A BC-loaded ZIF-67-derived CNF / CoS-Co9S8-NC composite material and a preparation and application method thereof

Abstract

The application discloses a BC loaded ZIF-67 derived CNF / CoS-Co9S8-NC composite material and a preparation and application method thereof, and preparation comprises the following steps: BC / ZIF-67 is prepared; BC / ZIF-67 is uniformly mixed with sulfur powder at a mass ratio of 1:4, is placed in a porcelain boat, and then is subjected to high-temperature sulfuration and carbonization treatment under an Ar atmosphere; firstly, the temperature is raised to 300 DEG C at a temperature raising rate of 2 DEG C / min, isothermal preservation is carried out for 4 h, then the temperature is raised to 600-700 DEG C at a temperature raising rate of 5 DEG C / min, isothermal preservation is carried out for 2-4 h, and a CNF / CoS-Co9S8-NC composite material is obtained; the material improves the shuttle effect of polysulfides, and after being applied to modify a diaphragm material, the Li-S battery has good rate performance and cycle stability; and the preparation method has the advantages of simple process, short preparation period and the like.

Description

TECHNICAL FIELD

[0001] The application relates to the field of functional materials, in particular to a BC-loaded ZIF-67 derived CNF / CoS-Co9S8-NC composite material and a preparation and application method thereof. BACKGROUND

[0002] Research shows that among the many compounds of cobalt sulfide, CoS, CoS2, Co3S4, Co9S8, etc. all show excellent adsorption and catalysis to polysulfides. And there is evidence that CoS has excellent chemical adsorption capacity for polysulfides, but if S is partially missing in CoS, the proportion of Co components will increase, which can improve the electrical conductivity and the electrocatalytic effect of promoting the conversion of polysulfides. Therefore, many researchers have designed a series of heterogeneous catalysts with CoS / Co9S8 polar heterostructures, which not only retain the polar adsorption of CoS, but also improve the electrical conductivity of Co9S8, which also improves the electrocatalytic activity of the polar catalyst to promote the conversion of LiPSs to Li2S2 / Li2S, effectively promoting the kinetics of the battery redox reaction. For example, [Wang N, Chen B, Qin K, et al. Rational design of Co9S8 / CoO heterostructures with well-defined interfaces for lithium sulfur batteries: A study of synergistic adsorption-electrocatalysis function [J]. Nano Energy, 2019, 60: 332-339] uses ZIF-67 as a template to successfully synthesize three-dimensional (3D) crumpled carbon nanosheets (CCNSs) decorated with different polar nanomaterials (Co / CoO, CoS / Co9S8 and CoS2), and uses them as an intermediate interlayer for Li-S batteries. Benefiting from the polar adsorption and electrocatalytic effect of the CoS / Co9S8 heterostructure and the high electrical conductivity of the three-dimensional (3D) crumpled carbon nanosheets, the CoS / Co9S8@CCNSs-modified interlayer effectively improves the adsorption and catalytic conversion of LiPSs to Li2S2 / Li2S. The electrochemical test results show that the Li-S battery using the CoS / Co9S8@CCNSs interlayer still has a discharge capacity of 911 mAh g -1 after 100 cycles at a current density of 0.2C, and has a specific capacity of 600 mAh g -1 after 500 cycles at 1C, showing excellent long cycle performance, which provides a new idea for the application of porous carbon / polar heterostructure sulfides in Li-S batteries.

[0003] However, the surface energy of ZIF-67 particles is high, and the particles are prone to stacking, thereby causing the adsorption and catalytic performance of polysulfides to be weakened. When used as an intermediate interlayer of a Li-S battery, the shuttle effect causes problems of battery capacity loss, shortened service life and reduced safety. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a BC-loaded ZIF-67-derived CNF / CoS-Co9S8-NC composite material which improves the shuttle effect of polysulfides, a preparation method and application thereof, and after being applied to modify a separator material, the Li-S battery has good rate performance and cycle stability, and the preparation method is simple in process and short in preparation period.

