Battery diaphragm, preparation method thereof and electrochemical device

Abstract

The invention discloses a battery diaphragm, a preparation method thereof and an electrochemical device. The battery diaphragm comprises a base membrane; the coating is arranged on at least one side surface of the base film; the coating contains cyclodextrin or a derivative thereof that contains polymer particles through the cavity. According to the battery diaphragm and the preparation method thereof, the cyclodextrin containing the polymer particles through the cavity or the derivative of the cyclodextrin is added into the coating of the battery diaphragm, so that the stability of the battery coating slurry can be improved, the coating is stable, and the powder falling phenomenon of the battery diaphragm is effectively improved. Meanwhile, the added cyclodextrin or the derivative thereof containing polymer particles through the cavity can provide more ion channels on the surface, so that the ionic conductivity of the diaphragm can be improved, and the internal resistance of the diaphragm is reduced at the same time.

Description

Technical Field

[0001] This application belongs to the field of battery separator material technology, and particularly relates to a battery separator and its preparation method and electrochemical device. Background Technology

[0002] As a key component in the structure of lithium-ion batteries, the separator plays a crucial role in conducting lithium ions while isolating the positive and negative electrodes, preventing electrons from passing through and causing short circuits. However, separator production has high barriers to entry, making it the last lithium battery component to be domestically produced. The production technology is challenging, requiring sophisticated equipment, resulting in high production costs. Coated separators, a type of separator product, are made by coating a functional coating onto a base membrane. This improves the separator's heat resistance, adhesion, and liquid absorption / retention capabilities, making it more suitable for high-rate discharge batteries and enhancing battery safety and reliability.

[0003] Existing mixed-coating separator products combine heat resistance and adhesion properties. Compared with multi-layer coated separators, the production process is simple and the cost is lower. However, they have higher internal resistance, poor low-temperature self-discharge performance, weaker adhesion, and higher powder shedding rate. Consequently, the thickness consistency of the mixed-coating separator is poor during battery assembly, resulting in poor cell cycle performance and faster cell capacity decay at low temperatures. Summary of the Invention

[0004] This application provides a battery separator and its preparation method. Adding cyclodextrin or its derivatives containing polymer particles through cavities to the coating of the battery separator can improve the stability of the battery coating slurry, reduce the internal resistance of the separator, and improve the phenomenon of powder shedding from the battery separator.

[0005] In a first aspect, this application provides a battery separator, comprising: a base membrane; a coating disposed on at least one side surface of the base membrane; the coating containing cyclodextrin or a derivative thereof containing polymer particles through cavities.

[0006] According to an embodiment of the first aspect of this application, the base film is selected from PE, PP, or a composite membrane of PE and PP.

[0007] According to an embodiment of the first aspect of this application, the porosity of the base membrane is 20% to 70%, and the air permeability is 70 sec / 100cc to 200 sec / 100cc.

[0008] According to an embodiment of the first aspect of this application, the thickness of the base film is 3 μm to 20 μm.

[0009] According to an embodiment of the first aspect of this application, the thickness of the coating is 1 μm to 3 μm.

[0010] According to an embodiment of the first aspect of this application, cyclodextrin or its derivatives are selected from β-cyclodextrin, γ-cyclodextrin, hydroxypropyl-β-cyclodextrin or combinations thereof.

[0011] According to the embodiments of the first aspect of this application, the degree of hydroxypropyl substitution in hydroxypropyl-β-cyclodextrin is 3.5 to 5.

[0012] According to an embodiment of the first aspect of this application, the polymer particles are selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, hexafluoropropylene, polymethyl methacrylate, polyethyl methacrylate, or combinations thereof.

[0013] According to the embodiments of the first aspect of this application, the swelling degree of the polymer particles is 20% to 120%, and the Tg is 30°C to 70°C.

[0014] According to the embodiments of the first aspect of this application, the swelling degree of the polymer particles is 40% to 110%, and the Tg is 45°C to 60°C.

[0015] According to an embodiment of the first aspect of this application, the average particle size D of the polymer particles is... 50 The thickness is 0.1 μm to 1 μm, optionally 0.1 μm to 0.8 μm, and further optionally 0.1 μm to 0.5 μm.

[0016] According to the embodiments of the first aspect of this application, the minimum inner diameter of the cavity of the cyclodextrin or its derivative is 0.3 μm to 1 μm, the minimum outer diameter of the cyclodextrin or its derivative is 0.4 μm to 10 μm, and the average particle size D of the polymer particles in the coating is... 90 ≤ The minimum inner diameter of the cavity of cyclodextrin or its derivatives.

[0017] According to an embodiment of the first aspect of this application, the minimum inner diameter of the cavity of the cyclodextrin or its derivative is equal to the average particle size D of the polymer particles in the coating. 90 ×(1~1.5).

[0018] According to an embodiment of the first aspect of this application, the content of cyclodextrin or its derivatives containing polymer particles through cavities in the coating is 5 wt.% to 10 wt.%.

[0019] According to an embodiment of the first aspect of this application, the mass ratio of polymer particles to cyclodextrin or its derivatives in the coating is 1:(1-2).

[0020] In a second aspect, this application provides a method for preparing a battery separator, comprising: providing a base membrane; providing a coating slurry containing polymer particles of cyclodextrin or its derivatives through a cavity; and coating the coating slurry onto at least one side surface of the base membrane to form a coating, thereby obtaining a battery separator containing the coating.

