Lithium-ion battery, positive electrode paste, positive electrode sheet and preparation method thereof

Abstract

The present invention provides a lithium-ion battery, a positive electrode paste, a positive electrode sheet and a preparation method thereof. The positive electrode paste includes an active material, a composite conductive agent, a composite binder and an additive having a competitive effect with the composite binder. The composite conductive agent includes a first conductive agent, a second conductive agent and a third conductive agent. The first conductive agent is selected from one or more of acetylene black, conductive carbon black and conductive graphite. The second conductive agent is carbon nanotubes, and the third conductive agent is graphene. The composite binder includes a first binder and a second binder. The first binder is PVDF prepared by emulsion polymerization method; the second binder is PVDF prepared by suspension polymerization method. An additive having a competitive effect with the composite binder in the existing paste components is added, so as to be able to inhibit problems such as gelation, jelly, agglomeration, etc. caused by intermolecular or intramolecular cross-linking of some fluoropolymer binder molecules.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular, to a lithium-ion battery, a positive electrode paste, a positive electrode sheet and a preparation method thereof. Background Art

[0002] Common active substances of positive electrode materials include lithium iron phosphate, lithium cobaltate, lithium manganate and ternary materials. Among them, the most commonly used is lithium iron phosphate with good thermal stability and chemical stability. However, the defect of lithium iron phosphate as a positive electrode material is its low electronic conductivity and low ionic conductivity. Moreover, with the improvement of the national policy requirements for the battery energy density, it is necessary to increase the proportion of the active substance in the positive electrode formula and reduce the proportion of the binder and the conductive agent. Therefore, a more efficient compound binder is needed. However, the inventors found in the research that the existing compound binders will cause problems such as gelation, jelly formation and agglomeration of the paste, and there is currently no effective solution to this problem. Summary of the Invention

[0003] The main object of the present invention is to provide a lithium-ion battery, a positive electrode paste, a positive electrode sheet and a preparation method thereof to solve the problems such as gelation, jelly formation and agglomeration of the existing positive electrode paste.

[0004] To achieve the above object, according to one aspect of the present invention, a positive electrode paste for a lithium-ion battery is provided. The positive electrode paste includes an active substance, a composite conductive agent, a composite binder and an additive having a competitive effect with the composite binder. Among them, the composite conductive agent includes a first conductive agent, a second conductive agent and a third conductive agent. The first conductive agent is selected from one or more of acetylene black, conductive carbon black and conductive graphite. The second conductive agent is carbon nanotubes. The third conductive agent is graphene. The composite binder includes a first binder and a second binder. The first binder is PVDF prepared by emulsion polymerization. The second binder is PVDF prepared by suspension polymerization.

[0005] Further, the additive is a substituted or unsubstituted aromatic acid compound or heteroaromatic acid compound. Preferably, the substituent in the substituted aromatic acid compound or heteroaromatic acid compound is a halogen. More preferably, the halogen is selected from F or Cl. Preferably, the aromatic acid compound or heteroaromatic acid compound has the following characteristics: (1) one or two carboxylic acid groups; (2) one or more conjugated bonds; (3) soluble. Preferably, the additive is selected from any one of the following compounds:

[0006]

[0007]

[0008] Further, by weight, the ratio of the active material: the composite conductive agent: the composite binder: the additive is: 98-95.5: 1-2.3: 1-2.2: 0.005-0.03. Preferably, the ratio of the active material: the composite conductive agent: the composite binder: the additive is: 98-95.5: 1-2.3: 1-2.2: 0.01-0.03; preferably, the active material is lithium iron phosphate.

[0009] To achieve the above object, according to the second aspect of the present invention, a method for preparing a positive electrode plate of a lithium ion battery is provided. The preparation method includes: mixing an active material, a composite conductive agent, a composite binder, and an additive having a competitive effect with the composite binder to obtain a positive electrode paste; coating the positive electrode paste on a current collector to obtain a precursor of the electrode plate; roll-pressing the precursor of the electrode plate to obtain a positive electrode plate of a lithium ion battery; wherein the composite conductive agent includes a first conductive agent, a second conductive agent, and a third conductive agent. The first conductive agent is selected from one or more of acetylene black, conductive carbon black, and conductive graphite. The second conductive agent is carbon nanotubes, and the third conductive agent is graphene; the composite binder includes a first binder and a second binder. The first binder is PVDF prepared by emulsion polymerization; the second binder is PVDF prepared by suspension polymerization.

