Mxene quantum dot modified nitrogen-doped graphene material, preparation method and isolating membrane

Abstract

The invention provides an Mxene quantum dot modified nitrogen-doped graphene material, a preparation method and an isolating membrane. The Mxene quantum dot modified nitrogen-doped graphene material comprises Mxene quantum dots and nitrogen-doped graphene, and based on the mass of the Mxene quantum dot modified nitrogen-doped graphene material, the mass percentage content of the Mxene quantum dots is 30%-60%. According to the Mxene quantum dot modified nitrogen-doped graphene material provided by the invention, a conductive-adsorption-catalysis interface can be constructed, the shuttle effect of polysulfide is effectively inhibited, rapid conversion of the polysulfide is promoted, and the cycle performance and rate capability of a lithium-sulfur battery are improved.

Description

Technical Field

[0001] This application relates to the technical field of battery materials, and specifically relates to an Mxene quantum dot modified nitrogen-doped graphene material, a preparation method thereof, and a separator membrane. Background Art

[0002] Lithium-sulfur batteries use elemental sulfur as the positive electrode active material, metallic lithium as the negative electrode, and an organic liquid electrolyte. It has an energy density as high as 2600 Wh / kg, making it have great application potential in the fields of portable electronics, electric vehicles, and large-scale energy storage. In addition, sulfur is rich in reserves, low in price, and environmentally friendly as a raw material, making lithium-sulfur batteries receive more and more attention.

[0003] However, the "solid-liquid-solid" multiphase conversion process involved in the positive electrode discharge process of lithium-sulfur batteries, and the long-chain polysulfides generated will dissolve in the organic electrolyte and shuttle between the positive and negative electrodes, resulting in a series of problems, including but not limited to low conductivity, shuttle effect, volume expansion, and slow reaction kinetics. The existence of these problems seriously restricts the practical application process of lithium-sulfur batteries.

[0004] To solve or alleviate the above problems, most research on lithium-sulfur batteries is dedicated to developing new positive electrode materials. In 2009, the Nazar research group constructed a mesoporous carbon-sulfur positive electrode material by filling sulfur into ordered mesoporous carbon CMK-3, greatly improving the discharge specific capacity and cycle stability of lithium-sulfur batteries. This strategy has become the most commonly used method to solve the problems of sulfur positive electrodes. By encapsulating sulfur in highly conductive porous carbon, the conductivity has been greatly improved, and at the same time, the dissolution and shuttle effect of lithium polysulfide have also been greatly improved.

[0005] In addition to improving the positive electrode materials, researchers have found that the functional modification of separator membranes may also become an effective strategy. However, the currently used functional materials for separator membrane modification are difficult to meet the above requirements at the same time, so it is necessary to further develop new functional materials to solve the above problems. Summary of the Invention

[0006] In view of the above problems existing in the prior art, this application proposes an Mxene quantum dot modified nitrogen-doped graphene material, a preparation method thereof, and a separator membrane. The Mxene quantum dot modified nitrogen-doped graphene material proposed in this application can construct a conductive-adsorptive-catalytic interface, effectively inhibit the shuttle effect of polysulfides and promote the rapid conversion of polysulfides, and improve the cycle performance and rate performance of lithium-sulfur batteries.

[0007] The first aspect of the present application provides a material of Mxene quantum dots modified nitrogen-doped graphene. The material of Mxene quantum dots modified nitrogen-doped graphene includes Mxene quantum dots and nitrogen-doped graphene. Among them, based on the mass of the material of Mxene quantum dots modified nitrogen-doped graphene, the mass percentage of Mxene quantum dots is 30% to 60%.

[0008] The second aspect of the present application proposes a preparation method of a material of Mxene quantum dots modified nitrogen-doped graphene. This preparation method is used to prepare the aforementioned material of Mxene quantum dots modified nitrogen-doped graphene.

[0009] The third aspect of the present application proposes a separator. At least one surface of the separator is loaded with the aforementioned material of Mxene quantum dots modified nitrogen-doped graphene or the material of Mxene quantum dots modified nitrogen-doped graphene prepared according to the aforementioned preparation method.

[0010] The fourth aspect of the present application proposes a preparation method of a separator. This preparation method is used to prepare the aforementioned separator loaded with the material of Mxene quantum dots modified nitrogen-doped graphene.

[0011] The fifth aspect of the present application provides a lithium-sulfur battery. The lithium-sulfur battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and the aforementioned separator loaded with the material of Mxene quantum dots modified nitrogen-doped graphene.

[0012] The sixth aspect of the present application provides a device. The device includes the aforementioned lithium-sulfur battery.

[0013] The technical solution of the present application can achieve the following beneficial effects:

[0014] The present application proposes a material of Mxene quantum dots modified nitrogen-doped graphene and applies it to the separator of a lithium-sulfur battery. Specifically, for the material of Mxene quantum dots modified nitrogen-doped graphene proposed in the present application, the strong adsorption ability of Mxene quantum dots is combined with the high conductivity, large specific surface area, and rich active sites of nitrogen-doped graphene. Among them, Mxene quantum dots have rich active adsorption sites and have a strong adsorption catalytic conversion ability for polysulfides. As a quantum dot carrier, nitrogen-doped graphene can not only serve as a physical barrier to spatially confine polysulfides but also serve as a conductive framework to provide a fast electron channel. Therefore, the combination of Mxene quantum dots and nitrogen-doped graphene can construct a conductive-adsorption-catalytic interface, effectively adsorb and catalyze polysulfides, inhibit their shuttle effect in the electrolyte, and promote the rapid conversion of polysulfides, improve the utilization rate of active materials, and thus enhance the cycle performance and rate performance of the lithium-sulfur battery. Description of the Drawings

[0015] Figure 1A bar chart schematically showing the comparison results of the rate performance tests of the lithium-sulfur batteries assembled in Example 6 and Comparative Example 2.

