Separator, secondary battery, and electric device

Abstract

A separator, a secondary battery, and an electric device, relating to the technical field of batteries. In the separator, phosphate-modified polymer particles are introduced into a polymer coating, and the liquid absorption rate of the separator soaked at 60°C for 8 hours and the thickness expansion rate of the separator soaked at 60°C for 8 hours are reasonably selected to meet a specific relationship, so that the swelling rate of the separator can be significantly reduced, and the adhesion property, electrolyte wettability, heat resistance and flame retardance of the separator are improved. Therefore, when the separator is applied to the preparation of a secondary battery, the prepared secondary battery has good cycle performance and charging and discharging performance, and has low internal resistance and excellent safety performance.

Description

Diaphragms, secondary batteries and electrical devices

[0001] This application claims priority to Chinese Patent Application No. 202410676472.2, filed on May 28, 2024, entitled "A diaphragm, a secondary battery and an electrical device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and in particular to a separator, a secondary battery, and an electrical device. Background Technology

[0003] As a crucial component of rechargeable batteries, the separator serves two main functions: first, it separates the positive and negative electrodes, preventing direct contact between the electrode materials and thus preventing internal short circuits; second, it acts as a migration channel for active ions, ensuring their free movement between the positive and negative electrodes. The structure and performance of the rechargeable battery separator affect the battery's capacity and lifespan, and to a large extent, determine its safety performance. Summary of the Invention

[0004] The purpose of this application is to solve the problems of poor cycle performance, high internal resistance, poor charge and discharge performance and insufficient safety of existing secondary batteries, and to provide a separator, secondary battery and electrical device with low swelling rate and excellent adhesion, electrolyte wettability, heat resistance, flame retardancy and ionic conductivity.

[0005] To achieve the above objectives, a first aspect of this application provides a diaphragm, comprising a base membrane and a polymer coating disposed on at least one side of the base membrane, the polymer coating comprising phosphate-modified polymer particles;

[0006] The diaphragm satisfies: 30≤R≤100;

[0007] Where R = η / B,

[0008] η% is the liquid absorption rate of the diaphragm after soaking at 60°C for 8 hours;

[0009] B% is the thickness expansion rate of the diaphragm after immersion at 60°C for 8 hours.

[0010] As an implementation scheme of this application, at least one of the following conditions must be met:

[0011] 1) The liquid absorption rate η% of the diaphragm after soaking at 60°C for 8 hours is 100-800%;

[0012] 2) The thickness expansion rate (B%) of the diaphragm after immersion at 60°C for 8 hours is 1-30%;

[0013] 3) The limiting oxygen index of the diaphragm is 25-41%.

[0014] As an embodiment of this application, the thickness of the polymer coating is 0.5 to 12 μm.

[0015] As an embodiment of this application, the average particle size of the phosphate-modified polymer particles is 0.1 to 10 μm.

[0016] As an embodiment of this application, the degree of crosslinking of the phosphate-modified polymer particles is 70-90%.

[0017] As an embodiment of this application, the phosphate-modified polymer particles include a core layer, a shell layer, and a core-shell transition layer located between the core layer and the shell layer; the glass transition temperature of the core layer is 80 to 160°C, and the glass transition temperature of the shell layer is (-50) to (-10)°C.

[0018] As an embodiment of this application, the core layer of the phosphate-modified polymer particles comprises the following components in parts by weight: 5 to 60 parts hard monomer, 1 to 25 parts crosslinking functional monomer, and 1 to 10 parts water-soluble comonomer.

[0019] As an embodiment of this application, the shell layer comprises the following components in parts by weight: 5 to 60 parts soft monomer, 5 to 20 parts unsaturated phosphate ester, and 0.1 to 2 parts initiator.

[0020] As an implementation scheme of this application, at least one of the following conditions must be met:

[0021] a. The hard monomer includes at least one of methyl methacrylate, ethyl methacrylate, and styrene;

[0022] b. The crosslinking functional monomer includes at least one of acrylamide, divinylbenzene, glycidyl methacrylate, vinyltriethoxysilane, vinyltrimethoxysilane, and trimethylolpropane trimethacrylate;

[0023] c. The water-soluble comonomer includes at least one of acrylic acid, methacrylic acid, maleic acid, and sodium styrene sulfonate;

[0024] d. The soft monomer includes at least one of ethyl acrylate, n-butyl acrylate, isooctyl acrylate, lauryl acrylate, lauryl methacrylate, and n-octyl methacrylate;

[0025] e. The unsaturated phosphate ester includes at least one of 2-hydroxyethyl methacrylate phosphate ester, 2-hydroxyethyl methacrylate phosphate ester, and alkyl acrylate phosphate ester;

[0026] f. The initiator includes at least one of tert-butyl hydroperoxide, sodium bisulfite, Brügmann initiator FF6M, vitamin C, sodium persulfate, ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile.

[0027] In a second aspect of this application, a secondary battery is provided, including a positive electrode, a negative electrode, and the separator described in this application.

[0028] As an embodiment of this application, the peel strength between the diaphragm and the positive electrode sheet is ≥8N / m.

[0029] In a third aspect of this application, an electrical device is provided, including the secondary battery described in this application.

[0030] Compared with the prior art, the beneficial effects of this application are:

[0031] The separator provided in this application introduces phosphate-modified polymer particles into the polymer coating, and at the same time, rationally selects the liquid absorption rate and thickness expansion rate of the separator after soaking at 60°C for 8 hours, so that the two satisfy a specific relationship, which can significantly reduce the swelling rate of the separator and improve the separator's adhesion, electrolyte wettability, heat resistance, flame retardancy and conductivity. When this separator is applied to the preparation of secondary batteries, the resulting secondary batteries have good cycle performance and charge-discharge performance, and the resulting secondary batteries have low internal resistance and excellent safety performance. Attached Figure Description

[0032] Figure 1 shows the particle size distribution of the phosphate-modified polymer particles prepared in Example 1. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0035] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0036] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0037] In one embodiment of this application, a diaphragm is provided, comprising a base membrane and a polymer coating disposed on at least one side of the base membrane, the polymer coating comprising phosphate-modified polymer particles;

[0038] The diaphragm satisfies: 30≤R≤100;

[0039] Where R = η / B,

[0040] η% is the liquid absorption rate of the diaphragm after soaking at 60°C for 8 hours;

[0041] B% is the thickness expansion rate of the diaphragm after immersion at 60°C for 8 hours.

