Method of making transition metal-doped bimetallic MOF-derived heterostructures, resulting products, and applications

Abstract

The application discloses a preparation method of a transition metal doped bimetallic MOF derived heterostructure, the obtained product and application, mixes Co salt, transition metal M salt, dimethyl imidazole and methanol uniformly, then stands to make metal ions combine with organic ligand, obtains bimetallic MOF precursor; the bimetallic MOF precursor is dispersed into ethanol, sodium molybdate and thioacetamide are dissolved in water, two kinds of solutions are stirred and mixed, temperature is raised to carry out solvothermal reaction, the reaction product is calcined under inert atmosphere, and the transition metal doped bimetallic MOF derived heterostructure is obtained.The heterostructure can effectively resist polysulfide, and the oxidation-reduction reaction kinetics of sulfur is accelerated, the "shuttle effect" of polysulfide is inhibited, the prepared battery diaphragm has excellent mechanical properties, the assembled lithium-sulfur battery has high discharge specific capacity and excellent cycle stability, and has wide application prospect in lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to a method for preparing a transition metal-doped bimetallic MOF-derived heterostructure, the resulting product, and its applications, belonging to the field of battery materials technology. Background Technology

[0002] With the continuous development of portable electronic devices and electric vehicles, lithium-ion batteries, due to their limited theoretical capacity and high cost, are unable to meet the ever-increasing energy storage demands. Therefore, the search for lithium-ion rechargeable batteries with good cycle performance, high energy density, and low cost has become a research hotspot. Among them, lithium-sulfur (Li-S) batteries, due to their high theoretical specific capacity (1675 mAh g⁻¹), are particularly promising. -1 The lithium-sulfur battery has attracted widespread attention due to its abundant sulfur resources and environmental friendliness. However, the practical application of lithium-sulfur batteries is still hindered by several challenges: (1) the inherent insulation of S and Li2S; (2) the "shuttle effect" of polysulfide intermediates (soluble polysulfides migrate from the cathode to the anode, reducing sulfur utilization and corroding lithium metal); (3) the slow reaction kinetics between polysulfides (LiPSs) and Li2S, resulting in poor electrochemical kinetics of sulfur in lithium-sulfur batteries.

[0003] The diaphragm as one of the important components of lithium-sulfur battery, mainly plays the role of electronic insulator, to prevent internal short circuit. Commercial diaphragm is usually a polymer film (PP, PE, etc.) containing a large number of micropores, the pore size is much larger than polysulfide, so the soluble polysulfide is easy to shuttle through the diaphragm micropore, which brings the problem of capacity loss of the battery. Therefore, it is necessary to modify the lithium-sulfur battery diaphragm, so that it can effectively adsorb lithium polysulfide and reduce the reaction activation energy, play a role in inhibiting the shuttle effect and accelerating the reaction kinetics, thereby improving the capacity and cycle stability of lithium-sulfur battery. Metal sulfide is considered to be a potential catalyst for lithium-sulfur battery due to its polarity and certain catalytic ability, but due to the inherent weak conductivity of sulfide and the single adsorption and catalytic function, it cannot meet the needs of fast transfer of electrons and ions, strong adsorption of polysulfide and fast redox reaction kinetics at the same time, so that 70% of the sulfur active material cannot be completely converted. Based on this, in order to accelerate the redox kinetics of polysulfide, heterostructure engineering is explored as a feasible strategy for Li-S battery by many researchers. Literature (Chemical Engineering Journal 441 (2022) 136006) designed MoS2 nanosheet decorated Co3S4 hollow polyhedron (Co3S4-MoS2), and applied it to adsorb tetracycline (TC) in aqueous solution. Literature (Applied Catalysis B: Environmental 264 (2020) 118514) used a double-template method to prepare MoS2@Co3S4 (MoS2@Co3S4 / NFA) supported on nanofiber aerogel and applied it to photocatalysis. Literature (Chemical Engineering Journal 475 (2023) 146324) designed and prepared Co3S4 / MoS2 heterostructure and fixed it on N-doped porous carbon (NPC), and explored its peroxidase-like activity. Literature (Applied Materials Today 26 (2022) 101311) used a precursor solubility control method to synthesize Co3S4-MoS2 heterostructure and applied it to HER catalytic reaction, which proved that there is electron transfer between the heterojunction interface, which improved the electron migration rate in the reaction process. However, it was found that the Co3S4-MoS2 heterostructure used in the battery diaphragm has the problem of insufficient adsorption and catalytic conversion of polysulfide. SUMMARY

