Lithium battery separator with gradient pore structure and method of making the same

Abstract

This invention discloses a lithium-ion battery separator with a gradient pore structure and its preparation method. The lithium-ion battery separator with a gradient pore structure is a layered structure comprising: a base film, a first coating, and a second coating. The first and second coatings are located on the same side of the base film. The first coating is connected to one side of the base film, and the second coating is connected to the first coating. The porosity of the first coating is 40-50%, and the porosity of the second coating is 30-40%. The first coating comprises large-pore porous alumina, and the second coating comprises small-pore porous alumina. This invention employs a double-layer structure design, with the two coatings having different pore sizes, thereby forming a gradient pore structure. This structure allows for gradual ion adaptation during battery charging and discharging, reducing migration energy barriers.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a lithium battery separator with a gradient pore structure and its preparation method. Background Technology

[0002] The lithium-ion battery separator, as an indispensable core component of the battery structure, undertakes a crucial dual task: on the one hand, it ensures the physical separation between the positive and negative electrodes, effectively preventing short-circuit accidents and building a solid defense for the safe operation of the battery; on the other hand, it also acts as a lithium-ion transport channel, allowing lithium ions to move smoothly to and from the battery during charging and discharging, thereby realizing the battery's energy storage and release functions. Therefore, improving the ionic conductivity of the separator has become the key to optimizing the overall performance of lithium-ion batteries and promoting their technological progress, and this research field has naturally become a frontier of materials science exploration.

[0003] With the increasing prevalence and rapid development of modern electronic devices, people are placing ever higher demands on the energy density and charging speed of batteries. Against this backdrop, effectively improving the ion transport efficiency and liquid retention capacity of lithium-ion battery separators has become particularly urgent and important. This not only requires researchers to continuously explore new ideas and methods in material design and synthesis, but also necessitates in-depth research and innovation in areas such as microstructure control and surface modification techniques, in order to develop a novel separator material with superior overall performance.

[0004] In conclusion, conducting in-depth and meticulous scientific research and technological innovation focused on the core issue of how to efficiently improve the ionic conductivity and liquid absorption / retention rate of lithium-ion battery separators is undoubtedly of paramount importance. This will not only powerfully promote the development of high-performance lithium-ion batteries but also provide solid support and guarantees for meeting the high standards required by future energy storage systems. Therefore, exploration and research in this field undoubtedly possess immeasurable value and potential. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a lithium battery separator with a gradient pore structure.

[0006] Another objective of this invention is to provide a method for preparing the lithium battery separator with the gradient pore structure described above. The method employs a layered coating process, in which a slurry containing large-pore porous alumina is first coated on one side of the base film to serve as the bottom layer, and then a slurry containing small-pore porous alumina is coated on the bottom layer containing large-pore porous alumina to construct a porous alumina coating with a gradient pore structure.

[0007] The objective of this invention is achieved through the following technical solution.

[0008] A lithium battery separator with a gradient pore structure is a layered structure comprising: a base film, a first coating layer, and a second coating layer. The first coating layer and the second coating layer are located on the same side of the base film. The first coating layer is connected to one side of the base film, and the second coating layer is connected to the first coating layer. The porosity of the first coating layer is 40-50%, and the porosity of the second coating layer is 30-40%. The first coating layer comprises: large-pore porous alumina, and the second coating layer comprises: small-pore porous alumina. By mass fraction, the ratio of large-pore porous alumina in the first coating layer to small-pore porous alumina in the second coating layer is (10-30):(10-30).

[0009] In the above technical solution, the particle size of the macroporous alumina is D50 = 0.6–0.8 μm, D90 = 1.4–1.6 μm, the pore size is 50–100 nm, and the specific surface area is 30–40 m². 2 / g.

[0010] In the above technical solution, the particle size of the small-pore porous alumina is D50 = 0.3~0.5μm, D90 = 0.8~1.2μm, the pore size is 10~20nm, and the specific surface area is 10~20m². 2 / g.

[0011] In the above technical solution, the thickness of the first coating is 1 to 2.5 μm, and the thickness of the second coating is 1 to 2.5 μm.

[0012] In the above technical solution, the first coating further includes: acrylate copolymer and ammonium polyacrylate. By mass parts, the ratio of macroporous alumina, acrylate copolymer in the first coating and ammonium polyacrylate in the first coating is (10-30): (1-4): (0.5-1), preferably (25-30): (1.8-4): (0.9-1).

