Cold-pressed high-adhesion non-fluoropolymer, coated diaphragm and preparation method of coated diaphragm

Abstract

The invention discloses a cold-pressed high-adhesion non-fluoropolymer, a coated diaphragm and a preparation method of the coated diaphragm, the cold-pressed high-adhesion non-fluoropolymer comprises non-fluoropolymer particles, the glass transition temperature of the non-fluoropolymer particles is-10 DEG C to 10 DEG C, the non-fluoropolymer particles are provided with inner cores and outer shells, the inner cores are provided with polymers A, the outer shells are provided with polymers B, and the polymers B are arranged in the outer shells. The polymer A and the polymer B are both formed by polymerizing a component C and a component D, the mass ratio of the component C in the polymer A is 85%-95%, and the mass ratio of the component C in the polymer B is 20%-30%; the coated diaphragm comprises a base diaphragm and a coating with a cold-pressed high-adhesion non-fluoropolymer, and the preparation method of the coated diaphragm comprises the following steps: firstly preparing a non-fluoropolymer particle emulsion, then preparing coating slurry, and then preparing the diaphragm. The coated diaphragm and an electrode plate have relatively strong adhesion in a cold-pressed mode (the temperature is 25-45 DEG C); and the cold pressing requirements of diaphragms and electrode plates can be met.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and particularly to a cold-pressed high-adhesion non-fluoropolymer and a method for preparing a coated separator thereof. Background Art

[0002] A lithium-ion battery mainly consists of four major parts: a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The separator is located between the positive and negative electrode sheets and plays a role of blocking and insulating. To improve problems such as the cycle performance of lithium-ion batteries, poor adhesion, and difficulty in shelling, a bonding layer is usually coated on the separator. The traditional bonding layer mainly uses PVDF. However, the bonding performance of PVDF is poor. Currently, a non-fluoropolymer with a core-shell structure has emerged on the market. When this non-fluoropolymer is applied to the bonding layer of the separator, a hot pressing method (temperature greater than 65 °C) is required to make the separator and the electrode sheet have high adhesiveness.

[0003] Nowadays, to reduce energy consumption, the bonding between the separator and the electrode sheet has gradually changed from a hot pressing method to a cold pressing method. However, the current non-fluoropolymers are not suitable for the cold pressing method, resulting in a small adhesive force between the separator and the electrode sheet under the cold pressing method, which cannot meet the cold pressing requirements of the separator and the electrode sheet. Summary of the Invention

[0004] Aiming at the deficiencies existing in the prior art, the present invention provides a cold-pressed high-adhesion non-fluoropolymer, a coated separator, and a method for preparing the coated separator, which can achieve a strong adhesive force between the coated separator and the electrode sheet under the cold pressing method (temperature of 25 °C to 45 °C), and can meet the cold pressing requirements of the separator and the electrode sheet.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A cold-pressed high-adhesion non-fluoropolymer includes non-fluoropolymer particles. The glass transition temperature of the non-fluoropolymer particles is -10 °C to 10 °C, and the non-fluoropolymer particles have a core and a shell; The core has polymer A, and the shell has polymer B. Both polymer A and polymer B are polymerized from component C and component D. Component C is a first type of polymerization monomer, and component D is a second type of polymerization monomer; The mass ratio of component C in the non-fluoropolymer particles is 33% to 56%; The mass ratio of component C in polymer A is greater than the mass ratio of component D in polymer A, and the mass ratio of component C in polymer A is 85% to 95%; The mass ratio of component C in polymer B is less than the mass ratio of component D in polymer B, and the mass ratio of component C in polymer B is 20% to 30%.

[0006] By setting non-fluorinated polymer particles composed of a core and a shell, the core has polymer A, and the shell has polymer B. Both polymer A and polymer B are polymerized from component C and component D. Component C is a first type of polymerization monomer, and component D is a second type of polymerization monomer. The mass ratio of component C in the entire non-fluorinated polymer particles is 33% - 56%; the mass ratio of component C in polymer A is 85% - 95%; the mass ratio of component C in polymer B is 20% - 30%; by using the mass ratio of component C in polymer A being greater than that of component D, it ensures that the core has a strong rigid structure and plays a role in supporting the integrity of the non-fluorinated polymer; and by using the mass ratio of component C in polymer B being less than that of component D, it ensures that the non-fluorinated polymer has a strong bonding effect during cold pressing, and the glass transition temperature of the non-fluorinated polymer particles is -10°C to 10°C. When this non-fluorinated polymer is applied to a coated separator, it can achieve a strong adhesive force (adhesive force greater than 2.5 N / m) between the coated separator and the electrode sheet under cold pressing (temperature is 25°C to 45°C), which can meet the cold pressing requirements of the separator and the electrode sheet; in addition, the non-fluorinated polymer has an inner hard and outer soft structure, the coated separator has a more appropriate compression ratio, and there is still a certain gap after the coated separator and the electrode sheet are cold-pressed and shaped, reducing the phenomenon of pore blockage after the non-fluorinated polymer is pressed and improving the battery performance.

[0007] In one embodiment, the mass ratio of polymer A in the core is greater than or equal to 98%, and the mass ratio of polymer B in the shell is greater than or equal to 98%.