[0005] In order to achieve the above-mentioned purpose, the following technical solutions are adopted in the present application:

[0006] A preparation method of a BC-loaded ZIF-67-derived CNF / CoS-Co9S8-NC composite material, comprising the following steps:

[0007] Step 1: 408 mg of 2-methylimidazole is dissolved in 20 ml of methanol to form an A solution;

[0008] 179 mg of Co(NO3)2·6H2O is dissolved in 20 ml of methanol to form a B solution, 50 mg of bacterial cellulose is added to the B solution and stirred uniformly;

[0009] Step 2: Then the A solution is quickly poured into the B solution containing bacterial cellulose, and after magnetic stirring to fully mix uniformly, it is left to stand at room temperature for 12 h, vacuum filtration and vacuum drying to obtain BC / ZIF-67;

[0010] Step 3: BC / ZIF-67 and sulfur powder are fully mixed uniformly according to a mass ratio of 1:4, placed in a porcelain boat, and then subjected to high-temperature sulfuration and carbonization treatment under an Ar atmosphere, first heated to 300℃ at a heating rate of 2℃ / min, and then heated to 600-700℃ at a heating rate of 5℃ / min, and kept for 2-4 hours to obtain a CNF / CoS-Co9S8-NC composite material.

[0011] The present application also has the following technical features:

[0012] Preferably, the magnetic stirring in step 2 is magnetic stirring for 10 min.

[0013] Preferably, the vacuum drying in step 2 is vacuum drying at 70℃ for 24 h.

[0014] The application also protects a CNF / CoS-Co9S8-NC composite material prepared by the above method and its application in modifying the separator of a Li-S battery, the application method comprising: after CNF / CoS-Co9S8-NC and PVDF are mixed and ground in a mass ratio of 8:2, NMP is added to prepare a uniform slightly flowing slurry, and the slurry is uniformly coated on a commercial polypropylene separator for a Li-S battery to obtain a CNF / CoS-Co9S8-NC modified separator.

[0015] Compared with the prior art, the application has the following technical effects:

[0016] The CNF / CoS-Co9S8-NC composite material with a heterogeneous structure catalyst is prepared by one-step sulfidation and carbonization of BC / ZIF-67 in a tube furnace under an argon atmosphere, the prepared CNF / CoS-Co9S8-NC composite material has a super-fine network structure of BC, the super-fine network structure provides a strong conductive network and has a certain physical limiting effect on polysulfides; and the strong conductive network can alleviate the agglomeration and stacking problem of ZIF-67, so that more active sites of the composite material are exposed; the CNF / CoS-Co9S8-NC composite material has a polar adsorption effect of the ZIF-67 derived CoS-Co9S8 heterogeneous structure and high electronic conductivity and electrocatalytic activity, which effectively improves the shuttle effect of polysulfides and also catalyzes the rapid conversion of LiPSs to Li2S2 / Li2S; after the CNF / CoS-Co9S8-NC composite material is applied to modify a separator material, the Li-S battery has good rate performance and cycle stability; the preparation method is simple and has a short preparation period. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The XRD graph of CNF / CoS-Co9S8-NC synthesized in Example 1 and Comparative Example 1 of the application;

[0018] Figure 2 The SEM graph of commercial bacterial cellulose BC used in the application;

[0019] Figure 3 The SEM graph of BC / ZIF-67 synthesized in Example 1 of the application;

[0020] Figure 4 The SEM graph of CNF / CoS-Co9S8-NC synthesized in Example 1 of the application;

[0021] Figure 5 The SEM graph of the surface morphology of a commercial polypropylene separator modified by CNF / CoS-Co9S8-NC synthesized in Example 1 of the application;

[0022] Figure 6 Figure 6 is a comparison chart of the rate performance of Li-S batteries using CNF / CoS-NC modified separators and CNF / CoS-Co9S8-NC modified separators synthesized in Example 1 and Comparative Example 1 of the present application;