[0010] Further, the additive is a substituted or unsubstituted aromatic acid compound or heteroaromatic acid compound; preferably, the substituent in the substituted aromatic acid compound or heteroaromatic acid compound is a halogen, and more preferably the halogen is selected from F or Cl; preferably, the aromatic acid compound or heteroaromatic acid compound has the following characteristics: (1) one or two carboxylic acid groups; (2) one or more conjugated bonds; (3) soluble; preferably, the additive is selected from any one of the following:

[0011]

[0012]

[0013] Further, the preparation method includes: Step S1, mixing the composite binder and the additive and adding them to a solvent to form a glue solution; Step S2, adding the first conductive agent and lithium iron phosphate to the glue solution in sequence to obtain a mixed solution; Step S3, adding the second conductive agent and the third conductive agent to the mixed solution and further mixing to obtain a positive electrode paste; Step S4, coating the positive electrode paste on a current collector to obtain a precursor of the electrode plate; Step S5, roll-pressing the precursor of the electrode plate to obtain a positive electrode plate of a lithium ion battery.

[0014] Further, steps S1, S2, and S3 are all stirred under vacuum conditions, and the stirring includes both revolution and rotation; preferably, the revolution speed in step S1 is 13 - 16 r / min, the rotation speed is 600 - 1000 r / min, and the stirring time is 180 - 200 minutes; preferably, the revolution speed in step S2 is 25 - 30 r / min, the rotation speed is 2500 - 3500 r / min, and the stirring time is 200 - 250 minutes; preferably, the revolution speed in step S3 is 18 - 22 r / min, the rotation speed is 1800 - 2200 r / min, and the stirring time is 75 - 90 minutes; preferably, the system viscosity of steps S1, S2, and S3 is controlled to be lower than 10000 mPa·S, and preferably the system viscosity of each step is controlled within 6000 - 8000 mPa·S.

[0015] Further, by weight, the ratio of active material: composite conductive agent: composite binder: additive is: 98 - 95.5: 1 - 2.3: 1 - 2.2: 0.001 - 0.03; preferably, the ratio of active material: composite conductive agent: composite binder: additive is: 98 - 95.5: 1 - 2.3: 1 - 2.2: 0.01 - 0.03; preferably, the current collector is a carbon-coated aluminum foil with conductive carbon black coatings on both sides; more preferably, the substrate thickness of the carbon-coated aluminum foil is 9 - 11 μm, and the single-sided thickness of the conductive carbon black coating is 0.8 - 1.1 μm; preferably, the positive electrode slurry is coated on the current collector by means of coating, and more preferably the coating speed is 6 - 10 m / min; preferably, the rolling speed is 8 - 12 m / min.

[0016] According to the third aspect of the present invention, there is provided a positive electrode sheet of a lithium-ion battery, which is prepared from any one of the above-mentioned slurries or by any one of the above-mentioned preparation methods.

[0017] According to the fourth aspect of the present invention, there is provided a lithium-ion battery, which includes a positive electrode sheet, and the positive electrode sheet is the above-mentioned positive electrode sheet.

[0018] Applying the technical solution of the present invention, the positive electrode slurry of the present application adds an additive that competes with the composite binder in the existing slurry components, thereby being able to inhibit problems such as gelation, jelly formation, and agglomeration caused by intermolecular or intramolecular crosslinking of some fluoropolymer binders. Detailed Embodiments

[0019] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0020] As mentioned in the background art, lithium iron phosphate is mostly used as the active material in existing lithium-ion batteries. However, the defects of lithium iron phosphate as the cathode material are its low electronic conductivity and low ionic conductivity. Therefore, in the existing slurry formulations, a compound binder is added to improve the energy density of the battery. However, the inventor found that the existing compound binder would cause problems such as gelation, jellification, and agglomeration of the slurry. To improve this situation, the present application conducted in-depth research based on the existing formulation and the type of compound binder. Finally, through various screenings, a class of compounds that can compete with the compound binder was further discovered, which can alleviate problems such as gelation, jellification, and agglomeration in the slurry.

[0021] Therefore, based on the above research, the applicant proposed the technical solution of the present application. In a typical embodiment of the present application, a positive electrode slurry for a lithium-ion battery is provided. The slurry includes an active material, a composite conductive agent, a composite binder, and an additive that has a competitive effect with the composite binder. Among them, the composite conductive agent includes a first conductive agent, a second conductive agent, and a third conductive agent. The first conductive agent is selected from one or more of acetylene black, conductive carbon black, and conductive graphite. The second conductive agent is carbon nanotubes, and the third conductive agent is graphene. The composite binder includes a first binder and a second binder. The first binder is PVDF prepared by emulsion polymerization. The second binder is PVDF prepared by suspension polymerization.