[0004] The application aims to provide a preparation method of a transition metal doped bimetallic MOF derived heterostructure and the obtained transition metal doped bimetallic MOF derived heterostructure. The heterostructure is prepared by using a bimetallic MOF as a template, the number of active sites is increased by doping a transition metal element, the electronic structure of Co is adjusted, the construction of the heterostructure accelerates the transmission of electrons, and the synergistic effect between the two components of the sulfide enables the heterostructure to effectively adsorb polysulfides when used as a battery separator electrocatalyst, accelerates the redox reaction kinetics of sulfur, suppresses the "shuttle effect" of polysulfides, and thus improves the capacity and cycle stability of a lithium-sulfur battery.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0006] A preparation method of a transition metal doped bimetallic MOF derived heterostructure, the method comprising the following steps:

[0007] (1) uniformly mixing Co salt, transition metal M salt, dimethyl imidazole and methanol, then allowing the metal ions to combine with the organic ligand to obtain a bimetallic MOF precursor;

[0008] (2) dispersing the bimetallic MOF precursor into ethanol to obtain solution 1; dissolving sodium molybdate and thioacetamide in water to obtain solution 2; stirring and mixing solution 1 and solution 2, and performing a solvothermal reaction under heating, and collecting the product after the reaction;

[0009] (3) calcining the product under an inert atmosphere to obtain a transition metal doped bimetallic MOF derived heterostructure.

[0010] Further, in step (1), the transition metal M can be selected from one of Fe, Ni, Zn, Cu, Mn and other transition metals, and is preferably Zn. The salt of the transition metal M is a soluble salt of the transition metal, such as a chloride or nitrate of the transition metal, and is preferably a nitrate of the transition metal.

[0011] Further, in step (1), the Co salt is a soluble salt of cobalt, such as a chloride or nitrate.

[0012] Further, in step (1), the molar amount of Co is 70-90% of the total molar amount of Co and the transition metal M, such as 70%, 80%, 90%, and is preferably 90%.

[0013] Preferably, in step (1), the transition metal M is Zn, and the sum of the molar amounts of Co and Zn is 3 mmol, and the molar ratio of Co to Zn is 9:1.

[0014] Further, in step (1), dimethylimidazole is used as the organic ligand, which mainly serves as a linker for metal ions. Dimethylimidazole connects Co and transition metal M ions to form a periodic net-like porous structure. The ratio of the total molar amount of Co salt and transition metal M salt to the molar amount of dimethylimidazole is 1:6-10, for example, 1:6, 1:7, 1:8, 1:9, 1:10, and preferably 1:8.

[0015] Further, in step (1), methanol is used as the solvent, which has two functions: one is to provide a reaction medium and mix the components uniformly, and the other is to act as a structure-directing agent. Methanol enhances the deprotonation ability in the solution, and finally forms a regular rhombic dodecahedron structure.

[0016] Further, in step (1), the concentration of Co salt, transition metal M salt, and dimethylimidazole in the solvent can control the particle size of the rhombic dodecahedron. The total concentration of Co salt and transition metal M salt in methanol is 0.01-0.06 mol / L, for example, 0.015 mol / L, 0.02 mol / L, 0.03 mol / L, 0.06 mol / L, and preferably 0.06 mol / L.

[0017] Further, in step (1), there is no particular requirement for the mixing order of Co salt, transition metal M salt, dimethylimidazole, and solvent. After mixing, the mixture is stirred at room temperature for 20-40 min, for example, 20 min, 30 min, 40 min, and the stirring speed is 200-400 r·min -1 , for example, 200 r·min -1 , 300 r·min -1 , 400 r·min -1 . After stirring, the solution is left to stand at room temperature for 12-24 h, for example, 12 h, 15 h, 18 h, 20 h, 24 h.

[0018] Further, in step (1), after standing, the sample is centrifuged, washed, and dried to obtain a bimetallic MOF precursor. Methanol is used for washing, and the drying temperature is 60-80℃, for example, 60℃, 70℃, 80℃, and preferably 70℃. The drying time is generally 9-13 hours, for example, 9 h, 10 h, 11 h, 12 h, 13 h, and preferably 12 h.

[0019] Further, in step (2), the mass ratio of the bimetallic MOF precursor to thioacetamide is 7-10:12, for example, 7:12, 8:12, 9:12, 10:12, and preferably 8:12.

[0020] Further, in step (2), the sodium molybdate can be anhydrous sodium molybdate or sodium molybdate dihydrate, and the molar ratio of sodium molybdate to thioacetamide is 1-3:8, for example, 1:8, 1.5:8, 2:8, 2.5:8, 3:8, and preferably 2.5:8.

[0021] Further, in step (2), the bimetallic MOF can be dispersed in ethanol by at least one of stirring, ultrasonic, etc., and the dispersion time is 10-30 min, for example, 10 min, 20 min, 30 min. Ethanol is a solvent, which provides a reaction medium, and the bimetallic MOF precursor can be decomposed in ethanol, which is beneficial to subsequent reactions. The amount of ethanol used as a solvent can be selected according to actual needs. Thioacetamide and sodium molybdate are dissolved in water, and the amount of water used as a solvent can be selected according to actual needs.

