Composite binder composition, positive electrode slurry, positive electrode plate and lithium ion battery

Abstract

The invention provides a composite binder composition, positive electrode slurry, a positive electrode plate and a lithium ion battery, and relates to the technical field of lithium ion batteries. The composite binder composition comprises a conductive network and a binding network; the conductive network is composed of a conductive polymer and a bonding polymer; the bonding network is composed of a bonding polymer and a zwitterionic polymer; the mass ratio of the bonding polymer to the conductive polymer to the zwitterionic polymer is (90-95): (3-7): (2-3). The composite binder composition disclosed by the invention realizes high conductivity, low solvent residue, high peel strength and long cycle life through a synergistic effect of a conductive-binding dual network and zwitterionic charge balance, and provides a solution with both performance and safety for a high-energy-density lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite binder composition, positive electrode slurry, positive electrode sheet, and lithium-ion battery, and particularly to a composite binder composition, positive electrode slurry, positive electrode sheet, and lithium-ion battery based on a conductive-bonding dual network and a zwitterionic charge balance mechanism. Background Technology

[0002] With the demand for clean energy, lithium-ion battery technology has developed rapidly. Polyvinylidene fluoride (PVDF) is generally used as a binder in the positive electrode slurry, but traditional PVDF has the following three limitations:

[0003] 1. Insufficient conductivity: Traditional PVDF is an insulating polymer, which requires a high proportion of conductive agents (such as carbon black) to build a conductive network, resulting in a limited loading of active materials (usually ≤95%), making it difficult to break through the energy density barrier.

[0004] 2. Solvent sensitivity: PVDF and N-methylpyrrolidone (NMP) are prone to elimination reaction under alkaline conditions, generating conjugated double bonds and initiating cross-linking, leading to slurry gelation and electrode microcracks.

[0005] 3. Insufficient mechanical properties: High areal density electrode sheets (≥25mg / cm³) 2 During cycling, the volume expansion of the active material can easily lead to a decrease in peel strength, which in turn reduces the cycle capacity retention rate.

[0006] To address the aforementioned issues with PVDF during homogenization and application, the industry employs dispersants, such as carboxylic acid dispersants, to improve its performance. However, while styrene-maleic acid copolymers can inhibit PVDF gelation, their carboxylic acid groups readily react with residual alkali on the surface of the positive electrode active material, leading to increased interfacial impedance. Furthermore, pure NMP systems tend to remain after high-temperature drying (NMP ≥ 100 ppm), exacerbating battery polarization.

[0007] Therefore, there is an urgent need to develop a positive electrode slurry that can address the poor conductivity of PVDF binders, low slurry stability, and low interfacial impedance.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The composite binder composition of this invention solves the problems of poor conductivity and low slurry stability of traditional PVDF binders through the synergistic effect of a conductive-bonding dual network and the balance of zwitterionic charges, providing a novel solution for high-energy-density lithium-ion batteries that combines low resistance, high peel strength, and long cycle life.

[0010] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0011] In a first aspect, the present invention provides a composite adhesive composition, wherein the composite adhesive composition comprises a conductive network and an adhesive network;

[0012] The conductive network is composed of a conductive polymer and a bonding polymer;

[0013] The bonding network is composed of a bonding polymer and a zwitterionic polymer;

[0014] The mass ratio of the bonding polymer, the conductive polymer and the zwitterionic polymer is (90-95):(3-7):(2-3);

[0015] The bonding polymer is a fluoropolymer with a molecular weight of 200,000 to 1,000,000, the conductive polymer is formed by oxidative polymerization, and the zwitterionic polymer contains >15 mol of sulfonic acid groups.

[0016] Furthermore, the bonding polymer comprises polyvinylidene fluoride.

[0017] Furthermore, the molecular weight of the polyvinylidene fluoride is 200,000 to 1,000,000.

[0018] Furthermore, the zwitterionic polymer includes sulfonate betaine acrylate.

[0019] Furthermore, the conductive polymer comprises poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate and a dopant.

[0020] Furthermore, the dopant includes dimethyl sulfoxide and / or ethylene glycol.

[0021] Furthermore, the amount of the dopant added accounts for 0.1 to 0.6% of the total mass of the conductive polymer, preferably 0.3 to 0.5%.

[0022] Furthermore, the content of sulfonic acid groups in the sulfonate betaine acrylate is >15 mol%.

[0023] Furthermore, the composite adhesive composition also includes a mixed solvent.

[0024] Furthermore, the solid content of the composite adhesive composition is 1-15 wt%.

[0025] Furthermore, the mixed solvent includes cyclohexanone and N-methylpyrrolidone.

[0026] Furthermore, the volume ratio of cyclohexanone to N-methylpyrrolidone is 1:(3-5).

[0027] In a second aspect, the present invention provides a method for preparing a composite adhesive composition as described in the first aspect, the method comprising:

[0028] The binder polymer and the zwitterionic polymer are dispersed in a mixed solvent to obtain a dispersion;

[0029] The dispersion and the conductive polymer are mixed to obtain the composite binder composition.

[0030] Furthermore, the dispersion rotation speed is 400-600 rpm, and the dispersion time is 20-40 min.

[0031] Furthermore, the mixing speed is 100-300 rpm, and the mixing time is 5-15 min.

[0032] Furthermore, the dispersion temperature is below 25°C.

[0033] Thirdly, the present invention provides a positive electrode slurry, the positive electrode slurry comprising an active material, a conductive agent, and a binder in a mass ratio of (94-97):(1-3):(2-4);

[0034] The active material includes lithium nickel cobalt manganese oxide and / or lithium iron phosphate;

[0035] The conductive agent includes carbon black and / or carbon nanotubes;

[0036] The adhesive includes the composite adhesive composition as described in the first aspect.

[0037] Furthermore, the lithium nickel cobalt manganese oxide includes a high-nickel ternary lithium nickel cobalt manganese oxide material with the chemical formula Li. a Ni x Co y Mn z M b O2;

[0038] Wherein, 0.9 < a ​​< 1.1, 0.7 < x ≤ 0.94, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1; element M is one or a combination of at least two of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0039] Furthermore, the lithium nickel cobalt manganese oxide includes a medium-nickel ternary lithium nickel cobalt manganese oxide material with the chemical formula Li. a1 Ni x1 Co y1 Mn z1 M1 b1 O2;

[0040] Among them, 0.9 < a1 < 1.1, 0.4 ≤ x1 ≤ 0.7, 0.1 ≤ y1 < 0.4, 0.05 ≤ z1 < 0.4, 0 ≤ b1 ≤ 0.1, and M1 is one or a combination of at least two of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0041] Fourthly, the present invention provides a method for preparing the positive electrode paste as described in the third aspect. The method for preparing the positive electrode paste includes:

[0042] Mixing and stirring the composite binder composition, the active material, and the conductive agent to obtain the positive electrode paste.

[0043] Furthermore, the mixing and stirring are carried out under vacuum.

[0044] Furthermore, the degree of vacuum for the mixing and stirring is -0.15 to -0.05 MPa, the rotation speed of the mixing and stirring is 700 to 900 rpm, and the time for the mixing and stirring is 30 to 90 min.

[0045] Fifthly, the present invention provides a positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector;

[0046] Among them, the positive electrode coating includes the positive electrode paste as described in the third aspect.

[0047] Furthermore, the positive electrode coating includes a three-dimensional conductive network formed on the surface of the conductive polymer, the binder polymer, and the conductive agent.

[0048] Furthermore, the positive electrode current collector includes an aluminum foil current collector.

[0049] Furthermore, the areal density of the positive electrode sheet is ≥ 24.5 mg / cm 2 .

[0050] Furthermore, after the positive electrode sheet is cycled 600 times at a 1C rate, the capacity retention rate is ≥ 90%, and the peel strength of the sheet is ≥ 0.18 N / cm 2 .

[0051] Sixthly, the present invention provides a method for preparing the positive electrode sheet as described in the fifth aspect. The method for preparing the positive electrode sheet includes:

[0052] Coating the positive electrode paste on the positive electrode current collector, followed by drying and rolling to obtain the positive electrode sheet.

[0053] Seventhly, the present invention provides a lithium-ion battery. The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; among them, the positive electrode sheet includes the positive electrode sheet as described in the fifth aspect.

[0054] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0055] (1) Improved conductivity:

[0056] Dual-network synergistic conductivity mechanism: Through the π-π conjugation of PEDOT:PSS and the physical entanglement of PVDF fluorocarbon chains, a surface conductive path is formed, which can reduce the electrode resistivity without chemical cross-linking, which is superior to the traditional PVDF system.

[0057] Interface compatibility optimization: The physical entanglement of the conductive network (PEDOT:PSS) and the bonding network (PVDF) avoids the interface separation problem of traditional carbon adhesive phase structures, ensuring continuous electron-ion transport paths and reducing electrode resistivity.

