Battery diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a battery diaphragm, a preparation method of the battery diaphragm and a lithium ion battery, and the battery diaphragm comprises a flexible film substrate, and a ceramic coating and a polydopamine coating which are sequentially arranged on the surface of the film substrate from inside to outside. According to the technical scheme, the ceramic coating and the polydopamine coating are compounded on the membrane substrate, so that the electrolyte affinity and the thermal stability of the battery diaphragm can be effectively improved, and the electrochemical performance and the use safety of a battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to battery separators and their preparation methods, and lithium-ion batteries. Background Technology

[0002] In recent years, with the gradual expansion and development of the new energy industry, lithium-ion batteries have been widely used in consumer electronics, new energy vehicles, energy storage systems, and industrial fields. The safety of lithium-ion batteries has always been a key performance focus during battery research and development. A lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte solution, and a separator. The separator, as a crucial component of the battery, serves two functions: isolating the positive and negative electrodes to prevent short circuits and providing migration pathways for lithium ions. Numerous studies have focused on improving the safety of lithium-ion batteries by modifying the separator.

[0003] The lithium-ion battery separators used in the industry are typically polyolefin microporous membranes, which have certain cost advantages and basic electrode isolation functions. However, this type of separator has two shortcomings. First, the separator itself lacks polar groups, resulting in insufficient electrolyte wettability and interfacial compatibility. Second, the separator has a low melting point (130-140℃), making it flammable and having poor thermal stability.

[0004] Therefore, developing safe and reliable lithium-ion batteries requires improving the electrolyte affinity and thermal stability of the battery separator. Summary of the Invention

[0005] This application proposes a battery separator and its preparation method, as well as a lithium-ion battery, aiming to improve the electrolyte affinity and thermal stability of the battery separator.

[0006] In a first aspect, embodiments of this application provide a battery separator, including a flexible membrane substrate and a ceramic coating and a polydopamine coating disposed sequentially from the inside to the outside on the surface of the membrane substrate.

[0007] In some embodiments, the ceramic coating comprises one or more materials selected from alumina, zirconium oxide, silicon oxide, cerium oxide, magnesium oxide, barium sulfate, and barium titanate.

[0008] In some embodiments, the ceramic coating is an alumina layer, the alumina layer comprising a first particle and a second particle, the first particle being an alumina particle with a particle size of less than 0.1 μm, the second particle being an alumina particle with a particle size of 0.1 μm to 1.0 μm, wherein the mass content of the first particle in the alumina layer is 10% to 40%, and the mass content of the second particle is 50% to 80%.

[0009] In some embodiments, the particle size of the first particle is D1, the particle size of the second particle is D2, and D1 / D2 = 0.10~0.20.

[0010] In some embodiments, the membrane substrate includes one or more materials selected from polyethylene, polypropylene, polyvinylidene fluoride, and polyimide.

[0011] In some embodiments, the thickness of the ceramic coating does not exceed 2.5 μm.

[0012] In some embodiments, the thickness of the polydopamine coating does not exceed 2.5 μm.

[0013] Secondly, embodiments of this application provide a method for preparing the battery separator described in the first aspect, comprising the following steps: A flexible membrane substrate is provided, on which a ceramic coating is disposed; A polydopamine coating is provided on the surface of the ceramic coating.

[0014] In some embodiments, the step of forming a ceramic coating on the membrane substrate includes: preparing a ceramic coating liquid, coating the ceramic coating liquid onto the surface of the membrane substrate, drying, and forming a ceramic coating on the membrane substrate. The ceramic coating liquid includes ceramic material, binder, and wetting agent. The ceramic material includes one or more of alumina, zirconium oxide, silicon oxide, cerium oxide, magnesium oxide, barium sulfate, and barium titanate.

[0015] In some embodiments, the ceramic coating liquid includes a ceramic material, which includes a first particle and a second particle. The first particle is an alumina particle with a particle size of less than 0.1 μm, and the second particle is an alumina particle with a particle size of 0.1 μm to 1.0 μm. In the ceramic material, the mass content of the first particle is 10% to 40%, and the mass content of the second particle is 50% to 80%.

