Core-shell type non-fluorine binder as well as preparation method and application thereof

Abstract

The invention relates to a core-shell type non-fluorine binder as well as a preparation method and application thereof. The core-shell type non-fluorine binder comprises a core structure and a shell structure, the core structure is formed by polymerizing an acrylonitrile monomer, an acrylic monomer and an acrylamide monomer, and the shell structure is formed by polymerizing an acrylonitrile monomer, an acrylate monomer and a sulfonic acid monomer. According to the scheme provided by the invention, the binder conforms to environmental protection laws and regulations, has the characteristics of good dispersity, excellent stripping force and good flexibility, can improve the dispersing performance of a main material and a conductive agent in the positive pole piece, and improves the stripping force and compaction density of the positive pole piece after coating and rolling; the energy density and the cycle performance of the lithium ion battery are effectively improved, and the lithium ion battery is suitable for the fields of consumer electronics, new energy automobile power batteries, energy storage equipment and the like.

Description

Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a core-shell non-fluorine binder and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are electrochemical energy storage devices that convert chemical energy into electrical energy and vice versa. They are widely used in consumer electronics, electric vehicles, and energy storage. The positive electrode materials typically include high-nickel ternary materials or lithium iron phosphate. These materials require a binder to maintain structural stability, especially when experiencing significant volume changes during charge and discharge. The binder not only provides mechanical strength but also ensures conductivity and ion transport in the electrode.

[0003] The primary positive electrode binder is polyvinylidene fluoride (PVDF). During the electrode manufacturing process, PVDF powder is dissolved in an NMP solvent system to create a glue solution. The main material and conductive agent are then added and stirred to create a positive electrode slurry, which is then coated onto aluminum foil to form the positive electrode. PVDF has long dominated due to its high chemical stability. However, its raw material (R142b), dichlorodifluoroethane, is a fluorocarbon that damages the ozone layer. Furthermore, in the highly alkaline environment of high-nickel positive electrodes, defluorination reactions easily occur, causing the slurry to gel, hindering battery performance.

[0004] Therefore, based on the introduction and restrictions of relevant environmental regulations within the lithium-ion battery industry, the introduction of non-fluorine binders has become a key breakthrough for the industry. Non-fluorine binders such as polyacrylonitrile-acrylic binders (PAN-AA) and hydrogenated nitrile rubber binders (HNBR) can replace the original PVDF system, which can cause environmental damage and potential risks to nature, and achieve the same functions and purposes as the main dispersing and bonding materials and conductive agents. However, due to the high Tg temperature (glass transition temperature) of polyacrylonitrile-acrylic polymers and the hard and brittle film, the electrode compaction is easily deteriorated during processing, and the peeling force is reduced after rolling, resulting in a decrease in capacity retention during the cycle. Hydrogenated nitrile rubber binders have low bonding strength and require a relatively high dosage, which will lead to a decrease in electrode density and restrict their application. Summary of the Invention

[0005] In order to solve or partially solve the problems existing in the related art, the present application provides a core-shell non-fluorine binder and its preparation method and application. The binder complies with environmental protection regulations and has the characteristics of good dispersibility, excellent peeling force and good flexibility. It can improve the dispersion performance of the main material and conductive agent in the positive electrode sheet, enhance the peeling force and compaction density of the positive electrode sheet after coating and rolling, effectively improve the energy density and cycle performance of lithium-ion batteries, and is suitable for consumer electronics, new energy vehicle power batteries, energy storage equipment and other fields.

[0006] In a first aspect, the present application provides a core-shell non-fluorine adhesive, comprising a core structure and an outer shell structure; wherein the core structure is formed by polymerizing acrylonitrile monomers, acrylic acid monomers, and acrylamide monomers, and the outer shell structure is formed by polymerizing acrylonitrile monomers, acrylate monomers, and sulfonic acid monomers.

[0007] In some embodiments, in the core structure, the mass ratio of acrylonitrile monomer, acrylic acid monomer and acrylamide monomer is (40-60): (30-50): (10-15).

[0008] In some embodiments, in the shell structure, the mass ratio of acrylonitrile monomer, acrylic acid ester monomer, and sulfonic acid monomer is (10-30): (60-80): (10-15).

[0009] In some embodiments, in the binder, the mass ratio of the core structure to the shell structure is (30-45): (55-70).

[0010] In some embodiments, the acrylic monomer is selected from at least one of itaconic acid, maleic acid, 2-furan acrylic acid, 2-thiophene acrylic acid, 2-ethyl acrylic acid, 2-vinylpyridine acrylic acid, 2-benzyl acrylic acid, 2-phenyl acrylic acid, and methacrylic acid.

[0011] In some embodiments, the acrylamide monomer is selected from at least one of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, and N-butylmethacrylamide.

[0012] In some embodiments, the acrylic acid ester monomer is selected from at least one of butyl methacrylate, isobutyl methacrylate, 4-hydroxybutyl acrylate, 5-hydroxypentyl acrylate, and 2,3-dihydroxypropyl acrylate.

[0013] In some embodiments, the sulfonic acid monomer is selected from at least one of vinyl sulfonic acid, sodium vinyl sulfonate, sodium allyl sulfonate, and sodium β-styrene sulfonate.

[0014] In some embodiments, the binder particle size D50 is ≤ 70 μm.

[0015] A second aspect of the present application provides a method for preparing a core-shell non-fluorine binder, comprising the following steps: 1) mixing seed monomers in a dispersion, adding an initiator to cause a polymerization reaction, and obtaining a first suspension containing a core structure; the seed monomers are acrylonitrile monomers, acrylic acid monomers, and acrylamide monomers; 2) adding reactive monomers to the first suspension, and then adding an initiator to cause polymerization reaction, thereby obtaining a second suspension containing the core-shell type non-fluorine binder; the reactive monomers are acrylonitrile monomers, acrylic acid ester monomers and sulfonic acid monomers.

[0016] In some embodiments, the polymerization reaction temperature in step 1) is 40° C. to 110° C., the reaction pressure is 0.1 MPa to 1 MPa, and the reaction time is 4 h to 6 h.

[0017] In some embodiments, the amount of the initiator added in step 1) is 0.5% to 1% of the total mass of the seed monomer.

[0018] In some embodiments, the polymerization reaction temperature in step 2) is 50° C. to 80° C., the reaction pressure is 0.1 MPa to 1 MPa, and the reaction time is 6 h to 8 h.

