Supporting Information

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1 Supporting Information Li 4 PS 4 I: A Li + Superionic Conductor synthesized by a Solvent-based Soft Chemistry Approach Stefan J. Sedlmaier*, Sylvio Indris, Christian Dietrich, Murat Yavuz, Christoph Dräger, Falk von Seggern, Heino Sommer, Jürgen Janek* * Karlsruhe Institute of Technology (KIT), Battery and Electrochemistry Laboratory (BELLA), Institute of Nanotechnology (INT), Hermann-von-Helmholtz-Platz 1, Eggenstein- Leopoldshafen, Germany stefan.sedlmaier@kit.edu, juergen.janek@phys.chemie.uni-giessen.de 1. Experimental details Syntheses All manipulations were carried out in an argon-filled glovebox (MBraun) with an O 2 and H 2 O content below 0.1 ppm or on a Schlenk line. Li 3 PS 4 DME was synthesized by reacting Li 2 S and P 2 S 5 in DME. In a typical approach Li 2 S (488.0 mg, mmol; Alfa Aesar 99.9 %) and P 2 S 5 (1.012 g, mmol; Sigma Aldrich 99 %) were mixed together, ground in an agate mortar and filled into a dried 100 ml Schlenk flask. After adding approx. 40 ml of anhydrous 1,2 dimethoxyethane (DME, Sigma Aldrich 99.5 %) the reaction mixture was stirred at room temperature for ten days. The formed colorless precipitate was filtered off, washed with DME and dried in vacuo. Li 3 PS 4 DME was obtained as a phase-pure, colorless powder. Li 4 PS 4 I was synthesized by reacting Li 3 PS 4 DME with LiI in DME. In a typical approach Li 3 PS 4 DME (500.0 mg, mmol) and LiI (247.7 mg, mmol; Sigma Aldrich %) were mixed together, ground in an agate mortar, and dispersed in approx. 10 ml of DME in the space of a dried Schlenk tube. While stirring the initial yellow color of the mixture vanished within one minute. After further stirring for 1 day, the DME was removed in vacuo and the remaining colorless solid was dried at 50 C until the pressure was below mbar. In a final step, further under vacuum, the solid was heated to 200 C for least 6 h. Li 4 PS 4 I was obtained as a colorless, slightly gray powder that is sensitive to moist air.

2 X-ray and neutron diffraction X-ray powder diffraction patterns were recorded using Stoe Stadi P diffractometers with Cu- K α1 and Mo-K α1 radiation. The samples were filled within an argon glovebox into borosilicate glass capillaries (Hilgenberg) with inner diameters of 0.48 and 0.28 mm (wall thickness 0.01 mm), respectively, and flame sealed. A Neutron powder diffraction measurement was made using the GEM diffractometer (ambient temperature) at the ISIS facility, Rutherford Appleton Laboratory, UK. The sample was contained in 6-mm-diameter thin-walled vanadium cans that were sealed with an indium gasket. Nuclear magnetic resonance (NMR) 31 P NMR measurements were carried out on a Bruker Advance 500 MHz spectrometer equipped with a commercial 2.5 mm MAS NMR double-resonance probe (ZrO 2 rotor was filled in the glovebox) at a spinning speed of 30 khz. The magnetic field strength was 11.7 T corresponding to the Larmor frequency of MHz. A rotor-synchronized Hahn-echo pulse sequence was used for data acquisition with a π/2 time of 2 µs and recycle delays of 60 s. Chemical shifts are referenced to H 3 PO 4 (85%). 7 Li NMR measurements were performed on a Bruker 200 MHz spectrometer at a magnetic field of 4.7 T corresponding to a Larmor frequency of 77.8 MHz. Static spectra were recorded with a single-pulse sequence and referenced to an aqueous 1M LiCl solution at 0 ppm. T 1 measurements were acquired with an inversion-recovery pulse sequence. Impedance Spectroscopy and DC conductivity measurement Electrical conductivity was measured by AC impedance spectroscopy, using a custom build electrochemical cell setup. A powdered sample of 120 mg Li 4 PS 4 I was placed between two stainless steel rods with 10 mm diameter and pressed at 3.5 tons (equivalent to 440 MPa) for 3 minutes. Electrochemical impedance analysis (EIS) was conducted in the temperature range of 25 C to 65 C using a SP300 impedance analyser (Biologic) at frequencies from 7 MHz to 100 mhz with an amplitude of 20 mv. Fitting of the impedance data was performed in the frequency range of 2 MHz to 10 Hz using a RQ element, representing lithium transport in the bulk and along grain boundaries in series with a RQ-Q element, representing ionic adsorption and charge transfer between the electrolyte and the stainless steel electrodes.the electronic partial conductivity was determined with the same setup via a simple polarization method, applying a voltage of 0.2 to 0.6 V in 0.1 V steps for 10 h each.