[0016] In some embodiments, the ceramic coating liquid includes ceramic material, binder and wetting agent, wherein the binder accounts for 8 to 12 wt% of the total solid content of the ceramic coating liquid.

[0017] In some embodiments, the ceramic coating liquid includes ceramic material, binder and wetting agent, wherein the wetting agent accounts for 0.05 to 0.15 wt% of the total solid content of the ceramic coating liquid.

[0018] In some embodiments, the step of forming a polydopamine coating on the ceramic coating surface includes: The expected amount of dopamine monomer was dissolved in a Tris buffer solution with a pH between 8.5 and 8.8 to form a dopamine coating solution of a predetermined concentration; The film substrate with the ceramic coating is placed in the dopamine coating solution and subjected to an oscillation reaction on a constant temperature shaker. After washing and drying, a polydopamine coating is formed on the surface of the ceramic coating.

[0019] Thirdly, embodiments of this application also propose a lithium-ion battery, including the battery separator as described in the first aspect.

[0020] Compared with the prior art, this technical solution has at least the following technical advantages: In this application, by composite ceramic coating and polydopamine coating on the membrane substrate, the electrolyte affinity and thermal stability of the battery separator can be effectively improved, thereby enhancing the electrochemical performance and safety of the battery. Specifically, by composite rigid ceramic coating on a flexible membrane substrate, the high-temperature resistance of the battery separator can be improved, effectively preventing battery separator shrinkage, reducing the risk of thermal runaway, delaying the occurrence of thermal runaway, and reducing the runaway peak temperature; it can also enhance the tensile strength and puncture resistance of the battery separator, thereby better resisting lithium dendrite puncture generated during battery cycling and reducing the risk of short circuit; and it can improve the wettability and electrolyte retention of the battery separator, increase ionic conductivity, and thus improve the rate performance and cycle life of the battery; in addition, the ceramic coating can also neutralize trace amounts of hydrofluoric acid (HF) in the electrolyte, reduce corrosion of internal battery materials, inhibit battery gas expansion, and extend battery life. Polydopamine contains functional groups such as catechol and amino groups, which provide hydrophilicity and metal ion coordination ability. In addition, it mimics the characteristics of mussel adhesive proteins and has a strong adhesion to various membrane substrates. Therefore, by further setting a polydopamine coating on the ceramic coating, the adhesion of the coating to the membrane substrate surface can be improved, and the electrolyte affinity of the battery separator can be further enhanced. Attached Figure Description

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Figure 1 This is a process flow diagram of the battery separator fabrication process in the embodiments of this application; Figure 2 This is a process flow diagram of the battery separator fabrication process in one embodiment of this application. Detailed Implementation

[0023] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0026] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0027] The lithium-ion battery separators used in the industry are typically polyolefin microporous membranes, which have certain cost advantages and basic electrode isolation functions. However, this type of separator has two shortcomings. First, the separator itself lacks polar groups, resulting in insufficient electrolyte wettability and interfacial compatibility. Second, the separator has a low melting point (130-140℃), making it flammable and having poor thermal stability.

[0028] Based on this, in a first aspect, embodiments of this application propose a battery separator.

[0029] In this embodiment, the battery separator includes a flexible membrane substrate and a ceramic coating and a polydopamine coating disposed sequentially from the inside to the outside on the surface of the membrane substrate.

