Mechanochemical Synthesis and Characterization of Metastable

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Mechanochemical Synthesis and Characterization of Metastable Hexagonal Li4SnS4 Solid Electrolyte Kento Kanazawa,† So Yubuchi,† Chie Hotehama,† Misae Otoyama,† Seiya Shimono,‡ Hiroki Ishibashi,‡ Yoshiki Kubota,‡ Atsushi Sakuda,† Akitoshi Hayashi,*,† and Masahiro Tatsumisago*,† †

Inorg. Chem. Downloaded from pubs.acs.org by UNIV OF TOLEDO on 08/09/18. For personal use only.

Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan ‡ Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan S Supporting Information *

ABSTRACT: A new crystalline lithium-ion conducting material, Li 4 SnS 4 with an ortho-composition, was prepared by a mechanochemical technique and subsequent heat treatment. Synchrotron X-ray powder diffraction was used to analyze the crystal structure, revealing a space group of P63/mmc and cell parameters of a = 4.01254(4) Å and c = 6.39076(8) Å. Analysis of a heat-treated hexagonal Li4SnS4 sample revealed that both lithium and tin occupied either of two adjacent tetrahedral sites, resulting in fractional occupation of the tetrahedral site (Li, 0.375; Sn, 0.125). The heat-treated hexagonal Li4SnS4 had an ionic conductivity of 1.1 × 10−4 S cm−1 at room temperature and a conduction activation energy of 32 kJ mol−1. Moreover, the heattreated Li4SnS4 exhibited a higher chemical stability in air than the Li3PS4 glass-ceramic.

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reported that the composite electrolytes (100 − x)Li3PS4· MxOy (MxOy: Fe2O3, ZnO, and Bi2O3) were effective in suppressing H2S gas generation.9 Furthermore, oxygen- or nitrogen-substituted 75Li2S·25P2S5 electrolytes exhibited a high chemical stability.10 To enhance the chemical stability in air, in the present study, we focused on a Li2S−SnS2 binary system. Sahu et al. proposed that the stability of the sulfide-based electrolyte when subjected to oxygen and moisture follows the theory of hard and soft acids and bases (HSAB).11 According to HSAB theory, replacing P with Sn results in an obvious increase in the stability considering its reactivity with oxygen and water. The Li2S−SnS2 solid electrolytes have demonstrated higher chemical stability in air than the phosphorus-based SEs. The use of the ortho-composition of Li4SnS4 and related materials for ASSBs has been reported recently. Kaib et al. reported that orthorhombic Li4SnS4 and Li4SnSe4 were obtained in pure form by liquid-phase synthesis using an aqueous solution.12,13 Sahu et al. reported that As-substituted Li 4 SnS 4 (Li3.833Sn0.833As0.1667S4) exhibited a high conductivity of 1.39 × 10−3 S cm−1 at 25 °C and high chemical stability in air.11 Jung et al. reported that (100 − x)Li4SnS4·xLiI glasses could be fabricated through liquid-phase synthesis.14 We also

INTRODUCTION Lithium-ion batteries (LIBs) are widely used for small-scale applications, such as smartphones and notebook computers. In recent years, they have also been adopted for large-scale applications such as electric vehicles (EVs). However, safety concerns regarding conventional LIBs, which use flammable organic-solvent electrolytes, limit their widespread commercial application. All-solid-state batteries (ASSBs) using inorganic solid electrolytes (SEs) are a promising alternative to conventional LIBs, as they have the potential to improve battery safety. Inorganic SEs, including thiophosphate (PS43−, P2S74−)- and thiogermanate (GeS44−)-based lithium-ion conductors, such as the Li10GeP2S12 (LGPS) family,1,2 Li7P3S11 glass-ceramic,3,4 and the argyrodite-type materials (Li6PS5X: X = Cl, Br),5 have higher conductivities than liquid electrolytes. Among them, Li9.54Si1.74P1.44S11.7Cl0.3 (from the LGPS family) demonstrated a high ionic conductivity of 2.5 × 10−2 S cm−1.6 Moreover, sulfide-based SEs have the advantage of being mechanically soft, allowing the preparation of dense pellets with a low porosity and favorable contact with an electrode simply by using a cold-pressing technique at room temperature.7 However, conventional sulfide-based SEs react with water and generate H2S. Our previous study revealed that the 75Li2S· 25P2S5 (mol %) glass and glass-ceramic have relatively high chemical stability in humid air compared to other Li2S−P2S5 glasses, such as 70Li2S·30P2S5 and 67Li2S·33P2S5.8 We also © XXXX American Chemical Society

