阅读说明：本技术 一种氮掺杂碳纳米片负载碳化物纳米颗粒改性隔膜及其制备方法和一种锂硫电池 (Nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm and preparation method thereof, and lithium-sulfur battery ) 是由 闵宇霖 代仁强 张鑫龙 时鹏辉 范金辰 徐群杰 朱晟 于 2020-12-07 设计创作，主要内容包括：本发明属于电化学材料领域,提供了一种氮掺杂碳纳米片负载碳化物纳米颗粒改性隔膜及其制备方法和一种锂硫电池,将含氮有机化合物研磨后加热,将粗产物再次研磨均匀得到前驱体,将前驱体、钼盐和双糖混合加热,将得到的颗粒溶于有机溶剂,在加入粘结剂得到混合液,将混合液涂敷在隔膜基底表面,得到改性隔膜。本发明提供的改性隔膜既保留了传统烯烃类隔膜优良的化学和电化学稳定性以及良好的机械强度,又对电池隔膜的孔径进一步限制,有效抑制了穿梭效应,改性隔膜耐高温、耐大电流充放电性能。本发明提供的包含改性隔膜的硫锂电池具有良好的锂离子传输性能、优异的机械强度、耐用性和电化学性能。(The invention belongs to the field of electrochemical materials, and provides a nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm and a preparation method thereof, and a lithium-sulfur battery. The modified diaphragm provided by the invention not only maintains the excellent chemical and electrochemical stability and good mechanical strength of the traditional olefin diaphragm, but also further limits the aperture of the battery diaphragm, effectively inhibits the shuttle effect, and has the performances of high temperature resistance and large current charge and discharge resistance. The sulfur lithium battery containing the modified diaphragm provided by the invention has good lithium ion transmission performance, excellent mechanical strength, durability and electrochemical performance.)

1. A preparation method of a nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm is characterized by comprising the following steps:

step 1, grinding a certain amount of nitrogen-containing organic compound, heating in an air environment, reacting with oxygen to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

step 2, mixing the precursor, molybdenum salt and disaccharide, and heating in a nitrogen atmosphere to obtain nitrogen-doped carbon nanosheet supported carbide nanoparticles;

step 3, dissolving the nitrogen-doped carbon nanosheet loaded carbide nanoparticles in an organic solvent, and then adding a binder to stir to obtain a mixed solution;

step 4, coating the mixed solution on the surface of a diaphragm substrate to obtain the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm,

wherein the nitrogen-containing organic compound is urea and/or melamine,

in step 2, the mass ratio of the precursor, the molybdenum salt and the disaccharide is 1: 0.5-1: 0.5-1,

in step 3, the mass ratio of the nitrogen-doped carbon nanosheet-supported carbide nanoparticles to the organic solvent to the binder is 8: 1-8: 1-8.

2. The preparation method of the nitrogen-doped carbon nanosheet supported carbide nanoparticle modified membrane of claim 1, wherein:

the diaphragm substrate is a polypropylene diaphragm and is provided with mesopores.

3. The preparation method of the nitrogen-doped carbon nanosheet supported carbide nanoparticle modified membrane of claim 1, wherein:

wherein the molybdenum salt is one or more of ammonium molybdate, ammonium tetrathiomolybdate or ammonium phosphomolybdate,

the disaccharide is one or more of sucrose, lactose or maltose,

the organic solvent is N-methyl pyrrolidone,

the binder is polytetrafluoroethylene or polyvinylidene fluoride.

4. The preparation method of the nitrogen-doped carbon nanosheet supported carbide nanoparticle modified membrane of claim 1, wherein:

wherein the binder is a perfluorosulfonic acid type polymer.

5. The preparation method of the nitrogen-doped carbon nanosheet supported carbide nanoparticle modified membrane of claim 1, wherein:

wherein in the step 1, the heating temperature is 500-550 ℃, the reaction time is 5-7 h,

in the step 2, the heating temperature is 750-850 ℃, and the reaction time is 1-3 h.