[0023] Figure 7 Figure 7 is a comparison chart of the cycle performance of Li-S batteries using CNF / CoS-NC modified separators and CNF / CoS-Co9S8-NC modified separators synthesized in Example 1 and Comparative Example 1 of the present application at a current density of 0.2C;

[0024] Figure 8 Figure 8 is a chart of the cycle performance of Li-S batteries using CNF / CoS-NC modified separators and CNF / CoS-Co9S8-NC modified separators synthesized in Example 1 of the present application at a current density of 2C;

[0025] Figure 9 Figure 9 is a comparison chart of the impedance of Li-S batteries using CNF / CoS-NC modified separators and CNF / CoS-Co9S8-NC modified separators synthesized in Example 1 and Comparative Example 1 of the present application;

[0026] Figure 10 Figure 10 is a comparison chart of the blocking effect of LiPSs of CNF / CoS-NC modified separators and CNF / CoS-Co9S8-NC modified separators synthesized in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0027] The specific content of the present application is further explained in detail in the following examples.

[0028] First, the raw materials appearing in the following examples are described:

[0029] Bacterial cellulose (BC) is a rich biopolymer in nature and is a functional biological nanomaterial with unique structural advantages. BC is composed of unique filamentous fibers with a fiber diameter of 50-100 nm and a length of about 20 μm. As shown in FIG. 1, the commercial BC used in the present application has a three-dimensional network structure with an ultra-fine network structure. Figure 2

[0030] The carbon nanofiber (CNF) in the present application is obtained by high-temperature carbonization of BC.

[0031] ​ZIF-67 is one of the MOFs materials, the unit molecular formula is C4H6N2.Co, the ligand is 2-methyl imidazole, and the coordination metal is Co, which can be prepared by mixing Co(NO3)2·6H2O and 2-methyl imidazole. ZIF-67 is treated by high-temperature solid-phase method of tube furnace sulfuration and carbonization, and CoS-Co9S8-NC can be obtained.

[0032] Example 1

[0033] 1) 408 mg of 2-methyl imidazole was dissolved in 20 ml of methanol to form solution A; 179 mg of Co(NO3)2·6H2O was dissolved in 20 ml of methanol to form solution B;

[0034] 2) 50 mg of bacterial cellulose was added to the B solution and stirred uniformly, then the A solution was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was placed at room temperature for 12 h, vacuum filtration and vacuum drying at 70℃ for 24 h to obtain BC / ZIF-67;

[0035] 3) BC / ZIF-67 and sulfur powder were mixed uniformly according to a mass ratio of 1:4, placed in a porcelain boat, and then treated by high-temperature sulfuration and carbonization under Ar atmosphere, with a temperature rising rate of 2℃ / min to 300℃, and then kept for 4 h, and then with a temperature rising rate of 5℃ / min to 700℃, and then kept for 2 h to obtain CNF / CoS-Co9S8-NC composite material.

[0036] The obtained CNF / CoS-Co9S8-NC composite material was used to prepare CNF / CoS-Co9S8-NC modified diaphragm for Li-S battery;

[0037] CNF / CoS-Co9S8-NC and PVDF (polyvinylidene fluoride) with a mass ratio of 8:2 were mixed and ground, then NMP (N-methyl pyrrolidone) was added to prepare a uniform slurry, which was uniformly coated on a commercial polypropylene diaphragm for Li-S battery to obtain a CNF / CoS-Co9S8-NC modified diaphragm.

[0038] Example 2

[0039] 1) 408 mg of 2-methyl imidazole was dissolved in 20 ml of methanol to form solution A; 179 mg of Co(NO3)2·6H2O was dissolved in 20 ml of methanol to form solution B;

[0040] 2) 50 mg of bacterial cellulose was added to the B solution and stirred uniformly, then the A solution was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was placed at room temperature for 12 h, vacuum filtration and vacuum drying at 70℃ for 24 h to obtain BC / ZIF-67;

[0041] 3) BC / ZIF-67 and sulfur powder were mixed uniformly at a mass ratio of 1:4, placed in a porcelain boat, and then subjected to high-temperature sulfuration and carbonization treatment under an Ar atmosphere, heated to 300°C at a heating rate of 2°C / min, kept at 300°C for 4 h, and then heated to 700°C at a heating rate of 5°C / min, kept at 700°C for 3 h to obtain CNF / CoS-Co9S8-NC composite material.

