Conducting Nanopaper: A Carbon-Free Cathode

Transcription

1 SUPPORTING INFORMATION Conducting Nanopaper: A Carbon-Free Cathode Platform for Li-O 2 Batteries Ji-Won Jung ab, Hyeon-Gyun Im ac, Daewon Lee ad, Sunmoon Yu a, Ji-Hoon Jang b, Ki Ro Yoon a, Yun Hyeok Kim a, John B. Goodenough b, Jungho Jin *e, Il-Doo Kim *a, Byeong-Soo Bae *a a Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea b Texas Materials Institute, The University of Texas at Austin, TX 78712, Austin, USA USA c Creative and Fundamental Research Division, Korea Electrotechnology Research Institute, Changwon-si, Gyeongsangnam-do, 51543, Republic of Korea d Carbon Resources Institute, Korea Research Institute of Chemical Technology (KRICT), 141 Gajeong-ro, Yuseong-gu, Daejeon 34114, Republic of Korea e School of Materials Science and Engineering, University of Ulsan, 93 Daehak-ro, Nam-gu, Ulsan 44610, Republic of Korea * Corresponding authors. address: bsbae@kaist.ac.kr, idkim@kaist.ac.kr and jinuine@ulsan.ac.kr

2 Table of contents S0. Experimental section... 1 S1. Schematic illustration of synthesis of AgCh-CNp... 4 S2. Photographs of AgNW with and without chitin in solvents... 5 S3. Dynamic Light Scattering (DLS) analyses... 6 S4. N 2 -adsorption and desorption measurement and SEM images of AgCh-CNp... 7 S5. Contact angles of electrolyte and water droplets on AgCh-CNp and CNFs... 8 S6. Electronic conductivities (I/V curves and calculated values)... 9 S7. First cycle data and SEM images after 1 st & 20 th cycle: CNps with different binders S8. TEM and HR-TEM images of AgCh-CNp after first recharge S9. XPS data of AgCh-CNp before and after cycling S10. Raman spectra and XPS data of AgCh-CNp S11. FT-IR data of AgCh-CNp S12. New combination: AgNW-RuO 2 NW-chitin CNp Table S1. Surface area and average pore size of AgCh-CNp Table S2. Gurley (time) values of AgCh-CNp and reference... 16

3 Experimental section Materials: Squid pen β-chitin (extracted according to conventional protocol), 1 1,1,1,3,3,3- hexafluoro-2-propanol (HFIP) (Halocarbon, USA), and silver nanowires dispersed in ethanol (AgNW/EtOH solution) (Nanopyxis, Korea) were used as received. Preparation of chitin solution: The chitin/hfip solution (0.1% w/v) was made by dissolving β-chitin powder in HFIP over a period of two days under stirring. HFIP is a toxic solvent and particular care is required during handling. All the following procedures were performed in a fume hood. Preparation of AgCh-CNp: 12 g of AgNW/EtOH solution (0.5 wt%) and 0.6 ml of chitin/hfip solution (0.1% w/v) were mixed in a 30 ml vial. The masses of the AgNW and the chitin were 0.06 g and g, respectively. Phase separation occurred after mixing due to the difference of chitin s solubility in HFIP and EtOH. In detail, bubbles of chitin/hfip alcogel were immediately precipitated to the bottom of the vial after mixing. Then, in order to bind the AgNW with chitin, this phase-separated mixture was sonicated for 2 min using an ultrasonic processor (VCX 500, SONICS & MATERIALS, power 500 W and frequency 22 khz). During the sonication process, the bubbles of chitin/hfip alcogel were broken up. Therefore, the chitin came out from the bubbles and became bound to the AgNWs. This sonication-assisted binding process was similar to the liquid liquid diffusion-based crystallization process. The ultrasonicated mixture was vacuum-filtrated for a few seconds using a glass microfiber filter (Whatman , pore size = 700 nm) to form the porous AgCh-CNp. For ease of stripping in the final step, a hydrophobic surface treatment was applied to this glass microfiber filter. The resultant wet AgCh-CNp attached to the glass microfiber filter was heat-treated at 100 C for 1 h to eliminate residual HFIP and EtOH. Finally, 45-µm-thick AgCh-CNp was obtained by stripping it from the glass microfiber filter. 1