[0019] In some embodiments, the amount of the initiator added in step 2) is 0.6% to 1% of the total mass of the reaction monomers.

[0020] The third aspect of the present application provides a positive electrode plate, comprising a current collector and a positive electrode material layer, wherein the positive electrode material layer is formed by coating a positive electrode slurry containing a positive electrode active material, a conductive agent and a binder on the surface of the current collector; wherein the binder is selected from the above-mentioned core-shell type non-fluorine binder or is prepared by the above-mentioned method.

[0021] In some embodiments, the positive electrode slurry has a solid content of ≥74% and a viscosity of 4000 cps to 8000 cps.

[0022] In some embodiments, based on the total mass of the positive electrode active material, the conductive agent, and the binder being 100%, the added amount of the binder is 1% to 2.5%.

[0023] A second aspect of the present application provides a lithium-ion battery comprising the above-mentioned positive electrode plate.

[0024] The technical solution provided in this application may include the following beneficial results: the use of the core-shell non-fluorine binder described in this application can not only meet environmental protection requirements, but also have high strength, toughness and high bonding properties, making it more suitable for positive electrode plates, and the preparation method is simple and low-cost, which is conducive to large-scale promotion and application.

[0025] The core-shell non-fluorine binder described in this application can also make the positive electrode main material (i.e., positive electrode active material) and the conductive agent more evenly dispersed, and the overall stability of the positive electrode slurry is good; it is beneficial to improve the fluidity of the slurry and the slurry coating interface. The interface after coating is uniform, free of particle scratches, and has good overall consistency; it also makes the positive electrode sheet flexible, the peeling force is significantly improved, and the internal resistance of the membrane is improved to a certain extent. The high-strength core constructed by acrylonitrile, acrylic acid, and acrylamide in the inner layer can ensure the strength of the binder during the cycle and the cohesion in the positive electrode sheet; and by introducing the soft monomer acrylate and the strong bonding sulfonic acid monomer, on the one hand, the flexibility of the binder is improved, the bonding area of ​​the binder to the electrode sheet and the toughness of the electrode sheet are improved, and on the other hand, the introduction of the sulfonic acid monomer can improve the dispersion of the main material particles, and improve the bonding to the main material and the conductive agent, thereby improving the capacity retention rate of the battery cell in the later stage of high-temperature cycling.

[0026] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other objects, features and advantages of the present application will become more apparent by describing in more detail exemplary embodiments of the present application in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the present application.

[0028] Figure 1 This is a schematic structural diagram of the core-shell non-fluorine binder shown in Example 1 of the present application. DETAILED DESCRIPTION

[0029] The embodiments of the present application will be described in more detail below. It should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present application more thorough and complete, and to fully convey the scope of the present application to those skilled in the art.

[0030] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit the application. Unless otherwise defined, all terms used herein have the same meaning as those generally understood by those of ordinary skill in the art to which the present invention belongs. Although any methods and materials equivalent to the methods and materials described herein can also be used in the implementation or testing of the present invention, preferred methods and materials are now described.

[0031] It should be understood that although the terms "first", "second", "third", etc. may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. Features defined as "first" or "second" may explicitly or implicitly include one or more of these features. The singular forms "a", "said", and "the" used in this application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0032] Where a numerical range is provided, it is understood that each intervening value between the upper and lower limits of the range and any other specified or intervening values ​​in the specified range is encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included in the smaller range and are also encompassed within the present invention, subject to any explicitly excluded limits in the specified range. Where a specified range includes one or two limits, ranges excluding either or both of those included limits are also encompassed within the present invention. In the description of this application, the meaning of "multiple" is two or more, unless otherwise specifically defined.

[0033] Positive electrode binders such as PVDF have long dominated due to their high chemical stability. However, their raw material, R142b difluorochloroethane, is a fluorocarbon that can damage the ozone layer. Furthermore, in the highly alkaline environment of high-nickel positive electrodes, defluorination reactions easily occur, leading to gelation of the slurry and restricting battery performance. Non-fluorinated binders such as polyacrylonitrile-acrylic binders (PAN-AA) and hydrogenated nitrile-butadiene rubber (HNBR) can replace the existing PVDF system, which has problems such as environmental damage and potential risks to nature, achieving the same functions and purposes as the main dispersing and bonding material and conductive agent. However, due to the high Tg (glass transition temperature) of polyacrylonitrile-acrylic polymers, the film is hard and brittle, which can lead to poor electrode compaction during processing and reduced peel strength after rolling, resulting in decreased capacity retention during cycling. Hydrogenated nitrile-butadiene rubber binders have lower bonding strength and require relatively high dosage, which can lead to reduced electrode density. Furthermore, they pose a risk of swelling at high temperatures, making them unsuitable for high-temperature energy storage applications.

[0034] In response to the above problems, the embodiments of the present application provide a core-shell non-fluorine binder and a preparation method thereof, as well as the application of the binder in positive electrode sheets and lithium-ion batteries. The binder complies with environmental protection regulations and has the characteristics of good dispersibility, excellent peeling force and good flexibility. It can improve the dispersion performance of the main material and conductive agent in the positive electrode sheet, enhance the peeling force and compaction density of the positive electrode sheet after coating and rolling, and effectively improve the energy density and cycle performance of the lithium-ion battery.

[0035] The core-shell non-fluorine binder provided in the embodiment of the present application includes a core structure and a shell structure, wherein the core structure is formed by polymerizing acrylonitrile monomer, acrylic acid monomer and acrylamide monomer, and the shell structure is formed by polymerizing acrylonitrile monomer, acrylate monomer and sulfonic acid monomer.

[0036] It should be noted that the core-shell non-fluorine binder provided in the embodiments of the present application is suitable for the positive electrode sheet of a lithium-ion battery.

[0037] This core-shell non-fluorinated binder contains no ozone-depleting fluorocarbons and is independent of the toxic solvent NMP (N-methylpyrrolidone). It is soluble in both aqueous and oil-based solvents, meeting environmental protection requirements. The core-shell structure, formed by the polymerization of acrylonitrile, acrylic acid, and acrylamide monomers, features high-strength, high-Tg functional groups. The appropriate monomer ratio facilitates bonding and connecting the primary material particles and the conductive agent, and helps adhere the positive electrode slurry to the positive current collector surface, forming a structurally stable positive electrode material layer without causing the film to become brittle. The shell, formed by the polymerization of acrylonitrile, acrylic acid, and sulfonic acid monomers, features highly elastic, tough, and highly dispersible functional groups. This improves the overall flexibility of the film, enhances the toughness of the electrode during the coating process, and improves the compaction density and peel strength of the electrode after rolling. It also improves the dispersion of the conductive agent and primary material particles, reduces the internal resistance of the electrode after coating and rolling, and enhances the capacity retention rate in the later stages of the battery cell cycle.

