Battery separator, method for manufacturing the same, and secondary battery

Abstract

The present application relates to the technical field of battery, especially to a battery separator, a preparation method thereof and a secondary battery. The battery separator comprises a base film and a coating layer arranged on at least one side surface of the base film; the coating layer comprises non-fluoropolymer particles and inorganic filler particles modified by a silane coupling agent; the surface density of the coating layer is 1.5-2.5 g / m 2 ; the mass proportion of the non-fluoropolymer particles in the coating layer is 10%-25%; the non-fluoropolymer particles are secondary agglomerated particles formed by primary particles; the D50 particle size of the primary particles is 0.4-0.6 μm; the secondary agglomerated particles satisfy the condition (D90-D10) / D50<1.3; and the glass transition temperature Tg of the secondary agglomerated particles is -5-5 ℃. The battery separator has excellent heat resistance and adhesion to the pole piece, and the secondary battery using the battery separator has more excellent cycle performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a battery separator, its preparation method, and a secondary battery. Background Technology

[0002] As one of the core components of a battery, the performance parameters of the separator directly affect various aspects of battery performance. Among these, the heat resistance of the separator is crucial to battery safety. Current technologies typically involve constructing a ceramic layer on the surface of the base membrane and further modifying it with an organic binder layer to improve the separator's heat resistance while ensuring adhesion between the separator and the electrode.

[0003] With the increasing urgency of cost reduction and efficiency improvement in the battery industry, separator manufacturing processes are also evolving towards higher efficiency. Traditional step-by-step coating processes are gradually being replaced by one-step coating technology. This technology prepares functional coatings by premixing ceramics and organic binders to form a composite slurry and then applying it in a single coat. For example, in Chinese patent application CN109065804A, a functional coating is obtained by mixing ceramics and aqueous PVDF emulsion and then applying it in a single coat. With the deepening implementation of the ban on fluorine, the application of fluorinated binder systems is strictly limited. Against this backdrop, non-fluorinated binders such as PMMA have gained widespread application in the separator field. For example, in the Chinese patent application with publication number CN115483500A, a coating is prepared by mixing PMMA with ceramic particles of a single size and then coating it in a single application. However, this technology still has the following problems in practical applications: as the PMMA particle size increases, the uniformity of particle distribution decreases, resulting in poor consistency of membrane thickness; large-sized particles are prone to encapsulating unreacted monomers, causing gas generation problems during cell cycling; excessively large particle size will significantly increase ion transport impedance, thereby causing safety hazards such as lithium plating.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a battery separator, its preparation method, and a secondary battery. The battery separator of this invention has good thickness uniformity, good heat resistance, and good adhesion. The secondary battery made using the battery separator of this invention has good cycle performance.

[0006] To achieve the above-mentioned objectives of the present invention, a first aspect of the present invention provides a battery separator, comprising a base film and a coating disposed on at least one surface of the base film; the coating comprises non-fluoropolymer particles and silane coupling agent modified inorganic filler particles, and the areal density of the coating is 1.5–2.5 g / m³. 2 In the coating, the non-fluoropolymer particles account for 10% to 25% by mass.

[0007] The non-fluoropolymer particles are secondary agglomerated particles formed by the agglomeration of primary particles. The D50 particle size of the primary particles is 0.4 to 0.6 μm. The D10, D50, and D90 particle sizes of the secondary agglomerated particles satisfy the following condition: (D90-D10) / D50 < 1.3.

[0008] The glass transition temperature (Tg) of the secondary agglomerates is -5 to 5℃.

[0009] In some embodiments, the particle size of the secondary agglomerates satisfies at least one of the following characteristics:

[0010] (1) The D50 particle size is 4.0–5.5 μm;

[0011] (2) D10 particle size > 2.0 μm;

[0012] (3) D90 particle size < 10.0 μm.

[0013] In some embodiments, the non-fluoropolymer particles comprise at least two types of secondary agglomerated particles with different particle sizes, the two types of secondary agglomerated particles with different particle sizes satisfying the following characteristics (1) and (2):

[0014] (1) D50 particle size is 4.0~5.5μm; D10 particle size is >2.0μm; D90 particle size is <10.0μm;

[0015] (2) The particle size of D50 is 1.2 to 1.6 μm; the particle size of D10 is 0.5 to 1.0 μm; and the particle size of D90 is 1.8 to 2.5 μm.

[0016] In some embodiments, the primary particle has a core and a shell covering the surface of the core; the molecular chain of the core includes a first structural unit, and the molecular chain of the shell includes a first structural unit and a second structural unit; the first monomer forming the first structural unit includes at least one of methacrylonitrile, styrene, and acrylonitrile, and the second monomer forming the second structural unit includes at least one of ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, and n-butyl acrylate.

[0017] In some embodiments, the mass percentage of the first structural unit in the primary particles is 20% to 30%.

[0018] In some embodiments, the coating has a field of view of 1 mm. 2 Within the region, the number of the non-fluoropolymer particles with a particle size ≥ 1.5 μm is N1, and satisfies: 2800 ≤ N1 ≤ 31000.

[0019] In some embodiments, the coating has a field of view of 1 mm. 2Within the region, the number of non-fluoropolymer particles with a diameter D1 > 1.2H is N. 2-1 And satisfy: N 2-1 <N1, 2400≤N 2-1 ≤26500; where H is the thickness of the silane coupling agent modified inorganic filler particles in the coating.

[0020] In some embodiments, after the coating of the battery separator is bonded to the release film and subjected to hot pressing, the coating has a field of view of 1 mm. 2 Within the region, the number of non-fluoropolymer particles with a diameter D2 ≥ 1.5H is N. 2-2 And satisfy: N 2-2 <N1, 2300≤N 2-2 ≤26000; wherein, the hot pressing conditions include: hot pressing at 85°C and 1MPa for 40s.

[0021] In some embodiments, the gloss of the coating is 10 to 20 GU.

[0022] In some embodiments, the adhesion force between the battery separator and the electrode after hot pressing is 1 to 5 N / m; the hot pressing conditions include: hot pressing at 85°C and 1 MPa for 80 seconds.

[0023] In some embodiments, the silane coupling agent includes at least one selected from vinyltriethylsilane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane, trimethylmethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and ureopropyltriethoxysilane.

[0024] In some embodiments, the mass ratio of silane coupling agent to unmodified inorganic filler particles in the silane coupling agent modified inorganic filler particles is (0.01~0.05):1.

[0025] In some embodiments, the inorganic filler particles include at least one selected from boehmite, alumina, magnesium oxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP. Further, the D50 particle size of the inorganic filler particles is 0.5–1.0 μm.

[0026] In some embodiments, the silane coupling agent modified inorganic filler particles account for 66% to 88% of the mass of the coating.

[0027] In some embodiments, the coating further includes at least one of an adhesive, a wetting agent, and a dispersant. Further, in the coating, the mass percentages of the adhesive, wetting agent, and dispersant are 3%–8%, 0.1%–0.5%, and 0.2%–0.6%, respectively.

[0028] In some embodiments, the base film includes at least one of a polyethylene base film and a polypropylene base film. Further, the thickness of the base film is 5–16 μm.

[0029] The second aspect of the present invention provides a method for preparing the battery separator provided in the first aspect of the present invention, comprising the following steps: mixing an emulsion containing non-fluoropolymer particles with inorganic filler particles modified by a silane coupling agent to obtain a slurry, coating the slurry onto at least one side surface of a base film, and drying to obtain the battery separator.

