A Low-Cost Lithium Battery Separator with High Electrolyte Infiltration and Its Preparation Method

Abstract

The present invention relates to the technical field of lithium battery separators, and particularly to a low-cost lithium battery separator with high electrolyte wettability, which includes a base film and a polymer coating applied to one or both sides of the base film. The polymer coating includes PVDF and PMMA materials; the polymer slurry is composed of mixed powder, compatibilizer, dispersant, thickener, binder, wetting agent, defoamer and ultrapure water, and the mixed powder is a mixture of PVDF and PMMA. Compared with the traditional lithium battery coated separator with a single PMMA coating, the present invention effectively inhibits the excessive swelling of PMMA through a small amount of PVDF homopolymer, thereby improving the ionic conductivity, reducing the cost, and developing a compatibilizer that is beneficial to the compatibility of PVDF and PMMA, enabling PVDF and PMMA to obtain better compatibility in the slurry, improving the stability of the slurry and the uniformity of coating.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and particularly to a low-cost lithium battery separator with high electrolyte wettability and a preparation method thereof. Background Art

[0002] The structure of a lithium battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The main function of the separator is to separate the positive electrode and the negative electrode of the battery to avoid short circuit between the positive and negative electrodes. Therefore, the separator needs to maintain good ion conductivity and electronic insulation. In industrial production, the separator prepared from polyolefin materials is generally called a base film. However, due to various performance deficiencies that may exist in the base film, the surface of the base film is often coated to make up for its various performance defects.

[0003] To improve the bonding ability between the separator and the electrode sheet, an organic coating is often applied to the surface of the base film to improve its adhesiveness. It is more mature to use PVDF-based substances as the organic coating. In actual use, it is not usually the homopolymer of PVDF that is coated. Generally, the copolymer of PVDF-HFP (polyvinylidene fluoride and hexafluoropropylene) is coated. The reason is that the swelling performance of the homopolymer of PVDF is poor and the ionic conductivity is low. Therefore, HPF is used to modify the PVDF copolymer and then coated. However, the cost of using PVDF-HFP materials is very high, which is a relatively heavy burden on enterprises.

[0004] PMMA (polymethyl methacrylate, commonly known as acrylic) has become one of the materials that can replace PVDF-HFP due to its affinity for the electrolyte, low price, and easy control of the glass transition temperature. However, when using only PMMA material for coating, there is a problem of excessive swelling. After PMMA swells excessively, it will block the pores of the separator, reducing the ionic conductivity of the separator.

[0005] Therefore, we propose a low-cost lithium battery separator with high electrolyte wettability and a preparation method thereof to solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to solve the deficiencies existing in the prior art, and to propose a low-cost lithium battery separator with high electrolyte wettability and a preparation method thereof.

[0007] A low-cost lithium battery separator with high electrolyte wettability includes a base film and a polymer coating applied to any one or both sides of the base film. The polymer coating includes PVDF and PMMA materials;

[0008] Polymer slurry, which is composed of raw materials in the following weight percentages: 6% - 13% of mixed powder, 5% - 15% of compatibilizer, 0.3% - 1.2% of dispersant, 2.5% - 7% of thickener, 5% - 13.5% of binder, 0.1% - 0.35% of wetting agent, 0.1% - 0.35% of defoaming agent, and the rest is ultrapure water;

[0009] The mixed powder is a mixture of PVDF and PMMA, and the weight ratio of PVDF:PMMA = 5 - 30:70 - 95.

[0010] Preferably, the base film is a polyolefin separator.

[0011] Preferably, the dispersant is an aliphatic amide, the thickener is sodium carboxymethyl cellulose, the binder is a polyacrylic acid, the wetting agent is an alkyl sulfate, and the defoaming agent is a polyether defoaming agent.