[0008] In one embodiment, the first type of polymerization monomer is selected from one or more of methyl methacrylate, ethyl methacrylate, methacrylonitrile, styrene, acrylonitrile, and methacrylonitrile.

[0009] In one embodiment, the second type of polymerization monomer is selected from one or more of 1-butene, 2-ethylhexyl acrylate, isooctyl acrylate, n-butyl acrylate, and isooctyl methacrylate.

[0010] A coated separator includes a base film and a coating. The coating is coated on at least one side of the base film, and the coating has the cold-pressing high-adhesion non-fluorinated polymer described above.

[0011] In one embodiment, the non-fluorinated polymer particles in the coating are non-fluorinated polymer primary particles or non-fluorinated polymer secondary particles.

[0012] In one embodiment, the areal density of the coating is 0.02 g / m² - 0.5 g / m².

[0013] In one embodiment, the compression ratio of the coating is 60% - 80%.

[0014] In one of the embodiments, the coating is a discontinuous coating.

[0015] A method for preparing a coated separator for preparing the coated separator includes the following steps: S1. Add deionized water and an emulsifier into a reaction kettle, stir evenly, introduce nitrogen to discharge the air in the reaction kettle, adjust the pH in the reaction kettle between 7.0 and 8.0, heat and pressurize the reaction kettle until the temperature and pressure in the reaction kettle are stable; drop a first type of polymerization monomer and a second type of polymerization monomer into the reaction kettle at different rates for a period of time T1, add an initiator after stirring evenly and react for a period of time T2; then repeat dropping the first type of polymerization monomer and the second type of polymerization monomer for a period of time T3, and continue to react for a period of time T4 to obtain a core particle emulsion; S2. Adjust the temperature and pressure in the reaction kettle, drop the first type of polymerization monomer and the second type of polymerization monomer into the core particle emulsion at different rates for a period of time T5, continue to react for a period of time T6, cool down and depressurize the reaction kettle to obtain a non-fluoropolymer primary particle emulsion; S3. Add the non-fluoropolymer primary particle emulsion obtained in S2 or the non-fluoropolymer secondary particle emulsion formed by agglomerating the non-fluoropolymer primary particle emulsion into deionized water, separator glue, a stabilizer and a wetting agent, stir evenly to obtain a coating slurry, and coat the coating slurry on the surface of the base film and dry it to obtain a coated separator.

[0016] Compared with the prior art, the present invention has obvious advantages and beneficial effects. Specifically, by setting non-fluorine polymer particles consisting of a core and a shell, the core has a polymer A, the shell has a polymer B, polymer A and polymer B are polymerized by a C component and a D component, the C component is a first type of polymerized monomer, the D component is a second type of polymerized monomer, the C component accounts for 33% to 56% by weight of the entire non-fluorine polymer particle; the C component accounts for 85% to 95% by weight of the polymer A; the C component accounts for 20% to 30% by weight of the polymer B; the C component accounts for a greater mass proportion in the polymer A than the D component, thereby ensuring that the core has a strong rigid structure, which plays a role in supporting the non-fluorine polymer. The integrity of the material; and the mass proportion of component C in polymer B is less than the mass proportion of component D, ensuring that the non-fluorinated polymer has a strong bonding effect during cold pressing, and the glass transition temperature of the non-fluorinated polymer particles is -10°C to 10°C. When the non-fluorinated polymer is applied to the coated diaphragm, the coated diaphragm and the electrode sheet can have a strong bonding force (bonding force greater than 2.5N / m) under cold pressing (temperature is 25°C to 45°C), which can meet the cold pressing requirements of the diaphragm and the electrode sheet; in addition, the non-fluorinated polymer adopts a hard-inside and soft-outside structure, and the coated diaphragm has a more suitable compression ratio. There is still a certain gap between the coated diaphragm and the electrode sheet after cold pressing and finalization, which reduces the phenomenon of pore blockage of the non-fluorinated polymer after being pressed, thereby improving battery performance.

[0017] In order to more clearly explain the structural features, technical means and specific purposes and functions achieved by the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments: BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of the non-fluorinated polymer primary particles of the present invention; Figure 2 is a schematic diagram of the non-fluorinated polymer secondary particles of the present invention; Figure 3 This is a Tg test graph of a non-fluorinated polymer according to Example 1 of the present invention; Figure 4 This is a TGA test chart of the non-fluorinated polymer of Example 1 of the present invention.

[0019] Description of the accompanying drawings: 1- shell, 2- core.

[0020] like Figure 1 As shown, the present invention discloses a cold-pressed high-adhesion non-fluoropolymer, comprising non-fluoropolymer particles. The glass transition temperature Tg of the non-fluoropolymer particles is -10°C to 10°C, and the non-fluoropolymer particles have a core and an outer shell.

[0021] The core has polymer A, and the shell has polymer B. Both polymer A and polymer B are polymerized from component C and component D. Component C is a first type of polymerization monomer, and component D is a second type of polymerization monomer.

[0022] The mass percentage of component C in the non-fluoropolymer particles is 33% - 56%.

[0023] The mass percentage of component C in polymer A is greater than that of component D in polymer A, and the mass percentage of component C in polymer A is 85% - 95%.

[0024] The mass percentage of component C in polymer B is less than that of component D in polymer B, and the mass percentage of component C in polymer B is 20% - 30%.