6. A nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm is characterized by comprising:

a diaphragm substrate and a modified functional layer coating the diaphragm substrate,

wherein the thickness of the modified functional layer is 300 nm-400 nm,

the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm has mesopores, the aperture of each mesopore is 50-100 nm,

the nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified diaphragm is prepared by the preparation method of the nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified diaphragm as claimed in any one of claims 1 to 5.

7. A lithium sulfur battery, comprising:

a positive electrode, a negative electrode and a separator,

wherein the separator is disposed between the positive electrode and the negative electrode,

the membrane is the nitrogen-doped carbon nanosheet supported carbide nanoparticle modified membrane of claim 6.

Technical Field

The invention belongs to the field of electrochemical materials, and particularly relates to a nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm, a preparation method thereof and a lithium-sulfur battery.

Background

As portable batteries are increasingly used in electronic devices and electric vehicles, people are pursuing long-term durability of lithium batteries, and conventional lithium ion batteries cannot meet the requirements. Since sulfur has the advantages of higher theoretical specific capacity and energy density, low price and environmental friendliness, a lithium-sulfur battery system which realizes the interconversion between electric energy and chemical energy by adopting sulfur or a sulfur-containing compound as a positive electrode and adopting a lithium or lithium storage material as a negative electrode gradually becomes the mainstream.

The lithium-sulfur battery is mainly composed of a positive electrode material, an electrolyte, a separator and a negative electrode material. The overall reaction equation isThe intermediate process of this reaction involves multiple redox reactions accompanied by a complex phase transition process of the sulfide. In particular, in the discharge process, elemental sulfur obtains electrons and is combined with lithium ions to gradually generate long-chain polysulfide Li₂S_n(4. ltoreq. n. ltoreq.8) which is very soluble in the electrolyte and therefore diffuses from the positive electrode structure through the electrolyteAs the discharge degree increases, polysulfide is further reduced until it is converted into short-chain Li₂S₂Or Li₂S, such short-chain polysulfides have low solubility and are precipitated from the electrolyte. During the charging process, however, the short-chain polysulfides lose electrons and are gradually oxidized to polysulfide intermediates and finally return to elemental sulfur.

At present, the problems existing in the charging and discharging processes of the lithium-sulfur battery are mainly as follows: (1) the electric conductivity of sulfur and lithium sulfide is low, and the volume change of sulfur particles in the charging and discharging process is large, so that the electrode structure is damaged; (2) an intermediate polysulfide generated in the charge-discharge process is highly dissolved in an organic electrolyte, so that active substance loss and energy consumption are caused; (3) the dissolved polysulfide diffuses to the cathode to form Li₂S or Li₂S₂Precipitation affects battery performance; (4) dissolved polysulphides are susceptible to shuttling effects. Shuttling effects and precipitation on the cathode surface can lead to low sulfur utilization, low coulombic efficiency of the sulfur anode, and faster capacity fade. (5) After the lithium metal of the negative electrode is subjected to a long-cycle charge and discharge process, lithium dendrites can slowly grow on the surface, and the lithium dendrites can penetrate through a diaphragm after a certain degree to cause a safety problem, and meanwhile, a part of lithium can slowly inactivate to become irreversible dead lithium after participating in a cycle for a large number of times.

The performance of the separator, which is one of the important components in the battery system, has an important influence on the battery performance. The diaphragm is positioned between the positive electrode and the negative electrode, so that the positive electrode and the negative electrode are prevented from contacting to generate short circuit in the charge-discharge cycle process, and lithium ions are allowed to freely migrate. The traditional olefin diaphragm such as polypropylene (PP) microporous membrane, Polyethylene (PE) microporous membrane, multilayer composite diaphragm (PP/PE two-layer composite or PP/PE/PP three-layer composite) produced by Celgard company and the like is the commonly used diaphragm of the lithium sulfur battery at present. The diaphragm has better chemical and electrochemical stability, good mechanical strength, lower production cost and controllable pore size. However, the diaphragm has important defects in high temperature resistance and high current resistance charge and discharge performance, and has huge potential safety hazard when being applied to a power lithium sulfur battery. Meanwhile, the conventional polyolefin separator cannot well inhibit the diffusion of polysulfide, an intermediate product, generated in the charging and discharging processes of the lithium-sulfur battery. In addition, the diaphragm prepared by electrostatic spinning has larger aperture, and polysulfide can easily penetrate through the diaphragm to reach the negative electrode, so that the corrosion of the surface of the lithium negative electrode influences the electrochemical performance. The mechanical property of the diaphragm prepared by electrostatic spinning is poor, and dendritic crystals generated in the battery circulation process are easy to pierce the diaphragm, so that potential safety hazards are caused.

