Composite separator and lithium-ion battery using the same

Abstract

The present invention provides a composite separator comprising a porous substrate and a porous active layer, the porous active layer being provided on at least one surface of the porous substrate, the porous active layer comprising a base coating layer and non-adhesive organic particles C embedded in the base coating layer, the base coating layer comprising inorganic particles A and adhesive polymer B, the base coating layer and the porous substrate being bonded by adhesive polymer B, the average thickness of the base coating layer being h, h ≥ 0.5 μm, the mass of non-adhesive organic particles C : mass of base coating layer = (2~20):(70~90), and the particle size distribution of non-adhesive organic particles C satisfying (a) and (b), where (a) is 1 <D 50 / h ≤ 5, and (b) is (D 90 -D 10 ) / D 50 The value is ≤ 3.

Description

[Technical Field]

[0001] This invention claims priority to the Chinese patent application filed with the Chinese National Intellectual Property Office on May 17, 2024, with application number 202410622530.3, and the Chinese patent application filed with the Chinese National Intellectual Property Office on May 17, 2024, with application number 202410622499.3, the entirety of the above applications is incorporated into this invention by reference.

[0002] The present invention relates to lithium-ion batteries, and more specifically to a composite separator and a lithium-ion battery using the same. [Background technology]

[0003] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, an electrolyte, and a battery case. Of these, the separator is one of the important inner layer components, primarily functioning to separate the positive and negative electrodes and prevent short circuits caused by contact between them. With the development of the new energy industry, the demand for lithium-ion battery capacity is increasing. Currently, it is common practice to increase the size of the cells to improve the capacity of lithium-ion batteries. However, as the cell size increases, the internal structure of the cell pack becomes more prone to loosening, resulting in insufficient mechanical strength. This can make it difficult to place the cells into the case, make assembly inconvenient, or worsen the displacement of the electrode sheets due to pressure on the cell pack during the assembly process, potentially damaging the cells. During the operation of lithium-ion batteries, as the number of charge-discharge cycles increases, the cells often deform. As the cell deformation increases, the overhang between the positive and negative electrodes can change significantly, potentially causing deformation of the lithium-ion battery itself, which seriously impacts the safety and reliability of the battery.

[0004] To suppress cell deformation, the current industry standard practice is to spray a coating layer containing PVDF onto the separator surface, thereby bonding the separator to the electrode sheet using the PVDF in the coating layer.

Summary of the Invention

Problems to be Solved by the Invention

[0005] PVDF on the surface of the separator is likely to rise to the composite surface between the separator and the electrode sheet during the processing, so the pores on the composite surface are blocked, the penetration of the electrolyte becomes poor, the lithium ion transmission path decreases, the internal resistance of the battery increases, and it affects the performance such as the rate characteristics of the battery.

Means for Solving the Problems

[0006] According to the first aspect of the present invention, a composite separator is provided. The composite separator includes a porous substrate and a porous active layer. The porous active layer is provided on at least one surface of the porous substrate. The porous active layer includes a base coating layer and non-adhesive organic particles C embedded in the base coating layer. The base coating layer includes inorganic particles A and an adhesive polymer B. The base coating layer and the porous substrate are adhered by the adhesive polymer B. When the average thickness of the base coating layer is h, h≥0.5 μm, and the mass of the non-adhesive organic particles C: the mass of the base coating layer = (2 - 20):(70 - 90), and the particle size distribution of the non-adhesive organic particles C satisfies (a) and (b), where (a) 1<D 50 / h≤5, (b) (D 90 -D 10 ) / D 50 ≤3. The ratio of the mass of the non-adhesive organic particles C to the mass of the base coating layer may be 2:90, 20:90, 2:70, 20:70, 10:80, etc., but is not limited to the listed values, and other unlisted values within the numerical range can be similarly applied. The ratio of the average particle size D 50 of the non-adhesive organic particles C to the average thickness h of the base coating layer may be 1.25, 2, 3, 4, 5, etc., but is not limited to the listed values, and other unlisted values within the numerical range can be similarly applied.

[0007] According to the second aspect of the present invention, a lithium ion battery is provided that includes a cell including an electrode sheet and the above composite separator.

Advantages of the Invention

[0008] In the composite separator provided by the present invention, the non-adhesive organic particles C can form prominent protrusion structures on the surface of the base coating layer. Thus, when the composite separator and the electrode sheet are combined, the composite separator realizes the connection with the electrode sheet by means of these protrusion structures. The protrusion structures are inserted into the active material coating layer of the electrode sheet so that the composite separator and the electrode sheet are combined by mechanical interlocking. Moreover, these protrusion structures suppress the direct contact between the electrode sheet and the base coating layer, thereby forming a certain gap between the electrode sheet and the composite separator, preventing the electrode sheet from directly adhering to the base coating layer of the composite separator. This avoids the blockage of the pores on the surface of the composite separator and the electrode sheet due to the floating of the adhesive polymer B in the base coating layer, and ensures the smooth transmission of lithium ions between the separator and the electrode sheet. Furthermore, by limiting the mass of the non-adhesive organic particles C and the base coating layer, and limiting the particle size distribution ((D 90 -D 10 ) / D 50 =0.5 - 3) of the non-adhesive organic particles C, it is ensured that there are a sufficient number of, uniform-sized and appropriate protrusion structures on the surface of the porous active layer, guaranteeing the stable connection between the composite separator and the electrode sheet. On the other hand, it is beneficial to further reduce the lithium ion transfer impedance in the cell composed of the composite separator and the electrode sheet, thereby enabling the lithium ion transfer resistance of the above cell to be maintained within a low level range for a long time, and enabling the cell to maintain a high-efficiency and stable lithium ion transfer effect for a long time.

Embodiments for Carrying out the Invention

[0009] In some embodiments, the particle size distribution of the non-adhesive organic particles C satisfies (D 90 -D 10 ) / D 50 =0.5 - 3. The particle size distribution (D 90 -D 10 ) / D50 The value may be 0.5, 1, 1.5, 2, 2.5, 3, etc., but it is not limited to the numbers listed, and other unlisted numbers within that range can be applied similarly.

[0010] The non-adhesive organic particles C according to this embodiment should be distinguished from the adhesive polymer B and are tack-free at room temperature (25°C ± 5°C).

[0011] In some examples, adhesive polymer B includes at least one of the following: polyvinylidene fluoride, poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-co-trichloroethylene), polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, poly(ethylene-co-vinyl acetate), polyimide, and polyethylene oxide.

[0012] In some examples, the non-adhesive organic particles C include an acrylic acid ester polymer, and the acrylic acid ester polymer includes at least one of the following: poly(methyl acrylate), poly(ethyl acrylate), poly(butyl acrylate), poly(methyl methacrylate), butyl acrylate-styrene copolymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-methyl methacrylate copolymer.

[0013] In some embodiments, the average thickness h of the base coating layer satisfies 1 μm ≤ h < 8 μm. The average thickness h of the base coating layer may be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, etc., but is not limited to the values ​​listed, and other unlisted values ​​within that range can be applied similarly. When the average thickness h of the base coating layer is within the above range, the composite separator can achieve a better balance between heat shrinkage resistance and lithium ion transport dynamics, and the D of non-adhesive organic particles C 50By adjusting the average thickness h of the base coating layer based on the fact that the average thickness h of the base coating layer satisfies a specific proportional relationship, the size of the gap between the composite separator and the electrode sheet when the composite separator and the electrode sheet are combined is indirectly controlled, thereby further improving the penetration effect of the electrolyte between the composite separator and the electrode sheet, while ensuring that the cell consisting of the composite separator and the electrode sheet has good structural stability.

