阅读说明：本技术 一种锂硫电池用隔膜及其制备方法 (Diaphragm for lithium-sulfur battery and preparation method thereof ) 是由 谢玉虎 李凯 陈萌 杨茂萍 于 2021-08-05 设计创作，主要内容包括：本发明公开了一种锂硫电池用隔膜及其制备方法,该隔膜包括多孔基材膜以及涂覆在所述多孔基材膜表面的吸附功能涂层；所述吸附功能涂层包括改性石墨烯/聚苯胺复合材料和粘结性聚合物；所述改性石墨烯/聚苯胺复合材料是先将氧化石墨烯进行磺酸化处理形成磺酸化石墨烯后,将磺酸化石墨烯与苯胺进行聚合反应制备得到,能够在磺酸化石墨烯的表面形成聚苯胺三维网络,从而增强对多硫化物的吸附能力,可有效改善由于改性石墨烯或聚苯胺单独使用的不足,显著提升锂硫电池的循环容量保持率和倍率充电性能。(The invention discloses a diaphragm for a lithium-sulfur battery and a preparation method thereof, wherein the diaphragm comprises a porous substrate film and an adsorption functional coating coated on the surface of the porous substrate film; the adsorption functional coating comprises a modified graphene/polyaniline composite material and a cohesive polymer; the modified graphene/polyaniline composite material is prepared by performing sulfonation treatment on graphene oxide to form sulfonated graphene, and then performing polymerization reaction on the sulfonated graphene and aniline, so that a polyaniline three-dimensional network can be formed on the surface of the sulfonated graphene, the adsorption capacity on polysulfide is enhanced, the defect that the modified graphene or polyaniline is used alone can be effectively overcome, and the cycle capacity retention rate and the rate charging performance of a lithium-sulfur battery are remarkably improved.)

1. A separator for a lithium-sulfur battery, characterized in that: the diaphragm comprises a porous substrate film and an adsorption functional coating coated on the surface of the porous substrate film; the adsorption functional coating comprises a modified graphene/polyaniline composite material and a cohesive polymer; the modified graphene/polyaniline composite material is prepared by performing sulfonation treatment on graphene oxide to form sulfonated graphene, and then performing polymerization reaction on the sulfonated graphene and aniline.

2. The separator for a lithium sulfur battery according to claim 1, characterized in that: the porous substrate membrane is a polyethylene membrane or a polypropylene membrane.

3. The separator for a lithium sulfur battery according to claim 1, characterized in that: the adhesive polymer is polyvinylidene fluoride resin or polyacrylonitrile.

4. The separator for a lithium sulfur battery according to any one of claims 1 to 3, characterized in that: the mass ratio of the modified graphene/polyaniline composite material to the adhesive polymer is (0.8-2): 100.

5. the method of preparing a separator for a lithium sulfur battery according to claim 4, wherein: the method comprises the following steps:

preparation of sulfonated graphene: dispersing graphene oxide in deionized water, adding isoamyl nitrite and 4-aniline sulfonic acid, reacting under a heating condition, and finally sequentially centrifuging, filtering, washing and drying the generated product to obtain sulfonated graphene;

preparing a modified graphene/polyaniline composite material: dispersing sulfonated graphene in water at low temperature to obtain a dispersion liquid; dissolving ammonium persulfate in a hydrochloric acid solution in a low-temperature environment, and adding aniline to obtain a mixed solution; slowly adding the mixed solution into the dispersion liquid, stirring in a low-temperature environment, and finally washing and drying the obtained product to obtain the modified graphene/polyaniline composite material;

preparation of a separator for a lithium-sulfur battery: dissolving a binding polymer in a solvent to obtain a binding solution; dispersing the modified graphene/polyaniline composite material in a binding solution to obtain coating slurry; and coating the coating slurry on one surface of the porous substrate membrane, and drying to obtain the diaphragm for the lithium-sulfur battery.

6. The method of manufacturing a separator for a lithium-sulfur battery according to claim 5, characterized in that: the graphene oxide is prepared by oxidizing graphite powder, and the method comprises the following specific steps: under the condition of ice-water bath, uniformly dissolving and dispersing graphite powder and sodium nitrate in concentrated sulfuric acid to obtain reaction liquid; slowly adding permanganate into the reaction solution, sequentially controlling the temperature of the reaction solution to be 15-25 ℃ for 1.3-1.7 hours, raising the temperature to be 30-40 ℃ and keeping the temperature for 0.8-1.2 hours, then adding deionized water into the reaction solution, raising the temperature of the reaction solution to be 90-100 ℃ and keeping the temperature for 30-50 minutes, finally adding hydrogen peroxide into the reaction solution, reacting for 50-70 minutes, and washing and drying a reaction product after the reaction is finished to obtain graphene oxide.

7. The method of manufacturing a separator for a lithium-sulfur battery according to claim 5, characterized in that: in the preparation step of the sulfonated graphene, the heating temperature is 90-110 ℃, and the heating time is 30-60 minutes.