Disclosure of Invention

The present invention is made to solve the above problems, and an object of the present invention is to provide a nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified separator, a method for preparing the same, and a lithium-sulfur battery.

The invention provides a preparation method of a nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm, which is characterized by comprising the following steps of: step 1, grinding a certain amount of nitrogen-containing organic compound, heating in an air environment, reacting with oxygen to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor; step 2, mixing the precursor, molybdenum salt and disaccharide, and heating in a nitrogen atmosphere to obtain nitrogen-doped carbon nanosheet supported carbide nanoparticles; step 3, dissolving the nitrogen-doped carbon nanosheet loaded carbide nanoparticles in an organic solvent, and then adding a binder to stir to obtain a mixed solution; and 4, coating the mixed solution on the surface of a diaphragm substrate to obtain the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm, wherein the nitrogen-containing organic compound is urea and/or melamine, and in the step 2, the mass ratio of the precursor to the molybdenum salt to the disaccharide is 1: 0.5-1: 0.5-1, in the step 3, the mass ratio of the nitrogen-doped carbon nanosheet loaded carbide nanoparticles to the organic solvent to the binder is 8: 1-8: 1-8.

In the preparation method of the nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified diaphragm provided by the invention, the diaphragm also has the following characteristics: the diaphragm substrate is a polypropylene diaphragm and is provided with mesopores.

In the preparation method of the nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified diaphragm provided by the invention, the diaphragm also has the following characteristics: wherein, the molybdenum salt is one or more of ammonium molybdate, ammonium tetrathiomolybdate or ammonium phosphomolybdate, the disaccharide is one or more of sucrose, lactose or maltose, the organic solvent is N-methylpyrrolidone, and the binder is polytetrafluoroethylene or polyvinylidene fluoride.

In the preparation method of the nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified diaphragm provided by the invention, the diaphragm also has the following characteristics: wherein the binder is a perfluorosulfonic acid polymer.

In the preparation method of the nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified diaphragm provided by the invention, the diaphragm also has the following characteristics: wherein, in the step 1, the heating temperature is 500-550 ℃, the reaction time is 5-7 h, and in the step 2, the heating temperature is 750-850 ℃, and the reaction time is 1-3 h.

The invention provides a nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm, which is characterized by comprising the following components in parts by weight: the membrane comprises a membrane substrate and a modified functional layer wrapping the membrane substrate, wherein the thickness of the modified functional layer is 300 nm-400 nm, the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified membrane is provided with a mesoporous, the aperture of the mesoporous is 50nm-100nm, and the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified membrane is prepared by a preparation method of the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified membrane.

The present invention provides a lithium-sulfur battery having features comprising: the carbon nano-sheet-loaded carbide nano-particle modified diaphragm is arranged between the anode and the cathode.

Action and Effect of the invention

According to the preparation method of the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm (hereinafter referred to as modified diaphragm), a certain amount of nitrogen-containing organic compound is ground and then heated in an air environment to react with oxygen to obtain a crude product, the crude product is ground again and uniformly to obtain a precursor, the precursor, molybdenum salt and disaccharide are mixed and heated in a nitrogen atmosphere to obtain nitrogen-doped carbon nanosheet loaded carbide nanoparticles, the nitrogen-doped carbon nanosheet loaded carbide nanoparticles are dissolved in an organic solvent, then a binder is added to be stirred to obtain a mixed solution, the mixed solution is coated on the surface of a diaphragm substrate to obtain the modified diaphragm, in addition, urea and melamine are used as the nitrogen-containing organic compound to provide a sufficient nitrogen source, and the mass ratio of the precursor, the molybdenum salt and the disaccharide is 1: 0.5-1: 0.5-1, so that the nanosheets can maintain enough active sites and an integral framework in the reaction process, and the mass ratio of the nitrogen-doped carbon nanosheets to the supported carbide nanoparticles to the organic solvent to the binder is 8: 1-8: 1-8, so that the nitrogen-doped carbon nanosheet-supported carbide nanoparticles can be better bonded to a commercial membrane.

