Supporting Information Lithium Bis(fluorosulfonyl)imide/Poly(ethylene oxide) Polymer Electrolyte for All Solid-State Li-S Cell Xabier Judez, Heng Zhang,*, Chunmei Li,*, José A. González-Marcos, Zhibin Zhou, Michel Armand, Lide M. Rodriguez-Martinez CIC Energigune, Parque Tecnológico de Álava, Albert Einstein 48, 01510 Miñano, Álava, Spain Department of Chemical Engineering, Faculty of Science and Technology, University of the Basque Country UPV-EHU, P.P. Box 644, 48080 Bilbao, Spain Key laboratory of Material Chemistry for Energy Conversion and Storage (Ministry of Education), School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan 430074, China *H.Z.: E-mail: hzhang@cicenergigune.com. *C.L.: E-mail: cli@cicenergigune.com. 1
Experimental Preparation of polymer membrane and S cathode The polymer electrolyte membranes based on PEO (viscosity average molecular weight (M v ) = 5 10 6 g mol 1, Sigma-Aldrich) and lithium salt (either LiFSI (battery grade, Suzhou Fluolyte, China) or LiTFSI (battery grade, Solvionic, France)) were prepared by conventional solvent casting method followed by hot-pressing. The detailed procedures could be found in previous work. 1 Three types of cathode laminates were made with 30, 40 and 50 wt % of sulphur, respectively. Composite sulfur cathode was prepared with elemental sulfur (99.5 wt %, Sigma-Aldrich), conductive carbon (Ketjen Black, KJ600, Akzo-Nobel), LiX/PEO electrolyte (X = FSI, TFSI) as remainder. The amount of conductive carbon was 15 wt % for all the prepared S cathodes. Ionic condcutivity The electrolyte ionic conductivity was measured by AC impedance spectroscopy using a VMP3 potentiostat (Biologic). The frequency ranged from 0.1 Hz to 1 MHz with a signal amplitude of 10 mv. A CR2032 type coin cell using two stainless steel (SS) blocking electrodes (SS SPEs SS) was assembled in an Ar filled glovebox and used for the measurement. The temperature was controlled by a Buchi Glass Oven B-585. Lithium-ion transference number The lithium-ion transference number (T + Li ) of the polymer electrolyte at 70 o C was measured by a combination measurement of ac impedance and dc polarization using a symmetric Li polymer electrolytes Li cell, as described by Watanabe and Bruce. 2,3 The surface of lithium metal was shaved with a spatula and was rolled before use. The cell was assembled in a glove box (H 2 O and O 2 < 0.1 ppm). The temperature of the cell was controlled by using a Buchi Glass Oven B-585. The cell was firstly heated to 70 o C during 4 h for obtaining a good contact. Then, the cell at 2
70 o C was subjected to a dc voltage ( V, 10 mv in this study) until a steady current was obtained (usually 2 3 hours in this study). The initial (I 0 ) and steady (I s ) currents (μa), which flown through the cell, were measured. The impedance spectra of the cell were recorded in the frequency range from 10 2 to 10 6 Hz with an oscillation voltage of 5 mv, before and after the dc polarization, to obtain the initial (R 0 b ) and final (R s b ) resistances (Ω) of the electrolyte, and the initial (R 0 1 ) and final (R s 1 ) resistances (Ω) of interfacial layers of the Li metal electrode/electrolyte. Based on these values for the parameters above, the lithium-ion transference number (T + Li ) was then calculated by Equation S1: Equation S1 Cyclic voltammetry measurement Cyclic voltammetry (CV) measurement of Li SPEs Al CR2032 coin cells was performed on a VMP3 potentiostat (Biologic) for investigating the electrochemical behaviour of Al electrode in the polymer electrolyte. Al electrode was used as working electrode, and Li metal was served as counter and reference electrodes. The CV voltammograms were measured between open circuit potential (OCP) to 5.0 V (vs. Li/Li + ) at a scan rate of 5 mv s 1 at 70 C. Cycling of Li-S polymer cell and post-mortem analysis Li-S polymer cells were assembled in an Ar filled glovebox using the prepared electrode as cathode, polymer electrolyte membrane as both electrolyte and separator, and Li metal (Sigma-Aldrich) as anode. The cycling performances of the cells were characterized galvanostatically at a constant current (CC) mode between 1.6 and 2.8 V at 70 C using a Maccor Battery Tester (Series 4000). Surface morphorlogies, cross-section images and elements mapping of the cycled Li-S polymer cells were studied by a field emission Quanta 200 FEG (FEI). 3