3 TG and DTA Thermogravimetric (TG) and differential thermal analysis (DTA) experiments were performed with powder samples using an STA 449C Jupiter thermal analyser (Netzsch) under dynamic argon atmosphere (30 ml min -1 ). SEM and EDX Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were performed using a LEO-1530 electron microscope (Carl Zeiss AG, Oberkochen, Germany) with a field emission source equipped with an EDX silicon drift detector (SSD) X-MAX 50mm 2 detector size (Oxford Instruments, Oxfordshire, UK). Powders were placed on an aluminum sample holder fixed with self-adhesive carbon plates (Plano GmbH, Wetzlar, Germany). EDX data collection and evaluation was carried out with the aid of the AZtec program package. 2. Thermogravimetric (TG) and Differential Thermal Analyses (DTA) of Li 3 PS 4 DME Figure S1. TG (solid) and DTA (dashed) curves of Li 3 PS 4 DME; recorded with a heating rate of 1 C min -1 ; 1 st step mass loss (up to 194 C): 33.4 %; theoretical mass loss for one DME molecule: 34.1 %.

4 3. Crystal structure of Li 3 PS 4 DME Table S1. Crystallographic data of Li 3 PS 4 DME and details of the data collection and relative structure solution and refinement (esd s in parentheses). Crystal Structure Data Formula Li 3 PS 4 C 4 H 10 O 2 formula mass / gmol crystal system tetragonal space group I4 1 /amd (no. 141, origin choice 1) cell parameter / Å a = (10) c = (6) cell volume / Å 3 V = (7) formula units Z / cell 8 X-ray density ρ / g cm (2) Data collection type of diffractometer Stoe Stadi P Geometry Debye-Scherrer Radiation CuK α1 (λ = Å) Temperature / K 298(2) 2θ range / data points 5425 number of observed reflections 179 Structure solution and refinement structure solution method charge flipping [1] structure refinement method least-squares method [2] program used TOPAS-Academic V5 [3] number of parameters 48 Background function / parameters shifted Chebyshev / 16 R p = R indices wr p = R bragg = GoF = Table S2. Atom coordinates, Wyckoff symbols and isotropic displacement parameters B iso / Å 2 for the atoms in Li 3 PS 4 DME in I4 1 /amd (no. 141, origin choice 1) (esd s in parentheses). atom Wyckoff symbol x y z occupancy B iso Li(1) 16g (15) (15) (5) Li(2) 8e (7) 1 3.9(7) P(1) 8e (12) 1 1.5(1) S(1) 16h (3) (6) 1 2.4(1) S(2) 16h (3) (7) 1 2.6(1) C(1) 16h (8) (3) 1 6.5(4) C(2) 32i (7) (14) (2) (6) O(1) 16h (7) (2) 1 6.0(3)

5 Figure S2. Rietveld refinement (observed, calculated diffraction patterns as well as difference profile) against powder X-ray (Cu-K α1 ) diffraction data; allowed peak positions are marked by vertical lines. Figure S3. Crystal structure of Li 3 PS 4 DME showing the arrangement of the PS 3-4 -tetrahedra (blue) and the Li + ions (green) as well as the DME molecules (C: gray, O red, H-atoms are omitted; the terminal CH 3 groups are distributed over two positions with occupancy ½).