[0038] In some embodiments, both the core structure and the shell structure are formed by suspension polymerization.

[0039] As can be understood, suspension polymerization is mainly used to synthesize beaded or granular polymers. Its basic principle is to disperse water-insoluble monomers in water in the form of droplets, disperse the droplets through mechanical stirring and dispersants, and the initiator dissolves in the monomer to initiate the polymerization reaction, eventually forming polymer particles with uniform particle size.

[0040] The core-shell non-fluorine binder is formed by suspension polymerization, which does not require a complicated synthesis process, and the raw materials are simple and easy to obtain, low in cost, and suitable for large-scale production; it is conducive to the large-scale application of the core-shell non-fluorine binder.

[0041] In some specific embodiments, in the core structure, the mass ratio of acrylonitrile monomer, acrylic acid monomer and acrylamide monomer is (40-60): (30-50): (10-15).

[0042] In some specific embodiments, in the shell structure, the mass ratio of acrylonitrile monomer, acrylic acid ester monomer and sulfonic acid monomer is (10-30): (60-80): (10-15).

[0043] In some specific embodiments, in the core-shell non-fluorine binder, the mass ratio of the core structure to the shell structure is (30-45): (55-70).

[0044] Through the reasonable proportion of the core structure monomer composition and the shell structure monomer composition and the proportion of the core structure and the shell structure, the core-shell type non-fluorine binder has both a high-strength core and a high-toughness and high-bonding shell, and the core and shell structures have a good synergistic effect, which is beneficial to the bonding of the main material particles and the conductive agent, and is also beneficial to the adhesion of the positive electrode slurry to the surface of the positive electrode collector; at the same time, the high strength, toughness and high dispersion structure of the outer layer can effectively improve the toughness of the electrode during the coating process and the compaction density and peeling force of the electrode after rolling, thereby improving the battery cycle capacity retention rate.

[0045] In some specific embodiments, the acrylic monomer is selected from at least one of itaconic acid, maleic acid, 2-furan acrylic acid, 2-thiophene acrylic acid, 2-ethyl acrylic acid, 2-vinylpyridine acrylic acid, 2-benzyl acrylic acid, 2-phenyl acrylic acid, and methacrylic acid.

[0046] In some specific embodiments, the acrylamide monomer is selected from at least one of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, and N-butylmethacrylamide.

[0047] In some specific embodiments, the acrylic acid ester monomer is selected from at least one of butyl methacrylate, isobutyl methacrylate, 4-hydroxybutyl acrylate, 5-hydroxypentyl acrylate, and 2,3-dihydroxypropyl acrylate.

[0048] In some specific embodiments, the sulfonic acid monomer is selected from at least one of vinyl sulfonic acid, sodium vinyl sulfonate, sodium allyl sulfonate, and sodium β-styrene sulfonate.

[0049] The core-shell non-fluorine binder of the embodiment of the present application is synthesized by suspension polymerization and has a particle size D50 ≤ 70 μm.

[0050] The core-shell non-fluorine binder of the embodiment of the present application can be anchored and bonded to the surface of the main material particles and the conductive agent particles through its highly dispersed shell functional groups, thereby improving the dispersion performance of the positive electrode main material and the conductive agent in the positive electrode slurry, and can also improve and reduce the slurry viscosity to a certain extent, enhance the slurry fluidity, and facilitate the coating of the slurry on the surface of the positive electrode current collector; and the flexibility-enhancing functional groups therein can improve the flexibility of the electrode, enhance the electrode peeling force after coating and rolling, and enhance the compaction density of the electrode, thereby enhancing the energy density of the battery cell.

[0051] The present invention also provides a method for preparing a core-shell non-fluorine binder, which comprises the following steps: 1) mixing seed monomers in a dispersion, adding an initiator to cause a polymerization reaction, and obtaining a first suspension containing a core structure; the seed monomers are acrylonitrile monomers, acrylic acid monomers, and acrylamide monomers; 2) adding reactive monomers to the suspension, and then adding an initiator to cause polymerization reaction, thereby obtaining a second suspension containing the core-shell type non-fluorine binder; the reactive monomers are acrylonitrile monomer, acrylate monomer and sulfonic acid monomer.

[0052] The polymerization in the above step 1) and step 2) can both be suspension polymerization, and the binder particles with a particle size D50≤70 μm are obtained by suspension polymerization.

[0053] In some embodiments, step 1) includes: 1-1) Dispersing a dispersant in an aqueous solvent to prepare a dispersion; 1-2) Acrylonitrile monomer, acrylic acid monomer and acrylamide monomer are mixed in a dispersion, and an initiator is added to cause a polymerization reaction to obtain a first suspension containing a core structure.

[0054] The dispersant is selected from at least one of sodium carboxymethyl cellulose, polyvinyl alcohol, sodium polyacrylate, sodium lauryl sulfate, and hexadecyltrimethylammonium bromide.

[0055] After the dispersant is dispersed in the aqueous solvent in step 1-1), it can be stirred at a speed of 100 rpm to 600 rpm to ensure that it is fully and evenly dispersed. Furthermore, the prepared dispersion can be pressurized to a pressure range of 0.1 MPa to 1 MPa.

[0056] In some embodiments, the amount of dispersant used is 0.5% to 3% of the total weight of the monomers. For example, it can be 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, or any value within the above range. An appropriate amount of dispersant and a pre-prepared dispersion liquid are beneficial to the dispersion stability of the monomers, prevent monomer aggregation or agglomeration, ensure uniform and controllable polymerization reaction, and obtain polymer particles with uniform particle size and regular morphology.

[0057] In some specific embodiments, in step 1-2), the mass ratio of the seed monomers acrylonitrile monomer, acrylic acid monomer, and acrylamide monomer is (40-60): (30-50): (10-15).

[0058] In some specific embodiments, the polymerization reaction temperature of step 1-2) is 40°C to 110°C, preferably 40°C to 80°C; the reaction pressure is 0.1 MPa to 1 MPa, preferably 0.1 MPa to 0.5 MPa; and the reaction time is 4 h to 6 h.