[0014] In some examples, the particle size distribution of the non-adhesive organic particles C is D 50 The average particle size D of non-adhesive organic particles C satisfies the condition = 3~8 μm. 50 The particle size may be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc., but is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied similarly. The particle size distribution of the non-adhesive organic particles C satisfying the above characteristics is advantageous in improving the structural stability of the porous active layer, allowing the non-adhesive organic particles C to be better embedded in the base coating layer and strengthening the bonding stability between the composite separator and the electrode sheet.

[0015] In some examples, the particle size distribution of the non-adhesive organic particles C is D 10 =0.5~4μm, D 90 The size of non-adhesive organic particles C is further satisfied. 10 The thickness may be 0.5 μm, 1 μm, 2.5 μm, 3 μm, 4 μm, etc., but it is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied in the same way. D of non-adhesive organic particles C 90 This could be 5 μm, 6.5 μm, 11 μm, 15 μm, 18 μm, etc., but it is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied similarly.

[0016] In some examples, the D of inorganic particle A 50 : Non-adhesive organic particles C of D 50 =(0.05~0.4):1. D of inorganic particle A 50 and non-adhesive organic particles C D50 The ratio may be 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, etc., but is not limited to the values ​​listed, and other unlisted values ​​within that range can be applied similarly. The present invention allows inorganic particles A and non-adhesive organic particles C to be firmly packed around non-adhesive organic particles C by comprehensively adjusting the average particle size of inorganic particles A and non-adhesive organic particles C. This allows non-adhesive organic particles C to be more firmly embedded in the base coating layer without reducing the porosity of the porous active layer. As a result, while maintaining a high porosity in the porous active coating layer, more transport channels can be provided for lithium ion entry into the base coating layer and lithium ion transport in the base coating layer. In other words, a cell to which the above composite separator is applied can maintain good structural stability in an operating state where lithium ions are transported rapidly, i.e., it can better meet the needs of rapid charging applications.

[0017] In some examples, the D of inorganic particle A 50 The average thickness h of the base coating layer is 1 (1 to 15), and the Mohs hardness of inorganic particle A is 2 to 10. 50 The ratio of inorganic particles A to the average thickness h of the base coating layer may be 1:1, 1:2.5, 1:5, 1:10, 1:15, etc., but is not limited to the values ​​listed, and other unlisted values ​​within that range can be applied similarly. The Mohs hardness of inorganic particles A may be 2, 3, 5, 5.5, 7, 10, etc., but is not limited to the values ​​listed, and other unlisted values ​​within that range can be applied similarly. By using inorganic particles A as the main component of the base coating layer and further comprehensively adjusting the size of inorganic particles A and the average thickness of the base coating layer based on the range of Mohs hardness of inorganic particles A, the filling of inorganic particles A in the base coating layer and the internal stress distribution can be limited, and a composite separator in which inorganic particles A and the base coating layer satisfy the above characteristics is excellent in both flexibility and heat shrinkage resistance.

[0018] In some examples, inorganic particles A include at least one of alumina (Al2O3), boehmite (AlOOH), titania (TiO2), and silica (SiO2).

[0019] In some embodiments, the Mohs hardness of the inorganic particle A is 2 to 5. The Mohs hardness of the inorganic particle A may be 2, 2.5, 3, 4, 5, etc., but is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied similarly.

[0020] In some examples, the particle size distribution of inorganic particle A is (D 90 -D 10 ) / D 50 The particle size distribution of inorganic particle A (D) satisfies = 0.5 to 2. 90 -D 10 ) / D 50 The value of may be 0.5, 1, 1.5, 1.8, 2, etc., but is not limited to the values ​​listed, and other values ​​not listed within that numerical range can be applied similarly. By ensuring that the particle size distribution of inorganic particles A satisfies the above conditions, the quality of the porous active layer as a coating layer can be further optimized. Specifically, the adhesion effect between the base coating layer and the porous substrate is improved, the heat shrinkage resistance of the base coating layer is improved, and the heat stability of the composite separator is enhanced. At the same time, the flatness of the base coating layer is improved, allowing for better control of the gap size between the composite separator and the electrode sheet.

[0021] In some embodiments, the non-adhesive organic particles C contain an acrylate-based polymer, and the glass transition temperature (Tg value) of the acrylate-based polymer is 30 to 90°C. The Tg value of the acrylate-based polymer may be 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, etc., but is not limited to the values ​​listed above, and other values ​​within that range that are not listed can be applied similarly. By using the above acrylate-based polymer as the non-adhesive organic particles C, a mechanical interlock structure between the composite separator and the electrode sheet can be more easily established, and the connection between the composite separator and the electrode sheet can be strengthened.

[0022] In some examples, the acrylic ester polymer includes at least one of the following: butyl acrylate-styrene copolymer, ethylene-acrylic acid copolymer, and ethylene-methyl methacrylate copolymer.

[0023] In some embodiments, the porous active layer has a mass ratio of inorganic particles A:adhesive polymer B:non-adhesive organic particles C = (70~90):(2~15):(2~20). The mass ratio of inorganic particles A, adhesive polymer B, and non-adhesive organic particles C may be 70:2:2, 70:15:20, 70:2:20, 70:15:2, 90:15:20, 90:2:2, 90:15:2, 90:2:20, etc., but is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied similarly.

[0024] In some embodiments, the porous active layer has a mass ratio of inorganic particles A:adhesive polymer B:non-adhesive organic particles C = (80~85):(7~12):(5~10). The mass ratio of inorganic particles A, adhesive polymer B, and non-adhesive organic particles C may be 80:7:5, 80:12:10, 80:7:10, 80:12:5, 85:12:10, 85:7:5, 85:7:10, 85:12:5, etc., but is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied similarly.

[0025] In some examples, the porous substrate is at least one selected from polyethylene, polypropylene, polybutene, and polypentene.

[0026] According to a second aspect of the present invention, a lithium-ion battery comprising a cell is provided, the cell comprising an electrode sheet and the composite separator.

[0027] In some embodiments, a composite separator and an electrode sheet are provided at a distance from each other in the cell, a porous active layer is provided on the surface of the composite separator facing the electrode sheet, the composite separator connects to the electrode sheet by non-adhesive organic particles C contained in the porous active layer, and a gap is formed between the electrode sheet and the base coating layer provided toward it after hot pressing, with an average gap width d = 0.05 to 3 μm after hot pressing. The average gap width d may be 0.05 μm, 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, etc., but is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied similarly. In each cell, the direction along the lamination direction of the electrode sheet and composite separator is defined as the average thickness direction, the total thickness of the cell is D, the total thickness of the porous substrate of the composite separator contained in the cell is d1, the total thickness of the base coating layer of the composite separator contained in the cell is d2, the total thickness of the electrode sheet contained in the cell is d3, the number of gaps is n, and the average width d of the gaps is calculated as D = (D - d1 - d2 - d3) / n.

[0028] In the lithium-ion battery cell described above, the composite separator can be firmly connected to the electrode sheet, and a gap of appropriate width is formed between the composite separator and the electrode sheet. By providing this gap, the lithium-ion transmission resistance between the composite separator and the electrode sheet is reduced, the cell can maintain good thickness uniformity for a long period of time, and can maintain a highly efficient and stable lithium-ion transmission effect for a long period of time.

