Suppressed Polysulfide Crossover in Li-S. Batteries Through a High-Flux Graphene Oxide. Membrane Supported on Sulfur Cathode

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1 Supporting Information Suppressed Polysulfide Crossover in Li-S Batteries Through a High-Flux Graphene Oxide Membrane Supported on Sulfur Cathode Mahdokht Shaibani,, Abozar Akbari, Phillip Sheath, Christopher D. Easton, Parama Chakraborty Banerjee, Kristina Konstas, Armaghan Fakhfouri, Marzieh Barghamadi,, Mustafa M. Musameh, Adam S. Best, Thomas Rüther, Peter J. Mahon, Matthew R. Hill, *,, ^ Anthony F. Hollenkamp, *, and Mainak Majumder *, Nanoscale Science and Engineering Laboratory (NSEL), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3168, Australia CSIRO, Clayton, VIC 3168, Australia Department of Chemistry and Biotechnology, Swinburne University of Technology, VIC 3122, Australia ^ Department of Chemical Engineering, Monash University, Clayton, VIC 3168, Australia Table of contents Section SI. Materials Section SII. Supporting Figures Figure S1 SEM images of uniformly coated sulfur cathode and poorly coated sulfur cathode Figure S2 Characterization of the porous structure of the microporous carbon Figure S3 High resolution C 1s XPS spectrum of carbon coated separator Figure S4 Cyclic voltammogram of GO coating alone Figure S5 Cyclic voltammogram of GO coated cathode Figure S6 FTIR spectrum of GO coated cathode Figure S7 High resolution C 1s XPS spectrum of GO coated cathode Figure S8 Effect of giving a resting time before cycling Figure S9 Capacity Contribution of the GO coating 1

2 Figure S10 Capacity retention of GO coated electrode after 400 cycles at different lower rates Figure S11 Influence of the structural order of GO membrane on the performance of Li-S cell Figure S12 Proposed electrical equivalent circuit (EEC) Figure S13 Comparison of the experimental and the simulated EIS data Figure S14 Effect of GO coating thickness on cyclability Figure S15 Effect of the conductive interlayer thickness on cyclability Figure S16 Cycling performance in a lino 3 -free electrolyte Section SIII. Supporting Tables Table S1 Calculated resistances of the different interfaces of cells with different separators Table S2 Survey data measured by XPS Table S3 Component fitting of high resolution S 2p spectra measured by XPS Table S4 Comparison of the performances of advanced Li-S cells Table S5 Comparison of the performances of Li-S cells with GO in their configuration. Section SI. Materials Graphite powder (SP-1 grade 325 mesh) was purchased from Bay Carbon Inc. Microporous carbon (Black Pearls 2000) was purchased from CABOT Co. Potassium persulfate, Phosphorus pentoxide, Potassium permanganate, Ammonium persulfate, N-methyl-2- pyrrolidinone, Bis(trifluoromethane)sulfonimide lithium salt and Lithium nitrate were purchased from Sigma-Aldrich and directly used without any further purification. Battery grade etched Al foil (30 µm thickness) was purchased from Japan Capacitor Industrial Co. Solupor 7P03A separator was purchased from Lydall, Inc., UK and Glass fiber BG03013 separator (0.203 mm, max pore size= 15.5 µm) was purchased from, Hollingsworth & Vose (H&V), USA. Cross-linked polyacrylate copolymer based hydrogel beads were purchased from Demi Co, Ltd, China. Cross-linked polyacrylate copolymer based hydrogel beads were purchased from Demi Co, Ltd, China. 2

3 Section SII. Supporting Figures a b GO coting S cathode 1 µm 1 µm Figure S1. Effect of the gap size of the doctor blade -which demonstrates the thickness of the GO membrane - on the coverage of the GO coating on the cathode: (a) SEM image of a GO coated cathode with a large enough gap size of the doctor blade showing uniform coverage of the cathode surface. (b) SEM image of a GO coated cathode with a not large enough gap size of the doctor blade revealing electrode areas which are not covered with the GO membrane. Decreasing the thickness of the coated GO membrane is limited only by the surface roughness of the cathode. 3

