阅读说明：本技术 一种五元单体共聚聚合物锂二次电池及其制备方法 (Five-membered monomer copolymerized polymer lithium secondary battery and preparation method thereof ) 是由 许晓雄 张秩华 崔言明 黄园桥 詹盼 于 2020-04-21 设计创作，主要内容包括：本发明公开了一种五元单体共聚聚合物锂二次电池,涉及锂二次电池领域,主要其电解质原料包括五种聚合物的单体,所述聚合物的单体为甲基丙烯酸甲酯,丙烯酸乙酯,丙烯酸丁酯,丙烯酸辛酯,丙烯腈,苯乙烯,乙酸乙烯,甲基丙烯酸缩水甘油酯和聚乙二醇二甲基丙烯酸酯中的五种,同时,必须包含苯乙烯、丙烯腈、乙酸乙烯和甲基丙烯酸缩水甘油酯中的一种。利用五种聚合物的单体进行共聚所得到的效果比单纯一种或五种以下的聚合物的单体进行聚合所得到凝胶电解质,具有更佳的机械强度、电导率、电化学稳定性综合性能。同时将其应用在锂二次电池中,能够有效地提高锂二次电池的循环稳定性。(The invention discloses a quinary monomer copolymer lithium secondary battery, which relates to the field of lithium secondary batteries, and mainly comprises five polymer monomers as electrolyte raw materials, wherein the polymer monomers are five of methyl methacrylate, ethyl acrylate, butyl acrylate, octyl acrylate, acrylonitrile, styrene, vinyl acetate, glycidyl methacrylate and polyethylene glycol dimethacrylate, and one of styrene, acrylonitrile, vinyl acetate and glycidyl methacrylate is required to be contained. The effect obtained by copolymerizing the monomers of the five polymers is better than that of the gel electrolyte obtained by polymerizing only one or less than five monomers of the polymers, and the gel electrolyte has the comprehensive properties of better mechanical strength, conductivity and electrochemical stability. Meanwhile, when the lithium ion battery is applied to the lithium secondary battery, the cycling stability of the lithium secondary battery can be effectively improved.)

1. A quinary monomer copolymerized polymer lithium secondary battery is characterized in that: the electrolyte raw material comprises five polymer monomers, wherein the polymer monomers are five of methyl methacrylate, ethyl acrylate, butyl acrylate, octyl acrylate, acrylonitrile, styrene, vinyl acetate, glycidyl methacrylate and polyethylene glycol dimethacrylate, and one of styrene, acrylonitrile, vinyl acetate and glycidyl methacrylate is required to be contained.

2. The lithium secondary battery of claim 1, wherein: the molar ratio of the monomers of the five polymers is (1-20) to (1-20).

3. A preparation method of a quinary monomer copolymer lithium secondary battery is characterized in that: comprises the following steps of (a) carrying out,

the method comprises the following steps: weighing monomers of the polymer according to claim 1 or 2, and mixing the monomers of the polymer with an electrolyte and an initiator to obtain a mixture;

step two: after winding or laminating the semi-finished product battery of the lithium ion battery, filling the mixture of the step one between layers of the semi-finished product battery;

step three: and heating the semi-finished battery with the mixture to copolymerize monomers of the polymer, and forming the battery to obtain the finished battery.

4. The method according to claim 3, wherein the method comprises the following steps: the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide tert-butyl peroxide and methyl ethyl ketone peroxide.

5. The method according to claim 4, wherein the method comprises the following steps: the initiator content is 0.1-5 wt% of the total monomer content of the polymer.

6. The method according to claim 3, wherein the method comprises the following steps: the electrolyte accounts for 10-85 wt% of the total weight of the mixture.

7. The method according to claim 3, wherein the method comprises the following steps: in the third step, the heating temperature is controlled at 60-100 ℃.

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a quinary monomer copolymer lithium secondary battery and a preparation method thereof.

Background

Most of the current lithium ion batteries use a liquid electrolyte system. The electrolyte system has very high lithium ion conductivity, but the low flash point and flammability characteristics are one of the reasons for causing the battery to be unsafe. In addition, metallic lithium has formed dendrites and dead lithium in a liquid chemical environment, which adversely affects the safety performance and the cyclability of the battery.

Therefore, in recent years research has been directed towards all-solid-state batteries based on purely inorganic solid electrolytes and all-solid-state batteries based on dry polymers (purely high molecular weight polymers plus lithium salts), which are thermodynamically stable. All-solid batteries using sulfide glass ceramic solid electrolytes, as disclosed in chinese patent 201480045908.2, may be connected internally in series. As disclosed in the chinese patent 201810516266.X, the main chain of the polymer electrolyte is a flexible and extendable aliphatic chain segment, and the hybridized boron ions are fixed on the main chain and are adsorbed and dissociated with the lithium ions, which is beneficial to the improvement of the mobility of the lithium ions and the improvement of the utilization rate of the lithium ions.

However, the current room-temperature ionic conductivity of the all-solid polymer electrolyte or the inorganic solid electrolyte still cannot reach the level of practical application of the lithium ion battery; in addition, the poor interfacial compatibility of solid electrolytes with solid electrode materials limits their further applications in lithium ion batteries. As a compromise, researchers have developed a polymer separator capable of gelling a liquid electrolyte, and the separator has been developed in recent years to have both high lithium ion conductivity of a liquid electrolyte and high safety of a solid electrolyte by a gel polymer electrolyte formed by swelling a polymer in a liquid electrolyte system.

