Lithium battery diaphragm and preparation method thereof

Abstract

The invention relates to the technical field of battery diaphragms, and provides a lithium battery diaphragm and a preparation method thereof. The lithium battery diaphragm is obtained by coating a base membrane with coating slurry on a single side, and the coating slurry comprises the following components in parts by weight: 30 parts of aluminum oxide, 5-10 parts of a binder, 0.1-1 part of a dispersant, 5-10 parts of a thickener, 0.01-0.1 part of a wetting agent and 40-90 parts of water, the aluminum oxide comprises rice-shaped aluminum oxide and spherical aluminum oxide; the grain size D50 of the rice-grain-shaped aluminum oxide is 0.7-1.5 microns, and the grain size D90 of the rice-grain-shaped aluminum oxide is 2.0-3.0 microns; the particle size D50 of the spherical aluminum oxide is 0.4-0.6 mu m, and the particle size D90 of the spherical aluminum oxide is 0.8-1.5 mu m. According to the technical scheme, the problem of poor heat resistance of the lithium battery diaphragm in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a lithium battery separator and a preparation method thereof. Background Art

[0002] In the internal structure of lithium batteries, the separator plays an important role. It can effectively prevent short circuits between the positive and negative electrodes, and at the same time enable lithium batteries to achieve efficient and stable charge and discharge cycles.

[0003] Traditional lithium battery separators are primarily made of polymer materials such as polyolefins, which generally meet safety requirements during normal use. However, due to their inherent poor heat resistance, polyolefin separators are prone to shrinkage in high-temperature environments, resulting in reduced battery performance and potentially even safety issues.

[0004] To improve the performance of lithium battery separators, one or more ceramic layers are usually applied to the surface of traditional separators. This method can improve the thermal stability and ion conductivity of the separator to a certain extent. However, due to the difficulty in accurately adjusting the material selection, material ratio and microstructure of the ceramic layer, the improvement of the separator's thermal stability is limited, which in turn affects the discharge performance of the battery.

[0005] Therefore, developing a lithium battery separator with excellent heat resistance is of great significance for ensuring the stable charge and discharge cycle of lithium batteries and extending the battery life. Summary of the Invention

[0006] The present invention provides a lithium battery separator and a preparation method thereof, which solves the problem of poor heat resistance of lithium battery separators in the related art.

[0007] The technical solutions of the present invention are as follows: The present invention provides a lithium battery separator, which is obtained by coating a coating slurry on one side of a base film, wherein the coating slurry comprises the following components in parts by weight: 30 parts of aluminum oxide, 5-10 parts of binder, 0.1-1 parts of dispersant, 5-10 parts of thickener, 0.01-0.1 parts of wetting agent, 40-90 parts of water; The alumina includes rice-shaped alumina and spherical alumina; The particle size of the rice-grained aluminum oxide is: D50 is 0.7-1.5 μm, D90 is 2.0-3.0 μm; The particle size of the spherical alumina is: D50 is 0.4-0.6 μm, and D90 is 0.8-1.5 μm.

[0008] In the lithium battery separator of the present invention, the rice-grained alumina in the alumina increases the tortuosity of the micropores by forming a staggered structure in the coating, which can reduce the self-discharge caused by the disordered migration of lithium ions. The rice-grained alumina has more surface active sites and can preferentially adsorb impurity ions in the electrolyte. In addition, the presence of spherical alumina can also reduce the overall interfacial resistance of the coating. Through the combined action of the rice-grained alumina and the spherical alumina, the electrolyte infiltration speed of the lithium battery separator and the liquid retention capacity of the lithium battery separator can be improved, and the coating in the lithium battery separator has a stronger ability to neutralize HF in the electrolyte, thereby improving the charge and discharge performance of the lithium battery separator as a whole.

[0009] As a further technical solution, the weight ratio of the rice-shaped alumina to the spherical alumina is 1:2~14, for example, it can be 1:2, 1:3, 1:4, 1:5, 1:7, 1:8, 1:9, 1:11, 1:14, preferably 1:5~14.

[0010] In the lithium battery separator of the present invention, the content ratio of rice-grained alumina and spherical alumina is regulated. When the weight ratio of rice-grained alumina to spherical alumina is 1:5~14, the heat resistance of the lithium battery separator can be further improved, and its longitudinal shrinkage rate can be reduced to below 1.7%, and its transverse shrinkage rate can be reduced to below 1.5%.

[0011] As a further technical solution, the alumina is composite alumina, and the raw materials of the composite alumina include spherical alumina and aluminum triacetylacetonate in a weight ratio of 30:3-7.