[0022] The positive electrode slurry of the present application adds an additive that has a competitive effect with the composite binder in the existing slurry components, thereby being able to inhibit problems such as gelation, jellification, and agglomeration caused by cross-linking between or within some fluoropolymer binder molecules.

[0023] The additive in the above positive electrode slurry is a substituted or unsubstituted aromatic acid compound or heteroaromatic acid compound. Aromatic acid compounds refer to those in which the carboxyl group is directly connected to the benzene ring or to the side chain on the benzene ring. Heteroaromatic acid compounds refer to those in which the carbon atoms in the benzene ring are replaced by heteroatoms such as N, S, or O. In the chemical structure of PVDF in the existing slurry, it is bonded by fluorine-carbon chemical bonds. This structure with short bond properties is prone to form a relatively stable bond with the surrounding hydrogen ions, resulting in phenomena such as gelation and agglomeration. By adding aromatic acid compounds and heteroaromatic acid compounds containing carboxyl groups, since carboxylate ions can provide H + ions, there are excess hydrogen ions in the slurry system that have a certain "attraction" with the F bonds, which weakens the binding force between F and H within or between some fluoropolymer binder molecules to a certain extent. Furthermore, it can inhibit cross-linking between or within some fluoropolymer binder molecules, and thus can inhibit problems such as gelation, jellification, and agglomeration of the slurry.

[0024] The above-mentioned aromatic acid compounds and heteroaromatic acid compounds can be substituted compounds, and the substituents are preferably groups with strong electron-withdrawing functions. In this application, the preferred substituent is halogen substitution, and the specific halogen atoms can be F, Cl or Br, and more preferably F or Cl.

[0025] In order to further enhance the competitive effect of the above-mentioned additives on the composite binder, that is, to further weaken the force between the hydrogen bonds between F in PVDF and H within or between its molecules, in a preferred embodiment of this application, the above-mentioned aromatic acid compounds and heteroaromatic acid compounds preferably have the following characteristics: (1) one or two carboxylic acid groups; (2) one or more conjugated bonds; (3) soluble. One or two carboxylic acid groups are used to provide H ions, and solubility is used to enable the additive to dissolve in the slurry, so that it can compete with PVDF, and the conjugated bonds make the compound have relatively strong reactivity.

[0026] In a preferred embodiment of this application, the additives in the above-mentioned slurry are selected from any one of the following:

[0027]

[0028]

[0029] Using the above specific types of additives can significantly extend the anti-gel time without increasing the resistivity, thereby improving the stripping strength of the electrode sheet.

[0030] The type ratio of each component in the above-mentioned slurry can be reasonably optimized through experiments on the basis of the existing formula to obtain an appropriate amount of the above-mentioned additives. In a preferred embodiment, by weight, the ratio of active material: composite conductive agent: composite binder: additive is: 98-95.5: 1-2.3: 1-2.2: 0.005-0.03. More preferably, by weight, the ratio of active material: composite conductive agent: composite binder: additive is: 98-95.5: 1-2.3: 1-2.2: 0.01-0.03. The positive electrode sheet prepared within the above-mentioned ratio range has the characteristics of a high proportion of active material, low internal resistance, and strong adhesion.

[0031] The above improvement plan is mainly aimed at the slurry with lithium iron phosphate as the active material, and of course it is also applicable to other active materials containing lithium iron phosphate.

[0032] In the second typical embodiment of the present application, a method for preparing a positive electrode plate of a lithium-ion battery is provided. The preparation method includes: mixing an active material, a composite conductive agent, a composite binder, and an additive having a competitive effect with the composite binder to obtain a positive electrode slurry; coating the positive electrode slurry on a current collector to obtain a precursor of the electrode plate; and roll-pressing the precursor of the electrode plate to obtain a positive electrode plate of the lithium-ion battery. Among them, the composite conductive agent includes a first conductive agent, a second conductive agent, and a third conductive agent. The first conductive agent is selected from one or more of acetylene black, conductive carbon black, and conductive graphite. The second conductive agent is carbon nanotubes. The third conductive agent is graphene. The composite binder includes a first binder and a second binder. The first binder is PVDF (polyvinylidene fluoride) prepared by emulsion polymerization. The second binder is PVDF prepared by suspension polymerization.

[0033] In the preparation method of the present application, by adding an additive having a competitive effect with the composite binder to the existing formula, problems such as gelation, jelly formation, and agglomeration caused by intermolecular or intramolecular cross-linking of some fluoropolymer binders can be inhibited, and the fluidity of the slurry is improved.

