CN109873199B

CN109873199B - Polymer dispersion liquid and application thereof

Info

Publication number: CN109873199B
Application number: CN201711249009.6A
Authority: CN
Inventors: 张洪章; 张华民; 陈雨晴; 李先锋; 曲超; 杨晓飞
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2017-12-01
Filing date: 2017-12-01
Publication date: 2021-11-16
Anticipated expiration: 2037-12-01
Also published as: CN109873199A

Abstract

The invention relates to a polymer dispersion and application thereof, wherein the dispersion consists of a solvent, lithium salt and a polymer; the polymer is dispersed in a solvent in a molecular form, and comprises one or more than two of polydioxolane, polyethylene glycol, polyvinylidene fluoride, polymethylsiloxane and styrene aliphatic olefin copolymer. The prepared polymer dispersion liquid improves the mechanical stability of a lithium battery negative electrode interface film (SEI), effectively prevents the interface film from being broken and falling through the flexibility of the polymer dispersion liquid, and greatly prolongs the cycle life of the lithium battery.

Description

Polymer dispersion liquid and application thereof

Technical Field

The present invention relates generally to dispersions of polymers and more particularly to their use in lithium batteries.

Technical Field

The lithium metal is used as an active material of the negative electrode of the lithium ion battery, so that the energy density of the battery can be improved to be more than 500Wh/kg, which is 2-3 times higher than that of the current commercial lithium ion battery, and the lithium metal has very attractive force. The potential of the lithium metal relative to the standard hydrogen electrode is-3.04V, and the lithium metal can react with most of the solvent and lithium salt to generate an SEI film. Expansion and contraction, the SEI film on the surface is difficult to maintain stable, resulting in continuous formation and breakage of the SEI film on the surface. This may cause rapid deterioration of battery performance due to consumption of electrolyte required for SEI formation. If a polymer having flexibility can be dispersed in an electrolyte, participate in the formation of an SEI film, and give the SEI film certain elasticity, it is effective to improve the properties of the SEI film.

Disclosure of Invention

The present invention is to solve the above problems and to provide a method for improving the stability of a negative electrode interface film of a lithium battery.

In order to achieve the purpose, the invention adopts the technical scheme that: by introducing insoluble polymer molecules into the electrolyte of a lithium battery using metallic lithium or silicon as the main active material of the negative electrode. The insoluble polymer molecule is polymerized by small molecule monomers in an in-situ polymerization mode. The small molecule monomer can be dissolved in the electrolyte, cannot be dissolved in the electrolyte after polymerization, but can be highly dispersed in the electrolyte. So that the protective layer is attached to the surface of the negative electrode to form a protective layer, the flexibility of an interfacial film (SEI) between the surface of the negative electrode and the electrolyte is increased, and cracking is prevented. Wherein, the conventional electrolyte solution is in direct contact with the protective layer, does not chemically react with the protective layer, and does not dissolve the protective layer. Thereby playing a role of protecting the cathode.

A polymer dispersion consisting of a solvent, a lithium salt and a polymer; wherein the polymer is highly dispersed in the form of small molecules in the solvent, rather than in a dissolved state. The detection method is to mix pure polymer with solvent, and the polymer is not dissolved.

A polymer dispersion consisting of a solvent, a lithium salt and a polymer; wherein the polymer is dispersed in a solvent in the form of molecules and comprises one or more than two of polydioxolane, polyethylene glycol, polyvinylidene fluoride, polymethylsiloxane and styrene aliphatic olefin copolymer; preferably polydioxolane;

the solvent comprises one or more than two of ester solvent and ether solvent;

wherein the ester solvent is an organic matter containing- (C ═ O) -O-C-functional groups, and comprises one or more than two monomers of carbonate, carboxylate or oxalate, or one or more than two polymers with polymerization degrees of 2-1000 in the carbonate, carboxylate or oxalate monomers; the preferable polymerization degree is 2-10;

wherein the ether solvent comprises one or more than two monomers of C2-C10 linear chain ether and C3-C10 cyclic chain ether, or one or more than two polymers with the polymerization degree of 2-1000 of C2-C10 linear chain ether and C3-C10 cyclic chain ether monomers, and the preferred polymerization degree is 2-10. The solvent is preferably ethylene glycol dimethyl ether.