4 a b Figure S2. Characterization of the porous structure of the microporous carbon used in this work for fabricating carbon coated separators: (a) N 2 adsorption isotherm at 77K, (b) Poresize distribution. Figure S3. High resolution C 1s XPS spectrum of carbon coated separator. 4

5 Figure S4. Control experiment on the GO coating on Al foil, without the sulfur cathode: Cyclic voltammetry at 0.1 mv s -1 in a potential window from 1.8 to 2.8 V vs Li + /Li 0. Figure S5. Cyclic voltammetry of GO coated electrode at 0.1 mv s -1 in a potential window from 1.8 to 2.8 V vs Li + /Li 0. 5

6 Figure S6. FTIR spectrum of graphene oxide coated electrode shows hydroxyls (broad peak at cm -1 ), carboxyls ( cm -1 ) and ethers and/or C-O- ( cm -1 ). Figure S7. High resolution C 1s XPS spectrum of graphene oxide coated electrode. Various carbon-oxygen functional groups, including hydroxyl, epoxy, and carboxylic acid, are likely present in the GO membrane as represented by the signal intensity at binding energies greater than ~ 286 ev, and supported by the FTIR results. 6

7 Figure S8. Effect of resting time before cycling: Putting a cell on rest for 24 h before cycling at a high 1 C rate allows for the electrolyte to diffuse through the GO layer and wet the sulfur cathode. Accordingly the cell starts at its highest capacity compared to a cell which was cycled immediately after assembly and requires some activation cycle to reach its maximum capacity. a b Figure S9. Capacity Contribution of the GO coating: (a) Charge discharge V-t profiles of GO coating at the same current density as a typical Li-S cell in this work in a potential window from 1.8 to 2.8 V vs Li + /Li 0. (b) Cycling performance comparison of GO coating at the same current density as a typical Li-S c ell in this work shows negligible capacity contribution from the GO coating. 7

8 Figure S10. Capacity retention of GO coated cathode after 400 cycles at different lower rates: After 400 cycles the cells can still maintain specific capacities of 1100 mah g -1 at 0.1 C, 985 mah g -1 at 0.2 C and 885 mah g -1 at 0.5 C rates providing one of the best performances demonstrated so far for a Li-S cell. 8

9 a b c Li Separator Sulfur cathode Li Go coated Separator Sulfur cathode Li Go coated Separator Sulfur cathode Predicted organization of graphene sheets in the Shear aligned GO film on the separator Predicted organization of graphene sheets in the Vacuum filtered GO film on the separator 1, 2 d e Figure S11. Influence of the structural order of the GO membrane on the electrochemical response and performance fading of the Li-s battery: (a) Configuration of a cell assembled with a bare separator, (b) configuration of a cell assembled with a shearaligned GO coated separator made by blade coating, (c) configuration of a cell assembled with a disordered GO coated separator made by vacuum filtration technique. (d) Comparing the 1 st cycle of cells a, b and c; (e) comparing the 5 th cycles of cells a, b and c. 9

10 Figure S12 Proposed electrical equivalent circuit (EEC) to analyse the impedance data of the cells containing a bare separator, an ordered and a disordered GO coated separators. In this study, complex nonlinear least square method was used to analyse the data. The fitting procedure, weighing modulus and circuit description codes are explained elsewhere. 3 Figure S13 Comparison of the experimental and the simulated (a) Nyquist, (b) Bode Z and (c) Bode phase angle plots of a cell assembled with a sheer aligned GO coated separator made by blade coating. A good agreement between the simulated and experimental data confirms the validity of the proposed EEC. (d) Error plot of the same cell shows less than 5 % error in Z, and the error in angle simulation was less 4 degree. 10

11 0.80 µm thick GO film on the 1.60 µm thick GO film on the cathode Figure S14. Effect of GO coating thickness on cyclability (1C rate): A thicker coating clearly interferes with both ion movement and mass transport. 11

12 a b c Figure S15. (a) Cross section SEM image of a relatively heavy carbon coated separator ( 15 µm and 0.7 mg cm -2 ), (b) SEM image of a lightweight carbon coated separator ( 6.5 µm and 0.24 mg cm -2 ), (c) Effect of the mass of the conductive interlayer on the cycling performance of GO coated cathodes. If we only consider the sulfur utilization (mah g -1 S) the specific capacity of the cell configured with a heavy conductive interlayer is slightly higher. However if we take into account the mass of the whole cathodic system (Cathode (sulfur+ conductive agent+ binder) + Additional layers (GO on the cathode and carbon on the separator) ), the total gravimetric capacity of the cell with a lightweight coating is 280 mah g -1 which is significantly higher than that of the cell with a heavy coating: 216 mah g