Received: April 16, 2018

A

DOI: 10.1021/acs.inorgchem.8b01049 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

H2S gas (ppm) were measured using a H2S sensor (GBL-HS; Ichinen Jikco Ltd.). Then, the generated H2S gas volume (V; cm3 g−1) was calculated using the following equation

reported on Li2S−SnS2 materials prepared by a mechanochemical synthesis process.15,16 In the present study, a Li4SnS4 glass-ceramic was synthesized using a mechanochemical technique and subsequent heat treatment. The crystal structure of the Li4SnS4 was identified, and characterization of the ionic conductivity and chemical stability in a moist environment was carried out.

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V=

C × L × 10−6 m

where C is the concentration of H2S gas (ppm), L is the volume of the desiccator (cm3), and m is the weight of the SE powder (g).

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EXPERIMENTAL SECTION

RESULTS AND DISCUSSION Figure 1a shows the XRD pattern for the as-milled Li4SnS4. No peaks that could be assigned to the starting materials were observed. Diffraction peaks which differed from those for orthorhombic Li4SnS4, as reported by Kaib et al.12 and MacNeil et al. (Figure S1),23 were observed. Very recently, Jung et al. reported on similar XRD patterns for Li4SnS4 that

The starting materials for preparing Li4SnS4 SEs were Li2S (99.9% purity) and SnS2 (99.5% purity), both of which were supplied by Mitsuwa Chemical Co., Ltd. These starting materials were weighed into stoichiometric ratios in an Ar-filled glovebox and then ball-milled in a 45 mL ZrO2 pot with 500 ZrO2 balls (ϕ = 4 mm) using a planetary ball mill apparatus (Fritsch Pulverisette 7) operating at 510 rpm for 40 h. After the mechanochemical processing, the resulting samples were heated above the crystallization temperature (Tc) for 2 h. The chemical compositions of the starting materials and prepared samples were determined using an inductively coupled plasma optical emission spectroscope (ICP-OES; SPS-3500, SII Nano Technology) for Li, Sn, and S, an ion analyzer (IA-300, DKK-TOA) for Li, and a CHNS analyzer (vario EL cube, Elementar). The chemical compositions of Li2S, SnS2, and Li4SnS4 were determined to be Li2.0S, Sn1.03S2, and Li4.0Sn1.0S4, respectively. The X-ray diffraction (XRD) patterns of the synthesized powders were obtained using an X-ray diffractometer (Rigaku SmartLab) with Cu Kα radiation. The diffraction data were collected every 0.02° over a 2θ range from 10 to 40°. To determine the crystal structure of the heat-treated Li4SnS4 sample at 260 °C, synchrotron XRD measurements were conducted at the BL02B2 beamline of SPring-8. A Debye−Scherrer diffractometer with a solid-state (MYTHEN) detector was used for the measurements at room temperature (ca. 25 °C).17 The specimen was sealed in a quartz capillary (approximately 0.3 mm in diameter) in a vacuum prior to being subjected to the XRD measurements. The incident beam wavelength was calibrated using CeO2 (NIST SRM Ceria 674b) and fixed at 0.79978 Å. The diffraction data were collected every 0.01° from 10.0 to 80.0° in 2θ. The diffraction peaks of the newly observed phase were indexed using the DICVOL program.18 Subsequent structural determination was undertaken using the charge-flipping method with the Superflip program,19 assuming kinematic diffraction intensities to generate all of the atomic positions in the unit cell. The output of the charge-flipping procedure is a scattering density map from which the atomic positions can be derived. The initial structure determined by the charge-flipping procedure was then refined using the Rietveld method and the RIETAN-FP software.20 The structure models were described using the VESTA software.21 The Raman spectra of the samples were measured using a Raman spectrophotometer (Lab-Ram HR-800; Horiba Jobin Yvon, Inc.) using the 514 nm line of an Ar+ ion beam. Differential thermal analysis (DTA) was carried out on the obtained powder samples, sealed in an Al pan in a dry Ar atmosphere, using a Rigaku thermal analyzer (Thermo-plus 8110). The heating rate was fixed to 10 °C min−1. The ionic conductivity was measured using an AC impedance method. The applied voltage was 50 mV, and measurements were taken over a frequency range of 10 Hz to 8 MHz. The mechanically milled samples were pelletized at a pressure of 540 MPa into pellets with a diameter of 10 mm, which were then heated to 260 °C to obtain a sintered body of Li4SnS4 glass-ceramic. The surfaces of the pellets were covered with a Au layer to form current collectors. The impedance spectra were recorded using an impedance analyzer (Solartron 1260). To test the stability of the SEs in humid air, 50 mg of SE powder was exposed to air at a temperature of 20−22 °C and a relative humidity of 70%. For comparison, Li3PS4 glass-ceramic SE powder was also synthesized22 and then exposed to air in the same manner. The SE powders were placed in a closed desiccator (2000 cm−1) in which the air was circulated by a small electric fan. The amounts of