[0042] The inventors of this application have discovered that the performance of the diaphragm is significantly correlated with the substances added to the polymer coating, as well as the liquid absorption rate and thickness expansion rate of the diaphragm itself after immersion at 60°C for 8 hours. On one hand, this application introduces phosphate-modified polymer particles into the polymer coating. The phosphate functional groups act as surfactants to a certain extent, achieving good wetting, emulsification, and solubilization effects, enhancing the compatibility between components in the polymer coating, avoiding emulsifier residue problems caused by adding emulsifiers, and improving the water resistance and surface properties of the polymer coating. Furthermore, the phosphate-modified polymer particles... The introduction of particles can also provide the polymer coating with excellent adhesion and ionic conductivity, as well as certain flame retardant properties. On the other hand, this application limits the liquid absorption rate η% of the separator after soaking at 60°C for 8 hours and the thickness expansion rate B% ​​of the separator after soaking at 60°C for 8 hours to satisfy the relationship: 30≤η / B≤100. This can significantly improve the separator's adhesion, electrolyte wettability, heat resistance, ionic conductivity and flame retardancy, while also significantly reducing the separator's swelling. Therefore, when this separator is applied to a secondary battery, the resulting secondary battery has good cycle performance and charge-discharge performance, and the secondary battery has low internal resistance and excellent safety performance.

[0043] For example, the separator satisfies 30≤R≤100, where R can be any point value or any two points within the range of 30≤R≤100, such as 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, etc. When the parameter R of the separator is within the above range, it can achieve a lower swelling ratio and better adhesion, electrolyte wettability, heat resistance, conductivity, and flame retardancy. This results in excellent cycle performance and charge / discharge performance of the corresponding secondary battery, as well as low internal resistance and high safety.

[0044] In one embodiment, the separator satisfies 40 ≤ R ≤ 90. For example, it can be 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, or any two values ​​within this range. The inventors of this application have discovered that when the separator is further selected to satisfy 40 ≤ R ≤ 90, the resulting separator exhibits superior overall performance, leading to better overall performance of the secondary battery when applied to it.

[0045] In one embodiment, the liquid absorption rate η% of the diaphragm after soaking at 60°C for 8 hours is 100-800%.

[0046] It should be noted that the test and calculation method for the liquid absorption rate η% of the diaphragm after soaking at 60℃ for 8 hours is as follows: The diaphragm is placed in the electrolyte (1M LiPF6, EC / EMC = 3:7) and soaked at 60℃ for 8 hours. The weights m0 and m1 before and after soaking are recorded, and the liquid absorption rate is calculated as follows: Liquid absorption rate η% = (m1-m0) / m0 × 100%.

[0047] For example, the liquid absorption rate η% of the diaphragm after soaking at 60°C for 8 hours can be any point value or any two-point range value between 100% and 800%, such as 100%, 120%, 140%, 160%, 180%, 200%, 220%, 240%, 260%, 280%, 300%, 320%, 340%, 360%, 380%, 400%, 420%, 440%, 460%, 480%, 500%, 520%, 540%, 560%, 580%, 600%, 620%, 640%, 660%, 680%, 700%, 720%, 740%, 760%, 780%, 800%, etc.

[0048] The inventors of this application have discovered that the liquid absorption rate η% of the separator after soaking at 60°C for 8 hours affects the wettability of the separator to the electrolyte and the swelling of the separator itself to a certain extent. When the liquid absorption rate η% of the separator after soaking at 60°C for 8 hours is further selected to be 100-800%, a good balance between high wettability and low swelling can be achieved, that is, the separator can simultaneously achieve excellent electrolyte wettability and low swelling, and other properties can also reach an excellent level at the same time. Based on the excellent electrolyte wettability and low swelling of the separator, when it is subsequently applied to the preparation of secondary batteries, the low internal resistance and excellent cycle performance of the secondary battery can also be achieved simultaneously.

[0049] In one embodiment, the liquid absorption rate η% of the separator after soaking at 60°C for 8 hours is 200-400%. For example, it can be 210%, 230%, 250%, 270%, 290%, 310%, 330%, 350%, 370%, 390%, or any two of these ranges. The inventors of this application have found that when the liquid absorption rate η% of the separator after soaking at 60°C for 8 hours is further selected to be 200-400%, the overall performance of the resulting separator is superior, and the overall performance of the corresponding secondary battery is also superior.

[0050] In one embodiment, the thickness expansion rate (B%) of the diaphragm after immersion at 60°C for 8 hours is 1-30%.

[0051] It should be noted that the test and calculation method for the thickness expansion rate B% ​​of the diaphragm after soaking at 60℃ for 8 hours is as follows: The diaphragm is placed in the electrolyte (1M LiPF6, EC / EMC = 3:7) and soaked at 60℃ for 8 hours. The thicknesses d0 and d1 before and after soaking are recorded, and the thickness expansion rate is calculated as follows: Thickness expansion rate B% ​​= (d1-d0) / d0 × 100%.

[0052] For example, the thickness expansion rate B% ​​of the diaphragm after soaking at 60°C for 8 hours can be any point value or any two-point range value between 1% and 30%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0053] The inventors of this application have discovered that the thickness expansion rate B% ​​of the separator after soaking at 60°C for 8 hours not only directly affects the swelling property of the separator itself, but also affects its wettability. When the thickness expansion rate B% ​​of the separator after soaking at 60°C for 8 hours is further selected to be 1-30%, the separator can achieve high electrolyte wettability while satisfying low swelling property, and other properties can also reach an excellent level simultaneously. Based on the separator satisfying low swelling property and high electrolyte wettability, the corresponding secondary battery also has low internal resistance and good cycle performance.

[0054] In one embodiment, the thickness expansion rate B% ​​of the diaphragm after soaking at 60°C for 8 hours is 2-10%. For example, it can be 2.2%, 2.4%, 2.6%, 2.8%, 3.2%, 3.4%, 3.6%, 3.8%, 4.2%, 4.4%, 4.6%, 4.8%, 5.2%, 5.4%, 5.6%, 5.8%, 6.2%, 6.4%, 6.6%, 6.8%, 7.2%, 7.4%, 7.6%, 7.8%, 8.2%, 8.4%, 8.6%, 8.8%, 9.2%, 9.4%, 9.6%, 9.8%, or any two of these ranges. The inventors of this application have discovered that when the thickness expansion rate B% ​​of the separator is further selected to be 2-10% after soaking at 60°C for 8 hours, the overall performance of the obtained separator is better, and correspondingly, the overall performance of the obtained secondary battery is also better.

[0055] In one embodiment, the electrolyte contact angle of the diaphragm is 16° to 31°. For example, it can be 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, or any two points within this range. The electrolyte contact angle is tested using a contact angle meter. The electrolyte used in the test is 1M LiPF6 with EC / EMC = 3:7. Specifically, 10 μL of electrolyte is dropped from a dropper onto the diaphragm surface at a time, and the instantaneous contact angle is measured.

[0056] In one embodiment, the limiting oxygen index of the diaphragm is 25-41%.

[0057] It should be noted that the limiting oxygen index of the diaphragm is tested using a limiting oxygen index tester.

[0058] For example, the limiting oxygen index of the diaphragm can be any point value or any two-point range between 25% and 41%, such as 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, etc.