[0021] According to an embodiment of the second aspect of this application, providing a coating slurry containing polymer particles of cyclodextrin or its derivatives through cavities comprises: adding cyclodextrin or its derivatives to an emulsion containing polymer particles for coating treatment, so that the polymer particles are contained in cavities of the cyclodextrin or its derivatives, to obtain a pretreatment solution; dispersing and refining ceramic powder, water, dispersant, and thickener to obtain a first dispersion slurry; adding the pretreatment solution to the first dispersion slurry to obtain a second dispersion slurry; and adding a binder to the second dispersion slurry to obtain a coating slurry containing cyclodextrin or its derivatives with internally coated polymers.

[0022] According to an embodiment of the second aspect of this application, the content of polymer particles in the emulsion containing polymer particles is 10 wt.% to 30 wt.%.

[0023] According to an embodiment of the second aspect of this application, the content of cyclodextrin or its derivatives containing polymer particles in the cavity of the pretreated solution is 26 wt.% to 35 wt.%.

[0024] According to an embodiment of the second aspect of this application, a first dispersion slurry is prepared by dispersing and refining ceramic powder (60wt% to 90wt% of the total mass of the coating), dispersant (0.5wt% to 3wt% of the total mass of the coating), thickener (1wt% to 3wt% of the total mass of the coating slurry), and water (40wt% to 60wt% of the total mass of the coating slurry). A pretreatment solution is added to the first dispersion slurry at a mass ratio of 1:(7 to 12) to obtain a second dispersion slurry. A binder (4wt% to 10wt% of the total mass of the coating) is added to the second dispersion slurry to obtain a coating slurry.

[0025] According to an embodiment of the second aspect of this application, the ceramic powder is selected from alumina, boehmite, titanium dioxide, barium titanate, or a combination thereof.

[0026] According to an embodiment of the second aspect of this application, the dispersant is selected from polycarboxylate salts, sodium dodecyl sulfate, methylpentanol, cellulose derivatives, polyacrylamide, glucon, fatty acid polyethylene glycol esters, or combinations thereof.

[0027] According to an embodiment of the second aspect of this application, the thickener is selected from carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, or a combination thereof.

[0028] According to an embodiment of the second aspect of this application, the adhesive is selected from acrylic acid, acrylic polymers, polyacrylonitrile, or combinations thereof.

[0029] According to an embodiment of the second aspect of this application, forming a coating by coating a coating slurry on at least one side surface of a base film includes: applying the coating slurry to at least one side surface of the base film using a coating device and performing a drying process to prepare a battery separator containing a coating.

[0030] Thirdly, this application provides an electrochemical device including the aforementioned battery separator.

[0031] The battery separator and its preparation method in this application improve the stability of the battery coating slurry by adding cyclodextrin or its derivatives containing polymer particles through cavities to the coating of the battery separator, thereby stabilizing the coating and effectively reducing the phenomenon of powder shedding from the battery separator. Simultaneously, the addition of cyclodextrin or its derivatives containing polymer particles through cavities provides more ion channels on the surface of the battery separator, which can improve the ionic conductivity of the battery separator and reduce its internal resistance. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the structure of a battery separator provided in one embodiment of this application.

[0034] Explanation of reference numerals in the attached figures: 1. Cyclodextrin or its derivatives; 2. Polymer particles; 3. Coating; 4. Base film; 5. Minimum outer diameter of the cavity of cyclodextrin or its derivatives; 6. Minimum inner diameter of the cavity of cyclodextrin or its derivatives. Detailed Implementation

[0035] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0036] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0037] The inventors of this application discovered during their research on the high powder shedding rate of existing diaphragms that the reason lies in the poor adhesion between the coating and the base film surface, as well as the weak bonding between the coatings.

[0038] To address the problems of the prior art, this application provides a battery separator, its preparation method, and an electrochemical device.

[0039] The battery separator provided in the embodiments of this application will be described below. Figure 1 A schematic diagram of the structure of a battery separator provided in one embodiment of this application is shown.

[0040] like Figure 1 As shown, the battery separator includes a base membrane 4; a coating 3 disposed on at least one side surface of the base membrane 4; the coating 3 contains cyclodextrin or its derivative 1 containing polymer particles 2 through a cavity.

[0041] In the battery separator of this application embodiment, adding cyclodextrin or its derivatives containing polymer particles through cavities to the coating of the battery separator can improve the stability of the battery coating slurry, making the coating stable and effectively improving the phenomenon of powder shedding from the battery separator. The added cyclodextrin or its derivatives containing polymer particles through cavities can provide more ion channels on the surface of the battery separator, which can improve the ionic conductivity of the separator and reduce the internal resistance of the separator.

[0042] The battery separator in this embodiment contains cyclodextrin or its derivative 1 in the coating 3. The cyclodextrin or its derivative 1 utilizes its own structural cavity to encapsulate polymer particles 2 (such as PMMA particles) within the cavity. It should be noted that... Figure 1 The image shows the size configuration of cyclodextrin or its derivatives containing polymer particles through a cavity. The cyclodextrin or its derivative 1 containing polymer particles 2 inside the cavity is configured such that some of the cyclodextrin or its derivative 1 within the cavity is located within the coating 3, while some of the cyclodextrin or its derivative 1 within the cavity extends outside the coating 3 or is located on the surface of the coating 3. Figure 1 The larger particles shown are intended to indicate that the cyclodextrin or its derivatives containing polymer particles 2 are uniformly distributed in the coating 3. In the actual battery separator, the cyclodextrin or its derivatives containing polymer particles in the cavity are distributed in the coating with a defined average particle size.

[0043] In some embodiments, the base membrane is selected from PE, PP, or a composite membrane of PE and PP.