8. The method of manufacturing a separator for a lithium-sulfur battery according to claim 5, characterized in that: in the preparation step of the modified graphene/polyaniline composite material, the low temperature is 0 ℃.

9. The method of manufacturing a separator for a lithium-sulfur battery according to claim 5, characterized in that: in the preparation step of the diaphragm for the lithium-sulfur battery, the solvent is acetone, and the mass concentration of the binder solution is 1-5%.

Technical Field

The invention belongs to the technical field of lithium-sulfur batteries, and particularly relates to a diaphragm for a lithium-sulfur battery and a preparation method thereof.

Background

The lithium-sulfur battery is a battery system which is made by using elemental sulfur as a positive electrode and metal lithium as a negative electrode. Due to its ultra-high theoretical specific energy, it has received much attention in recent years. But polysulfide (Li) generated during discharge of the lithium sulfur battery₂S_xWherein x is more than or equal to 4 and less than or equal to 8) is easy to dissolve in the electrolyte and can shuttle between the cathode and the anode, thereby obviously reducing the charge-discharge efficiency. To address this problem, small molecule sulfur allotropes are confined in a microporous carbon matrix, and the production of long chain polysulfides can be avoided due to space limitations. However, the microporous carbon material has small pore volume, so that the active substance sulfur cannot be loaded in a large amount, which is not beneficial to constructing a lithium sulfur battery with high energy density.

It is difficult for the polyolefin separator of the existing commercial application to inhibit migration of polysulfide. The modification of the diaphragm is mainly to coat corresponding carbon materials or metal oxides or sulfides on the diaphragm, strengthen the physical barrier to polysulfide in the charging and discharging process of the battery, and prevent the polysulfide from moving back and forth through physical and chemical adsorption.

Disclosure of Invention

Based on the method, the modified graphene/polyaniline composite material coated diaphragm is prepared by sulfonating graphene and polymerizing the sulfonated graphene and polyaniline, so that the problem of insufficient adsorption capacity of polysulfide by singly adopting graphene is solved.

In order to achieve the purpose, the invention adopts the following technical scheme:

a separator for a lithium-sulfur battery, comprising a porous substrate film and an adsorption function coating layer coated on the surface of the porous substrate film; the adsorption functional coating comprises a modified graphene/polyaniline composite material and a cohesive polymer; the modified graphene/polyaniline composite material is prepared by performing sulfonation treatment on graphene oxide to form sulfonated graphene, and then performing polymerization reaction on the sulfonated graphene and aniline. Further preferably, the porous substrate membrane is a polyethylene membrane or a polypropylene membrane; the adhesive polymer is polyvinylidene fluoride resin or polyacrylonitrile; the mass ratio of the modified graphene/polyaniline composite material to the adhesive polymer is (0.8-2): 100.

another object of the present invention is to provide a method for preparing the separator for a lithium-sulfur battery, comprising the steps of:

preparation of sulfonated graphene: dispersing graphene oxide in deionized water, adding isoamyl nitrite and 4-aniline sulfonic acid, reacting at 90-110 ℃ for 30-60 minutes, and finally sequentially centrifuging, filtering, washing and drying the generated product to obtain sulfonated graphene;

preparing a modified graphene/polyaniline composite material: dispersing sulfonated graphene in water at low temperature to obtain a dispersion liquid; dissolving ammonium persulfate in a hydrochloric acid solution in a low-temperature environment, and adding aniline to obtain a mixed solution; slowly adding the mixed solution into the dispersion liquid, stirring in a low-temperature environment, and finally washing and drying the obtained product to obtain the modified graphene/polyaniline composite material; preferably, the low temperature is 0 ℃.

Preparation of a separator for a lithium-sulfur battery: dissolving a binding polymer in a solvent to obtain a binding solution; preferably, the solvent is acetone, and the mass concentration of the binder solution is 1-5%. Dispersing the modified graphene/polyaniline composite material in a binding solution to obtain coating slurry; and coating the coating slurry on one surface of the porous substrate membrane, and drying to obtain the diaphragm for the lithium-sulfur battery.

As a preferred technical scheme, the graphene oxide is prepared by oxidizing graphite powder, and the method comprises the following specific steps: under the condition of ice-water bath, uniformly dissolving and dispersing graphite powder and sodium nitrate in concentrated sulfuric acid to obtain reaction liquid; slowly adding permanganate into the reaction solution, sequentially controlling the temperature of the reaction solution to be 15-25 ℃ for 1.3-1.7 hours, raising the temperature to be 30-40 ℃ and keeping the temperature for 0.8-1.2 hours, then adding deionized water into the reaction solution, raising the temperature of the reaction solution to be 90-100 ℃ and keeping the temperature for 30-50 minutes, finally adding hydrogen peroxide into the reaction solution, reacting for 50-70 minutes, and washing and drying a reaction product after the reaction is finished to obtain graphene oxide.