The modified diaphragm provided by the invention not only maintains the excellent chemical and electrochemical stability and good mechanical strength of the traditional olefin diaphragm, but also further limits the aperture of the battery diaphragm, effectively inhibits the shuttle effect, and has the performances of high temperature resistance and large current charge and discharge resistance. In addition, due to the nitrogen-rich characteristic of the modified functional layer, the polarity of the material is changed, and the modified functional layer has a good adsorption effect on polysulfide. The nitrogen-doped carbon nanosheet-supported carbide nanoparticles have catalytic performance and can accelerate the conversion of high-order polysulfides into low-order polysulfides. The sulfur lithium battery containing the modified diaphragm provided by the invention has good lithium ion transmission performance, excellent mechanical strength, durability and electrochemical performance.

Drawings

Fig. 1 is an XRD pattern of a modified functional layer of the modified separator prepared in example 1 of the present invention;

fig. 2 is a graph comparing rate performance of the lithium sulfur battery prepared in example 11 of the present invention and the battery using the commercial separator in comparative example 1;

fig. 3 is a graph comparing long cycle performance at 2C rate of the lithium sulfur battery prepared in example 11 of the present invention and the battery using the commercial separator in comparative example 1;

fig. 4 is a graph comparing long cycle performance at 5C rate of the lithium sulfur battery prepared in example 11 of the present invention and the battery using the commercial separator in comparative example 1;

fig. 5 is a graph comparing long cycle performance at 1C rate of the lithium sulfur battery prepared in example 12 of the present invention and the battery using the commercial separator in comparative example 2;

fig. 6 is a graph comparing CV curves of the lithium sulfur battery prepared in example 12 of the present invention and the battery using a commercial separator of comparative example 2;

fig. 7 is a graph comparing electrochemical impedances of a lithium sulfur battery prepared in example 11 of the present invention and a lithium sulfur battery prepared in comparative example 3.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the present invention easy to understand, the following describes a nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm, a preparation method thereof and a lithium sulfur battery in detail with reference to the following embodiments and the accompanying drawings.

The raw materials and reagents used in the examples of the present invention were all obtained from general commercial sources unless otherwise specified.

The preparation method of the nitrogen-doped carbon nanosheet loaded carbide nanoparticle modified diaphragm (hereinafter referred to as modified diaphragm) comprises the following steps:

step 1, grinding a certain amount of nitrogen-containing organic compound uniformly, heating in an air environment, reacting with oxygen to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

step 2, mixing the precursor, molybdenum salt and disaccharide, and heating in a nitrogen atmosphere to obtain nitrogen-doped carbon nanosheet supported carbide nanoparticles;

step 3, dissolving the nitrogen-doped carbon nanosheet loaded carbide nanoparticles in an organic solvent, and then adding a binder to stir to obtain a mixed solution;

and 4, coating the mixed solution on the surface of the diaphragm substrate to obtain the modified diaphragm.

Wherein the nitrogen-containing organic compound is urea and/or melamine, and the dosage of the nitrogen-containing organic compound is 5g-10 g.

In the step 2, the mass ratio of the precursor, the molybdenum salt and the disaccharide is 1: 0.5-1: 0.5-1.

In step 3, the mass ratio of the nitrogen-doped carbon nanosheet-supported carbide nanoparticles to the organic solvent to the binder is 8: 1-8: 1-8.

The diaphragm substrate is a polypropylene diaphragm which is a commercial diaphragm Clegard 2500 and has mesopores, and the thickness of the diaphragm is 100nm-200 nm.

The molybdenum salt is one or more of ammonium molybdate, ammonium tetrathiomolybdate or ammonium phosphomolybdate.

The disaccharide is one or more of sucrose, lactose or maltose.