[0013] In the above technical solution, the second coating further includes: acrylate copolymer and ammonium polyacrylate. By mass parts, the ratio of small-pore porous alumina, acrylate copolymer in the second coating and ammonium polyacrylate in the second coating is (10-30): (1-4): (0.5-1), preferably (25-30): (1.8-4): (0.9-1).

[0014] The above-mentioned method for preparing a lithium battery separator with a gradient pore structure includes: coating a first slurry containing large-pore porous alumina onto a base film, drying it to obtain a first coating layer on the base film; coating a second slurry containing small-pore porous alumina onto the surface of the first coating layer, drying it to obtain a second coating layer on the first coating layer, thereby obtaining a lithium battery separator with a gradient pore structure.

[0015] In the above technical solution, the drying temperature is 30-50℃ and the drying time is 1-4 minutes.

[0016] In the above technical solution, the coating speed is 10-30 m / min.

[0017] In the above technical solution, the first slurry includes: large-pore porous alumina, water, adhesive and dispersant. By mass parts, the ratio of large-pore porous alumina, water in the first slurry, adhesive in the first slurry and dispersant in the first slurry is (10-30): (50-90): (5-10): (0.5-1).

[0018] In the above technical solution, the preferred ratio of the following components by mass is (25-30):(50-70):(9-10):(0.9-1).

[0019] In the above technical solution, the second slurry includes: small-pore porous alumina, water, adhesive and dispersant. By mass parts, the ratio of small-pore porous alumina, water in the second slurry, adhesive in the second slurry and dispersant in the second slurry is (10-30): (50-90): (5-10): (0.5-1).

[0020] In the above technical solution, the preferred ratio of small-pore porous alumina, water in the second slurry, adhesive in the second slurry, and dispersant in the second slurry by mass parts is (25-30):(50-70):(9-10):(0.9-1).

[0021] In the above technical solution, the method for preparing the first slurry includes: mixing large-pore porous alumina, water, adhesive and dispersant until uniform to obtain the first slurry.

[0022] In the above technical solution, the method for preparing the second slurry includes: mixing small-pore porous alumina, water, adhesive and dispersant until uniform to obtain the second slurry.

[0023] In the above technical solution, the method for preparing the first slurry specifically includes the following steps:

[0024] Step 1: Mix large-pore porous alumina, water and dispersant, and stir at a rotation speed of 1000-3000 r / min and a revolution speed of 30-50 r / min for 10-30 min until homogeneous to obtain the first solution;

[0025] Step 2: Mix the first solution and the adhesive, and simultaneously stir and sonicate under vacuum for 10-40 minutes until homogeneous to obtain the first slurry. The vacuum degree of the vacuum environment is 0.06-0.08 kPa, the rotation speed of the stirring is 1000-3000 r / min, the revolution speed is 30-60 r / min, and the ultrasonic frequency is 5-8 kHz.

[0026] In the above technical solution, the method for preparing the second slurry specifically includes the following steps:

[0027] S1, mix small-pore porous alumina, water and dispersant, and stir at a rotation speed of 1000-3000 r / min and a revolution speed of 30-50 r / min for 10-30 min until uniform to obtain the second solution;

[0028] S2, the second solution and adhesive are mixed and simultaneously stirred and sonicated under vacuum for 10-40 minutes until homogeneous to obtain the second slurry. The vacuum degree of the vacuum environment is 0.06-0.08 kPa, the rotation speed of the stirring is 1000-3000 r / min, the revolution speed is 30-60 r / min, and the ultrasonic frequency is 5-8 kHz.

[0029] In the above technical solution, the dispersant is ammonium polyacrylate, and the adhesive is an acrylate copolymer solution.

[0030] In the above technical solution, the content of the acrylate copolymer in the acrylate copolymer solution is 20-40 wt%.

[0031] Applications of large-pore porous alumina and small-pore porous alumina to synergistically improve the ionic conductivity, liquid absorption rate, liquid retention rate, tensile strength and / or breakdown voltage of membranes.

[0032] Application of large-pore porous alumina and small-pore porous alumina in synergistic reduction of membrane shrinkage rate.

[0033] In the above technical solution, the diaphragm has a layered structure, which includes: a base film, a first coating and a second coating. The first coating and the second coating are located on the same side of the base film. The first coating is connected to one side of the base film, and the second coating is connected to the first coating. Large-pore porous alumina is located in the first coating, and small-pore porous alumina is located in the second coating. By mass fraction, the ratio of large-pore porous alumina in the first coating to small-pore porous alumina in the second coating is (10-30):(10-30).

