CN113540697B - Composite diaphragm and preparation method thereof - Google Patents

Abstract

The invention discloses a composite diaphragm and a preparation method thereof, wherein the composite diaphragm comprises a base membrane, and the surface of the base membrane is coated with a LICION type composite solid electrolyte coating; the LISICON type composite solid electrolyte coating contains a LISICON type composite solid electrolyte, and the electrolyte is obtained by in-situ polymerization of a hydrophobic monomer and an ionic conductor monomer on the surface of the LISICON type solid electrolyte. On one hand, the organic polymer polymerized by the hydrophobic monomer can better improve the wettability between the diaphragm and the electrolyte; on the other hand, the ion conductor polymer polymerized by the ion conductor monomer can construct an ion transmission passage between non-compact LISICON type solid electrolyte particles, so that the ion transmission rate is improved; in addition, the LISICON type solid electrolyte belongs to an inorganic material, has high thermal stability, can stabilize a low-melting-point basement membrane at high temperature, and reduces the thermal shrinkage and the short circuit risk of the cell at high temperature.

Description

A kind of composite diaphragm and preparation method thereof

technical field

The invention belongs to the technical field of lithium ion batteries, and in particular relates to a composite diaphragm and a preparation method thereof.

Background technique

Due to the advantages of high power density, low self-discharge rate, no memory effect and stable discharge voltage, lithium batteries have become the main choice for power batteries. The separator is a key component of lithium-ion batteries, which plays an important role in blocking the electrical conductivity of positive and negative electrodes and allowing the free passage of electrolyte ions.

The safety issues of power batteries are extremely complex, and the separator plays a crucial role in battery safety. During use, due to the puncture of the separator by lithium dendrites or the increase of the internal temperature of the cell, the shrinkage of the separator leads to an internal short circuit, resulting in positive The negative electrode is in direct contact, and a large amount of heat is released in a short time, which eventually leads to thermal runaway of the battery.

At present, the use of inorganic ceramic electrolytes with high thermal stability and high ionic conductivity as the coating layer has become a research hotspot. Lithium dendrites and other advantages can be used in liquid, semi-solid, quasi-solid, all-solid-state lithium batteries and metal lithium batteries. However, at present, during the preparation of inorganic solid electrolyte-coated separators, the coating layer is very easy to absorb water, which leads to an increase in the moisture content of the separator. In the subsequent use process, it takes a long time to bake to remove the moisture in the separator, which reduces the production efficiency.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a composite diaphragm and a preparation method thereof, which can reduce the baking time of the diaphragm, reduce the thermal shrinkage rate of the diaphragm, and improve the ion transmission rate.

To achieve the above object, the technical scheme adopted in the present invention is:

A composite diaphragm, comprising a base membrane, the surface of the base membrane is coated with a LISICON type composite solid electrolyte coating; the LISICON type composite solid electrolyte coating includes a LISICON type composite solid electrolyte, and the LISICON type composite solid electrolyte coating It is prepared by in-situ polymerization of LISICON-type solid electrolyte, hydrophobic monomer and ionic conductor monomer. Further, the material of the base film is polyethylene or polypropylene; the thickness of the LISICON type composite solid electrolyte coating is 0.2-20 μm.

As a preferred technical solution, the LISICON type composite solid electrolyte is prepared through the following steps:

S1. Dissolve the hydrophobic monomer and the ionic conductor monomer in a solvent to obtain a reaction solution; further preferably, the hydrophobic monomer is methyl methacrylate, vinyltrimethylsilane, an alkyl silane coupling agent, Hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2,2,2-trifluoroethyl methacrylate, dodecafluoroheptyl methacrylate, dodecafluoroheptyl acrylate, tridecafluoromethacrylate At least one of octyl ester and tridecafluorooctyl acrylate; the ion conductor monomer is lithium acrylate, lithium methacrylate, lithium maleate, (methyl vinyl ether copolymer maleate) lithium, fumaric acid At least one of lithium; the material ratio of the hydrophobic monomer and the ionic conductor monomer is 0.01 to 1; the solvent is deionized water, DMF, DMSO, N-methylpyrrolidone, methanol, ethanol, toluene or at least one of tetrahydrofuran.

