Diaphragm and battery comprising same

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a diaphragm and a battery comprising the diaphragm. The invention provides a diaphragm. The diaphragm comprises a substrate and a gluing layer arranged on at least one side surface of the substrate, the gluing layer comprises a plurality of glue points, each glue point comprises polymer particles and a plurality of blank areas, the polymer particles cover the substrate, and the blank areas do not cover the substrate; according to the maximum perimeter of a closed curve formed by the polymer particles in a single glue point, the circle area equivalent to the maximum perimeter is obtained and recorded as A2 mm < 2 >, the area of a blank area in the single glue point is recorded as A1 mm < 2 >, and A1 / A2 is larger than or equal to 15% and smaller than or equal to 50%; the difference value between the maximum height of the glue point and the minimum height of the glue point is recorded as H [mu] m, and H is greater than or equal to 1 and less than or equal to 4.9. According to the diaphragm provided by the invention, the battery has relatively good circulation and storage performance, and the self-discharge and internal short circuit of the battery are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and particularly relates to a separator and a battery comprising the same. BACKGROUND

[0002] In order to improve the energy density of lithium ion secondary batteries, the design of the battery tends to increase the compaction density of the pole piece and the amount of silicon doping. However, high compaction density will cause the pole piece assembly to be insufficiently infiltrated by electrolyte, and in addition, the silicon-based particles in the negative electrode will produce huge volume expansion during the charging and discharging process of the battery, causing the electrolyte to be squeezed out from between the positive and negative pole pieces. Both of the above factors will cause the overall battery to be short of liquid, affecting the transmission of lithium ions, resulting in problems such as cycle decay, poor performance, and interface black spots in the battery. SUMMARY

[0003] Therefore, the technical problem to be solved by the present application is to overcome the defects of insufficient liquid retention capacity of the pole piece assembly and large expansion stress of the silicon-based particles in the existing battery, resulting in poor cycle performance, poor storage performance, and large safety risk of the battery, so as to provide a separator and a battery comprising the same.

[0004] In a first aspect, the present application provides a separator, comprising a substrate and a glue coating layer arranged on at least one side surface of the substrate; the glue coating layer comprises a plurality of glue points, each of the glue points comprises polymer particles and a plurality of blank areas, the polymer particles cover the substrate, and the blank areas do not cover the substrate; according to the maximum perimeter of a closed curve formed by the polymer particles in a single glue point, a circular area equivalent to the maximum perimeter is obtained, denoted as A2 mm 2 , the area of the blank area in a single glue point is denoted as A1 mm 2 , and satisfies 15%≤A1 / A2≤50%; the difference between the maximum height of the glue point and the minimum height of the glue point is denoted as H μm, and satisfies 1≤H≤4.9.

[0005] As an optional implementation, the coating amount of the glue coating layer on one side surface of the substrate is 0.05 g / m 2 -5 g / m 2 .

[0006] As an optional implementation, the ratio of the area of the polymer particles in the glue coating layer to the area of one side surface of the substrate is 10%-25%.

[0007] As an optional implementation, the average diameter of the glue points is 50 μm-500 μm.

[0008] As an optional implementation, the height difference between the maximum value of the height of the glue points and the substrate is denoted as L μm, and satisfies 3≤L≤5.

[0009] As an optional implementation, the base film includes at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide, and a surface tension of the base film is F1 mN / m when a test liquid is tested, the test liquid is composed of 90% acrylate-styrene copolymer, 2% alkyl polyoxyethylene ether, 0.1% sodium carboxymethyl cellulose, and 7.9% butyl benzene latex by mass fraction, a platinum-gold plate is immersed in the test liquid, and a surface tension of the test liquid is F2 mN / m when the test is performed, and F1 is less than F2.

[0010] As an optional implementation, 5≤F2-F1≤20.

[0011] As an optional implementation, a coating amount of the adhesive layer on one side surface of the base film is 0.2g / m 2 -0.8g / m 2 .

[0012] As an optional implementation, an average diameter of the adhesive dots is 100μm-400μm.

[0013] As an optional implementation, a particle size of the polymer particles is 0.1μm-8μm.

[0014] As an optional implementation, a component of the polymer particles includes at least one of acrylate-based polymer, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, vinyl fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene acrylic acid copolymer, polyethylene, and polypropylene.

[0015] As an optional implementation, the adhesive layer includes a first additive, and the first additive includes at least one of polyvinylpyrrolidone, sodium linear alkyl benzene sulfonate, alkyl polyoxyethylene ether, sodium dodecyl sulfate, sodium 2-naphthalene sulfonate formaldehyde condensate, sodium methylene bisnaphthalene sulfonate, and alkyl sulfonate.

[0016] As an optional implementation, the adhesive layer includes a thickening agent, and the thickening agent includes at least one of sodium carboxymethyl cellulose, polyethylene oxide, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, gelatin, and sodium alginate.

[0017] As an optional embodiment, the adhesive layer includes an adhesive, which includes at least one of styrene-butadiene latex, styrene acrylic acid, polyacrylamide, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, modified paraffin resin, carbomer resin, polyacrylic acid or its derivatives, polyurethane acrylate, copolymer emulsion containing polyacrylate, polyurethane, and urethane.

[0018] As an optional implementation, the polymer particles in the coating layer have a mass content of 70%-95%.

[0019] As an optional implementation, the mass content of the first additive in the adhesive layer is 1.5%-10%.

[0020] As an optional implementation, the thickener content in the adhesive layer is 0.1%-20% by mass.

[0021] As an optional implementation, the adhesive content in the coating layer is 0.5%-25% by mass.

[0022] As an optional implementation, the mass content of the first additive in the adhesive layer is C%, and the mass content of the thickener in the adhesive layer is B, wherein C and B satisfy the following relationship: 4≤C / B≤50.

[0023] As an optional implementation, the first additive is alkyl polyoxyethylene ether, the thickener is sodium carboxymethyl cellulose, and the mass content C% of alkyl polyoxyethylene ether in the coating layer and the mass content B% of sodium carboxymethyl cellulose in the coating layer satisfy the following relationship: 4≤C / B≤20.

[0024] As an optional implementation, the mass content of the first additive in the adhesive layer is 2%-5%.

[0025] As an optional implementation, the polymer particles in the coating layer have a mass content of 70%-90%.

[0026] As an optional implementation, the thickener content in the adhesive layer is 0.1%-4.5% by mass.

[0027] As an optional implementation, the substrate further includes a heat-resistant layer disposed on at least one surface of the base film.

[0028] As an optional implementation, the surface tension of the heat-resistant layer was measured to be F3mN / m in the test liquid, which satisfies that F3 is less than F2.

[0029] As an optional implementation, 5 ≤ F2 - F3 ≤ 20.

[0030] As an optional implementation, the thickness of the heat-resistant layer on one side of the base film is 0.5 μm-5 μm.

[0031] As an optional implementation, the thickness of the substrate is 5μm-100μm.

[0032] In a second aspect, this application provides a battery, including a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, the separator including the separator described in the first aspect; As an optional implementation, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer comprising silicon-based particles; when the battery is under a charging limiting voltage state, the volume expansion force of the silicon-based particles is F4 N, the adhesive force between the adhesive dots and the negative electrode sheet is F5 N, and F5 and F4 satisfy: F5 / F4≥1; where F4=0.002(d1). 4 d1 is the particle size of the silicon-based particles, in μm; F5 = 0.01(d2 / 2) 2 ×(1-A1 / A2), where d2 is the diameter of the adhesive dot in μm.

[0033] As an optional implementation, 5 ≤ d1 ≤ 12.

[0034] As an alternative implementation, 5 ≤ F5 / F4 ≤ 25.

[0035] As an optional implementation, 50≤d2≤600.

[0036] As an optional implementation, the silicon content is 3%-15% based on the mass of the negative electrode active layer.

[0037] As an alternative implementation, 3 ≤ F4 ≤ 41.472.

[0038] As an optional implementation, the bonding strength F6 between the diaphragm and the negative electrode sheet is 3N / m-20N / m.