The organic solvent is N-methyl pyrrolidone.

The binder is polytetrafluoroethylene or polyvinylidene fluoride.

The binder is a perfluorosulfonic acid polymer, Nafion, available from sandenque energy science and technology limited, zhou pterong.

In the step 1, the heating temperature is 500-550 ℃, and the reaction time is 5-7 h.

In the step 2, the heating temperature is 750-850 ℃, and the reaction time is 1-3 h.

The preparation method of the positive pole piece of the lithium-sulfur battery comprises the following steps:

step S1, mixing the multi-walled carbon nano-tube and sulfur powder according to the mass ratio of 1:3, and then grinding to obtain uniformly ground powder;

and step S2, adding the powder into 5mL of carbon disulfide for dissolution, transferring the solution into a 100mL reaction kettle, and reacting for 10 hours at 155 ℃ in a nitrogen atmosphere to obtain the multi-walled carbon nanotube-sulfur (CNT-S), namely the positive pole piece.

Wherein the multi-walled carbon nanotubes are purchased from New Tianjin Crystal Material company and have the model of ECG-M.

The preparation method of the lithium-sulfur battery comprises the following steps:

CNT-S is used as a positive electrode, a lithium sheet is used as a negative electrode, a modified diaphragm is used as a diaphragm, 0.068g of 1% lithium nitrate, 28.708g of bis (trifluoromethyl) lithium sulfonate amide, 5mL of DOL and 5mL of DME are mixed together to be used as an electrolyte, and after the battery is assembled, the battery is kept stand for 6 hours to obtain the lithium-sulfur battery.

Wherein CNT-S is MWCNT-S (multi-walled carbon nanotube-sulfur).

< example 1>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 5g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 500 ℃, reacting the urea with oxygen for 5 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 0.5: mixing the components according to a mass ratio of 0.5, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 2 hours at 800 ℃ in a nitrogen atmosphere to obtain nitrogen-doped carbon nanosheet-supported carbide nanoparticles (hereinafter referred to as particles);

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:1:1, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 100nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is between 50nm and 100nm, the strength of the modified diaphragm is 120MPa, the toughness is 60MPa, and the thickness of the modified functional layer is 400 nm.

Fig. 1 is an XRD pattern of the modified functional layer of the modified separator prepared in this example.

As can be seen from fig. 1, the XRD pattern of the modified functional layer has no hetero-peak, which indicates that the material phase purity is high and the crystallinity is good.

< example 2>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 6g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 520 ℃, reacting the urea with oxygen for 5 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 0.5: mixing the materials according to the mass ratio of 0.5, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 2 hours at 780 ℃ in the nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:1:2, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 110nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is between 50nm and 100nm, the strength of the modified diaphragm is 100MPa, the toughness is 50MPa, and the thickness of the modified functional layer is 420 nm.

< example 3>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 7g of urea uniformly, then placing the ground urea into a ceramic crucible, heating the mixture in an air environment at 530 ℃, reacting the mixture with oxygen for 6 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 1: mixing the materials according to the mass ratio of 0.5, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 3 hours at 780 ℃ in the nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:2:2, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 120nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is between 60nm and 100nm, the strength of the modified diaphragm is 120MPa, the toughness is 50MPa, and the thickness of the modified functional layer is 500 nm.

< example 4>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 8g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 520 ℃, reacting the urea with oxygen for 7 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 1: mixing the materials according to the mass ratio of 0.5, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 1 hour at 800 ℃ in a nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:3:2, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 130nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

According to the test results, the modified diaphragm has mesopores with different sizes, the aperture is between 70nm and 100nm, the strength of the modified diaphragm is 150MPa, the toughness is 70MPa, and the thickness of the modified functional layer is 500 nm.

< example 5>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 9g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 540 ℃, reacting the urea with oxygen for 5 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 1:1, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 3 hours at 800 ℃ in a nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:4:2, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 140nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

According to the test results, the modified diaphragm has mesopores with different sizes, the aperture is between 30nm and 100nm, the strength of the modified diaphragm is 80MPa, the toughness is 60MPa, and the thickness of the modified functional layer is 500 nm.

