Vinyl monomer-sulfur copolymer for lithium-sulfur battery positive electrode and preparation method thereof
阅读说明：本技术 一类锂硫电池正极用乙烯基单体-硫共聚物及制备方法 (Vinyl monomer-sulfur copolymer for lithium-sulfur battery positive electrode and preparation method thereof ) 是由 封伟 赵付来 李瑀 冯奕钰 于 2018-08-26 设计创作，主要内容包括：本发明公开一类锂硫电池正极用乙烯基单体-硫共聚物及制备方法,通过单质硫与一类乙烯基单体在加热条件下直接进行共聚反应,得到一类具有电化学活性可用作锂硫电池正极材料的乙烯基单体-硫共聚物。该类共聚物的制备方法简单、成本低,具有优异的电化学性能。(The invention discloses a vinyl monomer-sulfur copolymer for a lithium-sulfur battery anode and a preparation method thereof. The preparation method of the copolymer is simple, low in cost and excellent in electrochemical performance.)
1. A kind of lithium sulphur battery positive pole uses vinyl monomer-sulphur copolymer, characterized by, melt copolymerization with simple substance sulphur and vinyl monomer, heat single substance sulphur to the molten state under keeping anaerobic condition, in order to make the sulphur ring formed by 8 sulphur atoms break at the room temperature, form the sulphur chain with two free radical end groups, keep anaerobic condition and add vinyl monomer, chain free radical in the molten sulphur initiates the carbon-carbon double bond in the vinyl monomer in order to carry on the free radical copolymerization, form vinyl monomer-sulphur copolymer, the sulphur content is 50-99 wt%, preferably 80-90 wt%; the general structural formula is shown as the following chemical formula:
whereinA monomer unit representing a vinyl monomer used, x is a polymerization degree of sulfur, and is 6 or more in view of a sulfur chain in which an 8-membered sulfur ring is cleaved to form a diradical end group; y is the degree of polymerization of the vinyl monomer and is 1 or more.
2. The vinyl monomer-sulfur copolymer as claimed in claim 1, wherein the vinyl monomer is 2-vinyl thiophene, N-vinyl pyrrolidone, 1-vinyl imidazole, 2-vinyl pyridine, 2-vinyl pyrazine or 2-vinyl furan.
3. The vinyl monomer-sulfur copolymer for a positive electrode of a lithium-sulfur battery according to claim 1 or 2, wherein y is 10 to 300, preferably 100 to 200.
4. The vinyl monomer-sulfur copolymer for the positive electrode of the lithium-sulfur battery as claimed in claim 1 or 2, wherein the mass percent of elemental sulfur is 50 to 99 wt%, and the mass percent of the vinyl monomer is 1 to 50 wt%; preferably, the mass percent of the elemental sulfur is 80-90 wt%, and the mass percent of the vinyl monomer is 10-20 wt%.
5. A preparation method of a vinyl monomer-sulfur copolymer for a lithium-sulfur battery anode is characterized in that elemental sulfur and a vinyl monomer are subjected to melt copolymerization, the elemental sulfur is heated to a molten state under the condition of keeping oxygen-free, so that a sulfur ring consisting of 8 sulfur atoms at normal temperature is broken to form a sulfur chain with a double-free radical end group, the vinyl monomer is added under the condition of keeping oxygen-free, and a chain free radical in the molten sulfur initiates a carbon-carbon double bond in the vinyl monomer to perform free radical copolymerization to form the vinyl monomer-sulfur copolymer, wherein the mass percent of the elemental sulfur is 50-99 wt%, and the mass percent of the vinyl monomer is 1-50 wt%.
6. The method for preparing the vinyl monomer-sulfur copolymer for the positive electrode of the lithium-sulfur battery as claimed in claim 5, wherein the mass percent of the elemental sulfur is 80 to 90 wt%, and the mass percent of the vinyl monomer is 10 to 20 wt%.
7. The method of claim 5 or 6, wherein the elemental sulfur is heated to a molten state, such as 160-200 ℃, preferably 170-185 ℃, by heating with an oil bath to form a clear orange molten phase.
8. The preparation method of the vinyl monomer-sulfur copolymer for the positive electrode of the lithium-sulfur battery according to claim 5 or 6, characterized in that the melting state of elemental sulfur is maintained, and the vinyl monomer is dripped for reaction, wherein the reaction time is 30-120min, the stirring speed is 200-400 r/min, and the dripping speed of the vinyl monomer is 1-10 ml/min; the reaction time is preferably 60-100min, the stirring speed is 250-350 r/min, and the speed of dripping vinyl monomer is 4-8 ml/min.
9. The method for preparing vinyl monomer-sulfur copolymer for positive electrode of lithium-sulfur battery as claimed in claim 5 or 6, wherein the oxygen-free state of the reaction system is maintained and the protection is performed by using inert protective gas such as nitrogen, helium or argon.
10. Use of the vinyl monomer-sulfur copolymer according to any one of claims 1 to 4 for producing a positive electrode material for a lithium-sulfur battery.
Technical Field
The invention relates to a high-sulfur-content polymer and a synthesis method thereof, belongs to the technical field of organic synthesis and lithium-sulfur battery preparation, and particularly relates to a vinyl monomer-sulfur copolymer for a lithium-sulfur battery anode and a preparation method thereof.