[0012] Preferably, the dispersant is one of polyacrylamide, octadeceneamine acetate, alkyl quaternary ammonium salt, aminopropylamine dioleate, polyethylene glycol type polyol, polyethyleneimine derivative, oleyl oleate; the binder is one of cyanoacrylate derivative binder, cyanoacrylate polyethylene glycol binder, acrylic binder, vinyl acetate polymer latex binder; the wetting agent is one of polyoxyethylene type surfactant, fatty acid surfactant, silanol type nonionic surfactant; the defoaming agent is one of higher alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene ethanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether and polydimethylsiloxane.

[0013] Preferably, the compatibilizer is composed of the following raw materials in parts by weight: 40 - 80 of PVDF homopolymer powder, 20 - 60 of methyl methacrylate liquid.

[0014] A preparation method of a low-cost lithium battery separator with high electrolyte wettability, comprising the following steps:

[0015] S1. Prepare polymer slurry:

[0016] S1-1. Take 0.3% - 1.2% of dispersant and 6% - 13% of mixed powder according to the mass ratio and put them into ultrapure water for premixing to obtain a first intermediate;

[0017] S1-2. Add 5% - 13.5% of binder and 2.5% - 7% of thickener to the first intermediate according to the mass ratio and continue stirring to obtain a second intermediate;

[0018] S1-3. Add a wetting agent in a mass ratio of 0.1% - 0.35% and an antifoaming agent in a mass ratio of 0.1% - 0.35% to the second intermediate, stir, and filter to remove iron to obtain a polymer slurry;

[0019] S2. Prepare a compatibilizer:

[0020] S2-1. Put PVDF homopolymer powder and methyl methacrylate liquid into ultrapure water in a ratio of 40 - 80:20 - 60, and stir and mix to obtain a mixed solution;

[0021] S2-2. Place the above-mentioned mixed solution in a gamma-ray environment, take it out after sufficient irradiation to obtain a compatibilizer;

[0022] S3. Modify the above-mentioned polymer slurry: Put 5 - 15 parts of the compatibilizer into 85 - 95 parts of the polymer slurry, stir and mix, and then let it stand to obtain the modified polymer slurry;

[0023] S4. Prepare a separator: Uniformly coat the prepared modified polymer slurry on the separator, bake it, and wind it up for standby.

[0024] Preferably, in step S1-1, the premixing time is 10 - 120 min, and the rotation speed is 400 - 900 rpm.

[0025] Preferably, in step S1-2, the mixing time is 20 - 80 min, and the rotation speed is 350 - 700 rpm.

[0026] Preferably, in step S1-3, the mixing time is 20 - 80 min, and the rotation speed is 150 - 550 rpm.

[0027] Preferably, in step S4, the microgravure roll coating process is adopted, and the modified polymer slurry is uniformly roll-coated on the separator through a coater.

[0028] The beneficial effects of the present invention are:

[0029] 1. Compared with the traditional lithium battery coating separator coated with PMMA single substance, the present invention effectively inhibits the excessive swelling of PMMA through a small amount of PVDF homopolymer, thereby improving the ionic conductivity and reducing the cost compared with the traditional PVDF-HFP material.

[0030] 2. The present invention develops a compatibilizer that is beneficial to the compatibility of PVDF and PMMA. The compatibilizer uses PVDF as the main chain, and MMA branches are grafted onto the PVDF main chain through gamma-ray irradiation, so that PVDF and PMMA can obtain better compatibility in the slurry, improving the stability of the slurry and the uniformity of coating.

[0031] 3. The diaphragm of the present invention is prepared by aqueous coating, which has less pollution and lower cost compared with oil-based coating. Detailed implementation manners

[0032] The present invention will be further described below in conjunction with specific embodiments.

[0033] Embodiment 1:

[0034] A low-cost lithium battery diaphragm with high electrolyte wettability, comprising a base film and a polymer coating coated on one or both sides of the base film, and the polymer coating includes PVDF and PMMA materials; the base film is a polyolefin diaphragm.

