阅读说明：本技术 氮掺杂碳包覆Co和/或Co3ZnC复合材料在制备锂硫电池隔膜中的应用 (Nitrogen-doped carbon-coated Co and/or Co3Application of ZnC composite material in preparation of lithium-sulfur battery diaphragm ) 是由 蔡欣 王梦蕊 周训富 方岳平 于 2020-12-23 设计创作，主要内容包括：本发明属于纳米材料和锂硫电池领域,公开了一种氮掺杂碳包覆Co和/或Co-3ZnC复合材料在制备锂硫电池隔膜中的应用。本发明首先将Pluronic F-127溶于水中,加入碳源双氰胺,再加入正二价钴盐、正二价锌盐,进一步搅拌后蒸干水分得到固体复合物,然后在N-2气体保护下进行高温碳化。此过程中双氰胺通过碳化得到N掺杂碳,且双氰胺在碳化过程产生的一氧化碳、二氧化碳、一氧化氮以及碳等还原性物质能够将钴锌还原碳化得到Co或Co-3ZnC,反应完成后即得目标产物。将N掺杂碳包覆Co和/或Co-3ZnC复合材料作为隔膜修饰材料运用刮刀法涂覆在商用隔膜上,应用于锂硫电池中可以有效提高锂硫电池的电化学性能。(The invention belongs to the field of nano materials and lithium-sulfur batteries, and discloses nitrogen-doped carbon-coated Co and/or Co 3 The ZnC composite material is applied to the preparation of the lithium-sulfur battery diaphragm. The method comprises the steps of firstly dissolving Pluronic F-127 in water, adding dicyandiamide as a carbon source, then adding divalent cobalt salt and divalent zinc salt, further stirring, evaporating to remove water to obtain a solid compound, and then adding N 2 And carrying out high-temperature carbonization under the protection of gas. This processThe N-doped carbon is obtained by carbonizing the dicyandiamide, and the cobalt and zinc can be reduced and carbonized to obtain Co or Co by reducing substances such as carbon monoxide, carbon dioxide, nitric oxide and carbon generated in the carbonizing process of dicyandiamide 3 ZnC, and obtaining a target product after the reaction is finished. Coating N-doped carbon with Co and/or Co 3 The ZnC composite material is used as a diaphragm modification material and coated on a commercial diaphragm by a scraper method, and can effectively improve the electrochemical performance of the lithium-sulfur battery when being applied to the lithium-sulfur battery.)

1. Nitrogen-doped carbon-coated Co and/or Co₃The ZnC composite material is applied to the preparation of the lithium-sulfur battery diaphragm.

2. The nitrogen-doped carbon-cladded Co and/or Co of claim 1₃The application of the ZnC composite material in the preparation of the lithium-sulfur battery diaphragm is characterized in that the nitrogen-doped carbon coats Co and/or Co₃The ZnC composite material is prepared by the following method:

(1) preparing a cobalt-zinc and dicyandiamide compound: firstly, dissolving Pluronic F-127 in water, adding dicyandiamide, stirring until the mixture is completely dissolved, then adding soluble divalent cobalt salt and divalent zinc salt, continuing stirring overnight, evaporating the obtained solution to remove water and drying to obtain a cobalt-zinc and dicyandiamide compound;

(2) preparation of Co₃ZnC @ NC: putting the solid cobalt-zinc and dicyandiamide compound obtained in the step (1) into a porcelain boat, and then adding into N₂Carbonizing at high temperature in the atmosphere, and obtaining nitrogen-doped carbon-coated Co and/or Co after the reaction is finished₃ZnC composite material.

3. The method of claim 2Is doped with nitrogen and coated with carbon₃The application of the ZnC composite material in preparing the lithium-sulfur battery diaphragm is characterized in that:

the soluble divalent cobalt salt in the step (1) is Co (NO)₃)₂ 6H₂O、CoCl₂ 6H₂O、Co(CH₃COO)₂ 4H₂At least one of O; the divalent zinc salt is Zn (NO)₃)₂ 6H₂O、ZnCl₂、Zn(CH₃COO)₂ 2H₂At least one of O.