[0022] Further, in step (2), after mixing solution 1 and solution 2, stirring at room temperature for 20-40 min, for example, 20 min, 30 min, 40 min, and the stirring speed is 200-400 r·min -1 , for example, 200 r·min -1 , 300 r·min -1 , 400 r·min -1 .

[0023] Further, in step (2), the solvothermal reaction is carried out in a reaction kettle and is divided into two stages. The first stage is the process of forming (MCo)3S4, and the solvothermal reaction temperature is 110-140℃, for example, 110℃, 120℃, 130℃, 140℃, and the reaction time is generally 3-5 hours, for example, 3 hours, 4 hours, 5 hours. Preferably, the reaction temperature is 120℃, and the reaction time is 4h. The second stage is the process of forming MoS2, and the solvothermal reaction temperature is 180-220℃, for example, 180℃, 190℃, 200℃, 210℃, 220℃, and the reaction time is generally 15-18h, for example, 15h, 16h, 17h, 18h, and the preferred reaction temperature is 180℃, and the reaction time is 16h.

[0024] Further, in step (2), after the solvothermal reaction is completed, the sample is centrifuged, washed, and dried to obtain a transition metal-doped bimetallic MOF-derived disulfide heterostructure. Ethanol is used for washing, and the drying temperature is 60-80℃, for example, 60℃, 70℃, 80℃, and preferably 70℃. The drying time is generally 9-13 hours, for example, 9h, 10h, 11h, 12h, 13h, and preferably 12h.

[0025] Further, in step (3), the product of step (2) is calcined under inert gas to remove impurities in the sample and improve the crystallinity of the product. The inert gas can be nitrogen, argon, etc., the calcination temperature is 320-360℃, for example, 320℃, 330℃, 340℃, 350℃, 360℃, preferably 350℃, and the calcination time is 2-2.5h.

[0026] The transition metal doped bimetallic MOF derived heterostructure prepared by the method has a 3D structure, wherein the transition metal elements are uniformly doped, the electronic structure of Co is adjusted, the construction of the heterostructure accelerates the transmission of electrons, and the synergistic effect between the two components of the sulfide enables the heterostructure to effectively adsorb polysulfides and accelerate the redox reaction kinetics of sulfur when the heterostructure is used as an electrocatalyst for a battery separator, thereby inhibiting the "shuttle effect" of polysulfides. Therefore, the application also provides a transition metal doped bimetallic MOF derived heterostructure prepared by the above method and the application of the heterostructure as an electrocatalyst for a battery separator.

[0027] The application also provides a modified battery separator, which comprises a battery separator body, and an electrocatalyst layer coated on the battery separator body, wherein the electrocatalyst layer contains the transition metal doped bimetallic MOF derived heterostructure. The coating of the transition metal doped bimetallic MOF derived heterostructure in the battery separator can inhibit the shuttle effect of polysulfides and improve the capacity and cycle stability of the battery.

[0028] Further, the electrocatalyst layer is coated on the upper surface or the lower surface of the battery separator body. The battery separator body is a polymer separator commonly used in batteries, for example, a polypropylene (PP) separator with micropores or a PE separator.

[0029] Further, the thickness of the electrocatalyst layer is 8-12μm.

[0030] Further, the electrocatalyst layer is composed of the transition metal doped bimetallic MOF derived heterostructure and a binder, and the mass ratio of the transition metal doped bimetallic MOF derived heterostructure to the binder is preferably 9:1. The binder can be a special adhesive for lithium-sulfur batteries, for example, one of LA133, polytetrafluoroethylene, etc.

[0031] Further, the preparation method of the modified battery separator is as follows: the transition metal doped bimetallic MOF derived heterostructure and the binder are uniformly stirred in proportion to form a slurry, the slurry is coated on the surface of the battery separator body, and the modified battery separator is obtained after drying.

[0032] The application also provides the application of the above-mentioned transition metal doped bimetallic MOF derived heterostructure or the modified battery separator in lithium-sulfur batteries.

[0033] In a specific embodiment of the present application, a method for assembling a lithium-sulfur battery is also provided, specifically comprising the following steps:

[0034] (1) Grinding sulfur powder and BP2000 carbon black in a mass percentage ratio of 70:30 for 30-40 minutes, and then placing them in an oven at 155℃ for 12 hours to obtain a sulfur-carbon positive electrode material;

[0035] (2) Mixing and grinding the sulfur-carbon positive electrode material, conductive carbon and LA133 binder in a mass ratio of 7:2:1 until uniform, coating the slurry on the surface of a carbon-coated aluminum foil, vacuum drying at 60℃, and then cutting into a circular sheet with a diameter of 8mm to obtain a sulfur-carbon electrode sheet;