Figure 1. (a) XRD patterns of as-milled Li4SnS4, Li2S, and SnS2. (b) XRD patterns of Li4SnS4 heated to 260 and 390 °C for 2 h, compared to that of orthorhombic Li4SnS4. B

DOI: 10.1021/acs.inorgchem.8b01049 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry had been prepared by liquid-phase synthesis.24 The XRD patterns were treated as “amorphous samples” in the article,24 and the obtained crystal phase was not identified. A crystalline phase was directly obtained during ball-milling of the Li2S− SnS2 system, although the amorphous phases are usually obtained in a Li2S−P2S5 system. Figure 1b shows XRD patterns of the samples that were heat-treated at 260 and 390 °C. A crystal phase with a higher degree of crystallization was obtained at 260 °C. The sample heat-treated at 390 °C was orthorhombic Li4SnS4 with a Pnma space group. The treatment temperatures of 260 and 390 °C were selected on the basis of the results of a DTA analysis of the as-milled Li4SnS4 (Figure 2). Several exothermic and

Figure 2. DTA curve of as-milled Li4SnS4.

Figure 3. (a) Rietveld refinements of synchrotron XRD data for Li4SnS4 heated to 260 °C. The measured data are shown in red, while the XRD profile calculated from the determined structure model is shown in blue. The difference between these curves is shown in green. The background is light blue. The inset shows the higher-angle data in more detail. (b) Schematic diagrams of the crystal structure of hexagonal Li4SnS4 as determined from the XRD analysis.

endothermic peaks were observed for a temperature range of 200−500 °C, with the characteristic exothermic peaks observed at 240 and 360 °C. The crystal phase obtained at the first exothermic peak was the metastable phase. Generally, the metastable phase has more free volume than the stable phase and is often advantageous in terms of ion conduction. Furthermore, such a structure often exhibits excellent symmetry, which again may be advantageous for ion conduction. For example, we have found a metastable crystal phase Li7P3S11, which is one of the solid electrolytes showing the highest conductivity of over 10−2 S cm−1 at 25 °C.4 Figure 3a shows the fitting results for the Rietveld refinements for the synchrotron XRD data for the metastable Li4SnS4. The refined cell parameters, R factors, and atomic coordinates are listed in Tables 1 and 2, respectively. Reliability factors based on the powder profile Rwp = 2.1% and Bragg intensity RI = 6.8% were obtained as a result of this refinement. The space group of the heat-treated Li4SnS4 was determined from the extinction rule h h l : l = 2n, h h h : h = 2n, which is characteristic of the space group P63/mmc (194). The procedure for constructing the model structure is shown below. First, the basic structure was constructed with only Sn and S, and the validity was confirmed by Rietveld analysis.

Second, Li was added to the 4f site and the validity was confirmed by Rietveld analysis. The occupancy of the tetrahedral site was a maximum of 0.5, since it cannot exist at adjacent tetrahedral sites simultaneously because of electrostatic repulsion. When Sn and Li occupy the 4f site, the maximum occupation rate of Li is 0.375. As shown in Figure 3b, the sulfur positions in the metastable Li4SnS4 very closely matched those of a hexagonal close-packed (hcp) lattice, while Li and Sn cations fractionally occupied the tetrahedral sites. The remaining Li ions were expected to exist in the channels along the c-axis, probably the 2a (octahedral), 2b (plane triangle), or 4e (c-axis) sites (Figure S2); however, their exact locations were not determined in the present study. When calculated for the space of the unit lattice, the octahedral 2a site appears to be too large, while the 2b site appears to be slightly too small for the Li. Thus, the remaining Li most likely exists at the 4e site and/or somewhere near the 2a site. Figure 4 shows Raman spectra of the as-milled and heattreated hexagonal Li4SnS4. A strong peak at around 345 cm−1 C

DOI: 10.1021/acs.inorgchem.8b01049 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Crystal Data for the Hexagonal Li4SnS4 chemical formula sum chemical formula weight crystal system space group Z value cell parameters a (Å) c (Å)

Li1.5Sn0.5S2 68.684 hexagonal P63/mmc (No. 194) 2

cell volume (Å3) density (calc.) density (meas.)