[0035] The polymer slurry is composed of the following raw materials in weight percentages: 6% of mixed powder, 5% of compatibilizer, 0.3% of dispersant, 2.5% of thickener, 5% of binder, 0.1% of wetting agent, 0.1% of defoaming agent. The mixed powder is a mixture of PVDF and PMMA, and PVDF:PMMA = 5:95.

[0036] In the above polymer slurry, the dispersant used is one of polyacrylamide, octadeceneamine acetate, alkyl quaternary ammonium salt, aminopropylamine dioleate, polyethylene glycol type polyol, polyethyleneimine derivative, and oleylaminoleate.

[0037] The thickener is sodium carboxymethyl cellulose (CMC solution).

[0038] The binder is one of cyanoacrylate derivative binder, cyanoacrylate polyethylene glycol binder, acrylic binder, and vinyl acetate polymer latex binder.

[0039] The wetting agent is one of polyoxyethylene type surfactant, fatty acid surfactant, and silanol type nonionic surfactant.

[0040] The defoaming agent is one of high-carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane.

[0041] A preparation method of a low-cost lithium battery diaphragm with high electrolyte wettability includes the following steps:

[0042] S1. Prepare the polymer slurry:

[0043] S1-1. Take 0.3% of the dispersant and 6% of the mixed powder according to the mass ratio and put them into ultrapure water and stir for 10 minutes, and the stirring speed is 400 rpm to obtain the first intermediate;

[0044] S1-2. Add 5% binder and 2.5% thickener to the obtained first intermediate, and continue stirring for 20 minutes at a stirring speed of 350 rpm to obtain a second intermediate;

[0045] S1-3. Add 0.1% wetting agent and 0.1% defoaming agent to the obtained second intermediate, and continue stirring for 20 minutes at a stirring speed of 150 rpm to obtain a polymer slurry.

[0046] S2. Prepare a compatibilizer:

[0047] S2-1. Put PVDF homopolymer powder and MMA (methyl methacrylate) liquid into ultrapure water in a ratio of 45:55, stir and mix to obtain a mixed solution. The stirring time is 20 minutes and the stirring speed is 500 rpm;

[0048] S2-2. Place the above-mentioned mixed solution in a gamma-ray environment, take it out after sufficient irradiation to obtain a compatibilizer.

[0049] S3. Modify the above polymer slurry: Take 5 parts of compatibilizer and 95 parts of polymer slurry, mix and stir for 20 minutes at a stirring speed of 500 rpm to obtain a modified polymer slurry.

[0050] S4. Prepare a separator: Adopt a microgravure roll coating process, and uniformly roll coat the prepared modified polymer slurry on a polyolefin separator through a coater, and then wind it up for standby after baking in an oven at 70°C.

[0051] The stirring speed and stirring time in this example and the following examples are for reference only, and only sufficient mixing needs to be ensured.

[0052] Example Two:

[0053] A low-cost lithium battery separator with high electrolyte wettability, comprising a base film and a polymer coating coated on either one or both sides of the base film. The polymer coating comprises PVDF and PMMA materials; the base film is a polyolefin separator.

[0054] The polymer slurry is composed of the following raw materials by weight percentage: 8% mixed powder, 10% compatibilizer, 0.92% dispersant, 10.5% thickener, 3.8% binder, 0.25% wetting agent, 0.25% defoaming agent. The mixed powder is a mixture of PVDF and PMMA, and PVDF:PMMA = 10:90.

[0055] In the above polymer slurry, the dispersant used is one of polyacrylamide, octadeceneamine acetate, alkyl quaternary ammonium salt, aminopropylamine dioleate, polyethylene glycol type polyol, polyethyleneimine derivative, oleyl amino oleate.

[0056] The thickener is sodium carboxymethyl cellulose (CMC solution).

[0057] The binder is one of cyanoacrylate derivative binder, cyanoacrylate polyethylene glycol binder, acrylic binder, and vinyl acetate polymer latex binder.

[0058] The wetting agent is one of polyoxyethylene type surfactants, fatty acid surfactants, and silanol nonionic surfactants.

