Composite diaphragm and preparation method thereof
阅读说明：本技术 一种复合隔膜及其制备方法 (Composite diaphragm and preparation method thereof ) 是由 张志勇 牛亚如 李洋 朱冠楠 王义飞 于 2021-06-28 设计创作，主要内容包括：本发明公开了一种复合隔膜及其制备方法,该复合隔膜包括基膜,基膜的表面涂覆有LISICON型复合固态电解质涂层；LISICON型复合固态电解质涂层中含有LISICON型复合固态电解质,该电解质是疏水单体和离子导体单体在LISICON型固态电解质的表面通过原位聚合所得。一方面,疏水单体聚合而成的有机聚合物可以更好地改善隔膜与电解液之间的润湿性；另一方面,离子导体单体聚合而成的离子导体聚合物能够在非致密LISICON型固态电解质颗粒之间构建离子传输通路,提升离子传输速率；此外,LISICON型固态电解质属无机材料,具有高的热稳定性,高温下可以稳定低熔点基膜,降低其热收缩和电芯高温下的短路风险。(The invention discloses a composite diaphragm and a preparation method thereof, wherein the composite diaphragm comprises a base film, and the surface of the base film 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.)
1. A composite separator comprising a base film, characterized in that: the surface of the base membrane is coated with an LISICON type composite solid electrolyte coating; the LISICON-type composite solid electrolyte coating comprises a LISICON-type composite solid electrolyte, and the LISICON-type composite solid electrolyte is prepared by in-situ polymerization of a LISICON-type solid electrolyte, a hydrophobic monomer and an ionic conductor monomer.
2. The composite membrane of claim 1, wherein: the LISICON type 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 LISICON type solid electrolyte into the reaction liquid in S1, and carrying out in-situ polymerization reaction after adding an initiator;
and S3, carrying out suction filtration, washing and vacuum drying on a product obtained by the in-situ polymerization reaction to finally obtain the LISICON type solid electrolyte, namely the LISICON type composite solid electrolyte, which is coated by the hydrophobic polymer and the ionic conductor polymer.
3. The composite membrane of claim 2, wherein: 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, fluoro heptyl methacrylate, dodecafluoroheptyl acrylate, tridecafluoroctyl methacrylate and tridecafluoroctyl 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.
4. The composite membrane of claim 2, 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 mass of the LISICON type solid electrolyte is 0.001-0.02.
5. The composite membrane of claim 2, wherein: the solvent is at least one of deionized water, DMF, DMSO, N-methyl pyrrolidone, methanol, ethanol, toluene or tetrahydrofuran.
6. The composite membrane of claim 1, wherein: the base film is made of polyethylene or polypropylene.
7. The composite membrane of claim 1, wherein: the thickness of the LISICON type composite solid electrolyte coating is 0.2-20 mu m.
8. The composite membrane of claim 1, wherein: the particle size distribution of the LISICON-type solid electrolyte is as follows: d50Greater than or equal to 200nm, dispersionThe chemical formula of the LISICON type solid electrolyte is Li1+xMxN2-x(PO4)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.
9. The method for producing a composite separator according to any one of claims 1 to 8, wherein: the method comprises the following steps:
uniformly mixing a binder, a stabilizer, an organic solvent and a LICION type 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.
10. The method for producing a composite separator according to claim 9, characterized in that: 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.
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a composite diaphragm and a preparation method thereof.
Background
Because of the advantages of high power density, low self-discharge rate, no memory effect, stable discharge voltage and the like, the lithium battery becomes the main choice of the power battery. The diaphragm is a key component of the lithium ion battery, and plays an important role in blocking the electronic conductance of the positive electrode and the negative electrode and allowing electrolyte ions to freely pass through in the battery.
The safety problem of the power battery is very complicated, the diaphragm plays a vital role in the safety of the battery, and in the using process, the lithium dendrite pierces the diaphragm or the internal temperature of the battery core rises to cause the internal short circuit of the diaphragm, so that the anode and the cathode are in direct contact, a large amount of heat is emitted in a short time, and finally the thermal runaway of the battery is caused.
At present, the inorganic ceramic electrolyte with high thermal stability and high ionic conductivity is taken as a coating layer to become a hot point of research, and the diaphragm taking the inorganic ceramic solid electrolyte as the coating layer has the advantages of good liquid absorption, high temperature resistance, high ionic conductivity, lithium dendrite inhibition and the like, and can be used in liquid, semi-solid, quasi-solid and all-solid lithium batteries and metal lithium batteries. However, in the preparation process of the inorganic solid electrolyte coating diaphragm, the coating layer is very easy to absorb water, so that the moisture of the diaphragm is increased, and the diaphragm needs to be baked for a long time in the subsequent use process, so that the production efficiency is reduced.
