An organic-inorganic composite microsphere, a battery separator, a preparation method thereof, and a battery

Abstract

The present invention discloses an organic-inorganic composite microsphere, a battery separator and its preparation method, and a battery. The preparation method of the organic-inorganic composite microsphere includes: mixing polyamic acid with a silicon source to prepare a first precursor microsphere, hydrolyzing it in a first hydrolysis solution, and then performing thermal imidization and dehydration treatment; or preparing a second precursor microsphere from a polyamic acid solution, then mixing it with TiOSO4 for a complexation reaction, hydrolyzing it in a second hydrolysis solution, and finally performing thermal imidization and dehydration treatment. The core-shell structure and size of the organic-inorganic composite microsphere prepared by the above method are uniform, and it has excellent thermal stability and wettability. It can be applied to the surface modification of a polyolefin separator to enhance the thermal stability and electrolyte wettability of the separator, and can ensure the consistency of the thickness of the modified layer formed on the surface of the polyolefin separator and the overall performance of the separator. Furthermore, when applied to a battery, it can improve the battery safety and cycling performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery separators, and in particular to an organic-inorganic composite microsphere, a battery separator, a preparation method thereof, and a battery. Background Art

[0002] As an efficient device for storing and converting chemical energy, lithium-ion batteries are widely used in portable electronic devices due to their high energy density, good rate performance, and environmental friendliness. A lithium-ion battery mainly consists of a positive electrode, a negative electrode, a separator, an electrolyte, an aluminum-plastic film, etc. As one of the important components of the battery, the separator can prevent short circuits caused by direct contact between the positive and negative electrodes, and at the same time provide a channel for ion transport.

[0003] Currently, most commercially available lithium-ion battery separators use polyolefin materials such as polyethylene and polypropylene. Since the microporous membranes prepared from polyethylene and polypropylene materials have stable chemical properties, high mechanical strength, good thermal closure performance, and low cost, polyolefin materials have been used to prepare separators in the early stage of lithium-ion battery research and development. Affected by the relatively low melting point and non-polarity of polyolefins, the thermal stability and electrolyte wettability of microporous polyolefin separators are also relatively poor, which hinders the uniform transport of lithium ions inside the battery and limits their application in high-energy density and high-rate lithium batteries. Surface modification of polyolefin separators can effectively improve the thermal stability and surface polarity of the separators to a certain extent, and improve the thermal stability and electrolyte wettability of the separators to facilitate the improvement of battery safety and cycle stability. Therefore, the surface modification of polyolefin separators is a current research hotspot. A common way to modify the surface of polyolefin separators is to set a modified layer on the surface of the separator. However, the existing surface coating modification methods have limited improvement in the thermal stability and electrolyte wettability of the separator, and the thickness consistency of the modified layers formed by some methods is poor. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention provides an organic-inorganic composite microsphere, a battery separator, a preparation method thereof, and a battery.

[0005] In a first aspect of the present invention, a preparation method of an organic-inorganic composite microsphere is provided, including the following steps:

[0006] S1. Mix polyamic acid with a silicon source to prepare a first precursor microsphere;

[0007] S2. Place the first precursor microsphere in a first hydrolysis solution for hydrolysis, and then perform thermal imidization and dehydration treatment to obtain an organic-inorganic composite microsphere.

[0008] The preparation method of the organic-inorganic composite microspheres according to the embodiments of the present invention has at least the following beneficial effects: In the preparation method of the organic-inorganic composite microspheres, polyamic acid and a silicon source are mixed to prepare a first precursor microsphere, and then the first precursor microsphere is placed in a first hydrolysis solution for hydrolysis to in-situ generate a Si(OH)4 hydrolysis coating layer on the surface of the first precursor microsphere. Then, through thermal imidization and dehydration treatment, PAA is imidized into polyimide (PI), and Si(OH)4 is dehydrated into SiO2 to obtain the product organic-inorganic composite core-shell nanometer microspheres. After the first precursor microsphere is prepared, hydrolysis treatment is carried out first, and then thermal imidization and dehydration treatment are carried out, which can avoid the excessive problem of high temperature on the hydrolysis reaction caused by heat treatment before hydrolysis. Thus, the core-shell structure of the prepared organic-inorganic composite microspheres can be more uniform, and the size can be uniform and consistent. The composite microspheres have excellent thermal stability and wettability, and can be applied to the surface modification of polyolefin diaphragms to enhance the thermal stability and electrolyte wettability of the diaphragms. And based on the uniformity of the structure and size of the prepared composite microspheres, the consistency of the thickness of the modified layer formed on the surface of the polyolefin diaphragm and the overall performance of the diaphragm can be ensured.

