A coating slurry, low impedance separator and method of making the same

Abstract

The application provides a coating slurry, a low-resistance diaphragm and a preparation method thereof, and relates to the technical field of lithium batteries. The preparation method of the coating slurry comprises the following steps: dispersing coating main materials and a binder in a solvent, dispersing at a first preset speed to obtain a concentrated solution; adding a solvent to the concentrated solution to dilute, dispersing at a second preset speed to obtain an intermediate system; adding a solvent to the intermediate system to dilute again, stirring at a third preset speed to obtain a finished product coating slurry. The method can prepare a slurry capable of forming a high-porosity coating through the gradient process of first dispersing and breaking the agglomeration of raw materials at a high speed and then reducing the speed to dilute and control the formation of a loose structure, so that the ion transmission impedance of the diaphragm is significantly reduced, and the ion conductivity and the pole piece adhesion are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery, in particular to a coating slurry, a low-impedance separator and a preparation method thereof. BACKGROUND

[0002] Secondary ion batteries, especially lithium-ion batteries and sodium-ion batteries, as the main electrochemical energy storage devices in modern times, their basic structure usually includes a positive electrode, a negative electrode, an electrolyte and a separator between the positive and negative electrodes. The separator is a key component inside the battery, and its core function is to physically separate the positive and negative electrodes to prevent internal short circuits, and at the same time, it also needs to provide an efficient transmission channel for ions in the electrolyte. Therefore, the microstructure and physicochemical properties of the separator, such as porosity, pore size distribution, ionic conductivity and thermal stability, directly determine the overall performance of the battery, including energy density, power characteristics, cycle life and most importantly safety. With the rapid development of electric vehicles, consumer electronics and large-scale energy storage, the market has put forward unprecedented requirements for the rapid charging capability and high power output performance of the battery, which makes it one of the key bottlenecks of technology development to reduce the internal resistance of the battery, especially the ion transmission impedance of the separator.

[0003] In order to improve the comprehensive performance of the separator, the existing technology generally adopts the strategy of coating a functional coating layer on the surface of a porous base film such as polyolefin (such as polyethylene or polypropylene). These coating layers are usually composed of inorganic particles (such as alumina, boehmite) and polymer binders (such as polyvinylidene fluoride). By introducing a functional coating layer, the high-temperature resistance and wettability of the separator to the electrolyte can be effectively improved. In terms of reducing the impedance of the separator, the existing technology mainly focuses on several directions: for example, developing new coating materials with higher ionic conductivity; or by changing the stretching process of the base film to regulate its pore structure; or special surface treatment of the finished separator to improve its interface characteristics. These schemes, although to some extent improve the performance of the separator, often focus on the chemical properties of the material itself or the physical structure of the base film, and there is still a lack of attention on how the coating process affects the microphysical packing structure of the coating layer and its deep relationship with the impedance.

[0004] However, the existing coated separator still has insurmountable technical defects in the preparation process. During the preparation and coating of the slurry, the particle materials in the coating tend to form a dense packing structure. This dense packing form will directly cause the effective porosity of the coating area to decrease significantly, making the transmission channel of lithium ions narrow or even blocked, thereby greatly increasing the resistance of ion migration. More seriously, the dense particle packing will form a more complex and tortuous pore network, and the ions need to take a longer path to shuttle in it, that is, the tortuosity of the channel is increased, which further deteriorates the ionic conductivity performance of the separator, leading to an increase in the overall impedance.

[0005] In summary, the existing coating separator technology generally faces a common problem, that is, the microstructure of the coating layer is difficult to achieve ideal control. The limitation of the preparation process makes the coating particles too dense, which comprehensively causes the problems of reduced porosity, increased tortuosity of the pores and insufficient electrolyte infiltration. These problems collectively result in high ion transport impedance of the separator, which limits the improvement of the high-rate charge and discharge performance of the secondary ion battery, and cannot fully meet the urgent demand for low-impedance core materials in the application scenarios of the next generation of high-power and fast-charging batteries.

[0006] Therefore, the present application is proposed. SUMMARY

[0007] The purpose of the present application is to provide a coating slurry, a low-impedance separator and a preparation method thereof. The coating slurry is prepared by a process of gradient speed reduction and stepwise dilution, which first disperses the secondary particle agglomerates of raw materials, and then controls the formation of a loose accumulation structure, thereby obtaining a slurry capable of forming a coating layer with high porosity and low tortuosity, and finally significantly reducing the ion transport impedance of the separator and improving the ionic conductivity.

[0008] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted:

[0009] In a first aspect, the present application provides a preparation method of a coating slurry, comprising:

[0010] dispersing the coating main material and the binder in the solvent, dispersing at a first preset speed to obtain a concentrated solution with a solid content of M1;

[0011] adding solvent to the concentrated solution for dilution, dispersing at a second preset speed lower than the first preset speed to obtain an intermediate system with a solid content of M2;

[0012] adding solvent to the intermediate system for dilution, stirring at a third preset speed lower than the second preset speed to obtain a finished coating slurry with a solid content of M3;

[0013] wherein the solid content satisfies the relationship: M1>M2>M3; the ratio of M1 / M3 is not less than 3, and the ratio of M2 / M3 is not less than 1.5.

[0014] In an optional embodiment, M1 is 40% to 80%.

[0015] In an optional embodiment, M2 is 10% to 35%.

[0016] In an optional embodiment, M3 is 8% to 20%.

[0017] In an optional embodiment, 3≤M1 / M3≤7.

[0018] In an optional embodiment, 1.5≤M2 / M3≤2; or, 1.6≤M2 / M3≤1.8.

[0019] In an optional embodiment, the first preset speed is 1300 rpm~1800 rpm.

[0020] In an optional embodiment, the second preset speed is 1000 rpm~1300 rpm.

[0021] In an optional embodiment, the third preset speed is 400 rpm~600 rpm.

