A battery separator with high ion permeability and its preparation method

Abstract

This invention discloses a battery separator with high ion throughput and its preparation method, comprising the following steps: coating a base membrane with an aqueous ceramic powder slurry to obtain a ceramic layer, wherein the mass ratio of ceramic powder, dispersant, water, hydroxymethyl cellulose and binder in the aqueous ceramic powder slurry is 15-40:0.3-1:38-75:0.3-1.2:2-10; immersing the base membrane coated with the ceramic layer in a boron phenolic resin slurry for impregnation coating to obtain a boron phenolic resin layer; wherein the mass ratio of boron phenolic resin, organic solvent and binder in the boron phenolic resin slurry is 5-30:30-50:0.05-0.5; and drying the base membrane coated with the ceramic layer and the boron phenolic resin layer to obtain the final product.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a battery separator with high ion throughput efficiency and its preparation method. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Lithium-ion batteries mainly consist of four parts: positive electrode material, negative electrode material, separator, and electrolyte. Among these, the separator, a thin film with a microporous structure, plays a crucial role in lithium batteries. On one hand, the separator separates the positive and negative electrodes to prevent short circuits caused by contact between them, while simultaneously allowing electrolyte ions to pass through, forming a charging and discharging circuit. On the other hand, the performance of the separator determines the battery's interface structure, internal resistance, and other factors, directly affecting the battery's capacity, cycle life, and safety performance. With the increasing reports of safety incidents involving new energy vehicles, society is placing greater emphasis on the safety of lithium batteries. Therefore, improving the safety performance of separators is paramount, and enhancing the high-temperature resistance of battery separators has become an urgent priority.

[0004] The industry typically uses inorganic ceramic materials or organic high-temperature resistant materials to coat and modify the surface of the separator. However, existing separator modification coatings can adversely affect the ion permeability of the separator to some extent, which in turn negatively impacts the battery's capacity, cycle performance, charge / discharge current density, and other performance characteristics. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a battery separator with high ion throughput efficiency and its preparation method.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a battery separator with high ion permeability, comprising the following steps:

[0008] A water-based ceramic powder slurry is coated onto a base film to obtain a ceramic layer. The mass ratio of ceramic powder, dispersant, water, hydroxymethyl cellulose and binder in the water-based ceramic powder slurry is 15-40:0.3-1:38-75:0.3-1.2:2-10.

[0009] A base film coated with a ceramic layer is immersed in a boron phenolic resin slurry for impregnation coating to obtain a boron phenolic resin layer; the mass ratio of boron phenolic resin, organic solvent and binder in the boron phenolic resin slurry is 5-30:30-50:0.05-0.5.

[0010] The base film coated with a ceramic layer and a boron phenolic resin layer is obtained by drying.

[0011] This invention employs a step-by-step coating process, first coating a layer of aqueous ceramic, then coating a layer of boron phenolic resin through impregnation with an organic solvent. The hydroxyl groups coated on the surface of the ceramic particles are polar groups, exhibiting oleophobicity, resulting in poor wettability between the ceramic layer and the electrolyte. In contrast, the boron phenolic resin coating exhibits oleophilicity. Compared to the ceramic layer, the outermost organic boron phenolic resin layer improves the discontinuity at the electrolyte-membrane interface, facilitating thorough electrolyte wetting and enhancing ion throughput efficiency.

[0012] The ceramic layer is coated near the separator using an aqueous solution, and then a boron phenolic resin layer is coated on the outside of the ceramic layer using an organic oil-based impregnation method. When the internal temperature of the battery is around 100℃, the separator will locally shrink due to heat. The outermost boron phenolic resin layer will cross-link and solidify under heat, providing some support to the separator and inhibiting its shrinkage to a certain extent.