S2. The LISICON type solid electrolyte is added to the reaction solution in S1, and an initiator is added to carry out an in-situ polymerization reaction; further, the total mass of the hydrophobic monomer and ion conductor monomer is compared with the mass ratio of the LISICON type solid electrolyte is 0.001~0.02.

S3. Perform suction filtration, washing and vacuum drying on the product obtained by the in-situ polymerization reaction, and finally obtain a LISICON type solid electrolyte which is co-coated by a hydrophobic polymer and an ion conductor polymer, that is, a LISICON type composite solid electrolyte.

；所述LISICON型固态电解质的化学式为Li_1+xM_xN_2-x(PO₄)₃；其中：0≤x≤0.5；M选自Al、Y、Ga、Cr、Fe中的一种；N选自Ti、Ge、Ta、Zr、Sn、V中的一种。As a preferred technical solution, the particle size distribution of the LISICON type solid electrolyte is: D ₅₀ ≥200 nm, and the dispersion degree is

; The chemical formula of the LISICON type solid electrolyte is Li _1+x M _x N _2-x (PO ₄ ) ₃ ; wherein: 0≤x≤0.5; M is selected from one of Al, Y, Ga, Cr, Fe ; N is selected from one of Ti, Ge, Ta, Zr, Sn, and V.

The present invention also provides the preparation method of the above-mentioned composite membrane, which comprises the following steps:

The binder, the stabilizer, the organic solvent and the LISICON type composite solid electrolyte are mixed uniformly to obtain a stable suspension; the suspension is coated on the surface of the base film, and the composite diaphragm is obtained after drying to remove the organic solvent. Further, the binder is polyvinylidene fluoride; the stabilizer is at least one of carboxymethyl cellulose, sodium alginate, sodium polyacrylate, and polyamide; the organic solvent is N-methyl cellulose At least one of pyrrolidone, acetonitrile, and tetrahydrofuran.

The beneficial effects of the present invention are:

The present invention improves its performance by coating the LISICON type composite solid electrolyte coating on the surface of the base film, wherein the LISICON type composite solid electrolyte coating contains LISICON type composite solid electrolyte, and the LISICON type composite solid electrolyte is a hydrophobic monomer and ion The conductor monomer is obtained by in-situ polymerization on the surface of the LISICON-type solid electrolyte. On the one hand, the organic polymer formed by the polymerization of hydrophobic monomers can better improve the wettability between the separator and the electrolyte; LISICON type solid electrolyte particles build ion transport paths between the particles to improve the ion transport rate; in addition, LISICON type solid electrolyte is an inorganic material with high thermal stability. It can stabilize the low melting point base film at high temperature and reduce its thermal shrinkage and cell high temperature. risk of short circuit.

The composite membrane provided by the invention has good hydrophobicity, high ionic conductivity, good wettability of electrolyte and low thermal shrinkage rate. Applied in the production of lithium-ion cells, it can save the cost of separator baking, ensure the charge and discharge rate performance of the cell, and reduce the risk of short circuit caused by the shrinkage of the separator.

Description of drawings

Fig. 1 is the Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid electrolyte pressed sheet contact angle test picture of the composite in Example 1;

FIG. 2 is a test picture of the contact angle of Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid-state electrolyte in Comparative Example 1.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

A preparation method of a composite diaphragm, specifically comprising the following steps:

(1) Put hexafluorobutyl acrylate:lithium acrylate=1:1 (material ratio) in toluene/methanol and stir to dissolve, then add Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ with D ₅₀ =500 nm Powder (mass of Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ powder: total mass of hexafluorobutyl acrylate and lithium methacrylate=99:1), stir for 1 h and add azobisisobutyronitrile (AIBN) to initiate The in-situ polymerization reaction was carried out under the condition of a water bath at 70°C. After 3 hours, the reaction was completed, and the product was suction filtered, washed with absolute ethanol, and dried in vacuum at 120°C for 12 hours. Finally, the composite Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid electrolyte was obtained, and the contact angle test (to water) was carried out on the tablet. The specific data are shown in Table 1.