[0009] In some embodiments of the present invention, in step S1, the silicon source is selected from at least one of tetramethyl orthosilicate, tetraethyl orthosilicate (TEOS), ethyl silicate, and tetrabutyl orthosilicate. The dosage of the silicon source can be added according to the fact that the finally generated SiO2 accounts for 10-40% (such as 10%, 15%, 20%, 30%, 40%) of the total mass of SiO2 and PI.

[0010] In step S1, the first precursor microsphere can be prepared by electrospinning. Specifically, a spinning solution can be prepared by mixing polyamic acid and a silicon source, and then electrospinning is carried out to obtain the first precursor microsphere. The electrospinning parameters can be controlled as follows: positive pressure +40 KV to +60 KV (preferably +50 KV), negative pressure -8 KV to -12 KV (preferably -10 KV), spraying distance 20-25 cm, and brushing rate 5-20 cm / s.

[0011] In addition, in step S1, the polyamic acid can be prepared by polymerizing a dianhydride monomer and a diamine monomer in an aprotic polar organic solvent. The dianhydride monomer can be selected from at least one of biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, hexafluorodiacid dianhydride, and bisphenol A type diether dianhydride; the diamine monomer can be selected from at least one of bis(4-aminophenyl) ether, p-phenylenediamine, 4,4'-diaminodiphenylmethane, and 4,4'-diamino-2,2'-bis(trifluoromethyl) biphenyl. The polymerization reaction can be carried out in an ice-water bath; after the polymerization reaction is completed, aging treatment can be further carried out to improve the uniformity of the molecular weight distribution, and the aging treatment can be carried out under the constant temperature condition of 45-55 °C (preferably 50 °C). Preferably, the viscosity of the prepared polyamic acid (i.e., PAA solution) is 0.01-1 dl / g. More preferably, the solid content of the PAA solution is 5-40%.

[0012] In some embodiments of the present invention, in step S2, the thermal imidization and dehydration treatment is a high-temperature treatment at 250-350 °C. That is, by high-temperature treatment at 250-350 °C, PAA is imidized into polyimide (PI), and Si(OH)4 is dehydrated into SiO2. The specific temperature of the high-temperature treatment can be controlled at 250 °C, 280 °C, 300 °C, 310 °C, 350 °C, etc., preferably 300 °C; the high-temperature treatment time can be controlled within 1-3 h, preferably 2 h. Due to the interaction between PAA and the silicon source, part of the silicon source will remain inside the polyamic acid nanospheres and cannot migrate out. During the cyclization of polyamic acid, the silicon source remaining inside reacts with the water generated during the imidization of PAA, and finally SiO2 particles will also be formed inside the PI, and finally a core-shell nanosphere with the structure of SiO2@(PI / SiO2) is obtained.

[0013] In some embodiments of the present invention, in step S2, the first hydrolysis solution is a mixed solution of alcohol and water, and the volume ratio of alcohol to water can be controlled at 1:(3-5), preferably 1:4. The alcohol can specifically be any one of ethanol and isopropanol.

[0014] In the second aspect of the present invention, a method for preparing an organic-inorganic composite microsphere is proposed, including the following steps:

[0015] S1. Prepare second precursor microspheres using a polyamic acid solution;

[0016] S2. Mix the second precursor microspheres with TiOSO4 for a complexation reaction, then place them in a second hydrolysis solution for hydrolysis, and then perform thermal imidization and dehydration treatment to obtain an organic-inorganic composite microsphere.