[0044] In some embodiments of this application, the thickness of the base film is 3 μm to 20 μm. Exemplarily, the thickness of the base film may be 3 μm, 4 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 17 μm, 18 μm, or 19 μm.

[0045] In some embodiments, the porosity of the base membrane is 20% to 70%, and the air permeability is 70 sec / 100cc to 200 sec / 100cc.

[0046] In some embodiments of this application, the coating thickness is 1 μm to 3 μm.

[0047] In some embodiments, cyclodextrin or its derivatives are selected from β-cyclodextrin, γ-cyclodextrin, hydroxypropyl-β-cyclodextrin, or combinations thereof. Based on the molecular weight of the water-free hydroxypropyl-β-cyclodextrin, the hydroxypropyl content should be between 19.6% and 26.3% by mass.

[0048] In some embodiments of this application, the degree of hydroxypropyl substitution in hydroxypropyl-β-cyclodextrin is 3.5–5. In these embodiments, because the degree of hydroxypropyl substitution of cyclodextrin varies, its solubility in the prepared pretreatment solution differs. Increasing the degree of hydroxypropyl substitution in β-cyclodextrin can improve its solubility and make it easier to obtain a saturated solution. Furthermore, compared to β-cyclodextrin, hydroxypropyl-β-cyclodextrin with the aforementioned degree of substitution exhibits better coating ability for polymer particles.

[0049] In some embodiments, the polymer particles are selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, hexafluoropropylene, polymethyl methacrylate (PMMA), polyethyl methacrylate, or combinations thereof.

[0050] The inventors of this application discovered that directly added polymer particles such as PMMA have poor stability and are prone to sedimentation after being formulated into coating slurries. In the solution of this application, PMMA polymer particles or other types of polymer particles are contained within cavities formed by cyclodextrin or its derivatives. The polymer particles are contained within these cavities, preventing them from detaching and thus preventing coating powdering. The cyclodextrin or its derivatives act as stabilizers, improving the stability of the coating slurry and ensuring more uniform distribution within it. Furthermore, the polymer particles dispersed within the cavities of the cyclodextrin or its derivatives can bond with the binder to form a network structure, enhancing the bonding strength between coating components and preventing powdering.

[0051] In some embodiments of this application, the swelling degree of the polymer particles is 20% to 120%, and the Tg is 30°C to 70°C. Optionally, the swelling degree of the polymer particles is 40% to 110%, and the Tg is 45°C to 60°C.

[0052] In some embodiments, the average particle size D of the polymer particles 50 The average particle size D is 0.1 μm to 1 μm, optionally 0.1 μm to 0.8 μm, and further optionally 0.1 μm to 0.5 μm. Exemplarily, the average particle size D of the polymer particles is... 50 The sizes are 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, and 1μm.

[0053] In the embodiments of this application, the polymer particles are granular or spherical and can be formulated into an emulsion containing polymer particles. The emulsion is then mixed with cyclodextrin and / or its derivatives at a certain temperature so that the polymer particles are contained within the cavities of the cyclodextrin and / or its derivatives, thereby preparing cyclodextrin and / or its derivatives containing polymer particles inside the cavities.

[0054] In the embodiments of this application, the minimum inner diameter of the cavity of cyclodextrin or its derivatives is 0.3 μm to 1 μm, the minimum outer diameter of cyclodextrin or its derivatives is 0.4 μm to 10 μm, and the average particle size D of the polymer particles in the coating is... 90 The minimum inner diameter of the cavity of the cyclodextrin or its derivative is ≤. For example, the minimum inner diameter of the cavity of the cyclodextrin or its derivative is 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm, and the minimum outer diameter of the cyclodextrin or its derivative is 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 9 μm, or 10 μm. The cyclodextrin or its derivative has a cavity that is wider at the top and narrower at the bottom, open at both ends, such as... Figure 1As shown, the minimum inner diameter 6 of the cavity is the inner diameter at the narrowest point at the bottom of the cavity, and the corresponding minimum outer diameter 5 is the outer diameter at the narrowest point at the bottom of the cavity. The average particle size D of the polymer particles in the coating... 90 The minimum inner diameter of the cavity of cyclodextrin or its derivatives enables the polymer particles to exist stably as a whole within the cavity of cyclodextrin or its derivatives, thereby coexisting stably with other components in the coating.

[0055] In some embodiments of this application, the minimum inner diameter of the cavity of the cyclodextrin or its derivative is equal to the particle size D of the polymer particles in the coating. 90 ×(1~1.5), that is, the minimum inner diameter of the cavity of cyclodextrin or its derivatives is equal to the average particle size D of the polymer particles. 90 The ratio is 1 to 1.5 times, which allows the polymer particles to fill the cavity of the cyclodextrin or its derivatives with a suitable particle size and makes them less likely to come out of the cavity.

[0056] In some embodiments of this application, the content of cyclodextrin or its derivatives containing polymer particles through cavities in the coating is 5 wt.% to 10 wt.%. Exemplarily, the content of cyclodextrin or its derivatives containing polymer particles through cavities in the coating may be 5.2 wt.%, 5.4 wt.%, 5.5 wt.%, 5.8 wt.%, 5.9 wt.%, 6 wt.%, 6.3 wt.%, 6.4 wt.%, 6.6 wt.%, 6.8 wt.%, 7.0 wt.%, 7.2 wt.%, 7.5 wt.%, 7.8 wt.%, 7.9 wt.%, 8.0 wt.%, 8.1 wt.%, 8.3 wt.%, 8.5 wt.%, 8.8 wt.%, 9.0 wt.%, 9.2 wt.%, 9.5 wt.%, 9.6 wt.%, or 9.8 wt.%.