[0039] As an optional implementation, the bonding strength F7 between the diaphragm and the positive electrode sheet is 3N / m-20N / m.

[0040] The technical solution of this application has the following advantages: This application provides a diaphragm, including a substrate and an adhesive layer disposed on at least one surface of the substrate; the adhesive layer includes a plurality of adhesive dots, each adhesive dot including polymer particles and a plurality of blank areas, the polymer particles covering the substrate, and the blank areas not covering the substrate; based on the maximum perimeter of the closed curve formed by the polymer particles in a single adhesive dot, a circular area equivalent to the maximum perimeter is obtained, denoted as A² mm. 2 The area of ​​the blank region in a single adhesive dot is denoted as A1 mm. 2 The following conditions must be met: 15% ≤ A1 / A2 ≤ 50%; the difference between the maximum height and the minimum height of the adhesive dots is denoted as H μm, satisfying 1 ≤ H ≤ 4.9. Thus, the separator and the electrode have good adhesion, which can restrain the volume expansion of silicon-based particles during cycling, maintain the stability of the electrode structure, alleviate the extrusion pressure on the separator, and thus improve the battery's cycle and storage performance (thickness expansion), reducing the battery's self-discharge and short-circuit rate. Simultaneously, the separator also has good ion permeability, which can increase the electrolyte wetting amount, thereby facilitating lithium ion transport, improving the uniformity of current distribution, preventing the separator from being punctured, and thus improving the battery's cycle performance and reducing self-discharge and short-circuit phenomena. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 This is a scanning electron microscope schematic diagram of a single adhesive dot in the adhesive layer of this application; Figure 2 This is a scanning electron microscope schematic diagram of several adhesive dots in the adhesive layer of this application. Detailed Implementation

[0043] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0044] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0045] Existing technologies enhance the adhesion between the separator and the electrode by applying an adhesive layer to the battery separator. Furthermore, by optimizing the agglomeration force and particle size of the polymer particles in the adhesive layer and increasing the thickness of the adhesive layer, a buffer space is provided for the volume expansion of the silicon-based particles, thus alleviating stress concentration. Currently, the common coating method for the adhesive layer is dot coating. Dot coating produces equidistant and uniform adhesive dots, resulting in good coating uniformity and meeting adhesion requirements. However, dot coating fills the adhesive dots with binder. On the one hand, the binder filling the dots is not conducive to suppressing the volume change of silicon-based particles, and the phenomenon of the separator being squeezed and punctured cannot be effectively alleviated. On the other hand, the areas on the separator covered with binder may also block the pores, affecting the separator's ion permeability and electrolyte retention capacity. Especially after hot pressing and silicon-based particle expansion, the ion permeability of the separator becomes even worse, and the electrolyte retention capacity also decreases significantly. Different ion permeability will cause uneven current distribution, and areas with high current density will overcharge and discharge, making these areas more vulnerable. When subjected to the expansion and compression of silicon-based particles, they are easily punctured by the sharp parts on the surface of the silicon-based particles, causing self-discharge and short circuits. At the same time, insufficient electrolyte retention capacity will seriously affect the lithium-ion transport rate, leading to problems such as battery cycle degradation and interface black spots.

[0046] In order to address the problems of poor ion permeability, insufficient liquid retention capacity, and limited suppression of volume changes of silicon-based particles in the diaphragms of related technologies, this application provides the following technical solution.

[0047] In a first aspect, this application provides a diaphragm, comprising a substrate and an adhesive layer disposed on at least one surface of the substrate; the adhesive layer comprises a plurality of adhesive dots, each adhesive dot comprising polymer particles and a plurality of blank areas, the polymer particles covering the substrate, and the blank areas not covering the substrate; based on the maximum perimeter of the closed curve formed by the polymer particles in a single adhesive dot, a circular area equivalent to the maximum perimeter is obtained, denoted as A² mm. 2 The area of ​​the blank region in a single adhesive dot is denoted as A1 mm. 2 The difference between the maximum height of the adhesive dot and the minimum height of the adhesive dot is denoted as H μm, and the difference between the maximum height of the adhesive dot and the minimum height of the adhesive dot is 1≤H≤4.9.

[0048] This application employs a dot coating method, where adhesive is applied to a substrate and dried to form several adhesive dots. During the drying process, due to surface tension, the adhesive in some areas diffuses outward or contracts inward, creating polymer protrusions of varying heights and blank areas that do not cover the substrate. Therefore, relative to the substrate, the highest point of the polymer protrusion is the maximum height of the adhesive dot, and the lowest point is the minimum height. It is understood that the minimum height of the adhesive dot is at least equal to the minimum particle size of a single polymer particle. Within a single adhesive dot, the polymer particles at the outermost edge of the dot are closely arranged, forming a continuous, closed curve. The area of ​​the circle equivalent to the circumference of this closed curve is denoted as A² mm. 2 The area of ​​the blank region in a single glue dot is denoted as A1 mm. 2 When the ratio of 15% ≤ A1 / A2 ≤ 50% is met, on the one hand, sufficient contact area between the adhesive dots and the electrode sheet is ensured, thus guaranteeing good adhesion. This restricts the volume expansion of silicon-based particles during cycling, helps maintain the stability of the electrode structure, alleviates the extrusion pressure on the separator, and improves the battery's cycle and storage performance, reducing self-discharge and short-circuit rates. On the other hand, the presence of appropriately sized blank areas increases the overall ion permeability of the separator and improves the electrolyte wetting amount, thereby facilitating lithium ion transport, improving the uniformity of current distribution, preventing separator puncture, and further improving battery cycle performance, reducing self-discharge and short-circuit phenomena. Simultaneously, this application controls the difference H between the maximum and minimum height of a single adhesive dot to be within the range of 1 μm-4.9 μm. This allows the separator to balance good adhesion, ion transport capacity, and electrolyte retention capacity, further improving battery cycle and safety performance.

[0049] This study found that if A1 / A2 is greater than 50% or H is greater than 4.9 μm, it indicates that the area of ​​the blank region in a single adhesive dot is too high, or the height distribution of a single adhesive dot varies too much. This will lead to poor adhesion between the separator and the electrode, making the battery prone to interface black spots. At the same time, it cannot effectively suppress the volume expansion of silicon-based particles, resulting in deterioration of the battery's cycle and storage performance, increased battery self-discharge, and a higher likelihood of internal short circuits. Conversely, if A1 / A2 is less than 15% or H is less than 1 μm, it means that the area of ​​the blank region in a single adhesive dot is too small, or the height distribution of a single adhesive dot tends to be uniform. This is not conducive to improving the overall ion permeability of the separator and its ability to retain electrolyte, thus hindering ion transport in the separator, resulting in uneven current distribution, failing to effectively improve the battery's cycle performance, and thus affecting the battery's storage performance. Furthermore, uneven current distribution will also make the separator unable to resist the volume expansion of silicon-based particles, making the separator easily punctured by the sharp parts of silicon-based particles, triggering battery self-discharge and internal short circuits.

[0050] It should be noted that, in this application, the testing method for H includes: obtaining a cross-section along the thickness direction of the diaphragm, taking a photograph of this cross-section using a scanning electron microscope (SEM) (5000x magnification), randomly selecting at least 50 adhesive dots from the obtained SEM image, and measuring the difference between the highest point and the lowest point of the polymer protrusion at each adhesive dot, which is H, in μm; when the H value of all tested adhesive dots satisfies 1μm-4.9μm, it can be considered that the H value of all adhesive dots on the diaphragm satisfies the aforementioned condition. For example, the difference H (in μm) between the maximum height and the minimum height of the adhesive dot can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 4.9, or a value within any two of the above values.