< example 6>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 10g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 525 ℃, reacting the urea with oxygen for 5 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 0.8: mixing the materials according to the mass ratio of 0.5, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 1.5 hours at 780 ℃ in the nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:5:2, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 150nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is between 90nm and 100nm, the strength of the modified diaphragm is 140MPa, the toughness is 70MPa, and the thickness of the modified functional layer is 450 nm.

< example 7>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 5.5g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 520 ℃, reacting the urea with oxygen for 6 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 0.6: mixing the materials according to the mass ratio of 0.5, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 2 hours at 800 ℃ in a nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:7:2, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 160nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is between 95nm and 100nm, the strength of the modified diaphragm is 125MPa, the toughness is 60MPa, and the thickness of the modified functional layer is 450 nm.

< example 8>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 6.5g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 540 ℃, reacting the urea with oxygen for 5.5 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 0.9: 1, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 2 hours at 780 ℃ in a nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:8:1, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 170nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is between 100nm and 120nm, the strength of the modified diaphragm is 150MPa, the toughness is 80MPa, and the thickness of the modified functional layer is 480 nm.

< example 9>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 7.5g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 540 ℃, reacting the urea with oxygen for 6.5 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 0.9: mixing the materials according to the mass ratio of 0.9, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 2 hours at 800 ℃ in a nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:8:2, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 180nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is between 110nm and 120nm, the strength of the modified diaphragm is 160MPa, the toughness is 90MPa, and the thickness of the modified functional layer is 470 nm.

< example 10>

This example details the modified separator and the method of making the same.

The preparation method of the modified membrane of the present example is as follows:

step 1, grinding 8.5g of urea uniformly, then placing the urea into a ceramic crucible, heating the urea in an air environment at 545 ℃, reacting the urea with oxygen for 6.5 hours to obtain a crude product, and grinding the crude product uniformly again to obtain a precursor;

and 2, mixing the precursor, ammonium molybdate and sucrose in a ratio of 1: 0.9: 1, placing the mixture in a ceramic crucible, and heating and reacting the mixture for 2 hours at 850 ℃ in a nitrogen atmosphere to obtain particles;

step 3, mixing the particles, N-methyl pyrrolidone and polyvinylidene fluoride together in a mass ratio of 8:8:3, and uniformly stirring to obtain a mixed solution;

and 4, coating the mixed solution on the surface of a commercial diaphragm Celgard 2500 with the thickness of 200nm by using a scraper to obtain the modified diaphragm.

The modified diaphragm obtained in the embodiment comprises a diaphragm substrate and a modified functional layer coated on the diaphragm substrate, wherein the diaphragm substrate is a commercial diaphragm Celgard 2500.

The modified membrane obtained in this example was tested using a scanning electron microscope and a stretcher.

The test result shows that the modified diaphragm has mesopores with different sizes, the aperture is 115nm-100nm, the strength is 170MPa, the toughness is 100MPa, and the thickness of the modified functional layer is 460 nm.

< example 11>

This example describes lithium sulfur batteries in detail.

The lithium sulfur battery of the present embodiment includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolytic solution.

Wherein the positive electrode is MWCNT-S, the negative electrode is a lithium sheet, the diaphragm is the modified diaphragm obtained in the embodiment 1, and the electrolyte is DOL/DME (volume ratio of 1: 1) + lithium bistrifluoromethylsulfonyl amide + 1% of lithium nitrate.

< example 12>

This example describes lithium sulfur batteries in detail.

The lithium sulfur battery of the present embodiment includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolytic solution.

Wherein the positive electrode is MWCNT-S, the negative electrode is a lithium sheet, the diaphragm is the modified diaphragm obtained in the embodiment 2, and the electrolyte is DOL/DME (volume ratio of 1: 1) + lithium bistrifluoromethylsulfonyl amide + 1% of lithium nitrate.

< example 13>

This example describes lithium sulfur batteries in detail.

The lithium sulfur battery of the present embodiment includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolytic solution.