[0030] In some embodiments, the method for preparing the emulsion containing non-fluoropolymer particles includes:

[0031] (a) An emulsifier, a first monomer, and a first initiator undergo a first polymerization reaction in a solvent to obtain a first emulsion; the first emulsion, the first monomer, the second monomer, and the second initiator are mixed and undergo a second polymerization reaction to obtain an emulsion containing primary particles;

[0032] (b) The emulsion containing primary particles is mixed and stirred with salt substances to obtain an emulsion containing non-fluoropolymer particles.

[0033] A third aspect of the present invention provides a secondary battery, including the battery separator described in the first aspect of the present invention.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) In the coating of the battery separator of the present invention, non-fluorinated polymer particles and inorganic filler particles are combined. The secondary agglomerated non-fluorinated polymer particles formed by the agglomeration of primary particles have an effective channel for ions to pass through, which helps to improve the ionic conductivity of the battery separator. At the same time, the particle size and Tg of the non-fluorinated polymer particles of the present invention meet certain requirements, ensuring the concentration of the non-fluorinated polymer particle size, which helps to improve the overall thickness consistency of the battery separator and the overall hardness of the battery cell.

[0036] (2) The primary particles of the non-fluorinated polymer of the present invention have a core-shell structure. By controlling the types of monomers constituting the core-shell structure, the core-shell structure has the characteristics of being soft on the outside and hard on the inside, which can not only improve the adhesion performance of the electrode sheet, but also improve the overall hardness of the battery cell.

[0037] (3) The battery separator of the present invention achieves a better balance between heat resistance and adhesion to the electrode by adjusting the ratio of non-fluoropolymer particles and inorganic filler particles in the coating and the surface density of the coating.

[0038] (4) The secondary battery using the battery separator of the present invention has better cycle performance. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the structure of the battery separator provided in an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the structure of the non-fluoropolymer secondary agglomerated particles provided in an embodiment of the present invention;

[0042] Figure 3 The above is a DSC test image of the non-fluoropolymer particles provided in Example 6 of the present invention;

[0043] Figure 4 The particle size distribution of the emulsion containing non-fluoropolymer particles provided in Example 6 of the present invention is shown in Figure 6.

[0044] Figure 5 The particle size distribution of the emulsion containing non-fluoropolymer particles provided in Example 7 of the present invention is shown in Figure 7.

[0045] Figure 6 This is a surface SEM image of the coating of the battery separator provided in Embodiment 6 of the present invention;

[0046] Figure 7 This is a cross-sectional SEM image of the coating of the battery separator provided in Embodiment 6 of the present invention;

[0047] Figure 8 This is a surface SEM image of the coating after hot pressing of the battery separator and release film provided in Embodiment 6 of the present invention.

[0048] Figure label:

[0049] 1-Base film; 2-Non-fluoropolymer particles; 3-Inorganic filler particles; 21-Primary particles; 211-Core; 212-Outer shell. Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0051] Figure 1 This is a schematic diagram of the structure of the battery separator provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of non-fluoropolymer secondary agglomerated particles provided in an embodiment of the present invention; the first aspect of the present invention provides a battery separator, including a base film 1 and a coating disposed on at least one surface of the base film 1; the coating includes non-fluoropolymer particles 2 and silane coupling agent modified inorganic filler particles 3; the areal density of the coating is 1.5 to 2.5 g / m³. 2 In the coating, the mass percentage of non-fluoropolymer particles 2 is 10%–25%.

[0052] The non-fluoropolymer particle 2 is a secondary agglomerated particle formed by the agglomeration of primary particles 21. The D50 particle size of the primary particles 21 is 0.4 to 0.6 μm. The D10, D50 and D90 particle sizes of the secondary agglomerated particles satisfy the following: (D90-D10) / D50 < 1.3.

[0053] The glass transition temperature (Tg) of the secondary agglomerates is -5 to 5℃.

[0054] In the coating of the battery separator of this invention, a composite of non-fluoropolymer particles and inorganic filler particles is used. The secondary agglomerated non-fluoropolymer particles, formed by the agglomeration of primary particles, have effective channels for ion passage. Simultaneously, by controlling the particle size of both the primary and secondary particles to meet certain conditions, the resistance of ion shuttle passage through the polymer can be reduced, effectively preventing lithium plating and improving the overall thickness consistency of the battery separator. When the D50 particle size of the primary particles is too small, it is difficult to ensure the particle size distribution of the secondary agglomerated particles, affecting the overall thickness consistency and gloss of the battery separator. This leads to severe localized lithium plating and easily reduces the effective adhesion sites with the electrodes, affecting adhesion and thus impacting the overall cycle performance of the battery cell. Conversely, when the D50 particle size of the primary particles is too large, it also affects the particle size distribution of the secondary agglomerated particles and the number of effective adhesion sites, while also affecting ion shuttle passage and leading to localized lithium plating. The present invention controls the D50 particle size of the primary particles to be 0.4 to 0.6 μm, for example, it can be a range of 0.4 μm, 0.42 μm, 0.45 μm, 0.48 μm, 0.5 μm, 0.52 μm, 0.55 μm, 0.58 μm, 0.6 μm or any combination thereof, in order to achieve a good balance in terms of adhesion, overall thickness uniformity and lithium plating.

[0055] The non-fluorinated polymer particles of this invention meet certain requirements in terms of particle size and Tg, ensuring the concentration of non-fluorinated polymer particle size, which helps to improve the overall thickness consistency of the battery separator and the overall hardness of the battery cell. This invention controls the D10, D50, and D90 particle sizes of the secondary agglomerated particles to satisfy (D90-D10) / D50 < 1.3, for example, it can be a range of 1.25, 1.22, 1.2, 1.18, 1.15, 1.1, 1.05, 1.0, 0.95, 0.9, or any combination thereof, to ensure a certain concentration of non-fluorinated polymer particle size, improve the consistency of battery separator thickness, and avoid the negative impact of excessively small particle sizes on adhesion performance and interfacial resistance. This invention regulates the glass transition temperature (Tg) of the secondary agglomerates to -5 to 5°C, for example, it can be within the range of -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, or any combination thereof, to balance adhesion and electrolyte wettability, thereby improving the cell's cycle performance. When the Tg of the secondary agglomerates is too high, they cannot effectively adhere to the electrode; when the Tg of the secondary agglomerates is too low, the adhesion between the battery separator and the electrode increases, easily leading to a decrease in local electrolyte wettability, and the battery separator suffers from severe local pore blockage after hot pressing with the electrode, which can easily lead to lithium plating problems and affect cycle performance.

[0056] The battery separator of the present invention achieves a better balance between heat resistance and adhesion to the electrode by controlling the ratio of non-fluoropolymer particles and inorganic filler particles in the coating and the areal density of the coating. For example, in different embodiments, the areal density of the coating can be 1.5 g / m³. 2 1.8g / m 2 2g / m 2 2.2g / m 2 2.5g / m 2 Or a range of any two of them; in the coating, the mass percentage of non-fluoropolymer particles can be 10%, 12%, 15%, 18%, 20%, 22%, 25% or a range of any two of them, in order to improve the adhesion performance, heat shrinkage performance and electrolyte wettability of the battery separator.

[0057] This invention improves the dispersion performance of non-fluoropolymer particles and inorganic filler particles in the coating by modifying inorganic filler particles, thus avoiding agglomeration. At the same time, it improves the rigidity of the coating and enhances the heat resistance of the battery separator.

[0058] In some embodiments, the particle size of the secondary agglomerates satisfies at least one of the following characteristics:

[0059] (1) The D50 particle size is 4.0 to 5.5 μm, for example, it can be 4.0 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.0 μm, 5.2 μm, 5.5 μm or any combination thereof;

[0060] (2) D10 particle size > 2.0 μm, for example, it can be a range of 2.1 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm or any combination thereof;

[0061] (3) D90 particle size < 10.0 μm, for example, can be 9.9 μm, 9.6 μm, 9.4 μm, 9.2 μm, 9.0 μm, 8.5 μm, 8.0 μm, 7.5 μm or any combination thereof.