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

[0035] 1. Optimization of pore size distribution: By designing pore size distributions of different sizes, the flow of electrolyte and ion transport can be effectively controlled. Larger pore sizes facilitate rapid electrolyte transport, thereby improving ionic conductivity, while smaller pore sizes prevent short circuits and improve the mechanical strength and heat resistance of the membrane;

[0036] 2. Construction of the dual-layer structure: A dual-layer structure design is adopted, with two coatings having different pore sizes, thus forming a gradient pore size structure. This structure allows ions to gradually adapt during battery charging and discharging, reducing migration energy barriers. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0038] Small-pore porous alumina (powder), large-pore porous alumina (powder): Suzhou Jinyi New Material Technology Co., Ltd.;

[0039] Acrylic copolymer solution: Baoding Lucky Imaging Materials Technology Co., Ltd.;

[0040] Ammonium polyacrylate: Shanghai Sanrui Polymer Materials Technology Co., Ltd.

[0041] Dual planetary mixer: XFZH-30L.

[0042] In the following examples and comparative examples, the particle size of the small-pore porous alumina is D50 = 0.325 μm, D90 = 0.812 μm, the pore size is 11.2 nm, and the specific surface area is 16.9 m². 2 / g.

[0043] In the following examples and comparative examples, the particle size of the macroporous alumina was D50 = 0.679 μm, D90 = 1.516 μm, the pore size was 60.2 nm, and the specific surface area was 31.1 m². 2 / g.

[0044] The water used in the following implementation is pure water.

[0045] In the following implementation, the base film is a PE film with a thickness of 9 μm.

[0046] Ionic conductivity: Test temperature was 25℃ and relative humidity was 60%.

[0047] Example 1

[0048] A method for preparing a lithium battery separator with a gradient pore structure includes: coating a first slurry containing large-pore porous alumina onto a base film at a speed of 15 m / min on one side, drawing it into a drying equipment via a traction roller, and drying it at 50°C for 1 min to obtain a first coating with a thickness of 2.1 μm on one side of the base film; coating a second slurry containing small-pore porous alumina onto the surface of the first coating at a speed of 15 m / min, drawing it into a drying equipment via a traction roller, and drying it at 50°C for 1 min to obtain a second coating with a thickness of 1 μm on the first coating, thereby obtaining a lithium battery separator with a gradient pore structure, wherein the porosity of the first coating is 41.2% and the porosity of the second coating is 33.5%.

[0049] The method for preparing the first slurry includes the following steps:

[0050] Step 1: Mix large-pore porous alumina, water and dispersant in a double planetary mixer, and stir for 10 minutes at a rotation speed of 1000 r / min and a revolution speed of 30 r / min until uniform to obtain the first solution. The dispersant is ammonium polyacrylate.

[0051] Step 2: Add adhesive to the first solution, and simultaneously stir and sonicate for 10 minutes in a dual planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain the first slurry. The vacuum degree of the vacuum environment is 0.06 kPa, the rotation speed of the stirrer is 1500 r / min, the revolution speed is 30 r / min, and the ultrasonic frequency is 5 kHz. By mass parts, the ratio of macroporous alumina, water in the first slurry, adhesive in the first slurry, and dispersant in the first slurry is 11:83.5:5:0.5. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0052] The method for preparing the second slurry includes the following steps:

[0053] S1, Small-pore porous alumina, water and dispersant are mixed in a double planetary mixer and stirred for 10 minutes at a rotation speed of 1000 r / min and a revolution speed of 30 r / min until uniform, to obtain a second solution. The dispersant is ammonium polyacrylate.

[0054] S2, add adhesive to the second solution, and simultaneously stir and sonicate for 10 minutes in a double planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain the second slurry. The vacuum degree of the vacuum environment is 0.06 kPa, the rotation speed of the stirrer is 1500 r / min, the revolution speed is 30 r / min, and the ultrasonic frequency is 5 kHz. By mass parts, the ratio of small-pore porous alumina, water in the second slurry, adhesive in the second slurry and dispersant in the second slurry is 11:83.5:5:0.5. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0055] The test data for the lithium battery separator with a gradient pore structure prepared in Example 1 are as follows:

[0056]

[0057]

[0058] Example 2

[0059] A method for preparing a lithium battery separator with a gradient pore structure includes: coating a first slurry containing large-pore porous alumina onto a base film at a speed of 20 m / min on one side, drawing it into a drying equipment via a traction roller, and drying it at 40°C for 2 min to obtain a first coating with a thickness of 2.2 μm on one side of the base film; coating a second slurry containing small-pore porous alumina onto the surface of the first coating at a speed of 20 m / min, drawing it into a drying equipment via a traction roller, and drying it at 40°C for 2 min to obtain a second coating with a thickness of 1.1 μm on the first coating, thereby obtaining a lithium battery separator with a gradient pore structure, wherein the porosity of the first coating is 45.3% and the porosity of the second coating is 35.6%.