4. The nitrogen doped carbon clad Co and/or Co of claim 2₃The application of the ZnC composite material in preparing the lithium-sulfur battery diaphragm is characterized in that:

the soluble divalent cobalt salt in the step (1) is Co (NO)₃)₂ 6H₂O; the divalent zinc salt is Zn (NO)₃)₂6H₂O。

5. The nitrogen doped carbon clad Co and/or Co of claim 2₃The application of the ZnC composite material in preparing the lithium-sulfur battery diaphragm is characterized in that:

the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1: 1-3;

the mass ratio of Pluronic F-127 to dicyandiamide in the step (1) is 1: 1-3;

the dosage of the soluble divalent cobalt salt and divalent zinc salt in the step (1) and the dosage of dicyandiamide meet the following requirements: the ratio of the molar amount of the soluble divalent cobalt salt and divalent zinc salt to the molar amount of dicyandiamide is 1: 13.2-17.7.

6. The nitrogen doped carbon clad Co and/or Co of claim 2₃The application of the ZnC composite material in preparing the lithium-sulfur battery diaphragm is characterized in that:

the high-temperature carbonization in the step (2) refers to heat preservation at 600-800 ℃ for 1-3 h.

7. Nitrogen doped carbon coated Co and/or Co prepared according to the method of claim 2₃The application of the ZnC composite material in preparing the lithium-sulfur battery diaphragm is characterized in that:

when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:3 and the high-temperature calcination in the step (2) is carried out at 700 ℃ for 1h, the obtained product is nitrogen-doped carbon-coated Co₃A ZnC composite material;

when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:3 and the high-temperature calcination in the step (2) is carried out at 700 ℃ for 2-3h, the obtained product is nitrogen-doped carbon-coated Co/Co₃A ZnC composite material;

when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:3, and the high-temperature calcination in the step (2) is to keep the temperature at 800 ℃ for 2-3h, the obtained product is a nitrogen-doped carbon-coated Co composite material;

when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:2-2.5, and the high-temperature calcination in the step (2) refers to heat preservation at 700 ℃ for 1-3h, the obtained product is nitrogen-doped carbon-coated Co/Co₃A ZnC composite material;

when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:2-2.5, and the high-temperature calcination in the step (2) is heat preservation at 800 ℃ for 2 hours, the obtained product is the nitrogen-doped carbon-coated Co composite material.

8. A lithium-sulfur battery separator is characterized by being prepared by the following method: coating nitrogen-doped carbon as claimed in any of claims 1 to 7 with Co and/or Co₃And grinding and uniformly mixing the ZnC composite material, the conductive agent and the binder in a solvent, uniformly coating the obtained slurry on a commercial diaphragm by a scraper method, and drying to form the lithium-sulfur battery diaphragm.

9. The lithium sulfur battery separator according to claim 8, wherein:

the conductive agent is a conductive agent super P; the binder is PVDF; the solvent is N-methyl pyrrolidone.

10. The lithium sulfur battery separator according to claim 8, wherein:

the nitrogen-doped carbon is coated with Co and/or Co₃The mass ratio of the ZnC composite material to the conductive agent to the binder is 8:1: 1.

Technical Field

The invention belongs to the field of nano materials and lithium-sulfur batteries, and particularly relates to nitrogen-doped carbon-coated Co and/or Co₃The ZnC composite material is applied to the preparation of the lithium-sulfur battery diaphragm.

Background

With the increasing global energy demand and the gradual exhaustion of fossil energy, there is an urgent need for the development and utilization of clean energy such as wind energy, solar energy, geothermal energy, etc. However, when the proportion of the photovoltaic power and the wind power which are combined into the existing power grid exceeds 10%, the local power grid is obviously impacted, so that the research and development of the efficient and safe electricity storage and energy storage technology is the key point for large-scale and efficient use of the energy. Compared with the currently applied lead-acid battery, nickel-metal hydride battery and lithium ion battery energy storage systems, the lithium-sulfur battery is considered to be a high-capacity energy storage system with great development potential after the lithium ion battery due to the advantages of high specific energy (2600 W.h/kg), cheap raw materials, environmental friendliness and the like.

