Bimetallic sulfide heterojunction modified diaphragm and its preparation method and application

Abstract

The present invention discloses a bimetallic sulfide heterojunction modified diaphragm, a preparation method thereof, and an application thereof. The technical solution comprises the following steps: synthesizing a bimetallic sulfide heterojunction material having a three-dimensional flower-like structure constructed by self-assembly of NiS2-WS2 heterojunction nanosheets by a one-step hydrothermal method; then preparing the bimetallic sulfide heterojunction material into a slurry and uniformly coating the slurry on one surface of a commercial polymer diaphragm, thereby finally obtaining a bimetallic sulfide heterojunction modified diaphragm and applying the slurry to a lithium-sulfur battery; the NiS2-WS2 heterojunction in the bimetallic sulfide heterojunction modified diaphragm can improve interfacial activity, increase surface catalytic active sites, optimize the adsorption capacity for polysulfides, and promote catalytic conversion, thereby effectively improving the rate performance and cycle stability of the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur battery diaphragm materials, and specifically refers to a bimetallic sulfide heterojunction modified diaphragm, a preparation method thereof, and application in lithium-sulfur batteries. Background Art

[0002] With the rapid development of electronic mobile devices and new energy vehicles, the demand for advanced energy storage devices is growing, which has promoted the rapid development of rechargeable battery systems. However, commercial lithium-ion batteries are limited by their theoretical specific capacity and energy density and cannot meet the needs of future development. In recent years, lithium-sulfur batteries have been widely used due to their high theoretical capacity (1675mAh g -1 ) and low cost make it one of the most promising energy storage devices. However, slow reaction kinetics and severe shuttle effect are stumbling blocks for the commercial application of lithium-sulfur batteries.

[0003] Modifying the separator is considered an effective strategy to limit the "shuttle effect." Non-polar carbon interlayers, such as porous carbon, carbon nanotubes, and graphene, have been widely used for separator modification. Physical adsorption suppresses the shuttle effect of polysulfides, thereby improving the electrochemical performance of batteries to a certain extent. However, the weak physical interaction between carbon materials and polysulfides is insufficient to limit the shuttling of polysulfides. Furthermore, strategies to limit polysulfide transport do not completely address the shuttle effect. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings and deficiencies of existing technologies by providing a bimetallic sulfide heterojunction-modified separator, its preparation method, and its application. The prepared bimetallic sulfide heterojunction material can improve interfacial polarity, enhance affinity for polysulfides, and promote catalytic conversion, thereby enhancing the electrochemical performance and cycling stability of lithium-sulfur batteries.

[0005] To achieve the above objectives, the first aspect of the present invention is to provide a method for preparing a bimetallic sulfide heterojunction modified membrane, wherein a bimetallic sulfide heterojunction material having a three-dimensional flower-like structure constructed by self-assembly of NiS2-WS2 heterojunction nanosheets is synthesized by a one-step hydrothermal method; the bimetallic sulfide heterojunction material is then made into a slurry and uniformly coated on one surface of a commercial polymer membrane, ultimately producing a bimetallic sulfide heterojunction modified membrane for application in lithium-sulfur batteries;

[0006] The three-dimensional flower-shaped bimetallic sulfide heterojunction modified diaphragm of the present invention comprises the following specific steps:

[0007] (1) Thiourea is used as the sulfur source, nickel chloride and sodium tungstate are used as the nickel source and tungsten source, respectively, and added to deionized water and stirred until completely dissolved. The mixed solution is then transferred to a high-temperature resistant reactor for reaction. The product is then centrifuged, washed several times with deionized water and ethanol, and dried at 60°C for 12 hours. This yields a heterojunction material.

[0008] The mass ratio of nickel chloride: sodium tungstate: thiourea is 1:5:20.

[0009] The reaction temperature is 270°C and the reaction time is 24h;

[0010] (2) The heterojunction material, conductive additive and binder prepared in step (1) are mixed, added into a solvent N-methylpyrrolidone (NMP), and stirred and dispersed uniformly to obtain a composite material slurry.

[0011] The mass ratio of the heterojunction material: conductive additive: binder is 8:1:1.

[0012] The conductive additive is carbon nanotubes, and the binder is PVDF.

[0013] (3) The composite material slurry is evenly coated on one side of the commercial polymer membrane substrate, and then dried in an oven at 60°C to obtain a three-dimensional flower-shaped bimetallic sulfide heterojunction modified membrane.

[0014] The present invention discloses a three-dimensional flower-shaped bimetallic sulfide heterojunction modified diaphragm for lithium-sulfur battery. The lithium-sulfur battery with the diaphragm intermediate layer prepared by the above method comprises a positive electrode, a negative electrode, a diaphragm, and an electrolyte, wherein the electrolyte has a molar concentration of 1 mol L -1 The cathode is a lithium metal sheet, and the cathode is a carbon nanotube / sulfur composite material, with the sulfur content being 70wt%.