[0058] (2) Slurry stability and anti-gelling:

[0059] Amphoteric charge balance mechanism: The sulfonic acid group (-SO3) of sulfonate betaine acrylate - ) and quaternary ammonium group (-N + (CH3)3) By inhibiting PVDF chain entanglement through electrostatic repulsion, the viscosity rebound rate of the slurry is much lower than that of the traditional PVDF system, thus solving the problem of PVDF elimination reaction in NMP solvent.

[0060] Solvent residue control: After drying, the cyclohexanone-NMP mixed solvent (volume ratio 1:3) has NMP residue ≤50ppm and cyclohexanone residue ≤0.3ppm, avoiding the high solvent residue risk of the pure NMP system.

[0061] (3) Mechanical properties and cycle life:

[0062] Improved peel strength: The dual-network structure enhances the cohesion of the electrode through hydrogen bonds and physical entanglement, resulting in a peel strength greater than that of traditional PVDF, effectively suppressing the shedding of active material from high areal density electrodes during cycling.

[0063] High cycle capacity retention: The zwitterionic charge balance mechanism alleviates the stress concentration caused by the volume expansion of the cathode material.

[0064] (4) Thermal stability and safety:

[0065] High temperature resistance: The sulfonic acid groups and quaternary ammonium groups of the zwitterionic polymer form a charge shielding effect, which inhibits the chain segment movement of PVDF during high temperature (>80℃) drying process, resulting in low solvent residue and no microcracks in the electrode. Attached Figure Description

[0066] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0067] Figure 1 This is a schematic diagram of the structure of a battery provided by the present invention.

[0068] Figure 2 This is a schematic diagram of the coating of the positive electrode sheet of a battery provided by the present invention.

[0069] Figure 3 This is a schematic diagram of the coating of the negative electrode sheet of a battery provided by the present invention.

[0070] Wherein, 10-shell; 20-positive terminal; 21-positive electrode post; 22-positive electrode coating area; 23-positive electrode empty foil area; 30-negative terminal; 31-negative electrode coating area; 32-negative electrode empty foil area.

[0071] Figure 4 This is a comparison chart of discharge capacity cycle life between Examples 1 and 6 and Comparative Example 1. Detailed Implementation

[0072] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0073] To provide a more detailed understanding of the features and technical content of the embodiments of the present invention, the implementation of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The accompanying drawings are for illustrative purposes only and are not intended to limit the embodiments of the present invention. In the following technical description, for ease of explanation, several details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be implemented without these details. In other cases, well-known structures and devices may be shown in a simplified manner to simplify the drawings.

[0074] The terms "first," "second," etc., used in the specification and accompanying drawings of the embodiments of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0075] In this embodiment of the invention, the terms "upper," "lower," "inner," "middle," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for better describing the embodiments of the invention and their implementations, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to require them to be constructed and operated in a specific orientation. Furthermore, some of the above terms may be used to indicate other meanings besides orientation or positional relationship; for example, the term "upper" may in some cases indicate a dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in the embodiments of the invention according to the specific circumstances.

[0076] Furthermore, the terms "set up," "connect," and "fix" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this invention according to the specific circumstances.

[0077] Unless otherwise stated, the term "multiple" means two or more.

[0078] In this embodiment of the invention, the character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0079] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0080] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0081] In a first aspect, the present invention provides a composite adhesive composition comprising a conductive network and an adhesive network;

[0082] The conductive network is composed of a conductive polymer and a bonding polymer;

[0083] The bonding network is composed of a bonding polymer and a zwitterionic polymer;

[0084] The mass ratio of the bonding polymer, the conductive polymer and the zwitterionic polymer is (90-95):(3-7):(2-3);

[0085] The bonding polymer is a fluoropolymer with a molecular weight of 200,000 to 1,000,000, the conductive polymer is formed by oxidative polymerization, and the zwitterionic polymer contains >15 mol of sulfonic acid groups.

[0086] As an optional embodiment, the bonding polymer includes polyvinylidene fluoride; the conductive polymer includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate and a dopant; and the zwitterionic polymer includes sulfonate betaine acrylate.

[0087] In this invention, the composite adhesive composition is a composite adhesive system based on a conductive-adhesive dual network and a zwitterionic charge balance mechanism; wherein, the conductive-adhesive dual network synergistic mechanism includes:

[0088] Conductive network: PEDOT:PSS forms a surface conductive path by physically entanglement with PVDF fluorocarbon chains through π-π conjugation, achieving low resistance without chemical cross-linking.

[0089] Bonding network: sulfonic acid groups (-SO3) in sulfonate betaine acrylate - ) and quaternary ammonium group (-N + (CH3)3) Improves dispersion stability by inhibiting PVDF chain entanglement through electrostatic repulsion.

[0090] Low-temperature dispersion (<25℃): to prevent PVDF crosslinking (from the Arrhenius equation K=A”·e^(-Ea / RT), the reaction rate is exponentially proportional to temperature) and solvent evaporation and gas generation.

[0091] It should be noted that the composite binder composition forms a conductive-bonding dual-network structure through physical entanglement (π-π conjugation) and hydrogen bonding, without chemical cross-linking. The physical entanglement includes the physical entanglement of the π-π conjugation of PEDOT:PSS with the fluorocarbon chains of PVDF, forming a surface conductive pathway. This achieves reduced electrode resistivity without chemical cross-linking, superior to traditional PVDF systems. The physical entanglement of the conductive network (PEDOT:PSS) and the bonding network (PVDF) avoids the interface separation problem of traditional carbon-based adhesive structures, ensuring continuous electron-ion transport paths and reducing electrode resistivity. Hydrogen bonding involves the formation of hydrogen bonds between sulfonate betaine and the sulfonic acid groups of PSS and the F atoms of PVDF, respectively enhancing the cohesion of the bonding network and bridging the conductive and bonding networks. Furthermore, the dual-network structure of this invention enhances electrode cohesion through hydrogen bonding and physical entanglement, resulting in a peel strength greater than traditional PVDF, effectively suppressing the shedding of active material from high-area-density electrodes during cycling.

[0092] As an optional embodiment, the mass ratio of the bonding polymer, the conductive polymer and the zwitterionic polymer is (90-95):(3-7):(2-3);

[0093] Among them, "90-95" can be, for example, 90, 90.5, 91, 91.5, 92, 95.5, 93, 93.5, 94, 95, etc.;

[0094] Among them, "3 to 7" can be, for example, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, etc.

[0095] Among them, "2 to 3" can be, for example, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, etc.

[0096] As an optional implementation, the molecular weight of the bonding polymer is 200,000 to 1,000,000, for example, it can be 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1,000,000, etc.

[0097] As an optional embodiment, the content of sulfonic acid groups in the zwitterionic polymer is >15 mol%, for example, it can be 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, etc.

[0098] As an optional implementation, the raw materials for preparing the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) include: 3,4-ethylenedioxythiophene (EDOT), polystyrene sulfonate (PSS), and an oxidizing agent.

[0099] As an optional implementation, the purity of the 3,4-ethylenedioxythiophene is ≥99.9%, for example, it can be 99.90%, 99.92%, 99.95%, 99.99%, etc.

[0100] As an optional implementation, the polystyrene sulfonic acid has a molecular weight of 500,000 to 1,000,000, for example, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, etc.

[0101] As an optional implementation, the polystyrene sulfonic acid contains ≥95% sulfonic acid groups, for example, 95%, 96%, 97%, 98%, 99%, etc.

[0102] As an optional implementation, the molar ratio of 3,4-ethylenedioxythiophene to polystyrene sulfonic acid is 1:(1.5-2), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc.

[0103] As an optional implementation, the oxidant includes ammonium persulfate (APS) and / or ferric chloride (FeCl3).

[0104] As an optional implementation, the molar ratio of 3,4-ethylenedioxythiophene to the oxidant is 1:(0.8 to 1.2), for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, etc.

[0105] As an optional implementation, the preparation method of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) includes:

[0106] (a) Monomer pre-dispersion: 3,4-ethylenedioxythiophene and polystyrene sulfonic acid solution were mixed and dispersed by ultrasonication to obtain a suspension;

[0107] (b) Oxidative polymerization reaction: An oxidant is added dropwise to the suspension obtained in step (a), and the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate is obtained by oxidative polymerization reaction.

[0108] As an optional implementation, in step (a), the mass percentage of polystyrene sulfonic acid in the polystyrene sulfonic acid solution is 5% to 10%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0109] As an optional implementation, in step (a), the ultrasonic dispersion temperature is 20-30°C, for example, it can be 20°C, 22°C, 24°C, 25°C, 26°C, 28°C, 30°C, etc.; the ultrasonic dispersion time is 20-40 min, for example, it can be 20°C, 22°C, 24°C, 25°C, 26°C, 28°C, 30°C, 32°C, 34°C, 35°C, 36°C, 38°C, 40°C, etc.