However, the development of lithium sulfur batteries has not yet achieved practical application on a scale, mainly due to several challenges faced by lithium sulfur batteries. Mainly comprises 1, insulation and volume expansion (80%) of elemental sulfur and polysulfide thereof in the charging and discharging process; 2. during the charging and discharging process, the polysulfide intermediate can be dissolved in the organic electrolyte, and can migrate to the negative electrode and the unstable lithium metal surface to generate self-discharge reaction during the charging process, and the resultant returns to the positive electrode to be oxidized, so that the shuttling effect is formed, the utilization rate of active substances is reduced, and the capacity loss and the cycle performance of the battery are reduced. Meanwhile, the problems of surface instability and dendritic crystals always exist when the metal lithium is used as a negative electrode, safety problems such as thermal runaway, short circuit explosion and the like are easily caused, and the popularization and application of the lithium-sulfur battery are also restricted.

In recent years, much research effort has been devoted to improving the performance of lithium sulfur batteries to realize practical applications of the lithium sulfur batteries. Wherein the separator is used as lithium-sulfur batteryOne of the important component parts in the cell system, the quality of the performance of which directly affects the electrochemical performance of the lithium-sulfur battery, is one of the important research points. The main research routes include finding new membranes and modifying existing commercial membranes. The modification of commercial separators has been widely studied because of the advantages of simplicity of operation and practicality compared to the search for a new separator. The nano carbon material as an excellent diaphragm modification material has good conductivity, and can physically anchor polysulfide in the charging and discharging processes of the lithium-sulfur battery, so that the cycle stability of the lithium-sulfur battery is effectively improved. However, the poor affinity between the non-polar carbon material and the polar polysulphide is not sufficient to effectively suppress the shuttling effect of the polysulphide during cycling. Thus, the search for a material having excellent conductivity, strong anchoring force, accelerated polysulfide interconversion and rapid Li⁺The modified separator with the advantages of diffusion rate and the like is an effective way for effectively improving the electrochemical performance of the lithium-sulfur battery and realizing the practical application of the lithium-sulfur battery.

Disclosure of Invention

To overcome the above disadvantages and shortcomings of the prior art, it is a primary object of the present invention to provide a nitrogen-doped carbon-coated Co and/or Co₃The ZnC composite material is applied to the preparation of the lithium-sulfur battery diaphragm.

The purpose of the invention is realized by the following scheme:

nitrogen-doped carbon-coated Co and/or Co₃The ZnC composite material is applied to the preparation of the lithium-sulfur battery diaphragm.

The nitrogen-doped carbon is coated with Co and/or Co₃The ZnC composite material is prepared by the following method:

(1) preparing a cobalt-zinc and dicyandiamide compound: firstly, dissolving Pluronic F-127 in water, adding dicyandiamide, stirring until the mixture is completely dissolved, then adding soluble divalent cobalt salt and divalent zinc salt, continuing stirring overnight, evaporating the obtained solution to remove water and drying to obtain a cobalt-zinc and dicyandiamide compound;

(2) preparing a nitrogen-doped carbon-coated cobalt zinc carbide composite material: putting the solid cobalt-zinc and dicyandiamide compound obtained in the step (1) into a porcelain boatThen in N₂Carbonizing at high temperature in the atmosphere, and obtaining nitrogen-doped carbon-coated Co and/or Co after the reaction is finished₃ZnC composite material.

The soluble divalent cobalt salt in the step (1) is Co (NO)₃)₂ 6H₂O、CoCl₂ 6H₂O、Co(CH₃COO)₂4H₂At least one of O, preferably Co (NO)₃)₂6H₂O; the divalent zinc salt is Zn (NO)₃)₂ 6H₂O、ZnCl₂、Zn(CH₃COO)₂ 2H₂At least one of O, preferably Zn (NO)₃)₂ 6H₂O；

The molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1: 1-3, preferably 1: 3.