[0051] The area ratio A1 / A2 of the blank area can be obtained by the following test method: Take a photograph of the diaphragm surface using a scanning electron microscope (5000x magnification). Randomly select a glue point from the obtained SEM image. Use image processing software (ImageJ) to measure the perimeter of the closed curve formed by the polymer particles at the outermost edge of the glue point. Calculate the area of ​​the circle equivalent to this perimeter, which is A2, in mm. 2 Next, the coverage area A1' of the polymer particles in the adhesive dots on the membrane substrate was measured using image processing software (Image J), ​​in mm. 2 Then, the area of ​​the blank region in the adhesive dots, A1 = A2 - A1'; finally, the value of A1 / A2 is calculated. At least 50 adhesive dots are repeatedly selected. When the A1 / A2 of all tested adhesive dots satisfies 15%-50%, it can be considered that the A1 / A2 of all adhesive dots on the diaphragm satisfies the aforementioned condition. For example, the area ratio A1 / A2 of the blank region can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc., or a value within any two of the above ranges.

[0052] According to the definition of a convex closed curve, "if the tangent at any point on a planar closed curve lies entirely on the same side, then the curve is called a convex closed curve." In some embodiments, the closed curve can be a non-convex closed curve. In this case, compared to a convex closed curve with the same perimeter, the non-convex closed curve has a concave region, such as... Figure 1 As shown in the black box, these concave areas also belong to the blank areas described in this application.

[0053] As an optional implementation, the amount of adhesive coating applied to one side surface of the substrate is 0.05 g / m². 2 -5g / m 2 In particular, it meets the requirement of 0.2g / m 2 -0.8g / m2 Within this range, it can further improve the bonding strength between the separator and the electrode, the overall ion permeability of the separator, and the electrolyte retention capacity. If the coating amount on one side surface of the substrate is greater than 5 g / m 2 If the membrane pores are partially blocked, ion transport is hindered, resulting in uneven current distribution and affecting battery cycling, self-discharge, and internal short circuits; if the coating amount of the adhesive layer on one side surface of the substrate is less than 0.05 g / m 2 This means that there are fewer polymer particles, the adhesion between the separator and the electrode is weaker, and the two are easily separated, resulting in black spots at the interface. At the same time, the ability to suppress the volume expansion of silicon-based particles is weaker, which affects the cycle and storage performance of the battery, and the ion transport path is longer.

[0054] The method for testing the amount of adhesive coating on one side surface of the substrate is to use methods known in the art. For example, a 1m × 0.5m area of ​​the adhesive coating is selected to test the areal density 1, and then a 1m × 0.5m area is selected on the substrate without the adhesive coating to test the areal density 2. That is, the amount of adhesive coating on one side surface of the substrate = areal density 1 - areal density 2; for example, the amount of adhesive coating on one side surface of the substrate (unit: g / m²) is... 2 The ) can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1, 1.5, 2, 3, 3.5, 4, 4.5, 5, etc., or a value within the range of any two of the above values.

[0055] As an optional implementation, the ratio of the area of ​​polymer particles in the coating layer to the area of ​​one side surface of the substrate is 10%-25%. Controlling the area ratio of polymer particles on the surface of the substrate can improve the adhesion between the separator and the electrode, and provide a suitable blank area ratio to improve the electrolyte retention capacity of the separator, alleviate the volume expansion of silicon-based particles, and benefit the battery's cycle performance, reducing self-discharge and internal short circuits. If it is greater than 25%, the blank area ratio is small, the overall ion permeability of the separator and the electrolyte retention capacity of the separator are poor, affecting ion transport performance, and the ability to suppress the volume expansion of silicon-based particles is weak. The separator may be punctured, which is detrimental to the battery's cycle performance, and worsens self-discharge and internal short circuits. If it is less than 10%, there are fewer polymer particles, the contact area between the separator and the electrode is smaller, the adhesion is poor, and the stability of the electrode structure is poor, thus affecting the battery's storage and cycle performance. For example, the ratio of the area of ​​the polymer particles in the coating layer to the area of ​​one side surface of the substrate can be 10%, 12%, 15%, 18%, 20%, 23%, 25%, or a value within the range of any two of the above values.

[0056] The ratio of the area of ​​polymer particles in the coating layer to the area of ​​one side surface of the substrate is obtained by a method known in the art. For example, a 1m × 0.5m area in the coating layer is selected, and the area of ​​polymer particles in this area is measured using a Keyence 7000, and then calculated.

[0057] As an optional implementation, the average diameter of the adhesive dots is 50μm-500μm, particularly within the range of 100μm-400μm. This increases the contact area between the separator and the electrode, improving adhesion and thus suppressing the expansion of silicon-based particles. It also reduces interfacial impedance, which is beneficial to the battery's cycle performance. If the average diameter of the adhesive dots is greater than 500μm, it means increased interfacial impedance, which is detrimental to the battery's cycle performance. Simultaneously, the overall ion permeability of the separator and its electrolyte retention capacity are poor, affecting ion transport performance and potentially leading to self-discharge and internal short circuits. If the average diameter of the adhesive dots is less than 50μm, the effective bonding contact area with the electrode is smaller, resulting in weaker suppression of silicon-based particle expansion, which is detrimental to the battery's cycle and storage performance, and worsens self-discharge and internal short circuits. The average diameter of the adhesive dots is determined using methods known in the art. For example, use a scanning electron microscope (SEM) to take 300x images, select 3-5 glue dots to measure their diameter, take ten images, and the average value is the average diameter of the glue dots; for example, the average diameter of the glue dots can be 50μm, 100μm, 200μm, 300μm, 400μm, 500μm, etc., or a value within any two of the above values.

[0058] As an optional implementation, the height difference between the maximum height of the adhesive dots and the substrate is denoted as L μm, satisfying 3≤L≤5. This can further improve the adhesion between the separator and the electrode, suppress the expansion of silicon-based particles, and enhance the ion transport performance of the separator, which is beneficial to the battery's cycle and storage performance, and improves the battery's self-discharge and internal short circuit. The height of the substrate is tested using methods known in the art. For example, if the separator with an adhesive layer on one side of the substrate is folded into 8 layers and the thickness L1 is measured, then the thickness of the separator L1' = L1 / 8. If the substrate is then folded into 8 layers and the thickness L2 is measured, then the thickness of the substrate L2' = L2 / 8, i.e., L = L1' - L2'. For example, L (unit μm) can be 3, 3.2, 3.5, 3.7, 4, 4.2, 4.5, 4.8, 5, etc., or a value within the range of any two of the above values.

[0059] As an optional implementation, the substrate includes a base film, the material of which includes at least one selected from polyethylene, polypropylene, polyethylene terephthalate, and polyimide. The adhesive layer is formed by drying an adhesive solution. Testing is performed under a test solution, and the surface tension of the base film is measured to be F1 mN / m. A platinum plate is immersed in the test solution, and the surface tension of the test solution is measured and recorded as F2 mN / m, satisfying that F1 is less than F2. Thus, by controlling the difference in surface tension between the base film and the adhesive solution, the dotted adhesive solution is caused to shrink or expand, and the adhesive solution aggregates, thereby increasing the height of the adhesive dots. This enhances the adhesion strength between the separator and the electrode, and also provides the separator with space to mitigate expansion, which is beneficial for the battery's cycle and storage performance.

[0060] The surface tension of the base film is tested using methods known in the art. For example, it is measured using the contact angle test method. The test steps include: adjusting the sample stage to be level, placing the base film to be tested on the sample stage, and using a microsyringe to drop a small drop of adhesive (about 2-5 μL) onto the base film; taking an image of the droplet with a camera, and analyzing its profile with a contact angle tester; calculating the contact angle θ using methods such as the tangent method and ellipse fitting method; and then using the formula in the contact angle tester to calculate the surface tension of the solid.

[0061] The surface tension of the adhesive solution was tested using methods known in the art. For example, the suspended plate method was used, with the following steps: Turning on the surface tension tester, calibrating the instrument, cleaning and installing the platinum plate on the instrument's hook, and zeroing the instrument; placing the sample dish containing the slurry stably on the lifting sample stage, and slowly raising the stage using the control software to immerse the platinum plate in the liquid; once the platinum plate is immersed, the surface tension of the liquid pulls it downwards. The sensor inside the instrument monitors this force and balances it with the opposing force. After the system stabilizes, the stable surface tension value displayed on the software interface is read or recorded. The instrument is cleaned after the test.

