阅读说明：本技术 一种介质电解质、锂离子电池及其制备方法 (Dielectric electrolyte, lithium ion battery and preparation method thereof ) 是由 孙晓玉 李炳江 王立群 郑浪 易祖良 刘奕凯 叶鑫 于 2020-07-09 设计创作，主要内容包括：本发明公开一种介质电解质,按照质量分数包括以下物质：6%至24%导电锂盐；70%至90%聚合物电解质基体；3%至6%增塑剂；本发明还公开了使用该介质电解质的锂离子电池,包括表面涂覆有准固态电解质的正极极片和锂负极片,锂负极片表面涂覆有所述的介质电解质；优选所述准固态电解质包括甲基丙烯酸甲酯、Li<Sub>1.5</Sub>Al<Sub>0.5</Sub>Ge<Sub>1.5</Sub>(PO<Sub>4</Sub>)<Sub>3</Sub>和介孔分子筛；本发明还公开了该介质电解质的制备方法；本发明利用介质电解质半固态凝胶的状态对锂金属化学稳定性良好,抑制锂枝晶的生长,从而获得了性能优异的锂离子电池。(The invention discloses a dielectric electrolyte which comprises the following substances in percentage by mass: 6% to 24% of a conductive lithium salt; 70% to 90% of a polymer electrolyte matrix; 3% to 6% of a plasticizer; the invention also discloses a lithium ion battery using the dielectric electrolyte, which comprises a positive pole piece and a lithium negative pole piece, wherein the surface of the positive pole piece is coated with the quasi-solid electrolyte; preferably, the quasi-solid electrolyte comprises methyl methacrylate and Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 And a mesoporous molecular sieve; the invention also discloses a preparation method of the dielectric electrolyte; the invention utilizes the state of the semi-solid gel of the dielectric electrolyte to have good chemical stability on lithium metal and inhibit the growth of lithium dendrite, thereby obtaining the lithium ion battery with excellent performance.)

1. A dielectric electrolyte, characterized by:

the material comprises the following substances in percentage by mass:

6 to 24 percent of conductive lithium salt;

70% to 90% of a polymer electrolyte matrix;

3 to 6 percent of plasticizer.

2. A dielectric electrolyte as claimed in claim 1, wherein: the conductive lithium salt is Li_1.5Al_0.5Ge_1.5(PO₄)₃。

3. A dielectric electrolyte as claimed in claim 1, wherein: the polymer electrolyte matrix is one or more of polyacrylonitrile, polyethylene oxide, polymethyl methacrylate and polyvinylidene fluoride.

4. A dielectric electrolyte as claimed in claim 1, wherein: the plasticizer is one or more of propylene carbonate, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate.

5. A dielectric electrolyte as claimed in claim 1, wherein: conductivity at room temperature of 10^-4S/cm。

6. A method for preparing a dielectric electrolyte as claimed in any one of claims 1 to 5, characterized in that: the method comprises the following steps:

dissolving a polymer electrolyte matrix in acetonitrile, stirring at the speed of 5000-;

and step two, adding the conductive lithium salt and the plasticizer in the amount into the mixture obtained in the step one, stirring at the speed of 5000-30000rpm, and obtaining the target product after the acetonitrile is completely evaporated.

7. The method for preparing a dielectric electrolyte according to claim 6, wherein: the mass of the acetonitrile is 3 to 5 times of the total mass of the raw materials for preparing the medium electrolyte.

8. The method for preparing a dielectric electrolyte according to claim 6, wherein: the process conditions of the step two are as follows:

the temperature is 20 ℃;

the stirring time was 24 hours.

9. A lithium ion battery comprises a positive pole piece and a lithium negative pole piece, wherein the surfaces of the positive pole piece and the lithium negative pole piece are coated with quasi-solid electrolyte, and the lithium ion battery is characterized in that:

the surface of the lithium negative electrode sheet is coated with the dielectric electrolyte as described in any one of claims 1 to 4.

10. The lithium ion battery of claim 9, wherein: the quasi-solid electrolyte comprises methyl methacrylate and Li_1.5Al_0.5Ge_1.5(PO₄)₃And a mesoporous molecular sieve.

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a dielectric electrolyte, a lithium ion battery using the dielectric electrolyte and a preparation method of the dielectric electrolyte.

Background

With the popularization of electric vehicles, the safety problem of high energy density lithium batteries is becoming more severe. Particularly, the electric automobile fire incidents reported at home and abroad in recent years are increasingly frequent, and the challenge of designing a battery with safety and energy density is more prominent.