The mass ratio of Pluronic F-127 to dicyandiamide in the step (1) is 1: 1-3, preferably 1: 2.

The dosage of the soluble divalent cobalt salt and divalent zinc salt in the step (1) and the dosage of dicyandiamide meet the following requirements: the ratio of the molar amount of the soluble divalent cobalt salt and divalent zinc salt to the molar amount of dicyandiamide is 1: 13.2-17.7, preferably 1: 13.2.

The step (1) of drying the obtained solution by distillation to dryness and drying refers to drying the solution by distillation in an oil bath pan at the temperature of 80 ℃, and then drying in an oven at the temperature of 60-80 ℃ overnight; the oil bath pan and oven temperatures are preferably both 80 ℃.

The water described in step (1) is used only as a reaction medium, so that the amount thereof is only required to be such that it can completely dissolve the added Pluronic F-127, dicyandiamide, and soluble divalent cobalt and zinc salts.

The high-temperature carbonization in the step (2) refers to heat preservation at the temperature of 600-800 ℃ for 1-3 h; preferably, the temperature is kept at 700 ℃ for 1-3 h.

The molar ratio of the soluble divalent cobalt salt and divalent zinc salt in step (1) and the high temperature carbonization in step (2) affect the composition of the final product.

Preferably, when the soluble divalent cobalt salt and the salt are used in step (1)The molar ratio of the divalent zinc salt is 1:3, and the high-temperature calcination in the step (2) means that when the temperature is kept at 700 ℃ for 1h, the obtained product is nitrogen-doped carbon-coated Co₃A ZnC composite material;

preferably, when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:3, and the high-temperature calcination in the step (2) refers to heat preservation at 700 ℃ for 2-3h, the obtained product is nitrogen-doped carbon-coated Co/Co₃A ZnC composite material;

preferably, when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:3, and the high-temperature calcination in the step (2) refers to heat preservation at 800 ℃ for 2-3h, the obtained product is a nitrogen-doped carbon-coated Co composite material;

preferably, when the molar ratio of the soluble divalent cobalt salt to the divalent zinc salt in the step (1) is 1:2-2.5, and the high-temperature calcination in the step (2) refers to heat preservation at 700 ℃ for 1-3h, the obtained product is nitrogen-doped carbon-coated Co/Co₃A ZnC composite material;

preferably, when the molar ratio of the soluble divalent n-cobalt salt to the divalent n-zinc salt in the step (1) is 1:2-2.5, and the high-temperature calcination in the step (2) refers to heat preservation at 800 ℃ for 2 hours, the obtained product is the nitrogen-doped carbon-coated Co composite material.

A lithium-sulfur battery separator prepared by the following method: the nitrogen-doped carbon prepared by the method is coated with Co and/or Co₃And grinding and uniformly mixing the ZnC composite material, the conductive agent and the binder in a solvent, uniformly coating the obtained slurry on a commercial diaphragm by a scraper method, and drying to form the lithium-sulfur battery diaphragm. Compared with the traditional commercial diaphragm, the modified diaphragm greatly improves the cycling stability of the lithium-sulfur battery.

The conductive agent is preferably a conductive agent super P; the binder is preferably PVDF; the solvent is preferably N-methylpyrrolidone (NMP).

The nitrogen-doped carbon is coated with Co and/or Co₃The mass ratio of the ZnC composite material to the conductive agent to the binder is 8:1: 1.

