High safety lithium ion battery separator and preparation method thereof

Abstract

The application discloses a high-safety lithium ion battery diaphragm, which comprises a base film and a composite coating on the base film, wherein the composite coating is formed by mixing 70-90 parts of a polymer matrix with 10-30 parts of lithium salt, and the polymer matrix is formed by polymerization of polyethylene glycol diacrylate, organic phosphate and inorganic filler modified by a silane coupling agent under the action of an initiator; and the application further discloses a preparation method of the lithium ion battery diaphragm. The inorganic filler with a double bond active group in the application is reacted with the polymer through a chemical bond, so that the dispersibility of the inorganic filler in the polymer is improved, the phenomenon of diaphragm powder falling is prevented, and the electrolyte wettability and thermal stability of the diaphragm are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery separator material, in particular to a high-safety lithium ion battery separator and a preparation method thereof. BACKGROUND

[0002] Lithium ion battery is widely used for its high specific energy, high working voltage, long cycle life, low self-discharge rate and environmental friendliness. Due to the characteristics of lithium ion battery, the abnormal temperature rise may occur in the battery under the conditions of needle puncture and overcharge. When the heat accumulates to the collapse temperature of the separator, the separator fails, the battery is punctured, and a large area short circuit occurs, which easily causes fire and explosion, resulting in irreparable loss. Therefore, the battery safety problem greatly restricts the development of downstream industries such as electric vehicles.

[0003] The separator is a crucial part of the lithium ion battery, which can ensure the free passage of lithium ions, form a loop, and prevent the positive and negative electrodes from contacting each other, thereby playing the role of electronic insulation and avoiding battery short circuit. Although the separator does not participate in the electrochemical reaction of the battery, the thickness, pore size and its distribution, porosity, closed pore temperature and puncture strength of the separator greatly affect the internal resistance, capacity, cycle performance and safety performance of the lithium battery. However, the traditional polyolefin separator has poor thermal stability and large size shrinkage at high temperature, which leads to short circuit of the positive and negative electrodes, and further easily causes combustion and explosion. SUMMARY

[0004] Therefore, the purpose of the present application is to overcome the shortcomings of the prior art, provide a high-safety lithium ion battery separator with high electrolyte wettability and thermal stability and flame retardancy, and a preparation method of the high-safety lithium ion battery separator, which is simple in operation and beneficial to industrialization.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] A high-safety lithium ion battery separator, comprising a base film and a composite coating on the base film, wherein the composite coating is formed by mixing 70-90 parts of a polymer matrix with 10-30 parts of lithium salt, and the polymer matrix is formed by polymerization of polyethylene glycol diacrylate, organic phosphate and inorganic filler modified by silane coupling agent under the action of an initiator.

[0007] Preferably, the structure of the polyethylene glycol diacrylate is as follows:

[0008] Wherein n=5-50.

[0009] Preferably, the structure of the organic phosphate is as follows:

[0010]

[0011] Preferably, the inorganic filler is one or more of boehmite, alumina, magnesium hydroxide, silica, titania, barium sulfate, calcium sulfate.

[0012] Preferably, the silane coupling agent is one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(beta-methoxyethoxy)silane, vinyltris(tert-butoxy)silane, vinyltris(tert-butylperoxy)silane, vinyltriacetoxysilane.

[0013] Preferably, the initiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, benzophenone, 2,4-dihydroxybenzophenone, Michler's ketone, 2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoyl phenyl phosphinic ethyl ester, 2-dimethylamino-2-benzyl-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, methyl benzoylformate, benzoic acid.

[0014] Preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluoromethylsulfonylimide, lithium perchlorate, lithium tetrafluoroborate, lithium bisoxalate borate.

[0015] Preferably, the base film is one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polypropylene, polyethylene, polyamide, polyimide, non-woven fabric.