[0059] In some specific embodiments, the initiator in step 1-2) is selected from a redox initiator or an azo initiator; specifically, it can be selected from azobisisobutyronitrile AIBN, azobisisobutyramidine hydrochloride VA-044, benzoyl peroxide BPO, dicumyl peroxide DCP, etc.

[0060] The amount of initiator added is 0.5% to 1% of the total mass of the seed monomer, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., or any value within the above range.

[0061] In some specific embodiments, in step 1-2), the seed monomer is added to the dispersion and then stirred at a speed of 100 rpm to 500 rpm, and the initiator is added and then stirred at a speed of 400 rpm to 500 rpm.

[0062] The above steps 1-2) are specifically as follows: Acrylonitrile monomer, acrylic acid monomer and acrylamide monomer are added to the dispersion, and the mixture is thoroughly stirred at a speed of 100 rpm to 500 rpm. The reaction temperature is adjusted to 40°C to 110°C, and the pressure of the reactor is 0.1 MPa to 1 MPa. An initiator is added in an amount of 0.5% to 1% of the total mass of the seed monomer, and the mixture is thoroughly stirred at a speed of 400 rpm to 500 rpm. Under the above temperature and pressure reaction conditions, the reaction is continued for 4 hours to 6 hours to obtain a first suspension containing a core structure.

[0063] In the first suspension, the particle size of the core structure is between 25 μm and 35 μm, and the viscosity of the first suspension is between 150 cps and 350 cps.

[0064] The kernel structure is as follows:

[0065] Wherein, a, b, and c in the above formula represent the degree of polymerization, a:b:c=(40~60):(30~50):(5~10).

[0066] A high-strength hard core design is made in the inner layer of the binder. The high-strength inner core constructed with acrylonitrile, acrylic acid, and acrylamide can ensure the strength of the binder during the cycle and the cohesion in the positive electrode.

[0067] In some specific embodiments, the mass ratio of the reaction monomers acrylonitrile monomer, acrylic acid ester monomer and sulfonic acid monomer in step 2) is (10-30): (60-80): (10-15).

[0068] In some specific embodiments, the polymerization reaction temperature in step 2) is 40°C to 110°C, preferably 50°C to 80°C; the reaction pressure is 0.1 MPa to 1 MPa, preferably 0.1 MPa to 0.5 MPa; and the reaction time is 6 h to 8 h.

[0069] In some specific embodiments, the initiator in step 2) is selected from a redox initiator or an azo initiator; specifically, it can be selected from azobisisobutyronitrile AIBN, azobisisobutyramidine hydrochloride VA-044, benzoyl peroxide BPO, dicumyl peroxide DCP, etc.

[0070] The amount of initiator added is 0.6% to 1% of the total mass of the reacting monomers, for example, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., or any value within the above range.

[0071] In some specific embodiments, in step 2), the reaction monomers are added to the first suspension and then stirred at a speed of 200 rpm to 600 rpm, and the initiator is added and then stirred at a speed of 300 rpm to 600 rpm.

[0072] The above step 2) is specifically as follows: Add the dispersion to the first suspension, then add acrylonitrile monomer, acrylate monomer and sulfonic acid monomer, stir thoroughly at a speed of 200 rpm to 600 rpm, adjust the reaction temperature to 40°C to 110°C, and the reactor pressure to 0.1 MPa to 1 MPa; add an initiator in an amount of 0.6% to 1% of the total mass of the reaction monomers, and stir thoroughly at a speed of 300 rpm to 600 rpm. Continue the reaction under the above temperature and pressure reaction conditions for 6 hours to 8 hours. When the conversion rate reaches 95%, add a terminator to terminate the reaction to obtain a second suspension containing a core-shell non-fluorine binder.

[0073] Wherein, in the second suspension, the particle size of the core-shell non-fluorine binder is ≤70 μm, and the viscosity of the second suspension is between 200 cps and 700 cps.

[0074] It can be understood that the above-mentioned stopper can be selected from thiol substances, such as dodecanethiol.

[0075] The structure of core-shell non-fluorinated binder is as follows:

[0076] Wherein, m, n, and p represent the degree of polymerization, m:n:p = (10-30): (60-80): (10-15); X represents a hydrogen group, a halogen-substituted or unsubstituted alkyl group of 2 to 8 carbon atoms.

[0077] A soft structure design is made on the outer layer of the adhesive. By introducing soft monomer acrylate and strong bonding sulfonic acid monomer, on the one hand, the flexibility of the adhesive is improved, and the bonding area of ​​the adhesive to the electrode and the toughness of the electrode are improved. On the other hand, the introduction of sulfonic acid monomer can improve the dispersion of the main material particles, and enhance the bonding between the main material and the conductive agent, thereby improving the capacity retention rate of the battery cell in the later stage of high-temperature cycling.

[0078] An embodiment of the present application further provides a positive electrode plate, which includes a positive electrode current collector and a positive electrode material layer located on the surface of the positive electrode current collector. The positive electrode material layer is formed by coating a positive electrode slurry on the surface of the positive electrode current collector.

[0079] The positive electrode current collector mentioned in the embodiments of this application is not particularly limited, as long as it is conductive and does not cause adverse chemical changes in the battery. It can be any material known to be suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector can be a metal material such as aluminum, stainless steel, nickel plating, titanium, tantalum, or a carbon material such as carbon cloth or carbon paper; preferably, aluminum foil.

[0080] The positive electrode material layer contains a positive electrode active material, a conductive agent, and a binder, wherein the binder is the core-shell non-fluorine binder described above. The positive electrode active material primarily provides a source of lithium ions and can be selected from lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium manganese oxide (LMO), lithium vanadium phosphate (LVP), etc. The conductive agent improves the conductivity of the electrode and can be selected from superconducting carbon black (SP), acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotubes (CNT), etc.

[0081] Based on the total mass of the positive electrode active material, the conductive agent, and the binder as 100%, the amount of the binder added is 1% to 2.5%, preferably 1.2% to 1.5%, and specifically, for example, 1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.5%, or any value within the above range.

[0082] Specifically, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (97.4-98): (0.8-1.5): (1.2-1.5).

[0083] The positive electrode slurry may also include a solvent, such as N-methylpyrrolidone (NMP) or water, to achieve a desired viscosity after mixing the positive electrode material, optional binder, and conductive agent. When NMP is used as the solvent, the viscosity of a 7% NMP slurry is 5000-7000 cps.