Wherein the positive electrode is MWCNT-S, the negative electrode is a lithium sheet, the diaphragm is the modified diaphragm obtained in the embodiment 3, and the electrolyte is DOL/DME (volume ratio of 1: 1) + lithium bistrifluoromethylsulfonyl amide + 1% of lithium nitrate.

< comparative example 1>

This comparative example details a lithium sulfur battery.

The lithium sulfur battery of the present comparative example includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

Wherein the anode is MWCNT-S, the cathode is a lithium sheet, the diaphragm is a modified diaphragm obtained from a commercial diaphragm Celgard 2500, and the electrolyte is DOL/DME (volume ratio of 1: 1) + lithium bistrifluoromethylsulfonyl amide + 1% of lithium nitrate.

The lithium-sulfur batteries obtained in example 11 and the comparative example were placed in a LANDCT2001 test system to measure the rate performance, under the following test conditions: constant current charging and discharging with voltage window of 1.7V-2.8V, charging and discharging environment at room temperature, specific capacity according to 1675mAh g of elemental sulfur^-1Calculation results in fig. 2.

The lithium sulfur batteries obtained in example 11 and this comparative example were placed in a LAND CT2001 test system, and the long cycle performance at a magnification of 1C was measured, to obtain FIG. 3.

Fig. 2 is a graph comparing rate performance of the lithium sulfur battery prepared in example 11 of the present invention and the battery using the commercial separator in this comparative example, and fig. 3 is a graph comparing long cycle performance at 2C rate of the lithium sulfur battery prepared in example 11 of the present invention and the battery using the commercial separator in this comparative example.

As can be seen from FIGS. 2 and 3, the specific capacity of the modified separator reached 1450mAhg at 0.1C^-1And the specific capacity of the commercial diaphragm battery is 900mAh g^-1The results show that the utilization rate of the lithium-sulfur battery containing the modified diaphragm to the active substance S is greatly improved, and even at 2C, the specific capacity of the lithium-sulfur battery containing the modified diaphragm is 752mAh g^-1The specific capacity of the commercial diaphragm lithium-sulfur battery is only 315mAh g^-1The battery with the modified separator still had 1094mAh g when it returned to 0.1C again^-1The specific capacity of the modified diaphragm shows that the modified diaphragm has good cycle reversibility.

The cells using the commercial separator in example 11 and the present comparative example were placed in the LANDCT2001 test system, respectively, and the long cycle performance at 5C rate was measured, to obtain fig. 4.

Fig. 4 is a graph comparing long cycle performance at 5C rate of the lithium sulfur battery prepared in example 11 of the present invention and the battery using the commercial separator in this comparative example.

As shown in FIG. 4, the initial specific capacity of the lithium-sulfur battery prepared in example 11 was 1033mAh g^-1Even after 900 cycles, 500mAh g still exists^-1The residue indicates that the modified separator has good electrochemical performance.

< comparative example 2>

This comparative example details a lithium sulfur battery.

The lithium sulfur battery of the present comparative example includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

Wherein the anode is MWCNT-S, the cathode is a lithium sheet, the diaphragm is a modified diaphragm obtained from a commercial diaphragm Celgard 2500, and the electrolyte is DOL/DME (volume ratio of 1: 1) + lithium bistrifluoromethylsulfonyl amide + 1% of lithium nitrate.

The lithium sulfur batteries prepared in example 12 and this comparative example were placed in a LAND CT2001 test system, and the long cycle performance at a magnification of 1C was measured, to obtain FIG. 5.

Fig. 5 is a graph comparing long cycle performance at 1C rate of the lithium sulfur battery prepared in example 12 of the present invention and the battery using the commercial separator in this comparative example.

As shown in FIG. 5, at the rate of 1C, the initial capacity of the lithium-sulfur battery prepared in example 12 is 1136mAh g-1, the specific capacity of the lithium-sulfur battery of the comparative example is only 846.7mAh g-1, after 1000 cycles, the specific capacity residual of the modified diaphragm battery is 400mAh g-1, and after 750 cycles, the specific capacity residual of the commercial diaphragm battery is 200mAh g-1, which indicates that the modified diaphragm has good cycle reversibility.