[0016] A preparation method of a high-safety lithium ion battery separator, comprising the following steps:

[0017] S1, polyethylene glycol diacrylate, organophosphate, silane coupling agent modified inorganic filler are weighed according to the mass ratio of 50-80:10-30:5-20, and dissolved in N,N-dimethylacetamide / acetone complex organic solvent, stirred at 50-100℃ for 1-3h, to obtain a uniform transparent solution;

[0018] S2, 0.1-1% of initiator and lithium salt with the total mass of polyethylene glycol diacrylate and organophosphate is added to the transparent solution prepared in S1, and continue to stir for 30-120min, to obtain a composite coating solution;

[0019] S3, the base film is soaked in the composite coating solution for 1-10min, and irradiated by ultraviolet light for 5-30min, to obtain a lithium ion battery separator.

[0020] The present application has the following advantages:

[0021] The inorganic filler modified by silane coupling agent contains double bond active groups, and under the condition of ultraviolet light, the double bond active groups are polymerized with polyethylene glycol diacrylate containing double bond and organic phosphate ester on the surface of base film to strengthen the adhesion between coating and base film, and the double bond polymerization forms crosslinked interpenetrating network structure to improve the mechanical strength and thermal stability of the separator.

[0022] The organic phosphate ester is introduced into the polymer matrix of the coating of the separator in the form of chemical bond, which plays the roles of flame retardation and crosslinking, and the polyethylene glycol diacrylate plays the roles of ion conduction and crosslinking, and the two synergistically improve the mechanical strength, flame retardation, ion migration rate and conductivity of the separator.

[0023] The inorganic filler with double bond active groups is reacted with the polymer through chemical bond to improve the dispersibility of the inorganic filler in the polymer, prevent the "powder dropping" phenomenon of the separator, and improve the electrolyte wettability and thermal stability of the separator.

[0024] The prepared separator has high safety and flame retardation, and the preparation method is simple and easy to operate, which is beneficial to industrialization. DETAILED DESCRIPTION

[0025] The following examples further describe the present application.

[0026] Example 1

[0027] A high-safety lithium ion battery separator includes a base film and a composite coating on the base film, and the composite coating is formed by mixing 70-90 parts of a polymer matrix with 10-30 parts of lithium salt, and the polymer matrix is formed by polymerization of polyethylene glycol diacrylate, organic phosphate ester and inorganic filler modified by silane coupling agent under the action of an initiator.

[0028] The base film is one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polypropylene, polyethylene, polyamide, polyimide and non-woven fabric.

[0029] The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluoromethylsulfonylimide, lithium perchlorate, lithium tetrafluoroborate and lithium bisoxalate borate.

[0030] The structural formula of the polyethylene glycol diacrylate is:

[0031] Wherein n=5-50.

[0032] The structural formula of the organic phosphate ester is

[0033]

[0034] The inorganic filler is one or more of boehmite, alumina, magnesium hydroxide, silica, titanium dioxide, barium sulfate, calcium sulfate.

[0035] The silane coupling agent is one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltri-t-butoxysilane, vinyltri-t-butylperoxysilane, vinyltriacetyloxy-silane.

[0036] The initiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, benzophenone, 2,4-dihydroxybenzophenone, Michler's ketone, 2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoyl phenyl phosphonate ethyl ester, 2-dimethylamino-2-benzyl-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, methyl benzoylformate, benzoic acid.

[0037] Example 2

[0038] A preparation method of a high-safety lithium ion battery diaphragm, comprising the following steps:

[0039] S1, 80 parts of polyethylene glycol diacrylate, 10 parts of organic phosphate, 5 parts of vinyltriethoxysilane modified barium sulfate are weighed and dissolved in 400 mL of N,N-dimethylacetamide / acetone composite organic solvent, stirred at 60°C for 2h, and a uniform transparent solution is obtained;

[0040] S2, 2-hydroxy-2-methyl-1-phenylpropanone initiator with a mass of 0.2% of the total mass of polyethylene glycol diacrylate and organic phosphate and 25 parts of lithium bis(trifluoromethylsulfonyl)imide are added to the transparent solution prepared in S1, and stirring is continued for 90 min to obtain a composite coating solution;

[0041] S3, the polyvinylidene fluoride film is soaked in the composite coating solution for 5 min, and irradiated with ultraviolet light for 5 min to obtain a lithium ion battery diaphragm.