4 Preparation of carbon nanofibers: For the reference electrode, free-standing carbon nanofibers (CNFs) without any kind of binder were synthesized by electrospinning and subsequent two-step calcinations. The electrospinning solution included 1 g of PAN dissolved in 6 g of N,N-dimethylformamide (DMF). After the electrospinning, the electrospun PAN NFs were thermally treated in a box furnace at 250 o C for 1 h in air atmosphere. Then, for carbonization, the stabilized NFs were heated to 1000 o C at a heating rate of 10 o C min -1 and maintained at that temperature for 2 h in a tube furnace surrounded by flowing Ar atmosphere. After cooling down, CNFs were finally obtained. Material characterization: Morphological elemental distribution of the AgCh-CNp was determined by field-emission scanning electron microscopy (FE-SEM, Nova 230, FEI), highresolution transmission electron microscopy, and energy-dispersive X-ray spectroscopy with a scanning transmission electron microscope (Tecnai F30 S-Twin, FEI for HR-TEM, EDS and STEM; Titan cubed G for ex situ HR-TEM). HR-TEM specimens were prepared using a focused ion beam (Quanta 3D FEG, FEI). Crystal structures of AgCh-CNp and Li 2 O 2 were characterized by X-ray diffractometer (D/MAX-2500, RIGAKU with Cu Kα (λ = 1.54 A )). In order to confirm the discharge products, Raman spectra and X-ray photoelectron spectroscopy were performed using ARAMIS (Horiba Jobin Yvon, France) with a 532 nm laser source and Thermo VG Scientific (MultiLab 2000). Electronic conductivities of all of samples were measured on the basis of I-V values (Semiconductor parameter analyzer, 4155A, HEWLETT PACKARD, USA). To verify unwanted by-products, Fourier-transform infrared (FT-IR) analyses were conducted. The surface area and porous features of AgCh- CNp were measured by the Brunauer-Emmett-Teller (BET) method (ASAP 2020 surface-area analyzer, Micromeritics, USA). The average particle size was measured by dynamic light scattering (DLS) analysis (ELS-Z2, Otsuka Electronics). The wettability tests of the AgCh- 2

5 CNp and CNFs were conducted by contact angle analyzer (Touch Type Phoenix 300 Touch, Surface Electro Optics). The gurley numbers of AgCh-CNp and CNFs were measured by PMI (Capillary Flow Porometer, CFP-1500AE, Porous Materials Inc, USA). Chemical stability of AgCh-CNp toward O - 2 : To confirm the stability of the chitin as a binder biopolymer, we put 0.4 g of the chitin powder and 0.4 g of KO 2 or Li 2 O 2 powder in a container and mixed them together by ball-milling with several ZrO 2 milling balls for 4 h. After ball-milling, the container was transferred to a glove box filled with Ar gas for XRD analysis. Electrochemical measurements: For Li-O 2 cell testing, punched conducting paper (AgCh- CNp, 11.8 Ø punch used) was installed as the air electrode in a Swagelok cell without the requirement of a large amount of any conducting agent (e.g., super P and ketjen black) and binders. The total weight of the AgCh-CNp was in the range 1.5 to 6.0 mg cm -2, due to the process of vacuum filtration that is not easy to control the horizontality. All of the Li-O 2 cells in this study were constructed in a glove box filled with Ar; the cell components were composed of AgCh-CNp with a gas diffusion layer (CNL Energy, GDL 10BC) to allow breathing of O 2 as cathode, Li metal as anode, and a separator (Whatman, glass microfiber filters, 12.8 Ø); as an electrolyte, 80 µl of 1 M bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) in tetra(ethylene) glycol dimethyl ether (TEGDME) was used. The cell performance was evaluated using a charge-discharge cycler (Maccor, USA). Cyclic voltammetry (CV) in the voltage range of V and Impedance spectroscopy (EIS) in the frequency range of Hz with 5 mv amplitude were performed by Zive SP1 (ZIVELAB). To avoid CO 2 and H 2 O contamination, all of the Li-O 2 cells were operated under 1 atm (760 Torr) of pure 3

6 O 2. Before each test, a 6 h rest time was taken for electrolyte uptake and O 2 equilibrium in the conducting paper. The entire evaluation process was conducted at room temperature. <Figure S1> Figure S1. Schematic illustration of a liquid diffusion-induced crystallization method to prepare AgCh-CNp. 4