[0017] According to the preparation method of the organic-inorganic composite microspheres in this embodiment of the present invention, it has at least the following beneficial effects: The preparation method of the organic-inorganic composite microspheres uses a polyamic acid solution to prepare the second precursor microspheres, and then mixes them with TiOSO4 for a complexation reaction. Specifically, -COOH on the surface of the second precursor microspheres reacts with TiO 2+ to undergo an adsorption complexation reaction; then it is placed in a second hydrolysis solution to allow TiO 2+ to undergo hydrolysis, in-situ generating TiO(OH)2, followed by thermal imidization and dehydration treatment to imidize PAA into polyimide (PI), and TiO(OH)2 dehydrates into TiO2, obtaining organic-inorganic composite core-shell nanometer microspheres. After preparing the first precursor microspheres by the above method, hydrolysis treatment is first carried out, and then thermal imidization and dehydration treatment are carried out, which can avoid the problem of excessive high temperature on the hydrolysis reaction caused by heat treatment before hydrolysis, so that the core-shell structure of the prepared organic-inorganic composite microspheres can be more uniform and the size can be uniform; the composite microspheres have excellent thermal stability and wettability, and can be applied to the surface modification of polyolefin diaphragms to enhance the thermal stability and electrolyte wettability of the diaphragms; and based on the uniformity of the structure and size of the prepared composite microspheres, it can ensure the consistency of the thickness of the modified layer formed on the surface of the polyolefin diaphragm and the overall performance of the diaphragm.

[0018] In step S1, the second precursor microspheres can also be prepared by electrospinning; the electrospinning parameters can be controlled as follows: positive pressure +40 KV to +60 KV (preferably +50 KV), negative pressure -8 KV to -12 KV (preferably -10 KV), spraying distance 20 to 25 cm, and brushing rate 5 to 20 cm / s. The polyamic acid solution can also be prepared by polymerizing dianhydride monomers and diamine monomers in an aprotic polar organic solvent. The dianhydride monomers can be selected from at least one of biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, hexafluorodiacid dianhydride, and bisphenol A type diether dianhydride; the diamine monomers can be selected from at least one of bis(4-aminophenyl) ether, p-phenylenediamine, 4,4'-diaminodiphenylmethane, and 4,4'-diamino-2,2'-bis(trifluoromethyl) biphenyl. The polymerization reaction can be carried out in an ice-water bath; after the polymerization reaction is completed, aging treatment can be further carried out to improve the uniformity of the molecular weight distribution, and the aging treatment can be carried out under a constant temperature condition of 45 to 55 °C (preferably 50 °C). Preferably, the intrinsic viscosity of the prepared polyamic acid (i.e., PAA solution) is 0.01 to 1 dl / g. Further preferably, the solid content of the PAA solution is 5 to 40%.

[0019] In some embodiments of the present invention, in step S2, the thermal imidization and dehydration treatment is a high-temperature treatment at 250-350 °C. That is, the PAA is imidized into polyimide (PI) and TiO(OH)2 is dehydrated into TiO2 through the high-temperature treatment at 250-350 °C. The high-temperature treatment time can be controlled within 1-3 h, preferably 2 h. In addition, in step S2, deionized water is used as the second hydrolysis solution.

[0020] In the third aspect of the present invention, an organic-inorganic composite microsphere is provided, which is prepared by any of the preparation methods of the organic-inorganic composite microspheres proposed in the first aspect of the present invention, or by any of the preparation methods of the organic-inorganic composite microspheres proposed in the second aspect of the present invention. The core-shell structure of the organic-inorganic composite microsphere is uniform, and the size is uniform. It has excellent thermal stability and wettability, and can be applied to the surface modification of polyolefin diaphragms, which can enhance the thermal stability and electrolyte wettability of the diaphragms.