[0030] In this application, by composite ceramic coating and polydopamine coating on the membrane substrate, the electrolyte affinity and thermal stability of the battery separator can be effectively improved, thereby enhancing the electrochemical performance and safety of the battery. Specifically, by composite rigid ceramic coating on a flexible membrane substrate, the high-temperature resistance of the battery separator can be improved, effectively preventing battery separator shrinkage, reducing the risk of thermal runaway, delaying the occurrence of thermal runaway, and reducing the runaway peak temperature; it can also enhance the tensile strength and puncture resistance of the battery separator, thereby better resisting lithium dendrite puncture generated during battery cycling and reducing the risk of short circuit; and it can improve the wettability and electrolyte retention of the battery separator, increase ionic conductivity, and thus improve the rate performance and cycle life of the battery; in addition, the ceramic coating can also neutralize trace amounts of hydrofluoric acid (HF) in the electrolyte, reduce corrosion of internal battery materials, inhibit battery gas expansion, and extend battery life. Polydopamine contains functional groups such as catechol and amino groups, which provide hydrophilicity and metal ion coordination ability. In addition, it mimics the characteristics of mussel adhesive proteins and has a strong adhesion to various membrane substrates. Therefore, by further setting a polydopamine coating on the ceramic coating, the adhesion of the coating to the membrane substrate surface can be improved, and the electrolyte affinity of the battery separator can be further enhanced.

[0031] In some embodiments, the membrane substrate includes one or more materials selected from polyethylene (PE), polypropylene (PP), polyvinylidene fluoride (PVDF), and polyimide (PI).

[0032] In some embodiments, the ceramic coating includes one or more materials selected from alumina, zirconium oxide, silicon oxide, cerium oxide, magnesium oxide, barium sulfate, and barium titanate.

[0033] In some embodiments, the ceramic coating is an alumina layer, which includes a first particle and a second particle. The first particle is an alumina particle with a particle size of less than 0.1 μm, and the second particle is an alumina particle with a particle size of 0.1 μm to 1.0 μm (inclusive). In the alumina layer, the mass content of the first particle is 10% to 40%, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any value between them, and the mass content of the second particle is 50% to 80%, specifically 50%, 60%, 70%, 80%, or any value between them.

[0034] In the above embodiments, a "synergistic filling effect" is formed between the first particle and the second particle. The second particle constitutes the skeleton structure of the alumina layer, and the first particle fills the gaps in the skeleton structure. This is beneficial to the improvement of the battery separator's air permeability, coating peeling force, electrolyte retention capacity, and thermal shrinkage performance.

[0035] In some embodiments, the particle size of the first particle is D1, and the particle size of the second particle is D2, where D1 / D2 = 0.10~0.20, specifically 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, or any value between them. Controlling the particle size ratio of the first and second particles within the above range is more beneficial for improving the electrolyte affinity and thermal stability of the battery separator.

[0036] In some embodiments, the thickness of the ceramic coating does not exceed 2.5 μm; and / or, the thickness of the polydopamine coating does not exceed 2.5 μm.

[0037] In some embodiments, the mass ratio of the membrane substrate, ceramic coating, and polydopamine coating in the battery separator is (80~95):(2~6):(5~15). Specifically, the mass fraction of the membrane substrate can be 80, 82, 84, 86, 88, 90, 92, 95, or any value between them; the mass fraction of the ceramic coating can be 2, 3, 4, 5, 6, or any value between them; and the mass fraction of the polydopamine coating can be 5, 7, 9, 11, 13, 15, or any value between them. Within this mass ratio range, it is beneficial to improve the electrolyte affinity and thermal stability of the battery separator.

[0038] Secondly, this application also proposes a method for preparing the above-mentioned battery separator.

[0039] Please see Figure 1 In this embodiment of the application, the method for preparing the battery separator includes the following steps: S10. A flexible membrane substrate is provided, and a ceramic coating is disposed on the membrane substrate; S20. A polydopamine coating is applied to the surface of the ceramic coating.

[0040] In this embodiment of the application, the step of forming a ceramic coating on the membrane substrate includes: preparing a ceramic coating liquid, coating the ceramic coating liquid onto the surface of the membrane substrate, drying, and forming a ceramic coating on the membrane substrate.

[0041] In some embodiments, the ceramic coating liquid includes a ceramic material, a binder, and a wetting agent. The ceramic material includes one or more of alumina, zirconium oxide, silicon oxide, cerium oxide, magnesium oxide, barium sulfate, and barium titanate.