Disclosure of Invention
The invention aims to provide a composite diaphragm and a preparation method thereof, wherein the composite diaphragm can reduce the baking time of the diaphragm, reduce the thermal shrinkage rate of the diaphragm and improve the ion transmission rate.
In order to achieve the purpose, the invention adopts the technical scheme that:
a composite separator comprising a base film, the surface of which is coated with a LISICON-type composite solid electrolyte coating; the LISICON-type composite solid electrolyte coating comprises a LISICON-type composite solid electrolyte, and the LISICON-type composite solid electrolyte is prepared by in-situ polymerization of a LISICON-type solid electrolyte, a hydrophobic monomer and an ionic conductor monomer. Further, the base film is made of polyethylene or polypropylene; the thickness of the LISICON type composite solid electrolyte coating is 0.2-20 mu m.
As a preferred technical scheme, the LISICON-type 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; more preferably, 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, fluoro heptyl methacrylate, difluoro 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 mass ratio of the hydrophobic monomer to the ionic conductor monomer is 0.01-1; the solvent is at least one of deionized water, DMF, DMSO, N-methyl pyrrolidone, methanol, ethanol, toluene or tetrahydrofuran.
S2, adding the LISICON type solid electrolyte into the reaction liquid in S1, and carrying out in-situ polymerization reaction after adding an initiator; further, the mass ratio of the total mass of the hydrophobic monomer and the ionic conductor monomer to the mass of the LISICON type solid electrolyte is 0.001-0.02.
And S3, carrying out suction filtration, washing and vacuum drying on a product obtained by the in-situ polymerization reaction to finally obtain the LISICON type solid electrolyte, namely the LISICON type composite solid electrolyte, which is coated by the hydrophobic polymer and the ionic conductor polymer.
As preferredAccording to the technical scheme, the particle size distribution of the LISICON type solid electrolyte is as follows: d50Greater than or equal to 200nm, dispersionThe chemical formula of the LISICON type solid electrolyte is Li1+xMxN2-x(PO4)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.
The invention also provides a preparation method of the composite diaphragm, which comprises the following steps:
uniformly mixing a binder, a stabilizer, an organic solvent and a LICION type 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. 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 at least one of N-methyl pyrrolidone, acetonitrile and tetrahydrofuran.
The invention has the beneficial effects that:
the performance of the base membrane is improved by coating the LISICON type composite solid electrolyte coating on the surface of the base membrane, wherein the LISICON type composite solid electrolyte coating contains a LISICON type composite solid electrolyte, and the LISICON type composite solid 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.
The composite diaphragm provided by the invention has the advantages of good hydrophobicity, high ionic conductivity, good electrolyte wettability and low thermal shrinkage. The diaphragm baking cost can be saved, the charging and discharging multiplying power performance of the battery cell is guaranteed, and the short circuit risk of the battery cell caused by diaphragm shrinkage is reduced.
Drawings
FIG. 1 shows Li complexed in example 11.4Al0.4Ti1.6(PO4)3Solid electrolyte sheet contact angle test pictures;
FIG. 2 shows Li in comparative example 11.4Al0.4Ti1.6(PO4)3Solid electrolyte sheet contact angle test pictures.
Detailed Description
The following will clearly and completely describe the technical solutions in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
The preparation method of the composite diaphragm specifically comprises the following steps:
(1) hexafluorobutyl acrylate: lithium acrylate 1: 1 (the mass ratio of the substances) is placed in toluene/methanol and stirred to be dissolved, and D is added50500nm Li1.4Al0.4Ti1.6(PO4)3Powder (Li)1.4Al0.4Ti1.6(PO4)3Mass of powder: total mass of hexafluorobutyl acrylate and lithium methacrylate 99: 1) stirring for 1h, adding an Azobisisobutyronitrile (AIBN) initiator, carrying out in-situ polymerization reaction under the condition of 70 ℃ water bath, after 3h, finishing the reaction, carrying out suction filtration on a product, washing with absolute ethyl alcohol, and drying in vacuum at 120 ℃ for 12 h. Finally obtaining the composite Li1.4Al0.4Ti1.6(PO4)3Solid electrolyte and its tablets were subjected to contact angle test (against water). The specific data are shown in Table 1.
(2) Get onThe above-mentioned complex Li1.4Al0.4Ti1.6(PO4)3Solid electrolyte, polyvinylidene fluoride (PVDF), polyamide and N-methylpyrrolidone (NMP), wherein the mass ratio of the PVDF to the NMP is 9: 0.5: 0.5: and 25, dispersing the four materials by using a planetary ball mill for 3 hours to obtain stable slurry.
(3) And (3) coating the stable slurry on a polyethylene base film through a micro-concave roller, wherein the coating thickness is 3 microns, and drying at 80 ℃ to obtain the composite diaphragm.
The obtained composite diaphragm is subjected to moisture content test and thermal shrinkage rate of 1h at 130 ℃. The specific data are shown in Table 2.