[0084] The preparation of positive electrode slurry includes: dispersing the non-fluorine core-shell binder in a solvent to make a glue solution, then adding a conductive agent, and adding the positive electrode active material (i.e., the main material) after uniform dispersion, and obtaining the positive electrode slurry after full dispersion.

[0085] The positive electrode slurry prepared by the above-mentioned binder is required to have a solid content of ≥74%, a viscosity of 4000cps~8000cps, and a fineness of ≤35μm.

[0086] Compared with conventional emulsion polymerized PVDF or conventional non-fluorine binders, the positive electrode slurry made with the core-shell non-fluorine binder has good fluidity, and the positive electrode active material and the conductive agent have good dispersion performance in the slurry; and its coating cross-section on the surface of the positive electrode current collector is uniform and has no abnormalities. The peeling force of the electrode after coating is improved to a certain extent, and it can also reduce the internal resistance of the membrane and improve the flexibility of the electrode, greatly improving the compaction window of the positive electrode roller pressing, thereby improving the high-temperature cycle capacity retention rate of the battery.

[0087] An embodiment of the present application also provides a lithium-ion battery, comprising the above-mentioned positive electrode plate, electrolyte, negative electrode plate and separator.

[0088] The electrolyte contains lithium salt, additives and solvent.

[0089] In some specific embodiments, the lithium salt includes one or more of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

[0090] Furthermore, the lithium salt concentration is 1.0 M to 1.5 M, for example, 1.0 M, 1.1 M, 1.2 M, 1.25 M, 1.3 M, 1.4 M, 1.5 M, or any value within the above range.

[0091] In some embodiments, the additive includes one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, propene sultone, methylene methanedisulfonate, pentafluoroethoxyphosphazene, dicyclohexylcarbonate, trimethyl imide phosphate, and hexamethylene diisocyanate. Fluorinated ethylene carbonate is preferred. Specifically, the concentration of fluoroethylene carbonate in the electrolyte is 0.05M to 0.5M, preferably 0.1M to 0.25M. Specific examples include 0.05M, 0.1M, 0.15M, 0.2M, 0.25M, 0.3M, 0.35M, 0.4M, 0.45M, 0.5M, or any value within the aforementioned range.

[0092] The fluoroethylene carbonate in the electrolyte can also be expressed as a mass fraction, and its addition amount can be 1wt% to 3wt%; for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.5wt%, 3wt%; preferably 2wt% to 2.5wt%.

[0093] In some specific embodiments, solvent comprises one or more in ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethyl propyl carbonate, ethyl propionate, propyl propionate, ethyl fluoroacetate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, propylene carbonate, gamma-butyrolactone, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl propionate, methyl butyrate, ethyl n-butyrate, methyl acrylate, ethyl acrylate.Preferably, solvent is selected from ethylene carbonate and ethyl methyl carbonate.More preferably, in solvent, the volume ratio of ethylene carbonate and ethyl methyl carbonate is (1~9):(1~9), specifically such as 1:9,2:8,3:7,4:6,5:5,6:4,7:3 etc., or any ratio within the above-mentioned range.

[0094] In some specific embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on the surface of the negative electrode current collector. The negative electrode current collector mentioned in the embodiments of the present application is not particularly limited, as long as it is conductive and does not cause adverse chemical changes in the battery. Typical enriched current collectors can be, for example, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector, preferably copper foil.

[0095] In some specific embodiments, a negative electrode active material, a binder, a conductive agent, a solvent, and the like are mixed to prepare a stable negative electrode slurry, which is then coated onto a negative electrode current collector to form a negative electrode material layer.

[0096] Among them, the negative electrode active material may include a compound capable of reversibly intercalating / deintercalating lithium ions, including a carbon-based active material, a silicon-based active material, or a mixture thereof. For example, artificial graphite, natural graphite, acetylene black, carbon nanotubes, graphene, elemental silicon, silicon-carbon composite materials, etc. The binder may be polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, and fluororubber. The solvent may include water, or an organic solvent such as N-methylpyrrolidone, in an amount such that the desired viscosity is obtained when the negative electrode active material and the optional binder and conductive agent are included.

[0097] In some specific embodiments, the separator of the battery can be a porous polymer film prepared from a polyolefin polymer (eg, ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer).

[0098] In the lithium-ion battery described herein, a separator is disposed between the positive and negative electrodes to prevent short circuits. The battery preparation process may include the following steps: overlapping the positive and negative electrode sheets via the separator, winding and folding them as needed, and then placing them within a housing; injecting an electrolyte into the housing and encapsulating the housing. Furthermore, overcurrent protection elements, guide plates, and the like may be placed within the housing as needed to prevent pressure buildup and overcharging and discharging within the electrochemical device.

[0099] In the lithium-ion battery of the embodiment of the present application, the formation condition after the battery is packaged is 0.1C charging to 4.6V.

[0100] The application fields of the lithium-ion batteries of the embodiments of the present application are not particularly limited, and can be used in consumer electronics, new energy vehicles, energy storage and other fields.

[0101] To make the present invention easier to understand, the present invention will be further described in detail below with reference to the following examples. These examples are merely illustrative and do not limit the scope of application of the present invention. Unless otherwise specified, the raw materials or components used in the present invention can be obtained through commercial channels or conventional methods.

[0102] Example 1 1) Add deionized water (approximately 55% of the reactor volume) to the reactor and introduce nitrogen to expel the remaining air. Add dispersants sodium carboxymethyl cellulose (0.25% by weight of the total monomer mass) and polyvinyl alcohol (0.3% by weight of the total monomer mass) and stir at 500 rpm to fully disperse the dispersants to obtain a dispersion. Adjust the reactor pressure to (0.7 ± 0.2) MPa.

[0103] 2) Add seed monomers (acrylonitrile: 2-phenylacrylic acid: N,N-dimethylacrylamide) to the dispersion at a ratio of 55:35:10 and stir thoroughly at 400 rpm. Adjust the reaction temperature to 60°C and the reactor pressure to approximately 0.3 MPa. Add initiator AIBN (0.6% by weight of the total seed monomer mass) and stir thoroughly at 500 rpm. Under these temperature and pressure conditions, react for 6 hours to obtain a first suspension containing the core bond. The particle size of the core structure is about 30 μm, and the viscosity of the suspension is about 250 cps.