[0013] When the temperature continues to rise, the membrane substrate experiences localized rupture, melting, or even complete thermal decomposition (the membrane undergoes violent decomposition at around 380℃, and the decomposition tends to stabilize at 600℃). When using boron phenolic resin alone for coating, the battery temperature rises, causing the membrane to rupture and melt. During the curing and cross-linking process of the boron phenolic resin, some small molecules volatilize, preventing the formation of a dense insulating layer. This results in problems such as cracking and collapse of the coating material, failing to achieve the function of isolating the positive and negative electrode materials. The boron phenolic resin layer undergoes complete curing and cross-linking upon heating, even carbonization (the initial decomposition temperature of boron phenolic resin is approximately 330℃, and the residual carbon rate can reach 75% under a nitrogen atmosphere). When the temperature rises to 200℃, the binder in the ceramic layer begins to melt and decompose, failing to bond the ceramic particles. The boron phenolic resin layer then acts as a bonding and supporting agent.

[0014] The BO bonds in the boron oxide ceramic material formed by carbonization form a cross-linked network in the phenolic resin, making the carbonized layer more compact and achieving high temperature resistance. Together with the inner ceramic particles, it plays a barrier role, preventing the positive and negative electrodes from directly contacting each other due to the diaphragm burn-through, which can cause internal short circuits and effectively improve the safety performance of the diaphragm.

[0015] Boron-phenolic resin is a high-temperature resistant material obtained by modifying the resin by introducing boron into the C and C bonds. The main raw materials for its synthesis are formaldehyde, phenol, and boric acid. The synthesis method is shown below:

[0016]

[0017] In some embodiments, the dispersant is selected from polyacrylamide.

[0018] In some embodiments, the D50 of the ceramic powder is 0.3-0.6 μm.

[0019] In some embodiments, the water-based ceramic powder slurry is prepared by grinding and dispersing a mixture of ceramic powder, dispersant and water, and then mixing it evenly with a hydroxymethyl cellulose solution.

[0020] Hydroxymethyl cellulose (HMC) solutions have high viscosity, making them difficult to grind, disperse, and mix. Furthermore, the continuous shearing during grinding causes HMC to decrease in viscosity, leading to a decline in the stability of the slurry system. Therefore, grinding and dispersing the ceramic powder and dispersant before mixing them with HMC can increase the viscosity of the slurry system, slowing down the settling and agglomeration of ceramic particles and ensuring the uniformity and stability of the slurry.

[0021] Preferably, the grinding speed is 800-1200 rpm.

[0022] In some embodiments, the ceramic slurry further includes a wetting agent selected from alkylphenol polyoxyethylene ethers. The main function of the wetting agent is to reduce the surface tension of the substrate separator, allowing the ceramic slurry to completely wet the substrate surface. Without the addition of a wetting agent, uneven coating, missed coating, and other defects may occur, leading to a short circuit in the battery.

[0023] In some embodiments, the curing agent is selected from dicumyl peroxide. Adding a curing agent to the boron phenolic resin improves its curing degree and prevents powdering.

[0024] In some embodiments, the thickness of the ceramic layer is 0.5-5 μm, and the thickness of the boron phenolic resin layer is 0.5-3 μm.

[0025] Secondly, the present invention provides a battery separator with high ion throughput efficiency, prepared by the aforementioned preparation method, comprising a base film, a ceramic layer located on one or both sides of the base film, and a boron phenolic resin layer located on the outer side of the ceramic layer.

[0026] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0027] In this invention, a ceramic layer is first coated on the surface of the diaphragm, and then a boron phenolic resin layer is coated on the surface of the ceramic layer. The boron phenolic resin is rich in hydroxyl groups, which makes the boron phenolic resin layer polar and gives the modified diaphragm good wettability. This can improve the discontinuity of the electrolyte-diaphragm interface, which is conducive to the full wetting of the electrolyte and thus improve the ion passage efficiency.

[0028] At temperatures above 200°C, the binder in the ceramic layer melts and decomposes, failing to continue binding the ceramic particles. However, the boron phenolic resin on the outer side of the ceramic layer provides good bonding and support for the ceramic particles. The combination of the inner and outer layers ensures that the coating still has a good barrier effect even at high temperatures, effectively improving the safety performance of the diaphragm. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a schematic diagram illustrating the manufacturing process of the diaphragm in this embodiment of the invention.