[0016] Figure 2 A comparison chart of the cycling performance of the lithium-sulfur batteries assembled in Example 6 and Comparative Example 2 under the 1C rate condition is schematically shown.

[0017] Figure 3 The ultraviolet absorption spectra of the supernatant after the polysulfide adsorption in Example 3 and Comparative Example 1 are schematically shown. Detailed implementation manners

[0018] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some but not all of the embodiments of the present application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as a limitation of the present application.

[0019] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0020] In the description herein, unless otherwise specified, "above" and "below" include the number itself.

[0021] Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0022] A list of items joined by the term "at least one of", "at least one", "at least one kind of", or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0023] Mxene quantum dot modified nitrogen-doped graphene material

[0024] One or more embodiments of the present application provide an Mxene quantum dot modified nitrogen-doped graphene material, which includes Mxene quantum dots and nitrogen-doped graphene. Among them, based on the mass of the Mxene quantum dot modified nitrogen-doped graphene material, the mass percentage content of the Mxene quantum dots is 30% to 60%.

[0025] The present application proposes an Mxene quantum dot modified nitrogen-doped graphene material and applies it to the separator of a lithium-sulfur battery. Specifically, the Mxene quantum dot modified nitrogen-doped graphene material proposed in the present application combines the strong adsorption ability of Mxene quantum dots with the high conductivity, large specific surface area, and rich active sites of nitrogen-doped graphene. Among them, Mxene quantum dots have rich active adsorption sites and have a strong adsorption catalytic conversion ability for polysulfides. As a quantum dot carrier, nitrogen-doped graphene can not only act as a physical barrier to spatially confine polysulfides but also act as a conductive skeleton to provide a fast electron channel. Therefore, the composite of Mxene quantum dots and nitrogen-doped graphene can construct a conductive-adsorption-catalytic interface, effectively adsorb and catalyze polysulfides, inhibit their shuttle effect in the electrolyte, and promote the rapid conversion of polysulfides, improve the utilization rate of active materials, and thus enhance the cycle performance and rate performance of lithium-sulfur batteries.

[0026] In some embodiments, based on the mass of the Mxene quantum dot-modified nitrogen-doped graphene material, the mass percentage of the Mxene quantum dots is 30% to 60%. If the mass percentage of the Mxene quantum dots is too high, the particles are prone to agglomeration, and it is not easy to obtain quantum dots, which affects the catalytic effect; if the mass percentage of the Mxene quantum dots is too low, the catalytic active sites are reduced and the catalytic performance is lowered; limiting the mass percentage of the Mxene quantum dots within the above range is beneficial to maximizing the synergistic effect of the quantum dots and the nitrogen-doped graphene material. In some embodiments, the mass percentage of the Mxene quantum dots is 30%, 35%, 40%, 45%, 50%, 55%, 60% or the range composed of any two of the above values.

[0027] In some embodiments, based on the mass of the Mxene quantum dot-modified nitrogen-doped graphene material, the mass percentage of the Mxene quantum dots is 35% to 50%. Limiting the mass percentage of the Mxene quantum dots within the above range is beneficial to further improving the catalytic performance of the Mxene quantum dot-modified nitrogen-doped graphene material.

[0028] In some embodiments, the particle size of the Mxene quantum dot-modified nitrogen-doped graphene material is 1 nm to 5 nm. In some embodiments, the particle size of the Mxene quantum dot-modified nitrogen-doped graphene material is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm or the range composed of any two of the above values. If the particle size of the Mxene quantum dot-modified nitrogen-doped graphene material is too large, the exposed active sites are reduced and the catalytic performance is lowered; if the particle size of the Mxene quantum dot-modified nitrogen-doped graphene material is too small, the preparation difficulty and cost are significantly increased; limiting the particle size of the Mxene quantum dot-modified nitrogen-doped graphene material within the above range is beneficial to exerting the best catalytic performance. In some embodiments, the particle size of the Mxene quantum dot-modified nitrogen-doped graphene material is 1 nm to 4 nm.

[0029] Preparation method of Mxene quantum dot-modified nitrogen-doped graphene material

[0030] One or more embodiments of the present application provide a preparation method of the aforementioned Mxene quantum dot-modified nitrogen-doped graphene material, and the preparation method includes:

[0031] S1. Provide Mxene nanosheets;

[0032] S2. Mix the Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate in a mass ratio of (2 to 6):10:(30 to 40):7; obtain a reaction product through a hydrothermal reaction, and the reaction product is frozen and dried to obtain the Mxene quantum dot-modified nitrogen-doped graphene material.

[0033] In some embodiments, the Mxene nanosheets include M a C b T d in the nanosheets, where M is at least one of Ti, Nb, Cr, and Mo; T is at least one of OH, O, and F; a takes a value of 1, 2, or 3, b takes a value of 1, 2, or 3, and d takes any value between 0 and 2.

[0034] In some embodiments, the Mxene nanosheets are Nb2CT d 、Ti2CT d 、Cr2TiC2T d 、Mo2TiC2T d 、Mo2TiC3T d and at least one of Mo2CT.

[0035] In some embodiments, in S2, the Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate are added to deionized water in a mass ratio of (3 - 5):10:(30 - 40):7 for mixing.

[0036] In some embodiments, the preparation method of the Mxene nanosheets includes: mixing Ti3AlC2 powder with the prepared HCl - LiF mixed solution, stirring at 40°C to 60°C for 24 h to 36 h to obtain a reaction product, and the reaction product is washed and vacuum dried to obtain Ti3C2T d powder, and the Ti3C2T d powder is ultrasonically treated, frozen, and dried to obtain Mxene nanosheets; where T is at least one of OH, O, and F, and d takes any value between 0 and 2.

[0037] In some embodiments, the above washing includes washing the reaction product with deionized water until it is neutral, and then washing it with an organic solvent 1 to 10 times.

[0038] In some embodiments, the conditions for the hydrothermal reaction in S2 are: temperature 120°C to 150°C; reaction time is 6 h to 12 h.