[0059] The inventors of this application have discovered that when the membrane coating of this application contains phosphate-modified polymer particles, the flame retardancy of the membrane can be effectively improved, and the limiting oxygen index of the membrane can reach the range of 25% to 41% of this application; thus, when applied to secondary batteries, it can significantly improve the safety performance of secondary batteries.

[0060] In one embodiment, the peel strength between the separator and the positive electrode sheet is ≥8 N / m.

[0061] It should be noted that the test method for the peel strength between the diaphragm and the positive electrode is as follows: after hot pressing the diaphragm and the positive electrode at 25℃, 5MPa and 15s, the 180° peel strength is tested and recorded using a universal tensile testing machine.

[0062] In one embodiment, the peel strength between the diaphragm and the positive electrode sheet is 8–14 N / m.

[0063] For example, the peel strength between the separator and the positive electrode can be any point value or any two-point range value between 8 and 14 N / m, such as 8.0 N / m, 8.2 N / m, 8.4 N / m, 8.6 N / m, 8.8 N / m, 9.0 N / m, 9.2 N / m, 9.4 N / m, 9.6 N / m, 9.8 N / m, 10.0 N / m, 10.2 N / m, 10.4 N / m, 1 0.6N / m, 10.8N / m, 11.0N / m, 11.2N / m, 11.4N / m, 11.6N / m, 11.8N / m, 12.0N / m, 12.2N / m, 12.4N / m, 12.6N / m, 12.8N / m, 13.0N / m, 13.2N / m, 13.4N / m, 13.6N / m, 13.8N / m, 14.0N / m.

[0064] The inventors of this application have discovered that when the membrane coating of this application includes phosphate-modified polymer particles and the liquid absorption rate η% and thickness expansion rate B% ​​of the membrane after immersion at 60°C for 8 hours satisfy the relationship given in this application, the resulting membrane not only exhibits good adhesion at high temperatures but also excellent adhesion at room temperature, as reflected in a peel strength ≥8 N / m at room temperature, specifically 8–14 N / m. Furthermore, when this application achieves good adhesion of the membrane at high temperatures and a peel strength ≥8 N / m at room temperature, its application in secondary batteries can effectively reduce the internal resistance of the secondary battery, realizing the preparation of low-internal-resistance secondary batteries.

[0065] In one embodiment, the ionic conductivity of the membrane is 2.4 to 2.9 ms / cm.

[0066] For example, the ionic conductivity of the membrane can be any point value or any two-point range between 2.4 and 2.9 ms / cm, such as 2.40 ms / cm, 2.42 ms / cm, 2.44 ms / cm, 2.46 ms / cm, 2.48 ms / cm, 2.50 ms / cm, 2.52 ms / cm, 2.54 ms / cm, 2.56 ms / cm, 2.58 ms / cm, 2.60 ms / cm, 2.62 ms / cm, 2.64 ms / cm, 2.68 ms / cm, 2.70 ms / cm, 2.72 ms / cm, 2.74 ms / cm, 2.76 ms / cm, 2.78 ms / cm, 2.80 ms / cm, 2.82 ms / cm, 2.84 ms / cm, 2.86 ms / cm, 2.88 ms / cm, and 2.90 ms / cm.

[0067] It should be noted that the test method for the ionic conductivity of the separator is as follows: the separator resistance Rs is measured by assembling a symmetrical cell, and the separator ionic conductivity is calculated with reference to the following formula: σs=d / Rs·S, where d is the separator thickness and S is the effective area of ​​the separator.

[0068] The inventors of this application have discovered that when the membrane coating of this application includes phosphate-modified polymer particles and the liquid absorption rate η% and thickness expansion rate B% ​​of the membrane after soaking at 60°C for 8 hours satisfy the relationship given in this application, the obtained membrane has good ionic conductivity; thereby, it can achieve excellent charge and discharge performance of the corresponding secondary battery.

[0069] In one embodiment, the thickness of the polymer coating is 0.5–12 μm.

[0070] For example, the thickness of the polymer coating can be any point value or any two-point range between 0.5 and 12 μm, such as 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, 10.5 μm, 11.0 μm, 11.5 μm, 12.0 μm, etc.

[0071] The inventors of this application have discovered that the thickness of the polymer coating not only affects the adhesion, flame retardancy, and heat resistance of the separator, but also affects the wettability, swelling, and conductivity of the separator to the electrolyte. When the thickness of the polymer coating is further selected to be 0.5–12 μm, the resulting separator and the secondary battery subsequently prepared have excellent comprehensive performance.

[0072] In one embodiment, the thickness of the polymer coating is 4–6 μm. The inventors of this application have discovered that when the thickness of the polymer coating is further selected to be in the range of 4–6 μm, the overall performance of the resulting separator and the subsequently prepared secondary battery is superior.

[0073] In one embodiment, the average particle size of the phosphate-modified polymer particles is 0.1 to 10 μm.

[0074] For example, the average particle size of the phosphate-modified polymer particles can be any point value or any two points between 0.1 and 10 μm, such as 0.1 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm, 9.5 μm, 10.0 μm, etc.

[0075] The inventors of this application have discovered that the average particle size of phosphate-modified polymer particles affects the uniformity of the polymer coating and the compatibility between substances, thereby affecting the performance of the phosphate-modified polymer particles. When the average particle size of the phosphate-modified polymer particles is further selected to be 0.1–10 μm, the polymer particles can effectively fulfill their function, improving the adhesion, flame retardancy, heat resistance, and ion conduction of the separator, and helping to achieve a lower swelling rate and higher electrolyte wettability of the separator; thus, it can achieve excellent cycle performance, charge-discharge performance, lower internal resistance, and good safety performance of the corresponding secondary battery.

[0076] In one embodiment, the average particle size of the phosphate-modified polymer particles is 1–6 μm. For example, it can be 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, etc. The inventors of this application have found that when the average particle size of the phosphate-modified polymer particles is further selected to be 1–6 μm, the resulting separator and the corresponding secondary battery exhibit superior overall performance.

[0077] In one embodiment, the degree of crosslinking of the phosphate-modified polymer particles is 70-90%.

[0078] It should be noted that the crosslinking degree of the phosphate-modified polymer particles is tested by using a Soxhlet extractor and employing the Soxhlet extraction method.

[0079] For example, the degree of crosslinking of the phosphate-modified polymer particles can be any point value or any two-point range value between 70% and 90%, such as 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88%, 90%, etc.

[0080] The inventors of this application have discovered that the degree of crosslinking of phosphate-modified polymer particles can affect their emulsification and thickening properties to a certain extent, and also affects the compatibility of components in the coating, thereby affecting the electrolyte wettability, heat resistance, adhesion, swelling, flame retardancy, and ion conduction of the separator. When the degree of crosslinking of the phosphate-modified polymer particles is further selected to be 70-90%, the resulting separator has excellent flame retardancy, electrolyte wettability, heat resistance, adhesion, and ion conduction, and the separator has low swelling characteristics. When further applied to secondary batteries, the resulting secondary batteries have good cycle performance and charge-discharge performance, and also have low internal resistance and high safety characteristics.