[0062] Further control of the particle size of secondary agglomerates to meet the above conditions can improve the uniformity of battery separator thickness, adhesion performance, and cycle performance of the battery cell.

[0063] In some embodiments, the non-fluoropolymer particles comprise at least two types of secondary agglomerated particles with different particle sizes, the two types of secondary agglomerated particles with different particle sizes satisfying the following characteristics (1) and (2):

[0064] (1) D50 particle size is 4.0~5.5μm; D10 particle size is >2.0μm; D90 particle size is <10.0μm;

[0065] (2) The particle size of D50 is 1.2 to 1.6 μm, for example, it can be 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm or any combination thereof; the particle size of D10 is 0.5 to 1.0 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm or any combination thereof; the particle size of D90 is 1.8 to 2.5 μm, for example, it can be 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm or any combination thereof.

[0066] The non-fluoropolymer particles of the present invention can be compounded using secondary agglomerates with large and small particle sizes. The particle size of the secondary agglomerates with large particle size satisfies the above-mentioned characteristic (1), and the particle size of the secondary agglomerates with small particle size satisfies the above-mentioned characteristic (2). Compared with using only secondary agglomerates with large particle size, the number of bonding sites of the battery separator obtained by compounding the two is relatively reduced, and the bonding force is slightly reduced, but the bonding performance requirements are still met. In addition, the battery separator still has excellent ionic conductivity and cycle performance, providing another option for the non-fluoropolymer particles used in the battery separator.

[0067] In some implementations, such as Figure 2 As shown, the primary particle 21 has a core 211 and a shell 212 covering the surface of the core 211. The molecular chain of the core includes a first structural unit, and the molecular chain of the shell includes a first structural unit and a second structural unit; the first monomer forming the first structural unit includes at least one of methacrylonitrile, styrene, and acrylonitrile, and the second monomer forming the second structural unit includes at least one of ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, and n-butyl acrylate.

[0068] The primary particles of the non-fluoropolymer of the present invention have a core-shell structure. By controlling the types of monomers constituting the core-shell structure, the core-shell structure has the characteristics of being soft on the outside and hard on the inside, which can not only improve the adhesion performance to the electrode sheet, but also improve the overall hardness of the battery cell.

[0069] In some embodiments, the mass percentage of the first structural unit in the primary particle is 20% to 30%, such as 20%, 22%, 25%, 28%, 30%, or any combination thereof. The first structural unit in the primary particle includes both the first structural unit in the core and the first structural unit in the outer shell. By optimizing the proportion of the first structural unit in the primary particle, the glass transition temperature of secondary agglomeration can be controlled, thereby improving the adhesion performance of the battery separator, the cell hardness, and the cell cycle performance.

[0070] In some embodiments, the ratio of the mass of the first and second monomers forming the outer shell to the mass of the first monomer forming the core is (6 to 9):1, for example, it can be a range of 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1 or any two of these, which helps to improve the soft outer and hard inner characteristics of the primary particles with the core-shell structure, and helps to improve the bonding performance and ensure the overall hardness of the cell.

[0071] In some embodiments, the coating is within a 1mm field of view. 2 Within the region, the number of non-fluoropolymer particles is N1, and satisfies: 2800≤N1≤31000. For example, the number of non-polymer particles can be 2800, 3000, 5000, 8000, 10000, 15000, 20000, 25000, 28000, 30000, 31000, or any combination thereof.

[0072] In some embodiments, the coating is within a 1mm field of view. 2 Within the region, the number of non-fluoropolymer particles with a diameter D1 > 1.2H is N. 2-1 And satisfy: N 2-1 <N1, 2400≤N 2-1 ≤26500, for example, can be a range of 2400, 2500, 2900, 5000, 8000, 10000, 15000, 20000, 24000, 26500 or any combination thereof; H is the thickness of the silane coupling agent modified inorganic filler particles in the coating.

[0073] In some embodiments, after the battery separator coating is bonded to the release film and subjected to hot pressing, the coating is within a 1mm field of view. 2 Within the region, the number of non-fluoropolymer particles with a diameter D2 > 1.5H is N2, and satisfies: N 2-2 <N1, 2300≤N 2-2 ≤26000, for example, can be a range of 2300, 2500, 2900, 5000, 8000, 10000, 15000, 20000, 24000, 26000 or any combination thereof; wherein, the hot pressing conditions include: hot pressing at 85℃ and 1MPa for 40s.

[0074] In some embodiments, the gloss of the coating is 10 to 20 GU, for example, it can be a range of 10 GU, 12 GU, 15 GU, 18 GU, 20 GU or any combination thereof.

[0075] In some embodiments, the adhesion force between the battery separator and the electrode after hot pressing is 1 to 5 N / m, for example, it can be a range of 1 N / m, 2 N / m, 3 N / m, 4 N / m, 5 N / m or any combination thereof; the hot pressing conditions include: hot pressing at 85°C and 1 MPa for 80 seconds.

[0076] In some embodiments, the silane coupling agent includes at least one selected from vinyltriethylsilane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane, trimethylmethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and ureopropyltriethoxysilane.

[0077] In some embodiments, the mass ratio of silane coupling agent to unmodified inorganic filler particles in the silane coupling agent modified inorganic filler particles is (0.01 to 0.05):1, for example, it can be a range of 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1 or any combination thereof.

[0078] In practice, the preparation of silane coupling agent modified inorganic filler particles includes, but is not limited to, mixing silane coupling agent and unmodified inorganic filler particles under high temperature and high pressure. The high temperature and high pressure conditions include a temperature of 80–100℃ and a pressure of 4–6 MPa.

[0079] In some embodiments, the inorganic filler particles include at least one selected from boehmite, alumina, magnesium oxide, tin dioxide, silicon dioxide, barium sulfate, LLZO, and LATP. Further, the D50 particle size of the inorganic filler particles is 0.5–1.0 μm, for example, it can be a range of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, or any combination thereof.

[0080] In some embodiments, the inorganic filler particles constitute 66% to 88% of the coating by mass, for example, a range of 66%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 86%, 88%, or any combination thereof. The ratio of non-fluoropolymer particles to inorganic filler particles is adjusted to improve adhesion, heat resistance, and other properties.

[0081] In some embodiments, the coating further includes at least one of an adhesive, a wetting agent, and a dispersant. Further, in the coating, the mass percentages of the adhesive, wetting agent, and dispersant are 3%–8%, 0.1%–0.5%, and 0.2%–0.6%, respectively.

[0082] In some embodiments, the adhesive includes at least one of polyacrylic acid, styrene-butadiene rubber, polyacrylate, polyamide, polyacrylonitrile, and polyvinyl alcohol.

[0083] In some embodiments, the wetting agent includes at least one of alkyl sulfates, sulfonates, polyoxyethylene alkylphenol ethers, polyoxyethylene fatty alcohol ethers, and alkylphenol polyoxyethylene ethers.

[0084] In some embodiments, the dispersant includes at least one of sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, sodium polyacrylate, potassium polyacrylate, silicate, and polyethylene glycol.

[0085] In some embodiments, the base film includes at least one of polyethylene (PE) base film and polypropylene (PP) base film. The base film can be either a single-layer base film or a double-layer base film, such as a single-layer PP base film, a single-layer PE base film, a double-layer PE / PP composite base film, or a double-layer PP / PP composite base film. Further, the thickness of the base film is 5–16 μm, for example, it can be 5 μm, 7 μm, 10 μm, 12 μm, 16 μm, or any combination thereof.