[0062] It should be noted that the test solution for testing the surface tension of the base film described in this application consists of the following components: by mass, 90% acrylate-styrene copolymer, 2% alkyl polyoxyethylene ether, 0.1% sodium carboxymethyl cellulose and 7.9% styrene-butadiene latex.

[0063] As an optional implementation, the difference between the surface tension of the adhesive and the surface tension of the base film is adjusted to satisfy: 5 ≤ F2 - F1 ≤ 20. This allows for further adjustment of the adhesive dot height, thereby improving the adhesion performance of the separator and ensuring the separator has both good ion transport performance and electrolyte retention capacity, which is beneficial for battery cycle and storage performance, and improves self-discharge and internal short circuit. If F2 - F1 < 5, the difference is too small, resulting in insufficient shrinkage or expansion of the adhesive, leading to a lower adhesive dot height. This cannot completely alleviate the expansion of silicon-based particles, which may puncture the separator. Furthermore, the electrolyte retention capacity is weak, affecting the uniformity of current distribution. This is detrimental to battery cycling, self-discharge, and internal short circuits. If F2-F1 > 20, the difference is too large, resulting in a high maximum height of the adhesive dots. Other protrusions in the adhesive dots that are far from the maximum height of the adhesive dots have poor adhesion to the electrode sheets, leading to poor adhesion and poor stability of the electrode structure. This affects the battery's cycling and storage performance and causes interface black spots. For example, the difference between the surface tension of the adhesive and the surface tension of the base film, F2-F1 (unit: mN / m), can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a value within any two of the above ranges.

[0064] As an optional implementation, the polymer particles have a particle size of 0.1 μm-8 μm. This results in a more uniform thickness of the adhesive layer, increasing the contact area between the separator and the electrode, thereby improving adhesion and enhancing the battery's cycle and storage performance, as well as reducing self-discharge and internal short circuits. If the polymer particle size is greater than 8 μm, the maximum height of the adhesive dots is higher, affecting adhesion, and the ion transport path is longer, which is detrimental to the battery's cycle and storage performance, potentially leading to self-discharge and internal short circuits. If the polymer particle size is less than 0.1 μm, it means the polymer particles are too small and prone to aggregation. Simultaneously, the adhesive dot height is low, resulting in weaker ability to restrain the volume expansion of silicon-based particles and weaker electrolyte retention capacity, affecting the battery's cycle performance and potentially leading to self-discharge and internal short circuits. The particle size of the polymer particles is determined using methods known in the art. For example, the particle size can be measured using a laser particle size analyzer; for instance, the particle size (in μm) of the polymer particles can be 0.1, 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, etc., or a value within the range of any two of the above values.

[0065] As an optional embodiment, the polymer particles comprise at least one of the following: acrylate polymers, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, fluoroethylene-hexafluoropropylene copolymer, ethylene-acrylic acid copolymer, polyethylene, and polypropylene; wherein the acrylate polymers comprise at least one of the following: polymethyl methacrylate, ethylhexyl acrylate, butyl acrylate, acrylate-acrylonitrile copolymer, acrylate-ethylene copolymer, acrylate-styrene copolymer, acrylate-acrylonitrile-ethylene copolymer, styrene-acrylate-acrylonitrile copolymer, ethylhexyl acrylate-methyl methacrylate copolymer, butyl acrylate-methyl methacrylate copolymer, methyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-ethyl acrylate-2-(diethylamino)acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, and ethyl acrylate-2-(diethylamino)acrylate. The acrylate polymer also contains hard segments, which can be prepared using conventional methods in the art, such as copolymerization with hard monomers, crosslinking with crosslinking agents, and chemical modification. This application further improves the adhesive properties of the adhesive dots by limiting the types of polymer particles.

[0066] As an optional implementation, the adhesive layer includes a first additive, which includes at least one of polyvinylpyrrolidone, sodium linear alkylbenzene sulfonate, alkyl polyoxyethylene ether, sodium dodecyl sulfate, sodium 2-naphthalenesulfonate formaldehyde condensate, sodium methylene bisnaphthalenesulfonate, and alkyl sulfonate.

[0067] As an optional implementation, the coating layer includes a thickener, which includes at least one of sodium carboxymethyl cellulose, polyethylene oxide, polyethylene oxide, polyvinyl alcohol, methylcellulose, hydroxypropyl methylcellulose, hydroxyethyl cellulose, gelatin, and sodium alginate.

[0068] As an optional embodiment, the adhesive layer includes an adhesive, which includes at least one of styrene-butadiene latex, styrene acrylic acid, polyacrylamide, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, modified paraffin resin, carbomer resin, polyacrylic acid or its derivatives, polyurethane acrylate, a copolymer emulsion containing polyacrylate, polyurethane, and urethane. The hard and soft segments of the polyacrylate in the copolymer emulsion containing polyacrylate are not required; conventional selection methods in the art are acceptable.

[0069] As an optional implementation, the coating layer may further include a dispersant, which may be selected conventionally in the art and is not limited in this application.

[0070] As an optional implementation, the polymer particle content in the coating layer is 70%-95% by mass. Particularly within this range, the height of the adhesive dots can be further controlled, allowing the separator to achieve excellent adhesion, electrolyte retention capacity, and ion transport performance. This is beneficial for battery cycle and storage performance, mitigating self-discharge and internal short circuits. If the polymer particle content in the coating layer is greater than 95%, it means that other components in the coating layer are fewer, resulting in limited improvement effects from the first additive, thickener, and binder. If the polymer particle content in the coating layer is less than 70%, the adhesive dot height is lower, leading to weaker mitigation of silicon-based particle expansion, less electrolyte wetting, and poorer ion transport performance of the separator. The mass content of the polymer particles in the coating layer is determined using methods known in the art. For example, it can be measured using thermogravimetric-pyrolysis gas chromatography-mass spectrometry. Exemplarily, the mass content of the polymer particles in the coating layer can be 70%, 75%, 80%, 85%, 90%, 95%, or a value within any two of the above ranges.

[0071] As an optional implementation, the mass content of the first additive in the adhesive layer is 1.5%-10%, particularly 2%-5%; thus, the first additive can further help increase the adhesive dot height, thereby improving the adhesion between the diaphragm and the electrode. The mass content of the first additive in the adhesive layer is determined using methods known in the art. For example, the mass content of the first additive in the adhesive layer can be 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a value within any two of the above ranges.

[0072] As an optional implementation, the mass content of the thickener in the coating layer is 0.1%-20%, especially when it meets the requirement of 0.1%-4.5%. This controls the fluidity of the adhesive solution, further increasing the height of the adhesive dots and preventing the adhesive dots from becoming too low due to high fluidity, thereby improving the adhesion between the diaphragm and the electrode. The mass content of the thickener in the coating layer is determined using methods known in the art. For example, it can be measured using thermogravimetric-pyrolysis gas chromatography-mass spectrometry. Exemplarily, the mass content of the thickener in the coating layer can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc., or values ​​within any two of the above ranges.

[0073] As an optional implementation, the adhesive content in the coating layer is 0.5%-25% by mass; this improves the bonding strength between the adhesive dots and the substrate, prevents the adhesive dots from falling off the substrate, and ensures the separator's effect on improving battery performance. The method for testing the adhesive content in the coating layer is a method known in the art. For example, it can be measured using thermogravimetric-pyrolysis gas chromatography-mass spectrometry. Exemplarily, the adhesive content in the coating layer can be 0.5%, 1%, 3%, 5%, 8%, 10%, 15%, 20%, 25%, etc., or a value within any two of the above ranges.

[0074] As an optional implementation, the mass content of the first additive in the coating layer is C%, and the mass content of the thickener in the coating layer is B%. C and B satisfy the following relationship: 4 ≤ C / B ≤ 50. This can further improve the bonding strength between the separator and the electrode, and ensure the electrolyte wetting amount, thereby ensuring ion transport performance. If C / B is greater than 50, it means that the amount of the first additive is greater than that of the thickener, which can increase the height of the adhesive dots more, increase the area ratio of the blank area, and affect the bonding strength between the separator and the electrode. If C / B is less than 4, it means that the amount of the first additive is less than that of the thickener, the height of the adhesive dots is lower, it cannot completely alleviate the expansion of silicon-based particles, and the electrolyte wetting amount of the separator is small and the ion permeability is poor. For example, C / B can be 4, 5, 8, 10, 12, 15, 17, 20, 25, 30, 35, 40, 45, 50, etc., or a value within the range of any two of the above values.