[0081] In one embodiment, the phosphate-modified polymer particles include a core layer, a shell layer, and a core-shell transition layer located between the core layer and the shell layer; the glass transition temperature of the core layer is 80 to 160°C, and the glass transition temperature of the shell layer is (-50) to (-10)°C.

[0082] For example, the glass transition temperature of the core layer can be any point value or any two-point range between 80 and 160°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, or 160°C; the glass transition temperature of the shell layer can be any point value or any two-point range between (-50) and (-10)°C, such as (-50)°C, (-45)°C, (-40)°C, (-35)°C, (-30)°C, (-25)°C, (-20)°C, (-15)°C, or (-10)°C.

[0083] The inventors of this application have discovered that by introducing phosphate-modified polymer particles with a core layer, a shell layer, and a core-shell transition layer between the core and shell layers, the problem of large polarity differences caused by abrupt changes in the traditional core and shell layers can be effectively alleviated. By introducing a core-shell transition layer between the core and shell layers, a gradual change trend between the core and shell layers can be achieved, avoiding the microphase structure separation caused by excessive polarity differences due to abrupt changes in the core-shell structure. This effectively achieves both the high adhesion resulting from the high polarity of the shell layer and the low swelling effect resulting from the high cross-linking of the core layer, thereby achieving excellent adhesion and low swelling of the separator as a whole, ultimately resulting in excellent cycle performance and low internal resistance of the secondary battery. Furthermore, the inventors of this application have discovered that when the glass transition temperature of the core layer is further selected to be 80–160°C and the glass transition temperature of the shell layer is (-50)–(-10)°C, the resulting separator exhibits even better adhesion, lower swelling, and superior other properties.

[0084] In one embodiment, the core layer of the phosphate-modified polymer particles comprises the following components in parts by weight: 5 to 60 parts hard monomer, 1 to 25 parts crosslinking functional monomer, and 1 to 10 parts water-soluble comonomer.

[0085] The inventors of this application have discovered that when the core layer of the phosphate-modified polymer particles is further selected to include the above-mentioned mass fractions of the components, not only can the glass transition temperature of the core layer of the phosphate-modified polymer particles be within the range given in this application, but the resulting core layer also has a high degree of cross-linking. This effectively prevents the phosphate-modified polymer particles from swelling by the electrolyte, thereby reducing the swelling of the separator and improving the cycle performance of the corresponding secondary battery.

[0086] In one embodiment, the core layer of the phosphate-modified polymer particles further includes deionized water.

[0087] In one embodiment, the shell layer of the phosphate-modified polymer particles comprises the following components in parts by weight: 5 to 60 parts soft monomer, 5 to 20 parts unsaturated phosphate ester, and 0.1 to 2 parts initiator.

[0088] The inventors of this application have discovered that when the components and mass fractions of the shell layer in the phosphate-modified polymer particles are further selected within the aforementioned range, on the one hand, the introduction of unsaturated phosphate esters can not only help achieve the flame-retardant properties of the separator and improve the safety of the corresponding secondary battery, but also help achieve good adhesion of the shell layer, improve the adhesion of the separator, and thus reduce the internal resistance of the corresponding secondary battery; on the other hand, the aforementioned components and contents can help achieve the glass transition temperature of the shell layer within the range given in this application, thereby ensuring excellent overall performance of the separator and the corresponding secondary battery.

[0089] In one embodiment, the shell layer of the phosphate-modified polymer particles further includes a buffer and deionized water.

[0090] In one embodiment, the shell layer of the phosphate-modified polymer particles further includes 0.01 to 0.5 parts of buffer and 50 to 100 parts of deionized water.

[0091] In one embodiment, the hard monomer includes at least one of methyl methacrylate, ethyl methacrylate, and styrene.

[0092] In one embodiment, the crosslinking functional monomer includes at least one of acrylamide, divinylbenzene, glycidyl methacrylate, vinyltriethoxysilane, vinyltrimethoxysilane, and trimethylolpropane trimethacrylate.

[0093] In one embodiment, the water-soluble comonomer includes at least one of acrylic acid, methacrylic acid, maleic acid, and sodium styrene sulfonate.

[0094] In one embodiment, the soft monomer includes at least one selected from ethyl acrylate, n-butyl acrylate, isooctyl acrylate, lauryl acrylate, lauryl methacrylate, and n-octyl methacrylate.

[0095] In one embodiment, the unsaturated phosphate ester includes at least one of 2-hydroxyethyl methacrylate phosphate ester, 2-hydroxyethyl methacrylate phosphate ester, and alkyl acrylate phosphate ester.

[0096] In one embodiment, the initiator includes at least one selected from tert-butyl hydroperoxide, sodium bisulfite, sodium salt of an organic sulfinic acid derivative, vitamin C, sodium persulfate, ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile.

[0097] In one embodiment, the buffer includes at least one of sodium bicarbonate, disodium hydrogen phosphate, and ammonium bicarbonate.

[0098] The inventors of this application have discovered that when the material types of the core and shell layers of the phosphate-modified polymer particles are further selected as the specific types mentioned above, phosphate-modified polymer particles with glass transition temperatures of the core and shell layers within the range of this application can be effectively prepared, thereby helping to achieve excellent overall performance of the separator and the corresponding secondary battery.

[0099] In one embodiment, the method for preparing the phosphate-modified polymer particles includes the following steps:

[0100] S1. Preparation of preemulsion A: Mix and stir the hard monomer, crosslinking functional monomer and water-soluble comonomer for 8-12 min, then add deionized water and continue stirring for 25-35 min to obtain preemulsion A;

[0101] S2. Preparation of preemulsion B: Mix the soft monomer, unsaturated phosphate ester and part of deionized water and stir for 25-35 minutes to obtain preemulsion B;

[0102] S3. Preparation of base solution C: Part of the deionized water and buffer in the shell material are mixed and heated to 65-75℃ to obtain base solution C;

[0103] S4. Preparation of initiator solution D: Dissolve the initiator in the remaining deionized water to obtain initiator solution D;

[0104] S5. Add pre-emulsion A and pre-emulsion B dropwise to a portion of initiator solution D at a certain flow rate ratio to carry out the reaction. When blue light appears, stop adding pre-emulsion A and pre-emulsion B, raise the temperature to 80-85℃, and keep the reaction at this temperature for 25-35 minutes.

[0105] S6. After the heat preservation reaction is completed, maintain the temperature and continue to add pre-emulsion A and pre-emulsion B dropwise at a certain flow rate ratio, and add the remaining initiator solution D. Control the dropwise addition rate so that the pre-emulsion and initiator solution D are added in 3 to 3.5 hours. After the dropwise addition is completed, raise the temperature to 86 to 90°C and keep the reaction at the temperature for 1.3 to 1.8 hours. After the reaction is completed, cool down to room temperature to obtain phosphate ester modified polymer particles.