[0025] The mass percentage of polymer A in the core is greater than or equal to 98%, and the mass percentage of polymer B in the shell is greater than or equal to 98%.

[0026] The glass transition temperature Tg of polymer A is greater than that of polymer B. The mass percentage of polymer B in the non-fluoropolymer particles is 60% - 80%. Due to the relatively low glass transition temperature Tg of polymer B, the separator can be bonded to the electrode sheet under cold pressing. When the proportion of polymer B is relatively large, it means that the mass proportion of polymer A decreases, and the overall compression ratio of the polymer increases. Although the bonding is improved, after the separator and the electrode sheet are cold-pressed, the coverage rate increases, which affects the shuttle of ions and the internal resistance becomes larger, and the cycle performance deteriorates. When the mass proportion of polymer B is relatively small, the bonding proportion that can be provided decreases, affecting the overall bonding effect. When using polymer B with a mass percentage of 60% - 80%, the separator can have relatively high adhesiveness to the electrode sheet and good cycle performance of the battery.

[0027] The first type of polymerization monomer is selected from one or more of methyl methacrylate, ethyl methacrylate, methacrylonitrile, styrene, acrylonitrile, and methacrylonitrile.

[0028] The second type of polymerization monomer is selected from one or more of 1-butene, 2-ethylhexyl acrylate, isooctyl acrylate, n-butyl acrylate, and isooctyl methacrylate.

[0029] The present invention also discloses a coated separator, including a base film and a coating. The coating is coated on at least one side of the base film, and the coating has the cold-pressing highly adhesive non-fluoropolymer.

[0030] The adhesive force between the coatings at room temperature is less than 0.5 N / m, which can prevent the separator from self-bonding during winding and has good practicability.

[0031] The adhesion force between the coating and the electrode sheet at 25°C to 45°C is greater than 2.5 N / m.

[0032] After the non-fluoropolymer particles are baked at a high temperature of 85°C, the particle size change rate of the non-fluoropolymer particles is less than 2%; the small change rate of the non-fluoropolymer particles at high temperature results in good stability of the non-fluoropolymer particles, and the particles will not collapse and block the holes of the separator after coating and drying, avoiding affecting ion shuttle.

[0033] The non-fluoropolymer particles in the coating are non-fluoropolymer primary particles or non-fluoropolymer secondary particles (refer to the appendix Figure 2 ), the D50 of the primary particles of the non-fluoropolymer particles is 0.4 μm to 0.6 μm, the secondary particles of the non-fluoropolymer particles are formed by agglomeration of primary particles, and the D50 of the secondary particles of the non-fluoropolymer particles is 3 μm to 6 μm.

[0034] The areal density of the coating is 0.02 g / m² to 0.5 g / m²; by using a coating with an areal density of 0.02 g / m² to 0.5 g / m², after the separator and the electrode sheet are cold-pressed, they have a high adhesion force.

[0035] The compression ratio of the coating is 60% to 80%.

[0036] The coating is a discontinuous coating.

[0037] The coverage rate of the discontinuous coating is 3% to 20%.

[0038] After the discontinuous coating is shaped at a temperature of 25°C to 45°C, the coverage rate is 5% to 35%; by using a coverage rate of 5% to 35%, the effective bonding area is increased, the adhesion force is improved, and the compression ratio of the coating is 60% to 80%. After the separator and the electrode sheet are cold-pressed, while ensuring the adhesion force, the battery has both a high ion shuttle ability and cycling performance.

[0039] The base film is selected from one of a single-layer PP film, a single-layer PE film, a double-layer PE / PP film, and a double-layer PP / PP film, and the thickness of the base film is 5 μm to 20 μm.

[0040] The present invention also discloses a method for preparing a coated separator, including the following steps: S1. Add deionized water and an emulsifier into a reaction kettle, stir evenly, introduce nitrogen to expel the air in the reaction kettle, adjust the pH in the reaction kettle to be between 7.0 and 8.0, heat and pressurize the reaction kettle until the temperature and pressure in the reaction kettle are stable; place the first type of polymerization monomer in a first burette, place the second type of polymerization monomer in a second burette, and respectively add the first type of polymerization monomer and the second type of polymerization monomer into the reaction kettle at different rates for a period of time T1, stir evenly and then add an initiator to react for a period of time T2; then continue to add the first type of polymerization monomer and the second type of polymerization monomer for a period of time T3. After stopping adding the first type of polymerization monomer and the second type of polymerization monomer, keep the temperature and pressure in the reaction kettle unchanged and continue to react for a period of time T4 to obtain a core particle emulsion.

[0041] It should be noted that in S1, the rates of adding the first type of polymerization monomer twice are the same, and the rates of adding the second type of polymerization monomer twice are the same. S2. Adjust the temperature and pressure in the reaction kettle, and respectively add the first type of polymerization monomer and the second type of polymerization monomer into the core particle emulsion at different rates for a period of time T5. After stopping adding the first type of polymerization monomer and the second type of polymerization monomer, keep the temperature and pressure in the reaction kettle unchanged and continue to react for a period of time T6. Cool down and depressurize the reaction kettle to obtain a non-fluoropolymer particle emulsion, wherein the non-fluoropolymer particle emulsion is a non-fluoropolymer primary particle emulsion.