[0012] In the lithium battery separator of the present invention, aluminum triacetylacetonate is used to perform a composite treatment on aluminum oxide. This improves the puncture resistance of the lithium battery separator while maintaining its heat resistance. This is presumably because the composite treatment with aluminum triacetylacetonate improves the interfacial bonding between the rice-shaped and spherical aluminum oxides and strengthens the bonding between the aluminum oxide and the base film. This reduces the aluminum oxide's resistance to detachment from the base film when subjected to external puncture forces, thereby improving the separator's puncture resistance.

[0013] In the lithium battery separator of the present invention, the weight ratio of spherical alumina and aluminum triacetylacetonate is regulated to 30:3~7, for example, it can be 30:3, 30:4, 30:4.5, 30:5, 30:5.5, 30:6, 30:7, preferably 30:5~6. When the weight ratio of spherical alumina and aluminum triacetylacetonate is 30:5~6, the puncture resistance of the lithium battery separator can be further improved, so that the puncture strength of the lithium battery separator is increased to 13.8~14.1N. When the weight ratio of spherical alumina and aluminum triacetylacetonate is outside the range of 30:5~6, the effect of improving the puncture resistance of the lithium battery separator is slightly worse.

[0014] As a further technical solution, the preparation method of the composite alumina comprises the following steps: A1. After dispersing the aluminum oxide in water, add a silane coupling agent and mix well to obtain a mixed solution I; A2, dispersing the aluminum triacetylacetonate in ethanol and mixing uniformly to obtain a mixed solution II; A3. Add the mixed solution II to the mixed solution I, stir evenly, concentrate, and dry to obtain the composite alumina.

[0015] In the lithium battery separator of the present invention, the silane coupling agent can be any one or more conventional silane coupling agents in the art, for example, it can be γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, preferably γ-aminopropyltriethoxysilane.

[0016] As a further technical solution, the amount of the silane coupling agent added is 1% to 3% of the weight of the spherical alumina.

[0017] As a further technical solution, the binder includes one or both of polyvinyl alcohol and sodium alginate, preferably polyvinyl alcohol.

[0018] As a further technical solution, the dispersant includes one or both of ammonium polyacrylate and sodium polyacrylate, preferably polyacrylamide.

[0019] As a further technical solution, the thickener includes one or more of a lithium carboxymethyl cellulose aqueous solution, a carboxymethyl cellulose aqueous solution, and a sodium carboxymethyl cellulose aqueous solution.

[0020] In the lithium battery separator of the present invention, the thickener is in the form of an aqueous solution, and the mass fraction of the thickener aqueous solution is 3% to 5%, for example, 3%, 3.5%, 4%, 4.5%, 5%, preferably 5%.

[0021] As a further technical solution, the wetting agent includes polyether-modified silicone.

[0022] The present invention provides a method for preparing a lithium battery separator, which is used to prepare the lithium battery separator, comprising the following steps: S1, mixing the dispersant, water and aluminum oxide uniformly to obtain a mixed solution; S2, adding a binder, a thickener and a wetting agent to the mixed solution, mixing them evenly to obtain a coating slurry; S3. Coating the coating slurry on one side of a base film and drying the base film to obtain the lithium battery separator.

[0023] As a further technical solution, in step S1, the mixing is carried out by stirring, the rotation speed of the stirring is 1500-3000 r / min, and the stirring time is 30-60 min; In step S2, the mixing is uniformly carried out by stirring and ultrasonication, the rotation speed of the stirring is 1000-2000 r / min, the revolution speed is 40-60 r / min, the ultrasonic frequency is 5-8 kHz, and the mixing time is 30-60 min.

[0024] As a further technical solution, during the single-sided coating, the coating speed is 10-30 m / min, and the thickness of the coating obtained after the single-sided coating is 3 μm.

[0025] As a further technical solution, the base film is a polyethylene base film or a polypropylene base film, preferably a polyethylene base film.

[0026] As a further technical solution, during the drying, the temperature is 50-80° C. and the time is 1-2 minutes.