The polymer and the solvent are matched, preferably polydioxolane and ethylene glycol dimethyl ether, wherein the mass ratio of the polydioxolane to the ethylene glycol dimethyl ether is 5-50%, and the more preferable range is 15-30%. The polymer dispersion liquid is prepared by polymerizing one or more than two monomers of dioxolane, ethylene oxide, vinylidene fluoride, methyl siloxane, styrene and C2-C4 aliphatic olefin; the monomer is dissolved in the solvent and then is polymerized in situ in the solvent to generate a polymer which is dispersed and insoluble in the solvent; polyethylene oxide polymerized from ethylene oxide is preferred. These polymers do not dissolve in the electrolyte solvent, but have strong interaction with the solvent and thus do not precipitate out.

The monomer to be polymerized is polymerized into the high polymer in situ by means of infrared, ultraviolet, ultrasonic, microwave and initiator. Preferably, the initiator initiates the polymerization. The initiator is a fluorosulfonic acid acidic catalyst or an azo free radical polymerization initiator.

The dispersion, the weight average molecular weight of the polymer is from 100 to 1 ten thousand; preferably 100 to 1 thousand. The dispersion has a polymer content of 1-35 wt%, preferably 5-20 wt%.

The lithium salt of the dispersion liquid is one or more than two of lithium hexafluorophosphate, lithium bis (trifluoromethyl) sulfonyl imide and lithium bis (fluoro) sulfonyl imide, and the mass content of the lithium salt in the polymer dispersion liquid is 20-60%, preferably 40-50%.

The polymer dispersion liquid is used as an electrolyte in a lithium ion battery, a lithium sulfur battery, a lithium air battery or a lithium ion super capacitor.

The polymer dispersion liquid is particularly suitable for batteries using simple substance lithium as a negative electrode active material.

Wherein the protective layer molecules contain an insoluble polymeric component. The protective layer has no obvious chemical loss and physical loss in the charging and discharging process of the battery.

The solvent used for the electrolyte also comprises a sulfone solvent and a nitrile solvent. Wherein the sulfone solvent is preferably sulfolane or dimethyl sulfoxide. The nitrile solvent is preferably acetonitrile.

Advantageous effects

The polymer dispersion liquid for the lithium battery provided by the invention has the following characteristics and beneficial effects:

(1) the dispersion liquid forms a protective film on the surface of the negative electrode, and the protective film is flexible and prevents the SEI film from falling off and cracking.

(2) The dispersion can prevent the electrolyte from generating continuous side reaction with the lithium sheet, and protect the metal lithium.

(3) The polymer dispersion liquid for the lithium battery provided by the invention does not influence the original battery assembly process, has strong practicability and has multiple advantages of performance, process and economy.

Drawings

FIG. 1 is a graph showing the cycle performance of a lithium/copper metal battery assembled with the polymer dispersion prepared in example 1;

FIG. 2 shows the performance of a lithium battery assembled with a conventional electrolyte of comparative example 1;

FIG. 3 shows the cycle performance of a lithium/copper metal battery assembled with the polymer dispersion prepared in example 2.

Detailed Description

The polymer dispersion and the method of using the same according to the present invention will be described in further detail below with reference to examples.

Example 1:

1g of lithium bistrifluoromethylsulfonyl imide is added into 7.5g of ethylene glycol dimethyl ether, and the mixture is strongly stirred to obtain a clear electrolyte. 2.5g of dioxolane and a perfluorosulfonic acid resin were added thereto, and heated to 70 ℃ to polymerize dioxolane into polydioxolane. After polymerization, it was still a clear liquid. And assembling a lithium/copper model battery using the polymer dispersion obtained above as an electrolyte. The battery pack transfer method of the lithium/copper model battery is as follows: and sequentially putting the stainless steel spring gasket, the lithium sheet, the electrolyte, the Celgard2325 diaphragm, the electrolyte and the wafer of the pure copper foil into the 2016 type button battery, wherein the dropping amount of the electrolyte is 40uL, and assembling the battery in a glove box filled with argon. And (5) stamping and packaging the model battery by using a press machine. The cell was tested in a constant current charge and discharge mode. Firstly, controlling the capacity discharge, and depositing 1mAh/cm on the surface of the copper foil²The metallic lithium of (4); then controlling the voltage (0.5V) to charge, so that the metal lithium on the copper foil is deposited back on the lithium sheet; the whole process is repeated. Under the condition of 1C high-rate rapid charge and discharge (deposition of 1 mAh/cm)²The time of the metal lithium is 1 hour), the cycle life of the dissolution and deposition of the metal lithium can reach 500 times, the average coulomb efficiency is 98.5 percent, and the excellent performance is shown (figure 1);

application example 1:

the polymer dispersion liquid prepared in example 1 was used in an ion battery in which lithium metal was used as a negative electrode and lithium iron phosphate was used as a positive electrode. Compared with the solution which is composed of unpolymerized dioxolane and glycol dimethyl ether and has the same mass ratio, the solution prepared in the example 1 can prolong the cycle life of the lithium ion battery from 200 times to 600 times, and has obvious practical value.