[0075] As an optional implementation, the first additive is an alkyl polyoxyethylene ether, the thickener is sodium carboxymethyl cellulose, and the mass content C% of the alkyl polyoxyethylene ether in the coating layer and the mass content B% of the sodium carboxymethyl cellulose in the coating layer satisfy the following relationship: 4≤C / B≤20. In this way, the ion transport performance of the diaphragm can be further improved, while the adhesion between the diaphragm and the electrode can be improved. Furthermore, when the first additive is an alkyl polyoxyethylene ether, only a small amount is needed to increase the height of the adhesive dots; while when the thickener is sodium carboxymethyl cellulose, the addition of sodium carboxymethyl cellulose will not affect the height of the adhesive dots.

[0076] It should be noted that, in preparing the adhesive coating, all raw materials for the coating are mixed to obtain an adhesive solution with a solid content of 1%-50% and a viscosity of 80 mPa·s-200 mPa·s. The solid content of the adhesive solution is measured according to GB / T 1725-1979; the viscosity of the adhesive solution is measured according to GB / T 9269-2009.

[0077] As an optional implementation, the substrate further includes a heat-resistant layer disposed on at least one surface of the base film; this can further improve battery safety and reduce self-discharge and short-circuit rate.

[0078] As an optional implementation, the surface tension of the heat-resistant layer is measured to be F3mN / m under the test liquid, satisfying that F3 is less than F2, especially within the range of 5≤F2-F3≤20. This difference in surface tension between the heat-resistant layer and the test liquid helps to increase the height of the adhesive dots and expand the area of ​​the blank region, thereby ensuring better adhesion strength between the separator and the electrode, which is beneficial to the cycle and storage performance of the battery. The surface tension of the heat-resistant layer is tested using methods known in the art. For example, it is measured using the contact angle test method. The test steps include: adjusting the sample stage to be level, placing the sample to be tested on the sample stage, and using a micro-syringe to drop a small drop of adhesive (approximately 2-5 μL) onto the heat-resistant layer; capturing an image of the droplet with a camera, analyzing its contour using a contact angle meter, calculating the contact angle θ using methods such as the tangent method and ellipse fitting method, and then using the contact angle meter to calculate the surface tension of the solid according to the formula. For example, the difference between the surface tension of the adhesive and the surface tension of the heat-resistant layer, F2-F3 (unit mN / m), can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc., or a value within the range of any two of the above values.

[0079] It should be noted that the test solution for testing the surface tension of the heat-resistant layer described in this application is specifically composed of the following components: by mass, 90% acrylate-styrene copolymer, 2% alkyl polyoxyethylene ether, 0.1% sodium carboxymethyl cellulose and 7.9% styrene-butadiene latex.

[0080] As an optional implementation, the thickness of the heat-resistant layer on one side of the base film is 0.5 μm-5 μm. This further improves battery safety, reduces self-discharge and internal short circuits, and increases electrolyte wetting, thereby enhancing ion transport performance and improving battery cycle performance. If the thickness of the heat-resistant layer on one side is greater than 5 μm, it occupies too much space, which is detrimental to the battery's energy density; if the thickness is less than 0.5 μm, the heat-resistant layer's resistance to foreign matter is weak, limiting its improvement in self-discharge and internal short circuits. The thickness of the heat-resistant layer on one side is determined using methods known in the art. For example, if a separator with a heat-resistant layer on one side of the base film is folded into 8 layers and its thickness L3 is measured, then the thickness L3' of the separator is L3' = L3 / 8. Then, if the base film is folded into 8 layers and its thickness L4 is measured, then the thickness L4' of the base film is L4' = L4 / 8. That is, the thickness of the heat-resistant layer on one side of the base film is L3' - L4'. For example, the thickness (in μm) of the heat-resistant layer on one side can be 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a value within any two of the above values. As an optional embodiment, the porosity of the heat-resistant layer is 20%-80%, further, 30%-50%. As an optional embodiment, the heat-resistant layer has pores with a pore size of 10nm-500nm, further, 10nm-50nm. By controlling the porosity of the heat-resistant layer and the pore size in the heat-resistant layer, ion transport performance can be further improved, which is beneficial to the cycle performance of the battery.

[0081] In some embodiments, the heat-resistant layer comprises heat-resistant particles and a heat-resistant layer binder, wherein the heat-resistant particles account for 90%-99% of the mass of the heat-resistant layer, and the heat-resistant layer binder accounts for 1%-10% of the mass of the heat-resistant layer. The heat-resistant particles include one or more of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium dioxide, barium titanate, melamine cyanurate, 1,3,5-triazine-2,4,6-triamine, and melamine trithiocyanate. The heat-resistant layer binder includes one or more of polyvinyl alcohol, styrene-butadiene rubber, ethylene-vinyl acetate copolymer, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polymethyl methacrylate, polybutyl methacrylate, styrene-acrylic latex, polyacrylonitrile, ethyl polyacrylate, polyvinyl acetate, polyacrylic acid, polyacrylate, polyvinylidene fluoride polyurethane, polyvinylidene fluoride-hexafluoropropylene, or copolymer systems derived from the above polymers.

[0082] As an optional implementation, the thickness of the substrate is 5μm-100μm; the thickness of the substrate is tested using methods known in the art. For example, if the substrate is folded into 8 layers and the thickness L2 is measured, then the thickness L2' of the substrate is L2 / 8; exemplaryly, the thickness of the substrate (in μm) can be 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, etc., or a value within the range of any two of the above values.

[0083] In a second aspect, this application provides a battery including a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, the separator including the separator described in the first aspect.

[0084] As an optional implementation, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer comprising silicon-based particles; when the battery is under a charging limiting voltage state, the volume expansion force of the silicon-based particles is F4 N, the adhesive force between the adhesive dots and the negative electrode sheet is F5 N / m, and F5 and F4 satisfy: F5 / F4≥1; where F4=0.002(d1). 4 d1 is the particle size of the silicon-based particles, in μm; F5 = 0.01(d2 / 2) 2 ×(1-A1 / A2), where d2 is the diameter of the adhesive dot in μm. It should be noted that F4 = 0.002(d1). 4 And F5=0.01(d2 / 2) 2 The F4 and F5 calculated by ×(1-A1 / A2) are only numerically equivalent. F4 refers to the volume expansion force of a single silicon-based particle, and d1 refers to the particle size of a single silicon-based particle in contact with the adhesive dot.

[0085] When the volume expansion force F4 of the silicon-based particles and the adhesion force F5 between the adhesive dots and the negative electrode sheet satisfy F5 / F4≥1, especially when 5≤F5 / F4≤25, it means that the volume expansion force of the silicon-based particles matches the adhesion force between the adhesive dots and the negative electrode sheet. In this way, the adhesive dots and the negative electrode sheet will not separate due to the expansion of the silicon-based particles, resulting in poor contact interface and increased interface impedance, which is beneficial to the cycle performance of the battery. Moreover, the electrode structure has good stability, ensuring the cycle and storage performance of the battery. At the same time, the local lithium-ion permeability of the separator is good and the current distribution is uniform, so that overcharging and discharging will not occur in various areas of the separator. This prevents the separator from being punctured by the sharp parts of the silicon-based particles, thereby reducing the self-discharge and short-circuit rate of the battery. Furthermore, controlling the F5 / F4 ratio appropriately avoids excessively strong adhesion between the adhesive dots and the negative electrode, which would hinder the electrolyte from entering the blank areas within the adhesive dots, thus impeding ion transport and affecting the battery's cycle performance. If F5 / F4 is less than 1, it means the separator has insufficient binding force against the volume expansion of the silicon-based particles and is prone to separation from the negative electrode, resulting in poor electrode structure stability and negatively impacting the battery's cycle and storage performance. For example, the ratio F5 / F4 of the adhesive force F5 between the adhesive dots and the negative electrode to the volume expansion force F4 of the silicon-based particles can be 1, 2, 3, 4, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 35, etc., or a value within any range of two of the above values.