[0029] In some embodiments, the method for manufacturing the cell includes stacking a composite separator and an electrode sheet in sequence, then performing a heat press treatment on the composite separator and electrode sheet, wherein the heat press temperature is 50 to 100°C and the heat press pressure is 600 to 3000 MPa. The heat press temperature may be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc., but is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied in the same way. The heat press pressure may be 600 MPa, 1000 MPa, 1500 MPa, 2000 MPa, 3000 MPa, etc., but is not limited to the values ​​listed, and other values ​​within that range that are not listed can be applied in the same way.

[0030] In some embodiments, the hot press temperature is 70-90°C and the hot press pressure is 1200-2000 MPa. The hot press temperature may be 70°C, 75°C, 80°C, 85°C, 90°C, etc., but is not limited to the values ​​listed, and other values ​​not listed within that range can be applied similarly. The hot press pressure may be 1200 MPa, 1500 MPa, 1700 MPa, 1800 MPa, 2000 MPa, etc., but is not limited to the values ​​listed, and other values ​​not listed within that range can be applied similarly.

[0031] [Example 1] 1. Fabrication of composite separators

[0032] (1) Fabrication of composite separators for the experimental group The composite separator of the experimental group comprises a porous substrate and a porous active layer coated on the surface of the porous substrate. The main components of the coating slurry for producing the porous active layer include inorganic particles A, adhesive polymer B, and non-adhesive organic particles C. In this example, as inorganic particles A, boehmite (with a Mohs hardness of 3 and D 10 =0.1μm, D 50 =0.4μm, D 90A particle size of 1.1 μm was used, polyvinyl acetate was used as the adhesive polymer B, and butyl acrylate-styrene copolymer (tg=55℃) was used as the non-adhesive organic particle C. The coating slurry used to prepare the composite separators in the experimental group was prepared by weighing the necessary materials in parts by mass, specifically weighing 80 parts of boehmite, 10 parts of polyvinyl acetate, 10 parts of butyl acrylate-styrene copolymer, 5 parts of leveling agent, and 120 parts of pure water, mixing the above materials, and stirring thoroughly until homogeneous. A polyethylene film was used as the porous substrate, and the coating slurry prepared as described above was applied to both sides of the porous substrate, and the coating thickness was controlled based on a predetermined porous active layer thickness to obtain a separator semi-finished product. The separator semi-finished product was transferred to an oven and thoroughly dried to form a porous active layer on both back-to-back sides of the porous substrate, which consisted of a base coating layer composed of inorganic particles A and adhesive polymer B, and non-adhesive organic particles C embedded in the base coating layer and protruding from the surface of the base coating layer, thereby preparing a composite separator. In this embodiment, different composite separators are obtained by adjusting the particle size distribution of non-adhesive organic particles C for blending the coating slurry and / or the average thickness h of the base coating layer during the process of producing the composite separators. The different composite separators are numbered, and the numbering of the composite separators and the characteristics of the corresponding structural compositions are shown in Table 1.

[0033] (2) Preparation of composite separators for the control group Furthermore, as a control, in this embodiment, a composite separator that does not contain non-adhesive organic particles C was prepared and used as the control separator. The method for preparing the control separator is as follows. The raw material composition of the coating slurry was formulated by referring to the composite separator of the experimental group in this embodiment, and inorganic particles A, adhesive polymer B, leveling agent and pure water were used in the same way as the formulation of the coating slurry. Here, when calculated by mass parts, 80 parts of inorganic particles A (boehmite), 10 parts of adhesive polymer B (polyvinyl acetate), 5 parts of leveling agent and 120 parts of pure water were used, and the above materials were mixed and stirred thoroughly until uniform to form an inorganic particle slurry. A polyethylene film was used as the porous substrate, and this porous substrate was the same polyethylene film used in the preparation of the composite separator of the experimental group. An inorganic particle slurry prepared as described above was applied to both sides of a porous substrate, and the application thickness was controlled based on a predetermined thickness of the porous active layer to obtain a separator semi-finished product. The separator semi-finished product was then transferred to an oven and thoroughly dried to form a porous active layer consisting of inorganic particles A and adhesive polymer B on both back-to-back sides of the porous substrate, thereby producing a control set composite separator, which is referred to as the control separator. The control separator differs from the composite separator of the experimental group described above in that it does not contain non-adhesive organic particles C.

[0034] Table 1 shows information on the composite separators and control separators of the experimental group prepared in this example. Except for differences in the particle size distribution of the selected non-adhesive organic particles C and the average thickness h of the base coating layer, the materials used and related processes for preparing these composite separators are strictly the same. Table 1 shows "D 50 " / h" refers to the D of non-adhesive organic particles C used in the composite separator. 50 This shows the ratio to the average thickness h of the base coating layer of the composite separator. Also, since the control separator does not use non-adhesive organic particles C in the manufacturing process, the column for non-adhesive organic particles C corresponding to the control separator in Table 1 is indicated with "-".

[0035] Table 1 shows information on the composition and structure of the composite separator.

[0036] [Table 1]

[0037] 2. Peeling force test of composite separator and electrode sheet

[0038] [Target Testers] The composite separator fabricated in this embodiment was used as the test subject.

[0039] [Test Method] (1) Preparation of a test positive electrode sheet Positive electrode sheet A is prepared as follows: Adhesive PVDF is added to NMP in a mass ratio of 1:8 and stirred to obtain glue solution. Then lithium iron phosphate (LFP), conductive agent acetylene black, and glue solution are mixed in a mass ratio of 97:1:2 and stirred under the action of a vacuum mixer until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is uniformly applied to the positive electrode current collector to a coating thickness of 120 μm. After drying at room temperature, it is transferred to an oven to continue drying, and then cold pressing and slitting are performed to obtain positive electrode sheet A.

[0040] Positive electrode sheet B is prepared as follows: Adhesive PVDF is added to NMP in a mass ratio of 1:8 and stirred to obtain glue liquid. Then, lithium iron phosphate (LFP), the positive electrode active material, acetylene black, and glue liquid are mixed in a mass ratio of 97:1:2 and stirred under a vacuum mixer until the system is homogeneous to obtain positive electrode slurry 1. Adhesive PVDF is added to NMP in a mass ratio of 1:8 and stirred to obtain glue liquid. Then, lithium iron phosphate (LFP), acetylene black, and glue liquid are mixed in a mass ratio of 97:1:2 and stirred under a vacuum mixer until the system is homogeneous. Then, butyl acrylate-styrene copolymer (Tg=55℃) with the same particle size distribution and amount used as the butyl acrylate-styrene copolymer used in the preparation of composite separators 1-3 is added and stirred thoroughly to obtain positive electrode slurry 2. Positive electrode slurry 1 is uniformly applied to the positive electrode current collector to a thickness of 119 μm. After drying at room temperature, positive electrode slurry 2 is uniformly applied to the surface of the coating layer formed by positive electrode slurry 1 to a thickness of 1 μm. After drying at room temperature, it is transferred to an oven for drying, and then positive electrode sheet B is obtained through cold pressing and slitting. The cold pressing and slitting operations are the same in the process of producing positive electrode sheet A and positive electrode sheet B.