[0042] The CNF / CoS-Co9S8-NC composite material obtained was used to prepare CNF / CoS-Co9S8-NC modified separator for Li-S batteries.

[0043] CNF / CoS-Co9S8-NC and PVDF (polyvinylidene fluoride) were mixed and ground at a mass ratio of 8:2, and then NMP (N-methyl pyrrolidone) was added to prepare a uniform slurry, which was uniformly coated on a commercial polypropylene separator for Li-S batteries to obtain a CNF / CoS-Co9S8-NC modified separator.

[0044] Example 3

[0045] 1) 408 mg of 2-methylimidazole was dissolved in 20 ml of methanol to form solution A; 179 mg of Co(NO3)2·6H2O was dissolved in 20 ml of methanol to form solution B;

[0046] 2) 50 mg of bacterial cellulose was added to solution B and stirred uniformly, and then solution A was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was left to stand at room temperature for 12 h, vacuum filtration and vacuum drying at 70°C for 24 h to obtain BC / ZIF-67;

[0047] 3) BC / ZIF-67 and sulfur powder were mixed uniformly at a mass ratio of 1:4, placed in a porcelain boat, and then subjected to high-temperature sulfuration and carbonization treatment under an Ar atmosphere, heated to 300°C at a heating rate of 2°C / min, kept at 300°C for 4 h, and then heated to 700°C at a heating rate of 5°C / min, kept at 700°C for 4 h to obtain CNF / CoS-Co9S8-NC composite material.

[0048] The CNF / CoS-Co9S8-NC composite material obtained was used to prepare CNF / CoS-Co9S8-NC modified separator for Li-S batteries.

[0049] CNF / CoS-Co9S8-NC and PVDF (polyvinylidene fluoride) were mixed and ground at a mass ratio of 8:2, and then NMP (N-methyl pyrrolidone) was added to prepare a uniform slurry, which was uniformly coated on a commercial polypropylene separator for Li-S batteries to obtain a CNF / CoS-Co9S8-NC modified separator.

[0050] Example 4

[0051] 1) 408 mg of 2-methylimidazole was dissolved in 20 ml of methanol to form solution A; 179 mg of Co(N03)2-6H20 was dissolved in 20 ml of methanol to form solution B;

[0052] 2) 50 mg of bacterial cellulose was added to the B solution and stirred evenly, then the A solution was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was placed at room temperature for 12 h, vacuum filtration and vacuum drying at 70°C for 24 h to obtain BC / ZIF-67;

[0053] 3) BC / ZIF-67 was mixed with sulfur powder at a mass ratio of 1:4, placed in a porcelain boat, and then subjected to high-temperature sulfuration and carbonization treatment under Ar atmosphere, heated to 300°C at a heating rate of 2°C / min, kept for 4 h, and then heated to 600°C at a heating rate of 5°C / min, kept for 2 h to obtain CNF / CoS-Co9S8-NC composite material.

[0054] The obtained CNF / CoS-Co9S8-NC composite material was used to prepare CNF / CoS-Co9S8-NC modified separator for Li-S battery;

[0055] CNF / CoS-Co9S8-NC and PVDF (polyvinylidene fluoride) were mixed and ground at a mass ratio of 8:2, then NMP (N-methyl pyrrolidone) was added to prepare a uniform slurry, which was uniformly coated on a commercial polypropylene separator for Li-S battery to obtain a CNF / CoS-Co9S8-NC modified separator.