[0110] As an optional implementation, in step (a), the power of the ultrasonic dispersion is 600-1000W, for example, 600W, 650W, 700W, 750W, 800W, 850W, 900W, 950W, 1000W, etc.; the frequency of the ultrasonic dispersion is 25-30kHz, for example, 25kHz, 26kHz, 27kHz, 28kHz, 29kHz, 30kHz, etc.

[0111] It should be noted that the mixing of 3,4-ethylenedioxythiophene and polystyrene sulfonic acid solution in step (a) above needs to be ultrasonically dispersed at a certain power and frequency to avoid local overheating that could lead to EDOT self-polymerization.

[0112] As an optional implementation, in step (b), the oxidative polymerization reaction is carried out under stirring conditions; the temperature of the oxidative polymerization reaction is 25-30°C, for example, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, etc.; the stirring speed is 200-400 rpm, for example, 200 rpm, 220 rpm, 240 rpm, 250 rpm, 260 rpm, 280 rpm, 300 rpm, 320 rpm, 340 rpm, 350 rpm, 360 rpm, 380 rpm, 400 rpm, etc.; the time of the oxidative polymerization reaction is 6-12 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc.

[0113] It should be noted that in step (b) above, the oxidant initiates the oxidative polymerization of EDOT, and PSS, as a dopant, binds to the PEDOT chain through electrostatic interaction to form a conductive composite poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS).

[0114] As an optional implementation, in step (b), the pH value is maintained at 1.5 to 2.5 during the oxidative polymerization reaction, for example, it can be 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc.

[0115] As an optional implementation, in step (b), the pH during the oxidative polymerization reaction is adjusted by dilute sulfuric acid.

[0116] It should be noted that the reason for adjusting the pH to be within the range of 1.5 to 2.5 in step (b) above is to prevent PSS precipitation.

[0117] As an optional embodiment, the preparation method of poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS) further includes (c) a post-processing step:

[0118] Dialysis purification: Transfer the reaction solution obtained in step (b) to a dialysis bag and dialyze with deionized water to remove unreacted monomers and small molecule impurities;

[0119] Concentration and drying: The solution purified by dialysis is concentrated and dried to form a dark blue colloidal solution.

[0120] As an optional implementation, in step (c), the dialysis is performed as follows: dialysis for 48 hours, with water changed every 6 hours.

[0121] As an optional implementation, in step (c), the concentration and drying are carried out in a vacuum drying oven.

[0122] As an optional implementation, in step (c), the temperature of concentration and drying is 50 to 70°C, for example, it can be 50°C, 52°C, 54°C, 55°C, 56°C, 58°C, 60°C, 62°C, 64°C, 65°C, 66°C, 68°C, 70°C, etc.

[0123] As an optional implementation, in step (c), the concentration to a solid content of 1 to 1.5% can be, for example, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0124] As an optional embodiment, the conductive polymer includes a dopant, the dopant being dimethyl sulfoxide (DMSO) and / or ethylene glycol.

[0125] In a preferred embodiment, the conductive polymer includes a dopant, the dopant being dimethyl sulfoxide (DMSO).

[0126] It should be noted that the purpose of adding dopants to the conductive polymer in this invention is to optimize conductivity. The dopants, as PEDOT dopants, enhance conjugation and improve conductivity.

[0127] As an optional implementation, the amount of the dopant added accounts for 0.1 to 0.6% of the total mass of the conductive polymer, for example, it can be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, etc.

[0128] It should be noted that the dopant added to the conductive polymer of the present invention needs to be maintained within the above range. Otherwise, excessive dopant will weaken the physical entanglement of π-π conjugation and PVDF, resulting in a decrease in dispersion stability. At the same time, excessive doping will also cause the conductive network to loosen and reduce the strength of the bonding network. The discontinuity of the conductive network will lead to increased local polarization during cycling, reducing capacity retention and peel strength.

[0129] In a preferred embodiment, the amount of the dopant added accounts for 0.3 to 0.5% of the total mass of the conductive polymer.

[0130] As an optional implementation, the doping method of the conductive polymer includes:

[0131] A dopant was added to the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS), and the mixture was stirred to obtain a conductive polymer containing the dopant.

[0132] As an optional implementation, the stirring temperature after adding the dopant is 50-70°C, for example, 50°C, 52°C, 54°C, 55°C, 56°C, 58°C, 60°C, 62°C, 64°C, 65°C, 66°C, 68°C, 70°C, etc.; the stirring time is 1-3 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.8 hours, 3 hours, etc.

[0133] As an optional embodiment, the present invention further includes structural verification of the poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS); and detection of CS bonds (1050 cm⁻¹) by FTIR. -1 ) and COC bond (1200cm -1 ), ensuring no chemical crosslinking peak (1700 cm⁻¹) -1 peak).

[0134] As an optional implementation, the sulfonic acid group content in the sulfonate betaine acrylate is >15mol%, for example, it can be 16mol%, 17mol%, 18mol%, 19mol%, 20mol%, etc.

[0135] As an optional implementation, the molecular weight of the sulfonate betaine acrylate is 50,000 to 100,000, for example, it can be 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, etc.

[0136] As an optional implementation, the molecular weight distribution (PDI) of the sulfonate betaine acrylate is <1.5, for example, it can be 1.4, 1.3, 1.2, 1.1, 1, etc.

[0137] As an optional implementation, the raw materials for preparing the sulfonated betaine acrylate include: a main monomer, a sulfonating agent, an initiator, a solvent, and a chain transfer agent.

[0138] As an optional embodiment, in the raw materials for preparing the sulfonate betaine acrylate, the main monomer includes dimethylaminoethyl acrylate (DMAEMA).

[0139] As an optional embodiment, the purity of the dimethylaminoethyl acrylate is ≥99.5%, for example, it can be 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, etc.

[0140] As an optional embodiment, in the raw materials for preparing the sulfonated betaine acrylate, the sulfonating agent includes 1,3-propanesulfonyl lactone (PSI).

[0141] As an optional implementation, the molar ratio of DMAEMA and PSI is 1:(1.2~2), for example, it can be 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, etc.

[0142] As an optional implementation, the purity of the 1,3-propanesulfonic acid lactone is ≥99.8%, for example, it can be 99.80%, 99.85%, 99.90%, 99.95%, 99.99%, etc.

[0143] As an optional implementation, in the raw materials for preparing the sulfonate betaine acrylate, the initiator includes azobisisobutyronitrile (AIBN) and / or ammonium persulfate (APS).

[0144] As an optional implementation, the content of the initiator is 0.5% to 1.5% of the mass of the main monomer, for example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.

[0145] As an optional embodiment, the chain transfer agent in the raw materials for preparing the sulfonate betaine acrylate includes dodecyl mercaptan (DDM).

[0146] As an optional implementation, the content of the chain transfer agent is 0.1% to 0.3% of the mass of the main monomer, for example, it can be 0.1%, 0.12%, 0.14%, 0.15%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.25%, 0.28%, 0.3%, etc.

[0147] As an optional implementation, the purity of the dodecyl mercaptan is ≥95%, for example, it can be 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, etc.

[0148] As an optional implementation, the method for preparing the sulfonate betaine acrylate includes:

[0149] (A) Quaternization reaction (introduction of sulfonic acid group): DMAEMA and PSI are dissolved in a solvent and subjected to quaternization reaction to obtain the quaternized product;

[0150] (B) Free radical copolymerization (polymer chain construction): Initiator and chain transfer agent are added to the quaternized product obtained in step (A), and sulfonate betaine acrylate is obtained through free radical copolymerization.

[0151] As an optional implementation, in step (A), the solvent includes DMF.

[0152] As an optional implementation, in step (A), the solid content of the raw material mixture obtained by dissolving DMAEMA and PSI in a solvent is 20-30%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0153] As an optional implementation, in step (A), the temperature of the quaternization reaction is 25-30°C, for example, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, etc.; the time of the quaternization reaction is 12-36h, for example, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, etc.

[0154] It should be noted that the reaction temperature in step (A) must be strictly ≤30℃ to avoid side reactions (such as self-polymerization).

[0155] As an optional implementation, in step (A), the molar ratio of DMAEMA to PSI is 1:(1.2 to 2); the excess ratio of PSI directly affects the sulfonic acid content (for every 0.1 increase in the molar ratio, the sulfonic acid content increases by 5 to 8 mol%).

[0156] As an optional implementation, in step (A), when it is necessary to increase the sulfonic acid content, the PSI feed ratio can be increased (up to 1:2) or the quaternization time can be extended (up to 36h).

[0157] As an optional implementation, in step (A), when it is necessary to reduce the sulfonic acid group content, a diluent can be added for copolymerization to dilute the sulfonic acid group density.

[0158] As an optional implementation, in step (A), the molar ratio of the diluent to DMAEMA is (0.1 to 0.5):1, for example, it can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, etc.

[0159] As an optional implementation, in step (A), the diluent includes hydroxyethyl acrylate (HEA).

[0160] As an optional implementation, in step (A), the verification method includes: using nuclear magnetic resonance (NMR) 1 The degree of quaternization of the quaternized products was determined by H NMR (characteristic peak δ = 3.2–3.5 ppm).