[0060] The method for preparing the first slurry includes the following steps:

[0061] Step 1: Mix large-pore porous alumina, water and dispersant in a double planetary mixer, and stir for 20 minutes at a rotation speed of 2000 r / min and a revolution speed of 40 r / min until uniform to obtain the first solution. The dispersant is ammonium polyacrylate.

[0062] Step 2: Add adhesive to the first solution, and simultaneously stir and sonicate for 20 minutes in a dual planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain the first slurry. The vacuum degree of the vacuum environment is 0.07 kPa, the rotation speed of the stirrer is 2000 r / min, the revolution speed is 40 r / min, and the ultrasonic frequency is 6 kHz. By mass parts, the ratio of macroporous alumina, water in the first slurry, adhesive in the first slurry, and dispersant in the first slurry is 20:71.2:8:0.8. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0063] The method for preparing the second slurry includes the following steps:

[0064] S1, Small-pore porous alumina, water and dispersant are mixed in a double planetary mixer and stirred for 20 minutes at a rotation speed of 2000 r / min and a revolution speed of 40 r / min until uniform, to obtain a second solution. The dispersant is ammonium polyacrylate.

[0065] S2, add adhesive to the second solution, and simultaneously stir and sonicate for 20 minutes in a double planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain the second slurry. The vacuum degree of the vacuum environment is 0.07 kPa, the rotation speed of the stirrer is 2000 r / min, the revolution speed is 40 r / min, and the ultrasonic frequency is 6 kHz. By mass parts, the ratio of small-pore porous alumina, water in the second slurry, adhesive in the second slurry and dispersant in the second slurry is 20:71.2:8:0.8. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0066] The test data for the lithium battery separator with a gradient pore structure prepared in Example 2 are as follows:

[0067]

[0068] Example 3

[0069] A method for preparing a lithium battery separator with a gradient pore structure includes: coating a first slurry containing large-pore porous alumina onto a base film at a speed of 30 m / min on one side, drawing it into a drying equipment via a traction roller, and drying it at 30°C for 4 min to obtain a first coating with a thickness of 2.2 μm on one side of the base film; coating a second slurry containing small-pore porous alumina onto the surface of the first coating at a speed of 30 m / min, drawing it into a drying equipment via a traction roller, and drying it at 30°C for 4 min to obtain a second coating with a thickness of 1 μm on the first coating, thereby obtaining a lithium battery separator with a gradient pore structure, wherein the porosity of the first coating is 48.2% and the porosity of the second coating is 39.5%.

[0070] The method for preparing the first slurry includes the following steps:

[0071] Step 1: Mix large-pore porous alumina, water and dispersant in a double planetary mixer, and stir for 30 minutes at a rotation speed of 3000 r / min and a revolution speed of 50 r / min until uniform to obtain the first solution. The dispersant is ammonium polyacrylate.

[0072] Step 2: Add adhesive to the first solution, and simultaneously stir and sonicate for 20 minutes in a dual planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain the first slurry. The vacuum degree of the vacuum environment is 0.08 kPa, the rotation speed of the stirrer is 3000 r / min, the revolution speed is 60 r / min, and the ultrasonic frequency is 8 kHz. By mass, the ratio of macroporous alumina, water in the first slurry, adhesive in the first slurry, and dispersant in the first slurry is 30:59:10:1. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0073] The method for preparing the second slurry includes the following steps:

[0074] S1, Small-pore porous alumina, water and dispersant are mixed in a double planetary mixer and stirred for 30 minutes at a rotation speed of 3000 r / min and a revolution speed of 50 r / min until uniform, to obtain a second solution. The dispersant is ammonium polyacrylate.