[0086] As an optional implementation, the particle size d1 μm of the silicon-based particles satisfies: 5 ≤ d1 ≤ 12. This results in a shorter transport path and smaller specific surface area between the silicon-based particles, reducing self-discharge. If d1 is greater than 12 μm, the transport path between the silicon-based particles is longer. If d1 is less than 5 μm, it means that the specific surface area of ​​the silicon-based particles is larger, leading to more side reactions and affecting self-discharge. The particle size d1 of the silicon-based particles is obtained using methods known in the art. For example, it can be measured using a laser particle size analyzer. Exemplarily, the particle size d1 (in μm) of the silicon-based particles can be 5, 6, 7, 8, 9, 10, 11, 12, etc., or a value within any two of the above ranges.

[0087] As an optional implementation, the diameter d2 μm of the adhesive dots satisfies: 50 ≤ d2 ≤ 600; thus, the diaphragm can achieve both good adhesion and ion transport performance. The diameter d2 of the adhesive dots is obtained by methods known in the art. For example, a photograph of the diaphragm surface is taken using a scanning electron microscope (5000x magnification). From the obtained SEM image, a specific adhesive dot is randomly selected, and the circumference of the closed curve formed by the polymer particles at the outermost edge of the adhesive dot is measured using image processing software (Image J). The diameter of the circle equivalent to this circumference is then deduced, which is the diameter d2 of the adhesive dot. For example, the diameter d2 (in μm) of the adhesive dot can be 50, 70, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, etc., or a value within any two of the above ranges.

[0088] As an optional implementation, the silicon content is 3%-15% based on the mass of the negative electrode active layer. This improves the battery's energy density and cycle performance. If the silicon content is greater than 15%, it means that silicon expands drastically; if the silicon content is less than 3%, it means that the high specific capacity characteristic of silicon cannot be utilized. The silicon content is tested using methods known in the art. For example, after discharging the battery to 0% SOC (battery voltage 3.0V), the negative electrode sheet is disassembled and soaked in dimethyl carbonate (DMC) solvent for 12 hours, then rinsed with DMC solvent to remove the lithium salt adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active coating can then be peeled off from the negative electrode current collector, and the negative electrode active coating is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the sample size is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25℃) to 900℃ at a rate of 10℃ / min, and held at 900℃ for 40min. This allows the non-silicon components in the negative electrode active coating to volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash content of the negative electrode active coating. The mass content of silicon in the negative electrode active material layer can be calculated based on the mass of the ash, using the following formula: Mass percentage of silicon (based on the total mass of the negative electrode active material layer) = 7 × mass of ash / (15 × mass of the test sample). For example, the silicon content can be 3%, 5%, 7%, 10%, 12%, 15%, or any value within the range of any two of the above values.

[0089] As an optional implementation, the volume expansion force F4N of the silicon-based particles satisfies: 3≤F4≤41.472; thus, the separator can be guaranteed to have both good adhesion and ion transport performance. If the volume expansion force F4 of the silicon-based particles is greater than 41.472N, the separator and the negative electrode may not be able to bond, and the adhesive dots may fail. If the volume expansion force F4 of the silicon-based particles is less than 3N, the capacity improvement of the silicon-based particles is limited. The volume expansion force F4 of the silicon-based particles is obtained by a method known in the art. For example, the in-situ expansion force analyzer can be used to measure the following steps: a thin substrate containing silicon-based particles is prepared and placed in the in-situ expansion force analyzer. The probe is fixed and clamped, and the material is charged. During the charging process, the volume of the material expands and compresses the probe, and the maximum value of the force measured by the probe is obtained. Then, the number of silicon-based particles n at the probe location is calculated by the areal density of the prepared substrate and the density of the material. Then, the volume expansion force F4 of the silicon-based particles is equal to the maximum value of the probe test pressure / n. For example, the volume expansion force F4 of the silicon-based particles (in N) can be 3, 5, 10, 20, 30, 40, 41.472, etc., or a value within the range of any two of the above values.

[0090] As an optional implementation, the adhesion strength F6 between the separator and the negative electrode is 3 N / m-20 N / m; as an optional implementation, the adhesion strength F7 between the separator and the positive electrode is 3 N / m-20 N / m. This ensures good interfacial contact between the separator and the electrode, resulting in low interfacial impedance, better ion transport performance, and improved battery cycle performance. If the adhesion strength between the separator and the electrode is greater than 20 N / m, the electrolyte wetting amount is insufficient, affecting the uniformity of ion permeation; if the adhesion strength is less than 3 N / m, there are too many gaps between the separator and the electrode, resulting in a longer ion transport path.

[0091] The bonding strength F6 between the separator and the negative electrode sheet is obtained by a method known in the art. For example, it can be obtained by a peel force test. Specifically, the sample after the separator and the negative electrode sheet are composited is cut into strips of a specific width, fixed on a universal testing machine, and then peeled at a constant rate of 100-300 mm / min at 180°. The peel force value is recorded in real time during the process, and the average peel force per unit width is the quantitative result of the bonding strength. For example, the bonding strength F6 (unit N / m) between the separator and the negative electrode sheet can be 3, 5, 7, 10, 12, 15, 18, 20, etc., or a value within the range of any two of the above values.

[0092] The bonding strength F7 between the separator and the positive electrode sheet is obtained by methods known in the art. For example, it can be obtained by a peel force test. Specifically, the sample after the separator and the positive electrode sheet are composited is cut into strips of a specific width, fixed on a universal testing machine, and then peeled at a constant rate of 100-300 mm / min at 180°. The peel force value is recorded in real time during the process, and the average peel force per unit width is the quantitative result of the bonding strength. For example, the bonding strength F7 (unit N / m) between the separator and the positive electrode sheet can be 3, 5, 7, 10, 12, 15, 18, 20, etc., or a value within any two of the above values.

[0093] It is understood that the battery described in the second aspect has excellent cycle performance due to having the separator described in the first aspect, and its self-discharge and internal short circuit are well improved; in addition, the battery's liquid retention is increased by 0.2g-0.5g, and the breakage rate is 100%.

[0094] Those skilled in the art will understand that the positive electrode sheet in the secondary battery of this application may include any technology disclosed in the prior art; in some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer, the positive current collector having two opposing surfaces in its own thickness direction, and the positive active layer disposed on either or both of the opposing surfaces of the positive current collector. The materials, composition, and manufacturing methods of the positive electrode sheet used in the lithium-ion battery of this application may include any technology disclosed in the prior art.

[0095] In some embodiments, the secondary battery of this application may also include an electrolyte, which may include any technology disclosed in the prior art; it is understood that the electrolyte includes organic solvents, lithium salts, and additives, and this application does not make specific limitations.

[0096] In some embodiments, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), fluoroethylene carbonate (FEC), and propylene trifluorocarbonate (TFPC).

[0097] In some embodiments, the electrolyte further includes a lithium salt, which includes one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroantimonyate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium 4,5-dicyano-2-trifluoromethylimidazolium (LiDTI), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate phosphate), lithium trifluoromethanesulfonate, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, lithium di(trifluoromethanesulfonyl)imide, lithium di(difluorophosphoryloxy)difluoroborate, and lithium tetra(difluorophosphoryloxy)borate.

[0098] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products. In all embodiments and comparative examples of this application, the unit % represents mass percentage.

