SUPPLEMENTARY INFORMATION

Transcription

1 SUPPLEMENTARY INFORMATION A) Structural refinement. The powder pattern was indexed (DICVOL04 [21]) in a triclinic cell, (space group P-1). The structures were then refined using the Rietveld method with the Fullprof program [22] (see Fig 1), starting with atomic coordinates found by FOX [23]. Crystallographic is summarized in Table 1 and 2 and selected interatomic distances and angles in Tables 3 and 4. Table 1: Lattice parameters and cell volumes for Li F Space Group P-1 Cell parameters a (Å) (3) b (Å) (3) c (Å) (3) α( ) (3) β( ) (3) γ( ) (3) Volume (Å 3 ) (16) Agreement factors χ Rp 20.4 Rwp 11.4 R Bragg 4.46 Table 2: Atomic coordinates for Li F Atom Site x y z Occupancy S 2i 0.321(2) 0.630(2) 0.248(2) 1 Fe1 1b 0 (-) 0 (-) ½ (-) 1 Fe2 1a 0 (-) 0 (-) 0 (-) 1 F 2i 0.123(3) 0.912(3) 0.758(2) 1 O1 2i 0.585(4) 0.747(3) 0.402(3) 1 O2 2i 0.098(4) 0.643(3) 0.345(3) 1 O3 2i 0.312(4) 0.357(4) 0.148(3) 1 O4 2i 0.278(3) 0.780(3) 0.109(3) 1 Li1 2i 0.36(2) 0.67(3) 0.82(2) ½ Li2 2i 0.21(3) 0.61(3) 0.73(2) ½ nature materials 1

2 supplementary information Table 3: Selected interatomic distances (Å) in Li F (<3Å) Fe1 O1(x2) 2.19(2) Fe2 O3(x2) 2.13(2) S O1 1.41(2) O2(x2) 2.18(2) O4(x2) 2.12(3) O2 1.52(3) F(x2) 2.00(2) F(x2) 1.99(2) O3 1.46(2) O4 1.46(3) Li1 O1 2.50(15) Li2 O1 2.45(17) O2 2.46(10) O2 1.80(15) O3 1.68(11) O2 2.73(16) O4 2.19(15) O3 2.33(15) F 1.98(16) O4 2.53(14) F 1.75(17) Table 4: angles ( ) for Li F Tetrahedra SO 4 O1-S-O O1-S-O O1-S-O O2-S-O O2-S-O O3-S-O Fe1 centered octahedra Fe2 centered octahedra F-Fe1-O F-Fe1-O O1-Fe1-O1 180 O1-Fe1-O O2-Fe1-O2 180 O2-Fe1-O2 180 F-Fe1-F 180 F-Fe2-O F-Fe2-O O3-Fe2-O3 180 O3-Fe2-O O4-Fe2-O4 180 O4-Fe2-O4 180 F-Fe2-F nature MATERIALS

3 supplementary information Table 5: Lattice parameters and cell volumes for F (indexed using DICVOL04 [21]) Space Group P-1 Cell parameters a (Å) (2) b (Å) (3) c (Å) (4) α( ) (4) β( ) (4) γ( ) (3) Volume (Å 3 ) (12) Agreement factors χ Rp 7.9 Rwp 9.5 B) Electrochemical information: The most elegant way to determine the nature (single phase vs. two phases) insertion process is to perform Potentiotastic (PITT) intermittent titration techniques. This technique consists of maintaining a constant potential until the current response reaches a set-up limit value. Presently, the experiment was run using 5 mv potential steps and a current limit of 0.06mA which correspond to a fixed rate of C/20.Below, we are reporting the second cycle Potential vs. Li + /Li courant (ma) x in Li 1-x F Fig. S1: The chronoamperometric response (red line) of the Li F electrode to a 5 mv stepwise scanning potential combined to a preset minimum current value limit equivalent to a galvanostatic rate of C/20. nature materials 3

4 supplementary information The current curves do not follow a Cottrel-type law indicative of a solid solution insertion process kinetically limited by Li + diffusion but rather a more limited diffusion step that can be linked to a two phase transition. This latter is even more evident during the early discharge that displays a hint of bell-shape type variation, reminiscent of a biphasic process kinetically limited by the two phases interfacial migration. To further strengthen this point experiments are presently running at a C/50 fixed rate. c) F thermal stability: Controlled high temperature XRD experiments on F powders were carried-out under similar conditions (up to 450 C in air) as Li F. The reported XRD patterns summarized in Fig. S2 indicate that this phase is stable up to around 375 C. Beyond, those temperatures, new peaks reminiscent of a decomposition process, appear. 400 C Intensity 350 C 325 C 300 C 200 C 100 C 30 C θ ( ), Cu kα Fig. S2: Temperature-controlled X-ray diffraction (λ Cu-Kα ) of FeSO4F d) Role of the ionic liquid: TGA measurements conducted in the presence of either O + ionic liquid, or O + ionic liquid + LiF are compared to those done with only ionic liquid or O. The behaviour of one highly hydrophobic ionic liquid (EMI-TFSI) is compared to that of a less hydrophobic one, EMI-Tf. Note that EMI-TFSI postpones the release of H 2 O until temperatures greater than 280 C, temperatures at which the double ion exchange reaction (H + for Li + and OH for F ) can proceed leading to the formation of Li F. 4 nature MATERIALS

5 supplementary information Weight lost EMI-TFSI EMI-Tf O + LiF + EMI-TFSI O + EMI-TFSI O + EMI-Tf O C/ minute Temperature ( C) Figure S3: Weight lost for various FeSO4.H20, LiF, EMI-TFSI, EMI_Tf mixtures showing clearly the efficiency of EMI-TFSI in delaying the water removal from FeSO4.H2O. This effect is less pronounced with EMI-Tf. e) Water stability of Li F: The sample was placed in water overnight and the recouped powder was washed with alcohol and acetone prior to be X-rayed. From the XRD pattern (Fig. S4) we could deduce its decomposition into LiF The presence of FeOOOF FeOOH (PCPDF ) LiF (PCPDF ) Fig. S4: XRD powder pattern of Li F after being left overnight into water nature materials 5