[0022] In an optional embodiment, the ratio of the particle D 50 to the primary particle size D 50 of the coating main material in the finished coating slurry is less than 30; or, the ratio of the particle D 50 to the primary particle size D 50 of the coating main material in the finished coating slurry is not higher than 20; or, the ratio of the particle D 50 to the primary particle size D 50 of the coating main material in the finished coating slurry is 15~20; and / or,

[0023] In an optional embodiment, the ratio of the particle D 50 to the secondary particle size D 50 of the coating main material in the finished coating slurry is less than 0.8; or, the ratio of the particle D 50 to the secondary particle size D 50 of the coating main material in the finished coating slurry is not higher than 0.6; or, the ratio of the particle D 50 to the secondary particle size D 50 of the coating main material in the finished coating slurry is 0.4~0.6; and / or,

[0024] The primary particle size of the coating main material is 150 nm~200 nm;

[0025] The secondary particle size of the coating main material is 5 μm~8 μm.

[0026] In an optional embodiment, the coating main material comprises at least one of polyvinylidene fluoride resin, polyvinylidene fluoride homopolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-methyl methacrylate copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-acrylic acid copolymer, polymethyl methacrylate, polyethylene, and acrylate polymer; and / or,

[0027] The adhesive comprises at least one of carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polymethacrylic acid, acrylonitrile copolymer, and styrene-butadiene rubber; and / or,

[0028] The mass ratio of the adhesive to the coating material is (5~20):100.

[0029] In an optional embodiment, the step of adding solvent again to the intermediate system for dilution, stirring at a third preset rate lower than the second preset rate, and obtaining a finished coating slurry with a solid content of M3 further includes:

[0030] Add a wetting agent to the intermediate system;

[0031] The wetting agent includes at least one of alkyl sulfate, sulfonate, polyoxyethylene alkylphenol ether, and polyoxyethylene fatty alcohol ether; and / or, the mass ratio of the wetting agent to the coating material is (1~5):100.

[0032] Thirdly, the present invention provides a coating slurry, which is prepared by the coating slurry preparation method described in any of the foregoing embodiments.

[0033] Fourthly, the present invention provides a method for preparing a low-impedance diaphragm, comprising:

[0034] The coating slurry as described in the foregoing embodiments is applied to at least one surface of the base film to form a coating layer;

[0035] The base film with the coating layer is dried to obtain the low-impedance separator.

[0036] Fifthly, the present invention provides a low-impedance diaphragm, which is prepared by the low-impedance diaphragm preparation method described in the foregoing embodiments.

[0037] In a sixth aspect, the present invention provides a battery comprising a low-impedance separator as described in the foregoing embodiments.

[0038] In a seventh aspect, the present invention provides an electrical device including a battery as described in the foregoing embodiments.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] The method for preparing this coating slurry, through a specific combination of step-by-step processing and gradient rate reduction, can effectively control the final aggregation state of the coating material particles in the slurry.

[0041] First, in the initial stage of the preparation process, a high-preset first rate is used to disperse the concentrated solution with high solid content. This high energy input generates strong shear force, which mainly serves to effectively break down the large secondary particle agglomerates present in the coating main powder, which is the raw material, into smaller particle units, laying the foundation for subsequent structure control.

[0042] Subsequently, the method involves adding solvent to the system stepwise, gradually decreasing the dispersion or stirring rate—specifically, the second preset rate is lower than the first preset rate, and the third preset rate is lower than the second preset rate. This gradient transition from high to low energy, and the gradient dilution from high to low concentration (defined by the ratios of M1 / M3 and M2 / M3), prevents the dispersed fine particles from re-aggregating into a dense structure during subsequent processing. Instead, this gentle post-processing method promotes the formation of a stable suspension system with relatively loose interparticle bonding and low bulk density.

[0043] Therefore, the coating slurry prepared using this method, when used to prepare battery separators, forms a coating with a loose, aggregated structure at the microscopic level. This loose structure increases the porosity of the coating and reduces the tortuosity of the ion transport channels, thereby significantly reducing the resistance of lithium / sodium ions passing through the separator. Ultimately, this reduces the overall impedance of the separator, improves the ionic conductivity, and also enhances the adhesion between the separator and the electrode sheets. Attached Figure Description

[0044] 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.

[0045] Figure 1 This is a schematic flowchart of the method for preparing the coating slurry provided in the embodiments of this application;

[0046] Figure 2 This is a scanning electron microscope image of the surface morphology of the diaphragm prepared in Example 1 of this application;

[0047] Figure 3 The image above is a scanning electron microscope image of the surface morphology of the diaphragm prepared in Comparison 1. Detailed Implementation

[0048] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0049] This application provides a method for preparing a coating slurry, including:

[0050] Step S1: Disperse the coating material and binder in a solvent at a first preset rate to obtain a concentrated solution with a solid content of M1.

[0051] This step is the initial stage of the entire preparation process and is also a high-energy-input mixing stage. In this step, solid powder raw materials (i.e., "coating agent" and "binder") are added to the liquid (i.e., "solvent") and vigorously mixed and dispersed using a high mechanical stirring speed (i.e., "first preset rate").

[0052] The solvent mentioned above can be water, or other solvents acceptable for membrane preparation, such as organic solvents.

[0053] The result obtained in this step is a viscous, high-concentration mixture, or "concentrated solution." This solution is characterized by a high proportion of solid components (coating agent and binder) in the total mass, which is quantified as "solid content M1."

[0054] Using a higher "first preset rate" can generate strong shear force. This force is very effective in breaking down naturally occurring, large particle clumps in raw material powder into smaller units, and ensures that these small particles are fully wetted by the solvent and initially evenly distributed.

[0055] In industrial production, this step can be achieved using equipment such as planetary mixers or high-speed dispersers. The "first preset rate" is the specific rotational speed parameter set for these devices, for example, it can be set to 1500 rpm.

[0056] Step S2: Add solvent to the concentrated solution for dilution, and disperse at a second preset rate lower than the first preset rate to obtain an intermediate system with a solid content of M2.