[0075] S2, add adhesive to the second solution, and simultaneously stir and sonicate for 20 minutes in a double planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain the second slurry. The vacuum degree of the vacuum environment is 0.08 kPa, the rotation speed of the stirrer is 3000 r / min, the revolution speed is 60 r / min, and the ultrasonic frequency is 8 kHz. By mass parts, the ratio of small-pore porous alumina, water in the second slurry, adhesive in the second slurry and dispersant in the second slurry is 30:59:10:1. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0076] The test data for the lithium battery separator with a gradient pore structure prepared in Example 3 are as follows:

[0077]

[0078]

[0079] Comparative Example 1

[0080] A method for preparing a diaphragm includes the following steps:

[0081] Step 1: Mix small-pore porous alumina, water and dispersant in a double planetary mixer, and stir for 30 minutes at a rotation speed of 3000 r / min and a revolution speed of 45 r / min until uniform to obtain a second solution. The dispersant is ammonium polyacrylate.

[0082] Step 2: Add adhesive to the second solution, and simultaneously stir and sonicate for 30 minutes in a dual planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain a slurry. The vacuum degree of the vacuum environment is 0.07 kPa, the rotation speed of the stirrer is 2500 r / min, the revolution speed is 50 r / min, and the ultrasonic frequency is 6 kHz. By mass, the ratio of small-pore porous alumina, water, adhesive and dispersant is 20:72.2:7:0.8. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0083] Step 3: Place the base film on a coating machine containing the slurry prepared in step 2, and coat one side of the base film with the slurry at a speed of 20 m / min. Then, pull the film into the drying equipment by the traction roller and dry it at 45°C for 2 min. A coating is obtained on one side of the base film, resulting in the diaphragm of Comparative Example 1.

[0084] The parameters of the membrane prepared in Comparative Example 1 are as follows:

[0085]

[0086] Comparative Example 2

[0087] A method for preparing a diaphragm includes the following steps:

[0088] Step 1: Mix large-pore porous alumina, water and dispersant in a double planetary mixer, and stir for 30 minutes at a rotation speed of 3000 r / min and a revolution speed of 40 r / min until uniform to obtain the first solution. The dispersant is ammonium polyacrylate.

[0089] Step 2: Add adhesive to the first solution, and simultaneously stir and sonicate for 30 minutes in a dual planetary mixer with ultrasonic oscillation function under vacuum until homogeneous, to obtain a slurry. The vacuum degree of the vacuum environment is 0.06 kPa, the rotation speed of the stirrer is 3000 r / min, the revolution speed is 40 r / min, and the ultrasonic frequency is 5 kHz. By mass, the ratio of macroporous alumina, water, adhesive and dispersant is 20:71.5:8:0.5. The adhesive is an acrylate copolymer solution (the content of acrylate copolymer in the acrylate copolymer solution is 20 wt%, and the acrylate copolymer is copolymerized from acrylic acid and acrylamide).

[0090] Step 3: Place the base film on a coating machine containing the slurry prepared in step 2, and coat one side of the base film with the slurry at a speed of 20 m / min. Then, pull the film into the drying equipment by the traction roller and dry it at 50°C for 1 min to obtain a coating on one side of the base film, thus obtaining the diaphragm of Comparative Example 2.

[0091] The parameters of the membrane prepared in Comparative Example 2 are as follows:

[0092]

[0093] Comparative Example 3

[0094] A method for preparing a heat-resistant alumina lithium battery separator includes the following steps:

[0095] Step 1: Mix conventional alumina (D10 = 0.218 μm, D50 = 0.502 μm, D90 = 1.556 μm, non-porous alumina), water, and dispersant in a double planetary mixer. First, stir at a rotation speed of 3000 r / min and a revolution speed of 50 r / min for 30 min, then sonicate at a frequency of 6 kHz for 20 min. Add adhesive, and simultaneously stir and sonicate in a double planetary mixer with ultrasonic oscillation function under vacuum for 20 min (vacuum degree of vacuum is 0.06 kPa, rotation speed of stirring is 2000 r / min, revolution speed is 40 r / min, ultrasonic frequency is 6 kHz) to obtain a slurry. The adhesive and dispersant are the same as those used in Example 1. The ratio of conventional alumina, water, adhesive, and dispersant by mass is 20:71.2:8:0.8.

[0096] Step 2: Place the base film on a coating machine containing the slurry prepared in Step 1, and coat one side of the base film with the slurry at a speed of 20 m / min. Then, pull the film into the drying equipment by the traction roller and dry it at 45°C for 2 min. A coating is obtained on one side of the base film, resulting in a heat-resistant alumina lithium battery separator.