[0041] (2) Preparation of a composite separator-positive electrode sheet for performing peel force tests. A 20mm x 300mm composite separator and the positive electrode sheet obtained as described above (positive electrode sheet A or positive electrode sheet B) were cut and stacked. The temperature of the hot press was set to 90°C, the pressure to 600kg, and the hot press time to 3s. The stacked separator / positive electrode sheet was firmly bonded using the hot press to form a composite of the composite separator and the positive electrode sheet. The composite separator-positive electrode sheet composites produced by the above operation were numbered as Specimen 1-1, Specimen 1-2, Specimen 1-3, Specimen 1-4, Specimen 1-5, Specimen 1-6, Specimen 1-7, Specimen 1-8, Specimen 1-9, Specimen 1-10, Specimen D1, Specimen D2, Specimen D3, Control Specimen A, and Control Specimen B. The corresponding numbers for these composite separator-positive electrode sheet composites, and the composite separators and positive electrode sheets included in them, are specifically shown in Table 2. The composite separator-positive electrode sheet composite is cut at its edge to a size of 10 mm x 150 mm. The composite separator and positive electrode sheet are lightly separated at the edge, and each is placed between the ends of a peel force testing machine. The machine is started, the composite separator and positive electrode sheet are peeled apart, and the peel strength at the time of peeling is recorded.

[0042] [Test Results] The test results are shown in Table 2. Composite separators 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10 all contain non-adhesive organic particles C, and the surface of the base coating layer of each composite separator is formed by non-adhesive organic particles C, providing a protruding structure in the tested prototypes. When the composite separator and the positive electrode sheet are pressed together, the non-adhesive organic particles C protruding from the surface of the base coating layer of the composite separator are pushed into the positive electrode active material coating layer of the positive electrode sheet, thereby connecting the composite separator and the positive electrode sheet through a mechanical interlock of the non-adhesive organic particles C. The resulting samples 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10 all showed high peeling forces, indicating good structural stability. In these samples, a certain gap is formed between the positive electrode sheet and the base coating layer of the composite separator. In the test subjects, the peeling forces measured for samples 1-3 and 1-5 were both relatively high, and the composite separators used in samples 1-3 and 1-5, respectively, can be firmly connected to the positive electrode sheet. The average particle size of the non-adhesive organic particles C contained in composite separators 1-8 and 1-9 is large, and it is somewhat difficult for these large non-adhesive organic particles C to penetrate the positive electrode active material coating layer. As a result, the stability in the positive electrode active material coating layer is somewhat low, and the peeling force measured in samples 1-8 and 1-9 is lower than that of sample 1-3. The peeling force between the composite separator and the electrode sheet measured in samples D1, D2, and D3 is clearly lower.In the process of manufacturing the composite separator D1, the non-adhesive organic particles C used have low particle size uniformity and a wide particle size distribution. In addition, the thickness of the base coating layer formed on the surface of the porous substrate is thin. As a result, although the non-adhesive organic particles C can form a sufficient amount of protrusions on the surface of the base coating layer, the protrusions differ in size. Consequently, some of the larger non-adhesive organic particles C are not firmly embedded in the thin base coating layer. In the subsequent bonding process between the composite separator D1 and the positive electrode sheet, the larger non-adhesive organic particles C contained in the porous substrate can be pushed into the positive electrode active material coating layer. However, further proximity between the composite separator D1 and the positive electrode sheet is also restricted. As a result, even if a considerable portion of the non-adhesive organic particles C protrude from the base coating layer of the composite separator D1, they cannot be pushed into the positive electrode active material coating layer of the positive electrode sheet. Furthermore, the prototype D1 obtained by combining the composite separator D1 and the positive electrode sheet may also have uneven thickness and be non-flat. This is due to the uneven particle size distribution of the non-adhesive organic particles C. As a result, the number of non-adhesive organic particles C that can effectively connect the composite separator D1 and the positive electrode sheet in the prototype D1 is small, and the thickness of the prototype D1 is uneven, resulting in low peeling force of the prototype D1. Because the base coating layer contained in the composite separator D2 is thin, it is difficult to firmly fix the non-adhesive organic particles C, and the non-adhesive organic particles C tend to detach from the porous active layer of the composite separator D2, resulting in low peeling force of the prototype D2. Because the particle size of the non-adhesive organic particles C used to fabricate the composite separator D3 is small, the non-adhesive organic particles C are basically completely embedded in the base coating layer of the composite separator D3, and no obvious protruding structures are generally visible on the surface of the base coating layer. As a result, when the composite separator D3 and the positive electrode sheet are pressed together, the base coating layer of the composite separator D3 is directly bonded with the positive electrode active material coating layer of the positive electrode sheet (positive electrode sheet A), and both the base coating layer of the composite separator D3 and the positive electrode active material coating layer of the positive electrode sheet (positive electrode sheet A) are bonded by the adhesive polymer B in the base coating layer of the composite separator D3. Because the distribution of the adhesive is non-uniform, the peeling force measured on the prototype D3 fabricated from the composite separator D3 is low.The control separator does not contain non-adhesive organic particles C, and the base coating layer of the control separator sample is flat with no prominent protruding structures. When preparing control sample A, the control separator is used to compound with the positive electrode sheet (positive electrode sheet A), and, as in the case of sample D3 above, the control separator sample and the positive electrode sheet are bonded by the adhesive polymer B in the base coating layer of the control separator. The resulting peeling force of control sample A is significantly lower than that of samples 1-3. When preparing positive electrode sheet B using the control separator, the positive electrode sheet (positive electrode sheet B) contains non-adhesive organic particles C in the positive electrode active material coating layer. However, during the processing of the positive electrode sheet, a cold press treatment is performed, causing some of the non-adhesive organic particles C in the positive electrode sheet to be crushed or damaged. As a result, the protruding structures formed on the surface of the positive electrode active material coating layer of the positive electrode sheet by the non-adhesive organic particles C are non-uniform. When a control separator is used to combine with a positive electrode sheet, the control separator and the positive electrode sheet (positive electrode sheet B) are connected by non-adhesive organic particles C. However, because the non-adhesive organic particles C connecting the control separator and the positive electrode sheet are non-uniform, the thickness of control sample B is also non-uniform, and the peeling force of control sample B is clearly lower than that of samples 1-3.

[0043] Table 2 shows the test results for composite separator-positive electrode sheet composites and their corresponding peeling forces.

[0044] [Table 2]

[0045] [Example 2] 1. Manufacturing of lithium-ion batteries

[0046] (1) Separator In this embodiment, the composite separator fabricated in Example 1 is used as a separator for manufacturing lithium-ion batteries.

[0047] (2) Preparation of the positive electrode sheet The positive electrode sheet A is manufactured in exactly the same way as the positive electrode sheet A in Example 1, and the materials used are the same. The positive electrode sheet B is manufactured in exactly the same manner as the positive electrode sheet B manufactured in Example 1, and the materials used are also the same.

[0048] (3) Fabrication of the negative electrode sheet The negative electrode sheet A is prepared as follows: Graphite, the negative electrode active material; acetylene black, the conductive agent; CMC, the thickener; and SBR, the adhesive, are mixed in a mass ratio of 96.2:0.8:1.2:1.8. Deionized water, the solvent, is then added to the resulting mixture, and the mixture is stirred under a vacuum mixer until the system is homogeneous to obtain a negative electrode slurry. The negative electrode slurry is uniformly applied to a negative electrode current collector to a coating thickness of 105 μm. After drying at room temperature, it is transferred to an oven for further drying, followed by cold pressing and slitting to obtain the negative electrode sheet A. The negative electrode sheet B is prepared as follows: After mixing graphite, the negative electrode active material, acetylene black, the conductive agent, CMC, the thickener, and SBR, the adhesive, in a mass ratio of 96.2:0.8:1.2:1.8, deionized water is added to the mixture and stirred under the action of a vacuum mixer until the system is homogeneous to obtain negative electrode slurry 1. After mixing graphite, the negative electrode active material, acetylene black, the conductive agent, CMC, the thickener, and SBR, the adhesive, in a mass ratio of 96.2:0.8:1.2:1.8, deionized water is added to the mixture and stirred under the action of a vacuum mixer until the system is homogeneous, butyl acrylate-styrene copolymer (tg=55℃) having the same particle size distribution and weight used as the butyl acrylate-styrene copolymer used in the process of preparing composite separators 1-3 is added and stirred thoroughly to obtain negative electrode slurry 2. Negative electrode slurry 1 is uniformly applied to the negative electrode current collector to a thickness of 104 μm. After drying at room temperature, negative electrode slurry 2 is uniformly applied to the surface of the coating layer formed by negative electrode slurry 1 to a thickness of 1 μm. After drying at room temperature, it is transferred to an oven for further drying, followed by cold pressing and slitting to obtain negative electrode sheet B. The cold pressing and slitting operations are the same in the process of producing negative electrode sheet A and negative electrode sheet B.