[0086] The second aspect of the present invention provides a method for preparing the battery separator provided in the first aspect of the present invention, comprising the following steps: mixing an emulsion containing non-fluoropolymer particles with inorganic filler particles modified by a silane coupling agent to obtain a slurry, coating the slurry on at least one side surface of a base film, and drying to obtain a battery separator.

[0087] In some embodiments, UV irradiation is used for drying, which helps to form a stronger bond between the silane coupling agent on the surface of the inorganic filler and the surface of the non-fluoropolymer particles. Furthermore, the UV irradiation uses a wavelength of 340–360 nm and an energy of 240–280 mJ / cm². 2 The irradiation time is 1 to 3 minutes.

[0088] In the preparation of the battery separator of the present invention, the coating can be achieved by a single coating, which is simple to operate.

[0089] In some embodiments, the method for preparing an emulsion containing non-fluoropolymer particles includes:

[0090] (a) An emulsifier, a first monomer, and a first initiator undergo a first polymerization reaction in a solvent to obtain a first emulsion; the first emulsion, the first monomer, the second monomer, and the second initiator are mixed and undergo a second polymerization reaction to obtain an emulsion containing primary particles;

[0091] (b) The emulsion containing primary particles is mixed and stirred with salt substances to obtain an emulsion containing non-fluoropolymer particles.

[0092] The emulsifier includes, but is not limited to, sodium dodecyl sulfate; the first and second initiators are each independently selected from persulfates, including but not limited to sodium persulfate, ammonium persulfate, or potassium persulfate; and the solvent includes water. The specific amounts of emulsifier, initiator, and solvent are adjusted according to the amounts used in conventional emulsion polymerization.

[0093] In some embodiments, the first monomer is added stepwise during the first polymerization reaction. For example, the first polymerization reaction may include: mixing and stirring an emulsifier and a solvent, adding a portion of the first monomer, then adding an initiator, reacting for 1 to 3 hours, then adding the remaining first monomer, reacting for 3 to 5 hours, to obtain a first emulsion.

[0094] The mass ratio of the first monomer added first to the remaining first monomer added later can be 1:(2~3).

[0095] In some embodiments, the mass ratio of the first monomer and the second monomer in the second polymerization reaction to the mass of the first monomer in the first polymerization reaction is (6-9):1.

[0096] In some embodiments, the salts include, but are not limited to, sodium sulfate. Furthermore, sodium sulfate may be added in solution form.

[0097] In some embodiments, the amount of salt substance used is 0.1% to 1.5% of the mass of the emulsion containing primary particles, for example, it can be a range of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, or any combination thereof.

[0098] In some embodiments, the salt is added in the form of an aqueous solution. Further, the concentration of the aqueous solution of the salt can be 0.05–0.1 mol / L, for example, 0.05 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, or any combination thereof. When the salt is added in the form of an aqueous solution, the amount added is calculated based on the amount of salt contained in the aqueous solution.

[0099] In some embodiments, in step (b), the mixing and stirring are performed under ultrasonic heating conditions. Further, the heating temperature is 40–50°C, the stirring speed is 400–850 rpm, preferably 450–550 rpm, and the stirring time is 1–3 h. By adjusting the heating temperature, stirring speed, and stirring time, an emulsion containing non-fluoropolymer particles with a satisfactory particle size distribution is obtained.

[0100] In some embodiments, the preparation of the emulsion containing non-fluoropolymer particles further includes diluting the material after mixing and stirring in step (b) with water to a target solid content. Further, the target solid content can be 15% to 25%, such as 15%, 18%, 20%, 22%, 25%, or any combination thereof.

[0101] In some embodiments, the slurry also includes at least one of a binder, a wetting agent, and a dispersant.

[0102] A third aspect of the present invention provides a secondary battery, including the battery separator of the first aspect of the present invention.

[0103] The secondary battery using the battery separator of the present invention has high battery capacity retention and good cycle performance.

[0104] Unless otherwise specified, the quantities mentioned in the following examples are by weight.

[0105] Example 1

[0106] This embodiment provides a method for preparing a battery separator, including the following steps:

[0107] (1) Add 300 parts of deionized water and 0.8 parts of sodium dodecyl sulfate to the reactor and stir evenly. Purge the air in the reactor with nitrogen gas. Add 3.2 parts of acrylonitrile monomer. Adjust the pH of the reaction system to about 7.5 with 0.05 mol / L NaOH aqueous solution. Heat to 85°C and pressurize to 5 MPa. Add 0.5 parts of sodium persulfate while stirring at 80 rpm. React for 2 hours. Reduce the stirring speed to 20 rpm and add 7.4 parts of acrylonitrile monomer. After reacting for 4 hours, reduce the pressure to atmospheric pressure and cool to room temperature to obtain the first emulsion.

[0108] (2) Add 0.8 parts of sodium persulfate to the first emulsion, stir evenly, then purge the air in the reactor with nitrogen, heat to 75°C, pressurize to 2MPa, stir at 35 rpm, and simultaneously add acrylonitrile and 2-ethylhexyl acrylate to the reactor using a burette. The dropping rate of acrylonitrile is 2.63 parts / h, and the dropping rate of 2-ethylhexyl acrylate is 19.75 parts / h. After dropping for 4 hours, stop dropping and maintain constant temperature and pressure (75°C / 2MPa) for 4 hours. Then reduce the pressure to atmospheric pressure and cool to room temperature to obtain an emulsion containing primary particles.

[0109] (3) Take the emulsion containing primary particles obtained in step (2), heat it to 45°C under ultrasonic conditions, add 0.08 mol / L sodium sulfate aqueous solution (the mass of sodium sulfate in the sodium sulfate aqueous solution is 0.3% of the mass of the emulsion containing primary particles), stir at 500 rpm for 2 hours, the primary particle emulsion breaks down and agglomerates, add water to dilute to 20% solid content, and obtain an emulsion containing non-fluoropolymer particles.

[0110] (4) Take 82 parts of boehmite with a D50 particle size of 0.8 μm and add it to the reactor. Add 1.4 parts of vinyltrimethoxysilane and 152 parts of deionized water. After stirring evenly, heat to 90°C, pressurize to 5 MPa, react for 8 hours, reduce the pressure to normal pressure and cool to room temperature. Then add 60 parts of the emulsion containing non-fluorinated polymer particles obtained in step (3), 5 parts of polyacrylate, 0.5 parts of sodium pyrophosphate, and 0.5 parts of polyoxyethylene alkylphenol ether. Stir evenly to obtain a mixed slurry.

[0111] (5) Using a microgravure coating method (microgravure line speed of 150 lines, depth of 60μm), the mixed slurry was coated onto a 7μm thick PE base film, and UV irradiation was turned on with a UV wavelength of 350nm and an energy of 260mJ / cm. 2 After irradiation for 2 minutes, the surface density of the coating was found to be 1.8 g / m³. 2 Battery separator.

[0112] Example 2

[0113] This embodiment refers to the preparation method of the battery separator in Embodiment 1, the difference being:

[0114] In step (1), the temperature was raised to 84.5°C and the pressure was increased to 5.2 MPa. The two additions of acrylonitrile were 3.8 parts and 8.8 parts, respectively.

[0115] In step (2), the temperature was increased to 75.3°C and the pressure was increased to 2.4 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 3.13 parts / h and 18.75 parts / h, respectively.

[0116] In step (3), the temperature is heated to 46°C under ultrasonic conditions and the stirring speed is 530 rpm;

[0117] In step (4), the amount of boehmite used is 85 parts, the amount of deionized water used is 156 parts, and the amount of emulsion containing non-fluoropolymer particles used is 55 parts.