[0057] In the embodiments of this application, the coating contains a low amount of cyclodextrin or its derivatives containing polymer particles in the cavity, which can effectively improve the stability of the battery separator, reduce the internal resistance of the separator, and improve the phenomenon of separator powder shedding.

[0058] In some embodiments of this application, the mass ratio of polymer particles to cyclodextrin or its derivatives in the coating is 1:(1-2). This mass ratio range allows for a more stable coating slurry, effectively reducing powder shedding and lowering the internal resistance of the battery separator. The cyclodextrin or its derivatives, which do not contain polymer particles within the cavity, utilize this cavity structure to contain other components in the coating (such as binders, ceramic powder, and thickeners). This, combined with the cyclodextrin or its derivatives containing polymer particles within the cavity, and the entanglement between the binder, ceramic powder, thickener, and polymer particles, prevents coating powder shedding. Simultaneously, the added cyclodextrin or its derivatives containing polymer particles through the cavity provides more ion channels on the battery separator surface, improving the ionic conductivity of the battery separator and effectively reducing its internal resistance. Furthermore, the simultaneous presence of polymer particles and binders in the coating further enhances the adhesion between the coating and the base film surface.

[0059] In a second aspect, this application provides a method for preparing a battery separator, comprising: providing a base membrane; providing a coating slurry containing polymer particles of cyclodextrin or its derivatives through a cavity; and coating the coating slurry onto at least one side surface of the base membrane to form a coating, thereby obtaining a battery separator containing the coating.

[0060] The battery separator preparation method of this application involves adding cyclodextrin or its derivatives, which contain polymer particles through cavities, to the coating slurry. This improves the stability of the coating slurry and reduces the internal resistance of the battery separator. Furthermore, the added cyclodextrin or its derivatives, which contain polymer particles through cavities, combine with other components in the coating slurry to comprehensively enhance the heat resistance of the battery separator. Simultaneously, the cavities of the cyclodextrin or its derivatives encapsulate ceramic powder and polymer particles, improving the adhesion strength between the coating and the base film, effectively reducing powder shedding from the battery separator, enhancing cell safety and cycle performance, and reducing coating costs.

[0061] In some embodiments of this application, a coating slurry containing polymer particles of cyclodextrin or its derivatives through cavities is provided, comprising: adding cyclodextrin or its derivatives to an emulsion containing polymer particles for coating treatment, so that the polymer particles are contained in cavities of cyclodextrin or its derivatives, to obtain a pretreatment solution; dispersing and refining ceramic powder, water, dispersant, and thickener to obtain a first dispersion slurry; adding the pretreatment solution to the first dispersion slurry to obtain a second slurry; and adding a binder to the second dispersion slurry to obtain a coating slurry containing polymer particles of cyclodextrin or its derivatives through cavities.

[0062] In the embodiments of this application, the coating treatment time for adding cyclodextrin or its derivatives to an emulsion containing polymer particles is from 10 minutes to 3 hours. Exemplary times include 20 minutes, 30 minutes, 45 minutes, 50 minutes, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.5 hours, 2.7 hours, and 3 hours. Preferably, it is from 1.5 hours to 2.5 hours.

[0063] In the embodiments of this application, the content of polymer particles in the emulsion containing polymer particles is 10 wt.% to 30 wt.%. For example, the emulsion containing polymer particles may be BM-2570 from Rayon. Alternatively, the emulsion containing polymer particles may be HD-6129 from Haodian.

[0064] In the embodiments of this application, the content of cyclodextrin or its derivatives containing polymer particles in the cavity of the pretreated solution is 26 wt.% to 35 wt%.

[0065] In the embodiments of this application, hydroxypropyl-β-cyclodextrin (abbreviated as HP-β-CD), also known as (2-hydroxypropyl)-β-cyclodextrin, introduces a hydroxypropyl group, altering the original compact and orderly crystalline molecular structure of β-cyclodextrin to form an amorphous mixture composed of components with various substitution forms. This helps to improve the water solubility and dissolution rate of HP-β-CD and its inclusion complexes. HP-β-CD and β-CD differ in their selectivity for the encapsulated substances. HP-β-CD is used as a stabilizer, emulsifier, deodorizer, etc., to enhance the stability of active ingredients, prevent oxidation, increase the water solubility of poorly soluble substances, and improve biocompatibility.

[0066] In the embodiments of this application, cyclodextrin or its derivatives can encapsulate polymer particles within the cavities of the cyclodextrin or its derivatives. The long-chain structure of the cyclodextrin itself acts as a connector for the entire coating, forming a unified coating and enhancing the bonding between coating components. This can suppress the floatation of the binder during the drying process of the coating slurry, resulting in stronger adhesion within the coating and effectively reducing powder shedding. Simultaneously, the cavities of the cyclodextrin or its derivatives, which are wider at the top and narrower at the bottom with openings at both ends, allow the polymer particles to bond with the binders and other components at both ends, further improving the bonding between components in the coating.

[0067] In the embodiments of this application, the amount of hydroxypropyl-β-cyclodextrin added satisfies the following conditions: the amount of hydroxypropyl-β-cyclodextrin used depends on the molecular size and polarity of the guest compound (i.e., polymer particles), and the inclusion of the host molecule (i.e., hydroxypropyl-β-cyclodextrin) with the guest compound molecules has a certain guest-to-mouse ratio, generally guest compound:host molecule = 1:(1~2). Therefore, the amount of hydroxypropyl-β-cyclodextrin added is generally 100 wt.% to 200 wt.% of the amount of polymer particles added.