[0057] In this step, more solvent is added to the concentrated solution obtained in the first step to dilute it. Simultaneously, the dispersion rate used (i.e., the "second preset rate") is reduced compared to the first step. After treatment, an "intermediate system" with a concentration between the initial and final concentrations is obtained. Its solid content ratio is "M2," and the value of M2 is lower than that of M1.

[0058] Reducing the dispersion rate means reducing the energy applied to the material. The advantage of this "slowing down" treatment is that it can maintain the dispersed state of the particles while avoiding the violent collision and re-aggregation of the already dispersed fine particles due to excessive energy. This is a transition from "powerful crushing" to "gentle regulation".

[0059] Specifically, this can be done in the existing stirring equipment; simply add the solvent and reduce the equipment's speed. For example, the speed can be reduced from 1500 rpm to 1200 rpm.

[0060] Step S3: Add solvent to the intermediate system again for dilution, and stir at a third preset rate lower than the second preset rate to obtain a finished coating slurry with a solid content of M3.

[0061] In this step, solvent is added again to the intermediate system obtained in the second step for final dilution. At this point, the stirring rate (i.e., the "third preset rate") is the lowest of the three steps. The final product is a "finished coating slurry" that can be directly used in subsequent coating processes. Its solids content is "M3," the lowest of the three stages.

[0062] The stirring is performed at a very low rate primarily to ensure that the newly added solvent is thoroughly mixed with the intermediate system without disrupting the existing particle suspension structure in the slurry. This gentle stirring helps stabilize the entire system, allowing the particles to remain uniformly suspended in the solvent in a relatively loose state.

[0063] Specifically, this can also be done in the mixing equipment by further reducing the speed. For example, the speed can be reduced from 1200 rpm to 500 rpm.

[0064] Furthermore, the solid content satisfies the following relationship: M1 > M2 > M3; the ratio of M1 / M3 is not less than 3, and the ratio of M2 / M3 is not less than 1.5.

[0065] The method provided in this embodiment quantifies the degree of "dilution" in the above three-step method.

[0066] Among them, M1>M2>M3: This inequality intuitively illustrates that the whole process is a continuous dilution process, and the solid content decreases at each step.

[0067] The ratio of M1 / M3 must be no less than 3. This constraint means that the solid content of the initial concentrated solution is at least three times that of the final slurry. It defines that the overall dilution range of the entire process must reach a relatively high level.

[0068] For example, if the final product slurry (M3) is required to have a solid content of 10%, then according to this condition, the solid content of the concentrated solution (M1) prepared in the first step must be at least 30% (i.e., 10% × 3).

[0069] The M2 / M3 ratio mentioned above is not less than 1.5. This constraint means that the solid content of the intermediate system is at least 1.5 times the solid content of the final finished pulp. It mainly defines the extent of the final dilution operation.

[0070] For example, if the solid content of the finished pulp (M3) is 10%, then the solid content of the intermediate system (M2) obtained in the second step must be at least 15% (i.e., 10% × 1.5).

[0071] By strictly defining this set of solid content ratios, the dilution process from concentrated to diluted is ensured to be significant and phased. This large-scale, controlled dilution creates sufficient space between particles, which is the key guarantee that they can form a loose rather than a densely packed structure.

[0072] In some implementations, M1 ≥ 40%; or, M1 is 40% to 80%; for example, it can be 40%, 50%, 60%, 70%, 80%, etc.

[0073] In some implementations, M2 is 10% to 35%. For example, it can be 10%, 20%, 30%, 35%, etc.

[0074] In some implementations, M3 is 8% to 20%. For example, it can be 8%, 9%, 10%, 11%, 12%, 15%, 18%, 20%, etc.

[0075] In some implementations, 3 ≤ M1 / M3 ≤ 7. For example, it can be 3, 4, 5, 6, 7, etc.

[0076] In some implementations, 1.5 ≤ M2 / M3 ≤ 2 (e.g., it can be 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.); or, 1.6 ≤ M2 / M3 ≤ 1.8.

[0077] In some implementations, the first preset speed is 1300 rpm to 1800 rpm. For example, it can be 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, etc.

[0078] In some implementations, the second preset speed is 1000 rpm to 1300 rpm. For example, it can be 1000 rpm, 1200 rpm, 1300 rpm, etc.

[0079] In some implementations, the third preset speed is 400 rpm to 600 rpm. For example, it can be 400 rpm, 500 rpm, 600 rpm, etc.

[0080] In some embodiments, the particles D in the finished coating slurry 50 The primary particle size D of the coating material 50 The ratio is less than 30; or, the particle size D in the finished coating slurry is... 50 The primary particle size D of the coating material 50 The ratio is not higher than 20; or, the particle size D in the finished coating slurry is... 50 The primary particle size D of the coating material 50 The ratio is 15 to 20 (for example, it can be 15, 16, 17, 18, 19, 20, etc.).

[0081] In some embodiments, the particles D in the finished coating slurry 50 The secondary particle size D of the coating material 50 The ratio is less than 0.8; or, the particle size D in the finished coating slurry is... 50 The secondary particle size D of the coating material 50 The ratio is not higher than 0.6; or, the particle size D in the finished coating slurry is... 50 The secondary particle size D of the coating material 50 The ratio is 0.4 to 0.6 (for example, it can be 0.4, 0.5, 0.6, etc.).

[0082] The primary particle size mentioned above refers to the size of the smallest, most basic individual particles that make up the powder. In this context, it is at the nanometer (nm) level, which is relatively small.

[0083] The aforementioned secondary particle size refers to the size of a larger particle cluster formed by many tiny primary particles attracting each other through physical forces. Here, it is on the micrometer (μm) scale, and is relatively larger than primary particles.

[0084] In some embodiments, the primary particle size of the coating material is 150nm~200nm; for example, it can be 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, etc.

[0085] In some embodiments, the secondary particle size of the coating material is 5μm to 8μm. For example, it can be 5μm, 6μm, 7μm, 8μm, etc.