[0042] Please see Figure 2 In some embodiments, the ceramic coating liquid includes a ceramic material, which includes first particles and second particles. The first particles are alumina particles with a particle size of less than 0.1 μm, and the second particles are alumina particles with a particle size of 0.1 μm to 1.0 μm. In the ceramic material, the mass content of the first particles is 10% to 40%, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any value between them; the mass content of the second particles is 50% to 80%, specifically 50%, 60%, 70%, 80%, or any value between them.

[0043] In the above embodiments, a "synergistic filling effect" is formed between the first particle and the second particle. The second particle constitutes the skeleton structure of the alumina layer, and the first particle fills the gaps in the skeleton structure. This is beneficial to the improvement of the battery separator's air permeability, coating peeling force, electrolyte retention capacity, and thermal shrinkage performance.

[0044] In some embodiments, the particle size of the first particle is D1, and the particle size of the second particle is D2, where D1 / D2 = 0.10~0.20, specifically 0.10, 0.12, 0.14, 0.16, 0.18, 0.20, or any value between them. Controlling the particle size ratio of the first and second particles within the above range is more beneficial for improving the electrolyte affinity and thermal stability of the battery separator.

[0045] In some embodiments, the ceramic coating liquid includes ceramic material and binder, wherein the binder accounts for 8 to 12 wt% of the total solid content of the ceramic coating liquid, specifically 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, or any value between them.

[0046] In some embodiments, the ceramic coating solution further includes a wetting agent, which accounts for 0.05 to 0.15 wt% of the total solid content of the ceramic coating solution, specifically 0.05 wt%, 0.07 wt%, 0.09 wt%, 0.11 wt%, 0.13 wt%, 0.15 wt%, or any value between them. Adding a wetting agent helps improve the electrolyte retention capacity of the battery separator.

[0047] In some embodiments, the step of forming a polydopamine coating on the surface of a ceramic coating includes: The expected amount of dopamine monomer was dissolved in a Tris buffer solution with a pH between 8.5 and 8.8 to form a dopamine coating solution of a predetermined concentration; The film substrate with ceramic coating is placed in dopamine coating solution and subjected to oscillation reaction on a constant temperature shaker. After washing and drying, a polydopamine coating is formed on the surface of the ceramic coating.

[0048] In some embodiments, the concentration of the dopamine coating solution is 1.5 mg / mL to 2.5 mg / mL, specifically 1.5 mg / mL, 1.7 mg / mL, 1.9 mg / mL, 2.1 mg / mL, 2.3 mg / mL, 2.5 mg / mL, or any value between them.

[0049] In some embodiments, the temperature at which the oscillation reaction is carried out on a constant-temperature shaker is 25°C.

[0050] In some embodiments, the period for oscillation reaction on a constant temperature shaker is 8h to 24h, specifically 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h or any value between them.

[0051] Thirdly, this application also proposes a lithium-ion battery, which includes a battery separator. The specific structure and preparation method of the battery separator are as described in the above embodiments. Since the lithium-ion battery adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0052] Example 1 A battery separator, the preparation method of which includes the following steps: (1) Preparation of ceramic coating liquid: First alumina particles (particle size of 0.05 μm) and second alumina particles (particle size of 0.5 μm) are dispersed in deionized water and stirred at a certain speed for 24 h. Lithium polyacrylate binder and wetting agent are added to the dispersion in sequence to obtain ceramic coating liquid. In the ceramic coating liquid, the binder, wetting agent, first alumina particles and second alumina particles account for 10 wt%, 0.1 wt%, 10 wt% (W1) and 79.9 wt% (W2) of the total solid content of the ceramic coating liquid, respectively.

[0053] (2) Using a coating machine, set the coating thickness and uniformly coat Al2O3 onto one side of the PP film substrate at a certain travel speed. Place the coated PP film substrate in an oven to dry overnight, and a ceramic coating will be formed on the surface of the PP film substrate.

[0054] (3) Preparation of dopamine coating solution: Dissolve a certain amount of dopamine monomer in Tris buffer solution with pH between 8.5 and 8.8 to form a 2 mg / mL dopamine coating solution.