[0056] Example 5

[0057] 1) 408 mg of 2-methylimidazole was dissolved in 20 ml of methanol to form solution A; 179 mg of Co(N03)2-6H20 was dissolved in 20 ml of methanol to form solution B;

[0058] 2) 50 mg of bacterial cellulose was added to the B solution and stirred evenly, then the A solution was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was placed at room temperature for 12 h, vacuum filtration and vacuum drying at 70°C for 24 h to obtain BC / ZIF-67;

[0059] 3) BC / ZIF-67 was mixed with sulfur powder at a mass ratio of 1:4, placed in a porcelain boat, and then subjected to high-temperature sulfuration and carbonization treatment under Ar atmosphere, heated to 300°C at a heating rate of 2°C / min, kept for 4 h, and then heated to 680°C at a heating rate of 5°C / min, kept for 3 h to obtain CNF / CoS-Co9S8-NC composite material.

[0060] CNF / CoS-Co9S8-NC composite material obtained is used to prepare CNF / CoS-Co9S8-NC modified diaphragm for Li-S battery;

[0061] CNF / CoS-Co9S8-NC and PVDF (polyvinylidene fluoride) in a mass ratio of 8:2 are mixed and ground, and then NMP (N-methyl pyrrolidone) is added to prepare a uniform slurry, which is uniformly coated on a commercial polypropylene diaphragm for Li-S battery to obtain the CNF / CoS-Co9S8-NC modified diaphragm.

[0062] Example 6

[0063] 1) 408 mg of 2-methylimidazole was dissolved in 20 ml of methanol to form solution A; 179 mg of Co(NO3)2·6H2O was dissolved in 20 ml of methanol to form solution B;

[0064] 2) 50 mg of bacterial cellulose was added to the B solution and stirred uniformly, then the A solution was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was placed at room temperature for 12 h, vacuum filtration and vacuum drying at 70°C for 24 h to obtain BC / ZIF-67;

[0065] 3) BC / ZIF-67 and sulfur powder were mixed uniformly in a mass ratio of 1:4, placed in a porcelain boat, and then high-temperature sulfuration and carbonization treatment was carried out under Ar atmosphere, the temperature was raised to 300°C at a rate of 2°C / min, and the temperature was kept for 4 h, then the temperature was raised to 650°C at a rate of 5°C / min, and the temperature was kept for 4 h to obtain CNF / CoS-Co9S8-NC composite material.

[0066] CNF / CoS-Co9S8-NC composite material obtained is used to prepare CNF / CoS-Co9S8-NC modified diaphragm for Li-S battery;

[0067] CNF / CoS-Co9S8-NC and PVDF (polyvinylidene fluoride) in a mass ratio of 8:2 are mixed and ground, and then NMP (N-methyl pyrrolidone) is added to prepare a uniform slurry, which is uniformly coated on a commercial polypropylene diaphragm for Li-S battery to obtain the CNF / CoS-Co9S8-NC modified diaphragm.

[0068] Comparative Example 1

[0069] 1) 408 mg of 2-methylimidazole was dissolved in 20 ml of methanol to form solution A; 179 mg of Co(NO3)2·6H2O was dissolved in 20 ml of methanol to form solution B;

[0070] 2) 50 mg of bacterial cellulose was added to the B solution and stirred evenly, then the A solution was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was placed at room temperature for 12 h, vacuum filtration and vacuum drying at 70°C for 24 h to obtain BC / ZIF-67;

[0071] 3) BC / ZIF-67 and sulfur powder were mixed evenly according to a mass ratio of 1:4, placed in a porcelain boat, and then high-temperature sulfuration and carbonization treatment was carried out under Ar atmosphere, the temperature was raised to 300°C at a rate of 2°C / min, and the temperature was kept for 4 h, then the temperature was raised to 700°C at a rate of 5°C / min, and the temperature was kept for 0 h to obtain CNF / CoS-NC composite material.