[0118] In step (5), the areal density of the coating is 1.6 g / m³. 2 .

[0119] Example 3

[0120] This embodiment refers to the preparation method of the battery separator in Embodiment 1, the difference being:

[0121] In step (1), the temperature is increased to 85.5°C and the pressure is increased to 5.2 MPa. The two additions of acrylonitrile are 4.4 parts and 10.2 parts, respectively.

[0122] In step (2), the temperature was raised to 76.0°C and the pressure was increased to 2.2 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 3.63 parts / h and 17.75 parts / h, respectively.

[0123] In step (3), the temperature is heated to 45.5°C under ultrasonic conditions and the stirring speed is 510 rpm;

[0124] In step (4), the amount of boehmite used is 70 parts, the amount of deionized water used is 104 parts, and the amount of emulsion containing non-fluoropolymer particles used is 120 parts.

[0125] In step (5), the areal density of the coating is 2.4 g / m³. 2 .

[0126] Example 4

[0127] This embodiment refers to the preparation method of the battery separator in Embodiment 1, the difference being:

[0128] In step (1), the temperature was raised to 84.5°C and the pressure was increased to 5.1 MPa. The two additions of acrylonitrile were 4.2 parts and 9.8 parts, respectively.

[0129] In step (2), the temperature is increased to 75.3°C and the pressure is increased to 2.5 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 3.50 parts / h and 18.00 parts / h, respectively.

[0130] In step (3), the temperature is heated to 46.5°C under ultrasonic conditions and the stirring speed is 480 rpm;

[0131] In step (4), the amount of boehmite used is 83 parts, the amount of deionized water used is 156 parts, and the amount of emulsion containing non-fluoropolymer particles is 55 parts.

[0132] In step (5), the areal density of the coating is 1.6 g / m³. 2 .

[0133] Example 5

[0134] This embodiment refers to the preparation method of the battery separator in Embodiment 1, the difference being:

[0135] In step (1), the temperature was raised to 84.6°C and the pressure was increased to 5.5 MPa. The two additions of acrylonitrile were 3.9 parts and 9.1 parts, respectively.

[0136] In step (2), the temperature is increased to 75.5°C and the pressure is increased to 2.0 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 3.25 parts / h and 18.50 parts / h, respectively.

[0137] In step (3), the temperature is heated to 44.5°C under ultrasonic conditions, and the stirring speed is 490 rpm;

[0138] In step (4), the amount of boehmite used is 70 parts, the amount of deionized water used is 104 parts, and the amount of emulsion containing non-fluoropolymer particles used is 120 parts.

[0139] In step (5), the areal density of the coating is 2.2 g / m³. 2 .

[0140] Example 6

[0141] This embodiment refers to the preparation method of the battery separator in Embodiment 1, the difference being:

[0142] In step (1), the temperature was raised to 85.6°C and the pressure was increased to 4.6 MPa. The two additions of acrylonitrile were 3.3 parts and 7.7 parts, respectively.

[0143] In step (2), the temperature is increased to 76.5°C and the pressure is increased to 1.8 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.75 parts / h and 19.50 parts / h, respectively.

[0144] In step (3), the temperature is heated to 44.8°C under ultrasonic conditions, and the stirring speed is 510 rpm;

[0145] In step (4), the amount of boehmite used is 76 parts, the amount of deionized water used is 128 parts, and the amount of emulsion containing non-fluoropolymer particles used is 90 parts.

[0146] In step (5), the areal density of the coating is 2.2 g / m³. 2 .

[0147] Example 7

[0148] This embodiment refers to the battery separator preparation method of Embodiment 6, the difference being that step (3) is different.

[0149] Step (3) of this embodiment includes: taking the emulsion containing primary particles obtained in step (2), heating it to 44.8°C under ultrasonic conditions, adding 0.08 mol / L sodium sulfate aqueous solution (the mass of sodium sulfate in the sodium sulfate aqueous solution is 0.3% of the mass of the emulsion containing primary particles), stirring at a stirring speed of 485 rpm for 2 hours, breaking down and agglomerating the primary particle emulsion, diluting it with water to a solid content of 20%, and obtaining the first emulsion containing non-fluoropolymer particles;

[0150] Take the emulsion containing primary particles obtained in step (2), heat it to 44.8°C under ultrasonic conditions, add 0.08 mol / L sodium sulfate aqueous solution (the mass of sodium sulfate in the sodium sulfate aqueous solution is 0.3% of the mass of the emulsion containing primary particles), stir at 820 rpm for 2 hours, the primary particle emulsion breaks down and agglomerates, add water to dilute to 20% solid content, and obtain the second emulsion containing non-fluoropolymer particles;

[0151] The first emulsion containing non-fluoropolymer particles and the second emulsion containing non-fluoropolymer particles are mixed at a mass ratio of 2:1 to obtain an emulsion containing non-fluoropolymer particles.

[0152] Comparative Example 1

[0153] Comparative Example 1 uses the same method for preparing the battery separator as in Example 1, except that:

[0154] In step (1), the temperature is increased to 85.0°C and the pressure is increased to 4.8 MPa. The two additions of acrylonitrile are 3.6 parts and 8.4 parts, respectively.

[0155] In step (2), the temperature is increased to 75.8°C and the pressure is increased to 1.9 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 3.00 parts / h and 19.00 parts / h, respectively.

[0156] In step (3), the temperature is heated to 43.8°C under ultrasonic conditions, and the stirring speed is 550 rpm;

[0157] In step (4), the amount of boehmite used is 86 parts, the amount of deionized water used is 168 parts, and the amount of emulsion containing non-fluoropolymer particles is 40 parts.

[0158] In step (5), the areal density of the coating is 1.6 g / m³. 2 .

[0159] Comparative Example 2

[0160] Comparative Example 2 uses the same method as Example 1 for preparing the battery separator, except that:

[0161] In step (1), the temperature was raised to 84.0°C and the pressure was increased to 4.5 MPa. The two additions of acrylonitrile were 3.9 parts and 9.1 parts, respectively.

[0162] In step (2), the temperature was raised to 74.2°C and the pressure was increased to 2.3 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 3.25 parts / h and 18.50 parts / h, respectively.

[0163] In step (3), the temperature is heated to 42.8°C under ultrasonic conditions and the stirring speed is 500 rpm;

[0164] In step (4), the amount of boehmite used is 64 parts, the amount of deionized water used is 80 parts, and the amount of emulsion containing non-fluoropolymer particles is 150 parts.

[0165] In step (5), the areal density of the coating is 2.4 g / m³. 2 .

[0166] Comparative Example 3

[0167] Comparative Example 3 uses the same method as Example 1 for preparing the battery separator, except that:

[0168] In step (1), the temperature is increased to 83.5°C and the pressure is increased to 5.5 MPa. The two additions of acrylonitrile are 4.1 parts and 9.5 parts, respectively.

[0169] In step (2), the temperature was raised to 74.0°C and the pressure was increased to 2.5 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 3.38 parts / h and 18.25 parts / h, respectively.

[0170] In step (3), the temperature is heated to 43.9°C under ultrasonic conditions and the stirring speed is 540 rpm;

[0171] In step (4), the amount of boehmite used is 84 parts, the amount of deionized water used is 160 parts, and the amount of emulsion containing non-fluoropolymer particles is 50 parts.

[0172] In step (5), the areal density of the coating is 1.3 g / m³. 2 .

