阅读说明：本技术 一种复合电解质及其应用 (Composite electrolyte and application 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：本发明公开一种复合电解质及其应用,复合电解质包括涂覆于锂负极的凝胶电解质和涂覆于正极的准固态电解质,凝胶电解质和准固态电解质相接触；准固态电解质中吸附有电解液；凝胶电解质和准固态电解质均含有相同的导电锂盐；本发明还公开了将复合电解质应用于锂离子电池；该发明通过两种电解质的配合兼顾抑制锂枝晶同时保证复合电解质具有良好的导电性。(The invention discloses a composite electrolyte and application thereof, wherein the composite electrolyte comprises a gel electrolyte coated on a lithium cathode and a quasi-solid electrolyte coated on an anode, and the gel electrolyte is contacted with the quasi-solid electrolyte; the quasi-solid electrolyte is absorbed with electrolyte; the gel electrolyte and the quasi-solid electrolyte both contain the same conductive lithium salt; the invention also discloses the application of the composite electrolyte to the lithium ion battery; the invention can inhibit lithium dendrite and ensure good conductivity of the composite electrolyte by matching two electrolytes.)

1. A composite electrolyte characterized by: the lithium battery comprises a gel electrolyte coated on a lithium cathode and a quasi-solid electrolyte coated on a positive electrode, wherein the gel electrolyte is in contact with the quasi-solid electrolyte; the quasi-solid electrolyte is absorbed with electrolyte;

both the gel electrolyte and the quasi-solid electrolyte contain the same conductive lithium salt.

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

3. A composite electrolyte as claimed in claim 2, wherein: the gel electrolyte comprises the following substances in percentage by mass:

Li_1.5Al_0.5Ge_1.5(PO₄)₃6% to 24%;

70% to 90% of a polymer electrolyte matrix;

3 to 6 percent of plasticizer.

4. A composite electrolyte as claimed in claim 3, wherein:

the polymer electrolyte matrix is one or more of polyacrylonitrile, polyethylene oxide, polymethyl methacrylate and polyvinylidene fluoride;

the plasticizer is one or more of propylene carbonate, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate.

5. A composite electrolyte as claimed in claim 2, wherein: the quasi-solid electrolyte comprises the following substances in percentage by mass:

the material comprises the following substances in percentage by mass:

methyl methacrylate 50% to 80%;

Li_1.5Al_0.5Ge_1.5(PO₄)₃10% to 30%;

10 to 30 percent of mesoporous molecular sieve.

6. A composite electrolyte as claimed in claim 5, wherein: the quasi-solid electrolyte comprises the following substances in percentage by mass:

70% of methyl methacrylate;

Li_1.5Al_0.5Ge_1.5(PO₄)₃20％；

10 percent of mesoporous molecular sieve.

7. A composite electrolyte as defined in claim 1, wherein:

the layer thickness of the composite electrolyte is 7 to 10 μm; wherein the content of the first and second substances,

the layer thickness of the gel electrolyte is 2 to 4 μm;

the layer thickness of the quasi-solid electrolyte is 3 to 8 μm.

8. A composite electrolyte as defined in claim 1, wherein: the conductivity is 4.1 to 5.7S/cm.

9. Use of a composite electrolyte according to any one of claims 1 to 8 in a lithium ion battery.

Technical Field

The invention relates to the technical field of chemical power supplies, in particular to a composite electrolyte and application thereof.

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 the all-solid battery cannot meet the requirement, mass production needs more exploration, the liquid battery is urgently converted into the solid battery, but the conductivity of the all-solid electrolyte is not ideal at present, so that the all-solid battery is slowly transited from the quasi-solid battery to the all-solid battery. 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.

Disclosure of Invention

The invention aims to provide a composite electrolyte, which can inhibit lithium dendrite and ensure good conductivity by matching two electrolytes.

In order to solve the technical problem, the technical scheme of the invention is as follows: a composite electrolyte comprises a gel electrolyte coated on a lithium cathode and a quasi-solid electrolyte coated on a cathode, wherein the gel electrolyte is in contact with the quasi-solid electrolyte; the quasi-solid electrolyte is absorbed with electrolyte;

both the gel electrolyte and the quasi-solid electrolyte contain the same conductive lithium salt.

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 electrolyte layer and the quasi-solid electrolyte layer are provided with the LAGP for conducting ions, when the gel electrolyte layer and the quasi-solid electrolyte layer are contacted, the resistance of interface resistance to lithium ion conduction is greatly reduced, the ion conduction between the gel electrolyte layer and the quasi-solid electrolyte layer is quicker, and the high conductivity of the composite electrolyte is obtained.

Preferably, the gel electrolyte comprises the following substances in percentage by mass:

Li_1.5Al_0.5Ge_1.5(PO₄)₃6% to 24%;

70% to 90% of a polymer electrolyte matrix;

3 to 6 percent of plasticizer.

The gel electrolyte is semisolid gel, has good chemical stability on lithium metal, has higher room temperature conductivity and temperature resistance, is coated on the surface of a lithium metal cathode, ensures the ionic conductivity, and simultaneously avoids the side reaction caused by the contact of a lithium electrode and electrolyte by separating the lithium electrode and the electrolyte, thereby inhibiting the growth of lithium dendrite. The problem that lithium metal is unstable in liquid electrolyte is avoided, the energy density of the quasi-solid battery using the lithium metal as a negative electrode is greatly improved, and meanwhile, the cycle and rate performance are not influenced.