[0021] In the fourth aspect of the present invention, a battery diaphragm is provided, which includes a polyolefin microporous base film and a modification layer provided on the surface of the polyolefin microporous base film. The modification layer is made of a material including an adhesive and the organic-inorganic composite microsphere proposed in the third aspect of the present invention. Both the polyolefin microporous base film and the organic-inorganic composite microspheres on its modification layer in the battery diaphragm have excellent electronic insulation properties, can effectively prevent electron migration, and have excellent thermal stability and electrolyte wettability, high mechanical strength, and good thickness consistency. It can be applied to the preparation of lithium-ion batteries and can effectively improve the safety and cycle performance of lithium-ion batteries.

[0022] Among them, the thickness of the polyolefin microporous base film can be controlled within 3-200 nm; in addition, its porosity can be 20%-80%, and the air permeability can be 50-200 s / 100 cc. The polyolefin microporous base film can specifically be any one of a polyethylene microporous base film, a polypropylene microporous base film, a polypropylene / polyethylene / polypropylene three-layer composite microporous base film, a polyvinylidene fluoride microporous base film, and a polyvinylidene fluoride-hexafluoropropylene microporous base film.

[0023] In addition, the adhesive can be a polymer adhesive, such as one or more of an aqueous PVDF emulsion, polyvinyl alcohol, polyethylene oxide, an acrylic water-soluble adhesive, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyvinylpyrrolidone.

[0024] In the fifth aspect of the present invention, a preparation method of the battery diaphragm proposed in the fourth aspect of the present invention is provided, including: mixing the organic-inorganic composite microsphere and the adhesive with a solvent to prepare a modification slurry; then coating the modification slurry on the surface of the polyolefin microporous base film and drying it to obtain the battery diaphragm.

[0025] Among them, the slurry can be specifically prepared by mixing the following components in parts by weight: 9-30 parts of organic-inorganic composite microspheres, 1-3 parts of adhesive, and 67-90 parts of solvent. The solvent can be water or a mixed solution of water and alcohol.

[0026] In the sixth aspect of the present invention, a battery is proposed, which includes the battery separator proposed in the fourth aspect of the present invention or the battery separator prepared by the preparation method of the battery separator proposed in the fifth aspect of the present invention. Based on the excellent thermal stability, electrolyte wettability, high mechanical strength, and good thickness consistency of the battery separator, the battery has excellent safety performance and cycling performance. Description of the Drawings

[0027] The following further describes the present invention with reference to the drawings and embodiments, where:

[0028] Figure 1 SEM image of the battery separator prepared in Example 3;

[0029] Figure 2 SEM image of the battery separator prepared in Example 4;

[0030] Figure 3 SEM image of the battery separator prepared in Comparative Example 2;

[0031] Figure 4 Test result diagram of the electrolyte wettability of the battery separators prepared in Examples 3-4, Comparative Example 2, and the polyethylene separator of Comparative Example 3. Detailed Embodiments

[0032] The following will clearly and completely describe the concept and technical effects of the present invention in combination with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0033] Example 1

[0034] In this example, an organic-inorganic composite microsphere was prepared, and its preparation method is as follows:

[0035] S1. Use the dianhydride monomer pyromellitic dianhydride and the diamine monomer bis(4-aminophenyl) ether, and use the aprotic polar N,N-dimethylformamide (DMF) as the solvent. Mix them according to the mass ratio of monomer to solvent of 1:1, and place them in an ice-water bath to synthesize a polyamic acid (PAA) solution with a solid content of 12 wt% through a polymerization reaction. Then place it under a constant temperature condition of 50 °C for aging treatment to obtain a polyamic acid (PAA) solution with a uniform molecular weight distribution and an intrinsic viscosity of 0.3 dl / g;

[0036] S2. Add tetraethyl orthosilicate (TEOS) with a mass ratio of 10% to the polyamic acid (PAA) solution finally prepared in step S1, and stir it sealed at room temperature for 6 h to prepare a clear, transparent and uniformly mixed PAA / TEOS mixture; then use the PAA / TEOS mixture as the spinning solution for electrospinning, and control the spinning parameters as positive pressure +50 KV, negative pressure -10 KV, spraying distance 20 cm, and brushing rate 10 cm / s to obtain the first precursor microspheres;