Comparative example 1:

1g of lithium bistrifluoromethylsulfonyl imide is added into 7.5g of ethylene glycol dimethyl ether, and the mixture is strongly stirred to obtain a clear electrolyte. With 2.5g dioxolane added, the average coulombic efficiency of the cell was only 88% without changing other conditions (fig. 2).

Comparative example 2:

1g of lithium bistrifluoromethylsulfonyl imide is added into 7.5g of ethylene glycol dimethyl ether, and the mixture is strongly stirred to obtain a clear electrolyte. 2.5g of the dioxolane after polymerization was added, and the polydioxolane could not be dissolved and could not form a uniform solution without changing other conditions.

Example 2:

1g of lithium bis (fluorosulfonyl) imide was added to 7.5g of polypropylene carbonate, and the mixture was vigorously stirred to obtain a clear electrolyte. 2.0g of ethylene oxide was added thereto, and the ethylene oxide was polymerized into polyethylene glycol by ultraviolet irradiation. After polymerization, it was still a clear liquid. The polymer dispersion liquid obtained above is used as electrolyte to assemble a lithium/copper model battery, the cycle life of the dissolution and deposition of the metal lithium can reach 300 times, and the average coulomb efficiency is 97.5 percent;

example 3:

1g of lithium bis (fluorosulfonyl) imide was added to 7.5g of polypropylene carbonate, and the mixture was vigorously stirred to obtain a clear electrolyte. 2.5g of ethylene oxide and 1mg of azobisisobutyronitrile were added thereto, and the ethylene oxide was polymerized into polyethylene glycol by ultraviolet irradiation. After polymerization, it was still a clear liquid. And the polymer dispersion liquid obtained above is used as electrolyte to assemble a lithium/copper model battery, the cycle life of the dissolution and deposition of the metal lithium can reach 300 times, and the average coulomb efficiency is 97.9 percent.

Claims

1. The application of a polymer dispersion liquid comprises a solvent, lithium salt and a polymer; the method is characterized in that: the polymer is dispersed in a solvent in the form of molecules and comprises one or two of polydioxolane and polyethylene glycol;

the polymer is polymerized by dioxolane or ethylene oxide monomer; the monomer is dissolved in the solvent and then is polymerized in situ in the solvent to generate a polymer which is dispersed and insoluble in the solvent;

the polymer dispersion liquid is used as an electrolyte in a lithium ion battery, a lithium sulfur battery, a lithium air battery or a lithium ion super capacitor;

the solvent comprises one or more than two of ester solvent and ether solvent;

the ester solvent is an organic matter containing- (C = O) -O-C-functional groups, and comprises one or more than two monomers of carbonate, carboxylate or oxalate, or one or more than two polymers with polymerization degrees of 2-1000 in the carbonate, carboxylate or oxalate monomers; wherein the ether solvent comprises one or more than two monomers of C2-C10 linear chain ether and C3-C10 cyclic chain ether, or one or more than two polymers with polymerization degree of 2-1000 in C2-C10 linear chain ether and C3-C10 cyclic chain ether monomers.

2. The use of claim 1, wherein:

the solvent comprises one or more than two of ester solvent and ether solvent;

wherein the polymerization degree of the ester solvent is 2-10;

wherein the polymerization degree of the ether solvent is 2-10;

the polymer and the solvent are matched with polydioxolane and ethylene glycol dimethyl ether, and the mass ratio of the polydioxolane to the ethylene glycol dimethyl ether is 5-50%.

3. Use according to claim 2, characterized in that: the mass ratio of the polydioxolane to the glycol dimethyl ether is 15-30%.

4. The use of claim 1, wherein: the weight average molecular weight of the polymer is from 100 to 1 ten thousand.

5. The use of claim 4, wherein: the weight average molecular weight of the polymer is from 100 to 1 thousand.

6. The use of claim 1, wherein: the mass content of the polymer in the polymer is 1-35%.

7. The use of claim 6, wherein: the mass content of the polymer in the polymer is 5-20%.

8. The use of claim 1, wherein: the lithium salt is one or more of lithium hexafluorophosphate, lithium bis (trifluoromethyl) sulfonyl imide and lithium bis (fluoro) sulfonyl imide, and the mass content of the lithium salt in the polymer dispersion liquid is 20-60%.

9. The use of claim 8, wherein: the mass content of the lithium salt in the polymer dispersion liquid is 40-50%.