[0039] In some embodiments, the hydrothermal reaction temperature in S2 is 120°C to 180°C. If the reaction temperature is too high, more defects will be generated on the surface of the quantum dots, thereby reducing the catalytic activity; if the reaction temperature is too low, the yield of the quantum dots will be too low, which will also reduce the catalytic activity; limiting the reaction temperature within the above range is beneficial to exerting the best catalytic performance of the Mxene quantum dot modified nitrogen-doped graphene material. In some embodiments, the hydrothermal reaction temperature is 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C or the range composed of any two of the above values.

[0040] In some embodiments, in the reaction kettle of S2, the reaction time is 6 h to 12 h; if the reaction time is too long, more defects will be generated on the surface of the quantum dots, thereby reducing the catalytic activity; if the reaction time is too short, the yield of the quantum dots will be too low, which will also reduce the catalytic activity; limiting the reaction time within the above range is beneficial to exerting the best catalytic performance of the Mxene quantum dot modified nitrogen-doped graphene material. In some embodiments, the reaction time is 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h or the range composed of any two of the above values.

[0041] In some embodiments, in S2, Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate are mixed in a mass ratio of (2 to 6):10:40:7. By adjusting the ratio between Mxene nanosheets and graphene oxide, the mass percentage content of Mxene quantum dots in the Mxene quantum dot modified nitrogen-doped graphene material is controlled.

[0042] In some embodiments, S2 includes adding Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate in a mass ratio of (2 to 6):10:40:7 to deionized water for mixing, ultrasonic treatment for 2 h to 4 h, and then transferring to a reaction kettle for hydrothermal reaction, controlling the hydrothermal reaction temperature to be 120°C to 180°C, and the hydrothermal reaction time to be 6 h to 24 h to obtain a reaction product, and the reaction product is washed, frozen, and dried to obtain the Mxene quantum dot modified nitrogen-doped graphene material.

[0043] In some embodiments, the washing in S2 includes washing the reaction product with deionized water until it is neutral, and then washing it with an organic solvent 1 to 10 times.

[0044] Separator membrane loaded with Mxene quantum dot modified nitrogen-doped graphene material and its preparation method

[0045] One or more embodiments of the present application provide a separator membrane loaded with Mxene quantum dot modified nitrogen-doped graphene material.

[0046] In some embodiments, the loading amount of the Mxene quantum dot-modified nitrogen-doped graphene material is 0.1 mg / cm 2 to 0.2 mg / cm 2 。The Mxene quantum dot-modified nitrogen-doped graphene material is not an active material and cannot intercalate and deintercalate lithium atoms. Under the condition of ensuring its function, the lower the loading amount, the better. In some embodiments, the loading amount of the Mxene quantum dot-modified nitrogen-doped graphene material is 0.1 mg / cm 2 , 0.11 mg / cm 2 , 0.12 mg / cm 2 , 0.13 mg / cm 2 , 0.14 mg / cm 2 , 0.15 mg / cm 2 , 0.16 mg / cm 2 , 0.17 mg / cm 2 , 0.18 mg / cm 2 , 0.19 mg / cm 2 , 0.2 mg / cm 2 or the range composed of any two of the above values. In some embodiments, the loading amount of the Mxene quantum dot-modified nitrogen-doped graphene material is 0.1 mg / cm 2 to 0.12 mg / cm 2 。

[0047] One or more embodiments of the present application provide a method for preparing a separator loaded with an Mxene quantum dot-modified nitrogen-doped graphene material, including the following steps:

[0048] N1. Grind the Mxene quantum dot-modified nitrogen-doped graphene material and polyvinylidene fluoride evenly according to a mass ratio of 90:10 to 95:5, add N-methylpyrrolidone, and stir evenly to obtain a slurry;

[0049] N2. Coat the slurry on at least one surface of the separator, and the coating areal density is 0.1 mg / cm 2 to 0.2 mg / cm 2 , and dry to obtain a separator loaded with an Mxene quantum dot-modified nitrogen-doped graphene material.

[0050] In some embodiments, the slurry is coated on one surface of the separator.

[0051] There are no particular limitations on the material and shape of the separator itself that can be used in the embodiments of the present application, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present application.

[0052] In some embodiments, the separator membrane includes a base film and a coating disposed on the base film. The base film includes at least one of a polyethylene film, a polypropylene film, a PP / PE / PP composite film, a polyimide film, an aramid film, a polyethylene terephthalate film, or a non-woven fabric. In some embodiments, the coating includes at least one of a polymer layer, an inorganic ceramic layer, or a mixed layer of a polymer and an inorganic ceramic layer.

[0053] In some embodiments, the inorganic ceramic layer includes inorganic particles and a binder. The inorganic particles include at least one of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0054] The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride - hexafluoropropylene).

[0055] Lithium - sulfur battery

[0056] One or more embodiments of the present application provide a lithium - sulfur battery, which includes a positive electrode plate, a negative electrode plate, an electrolyte, and the aforementioned separator membrane loaded with Mxene quantum dot - modified nitrogen - doped graphene material. During the charge and discharge process of the battery, active ions shuttle between the positive electrode plate and the negative electrode plate for insertion and extraction. The electrolyte functions to conduct ions between the positive electrode plate and the negative electrode plate. The separator membrane loaded with Mxene quantum dot - modified nitrogen - doped graphene material is disposed between the positive electrode plate and the negative electrode plate to prevent short - circuit between the positive and negative electrodes and allow ions to pass through.

[0057] Sulfur cathode

[0058] In some embodiments, the sulfur positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material contains the positive electrode active material.

[0059] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.

[0060] In some embodiments, the positive electrode active material may be a positive electrode active material for lithium-sulfur batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: elemental sulfur, sulfur-containing compounds, or mixtures thereof. The sulfur-containing compounds may particularly be Li2Sn (n≥1), organic sulfur compounds, or carbon-sulfur polymers ((C2S x ) n , where x = 2.5 to 50, and n≥2).