The invention firstly makesDissolving Pluronic F-127 as surfactant in water, adding dicyandiamide as carbon source, and respectively adding cobalt (NO) salt₃)₂ 6H₂O), divalent zinc salt (Zn (NO)₃)₂ 6H₂O), further stirring, evaporating to remove water to obtain solid compound, and adding N₂And under the protection of gas, carbonizing the obtained product at high temperature. In the process, dicyandiamide is carbonized to obtain N-doped carbon, and reducing substances such as carbon monoxide, carbon dioxide, nitric oxide and carbon generated in the carbonization process of dicyandiamide can reduce and carbonize cobalt and zinc to obtain Co or Co₃ZnC. Pluronic F-127 volatizes during the high temperature calcination process to form a pore structure on the surface of the N-doped carbon. Therefore, the target product of nitrogen-doped carbon-coated Co and/or Co is obtained after the reaction is finished₃ZnC composite material. Coating nitrogen-doped carbon with Co and/or Co₃The ZnC composite material is used as a diaphragm modification material and coated on a commercial diaphragm by a scraper method, and can effectively improve the electrochemical performance of the lithium-sulfur battery when being applied to the lithium-sulfur battery.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) nitrogen-doped carbon-coated Co and/or Co of the invention₃ZnC composite material (Co)₃[email protected]、Co/Co₃ZnC @ NC or Co @ NC) synthetic process is simple, and Co can be controlled by regulating and controlling the dosage of cobalt salt and zinc salt, high-temperature carbonization temperature and time₃The relative content of ZnC can be quickly amplified for industrialization.

(2) Nitrogen-doped carbon-coated Co and/or Co of the invention₃ZnC composite material (Co)₃[email protected]、Co/Co₃ZnC @ NC or Co @ NC) has a novel structure, and can greatly improve the electrochemical performance of the lithium-sulfur battery when being used as a diaphragm modification functional material of the lithium-sulfur battery.

Drawings

FIG. 1 shows the Co prepared in examples 1, 2 and 3₃[email protected]、Co/Co₃XRD patterns of ZnC @ NC and Co @ NC.

FIG. 2 is a PP/Co blend prepared in example 1₃Capacity voltage diagram of ZnC @ NC lithium-sulfur cell at 0.1C.

FIG. 3 PP/Co prepared in example 1₃Cycle performance diagram of ZnC @ NC lithium-sulfur cell at 0.5C.

FIG. 4 shows PP/Co prepared in example 2₃Capacity voltage diagram of ZnC @ NC lithium-sulfur cell at 0.1C.

FIG. 5 PP/Co prepared in example 2₃Cycle performance diagram of ZnC @ NC lithium-sulfur cell at 0.5C.

FIG. 6 is a graph of capacity voltage at 0.1C for PP/Co @ NC lithium sulfur cells prepared in example 3.

FIG. 7 cycle performance plot at 0.5C for PP/Co @ NC lithium sulfur cells prepared in example 3.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The reagents used in the examples are commercially available without specific reference.

The assembly and testing methods for lithium sulfur batteries described in the examples are as follows:

(1) PP/N doped carbon coated Co and/or Co₃Preparing a ZnC composite material modified diaphragm: coating nitrogen-doped carbon with Co and/or Co₃The ZnC composite material, the conductive agent super P and the binder PVDF are placed in an agate mortar in a mass ratio of 8:1:1, N-methyl pyrrolidone (NMP) is used as a solvent to be fully ground for 30 minutes, and then the obtained slurry is uniformly coated on a commercial diaphragm celgard2500(PP) by a doctor blade method. After sufficient drying, the resulting separator was cut into circular disks having a diameter of 16 mm.

(2) Preparing a positive pole piece: and (3) fully grinding 25% of super P and 75% of sublimed sulfur in an agate mortar for 15 minutes, then placing the ground materials in a stainless steel reaction kettle, then placing the stainless steel reaction kettle in an oven, preserving heat for 10 hours at 155 ℃, and obtaining the super P-S composite material after the reaction is finished. 80% super P-S, 10% super P and 10% PVDF were put in an agate mortar and sufficiently ground for 30 minutes using N-methylpyrrolidone (NMP) as a solvent, and then the resulting slurry was uniformly coated on an aluminum foil by a doctor blade method. After sufficient drying, the resulting pole pieces were cut into disks 14mm in diameter.