[0042] Example 3:

[0043] S1, 70 parts of polyethylene glycol diacrylate, 20 parts of organic phosphate, 10 parts of vinyl tri (β-methoxyethoxy) silane modified boehmite were weighed and dissolved in 400 mL of N, N-dimethylacetamide / acetone composite organic solvent, stirred at 100°C for 1h, a uniform transparent solution was obtained;

[0044] S2, 0.2% of benzophenone initiator and 25 parts of lithium difluoromethyl sulfonimide were added to the transparent solution prepared in S1, and the stirring was continued for 90 min to obtain a composite coating solution;

[0045] S3, the polytetrafluoroethylene film was immersed in the composite coating solution for 5 min, and then irradiated with ultraviolet light for 5 min to obtain a lithium ion battery separator.

[0046] Example 4:

[0047] S1, 60 parts of polyethylene glycol diacrylate, 30 parts of organic phosphate, 4 parts of vinyl tri-tert-butoxy silane and 6 parts of titanium dioxide inorganic filler modified by vinyl tri-tert-butyloxysilane and vinyl tri-tert-butyl peroxysilane were weighed and dissolved in 400 mL of N, N-dimethylacetamide / acetone composite organic solvent, stirred at 50°C for 3h, a uniform transparent solution was obtained;

[0048] S2, 0.2% of initiator 2,4,6-trimethylbenzoyl phenyl phosphonate and 25 parts of lithium perchlorate were added to the transparent solution prepared in S1, and the stirring was continued for 90 min to obtain a composite coating solution;

[0049] S3, the polyamide-based film was immersed in the composite coating solution for 5 min, and then irradiated with ultraviolet light for 5 min to obtain a lithium ion battery separator.

[0050] Example 5:

[0051] S1, 50 parts of polyethylene glycol diacrylate, 30 parts of organic phosphate, 20 parts of vinyl tri-tert-butyl peroxysilane coupling agent modified silica were weighed and dissolved in 400 mL of N, N-dimethylacetamide / acetone composite organic solvent, stirred at 60°C for 2h, a uniform transparent solution was obtained;

[0052] S2, 0.2% of 2,4,6-trimethylbenzoyl phenyl phosphonate and 43 parts of lithium bisoxalate borate were added to the transparent solution prepared in S1, and the stirring was continued for 90 min to obtain a composite coating solution;

[0053] S3, soak the non-woven fabric base film in the composite coating solution for 5 min, and irradiate with ultraviolet light for 5 min to obtain the lithium ion battery separator.

[0054] Example 6:

[0055] S1, weigh 60 parts of polyethylene glycol diacrylate, 30 parts of organic phosphate, and 5 parts of vinyl trimethoxysilane, 4 parts of vinyl tri(β-methoxyethoxy)silane and 3 parts of vinyl triacetoxy silane modified magnesium hydroxide, and dissolve in 400 mL of N, N-dimethylacetamide / acetone composite organic solvent, stir at 60℃ for 2h, get a uniform transparent solution;

[0056] S2, add 0.2% of methyl benzoylformate initiator and 11 parts of lithium hexafluorophosphate to the transparent solution prepared in S1, continue to stir for 90 min to obtain a composite coating solution;

[0057] S3, soak the polyvinylidene fluoride-hexafluoropropylene copolymer base film in the composite coating solution for 5 min, and irradiate with ultraviolet light for 5 min to obtain the lithium ion battery separator.

[0058] Comparative Example 1:

[0059] Commercial ceramic separator.

[0060] Test method:

[0061] Ignition time: take the same size 1cm*5cm strip-shaped separator, use the open flame to ignite, and start timing from the bottom end of the separator sample strip contacting the stable open flame source to successfully ignite and stop timing.

[0062] Thermal shrinkage test: according to GB / T 135l9-2016.