[0042] S3. Add deionized water, diaphragm glue, a stabilizer and a wetting agent to the non-fluoropolymer particle emulsion obtained in S2, stir evenly to obtain a coating slurry, coat the coating slurry on the surface of a base film and dry it to obtain a coated diaphragm.

[0043] In S2, the TGA residue of the non-fluoropolymer particles in a nitrogen atmosphere is 15% - 27%.

[0044] In S2, add a small amount of polyacrylic acid glue to the obtained non-fluoropolymer primary particle emulsion, then heat to a certain temperature and stir for a period of time to make the non-fluoropolymer primary particles in the non-fluoropolymer primary particle emulsion agglomerate to form non-fluoropolymer secondary particles. After cooling, a non-fluoropolymer secondary particle emulsion is obtained.

[0045] In S3, the non-fluoropolymer secondary particle emulsion can be used to replace the non-fluoropolymer primary particle emulsion.

[0046] In S3, the stabilizer is selected from one or more of carboxymethyl cellulose, polyvinyl alcohol, sodium carboxymethyl cellulose, sodium malus spectabilis, gelatin, and polyvinyl alcohol.

[0047] In S3, the wetting agent is selected from one or more of sulfonates, phosphates, fatty acid polyoxyethylene ethers, anionic surfactants, cationic surfactants, and alkylphenol polyoxyethylene ethers.

[0048] Example 1: S1. Add 300 parts of deionized water and 1 part of sodium alkyl sulfonate to a reaction kettle, stir evenly, introduce nitrogen to expel the air in the reaction kettle, adjust the pH of the reaction to be between 7.0 and 8.0, the stirring rate is 30 rpm / min, heat the reaction kettle to 85°C and pressurize it to 5 MPa, and wait for the temperature and pressure to stabilize; separately take 35.30 parts of acrylonitrile and 64.70 parts of 2-ethylhexyl acrylate in a burette, and add acrylonitrile and 2-ethylhexyl acrylate to the reaction kettle at a rate of 4.73 parts / h and 0.77 parts / h respectively in a uniform manner. After adding for 1 h, stop adding, keep the temperature and pressure unchanged, then add 0.6 part of potassium persulfate, and react for 1 h; then repeat the addition of acrylonitrile and 2-ethylhexyl acrylate, and end after adding for 3 h, keep the temperature and pressure unchanged, and continue to react for 1 h to obtain a core particle emulsion; S2. Adjust the temperature in the reaction kettle to 78°C and the pressure to 3 MPa, and continue to add acrylonitrile and 2-ethylhexyl acrylate to the reaction kettle at a rate of 2.05 parts / h and 7.70 parts / h respectively in a uniform manner for 8 h. Keep the temperature and pressure unchanged, and after reacting for 1 h, lower the temperature and reduce the pressure to obtain a non-fluoropolymer primary particle emulsion; S3. Take 50 parts of the non-fluoropolymer primary particle emulsion synthesized by reaction, add 100 parts of deionized water and mix, 1 part of styrene-butadiene rubber emulsion, 0.1 part of sodium carboxymethyl cellulose and 0.1 part of fatty acid polyoxyethylene ether and mix, stir evenly to obtain a coating slurry containing non-fluoropolymer primary particles. Adopt the microgravure roll coating method, adjust the microgravure speed ratio, and coat the coating slurry containing non-fluoropolymer primary particles onto the Enjie 7-μm base film, and dry it in an oven to obtain a non-fluoropolymer primary particle roll-coated separator with a surface density of 0.03 g / m2.

[0049] Example 2: The difference from Example 1 is that in S1, the reaction temperature and pressure are 84°C and 4.7 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 8.93 parts / h and 0.57 parts / h respectively; in S2, the reaction temperature and pressure are 79°C and 3.2 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.25 parts / h and 5.50 parts / h respectively; in S3, adjust the microgravure speed ratio to obtain a non-fluoropolymer primary particle roll-coated separator with a surface density of 0.08 g / m2.

[0050] Example 3: The differences from Example 1 are as follows: In S1, the reaction temperature and pressure are 85°C and 4.5 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 4.57 parts / h and 0.68 parts / h respectively; in S2, the reaction temperature and pressure are 79°C and 3.5 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.77 parts / h and 7.11 parts / h respectively; in S3, the microgravure speed ratio is adjusted to obtain a non-fluoropolymer primary particle roller-coated separator with a surface density of 0.05 g / m².

[0051] Example 4: The differences from Example 1 are as follows: In S1, the reaction temperature and pressure are 84°C and 5.2 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 8.87 parts / h and 0.88 parts / h respectively; In S2, the reaction temperature and pressure are 76°C and 3.0 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 1.60 parts / h and 6.02 parts / h respectively; Before S3 and after S2, there are S2-1 and S2-2. In S2-1, 200 parts of the non-fluoropolymer primary particle emulsion are taken into another reaction kettle, heated to 45°C, then ultrasonicated for 30 min with an ultrasonic power of 600 w, 1 part of 0.1 mol / L potassium nitrate solution is added, the mechanical rotation speed and revolution speed are adjusted to 300 rpm / min and 25 rpm / min, and stirred for 2 h to obtain a non-fluoropolymer secondary particle emulsion; In S2-2, 50 parts of the non-fluoropolymer secondary particle emulsion and 35 parts of deionized water are mixed, 1 part of styrene-butadiene rubber emulsion, 0.1 part of sodium carboxymethylcellulose and 0.1 part of fatty acid polyoxyethylene ether are added, stirred evenly to obtain a coating slurry containing non-fluoropolymer secondary particles, and by means of rotary spraying, the spraying flow rate is adjusted, and the coating slurry containing non-fluoropolymer secondary particles is sprayed onto the ENJET 7-μm base film, and dried in an oven to obtain a non-fluoropolymer secondary particle spray-coated separator with a surface density of 0.15 g / m².