[0049] (4) Assembly of the cell assembly The composite separator, positive electrode sheet, and negative electrode sheet were combined according to Table 3. The combined composite separator, positive electrode sheet, and negative electrode sheet were stacked in the order of positive electrode sheet, composite separator, and negative electrode sheet, and then subjected to a hot press treatment. The hot press temperature was 80°C, the hot press pressure was 1500 MPa, and the hot press time was 30 s, thereby obtaining a cell assembly.

[0050] (5) Electrolyte composition The electrolyte was formulated so that EC:PC:DMC:EMC = 30:5:20:45, with VC at 2% and LiPF6 at 12.5%.

[0051] (6) Assembly of lithium-ion batteries The cell assembly manufactured as described above is placed in the inner chamber of the battery case and dried. Then, the electrolyte prepared in this embodiment is injected into the inner chamber of the battery case, and the lithium-ion battery of this embodiment is obtained through processes such as vacuum sealing, standing, chemical conversion, and capacity separation. The lithium-ion batteries produced are numbered according to the combination of composite separator, positive electrode sheet, and negative electrode sheet used, and the correspondence between the lithium-ion batteries and the composite separator, positive electrode sheet, and negative electrode sheet used is shown in Table 3. Aside from the configuration of the cell assembly used, all other parts, materials, and manufacturing processes used in each lithium-ion battery are strictly the same.

[0052] 2. Performance testing of lithium-ion batteries [Target Testers] The lithium-ion battery fabricated in this example was used as the test subject.

[0053] [Test items and corresponding methods] For the cycle performance test, the battery was left standing for 60 minutes at 25°C, charged to 3.65V with a constant current and voltage of 1C (the constant current and voltage charging capacity was recorded as C0), left standing for 60 minutes, and discharged to 2.5V with a constant current of 1C (each constant current discharge capacity was recorded as C0). 1…n (to be recorded as), cycle capacity retention rate is (C 1…n / C0)*100%. For the DCR test, the battery was left standing for 60 minutes at 25°C, charged to 3.65V with a constant current and voltage of 1C, left standing for 60 minutes, and discharged to 2.5V with a 1C current (discharge capacity recorded as D). After leaving standing for 60 minutes, it was charged with a constant current until the battery capacity reached (50% SOC = (D / 2)). After leaving standing for 60 minutes (voltage V0 was recorded), it was charged for 10 seconds with a 1C current, left standing for 30 minutes (voltage V1 was recorded), and the current I was recorded. The charging DCR is (V1-V0) / I.

[0054] [Test Results] The test results are shown in Table 3.

[0055] In the cell assemblies contained in batteries 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, battery D1, battery D2, and control battery B, a gap of non-zero width is formed between the positive electrode sheet and the base coating layer directly facing it, and between the negative electrode sheet and the base coating layer directly facing it, with an average gap width d of 0.2 to 0.8 μm. On the other hand, in battery D3, manufactured using a composite separator, and control battery A, manufactured using a control separator, it is difficult to form a sufficient protruding structure on the surface of the base coating layer contained in both batteries. Therefore, in the cell assemblies contained in batteries D3 and control battery A, it is fundamentally difficult to form a gap of non-zero width between the positive electrode sheet and the base coating layer directly facing it, and between the negative electrode sheet and the base coating layer directly facing it. Batteries 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10 all demonstrated good cycle performance, as their capacity retention rates, measured after 1000 cycles, were all greater than 80%. In the above-mentioned battery, the connection between the composite separator and the positive electrode sheet and the negative electrode sheet is achieved by non-adhesive organic particles C contained in the composite separator. The more stable the connection between the composite separator and the positive electrode sheet and the negative electrode sheet, the higher the structural stability of the battery and the better the battery's cycle performance. Therefore, the relative relationship of the magnitude of the capacity retention rate measured in the above-mentioned battery basically matches the relative relationship of the magnitude of the peeling force measured in the composite separator-positive electrode sheet composite samples (samples 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10) corresponding to Example 1. On the other hand, the DCR measured for batteries 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10 were all 0.7 mΩ or less, indicating that these batteries were able to achieve efficient and smooth lithium-ion transmission during the test process and possessed excellent lithium-ion transmission dynamics characteristics.In all of the above-mentioned batteries, non-adhesive organic particles C are used to connect the composite separator to the positive electrode sheet and the negative electrode sheet. This creates a certain gap between the base coating layer of the composite separator and the positive and negative electrode sheets, which significantly improves the penetration of the electrolyte into the cell and enhances the lithium ion transmission efficiency between the positive and negative electrode sheets. As a result, the DCR value of the above-mentioned batteries can be maintained at a low level.

[0056] Compared to batteries 1-1, 1-2, 1-3, 1-4, 1-5, 1-6, 1-7, 1-8, 1-9, and 1-10, batteries D1, D2, D3, control battery A, and control battery B have significantly lower cycle retention rates and significantly higher DCR rates. Because the size of the non-adhesive organic particles C used to fabricate the composite separator D1 is non-uniform, the thickness of battery D1 is non-uniform, resulting in regional differences in the connection strength between the composite separator D1 and the positive and negative electrode sheets, which worsens the structural stability of battery D1. On the other hand, because of the non-uniform thickness, regional differences also exist in the lithium ion transmission path between the positive and negative electrode sheets, leading to poor consistency in the lithium ion transmission efficiency of battery D1. As the number of cycles increases, polarization occurs in battery D1, and the deterioration of lithium ion transmission between the positive and negative electrode sheets accumulates, ultimately resulting in a lower cycle retention rate and a higher DCR rate measured for battery D1. Because the base coating layer in composite separator D2 is thin, the fixing effect of the base coating layer on non-adhesive organic particles C is low. Consequently, as the number of cycles of battery D2 increases, the loosening of non-adhesive organic particles C from composite separator D2 increases, the structural stability of battery D2 deteriorates, and the cycle capacity retention rate measured in battery D2 decreases. Since there are no clearly protruding non-adhesive organic particles C on the surface of the base coating layer of both composite separator D3 and the control separator, in battery D3 and the control battery A, the composite separator and the positive electrode sheet and negative electrode sheet are bonded mainly by the adhesive polymer B contained in the base coating layer of the composite separator. This results in poorer battery structure stability compared to achieving connection between the composite separator and the positive electrode sheet and negative electrode sheet by mechanical interlock using non-adhesive organic particles C.Furthermore, as the number of cycles increases, the adhesive polymer B in the composite separator floats to the base coating layer, worsening the uneven distribution of adhesive polymer B in the base coating layer. The adhesive polymer B that floats to the composite surface between the composite separator and the positive or negative electrode sheet becomes locally concentrated, blocking the pores of the composite surface, which is unfavorable for the penetration of the electrolyte in the battery. This inhibits the movement of lithium ions between the positive or negative electrode sheet and the composite separator, resulting in a decrease in the capacity retention rate of battery D3 and control battery A, and an increase in DCR. Here, since the content of adhesive polymer B in the base coating layer of the control separator is higher than the content of adhesive polymer B in the base coating layer of composite separator D3, control battery A, which uses the control separator, has worse permeability and permeability of the base coating layer during the cycle process compared to battery D3, which uses composite separator D3. As a result, control battery A has the lowest capacity retention rate and the highest DCR among the tested batteries. On the other hand, in control battery B, the connection between the control separator and the positive electrode sheet and negative electrode sheet is also achieved by the mechanical interlock of non-adhesive organic particles C. However, control battery B is distinguished from other test subjects containing non-adhesive organic particles C in that the non-adhesive organic particles C included in control battery B are pre-fitted into the positive electrode active material coating layer (positive electrode sheet B) and the negative electrode active material coating layer (negative electrode sheet B). Since both the positive electrode sheet and negative electrode sheet undergo cold pressing during processing, the presence of non-adhesive organic particles C makes the cold pressing of the electrode sheet processing insufficient. As the number of cycles increases, the quality of the coating layer of the positive electrode active material and / or the negative electrode active material deteriorates. Cold pressing also damages and deforms the non-adhesive organic particles C protruding from the positive electrode active material coating layer and the negative electrode active material coating layer to a certain extent. This can result in uneven connection strength between the control separator and the positive electrode sheet and the negative electrode sheet, and uneven thickness in the control battery B. Consequently, as the number of cycles increases, lithium ion transport inside the control battery B does not proceed smoothly, and both the cycle performance and lithium ion dynamic transport characteristics of the control battery B deteriorate.