[0173] Comparative Example 4

[0174] Comparative Example 4 uses the same method as Example 1 for preparing the battery separator, except that:

[0175] In step (1), the temperature was raised to 83.8°C and the pressure was increased to 5.2 MPa. The two additions of acrylonitrile were 3.3 parts and 7.7 parts, respectively.

[0176] In step (2), the temperature was raised to 76.0°C and the pressure was increased to 2.1 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 2.75 parts / h and 19.50 parts / h, respectively.

[0177] In step (3), the temperature is heated to 42.9°C under ultrasonic conditions, and the stirring speed is 560 rpm;

[0178] In step (4), the amount of boehmite used is 70 parts, the amount of deionized water used is 104 parts, and the amount of emulsion containing non-fluoropolymer particles used is 120 parts.

[0179] In step (5), the areal density of the coating is 2.9 g / m³.2 .

[0180] Comparative Example 5

[0181] Comparative Example 5 uses the same method for preparing the battery separator as in Example 1, except that:

[0182] In step (1), the temperature was raised to 86.8°C and the pressure was increased to 4.7 MPa. The two additions of acrylonitrile were 3.6 parts and 8.4 parts, respectively.

[0183] In step (2), the temperature is increased to 75.8°C and the pressure is increased to 2.4 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 3.00 parts / h and 19.00 parts / h, respectively.

[0184] In step (3), the temperature is heated to 43.6°C under ultrasonic conditions, and the stirring speed is 480 rpm;

[0185] In step (4), the amount of boehmite used is 83 parts, the amount of deionized water used is 156 parts, and the amount of emulsion containing non-fluoropolymer particles is 55 parts.

[0186] In step (5), the areal density of the coating is 1.5 g / m³. 2 .

[0187] Comparative Example 6

[0188] Comparative Example 6 uses the same method for preparing the battery separator as in Example 1, except that:

[0189] In step (1), the temperature is raised to 85.8°C and the pressure is increased to 5.5 MPa. The two additions of acrylonitrile are 4.1 parts and 9.5 parts, respectively.

[0190] In step (2), the temperature was raised to 74.2°C and the pressure was increased to 2.5 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 3.38 parts / h and 18.25 parts / h, respectively.

[0191] In step (3), the temperature is heated to 46.6°C under ultrasonic conditions, and the stirring speed is 470 rpm;

[0192] In step (4), the amount of boehmite used is 82 parts, the amount of deionized water used is 152 parts, and the amount of emulsion containing non-fluoropolymer particles is 60 parts.

[0193] In step (5), the areal density of the coating is 1.6 g / m³. 2 .

[0194] Comparative Example 7

[0195] Comparative Example 3 uses the same method as Example 1 for preparing the battery separator, except that:

[0196] In step (1), the temperature is increased to 85.5°C and the pressure is increased to 4.8 MPa. The two additions of acrylonitrile are 2.4 parts and 5.6 parts, respectively.

[0197] In step (2), the temperature is increased to 76.0°C and the pressure is increased to 2.1 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.00 parts / h and 21.00 parts / h, respectively.

[0198] In step (3), the temperature is heated to 44.7°C under ultrasonic conditions, and the stirring speed is 555 rpm;

[0199] In step (4), the amount of boehmite used is 71 parts, the amount of deionized water used is 108 parts, and the amount of emulsion containing non-fluoropolymer particles used is 115 parts.

[0200] In step (5), the areal density of the coating is 2.2 g / m³. 2 .

[0201] Comparative Example 8

[0202] Comparative Example 8 uses the same method as Example 1 for preparing the battery separator, except that:

[0203] In step (1), the temperature was raised to 84.4°C and the pressure was increased to 5.6 MPa. The two additions of acrylonitrile were 5.3 parts and 12.3 parts, respectively.

[0204] In step (2), the temperature was raised to 74.0°C and the pressure was increased to 1.8 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 4.38 parts / h and 16.25 parts / h, respectively.

[0205] In step (3), the temperature is heated to 46.8°C under ultrasonic conditions, and the stirring speed is 450 rpm;

[0206] In step (4), the amount of boehmite used is 79 parts, the amount of deionized water used is 140 parts, and the amount of emulsion containing non-fluoropolymer particles used is 75 parts.

[0207] In step (5), the areal density of the coating is 2.0 g / m³. 2 .

[0208] Comparative Example 9

[0209] Comparative Example 9 uses the same method for preparing the battery separator as in Example 1, except that:

[0210] In step (1), the temperature is raised to 86.2°C and the pressure is increased to 5.6 MPa. The two additions of acrylonitrile are 3.5 parts and 8.1 parts, respectively.

[0211] In step (2), the temperature was raised to 75.5°C and the pressure was increased to 2.3 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate were 2.88 parts / h and 19.25 parts / h, respectively.

[0212] In step (3), the temperature is heated to 44.2°C under ultrasonic conditions, and the stirring speed is 545 rpm;

[0213] In step (4), the amount of boehmite used is 82 parts, the amount of deionized water used is 152 parts, and the amount of emulsion containing non-fluoropolymer particles is 60 parts.

[0214] In step (5), the areal density of the coating is 1.6 g / m³. 2 .

[0215] Comparative Example 10

[0216] Comparative Example 10 uses the same method for preparing the battery separator as in Example 1, except that:

[0217] In step (1), the temperature was raised to 86.2°C and the pressure was increased to 5.3 MPa. The two additions of acrylonitrile were 4.2 parts and 9.8 parts, respectively.

[0218] In step (2), the temperature is increased to 75.5°C and the pressure is increased to 1.9 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 3.50 parts / h and 18.00 parts / h, respectively.

[0219] In step (3), the temperature is heated to 46.5°C under ultrasonic conditions and the stirring speed is 510 rpm;

[0220] In step (4), the amount of boehmite used is 82 parts, the amount of deionized water used is 152 parts, and the amount of emulsion containing non-fluoropolymer particles is 60 parts.

[0221] In step (5), the areal density of the coating is 1.6 g / m³. 2 .

[0222] Comparative Example 11

[0223] Comparative Example 11 uses the same method for preparing the battery separator as in Example 1, except that:

[0224] In step (1), the temperature was raised to 85.6°C and the pressure was increased to 4.6 MPa. The two additions of acrylonitrile were 3.3 parts and 7.7 parts, respectively.

[0225] In step (2), the temperature is increased to 76.5°C and the pressure is increased to 1.8 MPa. The dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.75 parts / h and 19.50 parts / h, respectively.

[0226] In step (3), the temperature is heated to 44.8°C under ultrasonic conditions, and the stirring speed is 510 rpm;

[0227] In step (4), 76 parts of boehmite with a D50 particle size of 0.8 μm were added to the reactor, 128 parts of deionized water were added, and then 90 parts of the emulsion containing non-fluorinated polymer particles obtained in step (3), 5 parts of polyacrylate, 0.5 parts of sodium pyrophosphate, and 0.5 parts of polyoxyethylene alkylphenol ether were added and stirred evenly to obtain a mixed slurry.

[0228] In step (5), the areal density of the coating is 2.2 g / m³. 2 .

[0229] Experimental Example

[0230] 1. Glass transition temperature (Tg) and particle size testing

[0231] (1) Glass transition temperature Tg test: Take the emulsion containing non-fluorinated polymer particles from each example and comparative example, dry it, weigh 6-8 mg of sample, and test the glass transition temperature Tg by differential scanning calorimetry; test equipment: METTLERDSC3, test temperature range: -80 to 100℃, heating rate: 5℃ / min, after the test, integrate the test curve to obtain the glass transition temperature Tg of the test sample.

[0232] (2) Particle size test:

[0233] Take the emulsions containing primary particles from each example and comparative example, drop them into a Malvern 3000 tester to test the particle size. The test results show a refractive index of 1.52, an absorptivity of 0.1, and an opacity of 6%–18%, thus obtaining the D50 particle size of the primary particles (referred to as d50).