[0031] Figure 2 These are comparison curves of the membrane stretching prepared in the embodiments and comparative examples of this invention;

[0032] Figure 3 This is a comparison diagram of the electrolyte affinity test of the membranes prepared in Example 1(a) and Comparative Example 2(b) of the present invention. Detailed Implementation

[0033] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] The present invention will be further described below with reference to the embodiments.

[0035] Example 1

[0036] The preparation method of a battery separator with high ion permeability includes the following specific steps:

[0037] 1) Preparation of ceramic slurry:

[0038] Add 30 kg of alumina (D50 is 0.4 μm) and 0.5 kg of dispersant to 50 kg of water, stir for 60 min, and then perform pre-dispersion treatment. The pre-dispersion treatment is carried out using a planetary mixer with an orbital speed of 30 rpm and a rotational speed of 800 rpm.

[0039] The pre-dispersed alumina slurry was subjected to high-speed grinding and dispersion at a speed of 1000 rpm and a feed pump pressure of 0.2 MPa to obtain the alumina slurry.

[0040] Alumina slurry was added to 10 kg of 5% (w / w) aqueous hydroxymethyl cellulose solution and stirred for 30 min. Then, 4 kg of binder and 0.05 kg of wetting agent were added and stirred again to obtain ceramic slurry.

[0041] 2) Preparation of boron phenolic resin slurry:

[0042] 10 kg of boron phenolic resin was added to 50 kg of organic solvent, and then 0.1 kg of curing agent was added and stirred to prepare boron phenolic resin slurry.

[0043] 3) Coating of the diaphragm:

[0044] A 9μm PE base film was used, and the prepared ceramic slurry was used for double-sided coating. A gravure roller was used for coating, and the coating thickness on one side was controlled at 2μm. The coating speed ratio was 1.1. After coating, the film was dried at 85℃. After drying, the diaphragm coated with ceramic coating was wound up.

[0045] The diaphragm coated with ceramic coating was immersed in boron phenolic resin slurry for coating. The thickness of the boron phenolic resin coating was 1 μm, and the coating speed was 40 m / min. After drying, it was rolled up.

[0046] Example 2

[0047] The preparation method of a battery separator with high ion permeability includes the following specific steps:

[0048] 1) Preparation of ceramic slurry:

[0049] Add 30 kg of alumina (D50 is 0.5 μm) and 0.5 kg of dispersant to 50 kg of water, stir for 60 min, and then perform pre-dispersion treatment. The pre-dispersion treatment is performed using a planetary mixer with an orbital speed of 30 rpm and a rotational speed of 800 rpm.

[0050] The pre-dispersed alumina slurry was subjected to high-speed grinding and dispersion at a speed of 1000 rpm and a feed pump pressure of 0.2 MPa to obtain the alumina slurry.

[0051] Alumina slurry was added to 10 kg of 5% (w / w) aqueous hydroxymethyl cellulose solution and stirred for 30 min. Then, 4 kg of binder and 0.05 kg of wetting agent were added and stirred again to obtain ceramic slurry.

[0052] 2) Preparation of boron phenolic resin slurry:

[0053] 10 kg of boron phenolic resin was added to 50 kg of organic solvent, and then 0.1 kg of curing agent was added and stirred to prepare boron phenolic resin slurry.

[0054] 3) Coating of the diaphragm:

[0055] A 9μm PE base film was used, and the prepared ceramic slurry was used for double-sided coating. A gravure roller was used for coating, and the coating thickness on one side was controlled at 1.5μm. The coating speed ratio was 1.1. After coating, the film was dried at 85℃. After drying, the diaphragm coated with ceramic coating was wound up.

[0056] The diaphragm coated with ceramic coating was immersed in boron phenolic resin slurry for coating. The thickness of the boron phenolic resin coating was 1.5 μm, the coating speed was 40 m / min, and it was then dried and wound up.