Example 2
The preparation method of the composite diaphragm specifically comprises the following steps:
(1) vinyl trimethylsilane: lithium methacrylate ═ 1: 1 (the amount ratio of the substances) is placed in methanol and stirred to be dissolved, and D is added50500nm Li1.4Al0.4Ti1.6(PO4)3Powder (Li)1.4Al0.4Ti1.6(PO4)3And (3) powder quality: total mass of vinyltrimethylsilane and lithium methacrylate 99: 1) stirring for 1h, adding Azobisisobutyronitrile (AIBN), carrying out in-situ polymerization reaction in a water bath at 70 ℃, finishing the reaction after 3h, carrying out suction filtration on a product, washing with absolute ethyl alcohol, and drying in vacuum at 120 ℃ for 12 h. Finally obtaining the composite Li1.4Al0.4Ti1.6(PO4)3Solid electrolyte and its tablets were subjected to contact angle test (against water). The specific data are shown in Table 1.
(2) Taking the above-mentioned compound Li1.4Al0.4Ti1.6(PO4)3Solid electrolyte, polyvinylidene fluoride (PVDF), sodium alginate and N-methylpyrrolidone (NMP), wherein the mass ratio of the PVDF to the solid electrolyte is 9: 0.5: 0.5: and 25, dispersing the four materials by using a planetary ball mill for 3 hours to obtain stable slurry.
(3) And (3) coating the stable slurry on a polyethylene base film through a micro-concave roller, wherein the coating thickness is 3 microns, and drying at 80 ℃ to obtain the composite diaphragm.
The obtained composite diaphragm is subjected to moisture content test and thermal shrinkage rate of 1h at 130 ℃. The specific data are shown in Table 2.
Example 3
The preparation method of the composite diaphragm specifically comprises the following steps:
(1) mixing methyl methacrylate: lithium methacrylate ═ 3: 2 (mass ratio) is placed in methanol to be stirred and dissolved, and D is added50500nm Li1.4Al0.4Ti1.6(PO4)3Powder (Li)1.4Al0.4Ti1.6(PO4)3Mass of powder: total mass of methyl methacrylate and lithium maleate 98: 2) stirring for 1h, adding Azobisisobutyronitrile (AIBN), carrying out in-situ polymerization reaction in a water bath at 70 ℃, finishing the reaction after 3h, carrying out suction filtration on a product, washing with absolute ethyl alcohol, and drying in vacuum at 120 ℃ for 12 h. Finally obtaining the composite Li1.4Al0.4Ti1.6(PO4)3Solid electrolyte and its tablets were subjected to contact angle test (against water). The specific data are shown in Table 1.
(2) Taking the above-mentioned compound Li1.4Al0.4Ti1.6(PO4)3Solid electrolyte, polyvinylidene fluoride (PVDF), sodium alginate and N-methylpyrrolidone (NMP), wherein the mass ratio of the PVDF to the solid electrolyte is 9: 0.5: 0.5: and 25, dispersing the four materials by using a planetary ball mill for 3 hours to obtain stable slurry.
(3) And (3) coating the stable slurry on a polyethylene diaphragm through a micro-concave roller, wherein the coating thickness is 2 microns, and drying at 80 ℃ to obtain the composite diaphragm.
The obtained composite diaphragm is subjected to moisture content test and thermal shrinkage rate of 1h at 130 ℃. The specific data are shown in Table 2.
Comparative example 1
Selection of D not to be complexed50500nm Li1.4Al0.4Ti1.6(PO4)3Powders, likewise tableted, were tested for contact angle (to water). The specific data are shown in Table 1.
Comparative example 2
Selecting a polyethylene-based diaphragm, wherein the specific material structure is polypropylene-polyethylene-polypropylene. The test of moisture content and the test of heat shrinkage at 130 ℃ for 1 hour were also carried out, and the results are shown in Table 2.
The method for testing the water content refers to the Karl Fischer method (general method) for measuring the water content in chemical products GB/T6283 and 2008.
The results of testing the products prepared in the above examples and comparative examples are shown in tables 1 and 2 below:
TABLE 1 contact Angle (to Water) test results in examples and comparative examples
Contact Angle/° (for water)
Example 1
129.3
Example 2
133.5
Example 3
130.1
Comparative example 1
0
TABLE 2 moisture and Heat shrinkage test results in examples and comparative examples
From table 1, it can be seen that the LISICON-type solid electrolyte treated by the hydrophobic monomer has good hydrophobic property, the diaphragm coated by the LISICON-type solid electrolyte can effectively resist moisture in the air, and meanwhile, the organic component can improve the wettability of the organic electrolyte. As can be seen from table 2, the moisture content of the composite separator is lower than that of a common separator, which is beneficial to reducing the baking cost of the separator and the battery core; and the thermal shrinkage rate is obviously reduced, and the safety risk of the battery cell caused by the shrinkage of the diaphragm can be reduced.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
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