[0059] The defoaming agent is one of high-carbon alcohol fatty acid ester complexes, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane.

[0060] A preparation method of a low-cost lithium battery separator with high electrolyte wettability includes the following steps:

[0061] S1. Prepare the polymer slurry:

[0062] S1-1. Take 0.92% of the dispersant and 8% of the mixed powder by mass ratio and put them into ultrapure water and stir for 60 minutes at a stirring speed of 600 rpm to obtain the first intermediate.

[0063] S1-2. Add 3.8% of the binder and 10.5% of the thickener to the obtained first intermediate and continue to stir for 40 minutes at a stirring speed of 600 rpm to obtain the second intermediate.

[0064] S1-3. Add 0.25% of the wetting agent and 0.25% of the defoaming agent to the obtained second intermediate and continue to stir for 30 minutes at a stirring speed of 200 rpm to obtain the polymer slurry.

[0065] S2. Prepare the compatibilizer:

[0066] S2-1. Put the PVDF homopolymer powder and MMA (methyl methacrylate) liquid in a ratio of 55:45 into ultrapure water and stir and mix to obtain a mixed solution. The stirring time is 20 minutes and the stirring speed is 500 rpm.

[0067] S2-2. Place the aforementioned mixed solution in a gamma-ray environment, take it out after sufficient irradiation to obtain the compatibilizer.

[0068] S3. Modify the aforementioned polymer slurry: Take 10 parts of the compatibilizer and 90 parts of the polymer slurry and mix and stir them for 20 minutes at a stirring speed of 500 rpm to obtain the modified polymer slurry.

[0069] S4. Preparation of separator: Using the microgravure roll coating process, the prepared modified polymer slurry is evenly roll-coated on the polyolefin separator by a coater, and then wound up for standby after baking in an oven at 70°C.

[0070] Example 3:

[0071] A low-cost lithium battery separator with high electrolyte wettability, comprising a base film and a polymer coating coated on one or both sides of the base film arbitrarily, the polymer coating comprising PVDF and PMMA materials; the base film is a polyolefin separator.

[0072] The polymer slurry is composed of the following raw materials in weight percentages: 13% of mixed powder, 20% of compatibilizer, 1.2% of dispersant, 13.5% of thickener, 7% of binder, 0.35% of wetting agent, 0.35% of defoamer. The mixed powder is a mixture of PVDF and PMMA, and PVDF:PMMA = 30:70.

[0073] In the above polymer slurry, the dispersant used is one of polyacrylamide, octadeceneamine acetate, alkyl quaternary ammonium salt, aminopropylamine dioleate, polyethylene glycol type polyol, polyethyleneimine derivative, and oleyl amino oleate.

[0074] The thickener is sodium carboxymethyl cellulose (CMC solution).

[0075] The binder is one of cyanoacrylate derivative binder, cyanoacrylate polyethylene glycol binder, acrylic binder, and vinyl acetate polymer latex binder.

[0076] The wetting agent is one of polyoxyethylene type surfactants, fatty acid surfactants, and silanol non-ionic surfactants.

[0077] The defoamer is one of high-carbon alcohol fatty acid ester complexes, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane.

[0078] A preparation method of a low-cost lithium battery separator with high electrolyte wettability, comprising the following steps:

[0079] S1. Preparation of polymer slurry:

[0080] S1-1. Take 1.2% of dispersant and 13% of mixed powder 1 according to the mass ratio and stir in ultrapure water for 120 minutes at a stirring speed of 900 rpm to obtain a first intermediate;

[0081] S1-2. Add 7% of binder and 13.5% of thickener to the obtained first intermediate and continue stirring for 80 minutes at a stirring speed of 700 rpm to obtain a second intermediate;

[0082] S1-3. Add 0.35% wetting agent and 0.35% defoaming agent to the obtained second intermediate and continue stirring for 80 minutes at a stirring speed of 550 rpm to obtain a polymer slurry.