[0106] The inventors of this application have discovered that, when preparing phosphate-modified polymer particles using the method described in this application, without adding emulsifiers, the self-emulsifying effect of the added water-soluble comonomers and unsaturated phosphate esters can yield the product of this application, which includes a core layer, a shell layer, and a core-shell transition layer between the core and shell layers. On one hand, the preparation method provided in this application can achieve a gradient structure between the core and shell layers of the polymer particles, thereby effectively improving the compatibility between the core and shell layers, avoiding microphase separation, and fully utilizing the respective properties of the core and shell layers. On the other hand, without adding conventional emulsifiers, the adverse effects of emulsifiers can be effectively avoided. The prepared polymer particles have good monodispersity, with an average particle size within a suitable range, which is conducive to the stable performance of the polymer particles. Based on these two aspects, the phosphate-modified polymer particles prepared in this application can provide good adhesion and low swelling of the separator over a wide temperature range, and due to the introduction of phosphate esters, the resulting polymer coating also has good flame retardancy; thus, it can achieve excellent comprehensive performance for the corresponding secondary battery.

[0107] In one embodiment, the flow rate ratio n of preemulsion A and preemulsion B is 1 to 3.

[0108] For example, n can be any point value between 1 and 3 or any two points in a range, such as n being 1, 1.5, 2, 2.5, or 3.

[0109] The inventors of this application have discovered that the flow rate ratio of preemulsion A to preemulsion B affects the layered structure of phosphate-modified polymer particles, thereby affecting the compatibility of the core and shell layers of the polymer particles, and thus affecting the performance of the core and shell layers of the polymer particles. When the flow rate ratio of preemulsion A to preemulsion B is further selected to be 1 to 3, the resulting separator and the corresponding secondary battery have better overall performance.

[0110] In one embodiment, the polymer coating comprises the following components in parts by weight: 20-30 parts of the phosphate-modified polymer particles, 2-5 parts of water-based adhesive, 1-2 parts of wetting agent, and 60-80 parts of deionized water.

[0111] The inventors of this application have discovered that when the mass fraction of the components in the polymer coating is further selected within the above-mentioned range, the membrane can effectively achieve good adhesion and low swelling at both room temperature and high temperature. At the same time, the membrane also has excellent heat resistance, electrolyte wettability, flame retardancy and ion conduction; thereby achieving excellent comprehensive performance of the corresponding secondary battery.

[0112] In one embodiment, the waterborne adhesive includes at least one of polyvinyl alcohol, waterborne polyurethane, polyacrylonitrile, waterborne unsaturated polyester resin, and waterborne epoxy resin.

[0113] In one embodiment, the wetting agent includes at least one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and polyether-modified polysiloxane.

[0114] The inventors of this application have discovered that when the types of water-based adhesives and wetting agents are further selected to be the types described above, the resulting separator and the corresponding secondary battery exhibit even better overall performance.

[0115] In one embodiment, the base film includes a substrate and a ceramic layer disposed on at least one side of the substrate; the thickness of the ceramic layer is 1 to 4 μm.

[0116] In one embodiment, the thickness of the substrate is 8–10 μm.

[0117] In one embodiment, the substrate includes any one of polyethylene-based film, polypropylene-based film, and a composite film of polyethylene and polypropylene.

[0118] In one embodiment, the ceramic layer comprises the following components in parts by weight: 30-38 parts ceramic powder, 2-4 parts binder, 0.5-1 part dispersant, and 45-55 parts deionized water.

[0119] In one embodiment, the ceramic powder includes at least one of SiO2, Al2O3, TiO2, SnO2, and ZnO2.

[0120] In one embodiment, the adhesive includes at least one selected from polyvinylpyrrolidone, polyacrylate, polyvinyl alcohol, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

[0121] In one embodiment, the dispersant includes at least one of sodium polyacrylate, ammonium polyacrylate, styrene-maleic anhydride copolymer, and acrylate polymeric dispersant.

[0122] In one embodiment, the method for preparing the base film includes the following steps:

[0123] S1. Preparation of water-based slurry: Mix the dispersant and ceramic powder and stir at 1500-2000 r / min for 1-2 hours. Then add the binder and stir at 500-1000 r / min for 50-70 minutes to obtain the water-based slurry.

[0124] S2. Apply the aqueous slurry to at least one side of the substrate and dry it to obtain a base film.

[0125] In one embodiment, the coating method in step S2 includes gravure roller coating.

[0126] In one embodiment, the method for preparing the diaphragm includes the following steps:

[0127] S1. Mix the components of the polymer coating except for the wetting agent and disperse them at a speed of 500-1000 rpm for 60-120 min. After dispersion, add the wetting agent and stir at a speed of 1000-1500 rpm for 60-120 min to obtain a polymer slurry with a solid content of 10-15%.

[0128] S2. The polymer slurry is coated onto at least one side of the base film by roller coating or spraying, and dried at 60-80°C to obtain a diaphragm.

[0129] In one embodiment of this application, a secondary battery is provided, the secondary battery including the separator described in this application.

[0130] In one embodiment, the secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.

[0131] In one embodiment, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector; the positive active material layer includes a positive active material. This application does not limit the positive active material; any known positive active material can be used.

[0132] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; the negative electrode active material layer includes a negative electrode active material. This application does not limit the negative electrode active material; any known negative electrode active material can be used.

[0133] This application does not limit the composition of the electrolyte; any known electrolyte composition can be used to prepare the electrolyte.

[0134] In one embodiment, the separator of the secondary battery is disposed between the positive and negative electrodes.

[0135] In one embodiment of this application, an electrical device is provided, which includes the secondary battery described in this application.

[0136] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0137] Example 1

[0138] Embodiment 1 of this application provides a separator and a secondary battery. The preparation method of the secondary battery includes the following steps:

[0139] 1. Preparation of the diaphragm

[0140] (1) Preparation of phosphate-modified polymer particles

[0141] S1. Preparation of preemulsion A: 40 parts of hard monomer (20 parts of methyl methacrylate and 20 parts of styrene), 5 parts of crosslinking functional monomer (divinylbenzene) and 5 parts of water-soluble comonomer (sodium styrene sulfonate) are added to feed bottle 1 in sequence under stirring, mixed and stirred for 10 min, and then 40 parts of deionized water are added and stirred for another 30 min to obtain preemulsion A.

[0142] S2. Preparation of preemulsion B: 40 parts of soft monomer (20 parts of n-butyl acrylate and 20 parts of isooctyl acrylate), 5 parts of unsaturated phosphate ester (2-hydroxyethyl methacrylate phosphate ester), and 40 parts of deionized water are added to feed bottle 2 under stirring and mixed for 30 min to obtain preemulsion B.