[0052] Example 5: The differences from Example 4 are as follows: In S1, the reaction temperature and pressure are 83°C and 4.9 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 6.75 parts / h and 0.75 parts / h respectively; in S2, the reaction temperature and pressure are 77°C and 2.9 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.19 parts / h and 6.56 parts / h respectively; the mechanical rotation rate in S2-1 is 260 rpm / min; the spraying flow rate is adjusted in S2-2 to obtain a non-fluoropolymer secondary particle spray-coated separator with a surface density of 0.30 g / m².

[0053] Example 6: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 84 °C and 5.3 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 5.74 parts / h and 1.01 parts / h respectively; in S2, the reaction temperature and pressure are 80 °C and 2.8 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.19 parts / h and 6.94 parts / h respectively; in S2-1, the mechanical rotation speed is 340 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating weight of 0.48 g / m2.

[0054] Example 7: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 87 °C and 5.3 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 5.81 parts / h and 0.44 parts / h respectively; in S2, the reaction temperature and pressure are 79 °C and 3.3 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.44 parts / h and 6.94 parts / h respectively; in S2-1, the mechanical rotation speed is 290 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating weight of 0.12 g / m2.

[0055] Example 8: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 86 °C and 4.6 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 7.36 parts / h and 0.64 parts / h respectively; in S2, the reaction temperature and pressure are 78 °C and 2.8 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 1.87 parts / h and 6.63 parts / h respectively; in S2-1, the mechanical rotation speed is 270 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating weight of 0.25 g / m2.

[0056] Example 9: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 83 °C and 5.1 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 7.70 parts / h and 1.05 parts / h respectively; in S2, the reaction temperature and pressure are 80 °C and 3.1 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.19 parts / h and 5.93 parts / h respectively; in S2-1, the mechanical rotation speed is 320 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating weight of 0.40 g / m2.

[0057] Comparative Example 1: The differences from Example 1 are as follows: in S1, the reaction temperature and pressure are 86 °C and 4.6 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 7.92 parts / h and 1.08 parts / h respectively; in S2, the reaction temperature and pressure are 79 °C and 3.3 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.0 parts / h and 6.0 parts / h respectively; in S3, the microgravure speed ratio is adjusted to obtain a non-fluoropolymer primary particle roll-coated separator with a weight of 0.1 g / m2.

[0058] Comparative Example 2: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 84 °C and 4.6 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 6.58 parts / h and 0.42 parts / h respectively; in S2, the reaction temperature and pressure are 77 °C and 3.5 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.52 parts / h and 6.48 parts / h respectively; in S2-1, the mechanical rotation speed is 295 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a weight of 0.07 g / m2.

[0059] Comparative Example 3: The differences from Example 1 are as follows: in S1, the reaction temperature and pressure are 84 °C and 4.8 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 10.88 parts / h and 1.63 parts / h respectively; in S2, the reaction temperature and pressure are 78 °C and 2.7 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 1.56 parts / h and 4.69 parts / h respectively; in S3, the microgravure speed ratio is adjusted to obtain a non-fluoropolymer primary particle roll-coated separator with a weight of 0.03 g / m2.

[0060] Comparative Example 4: The differences from Example 1 are as follows: in S1, the reaction temperature and pressure are 84 °C and 4.7 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.13 parts / h and 0.38 parts / h respectively; in S2, the reaction temperature and pressure are 78 °C and 2.9 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.93 parts / h and 8.33 parts / h respectively; in S3, the microgravure speed ratio is adjusted to obtain a non-fluoropolymer primary particle roll-coated separator with a weight of 0.07 g / m2.

[0061] Comparative Example 5: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 82 °C and 4.7 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 8.46 parts / h and 1.05 parts / h respectively; in S2, the reaction temperature and pressure are 76 °C and 3.3 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 3.10 parts / h and 4.65 parts / h respectively; in S2-1, the mechanical rotation rate is 275 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating amount of 0.30 g / m².

[0062] Comparative Example 6: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 82 °C and 5.3 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 5.40 parts / h and 0.60 parts / h respectively; in S2, the reaction temperature and pressure are 76 °C and 2.8 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 0.95 parts / h and 8.55 parts / h respectively; in S2-1, the mechanical rotation rate is 285 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating amount of 0.30 g / m².

[0063] Comparative Example 7: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 85 °C and 5.4 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 6.13 parts / h and 0.13 parts / h respectively; in S2, the reaction temperature and pressure are 78 °C and 2.5 MPa, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 2.44 parts / h and 6.94 parts / h respectively; in S2-1, the mechanical rotation rate is 325 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating amount of 0.10 g / m².