[0027] The working principle and beneficial effects of the present invention are: In the preparation method of the lithium battery separator of the present invention, alumina includes rice-grained alumina and spherical alumina, and the rice-grained alumina and the spherical alumina have a synergistic effect. The rice-grained alumina forms an internal structure with staggered arrangement in the surface coating of the base membrane, and can form a skeleton support at high temperature. The spherical alumina can effectively fill the gaps between the rice-grained alumina, and can maintain a uniform pore size distribution to a certain extent, thereby avoiding blockage of the lithium battery separator pores. By using rice-grained alumina and spherical alumina in combination, and regulating the particle size D50 of the rice-grained alumina to 0.7~1.5μm and D90 to 2.0~3.0μm, and the particle size D50 of the spherical alumina to 0.4~0.6μm and D90 to 0.8~1.5μm, the two have a good pore complementary effect, which can effectively inhibit the melting shrinkage of the lithium battery separator, thereby effectively improving the heat resistance of the lithium battery separator. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 This is an electron microscope image of the rice-grained alumina in Example 2. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0031] In the following examples and comparative examples, rice-grained alumina was purchased from Anhui Yishitong Materials Technology Co., Ltd.; the model of polyvinyl alcohol was PVA 2488; the model of polyether-modified silicone was BYK306, purchased from Green Alliance (Jining) Chemical Technology Co., Ltd.; the content of aluminum triacetylacetonate was 99%, and the CAS number was 13963-57-0.

[0032] Example 1 A method for preparing a lithium battery separator comprises the following steps: S1. 0.1 parts of ammonium polyacrylate, 40 parts of water, 10 parts of rice-shaped aluminum oxide (D50: 0.7 μm, D90: 2.0 μm), and 20 parts of spherical aluminum oxide (D50: 0.4 μm, D90: 0.8 μm) were stirred in a double planetary mixer at a rotation speed of 1500 r / min for 60 minutes to obtain a mixed solution; S2. Add 5 parts of polyvinyl alcohol, 5 parts of 5% by mass sodium carboxymethyl cellulose aqueous solution, and 0.01 parts of polyether-modified silicone to the mixed solution, and mix them in a double planetary mixer with ultrasonic oscillation function at a rotation speed of 1000 r / min, a revolution speed of 40 r / min, and an ultrasonic frequency of 5 kHz for 60 minutes to obtain a coating slurry; S3. The coating slurry is coated on one side of a polyethylene-based film at a coating speed of 10 m / min to obtain a coating with a thickness of 3 μm. The coating is baked at 50° C. for 2 min to obtain a lithium battery separator.

[0033] Example 2 A method for preparing a lithium battery separator comprises the following steps: S1. 0.5 parts of ammonium polyacrylate, 64 parts of water, 10 parts of rice-shaped alumina (D50: 0.876 μm, D90: 2.123 μm), and 20 parts of spherical alumina (D50: 0.496 μm, D90: 1.064 μm) were stirred in a double planetary mixer at a rotation speed of 2000 rpm for 40 minutes to obtain a mixed solution. S2. Add 8 parts of polyvinyl alcohol, 8 parts of 5% by mass sodium carboxymethyl cellulose aqueous solution, and 0.05 parts of polyether-modified silicone to the mixed solution, and mix them in a double planetary mixer with ultrasonic oscillation function at a rotation speed of 1500 r / min, a revolution speed of 50 r / min, and an ultrasonic frequency of 6 kHz for 45 minutes to obtain a coating slurry; S3, coating the coating slurry on one side of a polyethylene film at a coating speed of 20 m / min to obtain a coating with a thickness of 3 μm, and baking the coating at 60° C. for 1.5 min to obtain a lithium battery separator; The electron microscope image of the rice-shaped aluminum oxide in Example 2 is as follows: Figure 1 shown.

[0034] Example 3 A method for preparing a lithium battery separator comprises the following steps: S1. 1 part of ammonium polyacrylate, 90 parts of water, 10 parts of rice-shaped aluminum oxide (D50: 1.5 μm, D90: 3.0 μm), and 20 parts of spherical aluminum oxide (D50: 0.6 μm, D90: 1.5 μm) were stirred in a double planetary mixer at a rotation speed of 3000 r / min for 30 minutes to obtain a mixed solution; S2. Add 10 parts of polyvinyl alcohol, 10 parts of a 5% by mass aqueous solution of sodium carboxymethyl cellulose, and 0.1 parts of polyether-modified silicone to the mixed solution, and mix them in a double planetary mixer with an ultrasonic oscillation function at a rotation speed of 2000 r / min, a revolution speed of 60 r / min, and an ultrasonic frequency of 8 kHz for 30 minutes to obtain a coating slurry; S3. The coating slurry is coated on one side of a polyethylene-based film at a coating speed of 30 m / min to obtain a coating with a thickness of 3 μm. The coating is baked at 80° C. for 1 min to obtain a lithium battery separator.

[0035] Example 4 The only difference between this embodiment and embodiment 2 is that, in this embodiment, 5 parts of rice-grained alumina and 25 parts of spherical alumina are added.

[0036] Example 5 The only difference between this embodiment and embodiment 2 is that, in this embodiment, 2 parts of rice-grained alumina and 28 parts of spherical alumina are added.