Background
Lithium batteries have so far been a major area of modern application for lithium source composites. Over the past few decades, lithium ion batteries have occupied the market for commercial batteries with their high battery voltage, low self-discharge rate, stable cycling performance. However, with the development of scientific technology, the demand for high energy density batteries in large energy storage systems, electric vehicles, and other energy applications is increasing. Therefore, development of new high-performance electrode materials for current lithium batteries is becoming a necessity. Lithium-sulfur batteries have the advantages of extremely high energy density (2567Wh/kg) and high specific capacity (1675mAh/g) which are far higher than those of the most advanced lithium ion batteries, and the raw materials of the lithium-sulfur batteries are cheap and have low pollution, so the lithium-sulfur batteries are a hot point of research. However, the performance of the lithium-sulfur battery is not up to the theoretical value due to the severe "shuttle effect" during the charging and discharging processes. To solve this problem, in recent years, sulfur-containing polymers have been used as a positive electrode material for lithium-sulfur batteries instead of elemental sulfur. The sulfur-containing polymer has chemical bonding force and physical entanglement effect on sulfur, and can effectively fix polysulfide which is an intermediate product of electrochemical reaction, thereby effectively inhibiting shuttle effect and improving the electrochemical performance of the positive electrode of the lithium-sulfur battery. Therefore, the development of new high-performance sulfur-containing polymers as cathode materials becomes one of the effective approaches to solve the "shuttle effect" of lithium-sulfur batteries.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a vinyl monomer-sulfur copolymer for a lithium-sulfur battery anode and a preparation method thereof.
The technical purpose of the invention is realized by the following technical scheme.
A kind of vinyl monomer-sulfur copolymer for lithium-sulfur battery positive electrode contains the following sulfur content: 50 to 99 wt.%, preferably 80 to 90 wt.%. The general structural formula of the vinyl monomer-sulfur copolymer prepared by melt free radical polymerization is shown as the following chemical formula:
The preparation method of the vinyl monomer-sulfur copolymer comprises the steps of carrying out melt copolymerization on elemental sulfur and a vinyl monomer, heating the elemental sulfur to a molten state under the condition of keeping oxygen-free condition, and enabling a sulfur ring consisting of 8 sulfur atoms at normal temperature
Vinyl monomers of the invention
In the preparation method, according to the mass percentage (namely the sum of the mass of the elemental sulfur and the mass of the vinyl monomer is 100 percent), the mass percentage of the elemental sulfur is 50 to 99 percent by weight, and the mass percentage of the vinyl monomer is 1 to 50 percent by weight; preferably, the mass percent of the elemental sulfur is 80-90 wt%, and the mass percent of the vinyl monomer is 10-20 wt%.
In the preparation process of the present invention, elemental sulphur is heated to a molten state, for example 160-200 c, preferably 170-185 c, using oil bath heating to form a clear orange molten phase.
In the preparation method, vinyl monomer is dripped into elemental sulfur of a molten phase under the condition of stirring, the mixture is continuously heated and stirred for reaction, the whole system is naturally cooled to the room temperature of 20-25 ℃ after the reaction, and the product is directly scraped out of a reaction container by a metal shovel.
In the preparation method, the melting state of elemental sulfur is maintained, and vinyl monomers are dripped for reaction, the reaction time is 30-120min, the stirring speed is 200-400 r/min, and the dripping speed of the vinyl monomers is 1-10 ml per minute.
In the preparation method of the invention, the reaction time is 60-100min, the stirring speed is 250-350 r/min, and the speed of dripping vinyl monomer is 4-8 ml per minute.
The anaerobic state of the reaction system is kept during the preparation method of the invention, and inert protective gas such as nitrogen, helium or argon is used for protection.
The general reaction formula of the copolymerization reaction in the invention is:
compared with the prior art, the technical scheme of the invention has the following beneficial effects: (1) the elemental sulfur can react with the vinyl monomer in any proportion to prepare the copolymer with high sulfur content, and the copolymer can be used as the anode material of the lithium-sulfur battery, so that the content of active substances in the anode is greatly improved; (2) the vinyl monomer-sulfur copolymer provided by the invention can be subjected to polymerization reaction only by heating without adding an additional solvent, and has the advantages of simple process and low cost; (3) the vinyl monomer-sulfur copolymer provided by the invention is used as a lithium-sulfur battery cathode material, and C and S in the polymer are combined in a covalent bond, so that polysulfide generated in the electrochemical reaction process is bound by copolymer molecules in a covalent bond form, and meanwhile, the entanglement effect of polymer chains has a physical binding effect on sulfur, so that the dissolution of the polysulfide can be inhibited, the volume expansion can be relieved, and the electrochemical performance can be improved.
Drawings
FIG. 1 is an infrared spectrum of a starting N-vinylpyrrolidine and a product N-vinylpyrrolidine-sulfur copolymer of example 2 of the present invention.
FIG. 2 is a matrix-assisted laser desorption ionization time-of-flight mass spectrum (MALDI-TOF-MS) of the product N-vinylpyrrolidine-sulfur copolymer of example 2 of the present invention.
FIG. 3 is a graph showing the charge and discharge cycles at 0.1C based on the mass of the copolymer of a battery assembled with the product N-vinylpyrrolidine-sulfur copolymer of example 2 of the present invention as a positive electrode material for a lithium sulfur battery.
Detailed Description
The present invention will be further described with reference to the following embodiments. The following examples of the present invention are given to further illustrate the present invention, but not to limit the scope of the present invention. The stirring speed was 250 rpm, and the vinyl monomer was added dropwise at a rate of 1 ml/min.