[0057] Example 3

[0058] The preparation method of a battery separator with high ion permeability includes the following specific steps:

[0059] 1) Preparation of ceramic slurry:

[0060] Add 20 kg of alumina (D50 of 0.3 μm) and 0.3 kg of dispersant to 40 kg of water, stir for 60 min, and then perform pre-dispersion treatment. The pre-dispersion treatment is carried out using a planetary mixer with an orbital speed of 30 rpm and a rotational speed of 800 rpm.

[0061] The pre-dispersed alumina slurry was subjected to high-speed grinding and dispersion at a speed of 1000 rpm and a feed pump pressure of 0.2 MPa to obtain the alumina slurry.

[0062] Alumina slurry was added to 10 kg of 5% (w / w) aqueous hydroxymethyl cellulose solution and stirred for 30 min. Then, 7 kg of binder and 0.08 kg of wetting agent were added and stirred again to obtain ceramic slurry.

[0063] 2) Preparation of boron phenolic resin slurry:

[0064] Add 5 kg of boron phenolic resin to 40 kg of organic solvent, then add 0.4 kg of curing agent and stir to make boron phenolic resin slurry.

[0065] 3) Coating of the diaphragm:

[0066] A 9μm PE base film was used, and the prepared ceramic slurry was used for double-sided coating. A gravure roller was used for coating, and the coating thickness on one side was controlled at 4μm. The coating speed ratio was 1.1. After coating, the film was dried at 85℃. After drying, the diaphragm coated with ceramic coating was wound up.

[0067] The diaphragm coated with ceramic coating was immersed in boron phenolic resin slurry for coating. The thickness of the boron phenolic resin coating was 2μm, and the coating speed was 40m / min. After drying, it was rolled up.

[0068] Example 4

[0069] The preparation method of a battery separator with high ion permeability includes the following specific steps:

[0070] 1) Preparation of ceramic slurry:

[0071] Add 20 kg of alumina (D50 of 0.4 μm) and 0.3 kg of dispersant to 40 kg of water, stir for 60 min, and then perform pre-dispersion treatment. The pre-dispersion treatment is performed using a planetary mixer with an orbital speed of 30 rpm and a rotational speed of 800 rpm.

[0072] The pre-dispersed alumina slurry was subjected to high-speed grinding and dispersion at a speed of 1000 rpm and a feed pump pressure of 0.2 MPa to obtain the alumina slurry.

[0073] Alumina slurry was added to 10 kg of 5% (w / w) hydroxymethyl cellulose aqueous solution and stirred for 30 min. Then, 2 kg of binder and 0.03 kg of wetting agent were added and stirred again to obtain ceramic slurry.

[0074] 2) Preparation of boron phenolic resin slurry:

[0075] Add 30 kg of boron phenolic resin to 30 kg of organic solvent, then add 0.5 kg of curing agent and stir to prepare boron phenolic resin slurry.

[0076] 3) Coating of the diaphragm:

[0077] A 9μm PE base film was used, and the prepared ceramic slurry was used for double-sided coating. A gravure roller was used for coating, and the coating thickness on one side was controlled at 3μm. The coating speed ratio was 1.1. After coating, the film was dried at 85℃. After drying, the diaphragm coated with ceramic coating was wound up.

[0078] The diaphragm coated with ceramic coating was immersed in boron phenolic resin slurry for coating. The thickness of the boron phenolic resin coating was 2μm, and the coating speed was 40m / min. After drying, it was rolled up.

[0079] Comparative Example 1

[0080] A 9μm PE base film was used without any coating treatment.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that the boron phenolic resin in Example 1 is replaced with phenolic resin, while everything else is the same as in Example 1.

[0083] Performance testing

[0084] The diaphragms prepared in the examples and comparative examples were tested respectively, and the heat shrinkage was tested at 200°C. The results are as follows.

[0085] Depend on Figure 2 The data shows that after the high-temperature resistant coating was applied, the mechanical strength of the diaphragm was not damaged, and its tensile strength did not decrease.