[0099] Example 1 This embodiment provides a method for preparing a battery, including: Positive electrode sheet: Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), and carbon nanotubes are mixed in a mass ratio of 96:1.2:2.8. Then, N-methylpyrrolidone (NMP) is added to adjust the solid content of the slurry to 65%, and the mixture is stirred under vacuum. The slurry is then coated on both sides of aluminum foil, and the surface density on one side is adjusted to 0.018 g / m². 2 Baking at 90℃, cold pressing to a thickness of 0.0099mm, cutting the electrode sheet to a width of 131mm, welding the electrode tabs and rolling it up; Negative electrode sheet: Graphite, silicon carbide particles, acetylene black, styrene-butadiene rubber, and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 75:20:1.5:2:1.5. Deionized water is added to adjust the slurry solid content to 70%, and the mixture is stirred under vacuum. The slurry is then coated onto copper foil, and the surface density on one side is adjusted to 0.0098 g / cm³. 2 The material is dried at 110℃, coated on both sides, and then the cold-pressed thickness is adjusted to 0.122mm. The electrode sheet is then cut to a width of 133mm, and the tabs are welded and the sheet is rolled up. The silicon content in the silicon-carbon particles is 50%. The diaphragm is made of PE base film (9μm thick) as the substrate layer. A heat-resistant layer (2μm thick, including Al2O3) is coated on one side of the substrate layer. An adhesive layer is coated on the surface of the heat-resistant layer away from the substrate layer and on the other side of the substrate layer. The adhesive layer is coated in a dot matrix manner. The parameters of each adhesive dot in the dot matrix are detailed in Table 1-2. The adhesive layer consists of: 90 wt% polymer particles (acrylate-styrene copolymer, particle size range 0.1 μm-8 μm), C wt% alkyl polyoxyethylene ether, B wt% sodium carboxymethyl cellulose, and 7.9 wt% styrene-butadiene latex. The adhesive layer is formed by coating with an adhesive solution. The surface tension F1 of the PE base film was tested to be 3 mN / m, the surface tension of the adhesive solution was F2 mN / m, and the surface tension F3 of the heat-resistant layer was 2.5 mN / m. It should be noted that the substrate of the adhesive layer coated on the surface of the substrate layer is the substrate layer, while the substrate of the adhesive layer coated on the surface of the heat-resistant layer is the heat-resistant layer. The positive electrode, separator, and negative electrode are wound in sequence, and hot-pressed (70℃, 15s, 1Mpa) to obtain the cell. After baking and electrolyte injection, the electrolyte (EC / EMC / PC mass ratio of 1:1:1; 0.5mol / L lithium hexafluorophosphate) is encapsulated and formed to obtain a secondary battery.

[0100] The preparation methods of Examples 2-26 and Comparative Examples 1-5 are basically the same as those of Example 1, with differences shown in Tables 1-2. " / " indicates that the item does not exist. In Tables 1-2, A2 mm... 2 A1 mm represents the area of ​​a circle equivalent to the maximum perimeter of the closed curve formed by polymer particles in a single adhesive dot within the adhesive layer. 2 d1 μm is the area of ​​the blank region in a single adhesive dot, H μm is the difference between the maximum and minimum height of the adhesive dot, L μm is the height difference between the maximum height of the adhesive dot and the substrate, F1 mN / m is the surface tension of the base film, F2 mN / m is the surface tension of the adhesive solution, F3 mN / m is the surface tension of the heat-resistant layer, F4 N is the volume expansion force of the silicon-based particles, F5 N / m is the adhesive force between the adhesive dot and the negative electrode plate, d1 μm is the particle size of the silicon-based particles, d2 μm is the diameter of the adhesive dot, F6 N / m is the adhesive strength between the separator and the negative electrode plate, and F7 N / m is the adhesive strength between the separator and the positive electrode plate.

[0101] Example 27 This embodiment provides a method for preparing a battery, which differs from Embodiment 1 in that the second step is different, and the negative electrode sheet and separator are different. The specific negative electrode sheet and separator in this embodiment are as follows: Negative electrode sheet: Graphite, silicon carbide particles, acetylene black, styrene-butadiene rubber, and CMC are mixed in a mass ratio of 89:6:1.5:2:1.5. Deionized water is added to adjust the slurry solid content to 70%, and the mixture is stirred under vacuum. The slurry is then coated onto copper foil, and the surface density on one side is adjusted to 0.0098 g / cm³. 2 The material is dried at 110℃, coated on both sides, and then the cold-pressed thickness is adjusted to 0.122mm. The electrode sheet is then cut to a width of 133mm, and the tabs are welded and rolled up. The silicon content in the silicon-carbon particles is 50%.

[0102] The diaphragm is made of PE base film (5μm thick) as the substrate layer. A heat-resistant layer (5μm thick, including Al2O3) is coated on one side of the substrate layer. An adhesive layer is coated on the surface of the heat-resistant layer away from the substrate layer and on the other side of the substrate layer. The adhesive layer is coated in a dot matrix manner. The parameters of each adhesive dot in the dot matrix are detailed in Table 1-2. The coating layer consists of: 89.4 wt% polymer particles (polymethyl methacrylate, particle size range of 0.1 μm-8 μm), C wt% polyvinylpyrrolidone, B wt% polyvinyl alcohol, and 5.9 wt% styrene acrylic acid.

[0103] Example 28 This embodiment provides a method for preparing a battery, which differs from Embodiment 1 in that the second step is different, and the negative electrode sheet and separator are different. The specific negative electrode sheet and separator in this embodiment are as follows: Negative electrode sheet: Graphite, silicon carbide particles, acetylene black, styrene-butadiene rubber, and CMC are mixed in a mass ratio of 65:30:1.5:2:1.5. Deionized water is added to adjust the slurry solid content to 70%, and the mixture is stirred under vacuum. The slurry is then coated onto copper foil, and the surface density on one side is adjusted to 0.0098 g / cm³. 2 The material is dried at 110℃, coated on both sides, and then the cold-pressed thickness is adjusted to 0.122mm. The electrode sheet is then cut to a width of 133mm, and the tabs are welded and rolled up. The silicon content in the silicon-carbon particles is 50%.

[0104] Separator: A PE base film (9 μm thick) is used as the substrate layer. A heat-resistant layer (0.5 μm thick, including Al2O3) is coated on one side of the substrate layer. An adhesive layer is coated on the surface of the heat-resistant layer away from the substrate layer and on the other side of the substrate layer. The adhesive layer is coated in a dot matrix manner. The parameters of each adhesive dot in the dot matrix are detailed in Table 1-2. The coating layer consists of: 90.3 wt% polymer particles (vinylidene fluoride-hexafluoropropylene copolymer, particle size range of 0.1 μm-8 μm), C wt% sodium dodecyl sulfate, B wt% gelatin, and 6 wt% polyacrylic acid.

[0105] Table 1. Variables in the Examples and Comparative Examples

[0106] Table 2 Variables for Example and Comparative Example 2

[0107] Test case 1. Cycle capacity retention: The batteries prepared in each embodiment and comparative example were placed in an environment of 25±2℃ and left to stand for 2 hours. They were then charged at a constant current of 1.2C to 4.15V, charged at a constant voltage of 4.15V to 1C, charged at a constant current of 1C to 4.2V, charged at a constant voltage of 4.2V to 0.7C, charged at a constant current of 0.7C to 4.25V, charged at a constant voltage of 4.25V to 0.45C, charged at a constant current of 0.45C to 4.48V, and discharged at 0.5C to 3V. This constitutes one charge-discharge cycle. The initial capacity was recorded. The cycle was repeated for 1000T. The capacity retention rate after 1000T cycles = (capacity after cycle / initial capacity) × 100%.

[0108] 2. Cyclic Thickness Expansion Rate: The batteries prepared in each embodiment and comparative example were placed in an environment of 25±2℃ and left to stand for 2 hours. They were then charged with a constant current of 1.2C to 4.15V, a constant voltage of 4.15V to 1C, a constant current of 1C to 4.2V, a constant voltage of 4.2V to 0.7C, a constant current of 0.7C to 4.25V, a constant voltage of 4.25V to 0.45C, a constant current of 0.45C to 4.48V, and discharged at 0.5C to 3V. The initial thickness was measured at this point. After 1000 cycles, the samples were left to stand at room temperature for about 2 hours. After the sample temperature cooled to room temperature, the thickness after cycling was measured. The thickness expansion rate after 1000T cycles = (thickness after cycles - initial thickness) / initial thickness × 100%.