[0068] Exemplarily, providing a coating slurry containing polymer particles of cyclodextrin or its derivatives through cavities includes: preparing a pretreatment solution: adding cyclodextrin or its derivatives to an emulsion containing polymer particles for coating treatment, and stirring thoroughly at 400 rpm to 800 rpm for 10 minutes to 2 hours to ensure that the polymer particles are contained within the cavities of the cyclodextrin or its derivatives, with the water bath temperature below the glass transition temperature (Tg) of the polymer particles; preparing the coating slurry: mixing 60 wt% to 90 wt% ceramic powder, 0.5 wt% to 3 wt% dispersant, and 40 wt% to 60 wt% water (by weight of the total coating slurry) using a high-speed mixer at 10 rpm. The mixture is dispersed at 00 rpm / 30 min to 1500 rpm / 30 min to obtain a dispersion product. Then, a thickener accounting for 1 wt% to 3 wt% of the total coating mass is added to the dispersion product, dispersed at a speed of 800 rpm to 1000 rpm, and refined by sand milling to obtain a first dispersion slurry. According to the mass ratio of pretreatment solution to first dispersion slurry 1:(7 to 12), pretreatment solution is added to the first dispersion slurry, and stirred at a speed of 350 rpm to 800 rpm for 10 to 30 minutes to obtain a second dispersion slurry. A binder accounting for 4 wt% to 10 wt% of the total coating mass is added to the second dispersion slurry to obtain a coating slurry.

[0069] For example, the water bath temperature is 40°C to 50°C. This temperature can be adjusted according to the glass transition temperature (Tg) of the polymer particles, ensuring that the water bath temperature is lower than the glass transition temperature (Tg) of the polymer particles. In the embodiments of this application, heating allows the polymer particles to quickly enter the cavity of the cyclodextrin or its derivatives, reducing reaction time and improving the coating efficiency of the cyclodextrin or its derivatives on the polymer particles.

[0070] In the embodiments of this application, the polymer particles are contained within the cavities of cyclodextrin or its derivatives, resulting in stronger adhesion to the base film. This also makes the slurry more stable, reduces sedimentation during coating slurry production, eliminates the need for wetting agents and other components, reduces foaming during the mixing process, and leads to a more consistent coating. Furthermore, separate stirring equipment is no longer required, reducing production costs.

[0071] In some embodiments, the ceramic powder is selected from alumina, boehmite, titanium dioxide, barium titanate, or combinations thereof.

[0072] In some embodiments, the dispersant is selected from polycarboxylates, sodium dodecyl sulfate, methylpentanol, cellulose derivatives, polyacrylamide, glucon, fatty acid polyethylene glycol esters, or combinations thereof.

[0073] In the embodiments of this application, a dispersant is added to ensure sufficient dispersion of the ceramic powder, thereby improving the dispersion effect of the ceramic powder. This reduces the agglomeration of ceramic powder particles, improves the consistency of the coating thickness, and optimizes the coating appearance.

[0074] In some embodiments of this application, the thickener is selected from carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, or combinations thereof. Carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose are selected as thickeners to improve the stability of the coating slurry.

[0075] In some embodiments of this application, the adhesive is selected from acrylic acid, acrylic polymers, polyacrylonitrile, or combinations thereof, and is added to improve the adhesion between the polymer and the base film.

[0076] In some embodiments of this application, the polymer particles are selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, hexafluoropropylene, polymethyl methacrylate, polyethyl methacrylate, or combinations thereof.

[0077] In some embodiments, the swelling degree of the polymer particles is 20% to 120%, and the Tg is 30°C to 70°C.

[0078] In some embodiments, the swelling degree of the polymer particles is 40% to 110%, and the Tg is 45°C to 60°C.

[0079] In some embodiments, the average particle size D of the polymer particles 50 The average particle size D is 0.1 μm to 1 μm, optionally 0.1 μm to 0.8 μm, and further optionally 0.1 μm to 0.5 μm. Exemplarily, the average particle size D of the polymer particles is... 50 The sizes are 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, and 1μm.

[0080] In the embodiments of this application, the polymer is in the form of particles or spheres, and can be formulated into an emulsion containing polymer particles, which is then mixed with cyclodextrin and / or its derivatives at a certain temperature, so that the polymer particles are coated in the cavity of the cyclodextrin or its derivatives, thereby preparing cyclodextrin or its derivatives containing polymer particles in the cavity, or cyclodextrin and its derivatives containing polymer particles in the cavity.

[0081] In some embodiments of this application, the minimum inner diameter of the cavity of cyclodextrin or its derivatives is 0.3 μm to 1 μm, the minimum outer diameter of cyclodextrin or its derivatives is 0.4 μm to 10 μm, and the average particle size D of the polymer particles in the coating is... 90 The minimum inner diameter of the cavity of the cyclodextrin or its derivative is ≤. For example, the minimum inner diameter of the cavity of the cyclodextrin or its derivative is 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm, and the minimum outer diameter of the cyclodextrin or its derivative is 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 9 μm, or 10 μm.

[0082] In some embodiments, the minimum inner diameter of the cavity of cyclodextrin or its derivatives is equal to the average particle size D of the polymer particles in the coating. 90 ×(1~1.5), that is, the average particle size of the polymer particles is less than or equal to the minimum inner diameter of the cavity of the cyclodextrin or its derivative, and can just fill the cavity of the cyclodextrin or its derivative.