Compared with the prior art, the invention has the beneficial effects that:

the diaphragm for the lithium-sulfur battery comprises a porous substrate film and an adsorption functional coating coated on the surface of the porous substrate film; the modified graphene/polyaniline composite material contained in the adsorption functional coating forms a polyaniline three-dimensional network on the surface of sulfonated graphene, can enhance the adsorption capacity to polysulfide, can effectively improve the defect that the modified graphene or polyaniline is used alone, and obviously improves the cycle capacity retention rate and the rate charging performance of the lithium-sulfur battery.

Detailed Description

In order that the invention may be more fully understood, reference will now be made to the specific embodiments illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Example 1

a. Preparing graphene oxide: 10g of graphite powder and 5g of sodium nitrate were uniformly dissolved and dispersed in 200ml of concentrated sulfuric acid, and then 25g of permanganic acid was slowly added to the reaction solution. After controlling the temperature at 20 ℃ for 1.5 hours, the temperature was raised to 35 ℃ for 1 hour, then deionized water was added to the reaction solution, and the temperature was raised to 95 ℃ for 40 minutes, and finally 120ml of hydrogen peroxide was added to the reaction solution, and the reaction was carried out for 1 hour. And after the reaction is finished, washing the product with deionized water, filtering, separating by using a centrifuge, ultrasonically cleaning the obtained product with deionized water for 40 minutes, and drying at 90 ℃ for 24 hours to obtain the graphene oxide.

b. Preparation of sulfonated graphene: 0.2g of the graphene generated above is dissolved in 50ml of deionized water to be subjected to ultrasonic treatment for 30 minutes, and then 1g of 4-aniline sulfonic acid with the concentration of 0.03M and 0.6ml of isoamyl nitrite are added to react for 12 hours at 80 ℃ under stirring. And centrifuging, filtering, washing with water, and freeze-drying to obtain sulfonated graphene.

c. Preparing a modified graphene/polyaniline composite material: 0.1g of modified graphene was dissolved in 10ml of deionized water, and stirred at 0 ℃ for 30 minutes. 0.5g of ammonium persulfate was dissolved in 15ml of a hydrochloric acid solution having a concentration of 1M and the temperature was controlled at 0 degrees Celsius, and then 0.02g of aniline was added to the hydrochloric acid solution of ammonium persulfate to form a mixed solution. This mixed solution is then slowly added to the dispersion of modified graphene. The solution was then stirred at 0 ℃. And washing the obtained product with ethanol and water, and then freeze-drying for 24 hours to obtain the modified graphene/polyaniline composite material.

d. Preparing a modified graphene/polyaniline composite material coating membrane: adding 0.1Kg of polyacrylonitrile into 4Kg of acetone to prepare a binder solution; and adding 0.8g of the graphene/polyaniline composite material prepared in the step into the binder solution, uniformly dispersing, and coating the surface of a polyethylene diaphragm with the thickness of 14 microns.

Example 2

Steps a-c correspond to example 1.

d. Preparing a modified graphene/polyaniline composite material coating membrane: adding 0.1Kg of polyacrylonitrile into 4Kg of acetone to prepare a binder solution; and (3) adding 1.2g of the graphene/polyaniline composite material prepared in the step into the binder solution, uniformly dispersing, and coating the surface of a polyethylene diaphragm with the thickness of 14 microns.

Example 3

Steps a-c correspond to example 1.

d. Preparing a modified graphene/polyaniline composite material coating membrane: adding 0.1Kg of polyacrylonitrile into 4Kg of acetone to prepare a binder solution; and (3) adding 2g of the graphene/polyaniline composite material prepared in the step into the binder solution, uniformly dispersing, and coating the surface of a polyethylene diaphragm with the thickness of 14 microns.

Comparative example 1 a commercially available 14 micron polyethylene separator.

Lithium sulfur button cells were made with the separators provided in examples 1, 2, 3 and comparative example 1, respectively, with the sulfur positive electrode following the sulfur: carbon black: and PVDF (polyvinylidene fluoride) is mixed and coated in a ratio of 7:1.5:1.5, and a lithium metal sheet is adopted as a negative electrode. Electrochemical performance is shown in table 1.

TABLE 1 electrochemical performance of snap-on electrodes prepared in each of examples and comparative examples

	Gram capacity (mAh/g)	Capacity retention after 100 cycles of 0.2C cycle	5C constant current charge ratio
				Example 1	1539	81.9％	72.8％
Example 2	1545	85.9％	73.8％
				Example 3	1538	83.4％	70.6％
Comparative example	1357	60.7％	38.3％

As can be seen from table 1, the modified separators provided in examples 1, 2, and 3 contribute to improvement in cycle capacity retention and rate charging performance of lithium sulfur batteries.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express one embodiment of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.