[0036] (3) Assembling a button cell in an argon-filled glove box, with the positive electrode being the sulfur-carbon electrode sheet, the negative electrode being metallic lithium, the separator being the battery separator modified by the transition metal-doped bimetallic MOF-derived heterostructure electrocatalyst of the present application, and the electrolyte composition being: 1 mol / L lithium bis(trifluoromethylsulfonyl)imide, 1-2wt% lithium nitrate, and a solvent being a mixture of 1,3-dioxolane (DOL) and dimethoxyethane (DME) in a volume ratio of 1:1.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] 1. The transition metal-doped bimetallic MOF-derived double sulfide heterostructure of the present application is prepared using a bimetallic MOF as a template, wherein each element is uniformly doped, the electronic structure of Co is adjusted, the construction of the heterostructure accelerates the transfer of electrons, and the synergistic effect between the two components of the sulfide enables the heterostructure to effectively adsorb polysulfides when used as a modified battery separator electrocatalyst, and to accelerate the redox reaction kinetics of sulfur and inhibit the "shuttle effect" of polysulfides.

[0039] 2. The preparation method of the present application is simple, the active components selected are all transition metal elements, the required raw materials are widely available, and the production cost is greatly reduced. The heterostructure obtained is stable in structure and excellent in catalytic performance.

[0040] 3. The battery separator modified by the transition metal-doped bimetallic MOF-derived double sulfide heterostructure obtained by the present application has excellent mechanical properties and stability, and does not show powder shedding after being bent and folded. When used in a lithium-sulfur battery, the lithium-sulfur battery assembled using the modified battery separator has a high specific discharge capacity (1455.5 mAh / g, 0.2C) and excellent cycle stability, and has a broad application prospect in lithium-sulfur batteries. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1X-ray diffraction (XRD) pattern of the transition metal doped bimetallic MOF derived heterostructured electrocatalyst (CoZn)3S4-MoS2 prepared in Example 1.

[0042] Figure 2 Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) images of the transition metal doped bimetallic MOF derived heterostructured electrocatalyst (CoZn)3S4-MoS2 prepared in Example 1.

[0043] Figure 3 Photos of the folding bending test of the battery separator modified with the transition metal doped bimetallic MOF derived heterostructured electrocatalyst (CoZn)3S4-MoS2 / PP prepared in Example 1.

[0044] Figure 4 Discharge specific capacity of the lithium-sulfur battery using the battery separator modified with the (CoZn)3S4-MoS2 electrocatalyst of Example 1 at different current densities. DETAILED DESCRIPTION

[0045] The application will be further described in the following specific examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present application.

[0046] Example 1

[0047] Preparation of Zn doped CoZn-MOFs derived heterostructured electrocatalyst, the method comprising:

[0048] 1. Dissolve 0.786 g (2.7 mmol) of Co(N03)2·6H20 and 0.089 g (0.3 mmol) of Zn(N03)2·6H20 in 30 mL of methanol to form a homogeneous solution, then pour it into 20 mL of methanol containing 1.97 g (24 mmol) of dimethylimidazole, and stir at a rotation speed of 200 r·min -1 for 30 min, and let it stand at room temperature for 24 h. Centrifuge the obtained precipitate, wash it with methanol, and dry it in an oven at 60 °C for 12 h to obtain CoZn-MOFs.

[0049] 2. Disperse 80 mg of CoZn-MOFs in 20 mL of ethanol, and ultrasonicate for 20 min. Meanwhile, add 0.12 g (1.6 mmol) of thioacetamide and 0.121 g (0.5 mmol) of Na2Mo04·2H20 in 20 mL of water, and after fully dissolving, add it to the CoZn-MOFs ethanol solution above, and stir at a rotation speed of 200 r·min -1After stirring for 20 min, the product was poured into a 100 mL reaction kettle, first reacted at 120 °C for 4 h, and then the temperature was raised to 200 °C for 16 h. After the reaction kettle was cooled, it was centrifuged, the product was washed with ethanol several times, and then dried in an oven at 60 °C for 12 h.

[0050] 3. The product was calcined at 350 °C for 2 h under N2to obtain the transition metal doped double metal MOF derived double sulfide heterostructure electrocatalyst (CoZn)3S4-MoS2.

[0051] As shown in FIG. 1, the heterostructure electrocatalyst was characterized by X-ray diffraction (XRD), and it can be seen from FIG. 1 that the heterostructure can be seen obvious diffraction peaks, corresponding to Co3S4(PDF #42-1448) and MoS2(PDF #37-1492), respectively. In addition, the synthesized (CoZn)3S4-MoS2 has no diffraction peaks of other impurity phases, meaning that the specified sample is synthesized. Figure 1 Figure 1 As shown in FIG. 2, the morphology of the heterostructure (CoZn)3S4-MoS2 is a hollow dodecahedron, and such a structure has a large specific surface area, which is beneficial to expose more active sites, promoting the adsorption and catalytic conversion of polysulfides. Further from the EDS, it can be seen that each element is uniformly distributed.