[0037] Example 6 The only difference between this embodiment and embodiment 4 is that in this embodiment, the alumina is composite alumina, and the preparation method of the composite alumina includes the following steps: A1. Disperse 30 parts of alumina (the weight ratio of rice-shaped alumina to spherical alumina is 1:5) in 50 parts of water, add 0.6 parts of γ-aminopropyltriethoxysilane, and mix well to obtain a mixed solution I. A2. Disperse 3 parts of aluminum triacetylacetonate in 10 parts of ethanol to obtain a mixed solution II; A3. Add mixed solution II to mixed solution I, stir evenly, concentrate, and dry to obtain composite alumina.

[0038] Example 7 The only difference between this embodiment and embodiment 6 is that in the preparation method of composite alumina in this embodiment, 5 parts of aluminum triacetylacetonate are added.

[0039] Example 8 The only difference between this embodiment and embodiment 6 is that in the preparation method of composite alumina in this embodiment, 6 parts of aluminum triacetylacetonate are added.

[0040] Example 9 The only difference between this embodiment and embodiment 6 is that in the preparation method of composite alumina in this embodiment, 7 parts of aluminum triacetylacetonate are added.

[0041] Comparative Example 1 The only difference between this comparative example and Example 2 is that in this comparative example, the rice-grained alumina with a particle size D50 of 0.876 μm and D90 of 2.123 μm is replaced by an equal amount of rice-grained alumina with a particle size D50 of 0.6 μm and D90 of 1.5 μm.

[0042] Comparative Example 2 The only difference between this comparative example and Example 2 is that in this comparative example, the rice-grained alumina with a particle size D50 of 0.876 μm and D90 of 2.123 μm is replaced by an equal amount of rice-grained alumina with a particle size D50 of 2 μm and D90 of 4 μm.

[0043] Comparative Example 3 The only difference between this comparative example and Example 2 is that in this comparative example, the spherical alumina with a particle size D50 of 0.496 μm and D90 of 1.064 μm is replaced by an equal amount of spherical alumina with a particle size D50 of 0.2 μm and D90 of 0.7 μm.

[0044] Comparative Example 4 The only difference between this comparative example and Example 2 is that in this comparative example, the spherical alumina with a particle size D50 of 0.496 μm and D90 of 1.064 μm is replaced by an equal amount of spherical alumina with a particle size D50 of 0.8 μm and D90 of 2 μm.

[0045] Comparative Example 5 The only difference between this comparative example and Example 2 is that in this comparative example, the rice-grained alumina with a particle size D50 of 0.876 μm and D90 of 2.123 μm is replaced by an equal amount of spherical alumina with a particle size D50 of 0.496 μm and D90 of 1.064 μm.

[0046] Comparative Example 6 The only difference between this comparative example and Example 2 is that in this comparative example, the spherical alumina with a particle size D50 of 0.496 μm and D90 of 1.064 μm is replaced by an equal amount of rice-grained alumina with a particle size D50 of 0.876 μm and D90 of 2.123 μm.

[0047] Experimental Example 1 The lithium battery separators prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were subjected to transverse (TD) and longitudinal (MD) heat shrinkage test according to the test method in GB / T 36363-2018 "Polyolefin Separators for Lithium Ion Batteries". The size of the lithium battery separator sample was 100 mm × 100 mm, and the thickness was 10 μm. The test results of transverse and longitudinal heat shrinkage were the average values ​​of three samples. The test results are shown in Table 1: Table 1 Heat resistance test results of Examples 1 to 5 and Comparative Examples 1 to 6

[0048] As can be seen from Table 1, compared with Comparative Examples 1 to 6, the shrinkage rate of the lithium battery separator prepared in Examples 1 to 5 is significantly reduced, indicating that the alumina includes two different shapes of alumina, rice-grained alumina and spherical alumina, and when the particle size D50 of the rice-grained alumina is adjusted to 0.7~1.5μm and D90 to 2.0~3.0μm, and the particle size D50 of the spherical alumina is adjusted to 0.4~0.6μm and D90 to 0.8~1.5μm, the heat resistance of the lithium battery separator can be effectively improved by using two aluminas with different shapes and particle sizes in combination.

[0049] Experimental Example 2 The lithium battery separators prepared in Examples 4 and 6 to 9 were subjected to a needle puncture strength test according to the test method in GB / T 36363-2018 "Polyolefin separators for lithium ion batteries". The thickness of the separator was 10 μm and the puncture rate was 110 mm / min. The test results are shown in Table 2: Table 2 Puncture resistance test results of Example 4 and Examples 6 to 9

[0050] As can be seen from Table 2, compared with Example 4, the puncture strength of the lithium battery separators prepared in Examples 6 to 9 is improved, indicating that the composite treatment of alumina with aluminum triacetylacetonate can effectively improve the puncture resistance of the lithium battery separator, and increase its puncture strength to above 13.2N.

