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Page 4 of 14 Liang et al. Energy Mater 2023;3:300006 https://dx.doi.org/10.20517/energymater.2022.63

Preparation of positive electrode
Sublimated sulfur and multi-walled carbon nanotubes (MWCNTs) were ball-milled at a ratio of 4:1 for 12 h
to obtain evenly mixed S/MWCNT materials. The S/MWCNT materials were kept in a reaction vessel at
155 °C for 12 h to obtain the S/MWCNT composite material. As shown in Supplementary Figure 1, the
sulfur ratio in S/MWCNT composite is 78.9%. The S/MWCNT composite material, Super P, and PVDF
dissolved in NMP in a mass ratio of 7:2:1 to obtain the sulfur cathode slurry. Therefore, the content of sulfur
in the cathode is 78.9% × 70% = 55.2%. The obtained slurry was evenly coated on Al foil with a scraper and
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baked at 60 °C for 12 h. The mass loading of S in the electrode was about 1.2 mg cm .

Material characterization
The phase analysis of the material was performed with a D/MAX2500V rotating target X-ray diffractometer
(XRD) at an angle of 10°-40°. Each material phase could then be determined by the position and intensity of
the different characteristic peaks corresponding to the standard Powder Diffraction File (PDF). The surface
morphology of the prepared materials was analyzed by using a Zeiss Gemini 500 thermal field emission
scanning electron microscope. The corresponding X-ray energy dispersive spectrometer (EDS) was used for
plane scanning to determine the type and distribution of elements. The morphology of the material was
characterized by scanning electron microscopy (SEM). Gold spraying was carried out before SEM
observations, and the spray time was set to 60 s.

Battery assembly and measurements
The batteries were assembled with a CR2032 battery shell. The S/MWCNT composite material was used as
the positive electrode and lithium metal as the negative electrode. Three different batteries were assembled
with a polypropylene (PP) separator, a GNF separator, and a CZGNF separator, respectively. In the case of
the CZGNF separator, the side containing ZIF-67 and C faced the positive electrode. The Li-S batteries
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employed 1.0 M lithium bis(fluoromethanesulfonyl)imide (LiTFSI) in dimethoxy ethane: dioxolane (DME:
DOL, 1:1 v/v) with 2.0 % LiNO as the electrolyte additive. The electrolyte was 50 μL and the
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electrolyte/sulfur ratio (E/S ratio) was 27 μL mg at the time of cell assembly. All the above operations were
carried out in a glove box filled with Ar. Electrochemical tests of the assembled batteries were carried out,
such as charging and discharge performance testing, cyclic performance testing, electrochemical impedance
spectroscopy (EIS), cyclic voltammetry (CV), etc.

RESULTS AND DISCUSSION
Figure 1 shows the synthesis and functional structure of the CZGNF nanofiber separator. The separator is a
two-layer structure, the first layer of pure gelatin-based nanofiber film is prepared by the electrospinning
method, and then on the basis of this layer, the ZIF-67-C -gelatin-based nanofiber separator is prepared by
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electrospinning method. Finally, the nanofiber separator is placed in an oven for drying to obtain the
CZGNF separators with different functions on both sides. The CZGNF diaphragm facing the positive side
can chemically adsorb polysulfides and provide conversion sites for lithium polysulfide, while the negative
side can improve the amount of lithium-ion migration and prevent lithium dendrites from being generated.

In this work, gelatin was used as the separator substrate. Fourier transform infrared (FTIR) analysis of GNF
separator was performed to verify its gelatin groups. Figure 2A shows that the characteristic peaks of gelatin
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groups are located around 1200-1650 cm and 2900-3100 cm -1[29] . Among them, the amine groups and
carboxyl groups of gelatins are hydrophilic groups, so that gelatin has a good liquid absorption rate and the
ionic conductivity of the gelatin substrate is improved. The XRD patterns of ZIF-67, GNF, and CZGNF
[Figure 2B] reflect the phase structures of the three separators. The XRD pattern of CZGNF separator did
not show strong reflections due to the low doping content of ZIF-67 particles, although the presence of
cobalt element could be proved in EDS analysis. In addition, the main peak in the XRD pattern for the
CZGNF separator corresponds to that of C (PDF#47-0787), which proves the successful doping of C .
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