CN110867550A

CN110867550A - Composite membrane for lithium-sulfur battery and preparation method thereof

Info

Publication number: CN110867550A
Application number: CN201911161854.7A
Authority: CN
Inventors: 解勤兴; 章敬斌
Original assignee: Tianjin Polytechnic University
Current assignee: Tianjin Polytechnic University
Priority date: 2019-11-25
Filing date: 2019-11-25
Publication date: 2020-03-06

Abstract

The invention discloses a composite membrane for a lithium-sulfur battery and a preparation method thereof. The method comprises the following specific steps: sequentially dispersing and dissolving 5-50 parts by mass of attapulgite, 5-30 parts by mass of a carboxylated carbon nanotube, 1-10 parts by mass of a pore-forming agent and 50-80 parts by mass of a film-forming organic polymer into an organic solvent, defoaming the obtained casting solution, preparing a film by using a phase inversion method, and drying. The composite membrane prepared by the method has good wettability to electrolyte, has good adsorption capacity to polysulfide generated in the charging and discharging process, and effectively inhibits the shuttle effect, thereby improving the cycle stability of the lithium-sulfur battery.

Description

Composite membrane for lithium-sulfur battery and preparation method thereof

Technical Field

The invention relates to the technical field of inorganic nonmetallic materials, in particular to a preparation method of an attapulgite/carbon nanotube synergistically modified composite membrane and application of the composite membrane in a lithium-sulfur battery.

Background

The lithium-sulfur battery has high theoretical specific capacity (1672mAh/g), higher energy density (2600Wh/kg), two relatively smooth discharge voltage platforms, more excellent performance compared with the traditional secondary battery, is considered to be one of the secondary batteries with the most development potential, and thus has attracted wide attention. However, elemental sulfur has low conductivity, and meanwhile, polysulfide which is easily dissolved in electrolyte can be generated in the charge-discharge cycle process of the sulfur positive electrode, so that the shuttle effect is generated, the available active substance quantity is reduced, and the utilization rate of the active substance is reduced, so that the battery has poor cycle stability, short cycle life and low coulombic efficiency, and the commercial application of the lithium-sulfur battery is greatly limited. In view of the above problems, one of the most common technical methods is to prepare a sulfur/carbon composite cathode material by compounding sulfur and a highly conductive carbon material such as porous carbon, graphene, carbon nanotube, etc., so as to improve the conductivity of the sulfur cathode, and to suppress the shuttle effect by adsorbing sulfur and polysulfide due to the nanoporous structure of the carbon material (electrochemical Acta, 2014, 116: 146-. The sulfur positive electrode prepared by this method is generally not high in active material content, thereby reducing the energy density of the lithium sulfur battery.

Disclosure of Invention

In order to overcome the defects of the prior art and solve the problems of poor cycle stability, low coulombic efficiency, low utilization rate of active substances and the like of a lithium-sulfur battery caused by a polysulfide shuttle effect, the attapulgite/carbon nanotube synergetic modified composite membrane is prepared by adopting the following technical scheme and is applied to the lithium-sulfur battery.

The technical scheme adopted by the invention is as follows: dispersing/dissolving 5-50 parts by mass of attapulgite, 5-30 parts by mass of a carboxylated carbon nanotube, 1-10 parts by mass of a pore-forming agent and 50-80 parts by mass of an organic polymer in an organic solvent in sequence, defoaming the obtained casting solution, preparing a membrane by using a phase inversion method, and drying.

The organic polymer used in the above steps is one or more of polyolefin, polyvinylidene fluoride, polysulfone, polyacrylonitrile and polyamide.

The organic solvent used in the above step is one or more of N, N-dimethylformamide, polyvinylpyrrolidone, dimethyl sulfoxide, dimethylacetamide and N-methyl-2-pyrrolidone.

The carbon nano tube used in the steps is one or two of a single-wall carbon nano tube and a multi-wall carbon nano tube.

The pore-forming agent used in the above step is one or more of a surfactant, lithium chloride, sodium chloride, lithium nitrate and sodium nitrate.

The composite membrane prepared by the steps can be directly coated on one side of the polymer diaphragm in the lithium-sulfur battery, or can be independently formed into a membrane and placed between the sulfur anode and the polymer diaphragm.

The composite membrane prepared by the invention has good wettability to electrolyte, has good adsorption capacity to polysulfide generated in the charging and discharging process, can effectively inhibit the shuttle effect, and can remarkably improve the cycle stability of the lithium-sulfur battery.

Drawings

FIG. 1 is a scanning electron micrograph of the product of example 1.

FIG. 2 is a scanning electron micrograph of the product of example 2.

FIG. 3 shows the static contact angle test of the products of examples 1 and 2.

Fig. 4 is a schematic view of an assembled lithium sulfur battery of example 4.

FIG. 5 is a graph of the cycle performance of a lithium sulfur cell assembled with the products of examples 1 and 2 as an interlayer.