[0061] In some embodiments, the positive electrode active material layer may further include a conductive material, which may be a carbon-based material, such as carbon black, graphite, graphene, activated carbon, carbon fiber, carbon nanotubes (CNT), etc. Additionally, metal fibers, such as metal meshes, etc.; metal powders, such as copper, silver, nickel, aluminum, etc.; or organic conductive materials, such as polyphenylene derivatives, etc. may also be used as the conductive material. The conductive materials may be used alone or in combination. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0062] In some embodiments, the positive electrode active material layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0063] In some embodiments, the positive electrode sheet may be prepared by the following method: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0064] Lithium anode

[0065] In some embodiments, the lithium negative electrode may be lithium metal or a lithium alloy.

[0066] Electrolyte

[0067] The electrolyte of the present application includes a lithium salt and a solvent.

[0068] In some embodiments, the electrolyte includes a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In some embodiments, the lithium salt is preferably LiTFSI, which can provide high ionic conductivity.

[0069] In some embodiments, the solvent includes at least one of a chain carbonate compound, a cyclic carbonate compound, a carboxylic acid ester compound, and an ether compound.

[0070] In some embodiments, the chain carbonate compound includes, but is not limited to, one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC).

[0071] In some embodiments, the cyclic carbonate compound includes, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene carbonate (VEC).

[0072] In some embodiments, the carboxylic acid ester compound includes, but is not limited to, one or more of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone.

[0073] In some embodiments, the ether compound includes at least one of 1,3-dioxolane (DOL), dimethoxyethane (DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0074] In some embodiments, the electrolyte may further optionally include an additive. For example, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may also include an additive capable of improving certain battery performance, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature or low-temperature performance of the battery, etc. In some embodiments, the additive is preferably lithium nitrate (LiNO3).

[0075] Separator

[0076] In some embodiments, a separator is provided between the positive electrode and the negative electrode to prevent short circuit. The separator applicable to the embodiments of the present application is the aforementioned separator loaded with Mxene quantum dot-modified nitrogen-doped graphene material. The present application will not elaborate here.

[0077] In some embodiments, the lithium-sulfur battery includes a lithium-sulfur secondary battery. The lithium-sulfur secondary battery may include an outer package, and the outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the lithium-sulfur secondary battery may also be a soft package, such as a pouch-type soft package. The material of the soft package may be plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0078] In some embodiments, the shape of the lithium-sulfur secondary battery is not particularly limited, and it may be cylindrical, square, or any other shape.

[0079] In some embodiments, the present application also provides a battery module. The battery module includes the above-mentioned lithium-sulfur battery. Since the battery module of the present application adopts the above-mentioned lithium-sulfur battery, it has at least the same advantages as the lithium-sulfur battery. The number of lithium-sulfur batteries included in the battery module of the present application may be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0080] In some embodiments, the present application also provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0081] Device

[0082] One or more embodiments of the present application provide a device, which includes at least one of the above-mentioned lithium-sulfur battery, battery module, or battery pack.

[0083] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, energy storage systems, etc. In order to meet the high-power and high-energy density requirements of the device for the lithium-sulfur battery, a battery pack or a battery module can be adopted.

[0084] In some other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device usually requires thin and light, and a lithium-sulfur battery can be used as the power source.

[0085] Hereinafter, the lithium-sulfur battery of the present application will be further elaborated in combination with specific embodiments and comparative examples.

[0086] Embodiments and Comparative Examples

[0087] Hereinafter, embodiments and comparative examples are given to further specifically illustrate the present application, but the present application is not limited to these embodiments as long as it does not deviate from its gist.

[0088] The materials and reagents used in the following embodiments are obtained by the preparation method of the present application or commercially available. The present application does not make specific limitations.

[0089] Preparation of Mxene Quantum Dots Modified Nitrogen-Doped Graphene Material

[0090] Example 1

[0091] S1. Add 10 g of Ti3AlC2 powder to the prepared 200 mL HCl-LiF mixed solution (HCl concentration is 10 mol / L, LiF concentration is 5 mol / L) for mixing. Stir at 40 °C for 24 h to remove the aluminum atomic layer to obtain a reaction product. Wash the reaction product with deionized water until neutral (pH value is 7), then wash it with ethanol 3 times, and vacuum dry at 80 °C to obtain multi-layer Ti3C2T d powder. Ultrasonically treat the multi-layer Ti3C2T d powder with deionized water for 4 h, and obtain Mxene nanosheets through freezing and drying;

[0092] S2. Add the Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate obtained in S1 to deionized water for mixing according to the mass ratio of Mxene nanosheets:graphene oxide:ammonia water:hydrazine hydrate = 5:10:40:7. Ultrasonically treat for 3 h, then transfer to a reaction kettle for water washing reaction. Control the reaction temperature at 120 °C and the reaction time at 12 h to obtain a reaction product. Wash the reaction product with deionized water until neutral (pH value is 7), then wash it with ethanol 3 times, and obtain the Mxene quantum dots modified nitrogen-doped graphene material through freezing and drying. Based on the mass of the Mxene quantum dots modified nitrogen-doped graphene material, the mass percentage content of Mxene quantum dots is 50%.

[0093] Example 2

[0094] S1. Add 10 g of Ti3AlC2 powder to the prepared 200 mL HCl-LiF mixed solution (HCl concentration is 10 mol / L, LiF concentration is 5 mol / L) for mixing. Stir at 50 °C for 24 h to remove the aluminum atomic layer to obtain a reaction product. Wash the reaction product with deionized water until neutral (pH value is 7), then wash it with ethanol 3 times, and vacuum dry at 80 °C to obtain multi-layer Ti3C2T d powder. Ultrasonically treat the multi-layer Ti3C2T d powder with deionized water for 2 h, and obtain Mxene nanosheets through freezing and drying;

[0095] S2. Mix the Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate obtained in S1 in a mass ratio of Mxene nanosheets:graphene oxide:ammonia water:hydrazine hydrate = 5:10:40:7 into deionized water, ultrasonically treat for 3 h, then transfer to a reaction kettle for a water washing reaction, control the reaction temperature at 120 °C, and the reaction time at 6 h to obtain a reaction product. Wash the reaction product with deionized water until neutral (pH value is 7), then wash with ethanol 3 times, and obtain the Mxene quantum dot modified nitrogen-doped graphene material through freezing and drying. Based on the mass of the Mxene quantum dot modified nitrogen-doped graphene material, the mass percentage content of the Mxene quantum dots is 50%.