[0083] In some embodiments, forming a coating by coating a coating slurry on at least one side surface of a base membrane includes: applying the coating slurry to at least one side surface of the base membrane using a coating device and drying it to prepare a battery separator containing a coating.

[0084] In some embodiments, the temperature for drying the base film coated with the coating slurry is 55°C to 80°C.

[0085] Thirdly, this application provides an electrochemical device including the aforementioned battery separator.

[0086] In some embodiments, the electrochemical device is a rechargeable secondary battery. In the battery, the battery separator serves as a membrane material that separates the positive and negative electrodes, preventing electrons from passing through while simultaneously allowing ions to pass through.

[0087] In some other embodiments of this application, the electrochemical device is an energy storage device, and in the energy storage device, the battery separator can also be used as a separator material to isolate the positive electrode and the negative electrode.

[0088] The following are some of the raw materials used in the examples and comparative examples and their available sources. Components, raw materials, and reagents not mentioned can be obtained through commercial channels: The polymer is PMMA emulsion (solid content 15%, main component is PMMA polymer particles, Tg 55℃), manufacturer: Ruiweng, model: BM-2570; hydroxypropyl-β-cyclodextrin, manufacturer: Shandong Zhiyuan Biotechnology; ceramic powder is boehmite, manufacturer: Shandong Guoci, model: HBO-070S; thickener is carboxymethyl cellulose, manufacturer: Suzhou Fosai, model: 1220; wetting agent is polyether-modified polysiloxane, manufacturer: BYK, model: BYK-20990; binder is acrylate, manufacturer: Shenzhen Chenyu, model: F15; dispersant is polycarboxylate, manufacturer: Xidema, model: DP-03.

[0089] Example 1

[0090] A method for preparing a battery separator, comprising:

[0091] Base film provided: Polyethylene (PE) film is used as the base film, wherein the thickness of the polyethylene base film is 9μm, the porosity is 42%, and the air permeability is 125sec / 100cc.

[0092] A coating slurry containing polymer particles of hydroxypropyl-β-cyclodextrin via a cavity is provided, comprising:

[0093] Preparation of the pretreatment solution: 1.5 kg of hydroxypropyl-β-cyclodextrin (degree of substitution 4) was added to 10 kg of PMMA polymer particle emulsion, wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles was 1. The mixture was stirred in a water bath at 40°C for 2 hours, during which the PMMA polymer particles were contained within the cavities of the hydroxypropyl-β-cyclodextrin. After heating and stirring, the mixture was cooled to room temperature (25°C) and filtered through a 100-mesh filter to obtain a cyclodextrin pretreatment solution containing PMMA polymer particles within its cavities. The average particle size D of the PMMA polymer particles was [not specified]. 50 The minimum inner diameter of the cavity of hydroxypropyl-β-cyclodextrin is 0.1 μm to 1 μm, which is equal to the average particle size D of the PMMA polymer particles in the coating. 90 ×(1~1.5).

[0094] Preparation of coating slurry: Weigh 30 kg of boehmite powder, 0.3 kg of dispersant, and 57 kg of water. Stir at 1000 rpm for 30 minutes to ensure complete dispersion of the powder. Then add 1.1 kg of thickener to obtain the first dispersion. Add 7.8 kg of pretreatment solution to the first dispersion, continue stirring until homogeneous, then add 3.5 kg of binder and stir again until homogeneous to obtain the coating slurry.

[0095] Coating slurry application: The coating slurry is fed into the feeding tank through an automatic feeding system and coated on both sides of the polyethylene film in the thickness direction by roller coating. The gravure roller has a line count of 180 lines / inch, a depth of 30μm, a coating speed of 100m / min, an oven temperature of 75℃, a speed ratio of 0.95, and a single-sided coating thickness of 2μm to prepare the battery separator.

[0096] Example 2

[0097] A method for preparing a battery separator differs from Example 1 in that the water bath temperature used in the step of preparing the pretreatment solution is 50°C.

[0098] Example 3

[0099] A method for preparing a battery separator differs from Example 1 in that the water bath temperature used in the step of preparing the pretreatment solution is 45°C.

[0100] Example 4

[0101] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 2.25 kg (degree of substitution is 4), wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 1.5, and the water bath temperature used is 45°C.

[0102] Example 5

[0103] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 3.0 kg (degree of substitution is 4), wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 2, and the water bath temperature used is 45°C.

[0104] Example 6

[0105] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 1.5 kg (degree of substitution is 4), wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 1, and the water bath temperature used is 35°C.

[0106] Example 7

[0107] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 1.5 kg (degree of substitution is 4), wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 1, and the water bath temperature used is 55°C.

[0108] Example 8

[0109] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 1.5 kg (degree of substitution is 4), wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 1, the water bath temperature is 45°C, and the water bath stirring time is shortened from 2 hours to 1 hour.

[0110] Example 9

[0111] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 1.5 kg (degree of substitution is 4), wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 1, the water bath temperature is 45°C, and the water bath stirring time is increased from 2 hours to 3 hours.

[0112] Example 10

[0113] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of β-cyclodextrin is 1.5 kg, wherein the mass ratio of β-cyclodextrin to PMMA polymer particles is 1, and the minimum inner diameter of the β-cyclodextrin cavity is equal to the average particle size D of the polymer particles in the coating. 90 ×(1~1.5), the water bath temperature is 45℃, and the water bath stirring time is 2 hours.