The sample was transferred without exposure to air by using a vacuum transfer holder. Table S1. Measured values for the parameters in Equation S1 and the corresponding calculated values of lithium-ion transference numbers (T Li + ) at 70 o C Electrolyte I 0 / μa I s / μa R b 0 / Ω R b s / Ω R l 0 / Ω R l s / Ω V / mv T Li + LiFSI/PEO 131 29 38 39 39 39 10 0.12 LiTFSI/PEO 215 56 17 17 23 23 10 0.15 4
Table S2. Cycling data of Li-S batteries using various type of solid polymer electrolytes (SPEs) reported in literature. Cathode Electrolyte Cycling performance Entry Composition S loading Composition Ionic conductivity / S cm 1 1 Cyclability / mah g sulfur Voltage range Temperature / C C-rate Ref. 1 S (50 wt %) Carbon (16 wt %) Electrolyte (34 wt %) 50 wt % Li[N(SO 2CF 3) 2]/PEO 4.9 10 4 (90 C ) 722 (1st cycle) vs. 270 (10th cycle) 1.5 2.7 90 0.05 ma cm 2 4 S (50 wt %) 2 Acetylene black (5 wt %) PEO (40 wt %) 50 wt % LiCF 3SO 3/PEO + Ti xo 2x-1 (x = 1, 2) 2.2 10 4 (90 C) 1650 (1st cycle) vs. 490 (10th cycle) 1.7 3.2 90 0.14 ma cm 2 5 LiCF 3SO 3 (5 wt %) 3 S/Carbon (1/1, 80 wt %) Super P (10 wt %) PVDF (10 wt %) 40 wt % LiCF 3SO 3/PEO + 10 wt % S-ZrO 2 + Li 2S. 1 10 4 (70 C) 400 (1st cycle) vs. 500 (30th cycle) 1.5 3.2 70 30 ma g 1 6 4 S/Carbon (67/33, 60 wt %) Acetylene black (20 wt %) PEO (20 wt %) 40 wt % Li[N(SO 2CF 3) 2]/PEO + SiO 2 (10 wt %) 5 10 4 (70 C) 1266 (1st cycle) vs. 823 (25th cycle) 1-3 70 0.1 ma cm 2 7 1600 (1st cycle) vs. 40 (10th 5 S / Acetylene black / PEO N. A. LiBF 4/PEO + Al 2O 3 (10 wt %) 3 10 4 (80 C) cycle) 1.7 3 80 0.07 ma cm 2 8 S (24 wt %) 6 Acetylene black (10 wt %) PEO (56 wt %) 24 wt % Li[N(SO 2CF 3) 2]/PEO + γ-lialo 2 (10 wt %) 10 4 (75 C) 609 (1st cycle) vs. 91 (10th cycle) 1.5 3.2 75 0.1 ma cm 2 9 PVDF (10 wt %) 5
Figure S1. Impedance spectra (upper) and time-dependence response of dc polarization (down) for the LiFSI/PEO electrolyte obtained on the symmetric Li SPEs Li cell at 70 C, being polarized with a potential of 10 mv. Figure S2. Discharge/charge profiles the Li-S cells using LiTFSI/PEO electrolyte at 70 ºC, with various sulfur contents at charge/discharge rate of 0.05/0.05C. 6
Figure S3. Cyclic voltammograms of Al current collector as working electrode at 70 C in the LiFSI/PEO (a) and LiTFSI/PEO (b) electrolytes. Figure S4. Electrochemical impedance spectroscopy (EIS) of the corresponding Al electrode after cyclic voltammograms experiments in Figure S3, (a) LiFSI/PEO, (b) LiTFSI/PEO. 7
Figure S5. (a) Discharge/charge profiles of the Li-S cells using the LiFSI/PEO electrolyte in the first cycle at a discharge/charge rate of 0.05/0.05C at 70 C. (b) Discharge capacity (mah per gram of total electrode weight) vs. cycle number for the LiFSI-based Li-S cells at 70 C. Reference (1) Lago, N.; Garcia-Calvo, O.; Lopez del Amo, J. M.; Rojo, T.; Armand, M. All-Solid-State Lithium-Ion Batteries with Grafted Ceramic Nanoparticles Dispersed in Solid Polymer Electrolytes. ChemSusChem 2015, 8, 3039 3043. (2) Evans, J.; Vincent, C. A.; Bruce, P. G. Electrochemical Measurement of Transference Numbers in Polymer Electrolytes. Polymer 1987, 28, 2324-2328. (3) Watanabe, M.; Nagano, S.; Sanui, K.; Ogata, N. Estimation Of Li + Transport Number in Polymer Electrolytes by the Combination of Complex Impedance and Potentiostatic Polarization Measurements. Solid State Ionics 1988, 28, 911-917. (4) Marmorstein, D.; Yu, T.; Striebel, K.; McLarnon, F.; Hou, J.; Cairns, E. Electrochemical Performance of Lithium/Sulfur Cells with Three Different Polymer Electrolytes. J. Power Sources 2000, 89, 219-226. (5) Shin, J.; Kim, K.; Ahn, H.; Ahn, J. Electrochemical Properties and Interfacial Stability of (PEO) 10 LiCF 3 SO 3 Ti n O 2n 1 Composite Polymer Electrolytes for Lithium/Sulfur Battery. Mater. Sci. Eng. B 2002, 95, 148-156. (6) Hassoun, J.; Scrosati, B. Moving to a Solid-State Configuration: A Valid Approach to Making Lithium-Sulfur Batteries Viable for Practical Applications. Adv. Mater. 2010, 22, 5198-5201. (7) Liang, X.; Wen, Z.; Liu, Y.; Zhang, H.; Huang, L.; Jin, J. Highly Dispersed Sulfur in Ordered Mesoporous Carbon Sphere as a Composite Cathode for Rechargeable Polymer Li/S Battery. J. Power Sources 2011, 196, 3655-3658. (8) Jeong, S. S.; Lim, Y. T.; Choi, Y. J.; Cho, G. B.; Kim, K. W.; Ahn, H. J.; Cho, K. K. Electrochemical Properties of Lithium Sulfur Cells Using PEO Polymer Electrolytes Prepared Under Three Different Mixing Conditions. J. Power Sources 2007, 174, 745-750. (9) Zhu, X.; Wen, Z.; Gu, Z.; Lin, Z. Electrochemical Characterization and Performance Improvement of Lithium/Sulfur Polymer Batteries. J. Power Sources 2005, 139, 269-273. 8