In order to further improve the energy density and safety performance of lithium ion batteries, solid state batteries have become a necessary approach. The conductivity of all-solid batteries can not meet the requirements, mass production needs more exploration, and lithium ion batteries for realizing industrialization, including global power batteries, are basically liquid lithium ion batteries.

No matter which electrolyte is organic, and the specific gravity of inflammable matters in the liquid lithium ion battery is larger by adding the diaphragm. Lithium dendrites may occur when the liquid lithium ion battery is operated under a large current, so that a diaphragm is punctured to cause short circuit damage; the electrolyte is an organic liquid, and tends to cause side reactions, oxidative decomposition, gas generation and combustion at high temperature. When the liquid lithium ion battery is severely impacted or the temperature of the battery is too high, the electrolyte is extremely easy to burn, and the battery is ignited and has more serious safety accidents.

Liquid cells are eagerly moving towards solid state cells, but the conductivity of all-solid electrolytes is now not ideal and will slowly transition from quasi-solid cells to all-solid cells. For a solid-state battery, metallic lithium is the most ideal negative electrode material, but a side reaction is easy to occur between the liquid electrolyte and the lithium metal, which causes the growth of lithium dendrites and reduces the coulombic efficiency of the battery, and is the bottleneck of the current development of quasi-solid-state batteries.

The patent application with the publication number of CN103855427A discloses a solid electrolyte, and the technical problem mainly solved is to provide a modified polymethyl methacrylate electrolyte with high mechanical strength and high electric conductivity, the specification of the modified polymethyl methacrylate electrolyte describes that the charge-discharge efficiency of the prepared lithium ion battery tested by 0.1C charge-discharge is not obviously improved, and the application effect of the modified polymethyl methacrylate electrolyte applied to a high energy density lithium battery needs to be further researched.

The development difficulty of the quasi-solid battery lies in the matching of the system, the lithium metal battery is an ideal negative electrode due to higher energy density, the quasi-solid battery taking the metal lithium as the negative electrode needs to match a reasonable solid electrolyte and electrolyte system, and simultaneously needs to inhibit the side reaction easily generated between the liquid electrolyte and the lithium metal.

Disclosure of Invention

The invention provides a dielectric electrolyte which has good chemical stability to lithium metal and inhibits the growth of lithium dendrite by utilizing the semi-solid gel state.

In order to solve the technical problem, the technical scheme of the invention is as follows: a dielectric electrolyte comprises the following substances in percentage by mass:

6 to 24 percent of conductive lithium salt;

70% to 90% of a polymer electrolyte matrix;

3 to 6 percent of plasticizer.

Preferably, the conductive lithium salt is Li_1.5Al_0.5Ge_1.5(PO₄)₃。Li_1.5Al_0.5Ge_1.5(PO₄)₃The gel-state dielectric electrolyte is an extremely fast ionic conductor with higher room-temperature ionic conductivity, and is obtained by compounding LAGP and a polymer electrolyte matrix, so that the gel-state dielectric electrolyte has the ionic conductivity of the fast ionic conductor LAGP and has the characteristics of high temperature resistance, easiness in production and protection on lithium metal; the consumption of the LAGP influences the conductive performance of the product dielectric electrolyte and the inhibition performance of the product on lithium dendrites, the larger the consumption of the LAGP is, the higher the ionic conductivity of the product is, but the more the LAGP is added, the weaker the inhibition effect of the product on the lithium dendrites is.

Preferably, the polymer electrolyte matrix is one or more of polyacrylonitrile, polyethylene oxide, polymethyl methacrylate and polyvinylidene fluoride. The polymer electrolyte matrix is mainly used for providing a gel state, coating the gel state on the surface of a lithium metal negative electrode, wrapping the lithium negative electrode, separating the lithium metal from an electrolyte, and preventing the electrolyte from carrying out side reaction with the lithium negative electrode to form a byproduct to influence the electrochemical performance of a system; on the other hand, the electrolyte uniformly dispersed in the LAGP in the gel state has the isolation effect and the flexible limiting effect on the surface of the lithium sheet, so that lithium dendrite is avoided from forming, and the good conductivity of the electrolyte at room temperature is ensured.

Preferably, the plasticizer is one or more of propylene carbonate, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate. The selection and the dosage of the plasticizer directly influence the conductivity of the invention, the plasticizer mainly influences the chain segment length of the polymer electrolyte matrix, and the conductivity of the product is increased and then reduced along with the increase of the dosage of the plasticizer.