[0055] (4) Place the PP film substrate with ceramic coating on the surface obtained in step (2) into the dopamine coating solution obtained in step (3), and shake it at a certain speed at 25°C for 12 h on a constant temperature shaker. Turn the membrane over every 4 h to ensure that polydopamine is uniformly coated on the surface of the membrane. After coating, wash with pure water and dry it to form a polydopamine coating on the surface of the ceramic coating, thus obtaining the battery membrane.

[0056] In the battery separator prepared in Example 1, the solid content of PP was 95 wt%, the solid content of DA (polydopamine) was 5 wt%, and the solid content of Al2O3 was 2 wt%.

[0057] Example 2 The difference from Example 1 is that: The thickness ratio of the PP membrane substrate, ceramic coating and polydopamine coating in the battery separator was adjusted so that the solid content of PP in the battery separator prepared in Example 1 was 90wt%, the solid content of DA (polydopamine) was 10wt%, and the solid content of Al2O3 was 4wt%.

[0058] Example 3 The difference from Example 1 is that: The thickness ratio of the PP membrane substrate, ceramic coating and polydopamine coating in the battery separator was adjusted so that the solid content of PP in the battery separator prepared in Example 1 was 85wt%, the solid content of DA (polydopamine) was 15wt%, and the solid content of Al2O3 was 6wt%.

[0059] Example 4 The difference from Example 1 is that: (1) Preparation of ceramic coating liquid: First alumina particles (particle size D1 is 0.05 μm) and second alumina particles (particle size D2 is 0.5 μm) are dispersed in deionized water and stirred at a certain speed for 24 h. Lithium polyacrylate binder and wetting agent are added to the dispersion in sequence to obtain ceramic coating liquid. In the ceramic coating liquid, the binder, wetting agent, first alumina particles and second alumina particles account for 10 wt%, 0.1 wt%, 40 wt% (W1) and 49.9 wt% (W2) of the total solid content of the ceramic coating liquid, respectively.

[0060] Example 5 The difference from Example 1 is that: (1) Preparation of ceramic coating liquid: First alumina particles (particle size D1 is 0.05 μm) and second alumina particles (particle size D2 is 0.5 μm) are dispersed in deionized water and stirred at a certain speed for 24 h. Lithium polyacrylate binder and wetting agent are added to the dispersion in sequence to obtain ceramic coating liquid. In the ceramic coating liquid, the binder, wetting agent, first alumina particles and second alumina particles account for 10 wt%, 0.1 wt%, 79.9 wt% (W1) and 10 wt% (W2) of the total solid content of the ceramic coating liquid, respectively.

[0061] Example 6 The difference from Example 1 is that: (1) Preparation of ceramic coating liquid: The first alumina particles (particle size D1 is 0.09 μm) and the second alumina particles (particle size D2 is 0.9 μm) are dispersed in deionized water and stirred at a certain speed for 24 h. The lithium polyacrylate binder and wetting agent are added to the dispersion in sequence to obtain the ceramic coating liquid. In the ceramic coating liquid, the binder, wetting agent, first alumina particles and second alumina particles account for 10 wt%, 0.1 wt%, 10 wt% (W1) and 79.9 wt% (W2) of the total solid content of the ceramic coating liquid, respectively.

[0062] Example 7 The difference from Example 1 is that: (1) Preparation of ceramic coating liquid: First alumina particles (particle size D1 is 0.09 μm) and second alumina particles (particle size D2 is 0.5 μm) are dispersed in deionized water and stirred at a certain speed for 24 h. Lithium polyacrylate binder and wetting agent are added to the dispersion in sequence to obtain ceramic coating liquid. In the ceramic coating liquid, the binder, wetting agent, first alumina particles and second alumina particles account for 10 wt%, 0.1 wt%, 10 wt% (W1) and 79.9 wt% (W2) of the total solid content of the ceramic coating liquid, respectively.