[0114] Example 11

[0115] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 2.1 kg (degree of substitution is 4), wherein the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 1.4, the water bath temperature is 40°C, and the water bath stirring time is 2 hours.

[0116] Example 12

[0117] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the pretreatment solution, the mass of hydroxypropyl-β-cyclodextrin is 2.7 kg (degree of substitution is 4), the mass ratio of hydroxypropyl-β-cyclodextrin to PMMA polymer particles is 1.8, the water bath temperature is 40°C, and the water bath stirring time is 2 hours.

[0118] Comparative Example 1

[0119] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the coating slurry, 30 kg of boehmite powder, 0.3 kg of dispersant, and 57 kg of water are weighed and stirred at 1000 rpm for 30 minutes to ensure complete dispersion of the powder. Then, 1.1 kg of thickener and 3.5 kg of PMMA emulsion are added, and after stirring until homogeneous, 3.5 kg of binder is added and stirred again until homogeneous to prepare the coating slurry.

[0120] Comparative Example 2

[0121] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the coating slurry, 30 kg of boehmite powder, 0.3 kg of dispersant, and 57 kg of water are weighed and stirred at 1000 rpm for 30 minutes to ensure complete dispersion of the powder. Then, 1.1 kg of thickener and 5.25 kg of β-cyclodextrin are added, and after stirring until homogeneous, 3.5 kg of binder is added and stirred again until homogeneous to obtain the coating slurry.

[0122] Comparative Example 3

[0123] A method for preparing a battery separator differs from Example 1 in that: in the step of preparing the coating slurry, 30 kg of boehmite powder, 0.3 kg of dispersant, and 57 kg of water are weighed and stirred at 1000 rpm for 30 minutes to ensure complete dispersion of the powder. Then, 1.1 kg of thickener and 5.25 kg of α-cyclodextrin are added, and after stirring until homogeneous, 3.5 kg of binder is added and stirred again until homogeneous to obtain the coating slurry.

[0124] Performance testing

[0125] The following performance tests were performed on the battery separators prepared in Examples 1-12 and Comparative Examples 1-3:

[0126] (1) Air permeability value was tested using a Wang Yan-style air permeability meter. The sampling width of the battery separator was 5cm strip.

[0127] (2) Thickness: The thickness was tested using a Marl thickness gauge, and the sample was a 5cm strip.

[0128] (3) Powder shedding rate: Five strip samples with a width of 2.5cm and a length of 25cm were cut and tested using a color fastness tester.

[0129] (4) Ionic conductivity and internal resistance test method: Cut a 19mm diameter circular battery separator sheet and immerse it in 1mol / L LiPF6 electrolyte, keeping it sealed and soaking for 5 hours. The mass ratio of organic solvent EC:DMC:EMC in the electrolyte is 1:1:1. Then, assemble the coin cell in the following order: positive electrode shell, battery separator (wetted with electrolyte), gasket, spring, and negative electrode shell. Assemble 4 batteries by increasing the number of battery separator layers (1, 2, 3, 4). After standing for 2 hours, test the impedance, i.e., the internal resistance. Linearly fit the resistance value and the corresponding number of battery separator layers according to R = k*1 to obtain the resistance value in the thickness direction of a single battery separator layer, where: R is the resistance value, 1 is the number of battery separator layers. Calculate the ionic conductivity of the battery separator according to the formula σ = d / RS, where: σ is the ion throughput of a single separator layer, d is the thickness of the battery separator, R is the resistance, and S is the cross-sectional area of ​​the battery separator perpendicular to the current direction.

[0130] The results of the battery separators prepared in Examples 1-12 and Comparative Examples 1-3 for the above-mentioned performance tests are recorded in Table 1 below.

[0131] Table 1

[0132]

[0133] It should be noted that the average membrane thickness in Table 1 is the average value of tests conducted at 5 points. The coating permeability increment represents the difference in permeability between the coated battery separator and the uncoated base membrane. Ionic conductivity characterizes the cycle performance of the battery separator; higher ionic conductivity indicates better ion conduction and superior electrical performance.

[0134] Comparing the preparation methods of the battery separators in Examples 1-12 and Comparative Examples 1-3, and the performance test data of the battery separators prepared in each example, it can be concluded that: The test data from the above examples show that the battery separator with hydroxypropyl-β-cyclodextrin containing polymer particles within the cavity has a lower internal resistance than the battery separator with β-cyclodextrin containing polymer particles within the cavity, and both are significantly lower than the internal resistance of the battery separator in Comparative Example 1 with only PMMA polymer particles added. This also proves that the performance of the battery separator with hydroxypropyl-β-cyclodextrin containing polymer particles within the cavity is superior to that of the battery separator with β-cyclodextrin containing polymer particles within the cavity. Furthermore, the powder shedding rate decreased significantly from over 4.1% to below 2.9%.

[0135] The test data from the above embodiments show that as the temperature of the pretreatment solution preparation is too high or too low, such as exceeding 50°C or falling below 40°C, the resistance and powder shedding rate of the prepared battery separator increase, while the ionic conductivity decreases. This proves that the optimal range for preparing the pretreatment solution is 40°C to 50°C.

[0136] The test data from the above embodiments show that both short and long reaction times for preparing the pretreatment solution lead to increased internal resistance of the battery separator, decreased ionic conductivity, and increased powder shedding rate. This proves that a reaction time of about 2 hours for preparing the pretreatment solution is the optimal time.

[0137] The test data from the above embodiments demonstrate that when the amount of cyclodextrin or its derivatives added is 100wt.% to 200wt.% of the PMMA polymer particles, it can simultaneously improve internal resistance, ionic conductivity, coating permeability, and powder shedding rate.