Detailed Description

Example 1: multi-walled carbon nanotube @ polyacrylonitrile composite membrane

And heating and refluxing the purified multiwalled carbon nanotube in a mixture of concentrated sulfuric acid and concentrated nitric acid (the volume ratio is 3: 1) at 70 ℃ for 100 minutes, filtering, washing with distilled water to be neutral, and drying to obtain the carboxylated multiwalled carbon nanotube. 0.0267 g of carboxylated carbon nanotubes was ultrasonically dispersed in 2.85 g of N, N-dimethylformamide solvent, and then 0.0042 g of porogen F127 and 0.24 g of polyacrylonitrile were sequentially added, and stirred at room temperature for 24 hours. The obtained casting solution was defoamed, scraped on a glass plate, and immersed in distilled water (coagulation bath). And (3) taking out the film after the film falls off from the glass plate, soaking the film in methanol for 6 hours, airing, and vacuum-drying at 60 ℃ for 12 hours to obtain the multi-walled carbon nanotube/polyacrylonitrile composite film, wherein the appearance is shown in figure 1.

Example 2: attapulgite/multi-walled carbon nanotube @ polyacrylonitrile composite membrane

The purified attapulgite is heated in the air at 300 ℃ for 2 hours. Heating and refluxing the multi-walled carbon nano-tube in a mixture of concentrated sulfuric acid and concentrated nitric acid (the volume ratio is 3: 1) at 70 ℃ for 100 minutes, filtering, washing with distilled water to be neutral, and drying to obtain the carboxylated multi-walled carbon nano-tube. 0.12 g of attapulgite and 0.04 g of carboxylated multi-walled carbon nano-tube are ultrasonically dispersed into 2.85 g of N, N-dimethylformamide solvent, then 0.0042 g of pore-making agent F127 and 0.24 g of polyacrylonitrile are sequentially added, and stirred for 24 hours at room temperature. The obtained casting solution was defoamed, scraped on a glass plate, and immersed in distilled water (coagulation bath). And (3) taking out the film after the film falls off from the glass plate, soaking the film in methanol for 6 hours, airing, and vacuum-drying at 60 ℃ for 12 hours to obtain the multi-walled carbon nanotube/polyacrylonitrile composite film, wherein the appearance is shown in figure 2.

Example 3: static contact Angle test

The hydrophilic properties of the composite membranes were analyzed by contact angle testing using a DSA100 contact angle measuring instrument manufactured by KRUSS, germany. The result is shown in fig. 3, the contact angle of the multi-walled carbon nanotube @ polyacrylonitrile composite film is 52.3 degrees, and the contact angle of the attapulgite/multi-walled carbon nanotube @ polyacrylonitrile composite film is 50.5 degrees.

Example 4: preparation of sulfur positive electrode

Sublimed sulfur and conductive carbon black are uniformly mixed according to the mass ratio of 4: 1, and are heated for 12 hours at the temperature of 155 ℃. And uniformly mixing the product, conductive carbon black and polyvinylidene fluoride in N-methyl pyrrolidone according to the mass ratio of 8: 1 to obtain slurry, and then coating the slurry on an aluminum foil current collector. Vacuum drying at 60 ℃ for 24 hours, and then cutting into a circular positive plate with the diameter of 13 mm.

Example 5: lithium sulfur battery assembly and performance testing

0.75M LiTFSI/DME + DOL (volume ratio 1: 1) is used as electrolyte, and 0.4M diphenyl disulfide and 0.25M LiNO are added₃As an additive, a 2430 type button cell was assembled with the above-described sulfur positive electrode under an argon atmosphere using a metal lithium sheet as a negative electrode according to fig. 4. A blue CT2001A type battery test system is adopted to carry out charge and discharge tests, and the voltage range is 1.7-2.8V. The result is shown in fig. 5, and the lithium-sulfur battery assembled by taking the attapulgite/multi-walled carbon nanotube @ polyacrylonitrile as the middle layer has excellent cycling stability.

Claims

1. A preparation method of a composite membrane for a lithium-sulfur battery comprises the following specific steps: dispersing/dissolving 5-50 parts by mass of attapulgite, 5-30 parts by mass of a carboxylated carbon nanotube, 1-10 parts by mass of a pore-forming agent and 50-80 parts by mass of an organic polymer in an organic solvent in sequence, defoaming the obtained casting solution, preparing a membrane by using a phase inversion method, and drying.

2. The method for preparing the composite membrane for the lithium-sulfur battery according to claim 1, wherein the organic polymer is one or more of polyolefin, polyvinylidene fluoride, polysulfone, polyacrylonitrile and polyamide.

3. The method of claim 1, wherein the organic solvent is one or more selected from the group consisting of N, N-dimethylformamide, polyvinylpyrrolidone, dimethyl sulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone.

4. The method of claim 1, wherein the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes.

5. The method for preparing the composite membrane for the lithium-sulfur battery according to claim 1, wherein the pore-forming agent is one or more of a surfactant, lithium chloride, sodium chloride, lithium nitrate and sodium nitrate.

6. A method of preparing a composite membrane for a lithium-sulfur battery, the composite membrane being obtainable by the method of any one of claims 1 to 5.

7. A composite membrane for a lithium-sulfur battery, which can be directly coated on one side of a polymer diaphragm in the lithium-sulfur battery or separately formed between a sulfur positive electrode and the polymer diaphragm.

8. The composite membrane for a lithium-sulfur battery as claimed in claims 6 and 7, which has good wettability to electrolyte, strong adsorption capability to polysulfide generated in the charging and discharging processes, and can effectively inhibit the shuttle effect, thereby greatly improving the cycle stability of the lithium-sulfur battery.