[0083] S2. Prepare a compatibilizer:

[0084] S2-1. Put PVDF homopolymer powder and MMA (methyl methacrylate) liquid into ultrapure water in a ratio of 80:20 and stir and mix to obtain a mixed solution. The stirring time is 20 minutes and the stirring speed is 500 rpm.

[0085] S2-2. Place the aforementioned mixed solution in a gamma-ray environment, take it out after sufficient irradiation to obtain a compatibilizer.

[0086] S3. Modify the aforementioned polymer slurry: Take 15 parts of the compatibilizer and 85 parts of the polymer slurry and mix and stir them for 20 minutes at a stirring speed of 500 rpm to obtain a modified polymer slurry.

[0087] S4. Prepare a separator: Adopt a microgravure roll coating process, and uniformly roll coat the prepared modified polymer slurry on a polyolefin separator through a coater, and then wind it up for standby after baking in an oven at 70°C.

[0088] Comparative Example 1:

[0089] For the above-mentioned embodiment, a Comparative Example 1 is provided. In this comparative example, pure PMMA organic particles are used for coating.

[0090] Prepare a slurry:

[0091] Put 0.92% dispersant and 8% PMMA powder into ultrapure water according to the mass ratio and stir for 60 minutes at a stirring speed of 600 rpm. Add 3.8% binder and 10.5% thickener to the obtained solution and continue stirring for 40 minutes at a stirring speed of 600 rpm. Then continue to add 0.25% wetting agent and 0.25% defoaming agent and continue stirring for 30 minutes at a stirring speed of 200 rpm to obtain a PMMA coating slurry.

[0092] Prepare a separator:

[0093] Adopt a microgravure roll coating process, and uniformly roll coat the prepared PMMA coating slurry on a polyolefin separator through a coater, and then wind it up for standby after baking in an oven at 70°C.

[0094] Comparative Example 2:

[0095] For the above-mentioned embodiment, a Comparative Example 2 is provided. In this comparative example, PVDF homopolymer organic particles are used for coating.

[0096] Preparation of slurry:

[0097] Dispersant of 0.92% and PVDF powder of 8% are put into ultrapure water according to the mass ratio and stirred for 60 minutes at a stirring speed of 600 rpm. 3.8% of binder and 10.5% of thickener are added to the obtained solution and stirred for another 40 minutes at a stirring speed of 600 rpm. Then 0.25% of wetting agent and 0.25% of defoaming agent are added and stirred for 30 minutes at a stirring speed of 200 rpm to obtain PMMA coating slurry.

[0098] Preparation of separator:

[0099] Using the microgravure roll coating process, the prepared PVDF coating slurry is evenly roll-coated on the polyolefin separator by a coater, and then wound up for standby after baking in an oven at 70 °C.

[0100] The performance comparisons of the composite separators prepared in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1:

[0101] Table 1. Performance comparisons of the composite separators prepared in Examples 1-3 and Comparative Examples 1-2

[0102]

[0103] It can be seen from the experiments that under the preparation conditions of Examples 1-3, at the same coating thickness, Examples 1-3 obviously have better puncture resistance than Comparative Example 1, and compared with Comparative Example 2, Examples 1-3 have better liquid absorption rate and peel strength. Because of their higher liquid absorption rate, the separators have better ionic conductivity.

[0104] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A low-cost lithium battery separator with high electrolyte wettability, characterized in that, it includes a base film and a polymer coating coated on one or both sides of the base film, and the polymer coating includes PVDF and PMMA materials; The polymer slurry is composed of the following raw materials in weight percentages: 6% - 13% of mixed powder, 5% - 15% of compatibilizer, 0.3% - 1.2% of dispersant, 2.5% - 7% of thickener, 5% - 13.5% of binder, 0.1% - 0.35% of wetting agent, 0.1% - 0.35% of defoaming agent, and the rest is ultrapure water; The compatibilizer has a PVDF main chain, and MMA branches are grafted onto the PVDF main chain through gamma-ray irradiation; The mixed powder is a mixture of PVDF and PMMA, and the weight ratio of PVDF:PMMA = 5 - 30:70 - 95.