(2) Take the above composite Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid electrolyte, polyvinylidene fluoride (PVDF), polyamide, N-methylpyrrolidone (NMP), and their mass ratio is 9:0.5 : 0.5: 25, and the four were dispersed with a planetary ball mill for 3 hours to obtain a stable slurry.

(3) Coat the stable slurry on the polyethylene base film through a gravure roll with a coating thickness of 3 microns, and obtain a composite membrane after drying at 80°C.

The obtained composite membrane was tested for moisture content and thermal shrinkage at 130 °C for 1 h. The specific data are shown in Table 2.

Example 2

A preparation method of a composite diaphragm, specifically comprising the following steps:

(1) Put vinyltrimethylsilane:lithium methacrylate=1:1 (material ratio) in methanol and stir to dissolve, then add Li _1.4 Al _0.4 Ti _1.6 (PO ₄ D ₅₀ =500 nm) ) ₃ powder (Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ powder mass: total mass of vinyltrimethylsilane and lithium methacrylate=99:1), stir for 1 h and add azobisisobutyronitrile (AIBN ), in-situ polymerization was carried out in a water bath at 70°C, the reaction was completed after 3 hours, and the product was suction filtered, washed with anhydrous ethanol, and dried in vacuum at 120°C for 12 hours. Finally, the composite Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid electrolyte was obtained, and the contact angle test (to water) was carried out on the tablet. The specific data are shown in Table 1.

(2) Take the above composite Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid electrolyte, polyvinylidene fluoride (PVDF), sodium alginate, N-methylpyrrolidone (NMP), and their mass ratio is 9: 0.5:0.5:25, the four were dispersed with a planetary ball mill for 3 hours to obtain a stable slurry.

(3) Coat the stable slurry on the polyethylene base film through a gravure roll with a coating thickness of 3 microns, and obtain a composite membrane after drying at 80°C.

The obtained composite membrane was tested for moisture content and thermal shrinkage at 130 °C for 1 h. The specific data are shown in Table 2.

Example 3

A preparation method of a composite diaphragm, specifically comprising the following steps:

(1) Methyl methacrylate: Lithium methacrylate=3:2 (material ratio) was dissolved in methanol with stirring, and then Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) with D ₅₀ =500 nm was added ₃ powder (the mass of Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ powder: the total mass of methyl methacrylate and lithium maleate = 98:2), stir for 1 h and add azobisisobutyronitrile (AIBN) , in-situ polymerization was carried out under the condition of 70 ℃ water bath, the reaction was finished after 3 hours, the product was suction filtered, washed with absolute ethanol, and dried in vacuum at 120 ℃ for 12 hours. Finally, the composite Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid electrolyte was obtained, and the contact angle test (to water) was carried out on the tablet. The specific data are shown in Table 1.

(2) Take the above composite Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ solid electrolyte, polyvinylidene fluoride (PVDF), sodium alginate, N-methylpyrrolidone (NMP), and their mass ratio is 9: 0.5:0.5:25, the four were dispersed with a planetary ball mill for 3 hours to obtain a stable slurry.

(3) Coat the stable slurry on the polyethylene-based diaphragm through a gravure roll with a coating thickness of 2 microns, and obtain a composite diaphragm after drying at 80°C.

The obtained composite membrane was tested for moisture content and thermal shrinkage at 130 °C for 1 h. The specific data are shown in Table 2.

Comparative Example 1

Li _1.4 Al _0.4 Ti _1.6 (PO ₄ ) ₃ powder with D ₅₀ =500 nm that has not been compounded was selected, and the same was pressed to measure the contact angle (to water). The specific data are shown in Table 1.

Comparative Example 2

The polyethylene-based diaphragm is selected, and the specific material structure is polypropylene-polyethylene-polypropylene. It was also tested for moisture content and thermal shrinkage at 130 °C for 1 h. The results are shown in Table 2.

The test method of moisture content refers to "GB/T 6283-2008 Determination of moisture content in chemical products Karl Fischer method (general method)".