[0161] As an optional implementation, in step (B), the free radical copolymerization reaction is carried out under a protective gas atmosphere.

[0162] As an optional implementation, in step (B), the protective gas includes nitrogen.

[0163] As an optional implementation, in step (B), the temperature of the free radical copolymerization reaction is 60-70°C, for example, 60°C, 62°C, 64°C, 65°C, 66°C, 68°C, 70°C, etc.; the time of the free radical copolymerization reaction is 6-8h, for example, 6h, 6.2h, 6.5h, 6.8h, 7h, 7.2h, 7.5h, 7.8h, 8h, etc.

[0164] It should be noted that the temperature of the free radical copolymerization reaction is 60-70℃. If the temperature is >70℃, it is easy to cause chain breakage and reduce the molecular weight.

[0165] As an optional embodiment, the method for preparing the sulfonate betaine acrylate further includes a (C) post-treatment step:

[0166] Centrifugation to remove impurities: Centrifuge the reaction solution obtained in step (B) to remove unreacted monomers and small molecule byproducts;

[0167] Dialysis purification: Transfer the centrifuged liquid to a dialysis bag and dialyze with deionized water to remove residual solvent and initiator;

[0168] Drying: The solution purified by dialysis is dried to obtain a white powdery product.

[0169] As an optional implementation, in step (C), the centrifugation speed is 7000-9000 rpm, for example, it can be 7000 rpm, 7200 rpm, 7400 rpm, 7500 rpm, 7600 rpm, 7800 rpm, 8000 rpm, 8200 rpm, 8400 rpm, 8500 rpm, 8600 rpm, 8800 rpm, 9000 rpm, etc.; the centrifugation time is 10-20 min, for example, it can be 10 min, 12 min, 14 min, 15 min, 16 min, 18 min, 20 min, etc.

[0170] As an optional implementation, in step (C), the dialysis is performed as follows: dialysis for 48 hours, with water changed every 6 hours.

[0171] As an optional implementation, in step (C), the drying temperature is 50 to 70°C, for example, it can be 50°C, 52°C, 54°C, 55°C, 56°C, 58°C, 60°C, 62°C, 64°C, 65°C, 66°C, 68°C, 70°C, etc.

[0172] As an optional implementation, in step (C), the product moisture content is dried to ≤0.5%, for example, it can be 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.05%, 0.01%, etc.

[0173] As an optional implementation, step (C) further includes sulfonic acid group detection, which includes determining the sulfur content (target > 15 mol%) by elemental analysis (EDS) or determining the sulfonic acid group concentration by acid-base titration.

[0174] As an optional embodiment, the composite adhesive composition further includes a mixed solvent.

[0175] As an optional embodiment, the solid content of the composite adhesive composition is 1 to 15 wt%, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, etc.

[0176] As an optional implementation, the mixed solvent includes cyclohexanone and N-methylpyrrolidone (NMP).

[0177] As an optional implementation, the volume ratio of cyclohexanone to N-methylpyrrolidone is 1:(3-5), for example, it can be 1:3, 1:3.2, 1:3.4, 1:3.5, 1:3.6, 1:3.8, 1:4, 1:4.2, 1:4.4, 1:4.5, 1:4.6, 1:4.8, 1:5, etc.

[0178] In a second aspect, the present invention provides a method for preparing a composite adhesive composition as described in the first aspect, the method comprising:

[0179] The binder polymer and the zwitterionic polymer are dispersed in a mixed solvent to obtain a dispersion;

[0180] The dispersion and the conductive polymer are mixed to obtain the composite binder composition.

[0181] As an optional embodiment, the bonding polymer and the zwitterionic polymer are dispersed in a mixed solvent; wherein the dispersion speed is 400-600 rpm, for example, 400 rpm, 420 rpm, 440 rpm, 450 rpm, 460 rpm, 480 rpm, 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm, 600 rpm, etc., and the dispersion time is 20-40 min, for example, 20 min, 22 min, 24 min, 25 min, 30 min, 32 min, 34 min, 35 min, 36 min, 38 min, 40 min, etc.

[0182] As an optional implementation, the dispersion temperature is below 25°C, for example, it can be 25°C, 24°C, 23°C, 22°C, 21°C, 20°C, etc.

[0183] As an optional implementation, the dispersion is carried out under vacuum; wherein the vacuum degree of the dispersion is -0.1 to -0.05 MPa, for example, it can be -0.1 MPa, -0.09 MPa, -0.08 MPa, -0.07 MPa, -0.06 MPa, -0.05 MPa, etc.

[0184] As an optional implementation, during the process of dispersing the binder polymer and the zwitterionic polymer in the mixed solvent, the raw materials are added in the following order: the binder polymer and the zwitterionic polymer are added to the mixed solvent.

[0185] As an optional embodiment, the dispersion and the conductive polymer are mixed; wherein the mixing speed is 100-300 rpm, for example, 100 rpm, 120 rpm, 140 rpm, 150 rpm, 160 rpm, 180 rpm, 200 rpm, 220 rpm, 240 rpm, 250 rpm, 260 rpm, 280 rpm, 300 rpm, etc., and the mixing time is 5-15 min, for example, 5 min, 6 min, 8 min, 10 min, 12 min, 14 min, 15 min, etc.

[0186] It should be noted that the dispersion and conductive polymer need to be mixed at the aforementioned low speed to avoid shear damage to the conductive polymer structure. PEDOT:PSS forms a surface conductive network by physically entangled with the PVDF fluorocarbon chain through π-π conjugation.

[0187] As an optional implementation, during the mixing of the dispersion and the conductive polymer, the raw materials are added in the following order: the conductive polymer is slowly added dropwise to the dispersion.

[0188] Thirdly, the present invention provides a positive electrode paste, and the positive electrode paste includes an active material, a conductive agent, and a binder with a mass ratio of (94 to 97):(1 to 3):(2 to 4).

[0189] As an optional implementation manner, the mass ratio of the active material, the conductive agent, and the binder is (94 to 97):(1 to 3):(2 to 4);

[0190] Among them, "94 to 97" can be, for example, 94, 94.5, 95, 95.5, 96, 96.5, 97, etc.;

[0191] Among them, "1 to 3" can be, for example, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, etc.;

[0192] Among them, "2 to 4" can be, for example, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, etc.

[0193] As an optional implementation manner, the active material includes lithium nickel cobalt manganese oxide and / or lithium iron phosphate.

[0194] As an optional implementation manner, the lithium nickel cobalt manganese oxide includes a high-nickel ternary lithium nickel cobalt manganese oxide material, and its chemical formula is Li a Ni x Co y Mn z M b O2;

[0195] Among them, 0.9 < a < 1.1, 0.7 < x ≤ 0.94, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1; the M element is one or a combination of at least two of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0196] As an optional implementation manner, the lithium nickel cobalt manganese oxide includes a medium-nickel ternary lithium nickel cobalt manganese oxide material, and its chemical formula is Li a1 Ni x1 Co y1 Mn z1 M1 b1 O2;

[0197] Among them, 0.9 < a1 < 1.1, 0.4 ≤ x1 ≤ 0.7, 0.1 ≤ y1 < 0.4, 0.05 ≤ z1 < 0.4, 0 ≤ b1 ≤ 0.1, and M1 is one or a combination of at least two of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0198] As an optional implementation manner, the lithium nickel cobalt manganese oxide includes LiNi 0.8 Co0.1 Mn 0.1 O2.

[0199] As an optional implementation, the lithium iron phosphate includes LiFePO4.

[0200] As an optional implementation, the conductive agent includes carbon black and / or carbon nanotubes;

[0201] As an optional implementation, the adhesive comprises a composite adhesive composition as described in the first aspect.

[0202] Fourthly, the present invention provides a method for preparing a positive electrode slurry as described in the third aspect, the method comprising:

[0203] The composite binder composition, active material, and conductive agent are mixed and stirred to obtain the positive electrode slurry.

[0204] As an optional implementation, the mixing and stirring of the composite adhesive composition, active material, and conductive agent is carried out under vacuum.

[0205] As an optional implementation, the vacuum degree of the mixing and stirring is -0.15 to -0.05 MPa, for example, it can be -0.15 MPa, -0.14 MPa, -0.12 MPa, -0.1 MPa, -0.08 MPa, -0.06 MPa, -0.05 MPa, etc.

[0206] As an optional implementation, the mixing speed is 700-900 rpm, for example, it can be 700 rpm, 720 rpm, 740 rpm, 750 rpm, 760 rpm, 780 rpm, 800 rpm, 820 rpm, 840 rpm, 850 rpm, 860 rpm, 880 rpm, 900 rpm, etc.

[0207] As an optional implementation, the mixing time is 30 to 90 minutes, for example, it can be 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, 90 minutes, etc.

[0208] As an optional implementation, during the mixing and stirring of the composite adhesive composition, active material and conductive agent, the raw materials are added in the following order: the active material and conductive agent are added to the composite adhesive composition in sequence.

