Department of Materials Science and Engineering, Research Institute of Advanced

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1 Supporting Information High Energy Organic Cathode for Sodium Rechargeable Batteries Haegyeom Kim 1, Ji Eon Kwon 2, Byungju Lee 1, Jihyun Hong 1, Minah Lee 3, Soo Young Park 2*, and Kisuk Kang 1,4 * 1. Department of Materials Science and Engineering, Research Institute of Advanced Materials (RIAM), Seoul National University, 1 Gwanak Road, Seoul , Republic of Korea 2. Center for Supramolecular Optoelectronic Materials (CSOM), Department of Materials Science and Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul , Republic of Korea. 3. Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 335 Science Road, Daejeon , Republic of Korea 4. Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul National University, Seoul , Republic of Korea * Corresponding Author. (S. Y. Park) Tel.: Fax.: address: parksy@snu.ac.kr

2 (K. Kang) Tel.: Fax.: address: 1. Experiments 1.1. Synthesis of C 6 Cl 4 O 2 /CMK composite The C 6 Cl 4 O 2 /CMK composite was prepared by a simple solution impregnation method. CMK-3 (100 mg) was added to 5 ml DMF solution containing C 6 Cl 4 O 2 (150 mg). Then, the solvent of mixture was slowly removed by spontaneous evaporation under ambient condition. The composite powder was carefully collected and the remnant solvent was fully removed under vacuum Calculation details We conducted geometry optimization and energy calculation of the molecules using density functional theory (DFT) calculation tool, Gaussian 09 quantum chemistry package. 1 All calculations were conducted with spin-unrestricted DFT, based on Becke-Lee-Yang-Parr (B3LYP) hybrid exchange-correlation functional 2-4 and the 6-311G(d,p) basis set. 5-7 Effect of the solvent was considered by using the polarizable continuum model (PCM). Dielectric constant = 70 was applied to model the electrolyte used in the experiment (EC:PC:DMC=45:45:10).

3 1.3. Characterization The molecular structure of the samples was analyzed with fourier transform infrared spectroscopy (FTIR, Hyperion 3000, Bruker, USA ). Thermogravimetric (TGA, Q-5000 IR, TA Instruments, USA) analysis was used to determine the content of C 6 Cl 4 O 2 in the composite. The morphology of the samples was verified using field-emission scanning electron microscopy (FE-SEM, SUPRA 55VP, Carl Zeiss, Germany). UV/Vis absorbance spectra of the samples were obtained using a V/650 spectrophotometer (Jasco Inc., Japan) in the range of nm Electrochemical measurements Electrodes were prepared by mixing the active material (C 6 Cl 4 O 2, 40 wt%) with poly (tetrafluoroethylene) binder (PTFE, 20 wt%) and conductive carbon black (Super-P, 40 wt%). Test cells were assembled in a glove box into a two-electrode configuration with a Na metal counter electrode. A separator of grade GF/F (Whatman, USA) was used. 1 M NaClO 4 electrolyte in a 45:45:10 mixture of ethylene carbonate, propylene carbonate, and dimethyl carbonate (Techno Semichem) was used. Electrochemical profiles were obtained using a multichannel potentio-galvanostat (WonATech).

4 2. Supporting Figures Figure S1. HOMO structure of C 6 F 4 O 2 and C 6 Cl 4 O 2 after accepting two electrons.

5 Figure S2. Typical charge/discharge profile of C 6 F 4 O 2.

6 Figure S3. Typical discharge profiles of C 6 Cl 4 O 2 electrodes in Na cells (upper) and Li cells (lower).

7 Figure S4. Ex situ XPS analysis of C 6 F 4 O 2. XPS peaks of a. Na 1s, b. O 1s, and c. Cl 2p during Na insertion and extraction. (black: before cycling, red: after discharge, blue: after charge)

8 Stored in the electrolyte Fresh powder Intensity (a. u.) Wavenumber (cm -1 ) Figure S5. Chemical stability of C 6 Cl 4 O 2 in the surrounding electrolyte. FTIR vibrations of C 6 Cl 4 O 2 powder were monitored after 24 hours storage in the electrolyte.

9 Figure S6. a. Photo image of (i) the fresh electrolyte and (ii) the electrolyte storing C 6 Cl 4 O 2 for 12 hours. b. FTIR spectra of the fresh electrolyte, the electrolyte storing C 6 Cl 4 O 2 for 12 hours, and C 6 Cl 4 O 2 power.

10 Figure S7. FTIR spectra of C 6 Cl 4 O 2 /CMK, C 6 Cl 4 O 2, and CMK. The molecular structure of C 6 Cl 4 O 2 was maintained after incorporation into the CMK matrix.

11 Figure S8. XPS analyses of a. O1s and b. Cl2p of C 6 Cl 4 O 2 /CMK composite (red) and C 6 Cl 4 O 2 (black). The general shapes of O 1s and Cl 2p peaks of C 6 Cl 4 O 2 molecules were not altered after confinement in carbon matrix. However, the peak positions were slightly shifted to higher binding energy, which indicates the change in the number of π-electrons of C 6 Cl 4 O 2 molecules. The up-shifts of binding energy results from the π-π interactions between carbon matrix and C 6 Cl 4 O 2 molecules. The strong π-π interactions in combination with physical confinement could partially suppress the dissolution of active molecules in the electrolyte.

12 Weight (%) ~42 % Temperature ( o C) Figure S9. Thermogravimetric (TGA) curve of C 6 Cl 5 O 2 /CMK. The C 6 Cl 4 O 2 content of the composite was ~42 wt% as determined by TGA analyses.

13 Figure S10. SEM images of a. C 6 Cl 4 O 2 power and b. C 6 Cl 4 O 2 /CMK composite. The C 6 Cl 4 O 2 was integrated into the CMK matrix without segregation. While micron-sized C 6 Cl 4 O 2 particles were observed in the initial mixture of C 6 Cl 4 O 2 and CMK, no such particles were observed in the composite material.

14 Figure S11. SEM image of C 6 Cl 4 O 2 /CMK. e. and f. EDS mapping images of O and Cl, respectively.

15 4 Voltage (V vs. Na) Capacity (mah g -1 ) Figure S12. Charge/discharge profile of CMK electrode.

16 Table S1. LUMO energy calculated at with/without applying implicit solvation model. The adoption of implicit solvation model upshifts LUMO levels of molecules by 0.1 ev in X=Br case, by 0.1~0.2 ev in X=Cl case and by 0.2~0.4 ev in X=F case, probably because elements with higher electronegativity are stabilized in environment of highly polar solvents. References 1. Frisch, M. Gaussian 09 revision D. 01, Lee, T.; Yang, W.; and Parr, R. Development of Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B, 1988, 37, Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields. J. Phys. Chem., 1994, 98, Becke, A. D. Density functional thermochemistry. III. The role of exact exchange. J. Chem. Phys., 1993, 98, Liang, Y.; Zhang, P.; Chen, J. Function-oriented design of conjugated carbonyl compound electrodes for high energy lithium batteries. Chem. Sci. 2013, 4, Burkhardt, S. E.; Bois, J.; Tarascon, J. M.; Henning, R. G.; Abruna, H. D. Li-Carboxylate Anode Structure-Property Relationships from Molecular Modeling. Chem. Mater. 2013, 25, Wang, H.; Sun, Z.; Zhang, Y.; Liang, M.; Jia, D.; Xue, S. Charge Transport Limitations of Redox Mediators in Dye-Sensitized Solar Cells: Investigation Based on a Quasi-Linear Model. J. Phys. Chem. C 2014, 118, 60