Preferably, the room temperature conductivity of the invention is 10^-4S/cm。

The second object of the present invention is to provide a method for producing a dielectric electrolyte, which can produce a dielectric electrolyte having excellent properties as described above by a simple and convenient production process.

In order to solve the technical problem, the technical scheme of the invention is as follows: a preparation method of the dielectric electrolyte comprises the following steps:

dissolving a polymer electrolyte matrix in acetonitrile, stirring at the speed of 5000-;

and step two, adding the conductive lithium salt and the plasticizer in the amount into the mixture obtained in the step one, stirring at the speed of 5000-30000rpm, and obtaining the target product after the acetonitrile is completely evaporated.

Preferably, the mass of acetonitrile is 3 to 5 times of the total amount of raw materials for preparing the dielectric electrolyte. The acetonitrile in the invention provides a reaction environment, the using amount of the acetonitrile influences the reaction degree, the using amount is too small, reactants are incompletely reacted, the adding amount is too large, the reaction is slow and the waste is easy.

The process conditions of the second step are preferably as follows:

the temperature is 20 ℃;

the stirring time was 24 hours.

The reaction degree is influenced by preferably controlling the stirring speed, the temperature and the time, reactants react most thoroughly under the process conditions, and the utilization rate of raw materials is highest.

A third object of the present invention is to provide a lithium ion battery which is excellent in cycle and rate performance.

In order to solve the technical problem, the technical scheme of the invention is as follows: a lithium ion battery comprises a positive pole piece and a lithium negative pole piece, wherein the surfaces of the positive pole piece and the lithium negative pole piece are coated with quasi-solid electrolyte, and the surface of the lithium negative pole piece is coated with the dielectric electrolyte.

Preferably, the quasi-solid electrolyte comprises methyl methacrylate and Li_1.5Al_0.5Ge_1.5(PO₄)₃And a mesoporous molecular sieve. The mesoporous molecular sieve is ZMS-5, HMS, MCM-41; one or more of SBA-15 and MSU, the mesoporous molecular sieve has the main function of absorbing electrolyte, and is matched with a medium electrolyte, and the two layered electrolytes synergistically improve the ionic conductivity between the anode and the cathode. According to the invention, the medium electrolyte and the quasi-solid electrolyte with poorer conductivity than the medium electrolyte are matched for use, LAGP conduction ions are used between the medium electrolyte and the solid electrolyte, the medium electrolyte and the quasi-solid electrolyte are contacted, so that the resistance of interface resistance to lithium ion conduction is greatly reduced, and the ion conduction between the medium electrolyte and the quasi-solid electrolyte is quicker;

meanwhile, the dielectric electrolyte is coated on the surface of the lithium metal anode, namely, the dielectric electrolyte is positioned between the lithium metal anode and the quasi-solid electrolyte to protect the lithium metal anode, and the dielectric electrolyte coated on the surface of the lithium metal always coats the lithium electrode by utilizing the gel material state to inhibit lithium dendrites.

Further preferably, the dielectric electrolyte is uniformly coated on two sides of the lithium metal anode, the thickness is between 2 and 5 microns, the thickness is too thin to completely cover the lithium metal anode, and the thickness is too large to influence the energy density of a system.

By adopting the technical scheme, the invention has the beneficial effects that:

the medium electrolyte is semisolid gel, has good chemical stability on lithium metal and higher room temperature conductivity and temperature resistance, can prevent side reaction between lithium metal and electrolyte when being coated on the surface of a lithium metal cathode, and can inhibit the growth of lithium dendrite;

the preparation method of the dielectric electrolyte is simple, and the prepared dielectric electrolyte has stable performance, high conductivity and good wrapping performance on a lithium electrode, and is beneficial to application of a lithium sheet as a negative electrode material;

the lithium ion battery dielectric electrolyte is matched with the LAGP-containing quasi-solid electrolyte, so that the ionic conductivity is ensured, and the lithium electrode and the electrolyte are isolated, so that the problem of instability of lithium metal in a liquid electrolyte is solved, the energy density of the quasi-solid battery using the lithium metal as a negative electrode is greatly improved, and the cycle and rate performance are not influenced.

Thereby achieving the above object of the present invention.

Drawings

Fig. 1 is a graph showing cycle performance of lithium ion batteries obtained in examples 1 to 4 of the present invention and comparative example.

Detailed Description

In order to further explain the technical solution of the present invention, the present invention is explained in detail by the following specific examples.