[0086] By defining a specific mathematical relationship between the initial particle size of the raw materials and the final particle size of the finished slurry, the uniqueness of this preparation method is conversely limited from the perspective of the result. This method can achieve a dual objective: effectively dispersing large agglomerates in the raw materials while controlling these dispersed particles to form moderately sized, loosely structured micro-agglomerates. It is precisely these loosely structured final particles within a specific particle size range that lay the foundation for the subsequent formation of a low-resistivity membrane coating.

[0087] In some embodiments, the coating material includes at least one selected from polyvinylidene fluoride resin, polyvinylidene fluoride homopolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-methyl methacrylate copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-acrylic acid copolymer, polymethyl methacrylate, polyethylene, and acrylate polymers; and / or,

[0088] The adhesive comprises at least one of carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polymethacrylic acid, acrylonitrile copolymer, and styrene-butadiene rubber; and / or,

[0089] The mass ratio of the adhesive to the coating material is (5~20):100. For example, it can be 5:100, 6:100, 7:100, 8:100, 9:100, 10:100, 12:100, 15:100, 18:100, 20:100, etc.

[0090] In some embodiments, step S3, which involves adding solvent again to the intermediate system for dilution and stirring at a third preset rate lower than the second preset rate to obtain a finished coating slurry with a solid content of M3, further includes:

[0091] Add a wetting agent to the intermediate system;

[0092] The wetting agent includes at least one of alkyl sulfate, sulfonate, polyoxyethylene alkylphenol ether and polyoxyethylene fatty alcohol ether; and / or, the mass ratio of the wetting agent to the coating material is (1~5):100 (for example, it can be 1:100, 2:100, 3:100, 4:100, 5:100, etc.).

[0093] In this embodiment of the application, a coating slurry is provided, which is prepared by the coating slurry preparation method described in any of the foregoing embodiments.

[0094] In this embodiment of the application, a method for preparing a low-impedance diaphragm is provided, comprising:

[0095] Step S4 involves coating the coating slurry as described in the foregoing embodiments onto at least one surface of the base film to form a coating layer.

[0096] This is an application process that transfers a liquid slurry onto a solid substrate. This step takes a coating slurry with a specific particle packing structure prepared by the aforementioned method and applies it uniformly to one or both surfaces of a porous "base film" (usually a material such as polyethylene or polypropylene).

[0097] After this step is completed, what is obtained is a base film with a layer of wet slurry on its surface. This wet slurry layer, or "coating layer", already has a loose granular structure at the microscopic level due to the special slurry.

[0098] The core advantage of this step is that it completely "replicates" the unique slurry physical morphology (i.e., the loose particle packing structure) carefully constructed in all the previous steps onto the base membrane surface. This is the foundation for achieving the final low impedance performance of the membrane.

[0099] Specifically, this coating process can be achieved in various ways, including but not limited to spraying, roller coating, blade coating, or spot coating. The choice of method depends on the specific requirements for coating thickness, uniformity, and production efficiency.

[0100] Step S5: Dry the base film with the coating layer to obtain the low-impedance separator.

[0101] This step involves the drying process of curing the moist semi-finished product into the final product. This step treats the base film with the moist coating layer by means of heating or blowing air, with the aim of removing solvents (such as water) from the coating layer.

[0102] After the solvent is removed, the solid components such as the coating material and binder are fixed on the surface of the base film, forming a porous and stable solid coating. The final product is a dried "low-impedance separator" that can be directly used for battery assembly.

[0103] The key advantage of this step is that, due to the special loose structure of the slurry used, the particles do not collapse and shrink into a dense, non-porous or low-porosity film during solvent evaporation due to surface tension or other factors. Instead, they retain their original loose packing morphology, thus forming abundant, interconnected ion transport channels in the final dry coating. It is this high-porosity, low-torsion microstructure, which is retained even after drying, that ensures the final membrane possesses the excellent property of "low impedance."

[0104] In this embodiment, a low-impedance diaphragm is provided, which is prepared by the low-impedance diaphragm preparation method described in the foregoing embodiments.

[0105] In this application embodiment, a battery is provided, including a low-impedance separator as described in the foregoing embodiments.

[0106] Because the separator is essentially a flexible, porous film, it can be cut into any shape and is suitable for various mainstream battery packaging processes and structures. Therefore, the specific types of batteries using this separator can include, but are not limited to: Prismatic Cells: In these rigid-shell batteries, the separator is used to isolate the stacked or wound positive and negative electrodes; Cylindrical Cells: For example, common 18650, 21700, or 4680 type batteries, the separator is a key material and is tightly wound together with the positive and negative electrodes to form the cell; Pouch Cells: In these batteries using aluminum-plastic film encapsulation, the separator is cut into sheets to isolate the stacked multilayer positive and negative electrodes; Button / Coin Cells: In rechargeable button cells, the separator is punched into a circle to isolate the stacked circular positive and negative electrodes.

[0107] In this application embodiment, an electrical device is provided, including a battery as described in the foregoing embodiments.

[0108] Because of its superior performance in terms of low internal resistance, high-rate charging and discharging, and high power output, any device integrating this battery will achieve faster charging speeds or stronger power performance. These electrical devices cover a wide range of applications, including but not limited to: in the transportation sector, such as pure electric vehicles, hybrid vehicles, and electric bicycles; in the portable electronic devices sector, such as smartphones, laptops, drones, and power tools; in the energy storage system sector, such as grid-scale energy storage stations, home energy storage systems, and uninterruptible power supplies (UPS); and other professional and consumer electronic products that require high power output or fast charging capabilities, such as industrial robots and portable medical devices.

[0109] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for the purpose of more detailed illustration and should not be construed as limiting the present invention in any way.

[0110] Table 1. Parameters related to coating main material, binder and wetting agent in the examples and comparative examples.

[0111]

[0112] The units for coating material, adhesive, and wetting agent are all kg; the ratios of adhesive / coating material and wetting agent / coating material are by mass.

[0113] Table 2. Solid content parameters in the examples and comparative examples

[0114]

[0115] The unit for solid content is %.