[0057] Table 3 shows the lithium-ion battery manufactured in this embodiment, its corresponding cell assembly, and the performance test results.

[0058] [Table 3]

[0059] [Example 3]

[0060] 1. Fabrication of composite separators This embodiment prepares a composite separator by referring to the method for preparing the composite separator in the experimental group of Example 1. Similar to the composite separator in the experimental group prepared in Example 1, the composite separator prepared in this embodiment includes a porous substrate and a porous active layer coated on the surface of the porous substrate. The main components of the coating slurry for preparing the porous active layer include inorganic particles A, adhesive polymer B, and non-adhesive organic particles C. In this embodiment, the adhesive polymer B and non-adhesive organic particles C used to prepare the coating slurry are the same materials used in the preparation of composite separators 1-3 in Example 1, namely, polyvinyl acetate is used as the adhesive polymer B, and butyl acrylate-styrene copolymer (tg=55℃, D 10 =2.5μm, D 50 =4μm, D 90Non-adhesive organic particles C (6.5 μm) are used. Unlike the composite separators 1-3 prepared in Example 1, which are prepared by combining the adhesive polymer B and non-adhesive organic particles C using different particle size distributions or different types of inorganic particles A, Table 4 shows the composite separators prepared using the coating slurry and the inorganic particles A contained therein. In this example, the coating slurry used to prepare the composite separator was obtained by weighing the necessary materials in parts by mass, specifically weighing 80 parts of inorganic particles A, 10 parts of polyvinyl acetate, 10 parts of butyl acrylate-styrene copolymer, 5 parts of leveling agent, and 120 parts of pure water, mixing these materials, and stirring thoroughly until homogeneous. The raw materials used to prepare the above coating slurry are exactly the same as the materials used to prepare composite separators 1-3 in Example 1, except for inorganic particles A. The film substrate used as the porous substrate in this example is the same polyethylene film used to prepare composite separators 1-3 in Example 1. The coating slurry prepared above is applied to both sides of the porous substrate, controlling the coating thickness based on a predetermined porous active layer thickness, to obtain a separator semi-finished product. The separator semi-finished product is transferred to an oven and thoroughly dried to form a porous active layer on both back-to-back sides of the porous substrate, which consists of a base coating layer composed of inorganic particles A and adhesive polymer B, and non-adhesive organic particles C embedded in the base coating layer and protruding from the surface of the base coating layer, thereby producing a composite separator. The composite separators produced in this embodiment are numbered composite separator 2-1, composite separator 2-2, composite separator 2-3, composite separator 2-4, composite separator 2-5, and composite separator 2-6, respectively. The compositional and structural characteristics of these composite separators are shown in Tables 4 and 5. For convenience of comparison, Tables 4 and 5 also show the compositional and structural characteristics corresponding to composite separator 1-3 in Example 1. 50 (A) is the D of inorganic particle A. 50 This means "D 50 (C) is D of non-adhesive organic particles C 50 This means "D 50 (A) / D 50 (C) is the D of inorganic particle A used in the composite separator.50 and non-adhesive organic particles C D 50 It means the ratio to, "D 50 (A) / h" is the D of inorganic particle A used in the composite separator. 50 and non-adhesive organic particles C D 50 It means the ratio of to.

[0061] Table 4 shows the composite separator and the inorganic particles A used therein.

[0062] [Table 4]

[0063] Table 5 shows information on the composition and structure of the composite separator.

[0064] [Table 5]

[0065] 2. Peeling force test of composite separator and electrode sheet

[0066] [Target Testers] The composite separator fabricated in this embodiment was used as the test subject.

[0067] [Test Method] (1) Preparation of test positive electrode sheet A The method for producing positive electrode sheet A and the materials used are exactly the same as in Example 1.

[0068] (2) Fabrication of composite separator-positive electrode sheet composite for peeling force testing The composite separator and cathode sheet A manufactured in this embodiment are manufactured by referring to the method for manufacturing the composite separator-cathode sheet composite in Example 1, and the composite separator and cathode sheet used for testing in this embodiment are combined according to this embodiment, except that the materials and methods used for manufacturing the composite separator-cathode sheet composite are exactly the same as those used for manufacturing the composite separator-cathode sheet composite in Example 1. The composite separator-cathode sheet composites manufactured in this embodiment are numbered 2-1, 2-2, 2-3, 2-4, 2-5, and 2-6, respectively, and the corresponding numbers and the composite separators and cathode sheets included in them are specifically shown in Table 6. The edges of the composite separator-positive electrode sheet composite were cut to a size of 10 mm x 150 mm. The composite separator and positive electrode sheet were lightly separated at the edges of the composite separator-positive electrode sheet composite, and each was placed between the ends of a peel force testing machine. The machine was started, and the composite separator and positive electrode sheet were peeled off. The peel strength at the time of peeling was recorded.

[0069] [Test Results] The test results are shown in Table 6. For the sake of comparison, Table 6 also shows the adhesive performance measured on prototype 1-3, which was made using composite separator 1-3 used in Example 1. The type and particle size distribution of non-adhesive organic particles C contained in composite separator 1-3, composite separator 2-1, composite separator 2-2, composite separator 2-3, composite separator 2-4, composite separator 2-5, and composite separator 2-6 are the same, and the difference between the above composite separators is the inorganic particles A used. As can be seen by comparing the peeling forces measured for samples 1-3, 2-1, 2-2, 2-3, and 2-4 to which composite separators 1-3, 2-1, 2-2, 2-3, and 2-4 were applied, when the composite separator uses inorganic particles A of the same material, the relative size of inorganic particles A and non-adhesive organic particles C affects the magnitude of the peeling force between the composite separator and the positive electrode sheet, and the D of inorganic particles A 50 and non-adhesive organic particles C D 50As the ratio to increases, the amount of small-sized particles in inorganic particles A increases, and these small-sized inorganic particles A are more easily filled into the gaps around the non-adhesive organic particles C. This improves the tightness of the porous active layer and is advantageous for firmly fixing the non-adhesive organic particles C to the porous active layer. Therefore, a stable connection is established between the composite separator and the positive electrode sheet, which is reflected in the increased peeling force measured in the composite consisting of the composite separator and the positive electrode sheet. Furthermore, as shown by comparing the peeling forces measured in samples 1-3, 2-5, and 2-6, there is a distinction in the magnitude of the peeling force between the composite separator and the positive electrode sheet even when inorganic particles A with different Mohs hardness are used.