[0104] 3) Add the dispersion to the reactor, followed by the monomers acrylonitrile: butyl methacrylate: vinyl sulfonic acid (20:65:15) (the mass ratio of the total mass of the seed monomers to the total mass of the monomers is 45:55). Disperse the mixture at 500 rpm and stir thoroughly. Adjust the reaction temperature to 70°C and the reactor pressure to approximately 0.5 MPa. Add the initiator AIBN (0.7% by weight of the total mass of the monomers) and stir thoroughly at 500 rpm. Continue the reaction at these temperature and pressure conditions for 8 hours. Once the conversion reaches 95%, add the terminator dodecanethiol to terminate the reaction, yielding a second suspension containing the core-shell non-fluorinated binder.

[0105] The core-shell type non-fluorine binder has a particle size D50≤70um and a second suspension viscosity of 500 cps. Figure 1 shown.

[0106] Example 2: The difference from Example 1 lies in the composition of the seed monomer in step 2).

[0107] Example 2A: The composition of the seed monomer is acrylonitrile:itaconic acid:maleic acid:methacrylamide:N,N-dimethylacrylamide=45:25:17:7:6. Other operations and parameters are the same as those in Example 1.

[0108] Example 2B: The composition of the seed monomer is acrylonitrile: 2-ethylacrylic acid: 2-phenylacrylic acid: N-hydroxymethylacrylamide: N-butylmethacrylamide = 55:15:15:7:8. Other operations and parameters are the same as those in Example 1.

[0109] Example 2C: The composition of the seed monomer is acrylonitrile: 2-thiophene acrylic acid: 2-vinylpyridine acrylic acid: methacrylamide: N-butyl methacrylamide = 40:25:25:7:3. Other operations and parameters are the same as in Example 1.

[0110] Example 2D: The composition of the seed monomer is acrylonitrile: 2-furan acrylic acid: 2-benzyl acrylic acid: acrylamide: N-butyl methacrylamide = 60:18:12:4:6. Other operations and parameters are the same as in Example 1.

[0111] Example 3: The difference from Example 2B lies in the composition of the reaction monomers in step 3).

[0112] Example 3A: The composition of the reaction monomers is acrylonitrile: isobutyl methacrylate: 4-hydroxybutyl acrylate: sodium allyl sulfonate = 30:25:32:13. Other operations and parameters are the same as those in Example 2B.

[0113] Example 3B: The composition of the reaction monomers is acrylonitrile: 4-hydroxybutyl acrylate: 2,3-dihydroxypropyl acrylate: sodium β-styrene sulfonate = 25:20:40:15. Other operations and parameters are the same as those in Example 2B.

[0114] Example 3C: The composition of the reaction monomers is acrylonitrile: 5-hydroxypentyl acrylate, 2,3-dihydroxypropyl acrylate: sodium vinyl sulfonate: sodium β-styrene sulfonate = 10:40:40:5:5. Other operations and parameters are the same as those in Example 2B.

[0115] Example 4: The difference from Example 3C is the mass ratio of the total mass of the seed monomers to the total mass of the reaction monomers.

[0116] Example 4A: The mass ratio of the total mass of the seed monomers to the total mass of the reaction monomers is 35:65. Other operations and parameters are the same as those of Example 3C.

[0117] Example 4B: The mass ratio of the total mass of the seed monomers to the total mass of the reaction monomers is 30:70. Other operations and parameters are the same as those of Example 3C.

[0118] Comparative Example 1 The difference from Example 1 is that the monomers in step 2) are added according to the ratio of acrylonitrile: acrylic acid: acrylamide: acrylic ester = 40:30:10:20; and step 3) is omitted. Other operations and parameters are the same as in Example 1.

[0119] The particle size of the synthesized non-fluorine binder is less than 70 μm and the viscosity is less than 600 cps.

[0120] Comparative Example 2 The difference from Example 1 is that in step 2), the monomers are added in a ratio of acrylonitrile:itaconic acid:maleic acid:methacrylamide:N,N-dimethylacrylamide = 55:15:15:7:8; step 3 is omitted. Other operations and parameters are the same as in Example 1.

[0121] The particle size of the synthesized non-fluorine binder is less than 70 μm and the viscosity is less than 600 cps.

[0122] Comparative Example 3 The difference from Example 1 is that 2) Evacuate the reactor to -0.09 MPa and inject vinylidene fluoride (VDF) monomer (purity ≥99.9%) via a metering pump. Seal the reactor and replace with nitrogen three times (releasing the pressure after each pressure increase to 0.5 MPa). Raise the temperature to 55°C. After the pressure stabilizes at 4.5 MPa (supercritical state), add 18 kg of vinylidene fluoride (VDF) monomer at a speed of 250 rpm. Pressurize 0.036 kg of diisopropyl peroxydicarbonate (IPP) initiator into the reactor using nitrogen. Maintain the temperature at (55 ± 1)°C for 6 h. When the conversion reaches approximately 88%, add a phenothiazine terminator to obtain PVDF particles <70 μm.

[0123] Comparative Example 4 The difference from Example 1 is that the monomer composition in step 3) is acrylonitrile: allyl carbonate: hydroxypropyl acrylate carbonate: acrylic acid sulfonate: methacrylic acid sulfonate = 35:15:25:10:15.

[0124] Performance Testing The binders prepared in the above examples and comparative examples were prepared into positive electrode slurries according to the configuration method of positive electrode slurries, and the positive electrode slurries were coated on the surface of the positive electrode collector to prepare positive electrode sheets. The performance of the positive electrode slurries and positive electrode sheets was tested.

[0125] 1) Slurry suspension stability test The binder is added to an N-methylpyrrolidone solvent and mixed evenly to form a paste. The conductive agents SP and CNT are then added and stirred to disperse evenly. Finally, the main cathode material, lithium cobalt oxide, is added and thoroughly stirred to form a uniform cathode slurry. The lithium cobalt oxide, conductive agents SP and CNT, and binder are prepared in a mass ratio of LCO:SP:CNT:binder = 97.6:0.6:0.6:1.2.

[0126] The changes in viscosity, fineness, and slurry sedimentation of the positive electrode slurries of each embodiment and comparative example were observed within 24 hours. The test results are shown in Table 1.

[0127] Table 1

[0128] Comparing the changes in the positive electrode slurries of the above examples and comparative examples reveals that the use of the modified core-shell non-fluorinated binder results in minimal changes in the positive electrode slurry viscosity, no sedimentation, and no change in fineness. Furthermore, the greater the proportion of the shell structure or the greater the number (or variety) of modifying groups, the lower the viscosity change.