[0063] Example 8 The difference from Example 1 is that: (1) Preparation of ceramic coating liquid: The first alumina particles (particle size D1 is 0.05 μm) and the second alumina particles (particle size D2 is 1 μm) are dispersed in deionized water and stirred at a certain speed for 24 h. The lithium polyacrylate binder and wetting agent are added to the dispersion in sequence to obtain the ceramic coating liquid. In the ceramic coating liquid, the binder, wetting agent, first alumina particles and second alumina particles account for 10 wt%, 0.1 wt%, 10 wt% (W1) and 79.9 wt% (W2) of the total solid content of the ceramic coating liquid, respectively.

[0064] Comparative Example 1 PP film substrate is used as battery separator.

[0065] Comparative Example 2 A battery separator, the preparation method of which includes the following steps: (1) Preparation of ceramic coating liquid: First alumina particles (particle size of 0.05 μm) and second alumina particles (particle size of 0.5 μm) are dispersed in deionized water and stirred at a certain speed for 24 h. Lithium polyacrylate binder and wetting agent are added to the dispersion in sequence to obtain ceramic coating liquid. In the ceramic coating liquid, the binder, wetting agent, first alumina particles and second alumina particles account for 10 wt%, 0.1 wt%, 10 wt% (W1) and 79.9 wt% (W2) of the total solid content of the ceramic coating liquid, respectively.

[0066] (2) Using a coating machine, set the coating thickness and uniformly coat Al2O3 onto one side of the PP film substrate at a certain travel speed. Place the coated PP film substrate in an oven to dry overnight, and a ceramic coating will be formed on the surface of the PP film substrate.

[0067] In the battery separator prepared in Comparative Example 2, the solid content of PP was 100 wt%, the solid content of DA (polydopamine) was 0 wt%, and the solid content of Al2O3 was 2 wt%.

[0068] Comparative Example 3 The difference from Comparative Example 1 is that: In the battery separator prepared in Comparative Example 3, the solid content of PP was 100 wt%, the solid content of DA (polydopamine) was 0 wt%, and the solid content of Al2O3 was 4 wt%.

[0069] Comparative Example 4 The difference from Comparative Example 1 is that: In the battery separator prepared in Comparative Example 4, the solid content of PP was 100 wt%, the solid content of DA (polydopamine) was 0 wt%, and the solid content of Al2O3 was 6 wt%.

[0070] Comparative Example 5 The difference from Example 1 is as follows: The ceramic coating and polydopamine coating are applied in different orders: the polydopamine coating is applied first on the PP film substrate, and then the ceramic coating is applied on the polydopamine coating.

[0071] Performance testing 1. Testing method: a. Thermal shrinkage rate The battery separator was placed in a 200℃ forced-air oven for 30 minutes and then removed. The area of ​​the battery separator before and after heat treatment was measured, and the thermal shrinkage rate of the battery separator at this temperature was calculated using formula (1-1). Thermal shrinkage rate (%) = (S0 - S1 / S0) 100% (1-1) Where S1 is the area of ​​the diaphragm after heat treatment, and S0 is the initial area of ​​the diaphragm.

[0072] b. Liquid absorption rate The wettability of the battery separator can be mainly determined by the electrolyte absorption rate. The test method for the absorption rate is as follows: Weigh the dried battery separator (M0) beforehand, then immerse it in the electrolyte for 1 hour. After wiping off the excess electrolyte on the surface of the battery separator, weigh it again (M1). Calculate the absorbance rate of the separator using formula (1-2): Liquid absorption rate (%) = (M1 - M0) / M0 × 100% (1-2) Table 1. Test results of Examples 1-3 and Comparative Examples 1-4

[0073] Table 2. Test results of Examples 1, 4-8 and Comparative Examples 5-6

[0074] By comparing Examples 1-3 and Comparative Examples 1-4, it can be demonstrated that when the mass ratio of membrane substrate, ceramic coating and polydopamine coating in the battery separator is close to (80~95):(2~6):(5~15), it is beneficial to improve the electrolyte affinity and thermal stability of the battery separator.