[0052] As shown in FIG. 2, the morphology of the heterostructure (CoZn)3S4-MoS2 is a hollow dodecahedron, and such a structure has a large specific surface area, which is beneficial to expose more active sites, promoting the adsorption and catalytic conversion of polysulfides. Further from the EDS, it can be seen that each element is uniformly distributed. Figure 2 Example 2

[0053] The transition metal doped double metal MOF derived electrocatalyst (CoZn)3S4-MoS2 was prepared according to the method of Example 1, except that in step 2, the amount of Na2MoO4·2H2O was 72.6 mg (0.3 mmol).

[0054] Example 3

[0055] The transition metal doped double metal MOF derived electrocatalyst (CoZn)3S4-MoS2 was prepared according to the method of Example 1, except that in step 1, the amount of Co(NO3)2·6H2O was adjusted to 0.698 g (2.4 mmol), and the amount of Zn(NO3)2·6H2O was adjusted to 0.178 g (0.6 mmol).

[0056] Example 4

[0057] The transition metal doped double metal MOF derived electrocatalyst (CoZn)3S4-MoS2 was prepared according to the method of Example 1, except that in step 1, the amount of Co(NO3)2·6H2O was adjusted to 0.698 g (2.4 mmol), and the amount of Zn(NO3)2·6H2O was adjusted to 0.178 g (0.6 mmol).

[0058] ​A transition metal doped double metal MOF derived electrocatalyst (CoZn)3S4-MoS2 was prepared following the method of Example 1, except that in Step 1, the amount of Co(N03)2-6H20 was adjusted to 0.611 g (2.1 mmol) and the amount of Zn(N03)2-6H20 was adjusted to 0.267 g (0.9 mmol).

[0059] Example 5

[0060] A Cu doped CoCu-MOFs derived double sulfide heterostructure electrocatalyst (CoCu)3S4-MoS2 was prepared following the method of Example 1, except that in Step 1, 0.698 g (2.4 mmol) of Co(N03)2-6H20 and 0.113 g (0.6 mmol) of Cu(N03)2-6H20 were dissolved in 30 mL of methanol to form a homogeneous solution, which was then poured into 20 mL of methanol containing 1.48 g (18 mmol) of 2-methylimidazole at a rotation speed of 200 r-min -1 under stirring for 30 min and left to stand at room temperature for 24 h. The obtained precipitate was centrifuged, washed with methanol and dried in an oven at 60 °C for 12 h to obtain CoCu-MOFs.

[0061] Example 6

[0062] A Ni doped CoNi-MOFs derived double sulfide heterostructure electrocatalyst (CoNi)3S4-MoS2 was prepared following the method of Example 1, except that in Step 1, 0.786 g (2.7 mmol) of Co(N03)2-6H20 and 0.088 g (0.3 mmol) of Ni(N03)2-6H20 were dissolved in 60 mL of methanol to form a homogeneous solution, which was then poured into 40 mL of methanol containing 1.97 g (24 mmol) of 2-methylimidazole at a rotation speed of 200 r-min -1 under stirring for 30 min and left to stand at room temperature for 24 h. The obtained precipitate was centrifuged, washed with methanol and dried in an oven at 60 °C for 12 h to obtain CoNi-MOFs.

[0063] Example 7

[0064] A Fe-doped CoFe-MOFs derived bisulfide heterostructure electrocatalyst (CoFe)3S4-MoS2was prepared following the procedure of Example 1, except that in Step 1, 0.089 g (0.3 mmol) of Zn(NO3)2·6H2O was replaced by 0.121 g (0.3 mmol) of Fe(NO3)2·9H2O; and in Step 2, “firstly react at 120 °C for 4 h, then increase the temperature to 200 °C for 16 h” was replaced by “firstly react at 110 °C for 5 h, then increase the temperature to 180 °C for 18 h”.

[0065] Example 8

[0066] A Mn-doped CoMn-MOFs derived bisulfide heterostructure electrocatalyst (CoMn)3S4-MoS2was prepared following the procedure of Example 1, except that in Step 1, 0.089 g (0.3 mmol) of Zn(NO3)2·6H2O was replaced by 0.086 g (0.3 mmol) of Mn(NO3)2·6H2O.

[0067] Comparative Example 1

[0068] 1. The same as Example 1.

[0069] 2. 80 mg of CoZn-MOFs was dispersed into 20 mL of ethanol and ultrasonicated for 20 min. Then 20 mL of an aqueous solution containing 0.12 g (1.6 mmol) of thioacetamide was added into the ethanol solution, which was stirred for 20 min and then poured into a 100 mL reaction kettle and reacted at 120 °C for 4 h. After the reaction kettle was cooled, the product was centrifuged, washed with ethanol for several times, and then dried in an oven at 60 °C for 12 h.