[0129] However, the slurry system using conventional non-fluorine binders, such as Comparative Example 1, and the non-fluorine binder containing only an inner core layer, such as Comparative Example 2, showed a significant increase in viscosity and particle flocculation; Comparative Example 3 used a PVDF system, and its slurry stability was poor, and the fineness was significantly deteriorated; the modified group of the shell structure used in Comparative Example 4 was different from the combination of acrylonitrile, acrylate and sulfonic acid substances described in the examples of the present application, and its slurry viscosity showed a more significant increase compared with the examples.

[0130] 2) Appearance test of coated electrode The positive electrode slurry was evenly coated onto an 8μm aluminum foil for the positive electrode current collector. After coating, the thickness was controlled to 120μm. After extrusion coating, the oven temperature was set at 110°C, 120°C, 125°C, 110°C, and 105°C, respectively. The coating interface was observed for defects such as pits, scratches, and pinholes. The test results are shown in Table 2.

[0131] Table 2

[0132] According to the comparison of the coating and baking interface of the positive electrode, it can be found that the non-fluorine binder modified with acrylate and sulfonic acid on the outer layer has greatly improved the overall dispersion, the particles are more evenly dispersed, the slurry has good stability, the coating interface is more uniform, and there are no obvious particle scratches.

[0133] Conventional non-fluorine binders, such as those in Comparative Example 1, or non-fluorine binders with only an inner core layer, such as those in Comparative Example 2, exhibit poor overall slurry fluidity and a certain probability of particle scratches, leading to poor interface quality. Using PVDF as a comparative sample, such as those in Comparative Example 3, also exhibits a small amount of thick edges and particle scratches.

[0134] 3) Diaphragm internal resistance test after coating The coated positive electrode sheet was cut into small discs with a diameter of 1 cm. The internal resistance of the discs was then measured using a diaphragm resistance meter. The test results are shown in Table 3.

[0135] Table 3

[0136] By comparing the changes in the internal resistance of the positive electrode sheets of the above-mentioned embodiments and comparative examples, it can be found that the internal resistance of the positive electrode sheets coated with the slurry made of the modified core-shell non-fluorine binder is significantly reduced compared to the conventional non-fluorine binders such as those in Comparative Examples 1 and 2. The internal resistance of the diaphragm of the embodiment is also significantly reduced compared to the conventional PVDF solution such as Comparative Example 3. The combination of acrylonitrile, acrylate and sulfonic acid as the outer shell component of the embodiment of the present application also has a certain degree of reduction in the internal resistance of the diaphragm compared to the outer shell component of Comparative Example 4.

[0137] According to the comparison of various examples, it can be found that as the proportion of acrylate and sulfonic acid functional groups in the shell structure increases, and as the modification ratio of the outermost layer increases, the internal resistance of the diaphragm decreases more significantly.

[0138] 4) Electrode peeling force test after coating The coated and rolled electrode was cut into 2cm x 20cm strips and attached to a steel plate. The electrode was stretched at a speed of 5cm / min to test the tensile peel strength of the undercoated electrode. The test results are shown in Table 4.

[0139] Table 4

[0140] The peel force of the electrode sheets in the comparative examples and comparative examples after slurry coating and baking shows that the peel force of the examples can reach over 10N, a significant improvement compared to the comparative examples. Furthermore, the peel force improvement becomes more pronounced with the addition of more modified monomers in the outermost layer or with a larger proportion of the shell structure. This is primarily due to the introduction of flexible monomers, such as acrylate functional groups, on the outer surface of the designed core-shell non-fluorinated adhesive, which improves the flexibility of the electrode and, to a certain extent, increases the bonding area. The introduction of sulfonic acid functional groups further enhances the peel force of the electrode sheet.

[0141] However, since Comparative Examples 1 and 2 use conventional non-fluorine adhesives, their peeling strength performance is poor; Comparative Example 3 uses a conventional PVDF solution, and its peeling strength performance is also poor; the shell component used in Comparative Example 4 is different from the functional group of the embodiment of the present application, and its peeling strength is slightly worse than that of the embodiment.

[0142] 5) Battery DC internal resistance DCR test The negative electrode active material, graphite, was mixed with a binder (SBR-CMC) and a conductive agent (carbon black) in a weight ratio of 95:3.5:1.5 and added to water as a solvent to prepare the negative electrode slurry. The negative electrode slurry was coated onto the negative electrode current collector copper foil and then cut into negative electrode sheets with a diameter of 12 mm after drying, roller pressing, and compaction.

[0143] In an argon-filled glove box with a water content of <10 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a 1:1 volume ratio to prepare a solvent. The electrolyte was then added with lithium hexafluorophosphate (LiPF) and the additive fluoroethylene carbonate (EFC) according to the required concentrations and mixed thoroughly. The concentration of LiPF was 1.2 M and that of EFC was 0.2 M.

[0144] A polyolefin porous membrane is used as the separator.

[0145] The positive electrode binders from the above examples and comparative examples were fabricated into corresponding positive electrode sheets (see Test 2), separators, and negative electrode sheets, which were stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked sheets and separators were then wound to form a battery cell. The cell was placed in a battery case, electrolyte was injected, and then packaged. The finished lithium-ion battery was then formed (charged to 4.6V at 0.1C) and aged.

[0146] At (20±2)°C, the battery was discharged at a rate of 4C for 15 seconds, and the DCR (mΩ) of the battery cell at room temperature was compared. The test results are shown in Table 5.

[0147] Table 5

[0148] By comparing the room-temperature DCR of the examples and comparative examples, it can be clearly found that the non-fluorine-containing adhesive modified by the shell structure having acrylate and sulfonic acid functional groups has a significantly lower DCR than the conventional non-fluorine-containing adhesive formulation, reaching below 45 mΩ. In addition, the DCR decreases more significantly as the proportion of acrylate and sulfonic acid functional groups in the shell layer increases.

[0149] However, it is difficult to achieve the DCR of 50 mΩ, especially below 45 mΩ, at room temperature as described in the embodiments of the present application by using conventional non-fluorine binders such as Comparative Example 1 or Comparative Example 2, or by using PVDF solutions, as well as core-shell non-fluorine binders with other shell structures.

[0150] 6) 60℃ cycle test The lithium-ion battery prepared in the above test 5) was cycled at 1C / 1C for 500 cycles at 60°C, and the capacity retention rate (%) of the battery cell was tested.