[0037] S3. Place the first precursor microspheres prepared in step S2 in a hydrolysis solution (ethanol and water with a volume ratio of 1:4), and carry out hydrolysis treatment at room temperature for 24 h. A Si(OH)4 hydrolysis coating layer is in-situ generated on the surface of the first precursor microspheres; then carry out high-temperature treatment at 300 °C for 2 h to imidize PAA into PI, and Si(OH)4 dehydrates into SiO2. And due to the interaction between PAA and TEOS, part of TEOS remains inside the polyamic acid nanomicrospheres and cannot migrate out. During the high-temperature treatment of the cyclization of polyamic acid, the residual TEOS inside reacts with the water generated during the imidization process of PAA, and finally SiO2 particles are also formed inside PI, and finally core-shell nanomicrospheres with a structure of SiO2@(PI / SiO2), that is, organic-inorganic composite microspheres are obtained.

[0038] Example 2

[0039] In this example, an organic-inorganic composite microsphere was prepared, and its preparation method is as follows:

[0040] S1. Prepare a polyamic acid (PAA) solution according to the same operation as in step S1 of Example 1;

[0041] S2. Use the polyamic acid (PAA) solution finally prepared in step S1 as the spinning solution for electrospinning, and control the spinning parameters as positive pressure +50 KV, negative pressure -10 KV, spraying distance 20 cm, and brushing rate 10 cm / s to obtain the second precursor microspheres;

[0042] S3. Place the second precursor microspheres prepared in step S2 into a TiOSO4 solution with a concentration of 0.2 mol / L, and carry out a complexation reaction at room temperature. Specifically, -COOH on the surface of the second precursor microspheres will react with TiO 2+ to undergo an adsorption complexation reaction; then place it into deionized water of the hydrolysis solution, and let TiO 2+ undergo hydrolysis to in-situ generate TiO(OH)2; then perform high-temperature treatment at 300 °C for 2 h to imidize PAA into polyimide (PI), and dehydrate TiO(OH)2 into TiO2, to obtain core-shell nanometer microspheres with a structure of PI@TiO2, that is, organic-inorganic composite microspheres.

[0043] Comparative Example 1

[0044] In this comparative example, an organic-inorganic composite microsphere was prepared, and its preparation method is as follows:

[0045] In this comparative example, the operations of steps S1 and S2 are the same as those of steps S1 and S2 in Example 1 to obtain the first precursor microspheres; the difference from the preparation method of the organic-inorganic composite microspheres in Example 1 is that: S3. Place the first precursor microspheres in a heat treatment environment at 280 °C for 30 min, and then put them into a hydrolysis solution (ethanol and water with a volume ratio of 1:4), and hydrolyze at room temperature for 24 h; then place it in a blast drying oven at 300 °C for high-temperature treatment for 2 h to obtain an organic-inorganic composite microsphere. Example 3

[0046] In this example, a battery separator was prepared, and its preparation method includes:

[0047] S1. Take 9 parts of the organic-inorganic composite microspheres prepared in Example 1, 1 part of sodium carboxymethyl cellulose (CMC), 1 part of polyvinylpyrrolidone (PVP), and 98 parts of a mixed solvent of water and ethanol with a volume ratio of 1:1, and place them in a homogenizer to homogenize at a speed of 8000 rpm for 1 h. After mixing evenly, filter with a 300-mesh sieve to obtain a modified slurry;

[0048] S2. Use a flat blade coater to scrape the modified slurry prepared in step S1 on a polyethylene microporous base film with a coating gap of 100 μm. The polyethylene microporous base film is purchased on the market, with a thickness of 3 - 200 nm, a porosity of 20% - 80%, and an air permeability of 50 - 200 s / 100 cc; after coating, place it in a clean bench to dry naturally, and then vacuum dry at 60 °C for 12 h to obtain the product battery separator. The battery separator includes a polyethylene microporous base film and a modified layer provided on the surface of the polyethylene microporous base film. The modified layer is prepared by mixing the organic-inorganic composite microspheres prepared in Example 1, an adhesive (CMC and PVP with a mass ratio of 1:1), and a solvent.