Further preferably, the polymer electrolyte matrix is one or more of polyacrylonitrile, polyethylene oxide, polymethyl methacrylate and polyvinylidene fluoride;

the plasticizer is one or more of propylene carbonate, ethylene carbonate, ethyl methyl carbonate and diethyl carbonate.

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.

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 quasi-solid electrolyte comprises the following substances in percentage by mass:

methyl methacrylate 50% to 80%;

Li_1.5Al_0.5Ge_1.5(PO₄)₃10% to 30%;

10 to 30 percent of mesoporous molecular sieve.

The quasi-solid electrolyte is prepared by filling a mesoporous molecular sieve with a polymer solid electrolyte, wherein the polymer solid electrolyte is prepared by using an in-situ polymerization method and taking methyl methacrylate as a framework and combining a phosphate-based material with high salt concentration, and the mesoporous molecular sieve is filled in the polymer solid electrolyte and can effectively absorb electrolyte and stably exist in the electrolyte; composite lithium salt Li in quasi-solid electrolyte_1.5Al_0.5Ge_1.5(PO₄)₃The (LAGP) and the mesoporous molecular sieve are dispersed in a polymer framework, so that on one hand, the mesoporous molecular sieve has excellent conductivity, and meanwhile, the mesoporous molecular sieve can absorb the electrolyte to the maximum extent, thereby avoiding the side reaction caused by excessive contact between the electrolyte and a positive electrode and a negative electrode, and avoiding the phenomena of battery ignition, explosion and the like caused by the combustion of the electrolyte during safety test;

compared with the solid electrolyte, the invention greatly improves the whole ion conductivity and the interface stability, and when the composite electrolyte is applied to the battery, the rate performance and the cycle life of the quasi-solid battery are greatly improved, and simultaneously, the safety performance is also improved.

It is further preferred that the quasi-solid electrolyte comprises the following substances in mass fraction:

70% of methyl methacrylate;

Li_1.5Al_0.5Ge_1.5(PO₄)₃20％；

10 percent of mesoporous molecular sieve.

Most preferably, the mesoporous molecular sieve is MCM-41, and the lithium ion battery prepared by matching the quasi-solid electrolyte and the gel electrolyte according to the proportion has the best cycle performance and rate capability.

Preferably the layer thickness of the composite electrolyte is 7 to 10 μm; wherein the content of the first and second substances,

the layer thickness of the gel electrolyte is 2 to 4 μm;

the layer thickness of the quasi-solid electrolyte is 3 to 8 μm.

The total thickness of the composite electrolyte is 7-10 um, and the thickness of the electrolyte is properly reduced on the premise of completely blocking the contact between a positive electrode and a negative electrode, so that the energy density of a system is favorably improved; the energy density of the battery prepared by the invention can reach over 320 Wh/kg. The gel electrolyte is positioned between the lithium metal anode and the quasi-solid electrolyte to play a role in protecting the lithium metal anode and inhibiting lithium dendrites; after the gel electrolyte is coated on the surface of the lithium metal negative electrode, the pole piece is not cold-pressed and is directly laminated or wound with the positive pole piece and the quasi-solid electrolyte layer; during packaging, the bare cell is subjected to battery shaping under the action of a small pressure (500-1000Kg), the interlayer distance between the gel electrolyte and the quasi-solid electrolyte layer can be reduced by the external force, so that the gel electrolyte layer and the quasi-solid electrolyte layer are tightly combined, the thickness of the gel electrolyte layer is between 2 and 4 microns, the lithium metal anode is completely covered and has certain deformation capacity, and the covering degree of the lithium metal cathode can be still ensured under a certain bending condition; the conductivity of the gel electrolyte is slightly inferior to that of the quasi-solid electrolyte, so that the thickness of the gel electrolyte layer cannot be too large, and the conductivity of the whole electrolyte layer is reduced due to too large proportion of the gel electrolyte.

The composite electrolyte of the present invention preferably has a conductivity of 4.1 to 5.7S/cm. The composite electrolyte has good conductivity.

The second purpose of the invention is to provide the application of the composite electrolyte in the lithium ion battery, and the cycle performance and the rate performance of the invention are excellent and stable.

In order to solve the technical problem, the technical scheme of the invention is as follows: the composite electrolyte is applied to a lithium ion battery. The negative electrode of the lithium ion battery can also be graphite and/or silicon carbon.

The composite electrolyte is applied to a lithium ion battery with a lithium metal cathode, the residual capacity percentage of the composite electrolyte is more than 91% after 100 cycles, and the 3C capacity retention rate can reach 97% at most.

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

the composite electrolyte comprises a gel electrolyte coated on the surface of a lithium metal anode, separates lithium metal from electrolyte, reduces side reactions between the lithium metal anode and liquid electrolyte, and inhibits the formation of lithium dendrites; meanwhile, the quasi-solid electrolyte effectively absorbs the electrolyte, and when the gel electrolyte is contacted with the quasi-solid electrolyte, because the gel electrolyte and the quasi-solid electrolyte both have the same type of conductive lithium salt, the interface resistance between the gel electrolyte and the quasi-solid electrolyte is greatly reduced, and the integral ionic conductivity and the interface stability of the composite electrolyte are greatly improved;

the composite electrolyte layer provided by the invention can apply lithium metal to a quasi-solid battery, and the obtained lithium ion battery has a stable structure, high energy density, high rate performance and long cycle performance, and meanwhile, the safety performance is also obviously improved.

Thereby achieving the above object of the present invention.

Drawings

Fig. 1 is a cycle curve for examples 1 to 5 of the present invention and a comparative lithium ion battery.

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.