[0063] Ion conductivity test: soak the separator in the electrolyte for 1h, then assemble the symmetric battery with steel sheet as the blocking electrode on the electrochemical workstation with frequency range of 0.1Hz to 10 6 Hz, calculate the ion conductivity according to the following working hours: σ=L / (R*S).

[0064] The test results are as follows:

[0065]

[0066] As can be seen from the above table, the lithium ion battery separator prepared by the present application has low thermal shrinkage, strong thermal stability, prolonged ignition time, and flame retardancy, and the ion conductivity is significantly improved.

[0067] Finally, it is to be explained that the above embodiments are only used to illustrate the technical solutions of the present application but not to limit the present application, and other modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art should be covered in the scope of claims of the present application as long as they do not depart from the spirit and scope of the technical solutions of the present application.

Claims

1. A high-safety lithium-ion battery separator, characterized in that, The invention includes a base film and a composite coating on the base film. The composite coating is composed of 70-90 parts of a polymer matrix and 10-30 parts of a lithium salt. The polymer matrix is ​​formed by polymerizing inorganic fillers modified with polyethylene glycol diacrylate, organophosphate ester and silane coupling agent under the action of an initiator. The structural formula of the polyethylene glycol diacrylate is as follows: n = 5 to 50; The structural formula of the organic phosphate ester is: The method for preparing the high-safety lithium-ion battery separator includes the following steps: S1. Weigh out polyethylene glycol diacrylate, organophosphate, and inorganic filler modified with silane coupling agent according to a mass ratio of 50-80:10-30:5-20, and dissolve them in N,N-dimethylacetamide / acetone composite organic solvent. Stir at 50-100℃ for 1-3 hours to obtain a uniform and transparent solution. S2. Add 0.1-1% of the total mass of polyethylene glycol diacrylate and organophosphate to the transparent solution prepared in S1, and continue stirring for 30-120 min to obtain the composite coating solution. S3. Immerse the base film in the composite coating solution for 1 to 10 minutes, and then irradiate it with ultraviolet light for 5 to 30 minutes to obtain the lithium-ion battery separator.

2. The high-safety lithium-ion battery separator as described in claim 1, characterized in that, The inorganic filler is one or more of boehmite, alumina, magnesium hydroxide, silicon dioxide, titanium dioxide, barium sulfate, and calcium sulfate.

3. The high-safety lithium-ion battery separator as described in claim 1, characterized in that, The silane coupling agent is one or more of vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, vinyltritert-butoxysilane, vinyltritert-butylperoxysilane, and vinyltriacetoxysilane.

4. The high-safety lithium-ion battery separator as described in claim 1, characterized in that, The initiator is one or more of the following: 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, benzophenone, 2,4-dihydroxybenzophenone, michidone, 2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, 2-dimethylamino-2-benzyl-1-[4-(4-morpholino)phenyl]-1-butanone, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, methyl benzoylcarbamate, and benzoic acid.

5. The high-safety lithium-ion battery separator as described in claim 1, characterized in that, The lithium salt is one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluoromethanesulfonylimide, lithium perchlorate, lithium tetrafluoroborate, and lithium dioxalate borate.

6. The high-safety lithium-ion battery separator as described in claim 1, characterized in that, The base film is one or more of the following: polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polypropylene, polyethylene, polyamide, polyimide, and nonwoven fabric.

7. A method for preparing a high-safety lithium-ion battery separator as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Weigh out polyethylene glycol diacrylate, organophosphate, and inorganic filler modified with silane coupling agent according to a mass ratio of 50-80:10-30:5-20, and dissolve them in N,N-dimethylacetamide / acetone composite organic solvent. Stir at 50-100℃ for 1-3 hours to obtain a uniform and transparent solution. S2. Add 0.1-1% of the total mass of polyethylene glycol diacrylate and organophosphate to the transparent solution prepared in S1, and continue stirring for 30-120 min to obtain the composite coating solution. S3. Immerse the base film in the composite coating solution for 1 to 10 minutes, and then irradiate it with ultraviolet light for 5 to 30 minutes to obtain the lithium-ion battery separator.

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