[0070] 3. 80 mg of the product of Step 2 was dispersed into 20 mL of ethanol and ultrasonicated for 20 min to obtain an ethanol dispersion. Meanwhile, 0.12 g (1.6 mmol) of thioacetamide and 0.121 g (0.5 mmol) of Na2MoO4·2H2O were added into 20 mL of water, which was stirred for 20 min and then added into the ethanol dispersion. After the reaction kettle was cooled, the product was centrifuged, washed with ethanol for several times, and then dried in an oven at 60 °C for 12 h. -1 3. 80 mg of the product of Step 2 was dispersed into 20 mL of ethanol and ultrasonicated for 20 min to obtain an ethanol dispersion. Meanwhile, 0.12 g (1.6 mmol) of thioacetamide and 0.121 g (0.5 mmol) of Na2MoO4·2H2O were added into 20 mL of water, which was stirred for 20 min and then added into the ethanol dispersion. After the reaction kettle was cooled, the product was centrifuged, washed with ethanol for several times, and then dried in an oven at 60 °C for 12 h.

[0071] 4. The product was calcined at 350 °C for 2 h under N2to obtain a transition metal-doped bimetallic MOF derived bisulfide heterostructure electrocatalyst (CoZn)3S4-MoS2.

[0072] Comparative Example 2

[0073] 1. Dissolve 0.87 g (3 mmol) of Co(N03)2-6H20 in 30 mL of methanol to form a uniform solution, then pour it into 20 mL of methanol containing 1.97 g (2.4 mmol) of dimethylimidazole, and stir at a rotation speed of 200 r-min -1 for 30 min, and stand at room temperature for 24 h. Centrifuge the obtained precipitate, wash it with methanol, and dry it in an oven at 60 °C for 12 h to obtain Co-MOFs.

[0074] 2. Disperse 80 mg of Co-MOFs in 20 mL of ethanol, and ultrasonicate for 20 min. Meanwhile, add 0.12 g (1.6 mmol) of thioacetamide and 0.121 g (0.5 mmol) of Na2Mo04-2H20 into 20 mL of water, and add the Co-MOF ethanol solution after the above-mentioned substances are fully dissolved, and stir at a rotation speed of 200 r-min -1 for 20 min, and then pour it into a 100 mL reaction kettle, and first react at 120 °C for 4 h, and then increase the temperature to 200 °C and react for 16 h. After the reaction kettle is cooled, centrifuge the product, wash it with ethanol for several times, and then dry it in an oven at 60 °C for 12 h.

[0075] 3. Calcine the product at 350 °C for 2 h under N2 to obtain a MOF-derived bisulfide heterostructure electrocatalyst Co3S4-MoS2.

[0076] Comparative Example 3

[0077] 1. Dissolve 0.786 g (2.7 mmol) of Co(N03)2-6H20 and 0.089 g (0.3 mmol) of Zn(N03)2-6H20 in 30 mL of methanol to form a uniform solution, then pour it into 20 mL of methanol containing 1.97 g (24 mmol) of dimethylimidazole, and stir at a rotation speed of 200 r-min -1 for 30 min, and stand at room temperature for 24 h. Centrifuge the obtained precipitate, wash it with methanol, and dry it in an oven at 60 °C for 12 h to obtain CoZn-MOFs.

[0078] 2. Disperse 80 mg of CoZn-MOFs in 20 mL of ethanol, and ultrasonicate for 20 min. Then add a 20 mL aqueous solution containing 0.12 g (1.6 mmol) of thioacetamide into the ethanol solution, and stir for 20 min, and then pour it into a 100 mL reaction kettle, and react at 120 °C for 4 h. After the reaction kettle is cooled, centrifuge the product, wash it with ethanol for several times, and then dry it in an oven at 60 °C for 12 h.

[0079] 3. Calcine the product at 350 °C for 2 h under N2 to obtain a transition metal-doped MOF-derived electrocatalyst (CoZn)3S4.

[0080] Comparative Example 4

[0081] 1. 0.12 g (1.6 mmol) of thioacetamide and 0.121 g (0.5 mmol) of Na2MoO4·2H2O were added to 40 mL of water, and stirred at 200 r·min-1for 20 min, and then poured into a 100 mL reaction kettle, and reacted at 120 °C for 4 h, and then the temperature was raised to 200 °C and reacted for 16 h. After the reaction kettle was cooled, the product was centrifuged, washed with ethanol for several times, and then dried in a 60 °C oven for 12 h. -1

[0082] 2. The product was calcined at 350 °C for 2 h under N2to obtain MoS2.