For example, chinese patent application No. 201780003336.5 discloses a gel polymer electrolyte power cell, which includes a negative electrode, a positive electrode, a gel polymer electrolyte and a separator, wherein the negative electrode active material layer includes graphite and a composite material dispersed in gaps of the graphite, and the positive electrode active material layer includes at least one of NCA, NCM and a lithium-rich manganese material; the polymer monomer is at least one of tripropylene glycol diacrylate (TPGDA) and pentaerythritol tetraacrylate (PEPETEA), and the initiator is at least one of Azobisisobutyronitrile (AIBN) and Benzoyl Peroxide (BPO).

For example, chinese patent application No. 201810593201.5 discloses a lithium battery polymer gel electrolyte, which comprises a compound polymer, a plasticizer and a lithium salt electrolyte, wherein during the preparation process, polyacrylonitrile is hydrolyzed, then the hydrolyzed polyacrylonitrile is acidified with strong acid, then the acidified polyacrylonitrile is dissolved, thionyl chloride is added, and after heating reaction, the solvent is recovered to obtain modified hydrolyzed polyacrylonitrile; then compounding the modified hydrolyzed polyacrylonitrile and the polyaldehyde group sodium alginate according to the mass ratio of 3: 1-5: 1 to obtain a compound polymer; and then mixing the compound polymer and the plasticizer, heating and stirring for reaction, adding the lithium salt electrolyte, stirring and mixing uniformly, and preparing the film to obtain the lithium battery polymer gel electrolyte. However, the present inventors have found that the gel polymer electrolytes of either type have drawbacks that are difficult to overcome in the course of research. For example, a polymer monomer is at least one of tripropylene glycol diacrylate and pentaerythritol tetraacrylate, and the polymer composition is single, so that the contradiction between decomposition caused by a large electrochemical potential difference between a high positive electrode potential and a low negative electrode potential in the battery cannot be solved at the same time. The porous polymer gel prepared by hydrolysis of the polyacrylonitrile has poor mechanical strength, and although the self-supporting microporous gel polymer membrane can absorb a large amount of electrolyte and shows high lithium ion conductivity, the polymer membrane can be partially corroded and dissolved by the electrolyte in the long-cycle process of the battery to change the mechanical strength of the membrane, so that potential danger is brought to the battery.

Disclosure of Invention

The invention aims to provide a quinary monomer copolymerized polymer lithium secondary battery, wherein a gel electrolyte prepared by polymerizing a quinary monomer has good mechanical strength and chemical stability, high ionic conductivity and thermal stability, and a preparation method of the gel electrolyte is simple and suitable for large-scale production.

The above object of the present invention is achieved by the following technical solutions:

the electrolyte material of the five-membered monomer copolymerized polymer lithium secondary battery comprises five polymer monomers, wherein the polymer monomers are five of methyl methacrylate, ethyl acrylate, butyl acrylate, octyl acrylate, acrylonitrile, styrene, vinyl acetate, glycidyl methacrylate and polyethylene glycol dimethacrylate, and one of styrene, acrylonitrile, vinyl acetate and glycidyl methacrylate is required to be contained.

Preferably, the molar ratio of the monomers of the five polymers is (1-20) to (1-20).

By adopting the technical scheme, the effect obtained by utilizing the monomers of the five polymers for copolymerization is better than that of the gel electrolyte obtained by polymerizing only one or less than five monomers of the polymers, and the gel electrolyte has better comprehensive properties of mechanical strength, conductivity and electrochemical stability.

And, one of styrene, acrylonitrile, vinyl acetate and glycidyl methacrylate must be contained, which is beneficial to increase the melting point of the polymer, and further improves the mechanical strength and high temperature resistance of the polymer, so as to play a good structural support role for the gel electrolyte.

A method for preparing a quinary monomer copolymer lithium secondary battery comprises the following steps,

the method comprises the following steps: weighing the monomer of the polymer, and mixing the monomer of the polymer with electrolyte and an initiator to obtain a mixture;

step two: after winding or laminating a positive plate, a negative plate battery and a diaphragm of the lithium ion battery, filling the mixture obtained in the step one into the layers of the semi-finished battery;

step three: heating the semi-finished battery with the mixture to copolymerize monomers of the polymer, and forming the battery to obtain a finished battery;

by adopting the technical scheme, after the electrolyte suitable for different anodes and cathodes is added into the monomer of the polymer before polymerization, the monomer can be kept in the generated polymer macromolecular chain segment, or in the hole caused by phase segregation or partial dissolution, so as to provide ion conductivity.

The quinary copolymer obtained by copolymerizing the monomers of the five polymers simultaneously has the physicochemical properties of various polymers to generate a synergistic effect, and simultaneously has high porosity, high mechanical strength, high electrochemical stability and high thermodynamic stability, thereby achieving the effect of high entropy.

In addition, the gel electrolyte prepared from the polymer can be added and polymerized after the traditional lithium ion battery containing the polyolefin diaphragm is assembled, is compatible with the traditional lithium ion battery production equipment, and is produced in large scale.

Preferably, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide tert-butyl peroxide, methyl ethyl ketone peroxide.

Preferably, the initiator content is 0.1 to 5 wt% of the total monomer content of the polymer.

Preferably, the electrolyte is present in an amount of 10 to 85 wt% of the total mixture.

Preferably, in the third step, the heating temperature is controlled to be 60-100 ℃.

In conclusion, the beneficial technical effects of the invention are as follows:

1. the monomers of five polymers are selected for copolymerization, so that the physical and chemical properties of various polymers generate synergistic effect, and the high-porosity, high-mechanical strength, high electrochemical stability and high thermodynamic stability are achieved, and the effect of high entropy is achieved;

2. the gel electrolyte prepared by the monomer of the polymer can be added and polymerized after the traditional lithium ion battery containing the polyolefin diaphragm is assembled, is compatible with the traditional lithium ion battery production equipment, and can be produced in large scale.

Detailed Description