[0072] The obtained CNF / CoS-NC composite material was used to prepare CNF / CoS-NC modified separator for Li-S battery;

[0073] CNF / CoS-NC and PVDF (polyvinylidene fluoride) with a mass ratio of 8:2 were mixed and ground, then NMP (N-methyl pyrrolidone) was added to prepare a uniform slurry, which was uniformly coated on a commercial polypropylene separator for Li-S battery to obtain a CNF / CoS-NC modified separator.

[0074] Comparative Example 2

[0075] 1) 408 mg of 2-methylimidazole was dissolved in 20 ml of methanol to form A solution; 179 mg of Co(NO3)2·6H2O was dissolved in 20 ml of methanol to form B solution;

[0076] 2) 50 mg of bacterial cellulose was added to the B solution and stirred evenly, then the A solution was quickly poured into the B solution containing BC, and after magnetic stirring for 10 min, it was placed at room temperature for 12 h, vacuum filtration and vacuum drying at 70°C for 24 h to obtain BC / ZIF-67;

[0077] 3) BC / ZIF-67 and sulfur powder were mixed evenly according to a mass ratio of 1:4, placed in a porcelain boat, and then high-temperature sulfuration and carbonization treatment was carried out under Ar atmosphere, the temperature was raised to 300°C at a rate of 2°C / min, and the temperature was kept for 4 h, then the temperature was raised to 600°C at a rate of 5°C / min, and the temperature was kept for 0 h to obtain CNF / CoS-NC composite material.

[0078] The obtained CNF / CoS-NC composite material was used to prepare CNF / CoS-NC modified separator for Li-S battery;

[0079] CNF / CoS-NC and PVDF (polyvinylidene fluoride) with a mass ratio of 8:2 were mixed and ground, and then NMP (N-methyl pyrrolidone) was added to prepare a uniform slurry, which was uniformly coated on a commercial polypropylene separator for Li-S batteries to obtain a CNF / CoS-NC modified separator.

[0080] The above examples all use CNF / CoS-Co9S8-NC prepared by the application as a modified separator for Li-S batteries. The Li-S batteries used are composed of a positive electrode, a negative electrode, a separator and an electrolyte. The positive electrode is MWCNTs / S, and the electrolyte is a Li-S battery electrolyte containing 1M (bis-trifluoromethylsulfonylimide lithium) LiTFSI + (1,2-dimethoxyethane) DME / (1,3-dioxolane) DOL (volume ratio 1:1) and adding 1% (wt) lithium nitrate (LiNO3). All assembly is carried out in an argon-filled glove box.

[0081] The CNF / CoS-Co9S8-NC composite material provided by the application is a BC-loaded ZIF-67-derived CNF / CoS-Co9S8-NC composite material with very excellent electrical conductivity and polarity, which is obtained by growing ZIF-67 on hydroxylated BC and then high-temperature sulfidation and high-temperature carbonization treatment. Figure 1 As shown in the figure, the Co in the CNF / CoS-Co9S8-NC synthesized in Example 1 and Comparative Example 1 is CoS-Co9S8 and CoS, respectively, which is caused by the change of carbonization holding time. When the carbonization holding time is prolonged, part of S in CoS escapes, forming a CoS-Co9S8 heterostructure. x S y When the carbonization holding time is prolonged, part of S in CoS escapes, forming a CoS-Co9S8 heterostructure.

[0082] The preparation method of the CNF / CoS-Co9S8-NC composite material disclosed by the application, the polar adsorption effect of CoS in the CoS-Co9S8 heterostructure formed and the high electronic conductivity and electrocatalytic activity of Co9S8 effectively improve the shuttle effect of polysulfides and also promote the kinetics of the redox reaction of LiPSs to Li2S conversion.