[0083] Comparative Example 5

[0084] 1. 0.87 g (3 mmol) of Co(NO3)2·6H2O was dissolved in 30 mL of methanol to form a uniform solution, and then poured into 20 mL of methanol containing 1.97 g (2.4 mmol) of dimethylimidazole, and stirred at 200 r·min-1for 30 min, and then left to stand at room temperature for 24 h. The obtained precipitate was centrifuged, washed with methanol, and dried in a 60 °C oven for 12 h to obtain Co-MOFs. -1

[0085] 2. 80 mg of Co-MOFs was dispersed in 20 mL of ethanol and ultrasonicated for 20 min. Then, 20 mL of an aqueous solution containing 0.12 g (1.6 mmol) of thioacetamide and 0.148 g (0.5 mmol) of Zn(NO3)2·6H2O was added to the ethanol solution, and stirred for 20 min, and then poured into a 100 mL reaction kettle, and reacted at 120 °C for 4 h. After the reaction kettle was cooled, the product was centrifuged, washed with ethanol for several times, and then dried in a 60 °C oven for 12 h.

[0086] 3. The product was calcined at 350 °C for 2 h under N2to obtain MOF-derived electrocatalyst Co3S4-ZnS.

[0087] Application Example 1

[0088] 80 mg of the electrocatalyst and 1.3 ml of LA133 binder were uniformly mixed to obtain a coating slurry, and the coating slurry was uniformly coated on one surface of a polypropylene separator to obtain a modified battery separator, and the coating layer had a thickness of about 10 μm. The electrocatalyst was the heterostructure electrocatalyst of Examples 1-8 and the products prepared in Comparative Examples 1-5, respectively.

[0089] Verification Example

[0090] 1. Fold bending experiment ​​

[0091] The modified battery separator prepared in the application example was subjected to bending and folding experiment. The method was as follows: the coated modified battery separator was cut into a circular piece with a diameter of 18 mm by using a puncher, then it was folded twice in succession, then it was opened to restore its original shape, and the powder shedding was observed.

[0092] The photos of the folding process of the battery separator modified by the (CoZn)3S4-MoS2 electrocatalyst of Example 1 are shown in Figure 3 After bending and folding, no powder shedding phenomenon occurred, indicating that the battery separator modified by the (CoZn)3S4-MoS2 electrocatalyst prepared in Example 1 had excellent mechanical properties and stability.

[0093] The bending and folding experiment results of other modified battery separators are shown in Table 1 below:

[0094] Table 1

[0095]

[0096]

[0097] 2. Discharge specific capacity and rate performance experiment of lithium-sulfur battery

[0098] 2.1 Preparation of carbon-sulfur positive electrode sheet:

[0099] The sulfur powder and BP2000 carbon black were ground at a mass ratio of 7:3 for 30 minutes, then were put into an oven at 155°C for 12 hours to obtain a sulfur-carbon positive electrode material. The sulfur-carbon positive electrode material, conductive carbon and LA133 binder were mixed and ground uniformly at a mass ratio of 7:2:1, then the slurry was coated on the surface of a carbon-coated aluminum foil, vacuum dried at 60°C, and cut into a circular piece with a diameter of 8 mm to obtain a sulfur-carbon electrode sheet.

[0100] 2.2 Preparation of lithium-sulfur battery:

[0101] A 2032 button-type lithium-sulfur battery was assembled. The sulfur-carbon positive electrode sheet was used as the positive electrode (diameter 8 mm), lithium sheet (diameter 16 mm) was used as the negative electrode, and the modified battery separator prepared in the application example (diameter 18 mm) was used as the separator. The electrolyte composition was: 1M lithium bis(trifluoromethylsulfonyl)imide, 2wt% anhydrous lithium nitrate, wherein the solvent was a mixture of 1,3-dioxolane (DOL) and dimethoxyethane (DME) at a volume ratio of 1:1.

[0102] 2.3 Electrochemical performance test

[0103] The electrochemical performance of different lithium-sulfur batteries was evaluated by constant current charge-discharge test (test voltage range 1.7-2.8V, current density 0.1C) on blue electric system, and the discharge specific capacity of lithium-sulfur battery was evaluated and compared; the test results are shown in Table 2, from Table 2, it can be seen that the lithium-sulfur battery using (CoZn)3S4-MoS2 / PP separator of Example 1 has the highest discharge specific capacity, the first circle discharge capacity is 1455.7 mAh / g at 0.1C current density, and the discharge capacity is greatly improved compared with each comparative example, which shows that the heterostructure catalyst and element doping have significant catalytic effect on the redox reaction of sulfur. The discharge specific capacity of the battery of Examples 2-8 is also higher than that of the battery of each comparative example.