[0116] Table 3. Particle size-related parameters in the examples and comparative examples

[0117]

[0118] Example 1:

[0119] This embodiment describes the preparation of a diaphragm.

[0120] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0121] Weigh 2.05 kg of deionized water, 8.9 kg of PVDF (primary particle size D50 of 160 nm, secondary particle size D50 of 6 μm) and 6.85 kg of binder (solid content 15%). First, premix and disperse the PVDF using a double planetary mixer at 1500 rpm for 1-2 hours. Then add 40 kg of deionized water and mix at 1200 rpm for 30 minutes. After that, transfer the mixture to a sand mill and mill it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent (solid content 20%) and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine, adjust the coating parameters to ensure the coating amount is within the standard range, dry after coating, roll up, and then slit into appropriate specifications to obtain the final product.

[0122] Example 2:

[0123] This embodiment describes the preparation of a diaphragm.

[0124] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0125] Weigh 2.05 kg of deionized water, 8.9 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix for 30 minutes at 1200 rpm. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 2.08 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine and adjust the coating parameters to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then slit it into appropriate specifications to obtain the final product.

[0126] Example 3:

[0127] This embodiment describes the preparation of a diaphragm.

[0128] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0129] Weigh 2.05 kg of deionized water, 8.9 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix for 30 minutes at 1200 rpm. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.05 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine and adjust the coating parameters to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then cut it into appropriate specifications to obtain the final product.

[0130] Example 4:

[0131] This embodiment describes the preparation of a diaphragm.

[0132] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0133] Weigh 2.05 kg of deionized water, 8.9 kg of PVDF, and 5.35 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix for 30 minutes at 1200 rpm. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine. Adjust the coating parameters appropriately to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then slit it into appropriate specifications to obtain the final product.

[0134] Example 5:

[0135] This embodiment describes the preparation of a diaphragm.

[0136] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0137] Weigh 2.05 kg of deionized water, 8.9 kg of PVDF, and 8.38 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix for 30 minutes at 1200 rpm. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine and adjust the coating parameters to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then cut it into appropriate specifications to obtain the final product.

[0138] Example 6:

[0139] This embodiment describes the preparation of a diaphragm.

[0140] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0141] Weigh 2.05 kg of deionized water, 8.9 kg of PVDF, and 10 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix for 30 minutes at 1200 rpm. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine and adjust the coating parameters to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then cut it into appropriate specifications to obtain the final product.

[0142] Example 7:

[0143] This embodiment describes the preparation of a diaphragm.

[0144] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0145] Weigh 2.05 kg of deionized water, 8.9 kg of PVDF, and 11.7 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix for 30 minutes at 1200 rpm. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine. Adjust the coating parameters appropriately to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then slit it into appropriate specifications to obtain the final product.

[0146] Example 8:

[0147] This embodiment describes the preparation of a diaphragm.

[0148] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0149] Weigh 2.05 kg of water, 6.69 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix at 1200 rpm for 30 minutes. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine and adjust the coating parameters to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then cut it into appropriate specifications to obtain the final product.

[0150] Example 9:

[0151] This embodiment describes the preparation of a diaphragm.

[0152] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0153] Weigh 2.05 kg of water, 11.21 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix at 1200 rpm for 30 minutes. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine and adjust the coating parameters to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then cut it into appropriate specifications to obtain the final product.

[0154] Example 10:

[0155] This embodiment describes the preparation of a diaphragm.

[0156] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0157] Weigh 2.05 kg of deionized water, 13.63 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix for 30 minutes at 1200 rpm. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine. Adjust the coating parameters appropriately to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then slit it into appropriate specifications to obtain the final product.

[0158] Example 11:

[0159] This embodiment describes the preparation of a diaphragm.

[0160] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0161] Weigh 2.05 kg of deionized water, 16.17 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then add 40 kg of deionized water and mix at 1200 rpm for 30 minutes. After that, transfer the mixture to a sand mill and grind it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine. Adjust the coating parameters appropriately to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then slit it into appropriate specifications to obtain the final product.

[0162] Example 12:

[0163] This embodiment describes the preparation of a diaphragm.

[0164] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0165] Weigh 2.05 kg of deionized water, 0.95 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them using a double planetary mixer for 0.5-1 hour at 1500 rpm. Then add 17.88 kg of PVDF and continue premixing and dispersing using a double planetary mixer for 1-1.5 hours at 1500 rpm. Next, add 40 kg of deionized water and stir for 30 minutes at 1200 rpm. Then, transfer the mixture to a sand mill and mill it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and stir with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture using a coating machine. Adjust the coating parameters appropriately to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then slit it into suitable specifications to obtain the final product.

[0166] Example 13:

[0167] This embodiment describes the preparation of a diaphragm.

[0168] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0169] Weigh 2.05 kg of deionized water, 2.35 kg of PVDF, and 6.85 kg of binder. First, premix and disperse them using a double planetary mixer for 0.5-1 hour at 1500 rpm. Then add 19.27 kg of PVDF and continue premixing and dispersing using a double planetary mixer for 1-1.5 hours at 1500 rpm. Next, add 40 kg of deionized water and stir for 30 minutes at 1200 rpm. Then, transfer the mixture to a sand mill and mill it twice at 1000 rpm. Finally, add 42.45 kg of deionized water and 1.55 kg of wetting agent and stir with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture using a coating machine. Adjust the coating parameters appropriately to ensure the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then slit it into suitable specifications to obtain the final product.

[0170] Comparative Example 1:

[0171] In this comparative example, a diaphragm was prepared.

[0172] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0173] Weigh out 84.5 kg of water, 8.9 kg of PVDF and 6.85 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then, transfer them to a sand mill and grind them twice at 1000 rpm. Finally, add 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine. Adjust the coating parameters appropriately to ensure the coating amount is within the standard range. After coating, dry and roll up the mixture. Then, cut it into appropriate specifications to obtain the final product.