[0234] Emulsions containing non-fluoropolymer particles from each example and comparative example were taken and dropped into a Malvern 3000 analyzer to test the particle size. The refractive index was 1.52, the absorptivity was 0.1, and the opacity was 6%–18%. The D10, D50, and D90 particle sizes of the non-fluoropolymer particles (secondary agglomerated particles) were obtained. The particle sizes of the first and second emulsions containing non-fluoropolymer particles in Example 7 were also tested.

[0235] The test results are shown in Table 1. Figure 3 This is a DSC test image of the non-fluoropolymer particles in Example 6 of the present invention. Figure 4 This is a particle size distribution diagram of the emulsion containing non-fluoropolymer particles in Example 6 of the present invention. Figure 5 This is a particle size distribution diagram of the emulsion containing non-fluorinated polymer particles in Example 7 of the present invention.

[0236] Table 1 Test Results 1

[0237]

[0238] 2. Battery separator performance test

[0239] (1) Air permeability growth rate test: air permeability growth rate = (battery separator air permeability - base membrane air permeability) / base membrane air permeability × 100%, where air permeability refers to the time required for 100mL of gas to pass through a fixed area separator.

[0240] (2) Thickness consistency test: Take the battery separator, select 3 points along the TD direction and 12 points along the MD direction, for a total of 36 points. Use a micrometer to test the thickness of each point, record all data, and calculate the standard deviation of the final result.

[0241] (3) Heat shrinkage test: Take the battery separator and cut a 100mm×50mm rectangular sheet along the MD direction. Test the lengths M1 and T1 in the MD and TD directions. Clamp the sheet with two A4 sheets of paper and put it into a 130℃ oven for 30 minutes. Test the lengths M2 and T2 in the MD and TD directions of the separator again. The heat shrinkage values ​​of the battery separator in the MD and TD directions are (M1-M2) / M1 and (T1-T2) / T1, respectively.

[0242] (4) Test of the number of non-fluoropolymer particles with a particle size ≥1.5μm in the battery separator coating: Take the battery separator and take electron microscopy images of the coated side at 3000x magnification. Take 30 images at this magnification and count the number of non-fluoropolymer particles with a particle size ≥1.5μm at each magnification. Finally, take the average value and convert the area at this magnification to the number of particles corresponding to 1mm. 2 The number of particles per square meter area indicates the coating thickness of the battery separator within 1 mm. 2 The number of non-fluoropolymer particles N1 with a particle size ≥ 1.5 μm within the region.

[0243] (5) Test of effective adhesion sites of battery separator coating:

[0244] ① Take a battery separator and perform electron microscopy on the coated side at 3000x magnification, capturing 30 points. Mark the diameter D1 of the non-fluoropolymer particles at this magnification. Simultaneously, take a cross-section of the battery separator and measure the thickness H of the ceramic layer in the area without non-fluoropolymer particles. Count the number of non-fluoropolymer particles where D1 > 1.2H. Finally, take the average value and convert the area at this magnification to the corresponding particle count for 1 mm. 2 The number of particles per 1 mm area is the result of the battery separator's particle count. 2 Number of effective adhesion sites N within the region 2-1 ;

[0245] ② Take the battery separator, attach the coated side of the battery separator to the release film, place it in a hot press, adjust the hot press temperature to 85℃ and the pressure to 1MPa, hot press for 40s, remove the hot-pressed sample, and peel off the release film; take an electron microscope image of the coated side of the hot-pressed battery separator, taking 30 images at 3000x magnification. The non-fluoropolymer particles are distributed in a pancake shape after hot pressing. Mark the diameter D2 of the non-fluoropolymer particles at this magnification, count the number of non-fluoropolymer particles with D2 > 1.5H, and finally take the average value. Convert the area at this magnification to the corresponding particle number in 1mm. 2 The number of particles per 1 mm area is the result of the battery separator's particle count. 2 Number of effective adhesion sites N within the region 2-2 .

[0246] In the quantity tests of (4) and (5), there were few cases where more than two non-fluoropolymer particles were connected. When counting, if more than two non-fluoropolymer particles were connected, they were counted as 1.

[0247] (6) Gloss test of battery separator: Lay the battery separator flat on the test bench (coating facing up), use a Color Spectrum Technology CS-380 gloss meter to test the gloss of the battery separator. The test angle is 85°, test 30 points, and take the average value to obtain the gloss of the battery separator.

[0248] (7) Adhesion test with electrode: The battery separator and electrode are cut into 3cm×5cm specifications. The coating surface of the electrode is attached to the coating of the battery separator. After adjusting the parameters of the hot press (1MPa, 80s, 85℃), the dry press is used. The adhesion between the separator and the electrode is tested by peeling at 180° with a peeling speed of 60mm / min. Finally, the adhesion between the battery separator and the electrode is obtained. The electrode is a cathode sheet. The coating surface of the electrode is composed of 95 parts lithium iron phosphate, 3.5 parts conductive carbon black, 1 part carbon nanotube, and 6 parts PVDF with a melting point of 150℃.

[0249] (8) Ionic conductivity test: In an argon-filled glove box, the battery separator was assembled into a 2016 button cell. An appropriate amount of electrolyte (EC:PC:EMC:DEC = 3:3:3:1, 2 mol / L LiPF6) was added. The AC impedance test in the electrochemical workstation was used to obtain σ = L / (Rb*A), where σ is the ionic conductivity (mS / cm), L is the thickness of the separator (cm), Rb is the intrinsic resistance of the separator (Ω), and A is the effective area (cm²).

[0250] (9) Capacity retention rate test: The battery separator, ternary positive electrode, and graphite negative electrode are stacked to form the battery cell. The battery is charged and discharged for 500 cycles at 0.3C. The capacity before and after the cycle is tested. Capacity retention rate = capacity after cycle / capacity before cycle.

[0251] The active layer of the ternary positive electrode sheet includes: 96.0wt% NCM (811), 1.5wt% conductive carbon black, 1.0wt% CNT and 1.5wt% PVDF; the active layer of the graphite negative electrode sheet includes: 96.0wt% graphite, 1.0wt% conductive carbon black, 1.5wt% CMC and 1.5wt% SBR.

[0252] (10) Lithium plating in the cell: The battery separator and ternary positive electrode (the same ternary positive electrode in the capacity retention test) and graphite negative electrode (the same graphite negative electrode in the capacity retention test) are stacked to form the cell. The battery is charged and discharged for 400 cycles at 1.0C. The cell is disassembled and the lithium plating problem is observed.

[0253] The battery separator performance test results are shown in Table 2. Figure 6 This is a surface SEM image of the coating of the battery separator in Embodiment 6 of the present invention. Figure 7 This is a cross-sectional SEM image of the coating of the battery separator in Embodiment 6 of the present invention. Figure 8 This is a surface SEM image of the coating after hot pressing of the battery separator and release film in Embodiment 6 of the present invention.

[0254] Table 2 Test Results 2

[0255]

[0256] As shown in Table 2, the battery separator of the present invention uses non-fluoropolymer particles that meet certain conditions, while controlling the proportion of non-fluoropolymer particles in the coating and the areal density of the coating, and using inorganic filler particles modified with silane coupling agent. This results in a battery separator with low gas permeability growth rate, good thickness uniformity, heat resistance, adhesion to the electrode, and good ionic conductivity. The battery assembled with it has high capacity retention and good cycle performance.