[0097] The heat-resistant alumina lithium battery separator prepared in Comparative Example 3 was tested, and the test results are shown in the table below:

[0098]

[0099] Comparative Example 4

[0100] A method for preparing a lithium battery separator with a gradient pore structure includes: coating a second slurry containing small-pore porous alumina (the same as the second slurry in Example 1) onto one side of a base film surface at a speed of 15 m / min; drawing the slurry into a drying equipment via a traction roller; drying at 50°C for 1 min; obtaining an A coating with a thickness of 2.1 μm on one side of the base film; coating a first slurry containing large-pore porous alumina (the same as the first slurry in Example 1) onto the surface of the A coating at a speed of 15 m / min; drawing the slurry into a drying equipment via a traction roller; drying at 50°C for 1 min; obtaining a B coating with a thickness of 1 μm on the A coating; and obtaining a lithium battery separator with a gradient pore structure, wherein the porosity of the A coating is 35.2% and the porosity of the B coating is 40.3%.

[0101] The parameters of the membrane prepared in Comparative Example 4 are as follows:

[0102]

[0103] In summary, this invention employs a dual-coating structure with two layers of coating having different pore sizes, thus forming a gradient pore structure. The gradient pore size design allows ions to gradually adapt to the different pore sizes as they enter the electrode material. This design enables a smooth transition for ions during migration. This structure allows for gradual ion adaptation during battery charging and discharging, reducing migration energy barriers. Under fast charging conditions, the gradient pore structure allows lithium ions to adhere more uniformly to the negative electrode, effectively suppressing lithium dendrite formation. Larger pore sizes provide more space for ion diffusion, reducing diffusion restrictions at the electrode-electrolyte interface. As the pore size decreases, ion movement within the channels is somewhat constrained, but this gradual adaptation helps improve overall ionic conductivity. The abundant pore structure of both small-pore and large-pore porous alumina enables the separator to have good liquid absorption and retention rates.

[0104] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A lithium battery separator with a gradient pore structure, characterized in that, It has a layered structure, which includes: a base film, a first coating and a second coating. The first coating and the second coating are located on the same side of the base film. The first coating is connected to one side of the base film, and the second coating is connected to the first coating. The porosity of the first coating is 40-50%, and the porosity of the second coating is 30-40%. The first coating includes: large-pore porous alumina with a pore size of 50-100 nm. The second coating includes: small-pore porous alumina with a pore size of 10-20 nm. By mass, the ratio of large-pore porous alumina in the first coating to small-pore porous alumina in the second coating is (10-30):(10-30).

2. The lithium battery separator with a gradient pore structure according to claim 1, characterized in that, The large-pore porous alumina has a particle size of D50 = 0.6–0.8 μm, D90 = 1.4–1.6 μm, and a specific surface area of ​​30–40 m². 2 / g.

3. The lithium battery separator with a gradient pore structure according to claim 1, characterized in that, The small-pore porous alumina has a particle size of D50 = 0.3–0.5 μm, D90 = 0.8–1.2 μm, and a specific surface area of ​​10–20 m². 2 / g.

4. The lithium battery separator with a gradient pore structure according to claim 1, characterized in that, The thickness of the first coating is 1 to 2.5 μm, and the thickness of the second coating is 1 to 2.5 μm.

5. The method for preparing a lithium battery separator with a gradient pore structure as described in any one of claims 1 to 4, characterized in that, include: A first slurry containing large-pore porous alumina is coated onto a base film and dried to obtain a first coating layer on the base film. A second slurry containing small-pore porous alumina is coated onto the surface of the first coating layer and dried to obtain a second coating layer on the first coating layer, thus obtaining a lithium battery separator with a gradient pore structure.

6. The preparation method according to claim 5, characterized in that, The first slurry comprises: macroporous alumina, water, adhesive and dispersant. By mass parts, the ratio of macroporous alumina, water in the first slurry, adhesive in the first slurry and dispersant in the first slurry is (10-30): (50-90): (5-10): (0.5-1).

7. The preparation method according to claim 5, characterized in that, The second slurry comprises: small-pore porous alumina, water, adhesive and dispersant. By mass parts, the ratio of small-pore porous alumina, water in the second slurry, adhesive in the second slurry and dispersant in the second slurry is (10-30): (50-90): (5-10): (0.5-1).

8. The preparation method according to claim 7, characterized in that, The dispersant is ammonium polyacrylate, and the adhesive is an acrylate copolymer solution.

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