[0015] The bimetallic sulfide heterojunction of the present invention is composed of NiS2 and WS2. The three-dimensional flower-like structure constructed by the self-assembly of heterojunction nanosheets provides a channel for the rapid diffusion of lithium ions. The NiS2-WS2 heterojunction can improve interfacial activity, increase surface catalytic active sites, optimize the adsorption capacity of polysulfides, and promote catalytic conversion, thereby effectively improving the rate performance and cycling stability of lithium-sulfur batteries.

[0016] Compared with traditional unmodified membranes, the main advantage of the present invention is that the three-dimensional flower-like structure provides a channel for the rapid diffusion of lithium ions, accelerating mass transfer and charge transfer during the sulfur reaction. In addition, the NiS2-WS2 heterojunction improves conductivity while enhancing the adsorption and catalytic conversion ability of polysulfides, thereby effectively suppressing the shuttle effect.

[0017] The present invention effectively controls the surface interface electronic structure of transition metal sulfides based on interface engineering strategies by controlling reaction parameters, thereby improving the adsorption capacity of polysulfides and the kinetics of sulfur redox reactions, thereby effectively improving the electrochemical performance and cycle stability of lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0019] Figure 1 This is a scanning electron microscope image of the three-dimensional flower-shaped bimetallic sulfide heterojunction material prepared in specific embodiment 1 of the present invention;

[0020] Figure 2 This is a transmission electron micrograph of the three-dimensional flower-shaped bimetallic sulfide heterojunction material prepared in specific embodiment 1 of the present invention;

[0021] Figure 3 is the XRD pattern of the heterojunction prepared in specific embodiment 1 of the present invention;

[0022] Figure 4 The performance diagram of lithium-sulfur batteries with separators modified with different materials prepared in the present invention at different rates;

[0023] Figure 5 This is a graph showing the cycling stability of lithium-sulfur batteries with separators modified with different materials prepared in the present invention; DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0025] Example 1

[0026] (1) Preparation of bimetallic sulfide heterojunction material: Thiourea, nickel chloride, and sodium tungstate were weighed in a molar ratio of 1:5:20, added to 100 ml of deionized water, and stirred until completely dissolved. The mixed solution was then transferred to a high-temperature hydrothermal reactor and reacted at 270°C for 24 hours. The product was then centrifuged, washed five times with deionized water and anhydrous ethanol, and dried at 60°C for 12 hours. The heterojunction nanomaterial was obtained.

[0027] (2) Preparation of a bimetallic sulfide heterojunction modified diaphragm: The heterojunction material obtained in step (1) was mixed with carbon nanotubes and PVDF in a ratio of 8:1:1 to obtain a uniform slurry. The slurry was then evenly coated on a polypropylene diaphragm using a 100 μm applicator and then dried in a vacuum oven at 60°C for 12 hours. Finally, a heterojunction modified diaphragm was obtained.

[0028] (3) Preparation of positive electrode: carbon nanotubes and sulfur were mixed in a mass ratio of 7:3 and fully ground, and then heat-treated in an oven at 165°C for 12 hours. Then, the carbon / sulfur composite material, conductive carbon and PVDF were added to an appropriate amount of N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 and stirred evenly. The slurry was then evenly coated on aluminum foil using a 150μm coater. After that, the slurry was vacuum-dried at 60°C for 12 hours and cut into 14mm diameter discs to obtain the positive electrode sheet of lithium-sulfur battery.

[0029] (4) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the heterojunction material modified diaphragm prepared above was used as the battery diaphragm, and the electrolyte was 1 mol L -1 A mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a 1:1 volume ratio, and 1% lithium nitrate was prepared. CR2025 coin cells were assembled in an argon atmosphere glove box.

[0030] (5) Conventional battery performance test: The LAND test system is used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.5 to 3V.

[0031] Example 2

[0032] (1) Preparation of pure NiS2 material: Nickel chloride and thiourea were weighed in a molar ratio of 1:20, added to 100 ml of deionized water, and stirred until completely dissolved. The mixed solution was then transferred to a high-temperature hydrothermal reactor and reacted at 270°C for 24 h. The product was then centrifuged, washed five times with deionized water and anhydrous ethanol, and dried at 60°C for 12 h. The NiS2 material was obtained.

[0033] (2) Preparation of a pure NiS2 material modified diaphragm: The NiS2 material obtained in step (1) was mixed with carbon nanotubes and PVDF in a ratio of 8:1:1 to obtain a uniform slurry. The slurry was then evenly coated on a polypropylene diaphragm using a 100 μm applicator and then dried in a vacuum oven at 60°C for 12 hours. Finally, a NiS2 modified diaphragm was obtained.

[0034] (3) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the NiS2 material modified diaphragm prepared above was used as the battery diaphragm, and the electrolyte was a concentration of 1 mol L -1 A mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a 1:1 volume ratio, and 1% lithium nitrate was prepared. CR2025 coin cells were assembled in an argon atmosphere glove box.

