Supporting information

Transcription

1 Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2017 Supporting information Capacity Retention of Lithium Sulfur Batteries enhanced with Nano-sized TiO 2 - Embedded Polyethylene Oxide Felix Lee a,#, Meng-Che Tsai a,#, Ming-Hsien Lin a, Yatim Lailun Ni mah a, Sunny Hy a, Chao- Yen Kuo a, Ju-Hsiang Cheng a, John Rick a, Wei-Nien Su b, *, and Bing-Joe Hwang a,c, * a NanoElectrochemistry Laboratory, Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan b NanoElectrochemistry Laboratory, Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan c National Synchrotron Radiation Research Center, 30076, Hsin-Chu, Taiwan # These authors contribute equally to this work *Corresponding author. Tel.: ; Fax: bjh@mail.ntust.edu.tw, wsu@mail.ntust.edu.tw S-1

2 Preparation of Polymer electrolyte and PEO/TiO 2 composite PEO/TiO 2 was prepared based on a previously published method by Hwang et al. 1, 2 with some modification to optimize the size of the TiO 2 nanoparticles. A stoichiometric amount of LiClO 4 (Acros) was dissolved in Tetrahydrofuron (THF) (Acros) solvent and stirred at room temperature. Referring to a similar process for sodium ion battery from our group, 3 the ratio of EO and Li was determined as wt% TiO 2 nanoparticles, prepared separately by a hydrothermal process, were dispersed in the solution mixture and the temperature of the mixture was raised to 70 C. After stirring for 30 minutes, PEO (molecular weight 600,000) was added to the previous solution and stirred for 24 hours. The excess volatile organic solvent was evaporated upon continuous stirring and the solution became highly viscous in nature. The mixture was then poured into a Teflon Petri dish (diameter 2 cm) and the solvent evaporated in an oven at 55 C for 6 h followed by conditioning in an Ar-filled glove box for 1 day. The final electrolyte film was 2 cm in diameter and 0.18 mm in thickness. The composite polymer electrolyte film was preserved in the glovebox for the remaining time. S-2

3 Cell design and in situ Raman measurement Figure S1(a) shows an exploded view of a common coin cell, which is assembled by common practice. Have the cathode ready as a dried sheet and put it on the Teflon plate with the current collector side down. Punch out the desired amount of electrode with the punch tool and place it in the center of the bottom cap. Slowly wetting the electrode with several drops of the electrolyte (typically 1M LiPF6 in EC/DEC 1:1vol). Place the separator (18 mm) on top of the electrode and moist the separator with the electrolyte nicely without bubbles. Put O-ring on top and take the Li anode (Ø 16 mm) gently in the case with the aid of plastic tweezers. Place the stainless current collector and a spring on that. Put the top cap to finalize the battery construction. Use cell crimper to obtain the coin cell. In order to realize in-situ Raman measurement, holes should be punched in the top cap, and Lithium metal in advance. A 0.17 mm thick quartz window was installed at the top of the hole, so that light can be illuminated directly on the electrode materials. The assembly sequence is similar, but in a reverse order as shown in Figure S1(b). S-3

4 (a) (b) Figure S1 (a) Normal coin cell assembly method; (b)in-situ Raman coin cell assemble method Green light laser (532 nm, 1mW) is used as the light source for Raman spectroscopy, with a 50X objective lens and TE cooled CCD (1024 X 256 pixels) integrated by Protrusttech Corp. Ltd. The electrochemical tests were performed with a potentiostat (Metrohm Autolab, PGSTAT 101) and a testing cell holder as shown in Figure S2. The voltage range was set between V for normal charging/discharging cycles and 2 5 V for over-charging /discharging tests. The laser exposure time was 10 s, with 10 times accumulation. Charging /discharging rate was 0.1 C, unless otherwise specified. The equipment is shown in Figure S2. S-4

5 Figure S2 In-situ Raman spectroscopy analysis device Charging-discharging performance For 0.1C at 60 C, the first two charging-discharging cycles of PEO and PEO/TiO 2 are shown in Figure S1(a). The rate capability based on the charge and discharging capacity is shown in Figure S1(b). It is to note that much severe polarization and capacity fading can be observed in PEO from the first two cycles. This figure has been added to the supporting information as Figure S1. S-5

6 o C, 0.1C-rate 1.5V - 3.0V (a) (b) Voltage /V vs. Li/Li PEO/TiO2 1st cy PEO/TiO2 2nd cy PEO 1st cy PEO 2nd cy Capacity /mah.g C 0.2C charge discharge 0.5C 1C 2C 0.1C Capacity /mah.g Cycle number Figure S3 (a) The first two cycles of charging-discharging curves of Li/S in PEO and PEO/TiO 2 electrolytes at 60 C and 0.1C; (b) Rate capability of Li/S in PEO and PEO/TiO 2 electrolytes based on charging and discharging capacities S-6

7 Table S1 Bader charge analysis for polysulfide and sulfur species before and after the adsorption on the different substrates Substrates Adsorbates Bader Charge (e - ) Li1 S1 S2 S3 S4 S5 S6 S7 S8 Li2 S_avg S_avg_diff S S Anatase TiO 2 (101) Li 2 S Li 2 S Li 2 S Li 2 S S S PEO chain Li 2 S Li 2 S Li 2 S Li 2 S S_avg: The average charge value for the polysulfides after adsorbed. S_avg_diff: The difference of the average charge for the polysulfides before/after adsorption on the substrates, which the positive value indicates the electron loss on sulfur. S-7

8 Reference 1. C. W. Lin, C. L. Hung, M. Venkateswarlu and B. J. Hwang, Journal of Power Sources, 2005, 146, Y.-C. Lin, J.-H. Cheng, M. Venkateswarlu, F.-M. Wang, R. Santhanam and B.-J. Hwang, Journal of the Chinese Chemical Society, 2012, 59, Yatim L. Ni'mah, M.-Y. Cheng, Ju H. Cheng, J. Rick and B.-J. Hwang, Journal of power sources, 2015, 278, S-8