[0174] Comparative Example 2:

[0175] In this comparative example, a diaphragm was prepared.

[0176] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0177] Weigh out 84.5 kg of water, 8.9 kg of PVDF and 5.35 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at a speed of 1500 rpm. Then, transfer them to a sand mill and grind them twice at a speed of 1000 rpm. Finally, add 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at a speed of 500 rpm. After discharging, coat the mixture on a machine. Adjust the appropriate coating parameters to ensure that the coating amount is within the standard range. After coating, dry and roll up the mixture. Then, cut it into appropriate specifications to obtain the final product.

[0178] Comparative Example 3:

[0179] In this comparative example, a diaphragm was prepared.

[0180] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0181] Weigh out 84.5 kg of water, 8.9 kg of PVDF and 8.38 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then, transfer them to a sand mill and grind them twice at 1000 rpm. Finally, add 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine. Adjust the appropriate coating parameters to ensure the coating amount is within the standard range. After coating, dry and roll up the mixture. Then, cut it into appropriate specifications to obtain the final product.

[0182] Comparative Example 4:

[0183] In this comparative example, a diaphragm was prepared.

[0184] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0185] Weigh out 84.5 kg of water, 8.9 kg of PVDF and 10 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at a speed of 1500 rpm. Then, transfer them to a sand mill and grind them twice at a speed of 1000 rpm. Finally, add 1.55 kg of wetting agent and mix them in a double planetary mixer for 10 minutes at a speed of 500 rpm. After discharging, coat the mixture on a machine and adjust the appropriate coating parameters to ensure that the coating amount is within the standard range. After coating, dry the mixture, roll it up, and then cut it into appropriate specifications to obtain the final product.

[0186] Comparative Example 5:

[0187] In this comparative example, a diaphragm was prepared.

[0188] Experimental methods: For specific parameters and conditions, please refer to Tables 1-3.

[0189] Weigh out 84.5 kg of water, 8.9 kg of PVDF and 11.7 kg of binder. First, premix and disperse them in a double planetary mixer for 1-2 hours at 1500 rpm. Then, transfer them to a sand mill and grind them twice at 1000 rpm. Finally, add 1.55 kg of wetting agent and mix with a double planetary mixer for 10 minutes at 500 rpm. After discharging, coat the mixture on a machine. Adjust the appropriate coating parameters to ensure the coating amount is within the standard range. After coating, dry and roll up the mixture. Then, cut it into appropriate specifications to obtain the final product.

[0190] Test experiment:

[0191] 1. Experimental Method:

[0192] The final products prepared in the above embodiments and comparative examples were tested for the following indicators:

[0193] (1) Coating amount (g / m 2 The method used is the gravimetric method. First, accurately weigh a base film of a known area (e.g., 10cm x 10cm). Then, coat and dry this base film, and accurately weigh its total weight again. The difference between the two weights is the weight of the coated material. Dividing this weight by the area of ​​the base film gives the coating amount per unit area.

[0194] (2) Coverage (%): Image analysis method was used. Scanning electron microscope (SEM) or optical microscope was used to take photographs of the surface after the diaphragm was coated. Then, image analysis software was used to calculate the percentage of the total field of view covered by the coating particles in the photograph, which is the coverage.

[0195] (3) Coating thickness (μm): First, the original average thickness of the base film is measured at multiple points using a thickness gauge (compliant with GB / T36363-2018 standard). Then, the total average thickness of the final product diaphragm is measured using the same method. Coating thickness = Total thickness of finished product - Original thickness of base film.

[0196] (4) Change in air permeability before and after coating (s / 100mL): Measured using an air permeability tester (e.g., a Gurley meter, conforming to GB / T36363-2018 standard). Air permeability refers to the time (in seconds) required for a certain volume of air (100 mL) to pass through a membrane of a specified area under constant pressure. Measure the air permeability of the base membrane and the finished membrane separately. Change in air permeability = Air permeability of the finished membrane - Air permeability of the base membrane.

[0197] (5) Impedance change before and after coating (Ω): This is an electrochemically calculated value (compliant with GB / T36363-2018 standard). The membrane sample is immersed in the electrolyte and then assembled into a symmetrical cell (e.g., stainless steel sheet / membrane / stainless steel sheet). Its AC impedance is tested using an electrochemical workstation. The impedance values ​​of the base membrane and the finished membrane are tested separately. Impedance change = Finished membrane impedance - Base membrane impedance.

[0198] (6) Change in ionic conductivity (S / cm): This is a calculated value based on impedance test results (compliant with GB / T36363-2018 standard). Ionic conductivity can be calculated using the formula σ=L / (R×A), where L is the membrane thickness, R is the measured impedance, and A is the test area. Calculate the ionic conductivity of the base membrane and the finished membrane separately. Change in ionic conductivity = Ionic conductivity of finished membrane - Ionic conductivity of base membrane.

[0199] (7) Hot-pressed electrode adhesion force (N / m): This is a peel strength test. The diaphragm sample and the positive (or negative) electrode are stacked together and hot-pressed at 80°C and 2MPa for 60 seconds. Then, the pressed sample is fixed on a tensile testing machine and a 180° peel test is performed at a speed of 300 mm / min. The force required during the peeling process is recorded and then divided by the width of the sample to obtain the adhesion force.

[0200] (8) Dust shedding (mg): This is for abrasion resistance testing. Using an abrasion fastness tester, a pre-weighed piece of lens paper is fixed to the abrasion head. The diaphragm sample is fixed on the test platform, and the abrasion head is rubbed back and forth on the diaphragm surface 5 times. After the test, the lens paper is removed and weighed again. Dust shedding = weight of lens paper after abrasion - weight of lens paper before abrasion.

[0201] (9) Surface morphology analysis: The microstructure of the membrane samples finally prepared in Example 1 and the comparative example was observed using a scanning electron microscope (SEM). The samples were sputter-coated with gold to enhance conductivity, and then photographed at an appropriate magnification to analyze the packing state, distribution uniformity and pore structure of the coating particles.