[0035] (4) Conventional battery performance test: The LAND test system is used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.5 to 3V.

[0036] Example 3

[0037] (1) Preparation of pure WS2 material: Sodium tungstate and thiourea were weighed in a 1:4 molar ratio, added to 100 ml of deionized water, and stirred until completely dissolved. The mixed solution was then transferred to a high-temperature hydrothermal reactor and reacted at 270°C for 24 h. The product was then centrifuged, washed five times with deionized water and anhydrous ethanol, and dried at 60°C for 12 h. WS2 material was obtained.

[0038] (2) Preparation of a pure WS2 material modified membrane: The NiS2 material obtained in step (1) was mixed with carbon nanotubes and PVDF in a ratio of 8:1:1 to obtain a uniform slurry. The slurry was then evenly coated on a polypropylene membrane using a 100 μm applicator and then dried in a vacuum oven at 60°C for 12 h. Finally, a WS2 modified membrane was obtained.

[0039] (3) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the WS2 material modified diaphragm prepared above was used as the battery diaphragm, and the electrolyte was a concentration of 1 mol L -1 A mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a 1:1 volume ratio, and 1% lithium nitrate was prepared. CR2025 coin cells were assembled in an argon atmosphere glove box.

[0040] (4) Conventional battery performance test: The LAND test system is used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.5 to 3V.

[0041] Comparative Example 1

[0042] (1) Preparation of carbon nanotube-modified separator: CNTs and PVDF were mixed in appropriate proportions to obtain a uniform slurry. The slurry was then evenly coated onto a polypropylene separator using a 100 μm applicator and then dried in a vacuum oven at 60°C for 12 h. Finally, a carbon nanotube-modified separator was obtained.

[0043] (2) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the carbon nanotube material modified diaphragm prepared above was used as the battery diaphragm, and the electrolyte was a concentration of 1 mol L -1 A mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a 1:1 volume ratio, and 1% lithium nitrate was prepared. CR2025 coin cells were assembled in an argon atmosphere glove box.

[0044] (3) Conventional battery performance test: The LAND test system is used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.5 to 3V.

[0045] Comparative Example 2

[0046] (1) Battery assembly: The sulfur / carbon nanotube electrode prepared above was used as the positive electrode, the metal lithium sheet was used as the negative electrode, the polypropylene separator was used as the battery separator, and the electrolyte was a 1 mol L -1 A mixed solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a 1:1 volume ratio, and 1% lithium nitrate was prepared. CR2025 coin cells were assembled in an argon atmosphere glove box.

[0047] (2) Conventional battery performance test: The LAND test system is used to perform charge and discharge tests on the above assembled batteries, with a voltage range of 1.5 to 3V.

[0048] Although the present invention has been described with reference to several specific embodiments, it should be understood that the invention is not limited to the specific embodiments disclosed, and the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for preparing a bimetallic sulfide heterojunction modified diaphragm, characterized in that The following steps are involved: (1) Sodium tungstate and thiourea are mixed with nickel chloride, added into deionized water and stirred until completely dissolved, then the mixed solution is transferred to a high temperature resistant reactor for hydrothermal reaction, and then the product is centrifuged, washed and dried to obtain a bimetallic sulfide heterojunction material having a three-dimensional flower-like structure constructed by self-assembly of NiS2-WS2 heterojunction nanosheets; (2) The bimetallic sulfide heterojunction material, the conductive agent and the binder obtained in step (1) are mixed and added into N-methylpyrrolidone to obtain a uniform slurry, and then the slurry is coated on the diaphragm and vacuum dried to obtain a bimetallic sulfide heterojunction modified diaphragm; The mass ratio of nickel chloride: sodium tungstate: thiourea in step (1) is 1:5:20; The hydrothermal reaction temperature in step (1) is 270° C. and the reaction time is 24 h.

2. The method for preparing a bimetallic sulfide heterojunction modified diaphragm according to claim 1, wherein: The washing and drying in step (1) are specifically as follows: washing with deionized water and ethanol, and then drying.

3. The method for preparing a bimetallic sulfide heterojunction modified diaphragm according to claim 1, wherein: The membrane in step (2) is any one of a cellulose membrane, a polyethylene membrane, a polypropylene membrane, an aramid membrane, a polyester membrane, Celgard 2400 and Celgard 2500.

4. The method for preparing a bimetallic sulfide heterojunction modified diaphragm according to claim 1, wherein: In the step (2), the conductive agent is carbon nanotubes, and the binder is any one of polyvinylidene fluoride, polytetrafluoroethylene and carboxymethyl cellulose.

5. A bimetallic sulfide heterojunction modified diaphragm prepared by the preparation method according to claim 1.

6. Use of the bimetallic sulfide heterojunction modified separator as claimed in claim 5 as a separator in a lithium-sulfur battery.

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