[0070] Table 6 shows the test results for composite separator-positive electrode sheet composites and their corresponding peeling forces.

[0071] [Table 6]

[0072] [Example 4]

[0073] 1. Manufacturing of lithium-ion batteries

[0074] (1) Separator In this embodiment, the composite separator fabricated in Example 3 is used as the separator for manufacturing lithium-ion batteries.

[0075] (2) Preparation of the positive electrode sheet The method for producing positive electrode sheet A and the materials used are exactly the same as in Example 1.

[0076] (3) Fabrication of the negative electrode sheet The method for producing negative electrode sheet A and the materials used are exactly the same as in Example 1.

[0077] (4) Assembling the cell assembly The composite separator prepared in Example 3 was combined with the positive electrode sheet and negative electrode sheet prepared in this example. The combined composite separator, positive electrode sheet, and negative electrode sheet were then stacked in the following manner to create a cell assembly. After stacking the positive electrode sheet and negative electrode sheet in order, a heat press treatment was performed with a heat press temperature of 80°C, a heat press pressure of 1500 MPa, and a heat press time of 30 s to obtain the cell assembly.

[0078] (5) Electrolyte composition The electrolyte used in this example is exactly the same as the electrolyte formulated in Example 2.

[0079] (6) Assembly of lithium-ion batteries The cell assembly prepared as described above is placed in the inner chamber of the battery case and dried. Then, the electrolyte prepared in this embodiment is injected into the inner chamber of the battery case, and the lithium-ion battery of this embodiment is obtained through processes such as vacuum sealing, standing, chemical conversion, and capacity separation. The specific operating procedures for the assembly process are exactly the same as those for the lithium-ion battery of Example 2. The lithium-ion batteries prepared are numbered according to the composite separator used, and the correspondence between the lithium-ion batteries and the composite separators used is shown in Table 7.

[0080] 2. Performance testing of lithium-ion batteries

[0081] [Target Testers] The lithium-ion battery fabricated in this example was used as the test subject.

[0082] [Test items and corresponding methods] (1) The cycle performance test is the same as the test method and test conditions used for the cycle performance test of the lithium-ion battery in Example 2. (2) The DCR test is the same as the test method and test conditions used for the DCR test of the lithium-ion battery in Example 2.

[0083] Test Results: The test results are shown in Table 7. Combining the test results from Example 3, the D of inorganic particle A is 50 and non-adhesive organic particles C D 50 As the ratio increases, the degree of stiffness of the connection between the composite separator and the electrode sheet after crimping increases, and the structural stability of the cell increases. As can be seen by comparing the test results of batteries 1-3, 2-1, and 2-3 in the test subjects of this embodiment, the ratio of inorganic particles A and non-adhesive organic particles C applied to the battery is D 50 As the ratio increases, the cycle capacity retention rate measured in the battery increases. This is because improving the structural stability of the battery by increasing the degree of densification of the porous active layer of the composite separator contributes to an improvement in the battery's cycle performance to some extent. Therefore, within a certain range, as the stability of the connection between the composite separator and the positive and negative electrode sheets improves, the structural stability of the battery improves, and the battery's cycle performance improves. However, as the degree of densification of the porous active layer continues to increase, the permeability of the composite separator deteriorates, which is unfavorable for the penetration of the electrolyte into the composite separator and inhibits lithium ion transport. Therefore, as can be seen from the test results of batteries 1-3, 2-2, and 2-4, the ratio of inorganic particles A and non-adhesive organic particles C applied to the battery is 50 As the ratio to the battery increased, the DCR value measured in the battery showed a clear upward trend. However, with increasing cycle counts, the battery's DCR effect accumulated, worsening lithium ion transport and conversely impairing the battery's cycle performance. Furthermore, as can be seen from the test results of batteries 1-3, 2-5, and 2-6, when the particle size distribution for constructing the porous active layer of the composite separator is the same, the overall performance of the battery corresponding to the composite separator made using inorganic particles A with a Mohs hardness of 3 is optimal.

[0084] Table 7 shows the lithium-ion battery and its corresponding cell assembly fabricated in this embodiment, as well as the results of performance tests.

[0085] [Table 7]

[0086] [Example 5]

[0087] 1. Fabrication of composite separators This embodiment prepares a composite separator by referring to the method for preparing the composite separator in the experimental group of Example 1. Similar to the composite separators of the experimental group prepared in Example 1, the composite separator prepared in this embodiment includes a porous substrate and a porous active layer coated on the surface of the porous substrate. The main components of the coating slurry for preparing the porous active layer include inorganic particles A, adhesive polymer B, and non-adhesive organic particles C. In this embodiment, the inorganic particles A and adhesive polymer B used to formulate the coating slurry are the same materials used to prepare composite separators 1-3 in Example 1, namely, boehmite (Mohs hardness 3, D 10 =0.1μm, D 50 =0.4μm, D 90In this example, inorganic particles (1.1 μm) are used as inorganic particles A, and polyvinyl acetate is used as adhesive polymer B. Unlike the preparation of composite separators 1-3 prepared in Example 1, different types of non-adhesive organic particles C are used to combine the inorganic particles A and adhesive polymer B to prepare different coating slurries. Table 8 shows the composite separators and the non-adhesive organic particles C contained therein that were prepared using different coating slurries. In this example, the coating slurry used to prepare the composite separator is prepared by weighing the necessary materials in parts by mass, specifically weighing 80 parts boehmite, 10 parts polyvinyl acetate, 10 parts non-adhesive organic particles C, 5 parts leveling agent, and 120 parts pure water, mixing the materials, and stirring thoroughly until homogeneous. In the raw materials used to prepare the above coating slurry, all materials other than non-adhesive organic particles C are strictly the same as the materials used to prepare composite separators 1-3 in Example 1. The film substrate used as the porous substrate in this embodiment is the same polyethylene film used in the production of composite separators 1-3 in Example 1. The coating slurry prepared above is applied to both sides of the porous substrate, controlling the coating thickness based on a predetermined porous active layer thickness, to obtain a separator semi-finished product. The composite separator is produced by transferring the separator semi-finished product to an oven and drying it thoroughly, thereby forming a porous active layer on both back-to-back sides of the porous substrate. The porous coating layer includes a base coating layer and non-adhesive organic particles C embedded in the base coating layer. The base coating layer is composed of inorganic particles A and adhesive polymer B, and the non-adhesive organic particles C protrude from the surface of the base coating layer. The composite separators produced in this embodiment are numbered composite separator 3-1, composite separator 3-2, and composite separator 3-3, respectively. The compositional and structural characteristics of the above composite separators are shown in Table 8. For convenience of comparison, Table 8 also shows the compositional and structural characteristics corresponding to composite separators 1-3 in Example 1. Table 8 shows "D 50 / h" is the D of non-adhesive organic particles C used in the composite separator. 50 This refers to the ratio of h to the average thickness of the base coating layer of the composite separator.