[0209] As an optional implementation, the viscosity of the positive electrode slurry is 4300–4700 mPa·s, for example, it can be 4200 mPa·s, 4350 mPa·s, 4400 mPa·s, 4450 mPa·s, 4500 mPa·s, 4550 mPa·s, 4600 mPa·s, 4650 mPa·s, 4700 mPa·s, etc. (Brookfield DV2T test, 50s) -1 Shear rate.

[0210] Fifthly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive coating coated on at least one side surface of the positive current collector.

[0211] As an optional implementation, the positive electrode coating comprises the positive electrode slurry as described in the third aspect.

[0212] As an optional implementation, the positive electrode coating includes a three-dimensional conductive network formed by a conductive polymer, a binder polymer, and a conductive agent surface.

[0213] As an optional implementation, the positive current collector includes an aluminum foil current collector.

[0214] As an optional implementation, the thickness of the aluminum foil current collector is 12 μm.

[0215] As an optional implementation, the areal density of the positive electrode sheet is ≥24.5 mg / cm³. 2 For example, it could be 24.5 mg / cm³ 2 25mg / cm 2 25.5 mg / cm 2 26mg / cm 2 27mg / cm 2 28mg / cm 2 29mg / cm 2 30mg / cm 2 wait.

[0216] In a preferred embodiment, the areal density of the positive electrode sheet is 24.5–25.5 mg / cm³. 2 .

[0217] As an optional implementation, the positive electrode retains a capacity of ≥90% and a peel strength of ≥0.18 N / cm after 600 cycles at 1C. 2 .

[0218] Sixthly, the present invention provides a method for preparing a positive electrode sheet as described in the fifth aspect, the method comprising:

[0219] After the positive electrode slurry is coated onto the positive electrode current collector, it is dried and rolled to obtain the positive electrode sheet.

[0220] As an optional implementation, the drying process includes: pre-drying at 60–100°C for 1–10 min; and then main drying at 60–100°C for 10–20 min.

[0221] As an optional implementation, the pre-baking temperature is 60 to 100°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc.

[0222] As an optional implementation, the pre-baking time is 1 to 10 minutes, for example, it can be 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc.

[0223] As an optional implementation, the temperature of the main oven is 60 to 100°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, etc.

[0224] As an optional implementation, the main baking time is 10 to 20 minutes, for example, it can be 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, etc.

[0225] In a preferred embodiment, the drying process includes: pre-drying at 80°C for 5 minutes; and then main drying at 80°C for 15 minutes.

[0226] As an optional implementation, the pressure of the roller is 5 to 15 MPa, for example, it can be 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa, 12 MPa, 13 MPa, 14 MPa, 15 MPa, etc.

[0227] As an optional implementation, the compacted density of the rolled electrode sheet is 2.4–3.8 g / cm³. 3 For example, it could be 2.4 g / cm³ 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 3g / cm 3 3.1g / cm 3 3.2g / cm 33.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 wait.

[0228] In a seventh aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode comprises the positive electrode as described in the fifth aspect.

[0229] As an optional implementation, the negative electrode sheet includes a graphite negative electrode sheet.

[0230] As an optional implementation, the negative electrode sheet includes a negative current collector and a negative electrode coating coated on at least one side of the negative current collector; wherein the negative electrode coating includes a negative electrode active material.

[0231] As an optional implementation, the energy density of the lithium-ion battery is ≥250Wh / kg.

[0232] As an optional implementation method, such as Figure 1 As shown, the lithium-ion battery includes a positive electrode, a negative electrode, and a solid electrolyte stacked together. A cylindrical battery core is wound to form a cylindrical shape, with the initial winding forming the electrode end at the cylindrical axis and the final winding forming the electrode end on the outer surface of the cylinder. It also includes a cylindrical housing 10, which houses the battery core. The top is the positive terminal 20, and the bottom is the negative terminal 30. A positive electrode post 21 is disposed on the positive terminal 20.

[0233] As an optional implementation, the lithium-ion battery is further provided with a positive electrode tab and a negative electrode tab at both ends. The battery core is connected to the negative electrode busbar by welding, the negative electrode busbar is connected to the housing 10 by welding, the battery core is connected to the positive electrode busbar by welding, an insulating sheet is placed on the positive electrode busbar, the positive electrode busbar is connected to the cap by welding, and the cap is connected to the housing 10 by a groove.

[0234] As an optional implementation method, such as Figure 2 As shown, the positive electrode of the lithium-ion battery includes a positive current collector and a positive coating coated on at least one side of the positive current collector. The positive current collector includes a positive coating area 22 and a positive empty foil area 23. At least a portion of the positive empty foil area 23 serves as a positive electrode tab, and the positive empty foil area 23 occupies 1 to 10% of the area of ​​the positive current collector.

[0235] As an optional implementation method, such as Figure 2As shown, the positive electrode sheet includes a strip-shaped positive electrode foil and a positive electrode coating area 22 and a positive electrode empty foil area 23 coated on the surface of the strip-shaped positive electrode foil.

[0236] As an optional implementation method, such as Figure 3 As shown, the negative electrode sheet includes a strip-shaped negative electrode foil and a negative electrode coating area 31 and a negative electrode empty foil area 32 coated on the surface of the strip-shaped negative electrode foil.

[0237] As an optional implementation, the positive electrode empty foil region 23 and the negative electrode empty foil region 32 are perpendicular to the winding direction and are formed into the top or bottom end face of the battery by methods such as flattening or cutting.

[0238] As an optional implementation, the electrode can be a single electrode, multiple electrodes, or a full electrode, preferably a full electrode.

[0239] As an optional implementation, the housing 10 can be a steel housing or an aluminum housing.

[0240] As an optional implementation, the ratio of the diameter to the height of the lithium-ion battery is >1.6, for example, it can be 1.65, 1.7, 1.75, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, etc.

[0241] As an optional implementation, the diameter of the lithium-ion battery is 20-50mm, for example, it can be 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm, etc.

[0242] As an optional implementation, the height of the lithium-ion battery is 60-180mm, for example, it can be 60mm, 70mm, 80mm, 90mm, 100mm, 110mm, 120mm, 140mm, 150mm, 160mm, 180mm, etc.

[0243] As an optional implementation, the method for preparing the lithium-ion battery includes:

[0244] Preparation of positive electrode sheet:

[0245] A positive electrode coating material is mixed and coated on at least one side of an aluminum foil, then dried and cold-pressed to obtain a positive electrode sheet.

[0246] Preparation of negative electrode sheet:

[0247] The negative electrode sheet comprises a negative current collector copper foil and a negative electrode slurry coated on both sides of the copper foil. By mass percentage, the negative electrode slurry comprises 96.0% silicon-carbon material (Si content 10.0 wt%), 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC), and 1.5% negative electrode binder polyacrylic acid (PAA). These substances are added to deionized water and stirred to form the negative electrode slurry with a solid content of 40%. The negative electrode slurry is then coated onto both sides of the copper foil, dried, and cold-pressed to form the negative electrode sheet with a compaction density of 1.5 g / cm³. 3 ;

[0248] Preparation of electrolyte:

[0249] An electrolyte is prepared by mixing lithium hexafluorophosphate with an organic solvent, wherein the concentration of lithium hexafluorophosphate in the electrolyte is 1.0 mol / L. The organic solvent comprises components in the following ratio: ethylene carbonate (EC): fluoroethylene carbonate (FEC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 15:15:20:50.

[0250] Assembly of lithium-ion batteries:

[0251] The positive and negative electrode sheets are rolled and slit separately, and then wound together with the separator to obtain a 21700 cylindrical battery core. The battery core is then welded to the connecting piece and installed into the battery casing. After completing the electrolyte injection, sealing and formation processes, this lithium-ion battery is obtained. The casing of this lithium-ion battery is cylindrical, with the following dimensions: diameter: 16-55 mm, length: 63-140 mm.

[0252] The battery core is welded to the electrical connector, installed into the battery casing, and then subjected to electrolyte injection, sealing, and formation processes to obtain the battery.

[0253] As an optional implementation, the present invention also provides an electrical device including a battery for providing power as described in this application.

[0254] (1) Method for testing the film resistance of the electrode: The film resistance of the positive electrode in the following embodiments and comparative examples was measured using the 46-probe method of the RM2610 resistance testing system (45 probes arranged in a square matrix, with 1 probe serving as a ground probe). The specific process is as follows:

[0255] ① The positive electrode sheet, which has been washed with dimethyl carbonate and vacuum dried at 60℃ for 6h, is divided into 40 square grid samples of 1.0cm×1.0cm to ensure that the sample surface is flat;

[0256] ② Select a square grid sample, place the sample on the testing device, and use a pressure gauge to adjust the pressure applied by the probe to ensure good contact between the probe and the sample, with a contact area of ​​0.01 cm². 2 During the test, a constant current is applied to the 20 outer probes, allowing the current to flow through the surface, interface, and current collector of the positive electrode. At the same time, the 25 middle probes measure the voltage change in real time. Since the surface, interface, and current collector of the positive electrode have significantly different resistances, the measured voltage will reflect these differences.