[0109] 3. Self-discharge: The batteries prepared in each embodiment and comparative example were placed in an environment of 25±2℃. After the batteries were formed, the open circuit voltage OCV1 of the battery was tested at time t1 after an interval of 24 hours. After resting for 72 hours, the open circuit voltage OCV2 of the battery was tested at time t2. The K value = ((OCV1-OCV2) / (t1-t2)) and the unit is mV.

[0110] 4. Short circuit rate: Apply 100V to the positive and negative terminals of the battery cell and measure the impedance. If the impedance is less than 2MΩ, it is considered a short circuit. If 1000 cells are tested, the short circuit rate = number of short circuits / total number of tests.

[0111] The test results are shown in Table 3.

[0112] Table 3 Test results of the examples and comparative examples

[0113] As can be seen from Tables 1-3, compared to Comparative Example 3 (where there are no blank areas within the adhesive dots), the cycle performance of Examples 1-28 has been improved to varying degrees, with a significant decrease in cycle thickness expansion rate, self-discharge, and short-circuit rate. This is because, in this application, the area ratio (A1 / A2) of the blank areas within the adhesive dots and the height (H) of the adhesive dots are reasonably controlled. This ensures sufficient contact area between the adhesive dots and the electrode, thereby guaranteeing good adhesion. At the same time, the separator also has good ion permeability, which can increase the wetting amount of the electrolyte, thus facilitating the transport of lithium ions. As a result, the battery provided by this application has better cycle performance, and the cycle thickness expansion rate, self-discharge, and short-circuit rate have also been improved to varying degrees.

[0114] Compared with Example 1, Comparative Examples 1-5 failed to reasonably control A1 / A2 or H. In Comparative Examples 2 and 4, the adhesion between the separator and the electrode deteriorated, affecting the battery's cycle life and thickness expansion rate. In Comparative Examples 1, 3 and 5, the overall ion permeability and electrolyte retention capacity of the separator were poor, ion transport was blocked, and it was easily punctured by the sharp parts of silicon-based particles, affecting the battery's cycle life and storage, and causing self-discharge and internal short circuit.

[0115] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A diaphragm, characterized in that, The system includes a substrate and an adhesive layer disposed on at least one surface of the substrate. The adhesive layer comprises a plurality of adhesive dots, each adhesive dot comprising polymer particles and a plurality of blank areas, wherein the polymer particles cover the substrate and the blank areas do not cover the substrate. A circular area equivalent to the maximum perimeter of the closed curve formed by the polymer particles in a single adhesive dot is obtained, denoted as A² mm. 2 The area of ​​the blank region in a single adhesive dot is denoted as A1 mm. 2 The difference between the maximum height of the adhesive dot and the minimum height of the adhesive dot is denoted as H μm, and the difference between the maximum height of the adhesive dot and the minimum height of the adhesive dot is 1≤H≤4.

9.

2. The diaphragm according to claim 1, characterized in that, The amount of adhesive coating applied to one side surface of the substrate is 0.05 g / m. 2 -5g / m 2 ; And / or, the ratio of the area of ​​the polymer particles in the coating layer to the area of ​​one side surface of the substrate is 10%-25%; And / or, the average diameter of the adhesive dots is 50 μm-500 μm; And / or, the height difference between the maximum height of the adhesive dot and the substrate is denoted as L μm, satisfying 3≤L≤5; And / or, the substrate includes a base film, the base film being made of at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide, and tested in a test solution, the surface tension of the base film being measured to be F1 mN / m. The test solution, by mass, consists of the following components: 90% acrylate-styrene copolymer, 2% alkyl polyoxyethylene ether, 0.1% sodium carboxymethyl cellulose, and 7.9% styrene-butadiene latex. The platinum plate was immersed in the test solution, and the surface tension of the test solution was measured to be F2 mN / m, which satisfies that F1 is less than F2.

3. The diaphragm according to claim 2, characterized in that, 5≤F2-F1≤20; And / or, the amount of adhesive coating applied to one side surface of the substrate is 0.2 g / m. 2 -0.8g / m 2 ; And / or, the average diameter of the adhesive dots is 100μm-400μm.

4. The diaphragm according to any one of claims 1-3, characterized in that, The polymer particles have a particle size of 0.1 μm-8 μm; The polymer particles are composed of at least one of the following: acrylate polymers, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, polyhexafluoropropylene, ethylene-hexafluoropropylene copolymer, ethylene-acrylic acid copolymer, polyethylene, and polypropylene. And / or, the adhesive layer includes a first additive, which includes at least one of polyvinylpyrrolidone, sodium linear alkylbenzene sulfonate, alkyl polyoxyethylene ether, sodium dodecyl sulfate, sodium 2-naphthalenesulfonate formaldehyde condensate, sodium methylene bisnaphthalenesulfonate, and alkyl sulfonate. And / or, the coating layer includes a thickener, the thickener including at least one of sodium carboxymethyl cellulose, polyethylene oxide, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, gelatin, and sodium alginate; And / or, the adhesive layer includes an adhesive, the adhesive including at least one of styrene-butadiene latex, styrene acrylic acid, polyacrylamide, polyvinyl alcohol, polyvinylpyrrolidone, polyethylene oxide, modified paraffin resin, carbomer resin, polyacrylic acid or its derivatives, polyurethane acrylate, copolymer emulsion containing polyacrylate, polyurethane, and urethane.

5. The diaphragm according to claim 4, characterized in that, The polymer particles in the coating layer have a mass content of 70%-95%; And / or, the mass content of the first additive in the adhesive layer is 1.5%-10%; And / or, the thickener content in the adhesive layer is 0.1%-20% by mass; And / or, the adhesive content in the adhesive layer is 0.5%-25% by mass; And / or, the mass content of the first additive in the adhesive layer is C%, and the mass content of the thickener in the adhesive layer is B%, where C and B satisfy the following relationship: 4≤C / B≤50.

6. The diaphragm according to claim 5, characterized in that, The first additive is alkyl polyoxyethylene ether, the thickener is sodium carboxymethyl cellulose, and the mass content C% of alkyl polyoxyethylene ether in the coating layer and the mass content B% of sodium carboxymethyl cellulose in the coating layer satisfy the following relationship: 4≤C / B≤20; And / or, the mass content of the first additive in the adhesive layer is 2%-5%; And / or, the polymer particle content in the coating layer is 70%-90% by mass; And / or, the thickener content in the adhesive layer is 0.1%-4.5% by mass.

7. The diaphragm according to any one of claims 2, 3, 5 or 6, characterized in that, The substrate further includes a heat-resistant layer disposed on at least one surface of the base film; Optionally, under test liquid, the surface tension of the heat-resistant layer is measured to be F3 mN / m, which satisfies that F3 is less than F2; Optional, 5≤F2-F3≤20; Optionally, the thickness of the heat-resistant layer on one side of the base film is 0.5 μm-5 μm; Optionally, the thickness of the substrate is 5μm-100μm.

8. A battery, comprising a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, characterized in that, The diaphragm comprises the diaphragm according to any one of claims 1-7; Optionally, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer comprising silicon-based particles; when the battery is in a charging limiting voltage state, the volume expansion force of the silicon-based particles is F4 N, the adhesive force between the adhesive dots and the negative electrode sheet is F5 N, and F5 and F4 satisfy: F5 / F4≥1; where F4=0.002(d1). 4 d1 is the particle size of the silicon-based particles, in μm; F5 = 0.01(d2 / 2) 2 ×(1-A1 / A2), where d2 is the diameter of the adhesive dot in μm.

9. The battery according to claim 8, characterized in that, 5≤d1≤12； And / or, 5≤F5 / F4≤25; And / or, 50≤d2≤600; And / or, based on the mass of the negative electrode active layer, the silicon content is 3%-15% by mass.

10. The battery according to claim 8, characterized in that, 3≤F4≤41.472； And / or, the bonding strength F6 between the diaphragm and the negative electrode sheet is 3N / m-20N / m; And / or, the bonding strength F7 between the diaphragm and the positive electrode is 3N / m-20N / m.

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