7 <Figure S2> Figure S2. Photographs of AgNW in EtOH, AgNW in EtOH/HFIP, AgNW-chitin in EtOH/HFIP, AgNW-PMMA in EtOH/HFIP, and AgNW-PVDF in EtOH/NMP solutions. 5

8 <Figure S3> Figure S3. Dynamic Light Scattering (DLS) analyses of (a) AgNW in EtOH, (b) AgNW in EtOH/HFIP, (c) AgNW-chitin in EtOH/HFIP, (d) AgNW-PMMA in EtOH/HFIP, and (e) AgNW-PVDF in EtOH/NMP solutions. 6

9 <Figure S4> Figure S4. (a) N 2 -sorption measurements of AgCh-CNps according to the varying weight ratio of AgNW to chitin. (b-d) SEM images of AgCh-CNps according to the varying weight ratio of AgNW to chitin; AgNW:chitin = 10:1 (b), 50:1 (c), and 100:1 (d). The yellow-dotted circles indicate chitin supporting AgNWs. The scale bars are 1 µm. 7

10 <Figure S5> Figure S5. Contact angles of (a,b) 1 M LiTFSI/TEGDME electrolyte and (c,d) water droplets on the surfaces of AgCh-CNp, and CNFs electrodes. 8

11 <Figure S6> (a) Current (A) AgNW-bare AgCh-CNp (100:1) CNFs AgPMMA-CNp (100:1) AgPVDF-CNp (100:1) (b) Material AgNW-bare AgCh-CNp (100:1) I/V [ma V -1 ] Material I/V [ma V -1 ] AgPMMA- CNp (100:1) AgPVDF- CNp (100:1) CNFs Voltage (V) Figure S6. (a) I-V curves of bare AgNW, CNps with different binders and CNFs. (b) I/V values corresponding to the slopes shown in (a). 9

12 <Figure S7> Figure S7. First full discharge/charge curves of the Li-O 2 cells with (a) AgCh-CNp, (b) AgPVDF-CNp, and (c) AgPMMA-CNp at 0.2 ma cm -2 with fixed cut-off voltages of 2.35 and 4.35 V vs. Li/Li +. (d-f) SEM images corresponding to (a-c) after first full recharge, respectively. Ex-situ SEM images of recharged (g) AgCh-CNp, (h) AgPVDF-CNp and (i) AgPMMA-CNp after 20th cycle. 10

13 <Figure S8> Figure S8. (a) TEM and (b) HR-TEM images of AgNW in AgCh-CNp after first recharge. 11

14 <Figure S9> bare AgCh-CNp Ag 3d Intensity (a. u.) After 1st charge Ag 2 O Ag AgO After 20th charge Binding energy (ev) Figure S9. XPS data of the AgCh-CNp before and after cycling. 12

15 <Figure S10> Figure S10. Raman spectra of AgCh-CNp to confirm (a) Li 2 O 2 and (b) Li 2 CO 3 after the first full discharge. (c) XPS data of AgCh-CNp after the first full discharge and charge 13

16 <Figure S11> Absorbance Li 2 CO 3 (electrolyte decomposition) 1st full discharge 50th recharge Li 2 O Wavenumber (cm -1 ) Li-acetate Li 2 CO 3 Li 2 O 2 air exposure Li 2 O 2 Figure S11. FT-IR data of AgCh-CNp after the first full discharge and 50th recharge. 14

17 <Figure S12> Figure S12. (a) SEM image of CNp composed of new combination (AgNW-RuO 2 NWschitin). (b) Discharge and charge profiles of the Li-O 2 cell with AgNW-RuO 2 NWs-chitin CNp for 5 cycles. 15

18 Table S1. Surface area and average pore size of AgCh-CNp according to the varying weight ratios of AgNW to chitin. AgNW:chitin Surface area (m 2 /g) Avg. Pore size (nm) 10 : : : Table S2. Gurley (time) values of commercially available glass paper and AgCh-CNp, showing respective air permeability. Sample Avg. Gurley value (sec/100ml/sq In.) Glass paper AgCh-CNp

19 Supporting Reference (1) Chaussard, G.; Domard, A. New Aspects of the Extraction of Chitin from Squid Pens. Biomacromolecules 2004, 5,