[0257] ③ Calculate the membrane resistance Rα according to Ohm's law and fitting analysis method. The membrane resistance of the grid sample obtained in step ② is R1. Then, using the same method, randomly select another 9 square grids on the above electrode to measure the membrane resistance. The obtained values ​​are recorded as R2, R3, R4, R5, R6, R7, R8, R9, and R10, respectively. Finally, by calculating the arithmetic mean of these values, the average membrane resistance Rβ of the actual tested positive electrode is obtained (Rβ=(R1+R2+R3+R4+R5+R6+R7+R8+R9+R10) / 10), so as to comprehensively evaluate the conductivity and uniformity of the positive electrode.

[0258] (2) Cycle capacity retention: The battery was placed in a 25°C constant temperature chamber for 4 hours and tested according to the following steps:

[0259] 1. Charge to 4.25V under constant current and constant voltage conditions at 0.1C, cut off current at 0.01C, and let stand for 10 minutes;

[0260] 2. Discharge at a constant current of 0.1C until the cutoff voltage is 2.5V, and let stand for 10 minutes;

[0261] 3. Charge to 4.25V under constant current and constant voltage conditions at 1C, with a cutoff current of 0.01C, and let stand for 10 minutes;

[0262] 4. Discharge under constant current at 1C until 2.5V cutoff, and let stand for 10 minutes, then record the capacity S1;

[0263] 5. Repeat steps 3 and 4 600 times and record the capacity S2.

[0264] 6. Capacity retention rate = S2 / S1 * 100%

[0265] (3) Test method for peel strength: Cut an electrode sheet of 40mm×100mm, fix the electrode sheet to the fixed clamp and the movable clamp with tape, initially stretch it in the opposite direction at 180°C with a force of 1N / m, and increase it by 0.1N / m each time until the active material coating and aluminum foil are peeled off, and measure the force applied during peeling.

[0266] (4) Test method for viscosity rebound rate: Select the positive electrode slurry before coating. The standard viscosity of the output is 4500±1000mpa·s. Use a rotational viscometer, No. 5 rotor, 20rpm speed to test the output viscosity, and record it as A.

[0267] The viscosity of the slurry was measured after 48 hours at a 20℃ environment and a -30℃ dew point, and recorded as B.

[0268] Viscosity rebound = (BA) / A*100%.

[0269] The technical solution of the present invention will be further described below with reference to the embodiments.

[0270] The raw material parameters for each of the following embodiments are shown below:

[0271]

[0272] Example 1

[0273] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the lithium-ion battery is prepared by the following steps:

[0274] I. Preparation of composite adhesive composition:

[0275] Preparation of I-1, PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate):

[0276] (a) Monomer pre-dispersion: EDOT monomer was mixed with PSS solution (mass concentration 8%) and dispersed by ultrasonication (ultrasonic power 800W, frequency 28kHz) at 25°C for 30min (molar ratio of EDOT to PSS 1:1.5) to form a uniform suspension.

[0277] (b) Oxidative polymerization reaction: Oxidant APS (molar ratio of EDOT to APS is 1:1) is slowly added dropwise to the suspension obtained in step (a), the temperature is maintained at 25°C, the stirring speed is 400 rpm, the pH is controlled at 1.5 using dilute sulfuric acid, and the reaction time is 6 h to obtain the oxidative polymerization reaction solution.

[0278] (c) Post-processing and purification: The oxidative polymerization reaction solution obtained in step (b) is transferred to a dialysis bag and dialyzed with deionized water for 48 hours (water is changed every 6 hours) to remove unreacted monomers and small molecule impurities; the dialysis solution is then concentrated in a vacuum drying oven at 60°C to a solid content of 1.5% to form a dark blue colloidal solution, namely PEDOT:PSS colloid.

[0279] (d) Conductivity optimization secondary doping: 0.3 wt% dimethyl sulfoxide was added to the PEDOT:PSS colloid obtained in step (c), and stirred at 60°C for 2 h to obtain a conductive polymer containing dopant DMSO.

[0280] Structural verification of PEDOT:PSS was performed; CS bonds (1050 cm⁻¹) were detected by FTIR. -1 ) and COC bond (1200cm -1 ), ensuring no chemical crosslinking peak (1700 cm⁻¹) -1 peak).

[0281] I-2, Preparation of sulfonate betaine acrylate:

[0282] (A) Quaternization reaction: DMAEMA and PSI were mixed at a molar ratio of 1:1.5 and dissolved in DMF (solid content 30%). The mixture was stirred at 30°C for 12 h to obtain the quaternized product.

[0283] (B) Free radical copolymerization reaction: Add AIBN (0.5% of monomer mass) and DDM (0.1% of monomer mass) to the quaternized product obtained in step (A), heat to 60°C, and react for 6 hours under nitrogen protection to obtain the reaction solution;

[0284] (C) Post-processing and purification: The reaction solution obtained in step (B) was centrifuged at 8000 rpm for 15 min to remove unreacted monomers and small molecule byproducts; the centrifuged solution was dialyzed with deionized water for 48 h (water was changed every 6 hours) to remove residual solvents and initiators; finally, the dialyzed solution was dried at 60 °C until the moisture content was ≤0.5% to obtain a white powder product.

[0285] Detection of sulfonic acid groups in sulfonate betaine acrylate: The detection of sulfonic acid groups includes elemental analysis (EDS) to determine the sulfur content, wherein the sulfonic acid group content is 18 mol%.

[0286] I-3. Preparation of composite adhesive composition:

[0287] ①Ingredients:

[0288]

[0289] ②Preparation method:

[0290] (1) Pre-dispersion: PVDF and sulfonated betaine acrylate were added to a mixed solvent of cyclohexanone and NMP to obtain a dispersion; wherein, the dispersion parameters were: mechanical stirring at 25℃ and 500rpm for 30min, and vacuum degree -0.08MPa.

[0291] (2) Low-speed mixing: PEDOT:PSS doped with 0.3wt% DMSO is slowly added dropwise to the dispersion obtained in step (1) to obtain the composite binder composition; wherein, the process parameters are: low-speed stirring at 200 rpm for 10 min to avoid shearing damage to the conductive polymer structure.

[0292] II. Preparation of positive electrode slurry:

[0293] ①Ingredients:

[0294]

[0295]

[0296] ②Preparation method:

[0297] According to the above proportions, positive electrode active material LiNi is added sequentially to the composite binder composition prepared in I-3. 0.8 Co 0.15 Al 0.05 O2 and conductive carbon black were then stirred under vacuum (-0.1 MPa) until the solid content reached 65%, at a speed of 800 rpm for 60 min; the viscosity of the slurry stabilized at 4500±1000 mPa·s, thus obtaining the positive electrode slurry.

[0298] III. Preparation of the positive electrode sheet:

[0299] The positive electrode slurry is coated onto a positive electrode aluminum foil current collector, and then dried and rolled to obtain the positive electrode sheet; wherein, the coating parameters include: aluminum foil (12μm) surface coating, and electrode sheet areal density of 25mg / cm³. 2 The drying process parameters include: segmented drying at 80℃ (pre-drying for 5 min → main drying for 15 min); the rolling pressing conditions include: pressure of 10 MPa, and electrode compaction of 3.5 g / cm³ after rolling. 3 .

[0300] IV. Lithium-ion batteries:

[0301] The lithium-ion battery is a 21700 all-tab cylindrical battery; the lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode includes the positive electrode prepared in III above; the diameter of the battery ranges from 21 to 46 mm, and the height ranges from 70 to 800 mm.

[0302] Preparation of the positive electrode sheet: as shown in step III above;

[0303] Preparation of the negative electrode sheet: The negative electrode sheet includes a negative current collector copper foil and a negative electrode slurry coated on both sides of the copper foil. By mass percentage, the negative electrode slurry comprises 96.0% silicon-carbon material (Si content 10.0 wt%), 1.5% carbon nanotubes, 1.0% thickener sodium carboxymethyl cellulose (CMC), and 1.5% negative electrode binder polyacrylic acid (PAA). These substances are added to deionized water and stirred to form the negative electrode slurry with a solid content of 40%. The negative electrode slurry is then coated on both sides of the copper foil, dried, and cold-pressed to form the negative electrode sheet with a compaction density of 1.5 g / cm³. 3 ;

[0304] Preparation of electrolyte: Lithium hexafluorophosphate is mixed with an organic solvent to obtain an electrolyte, and the concentration of lithium hexafluorophosphate in the electrolyte is 1.0 mol / L. The organic solvent comprises the following components in the following ratio: ethylene carbonate (EC): fluoroethylene carbonate (FEC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 15:15:20:50.