[0083] ZIF-67 and its derived cobalt sulfide, cobalt nitride and cobalt phosphide and other cobalt-containing compounds are polar compounds, which have chemical adsorption and catalytic effect on polysulfides and can effectively limit the "shuttle effect" of polysulfides. As shown in the figure, Figure 2 、 Figure 3 、 Figure 4As shown, the CNF / CoS-Co9S8-NC composite material disclosed in the present application also retains the ultra-fine network structure of BC, thus providing a strong conductive network and relieving the agglomeration and stacking problem of ZIF-67, so as to expose more active sites and improve the adsorption effect on polysulfides. Figure 5 As shown, after coating, the CNF / CoS-NC composite material synthesized in the present application is uniformly coated on the surface of the lithium-sulfur battery polypropylene separator. The CNF / CoS-Co9S8-NC composite material provided in the present application can effectively limit the "shuttle effect" of polysulfides through physical and chemical synergistic effects, and contains a CoS-Co9S8 heterostructure catalyst, which effectively improves the electrochemical performance of Li-S batteries, which provides a broad prospect for the commercial application of Li-S batteries.

[0084] The rate performance of the Li-S battery under different current densities was tested by using a LAND CT 2001A battery test system as Figure 6 As shown, the Li-S battery after using the CNF / CoS-Co9S8-NC composite material as a modified separator has better rate performance than the Li-S battery without using a modified separator, which proves that the material prepared by us has obvious effect on improving the electrochemical performance of Li-S batteries.

[0085] We also explored the long cycle stability of the CNF / Co-Co9S8-NC separator under small and large current densities, as Figure 7 and Figure 8 As shown, it shows a higher specific capacity under a current density of 0.2C; under a current density of 2C, the Li-S battery using the CNF / Co-Co9S8-NC separator has a specific capacity of 633.6mAhg -1 after 500 cycles, and the average capacity loss per cycle is only 0.016%, which has very excellent cycle stability.

[0086] Figure 9 The electrochemical impedance test of Figure 10 The LiPSs blocking effect comparison chart proves that the CNF / CoS-Co9S8-NC modified separator has very strong ability to block the shuttle of LiPSs.

[0087] The above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for preparing a BC-supported ZIF-67-derived CNF / CoS-Co9S8-NC composite material, characterized in that, Includes the following steps: Step 1: Dissolve 408 mg of 2-methylimidazole in 20 ml of methanol to form solution A; Dissolve 179 mg of Co(NO3)2·6H2O in 20 ml of methanol to form solution B. Add 50 mg of bacterial cellulose to solution B and stir well. Step 2: Then quickly pour solution A into solution B containing bacterial cellulose, stir magnetically until fully mixed, let stand at room temperature for 12 hours, vacuum filter and vacuum dry to obtain BC / ZIF-67; Step 3: Mix BC / ZIF-67 and sulfur powder thoroughly at a mass ratio of 1:4, place in a ceramic boat, and then perform high-temperature vulcanization and carbonization treatment under Ar atmosphere. First, heat to 300℃ at a heating rate of 2℃ / min and hold for 4 hours. Then, heat to 600-700℃ at a heating rate of 5℃ / min and hold for 2-4 hours to obtain CNF / CoS-Co9S8-NC composite material.

2. The method for preparing the BC-supported ZIF-67-derived CNF / CoS-Co9S8-NC composite material as described in claim 1, characterized in that, The magnetic stirring mentioned in step 2 is magnetic stirring for 10 minutes.

3. The method for preparing the CNF / CoS-Co9S8-NC composite material derived from BC-supported ZIF-67 as described in claim 1, characterized in that, The vacuum drying described in step 2 is vacuum drying at 70°C for 24 hours.

4. A CNF / CoS-Co9S8-NC composite material prepared by the method according to any one of claims 1 to 3.

5. The application of the CNF / CoS-Co9S8-NC composite material as described in claim 4 in a modified separator for Li-S batteries, characterized in that, CNF / CoS-Co9S8-NC and PVDF were weighed and mixed at a mass ratio of 8:2, then NMP was added to prepare a uniform, slightly flowing slurry. This slurry was then uniformly coated onto a commercial polypropylene separator for Li-S batteries to obtain a CNF / CoS-Co9S8-NC modified separator.

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