(3) Assembling the button cell: the following operations were all performed in a glove box filled with argon gas. The CR2025 button cell is assembled by using a lithium sheet as a negative electrode, super P-S as a positive electrode, a PP/nitrogen-doped carbon-coated cobalt zinc carbide composite material as a diaphragm and a LITFIS electrolyte (1.0M LitFSI in DOL: DME: 1 Vol% with 1.0% LiNO)₃Suzhou duo reagent) is an electrolyte. The dosage of the electrolyte is 15 mu L/mgs, and the commercial cell 2500(PP) is used for assembling the comparative battery to replace PP/Co₃ZnC @ NC.

(4) Testing of lithium-sulfur battery cycle stability: and standing the assembled battery for 24 hours, and performing constant current charge and discharge test on the assembled battery by using a Newware BTS battery test system under different current densities, wherein the voltage range of charge and discharge is 1.5-2.8V.

Example 1

The nitrogen-doped carbon-coated Co of this example₃ZnC composite material Co₃The preparation method of ZnC @ NC comprises the following specific steps:

1g of Pluronic F-127, 2g of dicyandiamide, 0.1303g of Co (NO)₃)₂ 6H₂O and 0.3994g Zn (NO)₃)₂6H₂And dissolving O in water completely, continuously stirring overnight, putting the solution into an oil bath pan at the temperature of 80 ℃, stirring the water to be dry, and putting the solution into an oven at the temperature of 80 ℃ for continuous drying. Finally, the dried sample is placed in a tube furnace in N₂Raising the temperature to 700 ℃ at a heating rate of 3 ℃/min under the protection of atmosphere, and carbonizing at high temperature for 1h to obtain a sample, namely Co₃[email protected]

Co in this example₃The XRD pattern of ZnC @ NC is shown in figure 1, Co₃The XRD diffraction pattern of the ZnC @ NC composite material has three main peaks, and the diffraction peaks positioned at 41.90 degrees, 48.79 degrees and 71.48 degrees respectively correspond to Co₃ZnC (PDF #29-0524) crystal planes (111), (200) and (220). And the characteristic peak at 2 θ ═ 26.5 ° corresponds to the (002) crystal plane of nitrogen-doped carbon. Shows the successful synthesis of Co₃[email protected]。

To be synthesized Co₃ZnC @ NC is used for modifying commercial diaphragm PP and then assembled into PP/Co₃The ZnC @ NC lithium-sulfur battery has a capacity-voltage diagram at 0.1C as shown in figure 2, and PP/Co can be seen from a specific capacity-voltage curve at 0.1C current density₃The initial discharge specific capacity of the ZnC @ NC battery is up to 1502.1mA h g^-1；PP/Co₃The cycling curve of the ZnC @ NC diaphragm cell at 0.5C is shown in FIG. 3. it can be seen from FIG. 3 that after 100 cycles, the capacity remains at 964.4mA hg g^-1The capacity retention rate is as high as 85.8 percent, which is far higher than that of an unmodified commercial diaphragm battery (387.1mA h g)^-1，66.7％)。

Example 2

Nitrogen doped carbon coated Co/Co of this example₃ZnC composite Co/Co₃The preparation method of ZnC @ NC comprises the following specific steps:

1g of Pluronic F-127, 2g of dicyandiamide, 0.1303g of Co (NO)₃)₂ 6H₂O and 0.2663g Zn (NO)₃)₂6H₂And dissolving O in water completely, continuously stirring overnight, putting the solution into an oil bath pan at the temperature of 80 ℃, stirring the water to be dry, and putting the solution into an oven at the temperature of 80 ℃ for continuous drying. Finally, the dried sample is placed in a tube furnace in N₂Raising the temperature to 700 ℃ at a heating rate of 3 ℃/min under the protection of atmosphere, and carbonizing the mixture at high temperature for 2 hours to obtain a sample, namely Co/Co₃[email protected]

Co/Co in this example₃The XRD pattern of ZnC @ NC is shown in figure 1, Co/Co₃The XRD diffraction pattern of the ZnC @ NC composite material has six main peaks, wherein diffraction peaks positioned at 41.90 degrees, 48.79 degrees and 71.48 degrees respectively correspond to Co₃ZnC (PDF #29-0524) crystal planes (111), (200) and (220), and diffraction peaks at 44.21 °, 51.52 ° and 75.85 ° correspond to the (111), (200) and (220) crystal planes of Co (PDF #15-0806), respectively. The characteristic peak at 2 θ ═ 26.5 ° corresponds to the (002) crystal plane of nitrogen-doped carbon. Shows that Co/Co is successfully synthesized₃[email protected]。