[0096] Example 3

[0097] S1. Add 10 g of Ti3AlC2 powder to the prepared 200 mL HCl-LiF mixed solution (HCl concentration is 10 mol / L, LiF concentration is 5 mol / L) for mixing. At 60 °C, stir for 24 h to remove the aluminum atomic layer to obtain a reaction product. Wash the reaction product with deionized water until neutral (pH value is 7), then wash with ethanol 3 times, and vacuum dry at 80 °C to obtain multi-layer Ti3C2T d powder. Ultrasonically treat the multi-layer Ti3C2T d powder with deionized water for 4 h, and obtain Mxene nanosheets through freezing and drying;

[0098] S2. Mix the Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate obtained in S1 in a mass ratio of Mxene nanosheets:graphene oxide:ammonia water:hydrazine hydrate = 5:10:40:7 into deionized water, ultrasonically treat for 3 h, then transfer to a reaction kettle for a water washing reaction, control the reaction temperature at 150 °C, and the reaction time at 6 h to obtain a reaction product. Wash the reaction product with deionized water until neutral (pH value is 7), then wash with ethanol 3 times, and obtain the Mxene quantum dot modified nitrogen-doped graphene material through freezing and drying. Based on the mass of the Mxene quantum dot modified nitrogen-doped graphene material, the mass percentage content of the Mxene quantum dots is 50%.

[0099] Example 4

[0100] S1. Add 10 g of Ti3AlC2 powder to the prepared 200 mL HCl-LiF mixed solution (HCl concentration is 10 mol / L, LiF concentration is 5 mol / L) for mixing. At 40 °C, stir for 24 h to remove the aluminum atomic layer to obtain a reaction product. Wash the reaction product with deionized water until neutral (pH value is 7), then wash with ethanol 3 times, and vacuum dry at 80 °C to obtain multi-layer Ti3C2T d powder. The multi-layer Ti3C2Td The powder was ultrasonically treated with deionized water for 4 h, and then obtained Mxene nanosheets through freezing and drying.

[0101] S2. The Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate obtained in S1 were added to deionized water for mixing at a mass ratio of Mxene nanosheets:graphene oxide:ammonia water:hydrazine hydrate = 3:10:40:7, and ultrasonically treated for 3 h. Then, it was transferred to a reaction kettle for water washing reaction. The reaction temperature was controlled at 120 °C, and the reaction time was 12 h to obtain a reaction product. The reaction product was washed with deionized water until neutral (pH value of 7), and then washed with ethanol three times. After freezing and drying, Mxene quantum dot-modified nitrogen-doped graphene material was obtained. Based on the mass of the Mxene quantum dot-modified nitrogen-doped graphene material, the mass percentage content of Mxene quantum dots was 30%.

[0102] Example 5

[0103] S1. 10 g of Ti3AlC2 powder was added to the prepared 200 mL HCl-LiF mixed solution (HCl concentration was 10 mol / L, LiF concentration was 5 mol / L) for mixing. At 40 °C, it was stirred for 24 h to remove the aluminum atomic layer, and a reaction product was obtained. The reaction product was washed with deionized water until neutral (pH value of 7), and then washed with ethanol three times. It was vacuum dried at 80 °C to obtain multi-layer Ti3C2T d powder, and the multi-layer Ti3C2T d powder was ultrasonically treated with deionized water for 4 h, and then obtained Mxene nanosheets through freezing and drying.

[0104] S2. The Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate obtained in S1 were added to deionized water for mixing at a mass ratio of Mxene nanosheets:graphene oxide:ammonia water:hydrazine hydrate = 6:10:40:7, and ultrasonically treated for 3 h. Then, it was transferred to a reaction kettle for water washing reaction. The reaction temperature was controlled at 120 °C, and the reaction time was 12 h to obtain a reaction product. The reaction product was washed with deionized water until neutral (pH value of 7), and then washed with ethanol three times. After freezing and drying, Mxene quantum dot-modified nitrogen-doped graphene material was obtained. Based on the mass of the Mxene quantum dot-modified nitrogen-doped graphene material, the mass percentage content of Mxene quantum dots was 60%.

[0105] Comparative Example 1

[0106] Graphene oxide, ammonia water, and hydrazine hydrate were added to deionized water in a mass ratio of graphene oxide: ammonia water: hydrazine hydrate = 10:40:7 for mixing, followed by ultrasonic treatment for 3 h. Then, it was transferred to a reaction kettle for stirring reaction. The reaction temperature was controlled at 150 °C, and the reaction time was 6 h to obtain a reaction product. The reaction product was washed with deionized water until neutral (pH value of 7), and then washed with ethanol three times. After freezing and drying, nitrogen-doped graphene was obtained.

[0107] To compare the adsorption of polysulfides by carbon materials and MXene quantum dot-modified nitrogen-doped graphene materials, typical Li2S4 was selected as a representative of polysulfides for visible adsorption experimental research. Sulfur powder and lithium sulfide in a certain stoichiometric ratio were dispersed in a mixed solution of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) (volume ratio 1:1), and stirred at 60 °C for 24 h to prepare a Li2S4 solution, where the concentration of Li2S4 was 0.1 mol / L. The above operations were all carried out in a glove box.