[0086] Electrolyte was titrated onto the surfaces of the membranes prepared in Example 1 and Comparative Example 2 for 5 minutes, and its diffusion rate was observed. The inner circle represents the degree of electrolyte diffusion within the membrane, while the outermost circle represents the coating diffusion rate. By comparing the diffusion rates of the outermost circle, it can be seen that boron phenolic resin has a greater affinity for the electrolyte and its diffusion rate is faster than that of phenolic resin, as shown in Table 1 and... Figure 3 As shown.

[0087] Table 1

[0088] Experimental sample MD(mm) TD(mm) Example 1 24.9 19.4 Comparative Example 2 19.9 17.4

[0089] By comparing the diaphragms prepared in the examples and comparative examples, the dense coating prepared in the examples played a certain role in buffering and protecting against the puncture of sharp substances, and the high-temperature resistant coating improved the needle penetration strength of the diaphragm to a certain extent, as shown in Table 2 below.

[0090] Table 2 Comparison of slurry particle size and diaphragm properties in the examples and comparative examples

[0091]

[0092] As shown in Table 2 of Examples 1 and 2, the particle size values ​​are similar, indicating that the slurry is uniformly mixed and dispersed. After coating, due to the impregnation of boron phenolic resin on the ceramic surface, the gaps between ceramic particles are filled by the boron phenolic resin, resulting in a certain increase in air permeability.

[0093] Table 3 Comparison of heat resistance and residual carbon rate of the diaphragms in the examples and comparative examples

[0094]

[0095] As shown in Table 3, after the membrane is modified with boron phenolic resin / ceramic slurry, under 200℃ heat shrinkage conditions, the membrane substrate becomes closed-cell, blocking ion exchange channels, and the membrane tends to shrink locally. However, the boron phenolic resin undergoes cross-linking and curing, adhering to the outermost layer of the membrane, inhibiting heat shrinkage and exhibiting superior heat shrinkage performance, thus avoiding direct contact between the positive and negative electrodes and preventing internal short circuits. The higher residual carbon rate also results in superior heat resistance and safety performance of the composite membrane.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a battery separator with high ion permeability, characterized in that: Includes the following steps: A water-based ceramic powder slurry is coated onto a base film to obtain a ceramic layer; The base film coated with the ceramic layer is immersed in boron phenolic resin slurry for immersion coating to obtain the boron phenolic resin layer. The base film coated with a ceramic layer and a boron phenolic resin layer is dried to obtain the final product. The mass ratio of ceramic powder, dispersant, water, hydroxymethyl cellulose and binder in the aqueous ceramic powder slurry is 15-40:0.3-1:38-75:0.3-1.2:2-10; The mass ratio of boron phenolic resin, organic solvent and curing agent in the boron phenolic resin slurry is 5-30:30-50:0.05-0.

5.

2. The method for preparing a battery separator with high ion permeability according to claim 1, characterized in that: The dispersant is polyacrylamide.

3. The method for preparing a battery separator with high ion permeability according to claim 1, characterized in that: The ceramic powder has a D50 of 0.3-0.6 μm.

4. The method for preparing a battery separator with high ion permeability according to claim 2, characterized in that: The method for preparing the aqueous ceramic powder slurry is as follows: after grinding and dispersing the mixture of ceramic powder, dispersant and water, it is then mixed evenly with hydroxymethyl cellulose solution to obtain the final product.

5. The method for preparing a battery separator with high ion permeability according to claim 4, characterized in that: The grinding speed is 800-1200 rpm.

6. The method for preparing a battery separator with high ion permeability according to claim 1, characterized in that: The ceramic powder slurry also includes a wetting agent, which is an alkylphenol polyoxyethylene ether.

7. The method for preparing a battery separator with high ion permeability according to claim 1, characterized in that: The curing agent is dicumyl peroxide.

8. The method for preparing a battery separator with high ion permeability according to claim 1, characterized in that: The thickness of the ceramic layer is 0.5-5 μm, and the thickness of the boron phenolic resin layer is 0.5-3 μm.

9. A battery separator with high ion permeability, characterized in that: Prepared by any one of the preparation methods described in claims 1-8, it comprises a base film, a ceramic layer located on one or both sides of the base film, and a boron phenolic resin layer located on the outside of the ceramic layer.

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