[0049] Example 4

[0050] In this example, a battery separator was prepared. The preparation method of the battery separator in this example was basically the same as that in Example 3. The difference from Example 3 was that the organic-inorganic composite microspheres prepared in Example 2 were used instead of the organic-inorganic composite microspheres prepared in Example 1 used in Example 3, and other operations were the same as those in Example 3.

[0051] Comparative Example 2

[0052] In this comparative example, a battery separator was prepared. The preparation method of the battery separator in this comparative example was basically the same as that in Example 3. The difference from Example 3 was that the organic-inorganic composite microspheres prepared in Comparative Example 1 were used instead of the organic-inorganic composite microspheres prepared in Example 1 used in Example 3, and other operations were the same as those in Example 3. Performance test

[0053] The battery separators prepared in Example 3, Example 4 and Comparative Example 2 were observed by scanning electron microscope respectively, and the obtained results were as shown in Figures 1 to 3 shown. By comparison Figures 1 to 3 it can be seen that the consistency of the separators prepared in Example 3 and Example 4 is better than that of the battery separator prepared in Comparative Example 2.

[0054] In addition, an unmodified conventional polyethylene separator (i.e., the polyethylene microporous base film used in Example 3) was used as Comparative Example 3, and the battery separators prepared in Example 3, Example 4 and Comparative Example 2 and the polyethylene separator of Comparative Example 3 were subjected to performance tests. The specific performance test parameters and methods included:

[0055] (A1) Thickness consistency σ

[0056] The specific test method was as follows: Take a section of each battery separator, measure the thickness every 20 cm, and test 30 values in total. Calculate its standard deviation σ to characterize the thickness consistency of the battery separator.

[0057] (A2) Wettability

[0058] The specific test method was as follows: Use a pipette to take 1 μL of electrolyte and drop it vertically on each battery separator, let it stand for one minute, and record the size of the electrolyte diffused on the surface of the battery separator. Among them, the electrolyte was LiPF6 with a molar concentration of 1 M, and its solvent was a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) with a volume ratio of 1:1:1.

[0059] (A3) Thermal shrinkage

[0060] The specific test method was as follows: Put the battery separator into an oven and heat it at an initial temperature of 25 ± 3 °C. The oven temperature was increased at a rate of 5 ± 2 °C / min to 130 °C, and after maintaining for 30 min, stop the test, and measure the shrinkage size ratio of the battery separator before and after baking.

[0061] The performances of the battery separators prepared in Examples 3 and 4 and Comparative Example 2, as well as the polyethylene separator of Comparative Example 3, were tested using the above methods. The test results of thickness uniformity and thermal shrinkage are shown in Table 1, and the test results of electrolyte wettability are as Figure 4 shown, Figure 4 where (a) - (d) sequentially represent the electrolyte wettability test result diagrams of the battery separator of Example 3, the battery separator of Example 4, the battery separator of Comparative Example 3, and the polyethylene separator of Comparative Example 3.

[0062] Table 1

[0063]

[0064]