[0151] Capacity retention rate = (500th discharge capacity / first discharge capacity) × 100% Table 6

[0152] By comparing the battery cell cycle capacity retention rates of the embodiments and comparative examples, it can be clearly found that the battery cell of the embodiment of the present application can still maintain a capacity retention rate of more than 85% after 500 cycles of high-temperature cycling, while the conventional non-fluorine binder or PVDF solution is below 85%. Therefore, the core-shell non-fluorine binder described in the embodiment of the present application is conducive to improving the cycle capacity retention rate of the battery, and can still have excellent cycle performance under high temperature conditions. This is mainly due to the use of a structure with high strength in the core and high toughness and high bonding in the outer layer, which can greatly improve the cohesion and peeling force of the binder. The polymerization design of the inner layer of acrylamide and acrylic acid can greatly retain the strength of the binder and enhance the cohesion of the binder; the outer layer improves the bonding of the binder to the main material through the introduction of acrylate and sulfonic acid functional groups, on the one hand, and improves the toughness of the electrode, improves the tensile fatigue resistance of the binder, and can ensure bonding to the main material in a long cycle. Therefore, the embodiment is relative to the comparative example, and the cycle capacity retention rate is improved.

[0153] This application designs and develops a new type of high-strength, high-toughness, high-adhesion, comprehensive core-shell non-fluorine binder and positive electrode formula, which has the following advantages: 1. Make the positive electrode main material (i.e. positive electrode active material) and conductive agent disperse more evenly, and the overall stability of the positive electrode slurry is good; 2. The new positive electrode binder is beneficial to improving the fluidity of the slurry and the slurry coating interface. The interface after coating is uniform, free of particle scratches, and has good overall consistency; 3. The new positive electrode non-fluorine binder has good flexibility, significantly improved peeling force, and improved diaphragm internal resistance to a certain extent; 4. The new positive electrode binder introduces soft monomer acrylate and strong bonding sulfonic acid monomer. On the one hand, it improves the flexibility of the binder, improves the bonding area of ​​the binder to the electrode and the toughness of the electrode. On the other hand, the introduction of sulfonic acid monomer can improve the dispersion of the main material particles, and enhance the bonding between the main material and the conductive agent, thereby improving the capacity retention rate of the battery cell in the later stage of high-temperature cycling.

[0154] The embodiments of the present application have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to the technology in the market, or to enable other persons skilled in the art to understand the embodiments disclosed herein.

Claims

1. A core-shell non-fluorine binder, characterized in that: It comprises a core structure and a shell structure; wherein the core structure is formed by polymerizing acrylonitrile monomer, acrylic acid monomer and acrylamide monomer, and the shell structure is formed by polymerizing acrylonitrile monomer, acrylate monomer and sulfonic acid monomer.

2. The core-shell non-fluorine adhesive according to claim 1, characterized in that: In the core structure, the mass ratio of acrylonitrile monomer, acrylic acid monomer and acrylamide monomer is (40-60): (30-50): (10-15); In the shell structure, the mass ratio of acrylonitrile monomer, acrylic acid ester monomer and sulfonic acid monomer is (10-30): (60-80): (10-15).

3. The core-shell non-fluorine adhesive according to claim 1, characterized in that: In the binder, the mass ratio of the core structure to the shell structure is (30-45): (55-70).

4. The core-shell non-fluorine adhesive according to claim 1, characterized in that: The acrylic acid monomer is selected from at least one of itaconic acid, maleic acid, 2-furan acrylic acid, 2-thiophene acrylic acid, 2-ethyl acrylic acid, 2-vinylpyridine acrylic acid, 2-benzyl acrylic acid, 2-phenyl acrylic acid, and methacrylic acid; And / or, the acrylamide monomer is selected from at least one of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, and N-butylmethacrylamide; And / or, the acrylic acid ester monomer is at least one selected from butyl methacrylate, isobutyl methacrylate, 4-hydroxybutyl acrylate, 5-hydroxypentyl acrylate, and 2,3-dihydroxypropyl acrylate; And / or, the sulfonic acid monomer is at least one selected from vinyl sulfonic acid, sodium vinyl sulfonate, sodium allyl sulfonate, and sodium β-styrene sulfonate.

5. The core-shell non-fluorine adhesive according to claim 1, characterized in that: The binder particle size D50 is ≤70 μm.

6. A method for preparing a core-shell non-fluorine binder, characterized in that: The following steps are involved: 1) mixing the seed monomers in the dispersion, adding an initiator to cause a polymerization reaction, and obtaining a first suspension containing the core structure; The seed monomers are acrylonitrile monomers, acrylic acid monomers and acrylamide monomers; 2) adding reactive monomers to the first suspension, and then adding an initiator to cause a polymerization reaction to obtain a second suspension comprising the core-shell non-fluorine-containing binder according to any one of claims 1 to 5; the reactive monomers are acrylonitrile monomers, acrylic acid ester monomers, and sulfonic acid monomers.

7. The preparation method according to claim 6, characterized in that The polymerization reaction temperature of step 1) is 40°C to 110°C, the reaction pressure is 0.1MPa to 1MPa, and the reaction time is 4h to 6h; And / or, the amount of the initiator added in step 1) is 0.5% to 1% of the total mass of the seed monomer; And / or, the polymerization reaction temperature in step 2) is 50° C. to 80° C., the reaction pressure is 0.1 MPa to 1 MPa, and the reaction time is 6 h to 8 h; And / or, the amount of the initiator added in step 2) is 0.6% to 1% of the total mass of the reaction monomers.

8. A positive electrode plate, characterized in that: The present invention comprises a current collector and a positive electrode material layer, wherein the positive electrode material layer is formed by coating a positive electrode slurry containing a positive electrode active material, a conductive agent and a binder on the surface of the current collector; wherein the binder is selected from the core-shell non-fluorine binder according to any one of claims 1 to 5 or is prepared by the method according to any one of claims 6 to 7.

9. The positive electrode sheet according to claim 8, characterized in that: The positive electrode slurry has a solid content of ≥74% and a viscosity of 4000cps to 8000cps.

10. The positive electrode sheet according to claim 8, characterized in that: Based on the total mass of the positive electrode active material, the conductive agent, and the binder as 100%, the added amount of the binder is 1% to 2.5%.

11. A lithium-ion battery, characterized in that: The positive electrode sheet comprises the positive electrode sheet according to any one of claims 8 to 10.

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