89.109(2) 2.56 g cm−3 2.55 g cm−3

X-ray wavelength (Å)

0.79978

4.01254(4) 6.39076(8)

reliability factors (%) Rwp = 2.1

R1 = 6.8

Table 2. Atomic Coordinates for Hexagonal Li4SnS4a S Sn Li

site

g

x

y

z

B (Å2)

2c 4f 4f

1 0.125 0.375

1/3 2/3 2/3

2/3 1/3 1/3

1/4 0.14127(6) 0.14127(6)

3.46(2) 2.04(2) 2.04(2)

a

The site for the 0.5 molar equivalent of Li has not been identified.

Figure 5. Temperature dependence of the ionic conductivity of hexagonal Li4SnS4. The inset shows the corresponding Nyquist plot at room temperature.

activation energy. The activation energy for ion conduction was calculated from the slope of the Arrhenius plot. The Li4SnS4 had a σ value of 1.1 × 10−4 S cm−1 at 25 °C and an Ea value of 32 kJ mol−1. The electronic conductivity was less than 1 × 10−8 S cm−1 at 25 °C. The hexagonal Li4SnS4, when heated to 260 °C, exhibited a slightly higher ionic conductivity than the orthorhombic Li4SnS4 (7.0 × 10−5 S cm−1 at 25 °C) as reported by Kaib et al.12 The mean atomic volumes, which are the cell volumes divided by the number of atoms in formula unit, of the orthorhombic and hexagonal Li4SnS4 were found to be 19.460 and 19.802 Å3, respectively. The free volume of the hexagonal Li4SnS4 is larger than that of the orthorhombic Li4SnS4, indicating that the structure of the hexagonal Li4SnS4 is potentially more favorable for ion conduction. It is thought that the conductivity will be enhanced by using favorable elements as substitutes, and further study is needed to identify highly conductive solid electrolytes. Figure 6 shows the H2S gas generation from the hexagonal Li4SnS4 and Li3PS4 glass-ceramic powders as a function of the exposure time in humid air. The amount of H2S gas generated from the hexagonal Li4SnS4 was considerably smaller than that derived from the Li3PS4 glass-ceramic reference sample. Thus, hexagonal Li4SnS4 exhibits a promising high ionic conductivity of 1.1 × 10−4 S cm−1 at room temperature as well as superior chemical stability in humid air.

Figure 4. Raman spectra of hexagonal Li4SnS4. (a) As-milled Li4SnS4 and (b) Li4SnS4 heat-treated at 260 and 390 °C.

and attributed to the thiostannate SnS44− ion was observed for the as-prepared and hexagonal Li4SnS4 samples, indicating that the SnS44− ion was not affected by the heat treatment. This result was consistent with the data for the crystal structure. An additional peak detected at around 290 cm−1 suggests the existence of a polyanion with the Sn coordinated with the S atoms, which differed from the SnS44−. Figure 5 shows the temperature dependence of the lithiumion conductivity of the hexagonal Li4SnS4 pellets sintered at 260 °C. The inset shows a Nyquist plot for a sintered pellet measured at room temperature. The impedance plots showed part of a semicircle in the high-frequency region and a straight line in the low-frequency region, suggesting that the sample is a typical ionic conductor. As the bulk and grain boundary contributions to impedance plots could not be differentiated, the conductivity value was determined from the total resistance (Rtotal), including the bulk and grain-boundary components. The ionic conductivity (σ) of the hexagonal Li4SnS4 obeyed the Arrhenius law expressed by σ = σ0 exp(−Ea/RT), where σ0 is a pre-exponential factor, R is the gas constant, and Ea is the D

DOI: 10.1021/acs.inorgchem.8b01049 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Specially Promoted Research for Innovative Next Generation Batteries (SPRING) project. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Synchrotron radiation experiments were performed at BL02B2 of SPring-8 with approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal No. 2016B0074). The authors thank Dr. S. Kawaguchi and Mr. M. Takemoto of JASRI for their kind help with data collection.