[0202] 2. Experimental Results:

[0203] Table 4. Particle size-related parameters in the examples and comparative examples

[0204]

[0205] In Table 4, the unit for coating amount is g / m². 2 The unit for coating thickness is μm; the unit for coverage is %; the unit for change in air permeability before and after coating is s / 100mL; the unit for change in impedance before and after coating is Ω; the unit for change in ionic conductivity is S / cm; the unit for adhesion of hot-pressed electrode is N / m; and the unit for powder shedding is mg.

[0206] The coating thickness is calculated by first measuring the total thickness of the final membrane (thickness after coating), and then subtracting the original thickness of the base film used before coating (base film thickness). This difference is the actual thickness of the coated layer.

[0207] Changes in air permeability before and after coating are a measure of the effect of the coating on the air permeability of the diaphragm. The calculation method is: resistance after coating - base membrane resistance = air permeability value (the unit is usually seconds / 100mL). The higher the value, the more difficult it is for gas to pass through, and the fewer or smaller the pores. This calculation result shows how much the coating increases the air permeability value.

[0208] The change in impedance before and after coating measures the ion transport impedance introduced by the coating itself. By calculating the difference between the total impedance of the finished separator and the original impedance of the base film (impedance after coating - base film impedance), the exact amount of additional resistance added by the coating can be determined. The smaller this value, the better the coating performance and the less negative impact it has on the battery's internal resistance.

[0209] Changes in ionic conductivity are another core indicator, measuring the impact of the coating on ionic conductivity. The calculation method is: Ionic conductivity after coating - Ionic conductivity of the base film. Higher ionic conductivity means smoother ion passage. Since the coating occupies some space, it usually leads to a decrease in overall ionic conductivity, so this difference is generally negative. A negative number closer to 0 (i.e., a smaller absolute value) means that the coating causes less damage to ionic conductivity and offers better performance.

[0210] In hot-pressed electrode bonding strength, the number before the slash (e.g., 1.3) represents the bonding strength between the separator and the positive electrode. The number after the slash (e.g., 0.2) represents the bonding strength between the separator and the negative electrode. This indicator measures the strength of the coating's ability to act as "glue" to bond the separator and electrode together.

[0211] Reference Appendix Figure 2 (Example 1) and Appendix Figure 3 (Comparative Example 1) shows the surface morphology analysis results.

[0212] 3. Analysis:

[0213] By comparing the data of the embodiment (using a three-step gradient decreasing dispersion process) and the comparative example (using a traditional one-step slurry preparation process), a clear conclusion can be drawn: the slurry preparation method proposed in this invention can significantly optimize the core electrochemical and mechanical properties of the diaphragm while maintaining basically the same physical parameters such as coating amount and thickness.

[0214] The core reason is that, as shown in Tables 2 and 3, the method in the examples, through a significant solids content gradient (M1 / M3 ≥ 3.71) and controlled decreasing dispersion, produced a slurry with smaller particle size and more uniform distribution (finished product D). 50 Specific secondary particle size D 50 The ratios of M1 and M3 are all ≤0.56, which results in a more porous coating with a superior pore structure. In contrast, the one-step method used in the comparative example has no gradient in solid content (M1 / M3≈1), leading to more severe particle agglomeration in the slurry (finished product D). 50 Specific secondary particle size D 50 When the ratio is ≥0.80, the resulting coating is denser. This fundamental structural difference directly leads to a significant difference in the following performance indicators.

[0215] (1) Impedance change (Ω) & Ionic conductivity change (S / cm) before and after coating: The above indicators are the two most critical indicators for evaluating membrane performance. As can be seen from Table 4, the impedance increase values ​​of all embodiments (0.03~0.05 Ω) are significantly lower than those of all comparative examples (0.07~0.08 Ω). Correspondingly, the decrease in ionic conductivity of the embodiments (-0.04 to -0.08 S / cm) is also significantly better than that of the comparative examples (-0.10 to -0.12 S / cm), that is, the loss of conductivity is smaller.

[0216] This fully demonstrates that the method of the present invention can effectively construct a low-impedance coating. The resulting loose porous structure provides a wider and more direct channel for the migration of lithium / sodium ions, reduces the tortuosity of the pores, thereby significantly reducing ion transport resistance and improving electrical conductivity.

[0217] (2) Adhesion strength of hot-pressed electrode sheets (N / m): Under the same amount of adhesive (e.g., Example 1 vs Comparative Example 1), the adhesion strength of the Example (1.3 / 0.2 N / m) was significantly higher than that of the Comparative Example (0.8 / 0.2 N / m). Throughout the test range, the Example generally showed superior adhesion performance.

[0218] This indicates that the slurry prepared in the embodiments of this application, due to its finer particles and more uniform dispersion, can better penetrate into the micropores on the base membrane and electrode surface, forming a stronger physical "rivet" effect and a larger contact area after hot pressing, thereby significantly improving the bonding strength between the diaphragm and the positive and negative electrodes.

[0219] (3) Powder loss (mg): The powder loss of all examples (0.3 mg ~ 0.6 mg) was significantly lower than that of the comparative examples (0.6 mg ~ 0.9 mg). For example, under the same ratio, the powder loss of Example 1 was only 0.3 mg, while that of Comparative Example 1 was as high as 0.8 mg.

[0220] Low powder shedding directly reflects stronger mechanical stability and cohesion of the coating. This complements the improved adhesion. A more uniform and loose particle packing structure allows the binder to more effectively "bond" the coated particles together and fix them to the base film, forming a more stable coating that is less prone to peeling off during friction.

[0221] (4) Change in air permeability before and after coating (s / 100mL): Under similar coating amounts and thicknesses, the increase in air permeability in the examples and comparative examples did not show a significant difference like that in impedance, but overall the examples performed equally or slightly better (i.e., the increase in air permeability was less). For example, the increase in air permeability in both Example 2 and Comparative Example 2 was 6 s / 100mL.