13 Figure S16. Cycling performance in a lino 3 -free electrolyte. Section SIII. Supporting Tables Table S1 Calculated resistances of the different interfaces of the cells containing bare separator, sheer aligned GO coated separator and disordered GO coated separator before and Sample R e (Ω) R int (Ω) R ct (Ω) Before after Before after Before after Bare separator Sheer aligned GO coated separator Disordered GO coated separator 13

14 after 5 cycles of CV 14

15 Table S2. Survey data measured by XPS (atomic percentage, %). Listed are the mean values (± deviation) based on +2 analyses points. Sample: Un-coated cycled cathode GO-coated cycled cathode Atomic% Mean Std Mean Std Na 1s F 1s O 1s N 1s C 1s S 2p Li 1s Si 2p Table S3. Component fitting of high resolution S 2p spectra measured by XPS (atomic percentage, %). Listed are the mean values (± deviation) based on 3 analyses points. Sample Un-coated cycled cathode GO-coated cycled cathode Atomic% Mean Std Mean Std S S S S S S S S 2p components: S 1: Li 2 S; S*-SO 3 (thiosulphate) S 2: Li 2 S 2 ; polysulfide (S terminal ) S 3: polysulfide (S bridge ) S 4: S 8 S 5: Range of oxidised and S+ groups S 6: Sulfite (RSO 3 ); RS(O)OR S 7: Sulfate (RSO 4 ); ROSO 2 OR, RSO 2 F 15

16 Table S4. Performance of the state of the art Li-S batteries. Sulfur Fraction (%) Sulfur Loading (mg cm -2 ) Interlyer weight (mg cm -2 ) Rate / cycle Discharge capacity at n th cycle per mass of (mah g -1 ) sulfur composite cathode a Values were extracted from the main texts. b Values were estimated from the relevant composite cathode +interlayer GO/Amylopectin host 4a 52 4 N/A 0.5 C (100) N/A Hollow core-shell interlinked carbon N/A 0.5 C (200) N/A spheres host 5a Mesoporous Carbon Nanotube host 6a N/A 0.1 C (100) N/A polar, high surface 48 area metallic oxide host 7a N/A 0.5 C (100) 0.5 C (100) g-c3n4 polar host 8a N/A 1 C (200) N/A PEDOT:PSScoated CMK- 3/sulfur composite 9a 43 1 N/A 0.2 C (150) N/A Phenyl sulfonated graphene/sulfur N/A 0.2 C (50) 0.2 C (400) GO on the separator 11b C (100) ~700 ~ 441 ~ 376 GO/O-CNT on the separator 12b C (100) ~ 750 ~ 487 ~ 300 CNF interlayer 13a C (100) Polypropylene/ Graphene Oxide/Nafion C (100) ~850 ~ 459 ~ 408 separator 14b SWCNT Modulated Separator 15b Graphene current collector + vacuum filtered graphene separator 16b This work C (100) 0.5 C (300) 0.75 A g -1 (100) C (100) ~ ~ N/A ~ ~950 ~665 ~ figures. 16

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18 Table S5. Comparison of the performances of Li-S cells with GO in their configuration. Electrolyte Rate 1 st discharge capacity, mah g -1 Discharge capacity at n th cycle, mah g -1 Coulombic efficiency, % GO/S cathode 17a Organic 0.1 C (16) 96.7 IL 0.1 C (50) GO/S/CTAB cathode 18b Organic 1.0 C ~860 ~640 (100) 96.7 IL 1.0 C ~860 ~680 (400) 96.3 GO/S/Amylopectin Organic 0.5 C (100) 98 cathode 4a GO coated separator 11b Organic 0.1 C ~1000 ~700 (100) This work Organic 1.0 C (100) ~100 Organic 1.0 C (400) Organic 0.2 C (100) a Values were extracted from the main texts. b Values were estimated from the relevant figures. 18

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