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(1) Kamaya, N.; Homma, K.; Yamakawa, Y.; Hirayama, M.; Kanno, R.; Yonemura, M.; Kamiyama, T.; Kato, Y.; Hama, S.; Kawamoto, K.; et al. A Lithium Superionic Conductor. Nat. Mater. 2011, 10, 682− 686. (2) Bron, P.; Johansson, S.; Zick, K.; Schmedt auf der Günne, J.; Dehnen, S.; Roling, B. Li10SnP2S12: An Affordable Lithium Superionic Conductor. J. Am. Chem. Soc. 2013, 135, 15694−15697. (3) Mizuno, F.; Hayashi, A.; Tadanaga, K.; Tatsumisago, M. New, highly ion-conductive crystals precipitated from Li2S-P2S5 glasses. Adv. Mater. 2005, 17, 918−921. (4) Seino, Y.; Ota, T.; Takada, K.; Hayashi, A.; Tatsumisago, M. A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries. Energy Environ. Sci. 2014, 7, 627−631. (5) Deiseroth, H.-J.; Kong, S.-T.; Eckert, H.; Vannahme, J.; Reiner, C.; Zais, T.; Schlosser, M. Li6PS5X: A Class Of Crystalline Li-rich Solids With An Unusually High Li+ Mobility. Angew. Chem., Int. Ed. 2008, 47, 755−758. (6) Kato, Y.; Hori, S.; Saito, T.; Suzuki, K.; Hirayama, M.; Mitsui, A.; Yonemura, M.; Iba, H.; Kanno, R. High-Power All-Solid-State Batteries Using Sulfide Superionic Conductors. Nat. Energy 2016, 1, No. 16030. (7) Sakuda, A.; Hayashi, A.; Tatsumisago, M. Sulfide Solid Electrolyte with Favorable Mechanical Property for All-Solid-State Lithium Battery. Sci. Rep. 2013, 3, No. 2261. (8) Muramatsu, H.; Hayashi, A.; Ohtomo, T.; Hama, S.; Tatsumisago, M. Structural Change Of Li2S−P2S5 Sulfide Solid Electrolytes in the Atmosphere. Solid State Ionics 2011, 182, 116−119. (9) Hayashi, A.; Muramatsu, H.; Ohtomo, T.; Hama, S.; Tatsumisago, M. Improvement Of Chemical Stability Of Li3PS4 Glass Electrolytes by Adding MxOy (M = Fe, Zn, And Bi) Nanoparticles. J. Mater. Chem. A 2013, 1, 6320−6326. (10) Fukushima, A.; Hayashi, A.; Yamamura, H.; Tatsumisago, M. Mechanochemical synthesis of high lithium ion conducting solid electrolytes in a Li2S-P2S5-Li3N system. Solid State Ionics 2017, 304, 85−89. (11) Sahu, G.; Lin, Z.; Li, J.; Liu, Z.; Dudney, N.; Liang, C. Airstable, High-conduction Solid Electrolytes of Arsenic-substituted Li4SnS4. Energy Environ. Sci. 2014, 7, 1053−1058. (12) Kaib, T.; Haddadpour, S.; Kapitein, M.; Bron, P.; Schröder, C.; Eckert, H.; Roling, B.; Dehnen, S. New Lithium Chalcogenidotetrelates, LiChT: Synthesis and Characterization of the Li+-Conducting Tetralithium ortho-Sulfidostannate Li4SnS4. Chem. Mater. 2012, 24, 2211−2219. (13) Kaib, T.; Bron, P.; Haddadpour, S.; Mayrhofer, L.; Pastewka, L.; Järvi, T. T.; Moseler, M.; Roling, B.; Dehnen, S. Lithium Chalcogenidotetrelates: LiChTSynthesis and Characterization of New Li+ Ion Conducting Li/Sn/Se Compounds. Chem. Mater. 2013, 25, 2961−2969. (14) Park, K. H.; Oh, D. Y.; Choi, Y. E.; Nam, Y. J.; Han, L.; Kim, J. Y.; Xin, H.; Lin, F.; Oh, S. M.; Jung, Y. S. Solution-Processable Glass LiI-Li4SnS4 Superionic Conductors for All-Solid-State Li-Ion Batteries. Adv. Mater. 2016, 28, 1874−1883.