[0065] From the thickness uniformity test results shown in Table 1, it can be seen that the thickness uniformity of the battery separators obtained in Examples 3 and 4 is significantly better than that of the battery separator obtained in Comparative Example 2. The difference between Comparative Example 2 and Example 3 lies in the organic-inorganic composite microspheres used. In Example 3, the organic-inorganic composite microspheres of Example 1 were used. After the first precursor microspheres were prepared, hydrolysis treatment was carried out first, followed by high-temperature imidization and dehydration treatment; while in Comparative Example 2, the organic-inorganic composite microspheres prepared in Comparative Example 1 were used. In its preparation process, after the first precursor microspheres were prepared, heat treatment was carried out first, followed by hydrolysis treatment, and then high-temperature treatment. Thus, it can be seen that in the preparation process of organic-inorganic composite microspheres, heat treatment before hydrolysis of the first precursor microspheres will affect the characteristics of the prepared organic-inorganic composite microspheres, and further significantly affect the thickness uniformity of the modified battery separator. The specific speculation is that the high temperature of the heat treatment before hydrolysis will lead to an excessive subsequent hydrolysis reaction, which will further affect the uniformity of the core-shell structure and the size consistency of the prepared composite microspheres, and then affect the thickness uniformity of the surface modification layer of the battery separator, resulting in poor thickness uniformity of the product battery separator. From this, it can be known that for the organic-inorganic composite microspheres of Examples 1 and 2, after the first precursor microspheres are prepared, hydrolysis treatment is carried out first, and then thermal imidization and dehydration treatment are carried out, which can avoid the problem of excessive high temperature on the hydrolysis reaction easily caused by heat treatment before hydrolysis, so that the core-shell structure of the prepared organic-inorganic composite microspheres can be more uniform, and the size is uniformly consistent. When this organic-inorganic composite microsphere is applied to the surface modification of the battery separator, it can ensure the thickness uniformity of the formed modification layer, and further ensure the consistency of the overall performance of the separator.

[0066] In addition, referring to the thermal shrinkage performance test results shown in Table 1 and Figure 4 the wettability test results shown, it can be seen that the battery separators with surface modification layers prepared in Examples 3 and 4 have significantly better thermal shrinkage performance and electrolyte infiltration performance than the unmodified conventional polyethylene separator of Comparative Example 3.

[0067] Application Example

[0068] The battery separator prepared above can be further applied to the preparation of lithium-ion batteries. To investigate the effect of the battery separator on battery performance when further applied to lithium-ion batteries, the inventor conducted specific application tests, including assembling the battery separators of Examples 3 and 4 and Comparative Examples 2 and 3 and a polyethylene separator into a battery cell device, and further testing its safety performance and cycle performance.

[0069] Specifically, assembling the battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and the above battery separator. Among them, the positive electrode sheet is made into a slurry by mixing 80 wt% of the active material lithium cobaltate, 10 wt% of Super P carbon, and 10 wt% of polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP), and then the prepared slurry is cast onto a clean carbon-coated aluminum foil and dried at 80 °C for 12 h; the negative electrode sheet is made into a slurry by mixing 80 wt% of the active material graphite, 10 wt% of Super P carbon, and 10 wt% of the binder styrene-butadiene rubber in water, and then the obtained slurry is cast onto a fresh copper foil and dried at 60 °C for 12 h; the electrolyte uses LiPF6 with a molar concentration of 1 M, and its solvent is a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) with a volume ratio of 1:1:1.

[0070] Using the battery separators of Examples 3 and 4 and Comparative Examples 2 and 3 and a polyethylene separator to assemble according to the above structure, corresponding battery cell samples 1 to 4 are obtained. Then, the safety performance and cycle performance of each battery cell sample are tested respectively, as follows:

[0071] (B1) Safety Performance of Battery Cell

[0072] The specific test method is: put the battery cell into an oven (suspension test), heat it with circulating hot air at an initial temperature of 25 ± 3 °C, the oven temperature is raised at a rate of 5 ± 2 °C / min to 132 ± 2 °C, and keep it for 30 min and then stop. During the test, monitor the surface temperature, ambient temperature, and voltage of the battery cell. Pass if there is no fire or explosion.

[0073] In addition, according to the method basically the same as above, the highest heating temperature of 132 ± 2 °C is adjusted to 135 ± 2 °C for testing.

[0074] Test the safety performance of battery cell samples 1 to 4 according to the above method, and the obtained results are shown in Table 2.

[0075] Table 2

[0076]

[0077] As can be seen from the results shown in Table 2, compared with the cell sample 4 prepared with the unmodified polyethylene separator of Comparative Example 3, the cell samples 1 and 2 using the surface-modified battery separators prepared in Examples 3 and 4 have a significantly better hot box passing rate than the cell sample 4. Thus, it can be seen that the organic-inorganic composite microspheres prepared in Examples 1 and 2 are applied to the surface modification of the polyolefin separator, which can improve the safety performance of the battery using the polyolefin separator.