[0257] The proportion of non-fluoropolymer particles in the coating affects the adhesion between the battery separator and the electrode. If the proportion of non-fluoropolymer particles is too low, the adhesion between the battery separator and the electrode will be poor, the interfacial resistance between the battery separator and the electrode will increase, and the cycle performance of the cell will be affected. If the proportion of non-fluoropolymer particles is too high, it will affect the thermal shrinkage performance of the battery separator, and the adhesion between the battery separator and the electrode will be too strong, resulting in reduced local electrolyte wetting and leading to lithium plating problems. Similarly, similar problems will occur if the coating amount of the battery separator is too high or too low, as shown in comparisons 1 to 4.

[0258] When the particle size distribution of non-fluoropolymer particles is too wide, the thickness uniformity of the battery separator is poor and the gloss of the battery separator is reduced. If the proportion of small particles in the non-fluoropolymer particles is too high, it is easy to cause the non-fluoropolymer particles to agglomerate, resulting in severe local lithium plating and a reduction in the effective bonding sites with the electrode. This leads to a decrease in the adhesion between the battery separator and the electrode, an increase in the interface resistance, and affects the cycle performance of the cell, as shown in Comparative Examples 5-6.

[0259] The glass transition temperature (Tg) of secondary agglomerates affects the adhesion between the battery separator and the electrode. When the Tg of secondary agglomerates is too low, the adhesion between the battery separator and the electrode increases, which can easily lead to a decrease in local electrolyte wettability and ultimately cause lithium plating problems. At the same time, if the Tg is too low, the shell stability of non-fluoropolymer particles can be reduced, and the battery separator and electrode will be severely blocked in some areas after hot pressing, thus affecting local lithium plating and cycle performance, as shown in Comparative Examples 7-8.

[0260] When the primary particle size of non-fluoropolymer particles is too small, the specific surface area increases, which easily leads to a wide particle size distribution during the preparation of secondary agglomerated particles. This affects the thickness uniformity and gloss, and at the same time reduces the effective bonding sites with the electrode, affecting adhesion and thus affecting the overall cycle performance of the cell. When the primary particle size of non-fluoropolymer particles is too large, it easily leads to a wide particle size distribution and an overall large particle size in the secondary agglomerated particles. This also affects the thickness uniformity and gloss, and reduces the effective bonding sites between the separator and the electrode. The adhesion between the battery separator and the electrode is weak, and the excessively large primary particle size seriously affects ion shuttle, resulting in severe local lithium plating in the cell, as shown in Comparative Examples 9-10.

[0261] In battery separator coatings, when inorganic filler particles are not pre-modified, the dispersion uniformity of non-fluoropolymer particles and inorganic filler particles is reduced during slurry preparation. This can easily lead to the formation of non-fluoropolymer particle clusters in the battery separator, resulting in severe lithium plating. At the same time, the heat resistance of the battery separator is reduced, as shown in Comparative Example 11.

[0262] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery separator, characterized in that, The system includes a base film and a coating disposed on at least one surface of the base film; the coating comprises non-fluoropolymer particles and silane coupling agent modified inorganic filler particles, and the areal density of the coating is 1.5–2.5 g / m³. 2 In the coating, the non-fluoropolymer particles account for 10% to 25% by mass. The non-fluoropolymer particles are secondary agglomerated particles formed by the agglomeration of primary particles. The D50 particle size of the primary particles is 0.41 to 0.6 μm. The D10, D50, and D90 particle sizes of the secondary agglomerated particles satisfy the following condition: (D90-D10) / D50 < 1.

3. The glass transition temperature Tg of the secondary agglomerates is -5 to 5℃; The non-fluoropolymer particles include at least two types of secondary agglomerated particles with different particle sizes, and the two types of secondary agglomerated particles with different particle sizes respectively satisfy the following characteristics (1) and (2): (1) D50 particle size is 4.0~5.5μm; D10 particle size is >2.0μm; D90 particle size is <10.0μm; (2) The particle size of D50 is 1.2 to 1.6 μm; the particle size of D10 is 0.5 to 1.0 μm; and the particle size of D90 is 1.8 to 2.5 μm.

2. The battery separator according to claim 1, characterized in that, The primary particle has a core and a shell covering the surface of the core; the molecular chain of the core includes a first structural unit, and the molecular chain of the shell includes a first structural unit and a second structural unit. The first monomer forming the first structural unit includes at least one of methacrylonitrile, styrene, and acrylonitrile; the second monomer forming the second structural unit includes at least one of ethyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, and n-butyl acrylate. In the primary particles, the mass percentage of the first structural unit is 20% to 30%.

3. The battery separator according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The coating has a field of view of 1 mm 2 Within the region, the number of the non-fluoropolymer particles with a particle size ≥ 1.5 μm is N1, and satisfies: 2800 ≤ N1 ≤ 31000; (2) The coating has a field of view of 1 mm 2 Within the region, the number of non-fluoropolymer particles with a diameter > 1.2H is N. 2-1 And satisfy: N 2-1 <N1, 2400≤N 2-1 ≤26500; where H is the thickness of the silane coupling agent modified inorganic filler particles in the coating; (3) After the coating of the battery separator is bonded to the release film and hot-pressed, the coating is within 1 mm of the field of view. 2 Within the region, the number of non-fluoropolymer particles with a diameter ≥ 1.5H is N. 2-2 And satisfy: N 2-2 <N1, 2300≤N 2-2 ≤26000; wherein, the hot pressing conditions include: hot pressing at 85°C and 1MPa for 40s; (4) The gloss of the coating is 10-20 GU; (5) The adhesion force between the battery separator and the electrode after hot pressing is 1 to 5 N / m; the hot pressing conditions include: hot pressing at 85°C and 1 MPa for 80 s.

4. The battery separator according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The silane coupling agent includes at least one of vinyltriethylsilane, vinyltrimethoxysilane, γ-aminopropyltriethoxysilane, trimethylmethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane and ureopropyltriethoxysilane; (2) In the silane coupling agent modified inorganic filler particles, the mass ratio of silane coupling agent to unmodified inorganic filler particles is (0.01~0.05):1; (3) The inorganic filler particles include at least one of boehmite, alumina, magnesium oxide, tin dioxide, silicon dioxide, barium sulfate, LLZO and LATP; (4) The D50 particle size of the inorganic filler particles is 0.5 to 1.0 μm; (5) In the coating, the mass percentage of the inorganic filler particles modified by the silane coupling agent is 66% to 88%.

5. The battery separator according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The coating further includes at least one of an adhesive, a wetting agent, and a dispersant; (2) In the coating, the mass percentages of the adhesive, wetting agent, and dispersant are 3%–8%, 0.1%–0.5%, and 0.2%–0.6%, respectively; (3) The base film includes at least one of polyethylene base film and polypropylene base film; (4) The thickness of the base film is 5 to 16 μm.

6. The method for preparing the battery separator according to any one of claims 1 to 5, characterized in that, The process includes the following steps: mixing an emulsion containing non-fluoropolymer particles with inorganic filler particles modified with a silane coupling agent to obtain a slurry; coating the slurry onto at least one side of a base membrane; and drying to obtain the battery separator.

7. The preparation method according to claim 6, characterized in that, The method for preparing the emulsion containing non-fluoropolymer particles includes: (a) An emulsifier, a first monomer, and a first initiator undergo a first polymerization reaction in a solvent to obtain a first emulsion; the first emulsion, the first monomer, the second monomer, and the second initiator are mixed and undergo a second polymerization reaction to obtain an emulsion containing primary particles; (b) The emulsion containing primary particles is mixed and stirred with salt substances to obtain an emulsion containing non-fluoropolymer particles.

8. A secondary battery, characterized in that, Includes the battery separator as described in any one of claims 1 to 5.

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