[0305] Assembly of lithium-ion batteries: After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator to obtain a 21700 cylindrical battery core. Then, the battery core is welded to the connecting piece and installed into the battery casing. After completing the electrolyte injection, sealing and formation processes, this lithium-ion battery is obtained. The casing of this lithium-ion battery is cylindrical. The tabs of the battery core are welded to the electrical connecting piece, installed into the battery casing, and electrolyte injection, sealing and formation processes are performed to obtain the battery.

[0306] Example 2

[0307] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that in step (d) of I-1, 0.5 wt% dimethyl sulfoxide is added to the PEDOT:PSS colloid obtained in step (c); that is, the conductive polymer in the composite binder composition is PEDOT:PSS doped with 0.5 wt% DMSO; the other steps are completely consistent with Example 1.

[0308] Example 3

[0309] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that in step (d) of I-1, 0.1 wt% dimethyl sulfoxide is added to the PEDOT:PSS colloid obtained in step (c); that is, the conductive polymer in the composite binder composition is PEDOT:PSS doped with 0.1 wt% DMSO; the other steps are completely consistent with Example 1.

[0310] Example 4

[0311] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that the PVDF with a molecular weight of 800,000 is replaced with an equal mass of PVDF with a molecular weight of 500,000 in the raw materials of the I-3 composite binder composition; the other steps are completely consistent with Example 1.

[0312] Example 5

[0313] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that the PVDF with a molecular weight of 800,000 is replaced with an equal mass of PVDF with a molecular weight of 1 million in the raw materials of the I-3 composite binder composition; the other steps are completely consistent with Example 1.

[0314] Example 6

[0315] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that in step (A) of I-2, the molar ratio of DMAEMA to PSI is adjusted to 1:2 to obtain sulfonate betaine acrylate with a sulfonic acid group content of 25 mol%; that is, the zwitterionic polymer in the composite binder composition is sulfonate betaine acrylate with a sulfonic acid group content of 25 mol%; the other steps are completely consistent with Example 1.

[0316] Example 7

[0317] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that in step (A) of I-2, the molar ratio of DMAEMA to PSI is adjusted to 1:1 to obtain sulfonate betaine acrylate with a sulfonic acid group content of 13 mol%; that is, the zwitterionic polymer in the composite binder composition is sulfonate betaine acrylate with a sulfonic acid group content of 13 mol%; the other steps are completely consistent with Example 1.

[0318] Example 8

[0319] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The only difference from Example 1 is that the mixed solvent of cyclohexanone and NMP with a volume ratio of 1:3 is replaced with an equal mass of cyclohexanone and NMP mixed solvent with a volume ratio of 1:2 in the raw materials of the I-3 composite binder composition. The other steps are completely consistent with Example 1.

[0320] Example 9

[0321] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The only difference from Example 1 is that the mass ratio of PVDF, PEDOT:PSS doped with 0.3wt% DMSO, and sulfonate betaine acrylate with a sulfonic acid group content of 18mol% in the raw materials of the I-3 composite binder composition is adjusted to 90.5:8:1.5. The other steps are completely consistent with Example 1.

[0322] Example 10

[0323] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that the mass ratio of active material, conductive agent, and binder in the raw materials of the positive electrode slurry II is adjusted to 96:2:2; the other steps are completely consistent with Example 1.

[0324] Example 11

[0325] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The only difference from Example 1 is that the mixed solvent of cyclohexanone and NMP with a volume ratio of 1:3 is replaced with an equal mass of cyclohexanone and NMP mixed solvent with a volume ratio of 1:5 in the raw materials of the I-3 composite binder composition. The other steps are completely consistent with Example 1.

[0326] Example 12

[0327] This embodiment provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that the mass ratio of active material, conductive agent, and binder in the raw materials of the positive electrode slurry II is adjusted to 90:5:5; the other steps are completely consistent with Example 1.

[0328] Comparative Example 1

[0329] This comparative example provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that the conductivity optimization secondary doping in step (d) of I-1 is no longer performed, that is, the conductive polymer does not contain the dopant DMSO; the other steps are completely consistent with Example 1.

[0330] Comparative Example 2

[0331] This comparative example provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that the PVDF with a molecular weight of 800,000 in the raw materials of the I-3 composite binder composition is replaced with an equal mass of PVDF with a molecular weight of 1.5 million; the other steps are completely consistent with Example 1.

[0332] Comparative Example 3

[0333] This comparative example provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery; the only difference from Example 1 is that in step (A) of I-2, the molar ratio of DMAEMA to PSI is adjusted to 1:0.8 to obtain sulfonate betaine acrylate with a sulfonic acid group content of 10 mol%; that is, the zwitterionic polymer in the composite binder composition is sulfonate betaine acrylate with a sulfonic acid group content of 10 mol%; the other steps are completely consistent with Example 1.

[0334] Comparative Example 4

[0335] This comparative example provides a composite binder composition, a positive electrode slurry, a positive electrode sheet, and a lithium-ion battery. The only difference from Example 1 is that the mass ratio of PVDF, PEDOT:PSS doped with 0.3wt% DMSO, and sulfonate betaine acrylate with a sulfonic acid group content of 18mol% in the raw materials of the I-3 composite binder composition is adjusted to 85:10:5; the other steps are completely consistent with Example 1.

[0336] Test Case

[0337] Test samples: Composite binder compositions, positive electrode slurries, positive electrode sheets and lithium-ion batteries provided in Examples 1-10; Composite binder compositions, positive electrode slurries, positive electrode sheets and lithium-ion batteries provided in Comparative Examples 1-6.

[0338] Test method:

[0339] ① Test viscosity rebound rate: Select the positive electrode slurry before coating. The standard viscosity of the output is 4500±1000 mpa·s. Use a rotational viscometer with a No. 5 rotor and a speed of 20 rpm to test the output viscosity, which is recorded as A. After the slurry is placed in an environment of 20℃ and at a dew point of -30℃ for 48 hours, test the viscosity and record it as B. Viscosity rebound = (BA) / A*100%.

[0340] ② Electrode resistivity: The film resistance of the positive electrode in the following embodiments and comparative examples was measured using the 46-probe method of the RM2610 resistance testing system (45 probes arranged in a square matrix, with 1 probe serving as a ground probe). The specific process is as follows:

[0341] i. The positive electrode sheet, which has been washed with dimethyl carbonate and vacuum dried at 60°C for 6 hours, is divided into 40 square grid samples of 1.0cm × 1.0cm to ensure that the sample surface is flat.

[0342] ii. Select a square grid sample, place the sample on the testing device, and use a pressure gauge to adjust the pressure applied by the probe to ensure good contact between the probe and the sample, with a contact area of ​​0.01 cm². 2During the test, a constant current is applied to the 20 outer probes, allowing the current to flow through the surface, interface, and current collector of the positive electrode. At the same time, the 25 middle probes measure the voltage change in real time. Since the surface, interface, and current collector of the positive electrode have significantly different resistances, the measured voltage will reflect these differences.

[0343] iii. Calculate the membrane resistance Rα according to Ohm's law and fitting analysis method. The membrane resistance of the grid sample obtained in step ② is R1. Then, using the same method, randomly select another 9 square grids on the above electrode to measure the membrane resistance. The obtained values ​​are recorded as R2, R3, R4, R5, R6, R7, R8, R9, and R10, respectively. Finally, by calculating the arithmetic mean of these values, the average membrane resistance Rβ of the actual tested positive electrode is obtained (Rβ = (R1 + R2 + R3 + R4 + R5 + R6 + R7 + R8 + R9 + R10) / 10), so as to comprehensively evaluate the conductivity and uniformity of the positive electrode.

[0344] ③ Test method for peel strength: Cut an electrode sheet of 40mm×100mm, fix the electrode sheet to the fixed clamp and the movable clamp with tape, initially apply a force of 1N / m to the reverse tension at 180°, increase the force by 0.1N / m each time, until the active material coating and aluminum foil are peeled off, and measure the force applied during peeling.

[0345] ④ Capacity retention test: After 600 cycles at 1C, take one battery and place it in a 25℃ constant temperature chamber for more than 4 hours, and perform the test according to the following steps:

[0346] (12) Charge the battery at 0.1C with constant current to 4.2V, and then charge it at 0.01C with constant current to 4.2V and let it stand for 5 minutes.

[0347] (13) Discharge the battery at a constant current of 0.1C until it is cut off at 2.5V, and let it stand for 5 minutes;

[0348] (14) Charge the battery at 1C with constant current to 4.2V, and then charge it at 0.01C with constant current to 4.2V and let it stand for 5 minutes.

[0349] (15) Discharge the battery under 1C conditions with constant current until 2.5V cutoff, let it stand for 5 minutes, read the capacity value C0 at this time, and let it stand for 5 minutes.

[0350] (16) Repeat steps (14) and (15) 600 times;

[0351] (17) The cycle performance of a single battery, i.e. capacity retention rate, is obtained by the ratio of the 600th discharge capacity to the 1st discharge capacity C0 in steps (14) and (15).