To synthesize Co/Co₃ZnC @ NC is used for modifying commercial diaphragm PP and then assembled into PP/Co₃The ZnC @ NC lithium-sulfur battery has a capacity-voltage diagram at 0.1C as shown in FIG. 4, and PP/Co can be seen from a specific capacity-voltage curve at 0.1C current density in FIG. 4₃ZnC @ NC electricityThe initial discharge specific capacity of the cell is up to 1483.2mA h g^-1；PP/Co/Co₃The cycle of the ZnC @ NC diaphragm battery under the current density of 0.5C is shown in figure 5, and as can be seen from figure 5, after 100 cycles of charge and discharge, the specific discharge capacity of the battery still maintains 876.4mA h g^-1The specific capacity retention rate is 80.5%. Is much higher than that of an unmodified commercial diaphragm battery (387.1mA h g)^-1，66.7％)。

Example 3

The preparation method of the nitrogen-doped carbon-coated Co composite material Co @ NC provided by the embodiment comprises the following specific steps:

1g of Pluronic F-127, 2g of dicyandiamide, 0.1303g of Co (NO)₃)₂ 6H₂O and 0.2663g Zn (NO)₃)₂6H₂And dissolving O in water completely, continuously stirring overnight, putting the solution into an oil bath pan at the temperature of 80 ℃, stirring the water to be dry, and putting the solution into an oven at the temperature of 80 ℃ for continuous drying. Finally, the dried sample is placed in a tube furnace in N₂Under the protection of atmosphere, the temperature is raised to 800 ℃ at the heating rate of 3 ℃/min, and the sample obtained after high-temperature carbonization for 2h is Co @ NC.

The XRD pattern of Co @ NC in this example is shown in FIG. 1, Co/Co₃The XRD diffraction pattern of the ZnC @ C composite material has three main peaks, and the diffraction peaks at 44.21 degrees, 51.52 degrees and 75.85 degrees respectively correspond to (111), (200) and (220) crystal faces of Co (PDF # 15-0806). The characteristic peak at 2 θ ═ 26.5 ° corresponds to the (002) crystal plane of nitrogen-doped carbon. Indicating the successful synthesis of Co @ NC. By comparison of Co₃[email protected]、Co/Co₃The XRD patterns of ZnC @ NC and Co @ NC show that as the calcination temperature and calcination time are increased, Co is added₃The relative content of ZnC is gradually reduced, and the relative content of Co is gradually increased, which shows that the Co in the system is gradually reduced₃ZnC is decomposed in the high-temperature pyrolysis process, then Zn atoms are volatilized, and Co atoms are continuously reduced into Co nano particles.

The synthesized Co @ NC is used for modifying the commercial diaphragm PP, and then the PP/Co @ NC lithium sulfur battery is assembled, wherein the capacity-voltage diagram of the lithium sulfur battery at 0.1C is shown in figure 6, and as can be seen from the specific capacity-voltage curve in figure 6, the initial discharge specific capacity of the PP/Co @ NC battery reaches 1374.8 at the current density of 0.1CmA h g^-1(ii) a The circulation of the PP/Co @ NC diaphragm battery under the current density of 0.5C is shown in figure 7, and as can be seen from figure 7, the specific discharge capacity of the battery is still kept at 620.5mA h g after 100 cycles of charge-discharge circulation^-1The specific capacity retention rate is 74.8%. Is much higher than that of an unmodified commercial diaphragm battery (387.1mA h g)^-1，66.7％)。

As is clear from the comparison of electrochemical performances, Co obtained in example 1₃The ZnC @ NC composite material has the best effect when being used as a modification layer of the lithium-sulfur battery diaphragm.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.