[0108] Take 2 mL of the Li2S4 solution prepared above, add 10 mg of the nitrogen-doped graphene prepared in Comparative Example 1, and let it stand for 2 h. The above operations were all carried out in a glove box. Test the adsorption of polysulfides by nitrogen-doped graphene.

[0109] Take 2 mL of the Li2S4 solution prepared above, add 10 mg of the MXene quantum dot-modified nitrogen-doped graphene material prepared in Example 3, and let it stand for 2 h. The above operations were all carried out in a glove box. Test the adsorption of polysulfides by the MXene quantum dot-modified nitrogen-doped graphene material.

[0110] For the test results of Comparative Example 1 and Example 3, please refer to Figure 3 。

[0111] Preparation of lithium-sulfur battery:

[0112] Example 6

[0113] Preparation of a separator loaded with Mxene quantum dot-modified nitrogen-doped graphene material: N1. The Mxene quantum dot-modified nitrogen-doped graphene material prepared in Example 1 was ground evenly with polyvinylidene fluoride (PVDF) in a mass ratio of 9:1, and a certain proportion of N-methylpyrrolidone (NMP) was added. After stirring evenly, a slurry was obtained; N2. The slurry was coated on one side surface of the separator (model Celgard 2400) with a coating areal density of 0.1 mg / cm 2 , and dried overnight in a vacuum oven at 60 °C to obtain a separator loaded with Mxene quantum dot-modified nitrogen-doped graphene material, which was made into a 19-mm-diameter disc with a mold for standby.

[0114] Preparation of sulfur / carbon nanotube composite positive electrode sheet: Sulfur solid powder and multi-walled carbon nanotubes were mixed evenly at a mass ratio of 8:2, and then heated at 155 °C for 12 h in an inert atmosphere to obtain a carbon nanotube positive electrode loaded with sulfur. The carbon nanotube positive electrode loaded with sulfur was weighed according to a mass ratio of 9:1 with the binder polyvinylidene fluoride (PVDF), and a certain proportion of N-methylpyrrolidone (NMP) was added and mixed to adjust into a slurry. The slurry was evenly coated on an aluminum foil current collector with a film coater, dried and cut into a positive electrode sheet with a diameter of 14 mm and weighed. The sulfur loading was 2 mg / cm 2 .

[0115] Preparation of negative electrode sheet: A metal lithium sheet with a thickness of 450 μm and a diameter of 15.6 mm was used as the negative electrode sheet.

[0116] Preparation of electrolyte: In a solvent composed of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) with a volume ratio of 1:1, 1 mol / L of LiTFSI was added as a lithium salt, and 2% of LiNO3 was added as an additive based on the mass of the solvent.

[0117] Preparation of lithium-sulfur battery: The sulfur / carbon nanotube composite positive electrode sheet, the separator loaded with Mxene quantum dot-modified nitrogen-doped graphene material, and the lithium metal negative electrode sheet of this example were assembled. Among them, the side of the separator loaded with Mxene quantum dot-modified nitrogen-doped graphene material was placed facing the positive electrode sheet side, and the electrolyte was injected to obtain a lithium-sulfur battery, where the liquid-sulfur ratio (E / S) was 10 μL / mg.

[0118] Example 7

[0119] Preparation of separator loaded with Mxene quantum dot-modified nitrogen-doped graphene material: N1. The Mxene quantum dot-modified nitrogen-doped graphene material prepared in Example 2 and polyvinylidene fluoride (PVDF) were ground evenly at a mass ratio of 9:1, and a certain proportion of N-methylpyrrolidone (NMP) was added and stirred evenly to obtain a slurry; N2. The slurry was coated on one side surface of the separator (model Celgard 2400) with a doctor blade, and the coating areal density was 0.1 mg / cm 2 , and dried overnight in a vacuum oven at 60 °C to obtain a separator loaded with Mxene quantum dot-modified nitrogen-doped graphene material, which was made into a round sheet with a diameter of 19 mm with a mold for standby.

[0120] The preparation methods of the sulfur / carbon nanotube composite positive electrode sheet, the negative electrode sheet, the electrolyte, and the lithium-sulfur battery are the same as those in Example 6.

[0121] Example 8

[0122] Preparation of a separator membrane loaded with Mxene quantum dot-modified nitrogen-doped graphene material: N1. Grind the Mxene quantum dot-modified nitrogen-doped graphene material prepared in Example 3 and polyvinylidene fluoride (PVDF) evenly according to a mass ratio of 9:1, add a certain proportion of N-methylpyrrolidone (NMP), and stir evenly to obtain a slurry; N2. Use a scraper to coat the slurry on one side surface of the separator membrane (model: Celgard 2400), and the coating areal density is 0.1 mg / cm 2 , and dry it overnight in a vacuum oven at 60 °C to obtain a separator membrane loaded with Mxene quantum dot-modified nitrogen-doped graphene material, and make it into a circular piece with a diameter of 19 mm using a mold for standby.

[0123] The preparation methods of the sulfur / carbon nanotube composite positive electrode sheet, negative electrode sheet, electrolyte, and lithium-sulfur battery are the same as those in Example 6.

[0124] Example 9

[0125] Preparation of a separator membrane loaded with Mxene quantum dot-modified nitrogen-doped graphene material: N1. Grind the Mxene quantum dot-modified nitrogen-doped graphene material prepared in Example 4 and polyvinylidene fluoride (PVDF) evenly according to a mass ratio of 9:1, add a certain proportion of N-methylpyrrolidone (NMP), and stir evenly to obtain a slurry; N2. Use a scraper to coat the slurry on one side surface of the separator membrane (model: Celgard 2400), and the coating areal density is 0.1 mg / cm 2 , and dry it overnight in a vacuum oven at 60 °C to obtain a separator membrane loaded with Mxene quantum dot-modified nitrogen-doped graphene material, and make it into a circular piece with a diameter of 19 mm using a mold for standby.