[0143] S3. Preparation of base solution C: Mix 10 parts of deionized water and 0.3 parts of buffer (sodium bicarbonate) and add them to a reactor equipped with a stirrer, cooler and heating device. Heat to 70°C to obtain base solution C.

[0144] S4. Preparation of initiator solution D: Dissolve 1 part of initiator (sodium persulfate) in 15 parts of deionized water to obtain initiator solution D;

[0145] S5. Set the speed of constant flow pump 1 (R1) and pump 2 (R2) so that pump speed R1 = R2. Simultaneously turn on the two pumps so that the pre-emulsion in feed bottle 1 (corresponding to pump 1) and feed bottle 2 (corresponding to pump 2) flows into the reactor. Add 30% initiator solution D to the reactor. When the reactor shows blue light, stop the two pumps, raise the temperature to 85°C, and keep the reaction at this temperature for 30 minutes.

[0146] S6. After the heat preservation reaction is completed, maintain the temperature at 85℃, turn on the two constant flow pumps, continue to add the pre-emulsion, and add the remaining initiator solution D. Control the dropping rate so that the pre-emulsion and initiator solution D are added in 3.2h. After the dropping is completed, raise the temperature to 88℃ and keep the reaction at the heat preservation temperature for 1.5h. After the reaction is completed, cool down to room temperature to obtain phosphate ester modified polymer particles.

[0147] The particle size distribution of the obtained phosphate-modified polymer particles is shown in Figure 1.

[0148] (2) Preparation of base film

[0149] S1. Preparation of water-based slurry: Take 0.8 parts of dispersant (sodium polyacrylate) and 34 parts of ceramic powder (SiO2), mix them, and stir at 1800 r / min for 1.5 h. After uniform dispersion, add 3 parts of binder (polyvinylpyrrolidone), and then stir at 800 r / min for 60 min to obtain water-based slurry.

[0150] S2. A water-based slurry is coated onto both sides of a 9μm thick substrate (polyethylene film) using gravure roller coating to form a 2μm thick ceramic layer, which is then dried to obtain the base film.

[0151] (3) Preparation of the diaphragm

[0152] S1. Add 70 parts of deionized water, 4 parts of water-based adhesive (polyacrylonitrile water-based adhesive), and 25 parts of phosphate ester modified polymer particles to a stirrer and disperse at 800 rpm for 120 min. Then add 2 parts of wetting agent (fatty alcohol polyoxyethylene ether) and stir at 1500 rpm for 120 min to obtain a polymer slurry with a solid content of 10%.

[0153] S2. The polymer slurry is sprayed onto both sides of the base film and dried at 70°C. The thickness of the polymer coating is 4.2 μm, thus obtaining the diaphragm.

[0154] 2. Preparation of secondary batteries

[0155] (1) Preparation of positive electrode sheet: The positive active material NCM613: conductive carbon black: polyvinylidene fluoride = 96.5:2:1.5 by mass ratio is mixed, and the mixture is coated on aluminum foil after being mixed with N-methylpyrrolidone as solvent and dried under vacuum at 90℃ to obtain the positive electrode sheet.

[0156] (2) Preparation of negative electrode sheet: Graphite: conductive carbon black: sodium carboxymethyl cellulose: styrene-butadiene rubber in a mass ratio of 96.5:0.5:1.5:1.5, mixed with deionized water as solvent, coated onto copper foil, and dried under vacuum at 90°C to obtain negative electrode sheet;

[0157] (3) The diaphragm, positive electrode and negative electrode are wound to form a multi-tab cell, and then hot-pressed (pressure 0.4Mpa, time 8s, hot-pressing temperature 85℃), baked, injected with liquid and formed in sequence to obtain a secondary battery.

[0158] Example 2

[0159] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of phosphate ester modified polymer particles. The preparation method of phosphate ester modified polymer particles in this embodiment includes the following steps:

[0160] S1. Preparation of preemulsion A: 20 parts of hard monomer (10 parts of methyl methacrylate and 10 parts of styrene), 10 parts of crosslinking functional monomer (divinylbenzene) and 5 parts of water-soluble comonomer (sodium styrene sulfonate) are added to feed bottle 1 in sequence under stirring, mixed and stirred for 10 min, and then 40 parts of deionized water are added and stirred for another 30 min to obtain preemulsion A.

[0161] S2. Preparation of preemulsion B: 40 parts of soft monomer (20 parts of n-butyl acrylate and 20 parts of isooctyl acrylate), 5 parts of unsaturated phosphate ester (alkyl acrylate phosphate ester), and 20 parts of deionized water are added to feed bottle 2 in sequence under stirring and mixed for 30 min to obtain preemulsion B.

[0162] S3. Preparation of base solution C: Mix 10 parts of deionized water and 0.1 parts of buffer (sodium bicarbonate) and add them to a reactor equipped with a stirrer, cooler and heating device. Heat to 75°C to obtain base solution C.

[0163] S4. Preparation of initiator solution D: Dissolve 1.5 parts of initiator (sodium persulfate) in 15 parts of deionized water to obtain initiator solution D;

[0164] S5. Set the speed of constant flow pump 1 (R1) and pump 2 (R2) so that pump speed R1 = 2R2, where 2 is the ratio of the two pump speeds. Simultaneously turn on both pumps so that the pre-emulsion in feed bottle 1 (corresponding to pump 1) and feed bottle 2 (corresponding to pump 2) flows into the reactor. Add 30% initiator solution D to the reactor. When the reactor shows blue light, stop both pumps, raise the temperature to 85℃, and keep the reaction at this temperature for 30 minutes.

[0165] S6. After the heat preservation reaction is completed, maintain the temperature at 85℃, turn on the two constant flow pumps, continue to add the pre-emulsion, and add the remaining initiator solution D. Control the dropping rate so that the pre-emulsion and initiator solution D are added in 3 to 3.5 hours. After the dropping is completed, raise the temperature to 88℃ and keep the reaction at this temperature for 1.5 hours. After the reaction is completed, cool down to room temperature to obtain phosphate ester modified polymer particles.

[0166] Example 3

[0167] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, in which the hard monomer is 20 parts of methyl methacrylate and 40 parts of styrene.

[0168] Example 4

[0169] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, where the soft monomer is 40 parts of n-butyl acrylate.

[0170] Example 5

[0171] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles. The crosslinking functional monomer is glycidyl methacrylate, and the water-soluble comonomer is acrylic acid.

[0172] Example 6

[0173] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate-modified polymer particles, in which 15 parts of unsaturated phosphate ester are used.

[0174] Example 7

[0175] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, in which the crosslinking functional monomer is 20 parts.

[0176] Example 8

[0177] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate-modified polymer particles, where the hard monomer is 30 parts of methyl methacrylate, the soft monomer is 50 parts of isooctyl acrylate, and the unsaturated phosphate ester is 10 parts.