[0064] Comparative Example 8: The differences from Example 4 are as follows: in S1, the reaction temperature and pressure are 85 °C and 4.7 MPa respectively, and the dropping rates of acrylonitrile and 2-ethylhexyl acrylate are 6.00 parts / h and 2.00 parts / h respectively; in S2-1, the mechanical rotation rate is 335 rpm / min; in S2-2, the spraying flow rate is adjusted to obtain a non-fluoropolymer secondary particle spray-coated separator with a coating amount of 0.40 g / m².

[0065] I. Performance test of core-shell binder: Tg Test: Dry the non-fluoropolymer emulsion, weigh 5 - 10 mg of the sample, and measure the Tg using differential scanning calorimetry. Testing equipment: METTLER DSC3. Testing temperature range: -80 - 150 °C, heating rate: 8 °C / min. During the test, heat up and cool down for the first time to eliminate the thermal history, and then measure the Tg of the non-fluoropolymer. After the test, integrate the test curve to obtain the Tg of the test sample.

[0066] Particle Size Test: Take the non-fluoropolymer primary particle emulsion or secondary particle emulsion, add a little dispersant, stir, and measure the particle size of the non-fluoropolymer using Malvern 3000. Test refractive index: 1.50, absorption rate: 0.1, light shielding rate: 8% - 18%. Finally, obtain the particle sizes of the non-fluoropolymer primary particles and secondary particles.

[0067] Deformation Rate Test: Use a scanning electron microscope to measure the particle size of the non-fluoropolymer primary particles, measure 30 groups, and take the average value d1. Then coat the non-fluoropolymer primary particles on the separator, use an oven to bake at 85 °C for 30 min, and also use a scanning electron microscope to measure the particle size of the non-fluoropolymer primary particles after baking, measure 30 groups, and take the average value d2. Then the deformation rate W of the non-fluoropolymer primary particles = (d2 - d1) / d1 * 100%; TGA Residue Test: Dry the non-fluoropolymer emulsion, weigh 5 - 10 mg of the sample, and conduct the test using a thermogravimetric analyzer. Testing equipment: Netzsch TGA209F1 from Germany. Testing gas atmosphere: N2. Testing temperature range: room temperature to 800 °C, heating rate: 10 °C / min. After the test, integrate and read the TGA residue.

[0068] Table 1 shows the test results of the raw material properties

[0069] II. Coated Separator Performance Test 1. Air Permeability Growth Rate: 1.1 Air Permeability Growth Rate of Coated Separator: Air permeability refers to the time required for 100 ml of gas to pass through a separator with a fixed area. Air permeability growth rate of coated separator = (air permeability of coated separator - air permeability of base film) / air permeability of base film * 100%; 1.2 Air Permeability Growth Rate of Coated Separator after Cold Pressing and Shaping: Take the coated separator and laminate it with a PET film first, then put the stacked coated separator and PET film into a hot press, adjust the temperature, time, and pressure of the hot press (25 °C or 45 °C, 1 min, 5 MPa respectively) for dry pressing, then take out the pressed separator and measure its air permeability. Air permeability growth rate of coated separator after dry pressing at room temperature = (air permeability of separator after dry pressing - air permeability of separator before dry pressing) / air permeability of separator before dry pressing * 100%; 2. Coverage Rate Test: 2.1 Test for the roller coating coverage rate of the non-fluoropolymer primary particles: Using a scanning electron microscope, magnify to a magnification of 8000x, measure the particle size d1 of the core-shell structured non-fluoropolymer primary particles, and at the same time calculate the number of particles n and the picture area S at this magnification. Then the coverage rate of the non-fluoropolymer primary particles = n * π * D2 / 4S. Randomly select 30 points to test with a scanning electron microscope according to this method, calculate the coverage rates of the 30 points, and take the average value, which is the roller coating coverage rate of the non-fluoropolymer primary particles.

[0070] 2.2 Test for the spraying coverage rate of the non-fluoropolymer secondary particles: Use a fully automatic coverage rate detector ZYGD-6040FLC (Guangzhou Zhongyi Optoelectronic Technology Co., Ltd.) to test the coverage rate of the sprayed particles. Adjust the annular light source to white light at 3400K, randomly test 30 points, with each point sized 60 * 40mm, and take the average value as the coverage rate of the sprayed separator.

[0071] 2.3 Coverage rate after cold pressing and shaping of the coated separator: Take the coated separator and first laminate it with a PET film. Then place the stacked coated separator and PET film together in a hot press, adjust the temperature, time, and pressure of the hot press (25°C or 45°C, 1 min, 5 MPa respectively) for dry pressing. Then take out the dried separator and test the coverage rate of the coated separator. The testing method is the same as that in 2.1 and 2.2.

[0072] 3. Coating compression ratio test: First, take the coated separator and measure its thickness with a Mahr Millimar C1216 (testing pressure 0.25N, testing head size 12mm). Test 30 groups and take the average value of the 30 groups to obtain the thickness H1 of a single-layer coated separator. Measure the thickness H0 of the base film in the same way. Then take the coated separator and the PET film, cut them into a size of 3 cm * 8 cm, overlap the coated surface of the coated separator with the corresponding PET film, adjust the parameters of the hot press (5 MPa, 10 s, 25°C or 45°C) and then perform dry pressing. Take out the coated separator and test the thickness H2 after dry pressing. Then the coating compression ratio = (H1 - H2) / (H1 - H0) * 100% 4. Adhesion force to the electrode sheet: (Cut the coated separator and the electrode sheet (the electrode sheet is a positive electrode sheet composed of 100 parts of lithium iron phosphate + 4 parts of conductive carbon black + 7 parts of PVDF with a melting point of 150°C) into strips of 2.5 cm * 8 cm. The coated surface of the electrode sheet corresponds to and overlaps with the coated surface of the separator. Adjust the parameters of the hot press (5 MPa, 40 s, 25°C or 45°C) and then perform dry pressing. Peel the dried sample in a 180° peeling manner along the long side direction, with a peeling speed of 50 mm / min. Finally, obtain the adhesion force between the coated separator and the electrode sheet.