[0051] Experimental Example 3 The lithium battery separator prepared in Example 2 was also subjected to the following performance tests: ① Air permeability test: The air permeability of lithium battery separators was tested according to the method in GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries". The separator sample size was 100 mm × 100 mm, and the test result was the average value of three samples. ② Liquid absorption and retention rate test: Cut a lithium battery separator sample with a size of 50mm×50mm, weigh the cut sample and record the mass as m1, and soak the weighed separator in the electrolyte for 30 minutes; Lay a layer of industrial wipe paper (size > 100mm×100mm) on the table, take out the soaked lithium battery separator sample, place it on the industrial wipe paper, and use another piece of industrial wipe paper to wipe the free electrolyte on the surface of the lithium battery separator sample. Weigh the dried separator sample and record the mass as m2; leave it for 1 hour, weigh it, and record the mass as m3; calculate the liquid absorption rate and liquid retention rate of the lithium battery separator according to the following formula: liquid absorption rate (%) = (m2-m1) / m1×100%, liquid retention rate (%) = (m3-m1) / m1×100%. The test results of liquid absorption rate and liquid retention rate are the average of 3 parallel lithium battery separator samples, and the calculation results are rounded to one decimal place; ③ Ionic conductivity test: The ionic conductivity of lithium battery separators was tested according to the method in GB / T 36363-2018 "Polyolefin separators for lithium ion batteries"; The test results are shown in Table 3: Table 3 Performance test results of Example 2

[0052] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium battery separator, obtained by coating a coating slurry on one side of a base film, characterized in that: The coating slurry comprises the following components in parts by weight: 30 parts of aluminum oxide, 5-10 parts of binder, 0.1-1 parts of dispersant, 5-10 parts of thickener, 0.01-0.1 parts of wetting agent, 40-90 parts of water; The alumina includes rice-shaped alumina and spherical alumina; The particle size of the rice-grained aluminum oxide is: D50 is 0.7-1.5 μm, D90 is 2.0-3.0 μm; The particle size of the spherical alumina is: D50 is 0.4-0.6 μm, and D90 is 0.8-1.5 μm.

2. A lithium battery separator according to claim 1, characterized in that: The weight ratio of the rice-shaped alumina to the spherical alumina is 1:2-14.

3. A lithium battery separator according to claim 1, characterized in that: The alumina is composite alumina, and the raw materials of the composite alumina include alumina and aluminum triacetylacetonate in a weight ratio of 30:3-7.

4. A lithium battery separator according to claim 3, characterized in that: The preparation method of the composite alumina comprises the following steps: A1. After dispersing the aluminum oxide in water, add a silane coupling agent and mix well to obtain a mixed solution I; A2, dispersing the aluminum triacetylacetonate in ethanol to obtain a mixed solution II; A3. Add the mixed solution II to the mixed solution I, stir evenly, concentrate, and dry to obtain the composite alumina.

5. The lithium battery separator according to claim 1, characterized in that: The binder includes one or both of polyvinyl alcohol and sodium alginate.

6. The lithium battery separator according to claim 1, characterized in that: The dispersant includes one or both of ammonium polyacrylate and sodium polyacrylate.

7. The lithium battery separator according to claim 1, characterized in that: The thickener includes one or more of lithium carboxymethyl cellulose aqueous solution, carboxymethyl cellulose aqueous solution, and sodium carboxymethyl cellulose aqueous solution.

8. The lithium battery separator according to claim 1, characterized in that: The wetting agent includes polyether-modified silicone.

9. A method for preparing a lithium battery separator, for preparing a lithium battery separator according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, mixing the dispersant, water and aluminum oxide uniformly to obtain a mixed solution; S2, adding a binder, a thickener and a wetting agent to the mixed solution, mixing them evenly to obtain a coating slurry; S3. Coating the coating slurry on one side of a base film and drying the base film to obtain the lithium battery separator.

10. The method for preparing a lithium battery separator according to claim 9, characterized in that: In step S1, the mixing is carried out by stirring, the rotation speed of the stirring is 1500-3000 r / min, and the stirring time is 30-60 min; In step S2, the mixing is uniformly carried out by stirring and ultrasonication, the rotation speed of the stirring is 1000-2000 r / min, the revolution speed is 40-60 r / min, the ultrasonic frequency is 5-8 kHz, and the mixing time is 30-60 min.

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