[0178] Example 9

[0179] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate-modified polymer particles. The hard monomer is 20 parts of methyl methacrylate, the soft monomer is 60 parts of isooctyl acrylate, and the unsaturated phosphate is 20 parts.

[0180] Example 10

[0181] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, where the hard monomer is 60 parts of methyl methacrylate and the soft monomer is 20 parts of butyl acrylate.

[0182] Example 11

[0183] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, where the hard monomer is 60 parts of methyl methacrylate, the soft monomer is 20 parts of butyl acrylate, and the crosslinking monomer is 15 parts.

[0184] Example 12

[0185] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, in which the water-soluble comonomer is 3 parts.

[0186] Example 13

[0187] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, in which the water-soluble comonomer is 10 parts.

[0188] Example 14

[0189] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, in which the water-soluble comonomer is 1 part.

[0190] Example 15

[0191] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, in which the crosslinking functional monomer is 1 part.

[0192] Example 16

[0193] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 lies in the preparation of the phosphate ester modified polymer particles, in which the crosslinking functional monomer is 25 parts.

[0194] Example 17

[0195] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 is in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 is that the thickness of the polymer coating sprayed onto the separator is 1 μm.

[0196] Example 18

[0197] This application provides a separator and a secondary battery. The difference between this embodiment and Embodiment 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Embodiment 1 is that the thickness of the polymer coating sprayed onto the separator is 12 μm.

[0198] Comparative Example 1

[0199] This application provides a separator and a secondary battery in comparative example. The difference between this embodiment and Example 1 is in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Example 1 is that no unsaturated phosphate ester is added in the preparation of the phosphate ester modified polymer particles.

[0200] Comparative Example 2

[0201] This application provides a separator and a secondary battery in comparative example. The difference between this embodiment and Example 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Example 1 lies in the preparation of the phosphate ester modified polymer particles, where R1 = 4R2.

[0202] Comparative Example 3

[0203] This application provides a separator and a secondary battery in comparative example. The difference between this embodiment and Example 1 lies in the preparation of the separator. The difference between the preparation method of the separator in this embodiment and Example 1 lies in the preparation of the phosphate ester modified polymer particles, where the hard monomer is 20 parts of methyl methacrylate, the soft monomer is 60 parts of isooctyl acrylate, and the crosslinking monomer is 15 parts.

[0204] The parameters of the examples and comparative examples are shown in Tables 1-2, and the parameter tests in Table 1 are shown in 1) to 5).

[0205] 1) The liquid absorption rate is the liquid absorption rate η% of the diaphragm after soaking at 60℃ for 8 hours. The specific test procedure is as follows: the diaphragm is placed in the electrolyte (1M LiPF6, EC / EMC = 3:7) and soaked at 60℃ for 8 hours. The weights m0 and m1 before and after soaking are recorded, and the liquid absorption rate is calculated. Liquid absorption rate η% = (m1-m0) / m0 × 100%.

[0206] 2) The thickness expansion rate is B% of the membrane after soaking at 60℃ for 8 hours. The specific test procedure is as follows: The membrane is placed in the electrolyte (1M LiPF6, EC / EMC = 3:7) and soaked at 60℃ for 8 hours. The thicknesses d0 and d1 before and after soaking are recorded, and the thickness expansion rate is calculated. Thickness expansion rate B% ​​= (d1-d0) / d0 × 100%.

[0207] 3) The average particle size of the polymer particles was obtained by measuring the particle size using a Malvern laser particle size analyzer;

[0208] 4) The degree of crosslinking of the polymer particles was obtained by Soxhlet extraction.

[0209] 5) The core glass transition temperature and the shell glass transition temperature were obtained by differential scanning calorimetry.

[0210] Table 1

[0211] The test parameters in Table 2 are shown in 1) to 5) below;

[0212] 1) Limiting Oxygen Index: The limiting oxygen index is tested using a limiting oxygen index tester. Specifically, a diaphragm sample of a certain size (120mm*6.5mm) is vertically clamped in a transparent combustion tube with a sample clamp, which contains an upward-flowing oxygen-nitrogen gas stream mixed in a certain proportion. The upper end of the sample is lit, and the subsequent combustion phenomenon is observed. The duration of combustion or the distance burned is recorded. If the combustion time of the sample exceeds 3 minutes or the flame front exceeds the 50mm mark, the oxygen concentration is reduced. If the combustion time of the sample is less than 3 minutes or the flame front does not reach the mark, the oxygen concentration is increased. This operation is repeated to gradually approach the specified value from both the upper and lower sides until the concentration difference between the two is less than 0.5%.

[0213] 2) Membrane conductivity: The ionic conductivity of the coated membrane is tested by assembling a symmetrical cell. Specifically, the membrane resistance Rs is measured by assembling a symmetrical cell, and the membrane ionic conductivity is calculated using the following formula: σs=d / Rs·S, where d is the membrane thickness and S is the effective area of ​​the membrane.

[0214] 3) Electrolyte contact angle: The contact angle was tested using a contact angle tester. The electrolyte used in the test was 1M LiPF6 with EC / EMC = 3:7. The specific process was to drop 10μL of electrolyte from the dropper onto the diaphragm surface and test its instantaneous contact angle.

[0215] 4) Peel strength of electrode: After hot pressing the diaphragm and the positive electrode under certain conditions, the 180° peel strength is tested using a universal tensile testing machine. The certain conditions are 85℃ & 5MPa & 15s and 25℃ & 5MPa & 15s respectively.

[0216] 5) Heat shrinkage rate: The shrinkage rate of the diaphragm in the longitudinal MD and transverse TD directions was tested at 100℃ for 1 hour, 150℃ for 1 hour, and 180℃ for 1 hour. The specific process is as follows: the initial length D0 is measured, and the diaphragm is placed in an oven at 100℃, 150℃, and 180℃ for 1 hour. After being taken out and cooled to room temperature, the length D1 at this time is measured. The shrinkage rate is (D0-D1) / D0*100%.

[0217] Table 2

[0218] Example of effect

[0219] The performance examples of this application test the performance of the prepared secondary battery, specifically including the following aspects:

[0220] 1) Cycle capacity retention rate: The battery is charged at a constant current of 1C to the cutoff voltage of 4.2V, then charged at a constant voltage to the cutoff current of 0.05C, rested for 5 minutes, and then discharged at a constant current of 1C to the cutoff voltage of 3.0V. The highest discharge capacity of the first 3 cycles is recorded as the initial capacity Q. When the cycle reaches 400 times, the discharge capacity Q1 of the last cycle is recorded. The 25℃ 1C cycle capacity retention rate of the battery is calculated according to the following formula: Cycle capacity retention rate = Q1 / Q × 100%;

[0221] 2) Internal resistance (DCR): At 25℃, the battery is charged at a constant current rate of 1C to 4.2V, charged at a constant voltage rate to 0.05C, then discharged at a rate of 1C for 40-50 minutes (20% SOC), and then discharged at the required rate (0.1-1C) for 10 seconds (sampling at 0.1s). The voltage drop ΔU and the current difference ΔI are recorded. Then DCR = ΔU / ΔI.