[0073] 5. Diaphragm self-adhesive force test: Take the coated diaphragm, cut the coated diaphragm into strips of 3 cm * 10 cm, take two diaphragms, overlap the coated surfaces correspondingly, and clamp the other two sides with PET diaphragms and put them into a hot press. Adjust the hot press parameters (0.5 MPa, 1 min, 25 °C) for dry pressing. After dry pressing, test the force required to separate the two diaphragms, which is the diaphragm self-adhesive force.

[0074] 6. Ionic conductivity performance: (Inside a glove box filled with argon, make the diaphragm into a 2016 button battery, add an appropriate amount of electrolyte (EC:PC:EMC = 2:3:2, 0.3 Mol / L LiPF6). It can be obtained by AC impedance testing in an electrochemical workstation that σ = L / (Rb * A), where σ is the ionic conductivity (mS / cm); L is the thickness of the diaphragm (cm); Rb is the intrinsic resistance of the diaphragm (Ω); A is the effective area (cm²)). 7. Capacity retention rate: The coated diaphragm, the ternary cathode electrode sheet, and the graphite anode electrode sheet are processed by a winding process. After winding, a cold pressing process (cold pressing and shaping at a temperature of 25 °C or 45 °C) is used to prepare a battery. The battery is charged and discharged 500 times at 1C, and the capacity before and after cycling is tested. The capacity retention rate = capacity after cycling / capacity before cycling.

[0075] Table 2 shows the test results of various properties of the coated diaphragm.

[0076] It can be seen from Table 2 that for the coated diaphragms prepared from the non-fluoropolymer in Examples 1 - 9, all properties are good. The adhesive force between the diaphragm and the electrode sheet under the cold pressing method is greater than 2.5 N / m. From this, it can be concluded that when the mass ratio of component C in the non-fluoropolymer to polymer A is greater than the mass ratio of component D, and the mass ratio of component C in the non-fluoropolymer to polymer B is less than the mass ratio of component D, the coated diaphragm and the electrode sheet can have a strong adhesive force under the cold pressing method (temperature is 25 °C - 45 °C).

[0077] Comparative example: When the non-fluoropolymer primary particles are coated with a high gram weight, the performance of the coated diaphragm deteriorates significantly compared to when coated with a low gram weight. When the non-fluoropolymer secondary particles are coated with a low gram weight, the performance of the coated diaphragm deteriorates significantly compared to when coated with a high gram weight. For example, in Comparative Examples 1 and 2, it is thus suitable to coat with non-fluoropolymer primary particles when the coated gram weight is low, and it is suitable to coat with non-fluoropolymer secondary particles when the coated gram weight is high.

[0078] The higher the proportion of the non-fluoropolymer outer shell in the total mass of the non-fluoropolymer, the greater the cold pressing adhesion force, but it is likely to cause self-adhesion of the separator, making it impossible to process. At the same time, the compression ratio of the non-fluoropolymer increases, affecting the air permeability and coverage rate after pressing. The performance of the coated separator deteriorates significantly, and the battery performance is relatively poor; when the proportion of the outer shell decreases, the cold pressing adhesion force of the coated separator decreases, the interfacial resistance value between the separator and the electrode sheet increases, and the battery cycle performance deteriorates, as shown in Comparative Examples 3 and 4. The higher the proportion of the first type of monomer in the outer shell of the non-fluoropolymer, the greater the overall Tg of the polymer, the weaker the adhesion force between the coated separator and the electrode sheet, the increase of the interfacial resistance value, and the deterioration of the battery cycle performance; the smaller the proportion of the first type of monomer in the outer shell, the smaller the overall Tg of the polymer, the increase of the adhesion force between the coated separator and the electrode sheet, but the coated separator is prone to self-adhesion, making it impossible to process, and the coverage rate and air permeability increase significantly after cold pressing, and the battery cycle performance deteriorates, as shown in Comparative Examples 5 and 6. The higher the proportion of the first type of monomer in the core of the non-fluoropolymer, the stronger the rigid structure of the overall polymer, the lower the compression ratio, the reduction of the effective adhesion area after cold pressing with the electrode sheet, the weakening of the adhesion, the increase of the interfacial resistance value, and the deterioration of the battery cycle performance; the lower the proportion of the first type of monomer in the outer shell, the lower the rigid structure of the polymer. When cold pressing with the electrode sheet, the non-fluoropolymer is prone to collapse, resulting in a large increase in the coverage rate and air permeability, and the battery cycle performance deteriorates, as shown in Comparative Examples 7 and 8.