[0352] The specific test results are shown in Table 1 below. Figure 4 As shown:

[0353] Table 1

[0354]

[0355]

[0356] Comparing Examples 8 and 11, it can be seen that reducing the NMP ratio leads to an increase in slurry viscosity rebound rate. This is because the reduced NMP ratio decreases solvent polarity and reduces slurry dispersion uniformity. Simultaneously, the decrease in NMP leads to increased solvent residue during baking, resulting in microcracks in the electrode. These microcracks accelerate electrolyte penetration and active material stripping during cycling, thus reducing capacity retention.

[0357] Combining Examples 10 and 12, it can be seen that when the proportion of active material decreases and the proportion of conductive agent and binder increases, the increase of small particle large specific surface area conductive agent will lead to an increase in the risk of particle agglomeration, a decrease in dispersion uniformity, and a direct decrease in energy density as the active material decreases.

[0358] Comparing Examples 1-3 with Comparative Example 1, it can be seen that increasing the DMSO content increases the viscosity rebound rate from 2.5% to 3.2%. This is because excessive DMSO weakens the physical entanglement of π-π conjugation and PVDF, leading to a decrease in dispersion stability. Simultaneously, DMSO, as a PEDOT dopant, enhances conjugation and conductivity; however, excessive DMSO leads to a loosening of the conductive network, reducing the strength of the bonding network. Discontinuities in the conductive network result in increased local polarization during cycling, reducing capacity retention and peel strength.

[0359] Comparing Examples 1, 4, and 5 with Comparative Example 2, it is evident that decreasing the molecular weight of PVDF leads to an increase in viscosity rebound rate and resistivity, while decreasing peel strength and capacity retention. This is because: the increased mobility of low molecular weight PVDF chain segments easily triggers slurry gelation; short-chain PVDF is difficult to form a continuous bonding network, resulting in a discontinuous conductive network structure; and the weakened mechanical entanglement of low molecular weight PVDF reduces the cohesive force within the electrode, accelerating the shedding of active material during cycling. However, excessively high molecular weight PVDF increases the difficulty of the homogenization process and makes it difficult to break up the molecular chains, which also negatively impacts electrode performance.

[0360] Comparing Examples 1, 6, and 7 with Comparative Example 3, it can be seen that when the sulfonic acid group content increases from 18 mol% to 25 mol%, the viscosity rebound rate of the slurry decreases, but the resistivity increases. This is because the sulfonic acid group (-SO3) - ) and quaternary ammonium group (-N +The electrostatic repulsion of PVDF inhibits chain entanglement and reduces the viscosity rebound of slurry caused by PVDF crosslinking. However, excessive sulfonic acid groups will react with free amino groups in NMP solvent to generate byproducts, which hinder electron transport.

[0361] Comparing Examples 1 and 9 with Comparative Example 4, it can be seen that when the proportion of PEDOT in the binder is increased, the viscosity rebound rate will change from 2.5% to 4%. This is because the excessive PEDOT:PSS colloid squeezes the space of PVDF chain segments, causing gelation. At the same time, the imbalance of the binder proportion leads to the weakening of the physical winding network. During the cycle, the insufficient bonding strength causes the active material to fall off, resulting in a decrease in capacity retention.

[0362] In summary, the composite binder system and battery based on a conductive-bonding dual network and a zwitterionic charge balance mechanism provided in this application have the following three main characteristics:

[0363] Synergy between conductive and adhesive dual networks: The π-π conjugate conductive network of PEDOT:PSS and the physically entangled adhesive network of PVDF need to be optimized in proportion to achieve a synergistic effect. Excessive conductive agent or adhesive will disrupt the balance.

[0364] zwitterionic charge balance: sulfonic acid group (-SO3) - ) and quaternary ammonium group (-N + Electrostatic repulsion can inhibit gelation, but the content needs to be controlled to avoid side reactions;

[0365] Solvent polarity control: By controlling the volume ratio of cyclohexanone to NMP, dispersibility is improved by reducing solvent polarity. Excessive NMP leads to drying residue and microcracks.

[0366] By adjusting and balancing the above parameters, the overall performance of the battery can be improved, the battery slurry homogenization process can be optimized, the battery cycle capacity retention rate can be optimized, and the kinetic performance can be improved.

[0367] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite adhesive composition, characterized in that, It includes a conductive network and a binding network; The conductive network is composed of a conductive polymer and a binding polymer; The binding network is composed of a binding polymer and an amphoteric ion polymer; The mass ratio of the binding polymer, the conductive polymer and the amphoteric ion polymer is (90-95):(3-7):(2-3); Among them, the binding polymer is a fluoropolymer with a molecular weight of 2 million to 1 million, the conductive polymer is formed by an oxidative polymerization reaction, and the content of sulfonic acid groups in the amphoteric ion polymer > 15 mol%; 2. The composite adhesive composition according to claim 1, characterized in that, The binding polymer includes polyvinylidene fluoride; the conductive polymer includes poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate and a dopant; the amphoteric ion polymer includes sulfobetaine acrylate.

3. The composite adhesive composition according to claim 1 or 2, characterized in that, The dopant includes dimethyl sulfoxide and / or ethylene glycol; Preferably, the addition amount of the dopant accounts for 0.1-0.6% of the total mass of the conductive polymer; Preferably, the composite binder composition further includes a mixed solvent; wherein, the solid content of the composite binder composition is 1-15 wt%; Preferably, the mixed solvent includes cyclohexanone and N-methylpyrrolidone; Preferably, the volume ratio of cyclohexanone to N-methylpyrrolidone is 1:(3-5).

4. A method for preparing a composite adhesive composition according to any one of claims 1 to 3, characterized in that, The preparation method of the composite binder composition includes: Disperse the binding polymer and the amphoteric ion polymer in the mixed solvent to obtain a dispersion; Mix the dispersion and the conductive polymer to obtain the composite binder composition; Preferably, the rotation speed of the dispersion is 400-600 rpm, and the dispersion time is 20-40 min; Preferably, the rotation speed of the mixing is 100-300 rpm, and the mixing time is 5-15 min; Preferably, the temperature of the dispersion is below 25 °C.

5. A positive electrode slurry, characterized in that, The positive electrode slurry includes an active material, a conductive agent and a binder with a mass ratio of (94-97):(1-3):(2-4); Among them, the active material includes lithium nickel cobalt manganese oxide and / or lithium iron phosphate; Among them, the conductive agent includes carbon black and / or carbon nanotubes; Among them, the binder includes the composite binder composition according to any one of claims 1-3.

6. The positive electrode slurry according to claim 5, characterized in that, The lithium nickel cobalt manganese oxide includes high-nickel ternary lithium nickel cobalt manganese oxide materials with the chemical formula Li. a Ni x Co y Mn z M b O2; Among them, 0.9 < a < 1.1, 0.7 < x ≤ 0.94, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1; the M element is one or a combination of at least two of Al, Mg, Zr, Ti, W, Nb, Mo, B; And / or, the lithium nickel cobalt manganese oxide includes medium-nickel ternary lithium nickel cobalt manganese oxide materials with the chemical formula Li. a1 Ni x1 Co y1 Mn z1 M1 b1 O2; Among them, 0.9 < a1 < 1.1, 0.4 ≤ x1 ≤ 0.7, 0.1 ≤ y1 < 0.4, 0.05 ≤ z1 < 0.4, 0 ≤ b1 ≤ 0.1, and M1 is one or a combination of at least two of Al, Mg, Zr, Ti, W, Nb, Mo, B.

7. A method for preparing a positive electrode slurry according to claim 5 or 6, characterized in that, The preparation method of the positive electrode slurry includes: Mix and stir the composite binder composition, the active material and the conductive agent to obtain the positive electrode slurry; Preferably, the mixing and stirring are carried out under vacuum; Preferably, the vacuum degree of the mixing and stirring is -0.15 to -0.05 MPa, the mixing and stirring speed is 700 to 900 rpm, and the mixing and stirring time is 30 to 90 min.

8. A positive electrode sheet, characterized in that, The positive electrode sheet includes a positive current collector and a positive electrode coating coated on at least one side of the positive current collector; Wherein, the positive electrode coating includes the positive electrode slurry as described in claim 5 or 6; the positive electrode coating includes a three-dimensional conductive network formed by a conductive polymer, a binder polymer and a conductive agent surface; Preferably, the positive current collector includes an aluminum foil current collector; Preferably, the areal density of the positive electrode sheet is ≥24.5 mg / cm³. 2 ; Preferably, after 600 cycles at 1C, the positive electrode retains ≥90% of its capacity and has a peel strength ≥0.18 N / cm. 2 .

9. A method for preparing a positive electrode sheet according to claim 8, characterized in that, The method for preparing the positive electrode sheet includes: After the positive electrode slurry is coated onto the positive electrode current collector, it is dried and rolled to obtain the positive electrode sheet.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; wherein the positive electrode includes the positive electrode as described in claim 8.

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