[0126] The preparation methods of the sulfur / carbon nanotube composite positive electrode sheet, negative electrode sheet, electrolyte, and lithium-sulfur battery are the same as those in Example 6.

[0127] Example 10

[0128] Preparation of a separator membrane loaded with Mxene quantum dot-modified nitrogen-doped graphene material: N1. Grind the Mxene quantum dot-modified nitrogen-doped graphene material prepared in Example 5 and polyvinylidene fluoride (PVDF) evenly according to a mass ratio of 9:1, add a certain proportion of N-methylpyrrolidone (NMP), and stir evenly to obtain a slurry; N2. Use a scraper to coat the slurry on one side surface of the separator membrane (model: Celgard 2400), and the coating areal density is 0.1 mg / cm 2 , and dry it overnight in a vacuum oven at 60 °C to obtain a separator membrane loaded with Mxene quantum dot-modified nitrogen-doped graphene material, and make it into a circular piece with a diameter of 19 mm using a mold for standby.

[0129] The preparation methods of the sulfur / carbon nanotube composite positive electrode sheet, negative electrode sheet, electrolyte, and lithium-sulfur battery are the same as those in Example 6.

[0130] Comparative Example 2

[0131] Preparation of the separator: Celgard 2400 separator was used as the separator in this comparative example.

[0132] Preparation of the sulfur / carbon nanotube composite positive electrode sheet: Sulfur solid powder and multi-walled carbon nanotubes were mixed evenly in a mass ratio of 8:2, and then heated in an inert atmosphere at 155 °C for 12 h to obtain a carbon nanotube positive electrode loaded with sulfur. The carbon nanotube positive electrode loaded with sulfur and the binder polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 9:1, and a certain proportion of N-methylpyrrolidone (NMP) was added and mixed to adjust into a slurry. The slurry was evenly coated on an aluminum foil current collector with a film coater, dried and cut into a pole piece with a diameter of 14 mm and weighed. The sulfur loading was 2 mg / cm 2 。

[0133] Preparation of the negative electrode sheet: A metal lithium sheet with a thickness of 450 μm and a diameter of 15.6 mm was used as the negative electrode sheet.

[0134] Preparation of the electrolyte: In a solvent composed of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME) with a volume ratio of 1:1, 1 mol / L of LiTFSI was added, and 2% of LiNO3 was added as an additive based on the solvent mass.

[0135] Preparation of the lithium-sulfur battery: The sulfur / carbon nanotube composite positive electrode sheet, Celgard 2400 separator, and lithium metal negative electrode sheet of this comparative example were assembled, and the electrolyte was injected to obtain a lithium-sulfur battery, where the liquid-to-sulfur ratio (E / S) was 10 μL / mg.

[0136] For the comparison results of the rate performance tests of the lithium-sulfur batteries assembled in Example 6 and Comparative Example 2, please refer to Figure 1 。

[0137] For the comparison results of the cycling performance of the lithium-sulfur batteries assembled in Example 6 and Comparative Example 2 under the condition of 1C rate, please refer to Figure 2 。

[0138] Test method

[0139] 1. Test method for the rate performance of lithium-sulfur batteries

[0140] The charge and discharge tests of the lithium-sulfur batteries in Examples 6-10 and Comparative Example 2 were all completed on a LAND CT2001A Blue Electric Battery Test System. The specific test method is as follows:

[0141] 1) Let the lithium-sulfur battery stand still for 4 h; 2) Discharge at 0.2 C to 1.8 V; after standing still for 10 min, charge at 0.2 C to 2.7 V; 3) Repeat step 2 five times; 4) After standing still for 10 min, discharge at 0.5 C to 1.8 V, and then stand still for 10 min and charge at 0.5 C to 2.7 V; 5) Repeat step 4 five times; 6) After standing still for 10 min, discharge at 1.0 C to 1.8 V, and then stand still for 10 min and charge at 1.0 C to 2.7 V; 7) Repeat step 6 five times; 8) After standing still for 10 min, discharge at 2.0 C to 1.8 V, and then stand still for 10 min and charge at 2.0 C to 2.7 V; 9) Repeat step 8 five times; 10) After standing still for 10 min, discharge at 3.0 C to 1.8 V, and then stand still for 10 min and charge at 3.0 C to 2.7 V; 11) Repeat step 10 five times; 12) After standing still for 10 min, discharge at 4.0 C to 1.8 V, and then stand still for 10 min and charge at 4.0 C to 2.7 V; 13) Repeat step 12 five times; 14) After standing still for 10 min, discharge at 5.0 C to 1.8 V, and then stand still for 10 min and charge at 5.0 C to 2.7 V; 15) Repeat step 14 five times; The average value of the discharge gram capacity for 5 times at each rate is taken as the discharge specific capacity at this rate.

[0142] 2. Cycling performance test method of lithium-sulfur battery under 1 C rate

[0143] 1) Let the lithium-sulfur batteries of Examples 6-10 and Comparative Example 2 stand still in an environment of 25 °C for 4 h to reach temperature equilibrium; 2) Discharge at 0.2 C to 1.8 V; 3) After standing still for 10 min, charge at 0.2 C to 2.7 V; 4) After standing still for 10 min, discharge at 1 C to 1.8 V; 5) After standing still for 10 min, charge at 1 C to 2.7 V; 6) Repeat steps 4-5 400 times, and take the ratio of the discharge specific capacity at the 400th time to the discharge specific capacity at the first 1 C discharge as the cycling capacity retention rate.

[0144] 3. Ultraviolet absorption spectroscopy test method

[0145] Add sulfur powder and lithium sulfide with a mass ratio of 3:1 to a mixed solution of 1,3-dioxolane (DOL) and dimethoxyethane (DME) (volume ratio 1:1), and stir at 60 °C for 24 h to prepare a 0.1 mol / L Li2S4 solution; Weigh 10 mg of Mxene quantum dot modified nitrogen-doped graphene material or nitrogen-doped graphene material and add it to 2 mL of Li2S4 solution, stand still and adsorb for 2 h, take the supernatant for ultraviolet absorption spectroscopy test, and use the blank Li2S4 solution as a reference.