[0222] 3) 4C discharge capacity retention rate (discharge rate performance): The battery is charged at a constant current of 0.33C to 4.2V, then charged at a constant voltage to the cutoff current of 0.05C, rested for 5 minutes, discharged at a constant current of 0.33C to 3V, rested for 5 minutes, charged at a constant current of 0.33C to 4.2V, then charged at a constant voltage to the cutoff current of 0.05C, rested for 5 minutes, discharged at a constant current of 4C to 2.5V, and rested for 5 minutes. The 4C discharge capacity retention rate (%) = discharge capacity at 4C rate / initial discharge capacity at 0.33C × 100%.

[0223] The performance test results are shown in Table 3.

[0224] Table 3

[0225] As can be seen from Table 3, when the technical solution of this application is adopted, the obtained secondary battery has good cycle stability and charge-discharge performance, and also has low internal resistance. Specifically, the cycle capacity retention rate of the obtained secondary battery is above 74%, the internal resistance is below 2.63mΩ, and the 4C discharge capacity retention rate is above 73%.

[0226] The results of Example 1 and Comparative Example 1 also show that when the separator satisfies 30≤R≤100 and the polymer coating includes phosphate-modified polymer particles, the excellent overall performance of the secondary battery of this application can be guaranteed.

[0227] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A separator comprising a base film and a polymer coating layer provided on at least one side of the base film, wherein, The polymer coating comprises phosphate-modified polymer particles. The diaphragm satisfies: 30≤R≤100; Wherein R=η / B, η% is the liquid absorption rate of the diaphragm soaked at 60℃ for 8h; B% is the thickness expansion rate of the diaphragm soaked at 60℃ for 8h.

2. The septum of claim 1, wherein, Satisfy at least one of the following conditions: 1) The liquid absorption rate η% of the diaphragm soaked at 60℃ for 8h is 100-800%; 2) The thickness expansion rate B% of the diaphragm soaked at 60℃ for 8h is 1-30%; 3) The limiting oxygen index of the diaphragm is 25-41%.

3. The septum of claim 1, wherein, The thickness of the polymer coating is 0.5-12μm.

4. The septum of claim 1, wherein, The average particle size of the phosphate-modified polymer particles is 0.1-10μm.

5. The septum of claim 1, wherein, The phosphate-modified polymer particles comprise a core layer, a shell layer and a core-shell transition layer between the core layer and the shell layer; the glass transition temperature of the core layer is 80-160℃, and the glass transition temperature of the shell layer is (-50)-(-10)℃.

6. The septum of claim 5, wherein, The core layer of the phosphate-modified polymer particles comprises the following components by mass: 5-60 parts of hard monomers, 1-25 parts of cross-linking functional monomers, and 1-10 parts of water-soluble comonomers. The shell layer comprises the following components by mass: 5-60 parts of soft monomers, 5-20 parts of unsaturated phosphates, and 0.1-2 parts of initiators.

7. The septum of claim 6, wherein, Satisfy at least one of the following: a. The hard monomers comprise at least one of methyl methacrylate, ethyl methacrylate, and styrene; b. The cross-linking functional monomers comprise at least one of acrylamide, divinylbenzene, glycidyl methacrylate, vinyltriethoxysilane, vinyltrimethoxysilane, and trimethylolpropane trimethacrylate; c. The water-soluble comonomers comprise at least one of acrylic acid, methacrylic acid, maleic acid, and sodium styrene sulfonate; d. The soft monomers comprise at least one of ethyl acrylate, n-butyl acrylate, isooctyl acrylate, lauryl acrylate, lauryl methacrylate, and n-octyl methacrylate; e. The unsaturated phosphates comprise at least one of 2-hydroxyethyl methacrylate phosphate, 2-hydroxyethyl methacrylate phosphate, and alkyl acrylate phosphate; f. The initiators comprise at least one of tert-butyl hydroperoxide, sodium bisulfite, sodium salt of organic sulfinic acid derivative, vitamin C, sodium persulfate, ammonium persulfate, potassium persulfate, dibenzoyl peroxide, and azobisisobutyronitrile.

8. The septum of claim 5, wherein, The shell layer further comprises a buffering agent and deionized water.

9. The septum of claim 8, wherein, The buffering agent comprises at least one of sodium bicarbonate, disodium hydrogen phosphate, and ammonium bicarbonate.

10. The septum of claim 1, wherein, The cross-linking degree of the phosphate-modified polymer particles is 70-90%.

11. The septum of claim 1, wherein, The polymer coating comprises the following components by mass: 20-30 parts of the phosphate-modified polymer particles, 2-5 parts of an aqueous adhesive, 1-2 parts of a wetting agent, and 60-80 parts of deionized water.

12. The septum of claim 11, wherein, Satisfy at least one of the following: 1) The aqueous adhesive comprises at least one of polyvinyl alcohol, aqueous polyurethane, polyacrylonitrile, aqueous unsaturated polyester resin, and aqueous epoxy resin; 2) The wetting agent comprises at least one of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, and polyether-modified polysiloxane.

13. The septum of claim 1, wherein, The base film comprises a base material and a ceramic layer arranged on at least one side of the base material; the thickness of the ceramic layer is 1-4 microns.

14. The septum of claim 13, wherein, The thickness of the base material is 8-10 microns.

15. The septum of claim 13, wherein, The base material comprises any one of a polyvinyl film, a polypropylene film, a polyvinyl and polypropylene composite base film.

16. The septum of claim 13, wherein, The ceramic layer comprises the following components by mass: 30-38 parts of ceramic powder, 2-4 parts of binder, 0.5-1 part of dispersant, 45-55 parts of deionized water.

17. The septum of claim 16, wherein, At least one of the following is satisfied: 1) The ceramic powder comprises at least one of SiO2, Al2O3, TiO2, SnO2 and ZnO2; 2) The binder comprises at least one of polyvinylpyrrolidone, polyacrylate, polyvinyl alcohol, sodium carboxymethyl cellulose, butadiene-styrene rubber and polyacrylic acid; 3) The dispersant comprises at least one of sodium polyacrylate, ammonium polyacrylate, styrene-maleic anhydride copolymer and acrylate high molecular dispersant.

18. A secondary battery, wherein, A secondary battery comprising the separator of any one of claims 1-17 and a positive electrode sheet and a negative electrode sheet, wherein the peel strength between the separator and the positive electrode sheet is greater than or equal to 8 N / m.

19. An electrical device, comprising: A secondary battery comprising the separator of claim 18.

20. The powered device of claim 19, wherein, The electric device comprises a mobile device, an electric vehicle, an electric train, a ship and a satellite, and an energy storage system.

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