[0222] This indicates that the method employed in this application significantly optimizes electrochemical performance without sacrificing the membrane's permeability. The loose structure also facilitates gas passage, thus maintaining a permeability level at least comparable to that of conventional dense coatings.

[0223] (5) Coating amount (g / m 2 Coverage (%) & Coating thickness (μm): These three items are the controlled variables in the experiment. By comparing the groups with the same formulations, such as Example 1 and Comparative Example 1, and Example 4 and Comparative Example 2, it can be seen that their coating amount, coverage, and coating thickness are all controlled at very similar levels.

[0224] This ensures the fairness of the experimental comparison and demonstrates that the significant advantages of the examples in electrochemical and mechanical performance do not stem from the use of more materials or a thicker coating, but entirely from the optimization of the coating microstructure resulting from the advanced slurry preparation process.

[0225] (6) Reference Appendix Figure 2 (Example 1) and Figure 3 (Comparative Example 1) The electron microscope images provided in the attached figures visually demonstrate the fundamental reason for the aforementioned performance differences: the significant differences in the microstructure of the coatings. A corresponding analysis is conducted using Example 1 and Comparative Example 1, which have identical formulations but differ only in their preparation processes:

[0226] Appendix Figure 3 The middle image shows the morphology of a relatively densely packed layer. Compared to product 1, it can be clearly seen that the coating particles are densely packed, forming a distinct "coffee ring" structure. The sparse pores between the particles undoubtedly severely hinder the passage of ions, which is the direct cause of its high impedance.

[0227] In stark contrast, Figure 2 The image shows a relatively "loosely packed" morphology, corresponding to the product of Example 1. The coating particles are uniformly distributed, forming an open and interconnected porous network structure. This loosely packed morphology provides abundant and unobstructed transport paths for ions, perfectly explaining the excellent performance of low impedance and high ionic conductivity as measured. Therefore, the visual evidence of the microstructure and the test data of the macroscopic performance are highly consistent, jointly demonstrating the advancement of the preparation method of this invention in constructing high-performance membrane coatings.

[0228] 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 therein. Such 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 method for preparing a coating slurry, characterized in that, include: The coating material and binder are dispersed in a solvent at a first preset rate to obtain a concentrated solution with a solid content of M1. The concentrated solution is diluted with solvent and dispersed at a second preset rate lower than the first preset rate to obtain an intermediate system with a solid content of M2. The intermediate system is diluted again with solvent, and stirred at a third preset rate lower than the second preset rate to obtain a finished coating slurry with a solid content of M3. The solid content satisfies the following relationship: M1 > M2 > M3; the ratio of M1 / M3 is not less than 3, and the ratio of M2 / M3 is not less than 1.

5.

2. The method for preparing the coating slurry as described in claim 1, characterized in that, M1 ≥ 40%; or, M1 is 40%~80%; and / or, M2 is 10%~35%; and / or, M3 is 8%~20%; and / or, 3≤M1 / M3≤7; and / or, 1.5 ≤ M² / M³ ≤ 2; or, 1.6 ≤ M² / M³ ≤ 1.8; and / or, The first preset speed is 1300 rpm to 1800 rpm; and / or, The second preset speed is 1000 rpm to 1300 rpm; and / or, The third preset speed is 400 rpm to 600 rpm.

3. The method for preparing the coating slurry as described in claim 1, characterized in that, The finished coating slurry contains particles D 50 The primary particle size D of the coating material 50 The ratio is less than 30; or, the particle size D in the finished coating slurry is... 50 The primary particle size D of the coating material 50 The ratio is not higher than 20; or, the particle size D in the finished coating slurry is... 50 The primary particle size D of the coating material 50 The ratio is 15-20; and / or, The finished coating slurry contains particles D 50 The secondary particle size D of the coating material 50 The ratio is less than 0.8; or, the particle size D in the finished coating slurry is... 50 The secondary particle size D of the coating material 50 The ratio is not higher than 0.6; or, the particle size D in the finished coating slurry is... 50 The secondary particle size D of the coating material 50 The ratio is 0.4 to 0.6; and / or, The primary particle size of the coating material is 150nm~200nm; and / or, The secondary particle size of the coating material is 5μm~8μm.

4. The method for preparing the coating slurry as described in claim 1, characterized in that, The coating material includes polyvinylidene fluoride resin and polyvinylidene fluoride. Trifluoroethylene copolymer, polyvinylidene fluoride methyl methacrylate copolymer, polyvinylidene fluoride Hexafluoropropylene copolymer, polyvinylidene fluoride At least one of acrylic copolymers, polymethyl methacrylate, polyethylene, and acrylate polymers; and / or, The adhesive comprises at least one of carboxymethyl cellulose, hydroxyethyl cellulose, polyacrylic acid, polymethacrylic acid, acrylonitrile copolymer, and styrene-butadiene rubber; and / or, The mass ratio of the adhesive to the coating material is (5~20):

100.

5. The method for preparing the coating slurry as described in claim 1, characterized in that, The intermediate system is diluted again with solvent, and stirred at a third preset rate lower than the second preset rate to obtain a finished coating slurry with a solid content of M3. The process also includes: Add a wetting agent to the intermediate system; The wetting agent includes at least one of alkyl sulfate, sulfonate, polyoxyethylene alkylphenol ether, and polyoxyethylene fatty alcohol ether; and / or, the mass ratio of the wetting agent to the coating material is (1~5):

100.

6. A coating slurry, characterized in that, It is prepared by the method for preparing the coating slurry as described in any one of claims 1-5.

7. A method for preparing a low-impedance diaphragm, characterized in that, include: The coating slurry as described in claim 6 is applied to at least one surface of the base film to form a coating layer; The base film with the coating layer is dried to obtain the low-impedance separator.

8. A low-impedance diaphragm, characterized in that, It is prepared by the method for preparing a low-impedance diaphragm as described in claim 7.

9. A battery, characterized in that, Includes the low-impedance diaphragm as described in claim 8.

10. An electrical-related device, characterized in that, Includes the battery as described in claim 9.

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