[0078] (B2) Cycle performance of the cell

[0079] The specific test method is as follows: The lithium battery cell is charged at a rate of 1C and discharged at a rate of 1C at room temperature, and 600 cycles are carried out in sequence, and the battery capacity before and after each cycle is recorded. The capacity retention rate after n cycles = (battery capacity after n cycles / battery capacity before cycling) × 100%.

[0080] According to the above method, the capacity retention rates of the cell samples 1 to 4 after 600 cycles were tested, and the obtained results are shown in Table 3.

[0081] Table 3

[0082]

[0083] As can be seen from the results shown in Table 3, compared with the cell sample 4 prepared with the unmodified polyethylene separator of Comparative Example 3, the cell samples 1 and 2 using the surface-modified battery separators prepared in Examples 3 and 4 have significantly better cycle performance than the cell sample 4. Thus, it can be seen that the organic-inorganic composite microspheres prepared in Examples 1 and 2 are applied to the surface modification of the polyolefin separator, which can improve the cycle performance of the battery using the polyolefin separator.

[0084] As can be seen from the above, in the preparation process of the organic-inorganic composite microspheres of the present application, after the first precursor microspheres are prepared, hydrolysis treatment is carried out first, and then thermal imidization and dehydration treatment are carried out, which can avoid the excessive problem of high temperature on the hydrolysis reaction caused by heat treatment before hydrolysis, so that the core-shell structure of the prepared organic-inorganic composite microspheres can be more uniform and the size can be uniform; the composite microspheres have excellent thermal stability and wettability, and can be applied to the surface modification of the polyolefin separator, which can enhance the thermal stability and electrolyte wettability of the separator; and based on the uniformity of the structure and size of the prepared composite microspheres, the consistency of the thickness of the modified layer formed on the surface of the polyolefin separator and the overall performance of the separator can be ensured, and then the application to the battery can improve the battery safety and cycle performance.

[0085] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing an organic-inorganic composite microsphere, characterized in that, It includes the following steps: S1. Prepare a first precursor microsphere by mixing polyamic acid and a silicon source; the polyamic acid is prepared by polymerizing a dianhydride monomer and a diamine monomer in an aprotic polar organic solvent and then subjecting it to an aging treatment; S2. Place the first precursor microsphere in a first hydrolysis solution for hydrolysis, and then perform thermal imidization and dehydration treatment to obtain an organic-inorganic composite microsphere.

2. The preparation method of the organic-inorganic composite microspheres according to claim 1, wherein In step S1, the silicon source is selected from at least one of tetramethyl orthosilicate, tetraethyl orthosilicate, ethyl silicate, and tetrabutyl orthosilicate.

3. The preparation method of the organic-inorganic composite microspheres according to claim 1, wherein In step S2, the thermal imidization and dehydration treatment is a high-temperature treatment at 250-350 °C.

4. The preparation method of the organic-inorganic composite microspheres according to claim 1, wherein, In step S2, the first hydrolysis solution is a mixed solution of alcohol and water.

5. An organic-inorganic composite microsphere, characterized in that, It is obtained by the preparation method of the organic-inorganic composite microsphere according to any one of claims 1 to 4.

6. A battery separator, characterized in that, It includes a polyolefin microporous base film and a modification layer provided on the surface of the polyolefin microporous base film, and the modification layer is prepared from a material including an adhesive and the organic-inorganic composite microsphere according to claim 5.

7. The preparation method of the battery separator according to claim 6, characterized in that, It includes: Mix the organic-inorganic composite microsphere, the adhesive and a solvent to prepare a modification slurry; then coat the modification slurry on the surface of the polyolefin microporous base film and then dry it to obtain a battery separator.

8. A battery, characterized in that, It includes the battery separator obtained by the preparation method of the battery separator according to claim 6 or the battery separator according to claim 7.

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