[0075] By comparing Example 1 with Comparative Example 5, it can be demonstrated that compared to first setting a ceramic coating on the membrane substrate and then setting a polydopamine coating, it is more beneficial to enhance the adhesion between the membrane substrate and its surface membrane layer, thereby making the improvement of electrolyte affinity and thermal stability of the battery separator more significant.

[0076] By comparing Example 1 with Examples 4-8, it can be demonstrated that when the ceramic coating is an alumina layer, controlling the mass content of the first particle in the range of 10% to 40%, controlling the mass content of the second particle in the range of 50% to 80%, and controlling the particle size ratio of the first particle and the second particle in the range of 0.10 to 0.20 are more conducive to improving the electrolyte affinity and thermal stability of the battery separator.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A battery separator, characterized in that, It includes a flexible membrane substrate, and a ceramic coating and a polydopamine coating disposed sequentially from the inside to the outside on the surface of the membrane substrate.

2. The battery separator as described in claim 1, characterized in that, The ceramic coating comprises one or more materials selected from alumina, zirconium oxide, silicon oxide, cerium oxide, magnesium oxide, barium sulfate, and barium titanate.

3. The battery separator as described in claim 1, characterized in that, The ceramic coating is an alumina layer, which includes a first particle and a second particle. The first particle is an alumina particle with a particle size of less than 0.1 μm, and the second particle is an alumina particle with a particle size of 0.1 μm to 1.0 μm. In the alumina layer, the mass content of the first particle is 10% to 40%, and the mass content of the second particle is 50% to 80%.

4. The battery separator as described in claim 3, characterized in that, The particle size of the first particle is D1, and the particle size of the second particle is D2, where D1 / D2 = 0.10~0.

20.

5. The battery separator as described in claim 1, characterized in that, The membrane substrate includes one or more materials selected from polyethylene, polypropylene, polyvinylidene fluoride, and polyimide.

6. The battery separator according to any one of claims 1-5, characterized in that, The thickness of the ceramic coating does not exceed 2.5 μm; and / or, The thickness of the polydopamine coating does not exceed 2.5 μm.

7. A method for preparing a battery separator as described in any one of claims 1-6, characterized in that, Includes the following steps: A flexible membrane substrate is provided, on which a ceramic coating is disposed; A polydopamine coating is provided on the surface of the ceramic coating.

8. The preparation method according to claim 7, characterized in that, The step of forming a ceramic coating on the membrane substrate includes: preparing a ceramic coating solution, coating the ceramic coating solution onto the surface of the membrane substrate, and drying to form a ceramic coating on the membrane substrate; the preparation method further includes at least one of the following features (1)-(4): (1) The ceramic coating liquid includes ceramic material, binder and wetting agent, wherein the ceramic material includes one or more of alumina, zirconium oxide, silicon oxide, cerium oxide, magnesium oxide, barium sulfate and barium titanate; (2) The ceramic coating liquid includes ceramic material, which includes first particles and second particles. The first particles are alumina particles with a particle size of less than 0.1 μm, and the second particles are alumina particles with a particle size of 0.1 μm to 1.0 μm. In the ceramic material, the mass content of the first particles is 10% to 40%, and the mass content of the second particles is 50% to 80%. (3) The ceramic coating liquid includes ceramic material, binder and wetting agent, wherein the binder accounts for 8-12 wt% of the total solid content of the ceramic coating liquid; (4) The ceramic coating liquid includes ceramic material, binder and wetting agent, wherein the wetting agent accounts for 0.05~0.15 wt% of the total solid content of the ceramic coating liquid.

9. The preparation method according to claim 7, characterized in that, The step of applying a polydopamine coating to the surface of the ceramic coating includes: The expected amount of dopamine monomer was dissolved in a Tris buffer solution with a pH between 8.5 and 8.8 to form a dopamine coating solution of a predetermined concentration; The film substrate with the ceramic coating is placed in the dopamine coating solution and subjected to an oscillation reaction on a constant temperature shaker. After washing and drying, a polydopamine coating is formed on the surface of the ceramic coating.

10. A lithium-ion battery, characterized in that, Includes the battery separator as described in any one of claims 1-6.

Images