2. A low-cost lithium battery separator with high electrolyte wettability according to claim 1, characterized in that, the base film is a polyolefin separator.

3. A low-cost lithium battery separator with high electrolyte wettability according to claim 1, characterized in that, the dispersant is an aliphatic amide type, the thickener is a sodium carboxymethyl cellulose type, the binder is a polyacrylic acid type, the wetting agent is an alkyl sulfate type, and the defoaming agent is a polyether type defoaming agent.

4. A low-cost lithium battery separator with high electrolyte wettability according to claim 1, characterized in that, the dispersant is one of polyacrylamide, octadeceneamine acetate, alkyl quaternary ammonium salt, aminopropylamine dioleate, polyethylene glycol type polyol, polyethyleneimine derivative, oleyl amino oleate, etc.; the binder is one of cyanoacrylate derivative binder, cyanoacrylate polyethylene glycol binder, acrylic acid binder, vinyl acetate polymer latex binder, etc.; the wetting agent is one of polyoxyethylene type surfactant, fatty acid surfactant, silanol type non-ionic surfactant, etc.; the defoaming agent is one of high carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene ethanolamine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether, and polydimethylsiloxane.

5. A low-cost lithium battery separator with high electrolyte wettability according to claim 1, characterized in that, the compatibilizer is composed of the following raw materials in parts by weight: 40 - 80 of PVDF homopolymer powder, 20 - 60 of methyl methacrylate liquid.

6. A preparation method of a low-cost lithium battery separator with high electrolyte wettability, characterized in that, it includes the following steps: S1. Prepare the polymer slurry: S1-1. Take 0.3% - 1.2% of the dispersant and 6% - 13% of the mixed powder according to the mass ratio and put them into ultrapure water for premixing to obtain the first intermediate; The mixed powder is a mixture of PVDF and PMMA, and the weight ratio of PVDF:PMMA = 5 - 30:70 - 95; S1-2. Add 5% - 13.5% of the binder and 2.5% - 7% of the thickener to the first intermediate according to the mass ratio and continue stirring to obtain the second intermediate; S1-3. Add 0.1% - 0.35% wetting agent and 0.1% - 0.35% defoaming agent to the second intermediate according to the mass ratio, stir, and filter to remove iron to obtain a polymer slurry; S2. Prepare a compatibilizer: S2-1. Put PVDF homopolymer powder and methyl methacrylate liquid into ultrapure water in a ratio of 40 - 80:20 - 60, stir and mix to obtain a mixed solution; S2-2. Place the above-mentioned mixed solution in a gamma-ray environment, take it out after sufficient irradiation to obtain a compatibilizer; S3. Modify the aforementioned polymer slurry: Put 5 - 15 parts of the compatibilizer into 85 - 95 parts of the polymer slurry, stir and mix, then let it stand to obtain a modified polymer slurry; S4. Prepare a separator: Uniformly coat the prepared modified polymer slurry on the separator, bake, and wind it up for standby.

7. According to the method for preparing a low-cost lithium battery separator with high electrolyte wettability as described in claim 6, it is characterized in that in step S1-1, the premixing time is 10 - 120 min and the rotation speed is 400 - 900 rpm.

8. According to the method for preparing a low-cost lithium battery separator with high electrolyte wettability as described in claim 6, it is characterized in that , in step S1-2, the mixing time is 20 - 80 min and the rotation speed is 350 - 700 rpm.

9. According to the method for preparing a low-cost lithium battery separator with high electrolyte wettability as described in claim 6, it is characterized in that , in step S1-3, the mixing time is 20 - 80 min and the rotation speed is 150 - 550 rpm.

10. According to the method for preparing a low-cost lithium battery separator with high electrolyte wettability as described in claim 6, it is characterized in that , in step S4, the microgravure roll coating process is adopted, and the modified polymer slurry is uniformly roll-coated on the separator through a coater.

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