[0146] 4. Test method for particle size of Mxene quantum dot modified nitrogen-doped graphene material

[0147] The sample powder was added to absolute ethanol and dispersed evenly by ultrasonic waves. After that, it was dropped onto the ultra-thin carbon film with a dropper and dried in vacuum. Then, it was observed using a JEM-2100F high-resolution transmission electron microscope produced by JEOL Ltd. of Japan, and the particle size was statistically analyzed.

[0148] 5. Testing method for mass percentage content of Mxene quantum dots

[0149] The thermogravimetric curves of Mxene quantum dots, nitrogen-doped graphene materials, and Mxene quantum dot-modified nitrogen-doped graphene materials with different ratios were respectively tested under nitrogen conditions from 0 to 700 °C, and then the mass percentage content of Mxene quantum dots in the composite material could be calculated.

[0150] Please refer to Table 1 below for the test results.

[0151] Table 1

[0152]

[0153] It can be seen from Table 1 that the rate performance of the lithium-sulfur batteries in Examples 6-10 at 0.2C, 0.5C, 1.0C, 2.0C, 3.0C, 4.0C, and 5.0C is significantly better than that of the lithium-sulfur battery in Comparative Example 2; the discharge specific capacity of the lithium-sulfur batteries in Examples 6-10 when cycled to 400 cycles at a rate of 1C is significantly higher than that of the lithium-sulfur battery in Comparative Example 2. The reason lies in that the MXene quantum dot-modified nitrogen-doped graphene material proposed in this application combines the strong adsorption ability of MXene quantum dots with the high conductivity, large specific surface area, and rich active sites of nitrogen-doped graphene. Among them, MXene quantum dots have rich active adsorption sites and have a strong adsorption and catalytic conversion ability for polysulfides. As a quantum dot carrier, nitrogen-doped graphene can not only act as a physical barrier to spatially confine polysulfides but also act as a conductive framework to provide a fast electron channel. Therefore, the composite of MXene quantum dots and nitrogen-doped graphene can construct a conductive-adsorption-catalytic interface, effectively adsorb and catalyze polysulfides, inhibit their shuttle effect in the electrolyte, and promote the rapid conversion of polysulfides, improve the utilization rate of active materials, and thus enhance the cycle performance and rate performance of lithium-sulfur batteries.

[0154] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those of ordinary skill in the art will recognize that some modifications and changes can be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A material of Mxene quantum dots modified nitrogen-doped graphene, characterized in that, The Mxene quantum dot modified nitrogen-doped graphene material comprises Mxene quantum dots and nitrogen-doped graphene, wherein, based on the mass of the Mxene quantum dot modified nitrogen-doped graphene material, the mass percentage content of the Mxene quantum dots is 30% to 60%.

2. The material of Mxene quantum dots modified nitrogen-doped graphene according to claim 1, characterized in that, Based on the mass of the Mxene quantum dot modified nitrogen-doped graphene material, the mass percentage content of the Mxene quantum dots is 35% to 50%.

3. The material of Mxene quantum dots modified nitrogen-doped graphene according to claim 1, characterized in that, The particle size of the Mxene quantum dot modified nitrogen-doped graphene material is 1 nm to 5 nm.

4. A preparation method of the material of Mxene quantum dots modified nitrogen-doped graphene according to any one of claims 1 to 3, characterized in that, The preparation method comprises:[[]] S1. Provide Mxene nanosheets; S2. Mix the Mxene nanosheets, graphene oxide, ammonia water, and hydrazine hydrate in a mass ratio of (2 to 6):10:(30 to 40):7; obtain a reaction product through hydrothermal reaction, and freeze-dry the reaction product to obtain the Mxene quantum dot modified nitrogen-doped graphene material.

5. The preparation method according to claim 4, characterized in that, The Mxene nanosheets include at least one of M a C b T d in the nanosheets, where M is at least one of Ti, Nb, Cr, and Mo; T is at least one of OH, O, and F; a takes a value of 1, 2, or 3, b takes a value of 1, 2, or 3, and d takes any value between 0 and 2.

6. The preparation method according to claim 5, characterized in that, The preparation method further satisfies at least one of the following conditions:[[]] (1) In S2, the Mxene nanosheets, the graphene oxide, the ammonia water, and the hydrazine hydrate are added to deionized water in a mass ratio of (3 to 5):10:(30 to 40):7 for mixing; (2) In S2, the conditions of the hydrothermal reaction are: the reaction temperature is 120°C to 150°C; the reaction time is 6 h to 12 h.

7. A separator, characterized in that, At least one surface of the separator membrane is loaded with the Mxene quantum dot modified nitrogen-doped graphene material according to any one of claims 1 to 3 or the Mxene quantum dot modified nitrogen-doped graphene material prepared by the preparation method according to any one of claims 4 to 6.

8. The separator according to claim 7, characterized in that, The loading amount of the Mxene quantum dot modified nitrogen-doped graphene material is 0.1 mg / cm 2 to 0.2 mg / cm 2 .

9. A preparation method of the separator according to any one of claims 7 or 8, characterized in that, The preparation method comprises:[[]] N1. Grind the Mxene quantum dot modified nitrogen-doped graphene material and polyvinylidene fluoride evenly in a mass ratio of 90:10 to 95:5, add N-methylpyrrolidone, and stir evenly to obtain a slurry; N2. Coat the slurry on the surface of the separator membrane with a coating areal density of 0.1 mg / cm 2 to 0.2 mg / cm 2 , and obtain a separator membrane loaded with the Mxene quantum dot modified nitrogen-doped graphene material after drying.

10. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and the separator membrane loaded with the Mxene quantum dot modified nitrogen-doped graphene material according to claim 9.

11. A device, characterized in that, The device comprises the lithium-sulfur battery according to claim 10.

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