The detection result of the product that each above-mentioned embodiment and comparative example make are shown in following table 1 and table 2:

Table 1. Contact angle (to water) test results in examples and comparative examples

Table 2. Test results of moisture and thermal shrinkage in Examples and Comparative Examples

It can be seen from Table 1 that the LISICON type solid electrolyte treated with the hydrophobic monomer has good hydrophobic properties. The separator coated with this type of LISICON type solid electrolyte can effectively resist the moisture in the air, and the organic components can improve the Wetting properties of organic electrolytes. It can be seen from Table 2 that the moisture content of the composite diaphragm is lower than that of the ordinary diaphragm, which is beneficial to reduce the baking cost of the diaphragm and the battery core; and the thermal shrinkage rate is significantly reduced, which can reduce the electric power caused by the diaphragm shrinkage. core security risk.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, and substitutions can be made in these embodiments without departing from the principle and spirit of the invention and modifications, the scope of the present invention is defined by the appended claims and their equivalents.

Claims (8)

1. A composite separator comprising a base film, characterized in that: the surface of the base film is coated with a composite solid electrolyte coating; the composite solid electrolyte coating comprises a composite solid electrolyte, and the composite solid electrolyte is prepared from a solid electrolyte, a hydrophobic monomer and an ionic conductor monomer through in-situ polymerization;

the composite solid electrolyte is prepared by the following steps:

s1, dissolving a hydrophobic monomer and an ionic conductor monomer in a solvent to obtain a reaction solution;

s2, adding the solid electrolyte into the reaction liquid in the S1, and carrying out in-situ polymerization reaction after adding the initiator;

s3, carrying out suction filtration, washing and vacuum drying on a product obtained by the in-situ polymerization reaction to finally obtain a solid electrolyte, namely a composite solid electrolyte, coated by the hydrophobic polymer and the ionic conductor polymer;

the hydrophobic monomer is at least one of methyl methacrylate, vinyl trimethylsilane, alkyl silane coupling agent, hexafluorobutyl acrylate, hexafluorobutyl methacrylate, 2, 2, 2-trifluoroethyl methacrylate, dodecafluoro heptyl acrylate, tridecafluorooctyl methacrylate and tridecafluorooctyl acrylate; the ion conductor monomer is at least one of lithium acrylate, lithium methacrylate, lithium maleate, (methyl vinyl ether copolymerized maleic acid) lithium and lithium fumarate;

the chemical formula of the solid electrolyte is Li _1+x M _x N _2-x (PO ₄ ) ₃ (ii) a Wherein: x is more than or equal to 0 and less than or equal to 0.5; m is selected from one of Al, Y, Ga, Cr and Fe; n is selected from one of Ti, Ge, Ta, Zr, Sn and V.

2. The composite membrane of claim 1, wherein: the mass ratio of the hydrophobic monomer to the ionic conductor monomer is 0.01-1; the mass ratio of the total mass of the hydrophobic monomer and the ionic conductor monomer to the solid electrolyte is 0.001-0.02.

3. The composite membrane of claim 1, wherein: the solvent is at least one of deionized water, DMF, DMSO, N-methyl pyrrolidone, methanol, ethanol, toluene or tetrahydrofuran.

4. The composite membrane of claim 1, wherein: the base film is made of polyethylene or polypropylene.

5. The composite membrane of claim 1, wherein: the thickness of the composite solid electrolyte coating is 0.2-20 mu m.

6. The composite membrane of claim 1, wherein: the particle size distribution of the solid electrolyte is as follows: d ₅₀ Greater than or equal to 200 nm, dispersion

。

7. The method for producing a composite separator according to any one of claims 1 to 6, wherein: the method comprises the following steps:

uniformly mixing a binder, a stabilizer, an organic solvent and a composite solid electrolyte to obtain a stable suspension; and coating the suspension on the surface of the base film, and drying to remove the organic solvent to obtain the composite diaphragm.

8. The method for producing a composite separator according to claim 7, wherein: the binder is polyvinylidene fluoride; the stabilizer is at least one of carboxymethyl cellulose, sodium alginate, sodium polyacrylate and polyamide; the organic solvent is at least one of N-methyl pyrrolidone, acetonitrile and tetrahydrofuran.

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