[0079] In summary, the present invention provides non-fluoropolymer particles composed of a core and an outer shell. The core has polymer A, and the outer shell has polymer B. Both polymer A and polymer B are polymerized from component C and component D. Component C is the first type of polymerization monomer, and component D is the second type of polymerization monomer. The mass proportion of component C in the entire non-fluoropolymer particles is 33% - 56%; the mass proportion of component C in polymer A is 85% - 95%; the mass proportion of component C in polymer B is 20% - 30%; by using the mass proportion of component C in polymer A being greater than that of component D, it ensures that the core has a strong rigid structure and plays a role in supporting the integrity of the non-fluoropolymer; and by using the mass proportion of component C in polymer B being less than that of component D, it ensures that the non-fluoropolymer has a strong adhesion effect during cold pressing. Moreover, the glass transition temperature of the non-fluoropolymer particles is -10°C to 10°C. When this non-fluoropolymer is applied to the coated separator, it can achieve a strong adhesion force (adhesion force greater than 2.5 N / m) between the coated separator and the electrode sheet under cold pressing (temperature is 25°C to 45°C), meeting the cold pressing requirements of the separator and the electrode sheet; in addition, the non-fluoropolymer adopts an inner-hard and outer-soft structure, the coated separator has a more appropriate compression ratio, and there is still a certain gap after the coated separator and the electrode sheet are cold-pressed and shaped, reducing the phenomenon of pore blockage after the non-fluoropolymer is pressed, and improving the battery performance.

[0080] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the actual technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A cold pressed high adhesion non-fluorine polymer, characterized in that: The invention comprises non-fluorine polymer particles, wherein the glass transition temperature of the non-fluorine polymer particles is -10°C to 10°C, and the non-fluorine polymer particles have a core and an outer shell; The inner core has a polymer A, and the outer shell has a polymer B. The polymer A and the polymer B are both polymerized by a component C and a component D. The component C is a first type of polymerized monomer, and the component D is a second type of polymerized monomer. The mass proportion of the C component in the non-fluorinated polymer particles is 33% to 56%; The mass proportion of the C component in polymer A is greater than the mass proportion of the D component in polymer A, and the mass proportion of the C component in polymer A is 85% to 95%; The mass proportion of the C component in polymer B is less than the mass proportion of the D component in polymer B, and the mass proportion of the C component in polymer B is 20% to 30%.

2. The cold-pressed high-adhesion non-fluorine polymer according to claim 1, characterized in that: The mass proportion of the polymer A in the inner core is greater than or equal to 98%, and the mass proportion of the polymer B in the outer shell is greater than or equal to 98%.

3. The cold-pressed high-adhesion non-fluorine polymer according to claim 1, characterized in that: The first type of polymerizable monomer is selected from one or more of methyl methacrylate, ethyl methacrylate, methacrylonitrile, styrene, acrylonitrile and methacrylonitrile.

4. The cold-pressed high-adhesion non-fluorine polymer according to claim 1, characterized in that: The second type of polymerizable monomer is selected from one or more of 1-butene, 2-ethylhexyl acrylate, isooctyl acrylate, n-butyl acrylate, and isooctyl methacrylate.

5. A coated diaphragm, comprising a base film and a coating, wherein the coating is coated on at least one side of the base film, and the coating comprises the cold-pressed high-adhesion non-fluorine polymer according to any one of claims 1 to 4.

6. The cold-pressed high-adhesion non-fluorine polymer according to claim 5, characterized in that: The non-fluorinated polymer particles in the coating are non-fluorinated polymer primary particles or non-fluorinated polymer secondary particles.

7. The coated diaphragm according to claim 5, characterized in that The surface density of the coating is 0.02 g / m² to 0.5 g / m².

8. The coated diaphragm according to claim 5, characterized in that The compression ratio of the coating is 60% to 80%.

9. The coated diaphragm according to claim 5, characterized in that The coating is a discontinuous coating.

10. A method for preparing a coated diaphragm, for preparing the coated diaphragm according to any one of claims 5 to 9, characterized in that: The following steps are involved: S1, adding deionized water and an emulsifier into a reactor and stirring them evenly, introducing nitrogen to exhaust the air in the reactor, adjusting the pH in the reactor to between 7.0 and 8.0, heating and pressurizing the reactor until the temperature and pressure in the reactor are stable; respectively adding a first type of polymerizable monomer and a second type of polymerizable monomer to the reactor at different rates for a period of time T1, stirring them evenly, adding an initiator to react for a period of time T2; then repeatedly adding the first type of polymerizable monomer and the second type of polymerizable monomer for a period of time T3, and continuing the reaction for a period of time T4 to obtain a core particle emulsion; S2, adjusting the temperature and pressure in the reactor, respectively adding the first type of polymerizable monomer and the second type of polymerizable monomer to the core particle emulsion at different rates for a period of time T5, continuing the reaction for a period of time T6, and cooling and depressurizing the reactor to obtain a non-fluorinated polymer primary particle emulsion; S3, adding deionized water, diaphragm glue, stabilizer and wetting agent to the non-fluorine polymer primary particle emulsion obtained in S2 or the non-fluorine polymer secondary particle emulsion formed by agglomeration of the non-fluorine polymer primary particle emulsion, stirring evenly to obtain a coating slurry, applying the coating slurry to the surface of the base film and drying to obtain a coated diaphragm.

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