The lithium sulfur batteries of example 12 and this comparative example were placed in a test system of CHI660e at 0.1mV s^-1CV testing at sweep rate, resulted in FIG. 6.

Fig. 6 is a graph comparing CV curves of the lithium sulfur battery prepared in example 12 of the present invention and the battery of the present comparative example using a commercial separator.

As shown in fig. 6, the battery assembled with the modified separator has a larger peak area, indicating that it has a higher charge transfer capability, and the lithium-sulfur battery prepared in example 12 has a higher redox current, indicating that the modified separator has good electrochemical properties.

< comparative example 3>

This comparative example details a lithium sulfur battery.

The lithium sulfur battery of the present comparative example includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

Wherein the anode is MWCNT-S, the cathode is a lithium sheet, the diaphragm is a modified diaphragm obtained from a commercial diaphragm Celgard 2500, and the electrolyte is DOL/DME (volume ratio of 1: 1) + lithium bistrifluoromethylsulfonyl amide + 1% of lithium nitrate.

The lithium sulfur batteries prepared in example 11 and this comparative example were each placed in an electrochemical workstation for testing in the range of 10hz to 10MHZ with a test voltage oscillation of 5mV, giving fig. 7.

Fig. 7 is a graph comparing electrochemical impedances of a lithium sulfur battery prepared in example 11 of the present invention and a lithium sulfur battery prepared in this comparative example.

As shown in fig. 7, the electrochemical impedance of the lithium-sulfur battery prepared in example 11 was 15 Ω, while the electrochemical impedance of the lithium-sulfur battery of the comparative example was 50 Ω, and the electrochemical impedance of the lithium-sulfur battery comprising the modified separator was significantly lower than that of the commercial PP separator lithium-sulfur battery, indicating that the charge transfer impedance of the lithium-sulfur battery comprising the modified separator was small and the electrochemical performance of the battery was significantly improved.

Effects and effects of the embodiments

According to embodiments 1 to 10, a method for preparing a nitrogen-doped carbon nanosheet-supported carbide nanoparticle modified diaphragm (hereinafter referred to as a modified diaphragm) includes grinding a certain amount of nitrogen-containing organic compound, heating the ground nitrogen-containing organic compound in an air environment, reacting the ground nitrogen-containing organic compound with oxygen to obtain a crude product, grinding the crude product again to obtain a uniform precursor, mixing the precursor, a molybdenum salt and a disaccharide, heating the mixture in a nitrogen atmosphere to obtain nitrogen-doped carbon nanosheet-supported carbide nanoparticles, dissolving the nitrogen-doped carbon nanosheet-supported carbide nanoparticles in an organic solvent, adding a binder to stir the mixture to obtain a mixed solution, coating the mixed solution on the surface of a diaphragm substrate to obtain the modified diaphragm, and applying urea and melamine as the nitrogen-containing organic compound to provide a sufficient nitrogen source, wherein the mass ratio of the precursor, the molybdenum salt and the disaccharide is 1: 0.5-1: 0.5-1, so that the nanosheets can maintain enough active sites and an integral framework in the reaction process, and the mass ratio of the nitrogen-doped carbon nanosheets to the supported carbide nanoparticles to the organic solvent to the binder is 8: 1-8: 1-8, so that the nitrogen-doped carbon nanosheet-supported carbide nanoparticles can be better bonded to a commercial membrane.

According to examples 11 to 13 and comparative examples 1 to 3, the modified diaphragm not only maintains the excellent chemical and electrochemical stability and good mechanical strength of the traditional olefin diaphragm, but also further limits the aperture of the battery diaphragm, effectively inhibits the shuttle effect, and has high temperature resistance and high current charge and discharge resistance. In addition, due to the nitrogen-rich characteristic of the modified functional layer, the polarity of the material is changed, and the modified functional layer has a good adsorption effect on polysulfide. The nitrogen-doped carbon nanosheet-supported carbide nanoparticles have catalytic performance and can accelerate the conversion of high-order polysulfides into low-order polysulfides. The sulfur lithium battery containing the modified diaphragm provided by the invention has good lithium ion transmission performance, excellent mechanical strength, durability and electrochemical performance.

The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.