6 4. Reaction Scheme Figure S4. Reaction scheme illustrating the reaction of Li3PS4 DME with LiI in DME resulting in a precursor compound from which Li4PS4I crystallizes after heat treatment in vacuum. 5. Thermogravimetric (TG) and Differential Thermal Analyses (DTA) of the precursor 'Li3PS4 DME LiI' -1 Figure S5. TG (solid) and DTA (dashed) curves of Li3PS4 DME LiI; recorded with a heating rate of 1 C min ; 1 step mass loss (up to 184 C): 24.8 %; theoretical mass loss for one DME molecule: 22.3 %. st

7 6. Scanning electron microscopy (SEM) images of Li4PS4I and energy dispersive X-ray spectroscopy (EDX) Figure S6. SEM images of microcrystalline Li3PS4I; EDX data qualitatively confirm the elements P, S, and I and semiquantitatively reflect the composition (atom% ratio S : P = 2.9; P : I = 1.7). 7. Crystal structure of Li4PS4I Table S3. Crystallographic data of Li4PS4I and details of the data collections and relative structure solution and refinement (esd s in parentheses). Crystal Structure Data Formula Li4PS4I -1 formula mass / gmol crystal system tetragonal space group P4/nmm (no. 129, origin choice 2) a = (12) cell parameter / Å c = (11) 3 cell volume / Å V = (15) formula units Z / cell 2-3 X-ray density ρ / g cm 2.449(6) Data collection type of diffractometer Geometry Radiation Temperature / K data points number of observed reflections Structure solution and refinement structure solution method structure refinement method program used number of parameters Background function R indices Stoe Stadi P and GEM (ISIS facility) Debye-Scherrer MoKα1 (λ = Å), TOF neutrons 298(2) [1] charge flipping [2] least-squares method, combined (X-ray and neutron) refinement [3] TOPAS-Academic V5 158 shifted Chebyshev Rp = wrp = Rbragg = GoF =

8 Table S4. Atom coordinates, Wyckoff symbols and isotropic displacement parameters B iso / Å 2 for the atoms in Li 4 PS 4 I in P4/nmm (no. 129, origin choice 2) (esd s in parentheses). atom Wyckoff symbol x y z occupancy B iso I(1) 2c (11) (2) S(1) 8i (9) (2) (3) P(1) 2b (5) Li(1) 2c (4) 0.68(3) 2.5(5) Li(2) 2a (4) 2.5(5) Li(3) 8j 0.454(2) 0.454(2) 0.585(3) 0.38(2) 2.5(5) Li(4) 4d (3) 2.5(5) Li(5) 8i (2) 0.11(2) 0.08(2) 2.5(5)

9 Figure S7. Observed (black lines) and calculated (red lines) neutron powder diffraction patterns as well as difference profiles of the Rietveld refinements of Li 4 PS 4 I against GEM data at room temperature; peak positions are marked by blue (main phase), and green (LiI) vertical lines.

10 Table S5. Selected interatomic distances / pm and angles / in Li 4 PS 4 I (e.s.ds. in parentheses) Li(1)-S 267.4(5) Li(2)-S 241.0(1) Li(3)-S 261.0(15), 258.0(16) Li(4)-S 279.6(9) Li(5)-S 244.6(98), 229.8(71) Li(1)-I 331.3(21), 261.7(21) Li(3)-I 289.9(16) Li(4)-I 313.3(1) Li(5)-I 311.4(104) P-S 204.1(1) S-P-S (1), (1) P solid-state NMR spectrum of Li 4 PS 4 I Figure S8. 31 P NMR spectrum of a sample of Li 4 PS 4 I.

11 9. Conductivity and polarization measurements Li 4 PS 4 I Figure S9. a) Impedance spectra (black circles) measured at different temperatures and the fits (red line, equivalent circuit in the top left corner); b) DC polarization experiments proving the ionic character of Li 4 PS 4 I. 10. Thermogravimetric (TG) and Differential Thermal Analyses (DTA) of Li 4 PS 4 I Figure S10. TG (solid) and DTA (dashed) curves of Li 4 PS 4 I; recorded with a heating rate of 5 C min -1.

12 11. References [1] G. Oszlányi, A. Süto, Acta Crystallogr., Sect. A: Found. Crystallogr. 2004, 60, 134. [2] Bergmann, J.; Kleeberg, R.; Haase, A.; Breidenstein, B. Mat. Sci. Forum 2000, , 303. [3] Coelho, A. A. TOPAS Academic: General Profile and Structure Analysis Software for Powder Diffraction Data, 5 th ed.; Bruker AXS: Karlsruhe, Germany, 2012.