Figure 6. H2S gas generation from hexagonal Li4SnS4 and Li3PS4 glass-ceramic powders upon exposure to humid air.

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CONCLUSIONS A novel lithium-ion conducting hexagonal Li4SnS4 material was synthesized using a mechanochemical process and subsequent heat treatment. In the hexagonal Li4SnS4, lithium and tin randomly shared one of two facing tetrahedral sites. The ionic conductivity of the hexagonal Li4SnS4 was 1.1 × 10−4 S cm−1 at 25 °C, which is higher than that of orthorhombic Li4SnS4. In addition, the hexagonal Li4SnS4 exhibited a higher chemical stability in humid air than the Li3PS4 glass-ceramic.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01049. Listings of schematics of the crystal structure of orthorhombic Li4SnS4 and expected sites for remaining Li for hexagonal Li4SnS4 (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*Phone: +81-72-2549331. Fax: +81-72-2549334. E-mail: [email protected]. *E-mail: [email protected]. ORCID

Atsushi Sakuda: 0000-0002-9214-0347 Akitoshi Hayashi: 0000-0001-9503-5561 Author Contributions

A.S., A.H., and M.T. conceived the study. K.K., S.Y., C.H., M.O., S.S., H.I., and Y.K. performed the experiments. K.K. and A.S. drafted most of the paper. All of the authors analyzed the data and commented on the manuscript. Funding

This research was financially supported by the Japan Science and Technology Agency (JST), Advanced Low Carbon Technology Research and Development Program (ALCA), E

DOI: 10.1021/acs.inorgchem.8b01049 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (15) Sakuda, A.; Kuratani, K.; Takeuchi, T.; Kiuchi, H.; Kawaguchi, T.; Shikano, M.; Sakaebe, H.; Kobayashi, H. Cubic Rocksalt Li2SnS3 and a Solid Solution with Li3NbS4 Prepared by Mechanochemical Synthesis. Electrochemistry 2017, 85, 580−584. (16) Kanazawa, K.; Yubuchi, S.; Hayashi, A.; Tatsumisago, M. In 55th Symposium on Basic Science of Ceramics; 2017, 2C01, p 148. (17) Kawaguchi, S.; Takemoto, M.; Osaka, K.; Nishibori, E.; Moriyoshi, C.; Kubota, Y.; Kuroiwa, Y.; Sugimoto, K. Highthroughput powder diffraction measurement system consisting of multiple MYTHEN detectors at beamline BL02B2 of SPring-8. Rev. Sci. Instrum. 2017, 88, No. 085111. (18) Boultif, A.; Louer, D. Powder Pattern Indexing With the Dichotomy Method. J. Appl. Crystallogr. 1991, 24, 987−993. (19) Palatinus, L.; Chapuis, G. Superflip - a Computer Program for the Solution of Crystal Structures by Charge Flipping in Arbitrary Dimensions. J. Appl. Crystallogr. 2007, 40, 786−790. (20) Izumi, F.; Momma, K. Three-Dimensional Visualization in Powder Diffraction. Solid State Phenom. 2007, 130, 15−20. (21) Momma, K.; Izumi, F. VESTA 3 for Three-dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44, 1272−1276. (22) Hayashi, A.; Hama, S.; Minami, T.; Tatsumisago, M. Formation of superionic crystals from mechanically milled Li2S-P2S5 glasses. Electrochem. Commun. 2003, 5, 111−114. (23) MacNeil, J. H.; Massi, D. M.; Zhang, J.; Rosmus, K. A.; Brunetta, C. D.; Gentile, T. A.; Aitken, J. A. Synthesis, Structure, Physicochemical Characterization and Electronic Structure of Thiolithium Super Ionic Conductors, Li4GeS4 and Li4SnS4. J. Alloys Compd. 2014, 586, 736−744. (24) Choi, Y. E.; Park, K. H.; Kim, D. H.; Oh, D. Y.; Kwak, H. R.; Lee, Y. G.; Jung, Y. S. Coatable Li4SnS4 Solid Electrolytes Prepared from Aqueous Solutions for All-Solid-State Lithium-Ion Batteries. ChemSusChem 2017, 10, 2605−2611.

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DOI: 10.1021/acs.inorgchem.8b01049 Inorg. Chem. XXXX, XXX, XXX−XXX