[0088] Table 8 shows information on the composition and structure of the composite separator.

[0089] [Table 8]

[0090] 2. Test subjects for peeling force test of composite separator and electrode sheet The composite separator fabricated in this embodiment was used as the test subject.

[0091] [Test Method] (1) Preparation of test positive electrode sheet A The method for producing positive electrode sheet A and the materials used are exactly the same as in Example 1.

[0092] (2) Fabrication of composite separator-positive electrode sheet composite for peeling force testing The composite separator and cathode sheet A manufactured in this embodiment are prepared by referring to the method for manufacturing the composite separator-cathode sheet composite in Example 1, and the materials and methods used to manufacture the composite separator-cathode sheet composite in this embodiment are exactly the same as those used in Example 1, except that the composite separator and cathode sheet used are combined according to this embodiment. The composite separator-cathode sheet composites manufactured in this embodiment are numbered 3-1, 3-2, and 3-3, respectively, and the corresponding numbers and the composite separators and cathode sheets included in them are specifically shown in Table 9. The edges of the composite separator-positive electrode sheet composite are cut to a size of 10 mm x 150 mm. The composite separator and positive electrode sheet are lightly separated at the edges of the composite separator-positive electrode sheet composite, and each is clamped at both ends of a peel force testing machine. The machine is started, the composite separator and positive electrode sheet are peeled apart, and the peel strength at the time of peeling is recorded.

[0093] [Test Results] The test results are shown in Table 9. For convenience of comparison, Table 9 also shows the measured adhesive performance of prototype 1-3, which was prepared using composite separator 1-3 in Example 1. The difference between composite separator 1-3, composite separator 3-1, composite separator 3-2, and composite separator 3-3 lies in the fact that the composite separators are prepared using non-adhesive organic particles C with different Tg values. According to the peel force test results of this example, all of the above composite separators can form a structurally stable composite with the positive electrode sheet. In the test subjects of this example, prototype 1-3, which includes composite separator 1-3, and prototype 3-1, which includes composite separator 3-1, showed higher measured peel forces, indicating that a more reliable connection can be established between the composite separator and the positive electrode sheet using non-adhesive organic particles C with a Tg value of 30-90°C.

[0094] Table 9 shows the results of peel force tests for composite separator-cathode sheet composites and their corresponding components.

[0095] [Table 9]

[0096] [Example 6]

[0097] 1. Manufacturing of lithium-ion batteries (1) Separator In this embodiment, the composite separator fabricated in Example 5 is used as the separator for manufacturing the lithium-ion battery.

[0098] (2) Preparation of the positive electrode sheet The method for producing positive electrode sheet A and the materials used are exactly the same as in Example 1.

[0099] (3) Fabrication of the negative electrode sheet The method for producing negative electrode sheet A and the materials used are exactly the same as in Example 1.

[0100] (4) Assembly of the cell assembly The composite separator prepared in Example 5 is combined with the positive electrode sheet and negative electrode sheet prepared in this example, and the combined composite separator, positive electrode sheet, and negative electrode sheet are used to manufacture a cell assembly as described below. The positive electrode sheet, composite separator, and negative electrode sheet are stacked in order, and then a hot press is performed at a hot press temperature of 80°C, a hot press pressure of 1500 MPa, and a hot press time of 30 s to obtain the cell assembly.

[0101] (5) Electrolyte composition The electrolyte used in this example is exactly the same as the electrolyte prepared in Example 2.

[0102] (6) Assembly of lithium-ion batteries The cell assembly prepared as described above is placed in the inner chamber of the battery case and dried. Then, the electrolyte prepared in this embodiment is injected into the inner chamber of the battery case, and the lithium-ion battery of this embodiment is obtained through processes such as vacuum sealing, standing, chemical conversion, and capacity separation. The specific operating procedures for the assembly process are exactly the same as those for the lithium-ion battery assembly of Example 2. The lithium-ion batteries prepared are numbered according to the composite separator used, and the correspondence between the lithium-ion batteries and the composite separators used is shown in Table 10.

[0103] 2. Performance testing of lithium-ion batteries

[0104] [Target Testers] The lithium-ion battery fabricated in this example was used as the test subject.

[0105] [Test items and corresponding methods] (1) The cycle performance test is the same as the test method and test conditions used for the cycle performance test of the lithium-ion battery in Example 2. (2) The DCR test is the same as the test method and test conditions used for the DCR test of the lithium-ion battery in Example 2.

[0106] [Test Results] The test results are shown in Table 10. Statistical analysis of the measurement results in this embodiment revealed that batteries 1-3, 3-1, 3-2, and 3-3 all achieved high cycle capacity retention rates, and their corresponding DCRs were all at low levels. This indicates that these batteries all possess good cycle characteristics and lithium-ion transfer dynamics performance.

[0107] Table 10 shows the lithium-ion batteries fabricated in this embodiment, their corresponding cell assemblies, and the performance test results.

[0108] [Table 10]

Claims

1. A composite separator, It comprises a porous substrate and a porous active layer, The porous active layer is provided on at least one surface of the porous substrate, and the porous active layer comprises a base coating layer and non-adhesive organic particles C embedded in the base coating layer, the base coating layer comprises inorganic particles A and adhesive polymer B, and the base coating layer is bonded to the porous substrate by the adhesive polymer B. If the average thickness of the base coating layer is h, then h ≥ 0.5 μm. The mass of the non-adhesive organic particles C : the mass of the base coating layer = (2 to 20) : (70 to 90), The particle size distribution of the non-adhesive organic particles C satisfies (a) and (b), where (a) is 1 < D ５０ / h ≤ 5, and (b) is (D ９０ -D １０ ) / D ５０ ≤ 3, Composite separator.

2. The average thickness h of the base coating layer satisfies 1 μm ≤ h < 8 μm. The composite separator according to claim 1.

3. The particle size distribution of the non-adhesive organic particles C is D ５０ = satisfies the requirements of 3 to 8 μm, The composite separator according to claim 2.

4. D of the inorganic particle A ５０ : Non-adhesive organic particles C of D ５０ = (0.05 to 0.4): 1 The composite separator according to claim 1.

5. D of the inorganic particle A ５０ The average thickness h of the base coating layer is 1 (1 to 15), and the Mohs hardness of the inorganic particles A is 2 to 10. The composite separator according to claim 4.

6. The particle size distribution of the inorganic particle A satisfies ([D ９０ - D １０ ) / D ５０ = 0.5 to 2. The composite separator according to claim 5.

7. The non-adhesive organic particles C include an acrylate-based polymer, and the glass transition temperature of the acrylate-based polymer is 30°C to 90°C. A composite separator according to any one of claims 1 to 6.

8. In the porous active layer, the ratio of parts by mass of inorganic particles A:adhesive polymer B:non-adhesive organic particles C is (70-90):(2-15):(2-20). The composite separator according to claim 7.

9. A cell comprising an electrode sheet and a composite separator according to any one of claims 1 to 8, Lithium-ion battery.

10. In the cell, the composite separator is provided at a distance from the electrode sheet, the porous active layer is provided on the surface of the composite separator facing the electrode sheet, the composite separator is connected to the electrode sheet by the non-adhesive organic particles C contained in the porous active layer, a gap is formed between the electrode sheet and the base coating layer provided facing it after hot pressing, and the average width d of the gap after hot pressing is 0.05 to 3 μm. The lithium-ion battery according to claim 9.

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