[0138] As can be seen from the comparison of the above embodiments and comparative examples, the battery separators of Comparative Examples 1-3 with only PMMA polymer particles or only β-cyclodextrin cannot effectively reduce the internal resistance of the battery separator. Their internal resistance and powder shedding rate are significantly higher than those of the battery separator of Example 3 with hydroxypropyl-β-cyclodextrin with polymer particles inside the cavity, and also higher than those of the battery separator of Example 10 with β-cyclodextrin with polymer particles inside the cavity. This also proves that coating polymer particles in the cavity of cyclodextrin or its derivatives can effectively reduce the internal resistance and powder shedding rate of the battery separator.

[0139] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A battery separator, characterized by, The battery separator comprises: a base film; a coating layer provided on at least one side surface of the base film; the coating layer contains cyclodextrin or its derivative containing polymer particles by cavities.

2. The battery separator of claim 1, wherein, Any one of the following requirements is met: the base film is selected from PE, PP, or a composite separator of PE and PP; the cyclodextrin or its derivative is selected from β-cyclodextrin, γ-cyclodextrin, hydroxypropyl-β-cyclodextrin, or a combination thereof; the polymer particles are selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, hexafluoropropylene, polymethyl methacrylate, polyethyl methacrylate, or a combination thereof; the thickness of the coating layer is 1 μm to 3 μm.

3. The battery separator of claim 1 or 2, wherein, Any one of the following requirements is met: the thickness of the base film is 3 μm to 20 μm; the porosity of the base film is 20% to 70%, and the air permeability is 70 sec / 100cc to 200 sec / 100cc; the swelling degree of the polymer particles is 20% to 120%, and the Tg is 30°C to 70°C; optionally, the swelling degree of the polymer particles is 40% to 110%, and the Tg is 45°C to 60°C; The average particle diameter D of the polymer particles is 0.1 to 1 μm. 50 is 0.1 μm to 1 μm.

4. The battery separator of claim 1 or 2, wherein, At least one of the following requirements is met: the content of the cyclodextrin or its derivative containing the polymer particles by cavities in the coating layer is 5 wt.% to 10 wt.%. The minimum inner diameter of the cavity of the cyclodextrin or its derivative is 0.3 μm to 1 μm, the minimum outer diameter of the cyclodextrin or its derivative is 0.4 μm to 10 μm, and the average particle diameter D 90 ≤ the minimum inner diameter of the cavity of the cyclodextrin or its derivative; the minimum inner diameter of the cavity of said cyclodextrin or derivative thereof is equal to the average particle size D of said polymer particles in said coating 90 x (1-1.5).

5. A method of producing a battery separator as claimed in any one of claims 1 to 4, characterised in that, The battery separator comprises: providing a base film; providing a coating slurry of cyclodextrin or its derivative containing polymer particles by cavities; coating the coating slurry on at least one side surface of the base film to form a coating layer, thereby preparing a battery separator comprising the coating layer.

6. The production method according to claim 5, wherein The provision of the coating slurry of cyclodextrin or its derivative containing polymer particles by cavities comprises: adding cyclodextrin or its derivative to an emulsion containing polymer particles for coating treatment, so that the polymer particles are contained in the cavities of the cyclodextrin or its derivative, thereby preparing a pretreatment solution; dispersing and refining ceramic powder, water, dispersant, and thickening agent to prepare a first dispersion slurry; adding the pretreatment solution to the first dispersion slurry to prepare a second dispersion slurry; adding a binder to the second dispersion slurry to prepare a coating slurry containing cyclodextrin or its derivative with internal coated polymer.

7. The production method according to claim 6, wherein Any one of the following requirements is met: the content of the polymer particles in the emulsion containing polymer particles is 10 wt.% to 30 wt.%; the content of the cyclodextrin or its derivative containing polymer particles by cavities in the prepared pretreatment solution is 26 wt.% to 35 wt%; dispersing and refining 60 wt.% to 90 wt.% of ceramic powder, 0.5 wt.% to 3 wt.% of dispersant, and 1 wt.% to 3 wt.% of thickening agent based on the total mass of the coating layer, and 40 wt.% to 60 wt.% of water based on the total mass of the coating slurry, thereby preparing a first dispersion slurry; adding the pretreatment solution to the first dispersion slurry according to a mass ratio of pretreatment solution to first dispersion slurry of 1:(7-12), thereby preparing a second dispersion slurry; adding 4 wt.% to 10 wt.% of a binder based on the total mass of the coating layer to the second dispersion slurry, thereby preparing a coating slurry.

8. The production method according to claim 6 or 7, characterized by, Any one of the following requirements is met: the ceramic powder is selected from alumina, boehmite, titanium oxide, barium titanate, or a combination thereof; The dispersing agent is selected from the group consisting of polycarboxylate, sodium dodecyl sulfate, methyl amyl alcohol, cellulose derivatives, polyacrylamide, guar gum, fatty acid polyethylene glycol ester, or a combination thereof; The thickening agent is selected from the group consisting of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, or a combination thereof; The binder is selected from the group consisting of acrylic acid, acrylic acid polymer, polyacrylonitrile, or a combination thereof.

9. The preparation method according to claim 5, characterized in that, The coating of the coating slurry on at least one side surface of the base film to form a coating layer comprises: The coating of the coating slurry on at least one side surface of the base film using a coating device and drying treatment to prepare a battery separator comprising a coating layer.

10. An electrochemical device, characterized by, The battery separator as claimed in any one of claims 1-4.

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