. A Systematic Study of 25Mg NMR in Paramagnetic Transition Metal Oxides: Applications to Mg-Ion Battery Materials. Phys. Chem. Chem. Phys. 2017, 19, 613−625. (30) Grey, C. P.; Dupre, N. NMR Studies of Cathode Materials for Lithium-Ion Rechargeable Batteries. Chem. Rev. 2004, 104, 4493− 4512. (31) Dupree, R.; Smith, M. E. Solid-State Magnesium-25 NMRSpectroscopy. J. Chem. Soc., Chem. Commun. 1988, 1483−1485. (32) Fang, C.; Van Bruggen, C.; De Groot, R.; Wiegers, G.; Haas, C. The Electronic Structure of the Metastable Layer Compound. J. Phys.: Condens. Matter 1997, 9, 10173. (33) Sleight, A. W.; Bither, T. A. Chromium Chalcogenides Prepared at High Pressure and the Crystal Growth of Chromium Sesquisulfide. Inorg. Chem. 1969, 8, 566−569. (34) Panchakarla, L. S.; Lajaunie, L.; Tenne, R.; Arenal, R. Atomic Structural Studies on Thin Single-Crystalline Misfit-Layered Nanotubes of TbS-CrS2. J. Phys. Chem. C 2016, 120, 15600−15607. (35) Panchakarla, L. S.; Popovitz-Biro, R.; Houben, L.; DuninBorkowski, R. E.; Tenne, R. Lanthanide-Based Functional MisfitLayered Nanotubes. Angew. Chem., Int. Ed. 2014, 53, 6920−6924.
REFERENCES
(1) Muldoon, J.; Bucur, C. B.; Gregory, T. Quest for Nonaqueous Multivalent Secondary Batteries: Magnesium and Beyond. Chem. Rev. 2014, 114, 11683−11720. (2) Yoo, H. D.; Shterenberg, I.; Gofer, Y.; Gershinsky, G.; Pour, N.; Aurbach, D. Mg Rechargeable Batteries: An On-Going Challenge. Energy Environ. Sci. 2013, 6, 2265−2279. (3) Aurbach, D.; Cohen, Y.; Moshkovich, M. The Study of Reversible Magnesium Deposition by in-situ Scanning Tunneling Microscopy. Electrochem. Solid-State Lett. 2001, 4, A113−A116. (4) Matsui, M. Study on Electrochemically Deposited Mg Metal. J. Power Sources 2011, 196, 7048−7055. (5) Sa, N.; Kinnibrugh, T. L.; Wang, H.; Sai Gautam, G.; Chapman, K. W.; Vaughey, J. T.; Key, B.; Fister, T. T.; Freeland, J. W.; Proffit, D. L.; Chupas, P. J.; Ceder, G.; Bareno, J. G.; Bloom, I. D.; Burrell, A. K. Structural Evolution of Reversible Mg Insertion into a Bilayer Structure of V2O5·nH2O Xerogel Material. Chem. Mater. 2016, 28, 2962−2969. (6) Gershinsky, G.; Yoo, H. D.; Gofer, Y.; Aurbach, D. Electrochemical and Spectroscopic Analysis of Mg2+ Intercalation into Thin Film Electrodes of Layered Oxides: V2O5 and MoO3. Langmuir 2013, 29, 10964−10972. (7) Tao, Z.-L.; Xu, L.-N.; Gou, X.-L.; Chen, J.; Yuan, H.-T. TiS2 Nanotubes as the Cathode Materials of Mg-ion Batteries. Chem. Commun. 2004, 2080−2081. (8) Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich, M.; Levi, E. Prototype Systems for Rechargeable Magnesium Batteries. Nature 2000, 407, 724−727. (9) Ling, C.; Zhang, R.; Mizuno, F. Quantitatively Predict the Potential of MnO2 Polymorphs as Magnesium Battery Cathodes. ACS Appl. Mater. Interfaces 2016, 8, 4508−4515. (10) Incorvati, J. T.; Wan, L. F.; Key, B.; Zhou, D.; Liao, C.; Fuoco, L.; Holland, M.; Wang, H.; Prendergast, D.; Poeppelmeier, K. R.; Vaughey, J. T. Reversible Magnesium Intercalation into a Layered Oxyfluoride Cathode. Chem. Mater. 2016, 28, 17−20. (11) Gummow, R.; De Kock, A.; Thackeray, M. Improved Capacity Retention in Rechargeable 4 V Lithium/Lithium-Manganese Oxide (Spinel) Cells. Solid State Ionics 1994, 69, 59−67. (12) Kim, J.-H.; Myung, S.-T.; Yoon, C.; Kang, S.; Sun, Y.-K. Comparative Study of LiNi0.5Mn1.5O4‑δ and LiNi0.5Mn1.5O4 Cathodes Having Two Crystallographic Structures: Fd3̅m and P4332. Chem. Mater. 2004, 16, 906−914. (13) Kim, C.; Phillips, P. J.; Key, B.; Yi, T.; Nordlund, D.; Yu, Y. S.; Bayliss, R. D.; Han, S. D.; He, M.; Zhang, Z. Direct Observation of Reversible Magnesium Ion Intercalation into a Spinel Oxide Host. Adv. Mater. 2015, 27, 3377−3384. (14) Okamoto, S.; Ichitsubo, T.; Kawaguchi, T.; Kumagai, Y.; Oba, F.; Yagi, S.; Shimokawa, K.; Goto, N.; Doi, T.; Matsubara, E. Intercalation and Push-Out Process with Spinel-to-Rocksalt Transition on Mg Insertion into Spinel Oxides in Magnesium Batteries. Adv. Sci. 2015, 2, 1500072. (15) Liu, M.; Jain, A.; Rong, Z.; Qu, X.; Canepa, P.; Malik, R.; Ceder, G.; Persson, K. A. Evaluation of Sulfur Spinel Compounds for Multivalent Battery Cathode Applications. Energy Environ. Sci. 2016, 9, 3201−3209. (16) Bruce, P. G.; Krok, F.; Nowinski, J.; Gibson, V. C.; Tavakkoli, K. Chemical Intercalation of Magnesium into Solid Hosts. J. Mater. Chem. 1991, 1, 705−706. (17) Canepa, P.; Bo, S.-H.; Gautam, G. S.; Key, B.; Richards, W.; Shi, T.; Tian, Y.; Wang, Y.; Li, J.; Ceder, G. High Magnesium Mobility in Ternary Spinel Chalcogenides. Nat. Commun. 2017, 8, 1759. (18) Sun, X.; Bonnick, P.; Duffort, V.; Liu, M.; Rong, Z.; Persson, K. A.; Ceder, G.; Nazar, L. F. A High Capacity Thiospinel Cathode for Mg Batteries. Energy Environ. Sci. 2016, 9, 2273−2277. (19) Zhang, X.; Stevanović, V.; d’Avezac, M.; Lany, S.; Zunger, A. Prediction of A2BX4 Metal-Chalcogenide Compounds via FirstE
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