[0104] Table 2 Discharge specific capacity (mAh / g) of different batteries at 0.1C

[0105]

[0106]

[0107] The rate performance was studied by applying different current densities, as shown in Table 3. Figure 4 The discharge specific capacity of lithium-sulfur battery using (CoZn)3S4-MoS2 / PP separator of Example 1 at 0.2C, 0.4C, 0.6C, 1C, 2C rate is 1405.9 mAh / g, 1159.9 mAh / g, 1052.6 mAh / g, 950.3 mAh / g, 802.7 mAh / g, respectively, and the capacity can still reach 1109 mAh / g at 0.4C rate after the rate returns to 0.4C, which is only 4% lower than the capacity at 0.4C, indicating that the battery using (CoZn)3S4-MoS2 catalyst modified separator has good capacity reversibility. The discharge specific capacity of lithium-sulfur battery using modified separators of Examples 2-8 and Comparative Example 1 decreases by 10%-15% from 0.2C through 0.4C, 0.6C, 1C, 2C and then back to 0.4C. The discharge specific capacity of lithium-sulfur battery using modified separators of Comparative Examples 2-5 decreases by 15-20% from 0.2C through 0.4C, 0.6C, 1C, 2C and then back to 0.4C.

[0108] From the above experiments, it can be seen that the transition metal doped bimetallic MOF derived heterostructure increases the number of active sites by doping transition metal elements, adjusts the electronic structure of cobalt, the construction of heterostructure accelerates the transfer of electrons, and the synergistic effect between the two components of sulfide makes the electrocatalyst modified separator can effectively adsorb polysulfide and accelerate the kinetics of sulfur redox reaction.

[0109] Although the above embodiments have been described in detail, it should be understood that these are only some embodiments of the present application, but not all embodiments, and other embodiments can be obtained without creativity on the basis of the above embodiments, and these embodiments all belong to the protection scope of the present application.

Claims

1. A method for preparing a transition metal-doped bimetallic MOF-derived heterostructure, characterized in that The method comprises the following steps: (1) uniformly mixing a Co salt, a transition metal M salt, dimethyl imidazole and methanol, and then allowing metal ions to combine with organic ligands to obtain a double-metal MOF precursor by standing; (2) dispersing the double-metal MOF precursor into ethanol to obtain solution 1; dissolving sodium molybdate and thioacetamide in water to obtain solution 2; stirring and mixing solution 1 and solution 2, and performing a solvothermal reaction by increasing the temperature, and collecting the product after the reaction; (3) calcining the product in an inert atmosphere to obtain a transition metal-doped double-metal MOF derived heterostructure; In step (1), the molar amount of Co is 70-90% of the total molar amount of Co and the transition metal M. In step (2), the mass ratio of the double-metal MOF precursor to thioacetamide is 7-10:12; and the molar ratio of sodium molybdate to thioacetamide is 1-3:

8. In step (2), during the solvothermal reaction, the temperature is first increased to 110-140°C for 3-5 hours, and then increased to 180-220°C for 15-18 hours. In step (3), the calcination temperature is 320-360°C, and the calcination time is 2-2.5 hours.

2. The method of claim 1, wherein: In step (1), at least one of the following conditions is included: Condition 1, the transition metal M is selected from Fe, Ni, Zn, Cu or Mn; Condition 2, the molar amount of Co is 90% of the total molar amount of Co and the transition metal M; Condition 3, the ratio of the sum of the molar amounts of Co and the transition metal M to the molar amount of dimethyl imidazole is 1:6-10; Condition 4, the concentration of the total amount of the Co salt and the transition metal M salt in methanol is 0.01-0.06 mol / L; Condition 5, after mixing the Co salt, the transition metal M salt, dimethyl imidazole and methanol, stirring at room temperature for 20-40 minutes, and then standing at room temperature for 12-24 hours.

3. The method of claim 2, wherein: In step (1), the transition metal M is selected from Zn.

4. The method of claim 2 wherein: In step (1), the ratio of the sum of the molar amounts of Co and the transition metal M to the molar amount of dimethyl imidazole is 1:

8.

5. The method of claim 1 or 2, wherein: In step (1), the Co salt and the transition metal M salt are soluble salts of Co and the transition metal M.

6. The method of claim 5 wherein: In step (1), the Co salt and the transition metal M salt are chlorides or nitrates of Co and the transition metal M.

7. The transition metal-doped double-metal MOF derived heterostructure prepared by the method of any one of claims 1-6.

8. The use of the transition metal-doped double-metal MOF derived heterostructure of claim 7 as an electrocatalyst for a battery separator.

9. A modified battery separator characterized by: The battery separator comprises a battery separator body, and an electrocatalyst layer is coated on the battery separator body, wherein the electrocatalyst layer contains the transition metal-doped double-metal MOF derived heterostructure of claim 7.

10. The modified battery separator of claim 9, characterized by: The coating thickness of the electrocatalyst layer on the battery separator body is 8-12 μm.

11. The use of the transition metal-doped double-metal MOF derived heterostructure of claim 7 or the modified battery separator of claim 9 or 10 in a lithium-sulfur battery.

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