Supplementary Information

A Facile Strategy toward Sodium-ion

Batteries with Ultra-long Cycle Life and

High Initial Coulombic Efficiency: Free-

standing Porous Carbon Nanofiber Film

Derived from Bacterial Cellulose

EXPERIMENTAL SECTION

Material synthesis

The BC membrane was bought from Hainan Yide Foods Co, Ltd. Firstly, the

membrane was washed by deionized water and cut into small pieces. The pieces were

frozen in liquid nitrogen (-196 °C), subsequently freeze-dried in lyophilizer. Finally,

the as-obtained samples were carbonized in an argon atmosphere at 5 °C min-1 to 1100

°C，1300 °C and 1500 °C for 6h respectively.

Material Characterization

The morphology of CNFs was investigated by field emission SEM (SU8200, Hitachi)

and TEM (JEOL, JEM-2100F). The crystal was study by XRD (TTR-III, Rigaku,

Japan) with a Cu Kα radiation. Raman scattering spectra were recorded with a

Renishaw System 2000 spectrometer. The elements content and chemical state of

samples were analyzed by XPS (Thermo-VG Scientific, ESCALAB 250).An ASAP

2020 Accelerated Surface Area and Porosimetry instrument was used to measure the

materials’ nitrogen adsorption and desorption isotherms

Electrochemical Measurements

The electrochemical experiments were conducted in CR2032 coin cells assembled in

an argon-filled glove box. The as-obtained films can directly use as electrode (about

0.5 mg cm-2). The electrolyte was 1M sodium triflate (NaOTf) dissolved in diglyme.

Using sodium foil and Whatman GF/D glass fibers as counter electrode and separator,

respectively. A battery test system (Neware, BTS-610) was applied to evaluate the

charge/discharge profiles with a voltage window of 0.001-3 V. CV curves were

acquired from electrochemical workstation (CHI 660D, Chenhua Instrument

Company, Shanghai, China). Electrochemical impedance spectroscopy (EIS) was also

conducted on the electrochemical workstation in the frequency range from 0.01 Hz to

100 kHz.

Figure S1. SEM images of bacterial cellulose.

Figure S2. The digital photo of the cross section of the bacterial cellulose.

Figure S3. SEM images of a) CNFs-1100 and b) CNFs-1500.

Figure S4. Fitted Raman spectra of a) CNFs-1100, b) CNFs-1300 and c) CNFs-1500.

Figure S5. The curve of TGA of bacterial cellulose.

Figure S6. a) XPS spectra of CNFs-1100, CNFs-1300 and CNFs-1500. XPS C 1s of b) CNFs-

1100, c) CNFs-1300 and d) CNFs-1500.

Figure S7. CV curves for first three cycles at a scan rate of 0.1 mV s-1 of CNFs-1100.

Figure S8. CV curves for first three cycles at a scan rate of 0.1 mV s-1 of CNFs-1500.

Figure S9. Galvanostatic charge/discharge curves for first three cycles at 0.2 A g-1 of CNFs-1100.

Figure S10. Galvanostatic charge/discharge curves for first three cycles at 0.2 A g-1 of CNFs-1500.

Figure S11. Galvanostatic charge/discharge curves at different rate of a) CNFs-1100, b) CNFs-

1300 and c) CNFs-1500.

Figure S12. SEM images of CNFs-1300 after rate performance test.

Figure S13. a) Galvanostatic charge/discharge curves for first three cycles and b) Cycling stability

at 0.2 A g-1 of CNFs-1300 for NaClO4 in EC/DMC electrolyte.

Figure S14. Rate capacity at different rates as indicated of CNFs-1300 for NaClO4 in EC/DMC

electrolyte.

Figure S15. Nyquist plots of the CNFs-1300 electrodes in DGM and EC/DMC electrolytes after 5 cycles.