[0034] In another preferred embodiment, the above preparation method includes: mixing the composite binder and the additive and adding them to a solvent to form a glue solution; adding the first conductive agent (such as conductive carbon black) and lithium iron phosphate to the glue solution in sequence to obtain a mixed solution; adding the second conductive agent (carbon nanotubes) and the third conductive agent (graphene) to the mixed solution for further mixing to obtain a slurry; coating the slurry on a current collector to obtain a precursor of the electrode plate; and roll-pressing the precursor of the electrode plate to obtain a positive electrode plate.

[0035] In the step of mixing the composite binder and the additive and adding them to a solvent to form a glue solution, it is prepared by stirring under vacuum. The above solvent is preferably N-methylpyrrolidone. The vacuum degree is preferably -100 to -95 KPa. The stirring includes revolution and rotation. Preferably, the revolution speed is 13 to 16 r / min, the rotation speed is 600 to 1000 r / min, and the stirring time is 180 to 200 minutes. The steps after adding the first conductive material and lithium iron phosphate are also preferably stirred and mixed evenly under vacuum conditions, and further preferably the vacuum degree conditions are the same as above. The revolution speed of the stirring is 25 to 30 r / min, the rotation speed is 2500 to 3500 r / min, and the stirring time is 200 to 250 minutes. After adding the second conductive material and the third conductive material, it is also preferably stirred and mixed evenly under vacuum conditions, and further preferably the vacuum degree conditions are the same as above. The revolution speed of the stirring is 18 to 22 r / min, the rotation speed is 1800 to 2200 r / min, and the stirring time is 75 to 90 minutes.

[0036] During the preparation process, it is preferred to control the system viscosity of each step to be lower than 10000 mPa·S, and preferably the viscosity is controlled at 6000 - 8000 mPa·S.

[0037] In the above preparation method, as long as an additive that can compete with the composite binder is selected, it can inhibit the cross-linking within and / or between the molecules of the composite binder, thereby inhibiting the gelation, jellification, and agglomeration phenomena of the slurry. To further improve the agglomeration and gelation phenomena of the slurry, in a preferred embodiment, the above additive is a substituted or unsubstituted aromatic acid compound or heteroaromatic acid compound; preferably, the additive is selected from any one of the following:

[0038]

[0039]

[0040] Using the above types of additives has a stronger anti-gelation and anti-agglomeration effect.

[0041] In the above preparation method, the type ratio of each component in the above slurry can be reasonably optimized through experiments on the basis of the existing formula to obtain an appropriate amount of the above additive. In a preferred embodiment, by weight, the ratio of the active material: composite conductive agent: composite binder: additive is: 98 - 95.5: 1 - 2.3: 1 - 2.2: 0.005 - 0.03; more preferably, the ratio of the active material: composite conductive agent: composite binder: additive is: 98 - 95.5: 1 - 2.3: 1 - 2.2: 0.01 - 0.03; the positive electrode sheet prepared within the above ratio range has the characteristics of a high proportion of active material, low internal resistance, and strong adhesion.

[0042] The above improvement scheme is mainly for the slurry with lithium iron phosphate as the active material, and of course it is also applicable to other active materials containing lithium iron phosphate. Therefore, it is preferred that the above active material is lithium iron phosphate.

[0043] During the above preparation process, the current collector is a carbon-coated aluminum foil with conductive carbon black coatings on both sides. Preferably, the substrate thickness of the carbon-coated aluminum foil is 9 - 11 μm, preferably 10 μm; the single-sided thickness of the conductive carbon black coating is 0.8 - 1.1 μm, preferably 1 μm.

[0044] In the step of coating the slurry on the current collector above, the coating is carried out by means of coating. Preferably, the coating speed is 6 - 10 m / min, more preferably 8 m / min. After coating, it is dried (preferably dried in an oven) and roll-pressed into shape, where the roll-pressing speed is 8 - 12 m / min, preferably 10 m / min.

[0045] In the third typical embodiment of the present application, a positive electrode sheet for a lithium-ion battery is provided. The positive electrode sheet is prepared from any of the above-mentioned slurries or by any of the above-mentioned preparation methods. The positive electrode sheet prepared in the present application has the characteristics of a high proportion of active material, low internal resistance, and strong adhesion.

[0046] In the fourth typical embodiment of the present application, a lithium-ion battery is provided. The lithium-ion battery includes a positive electrode sheet, and the positive electrode sheet is the above-mentioned positive electrode sheet. The positive electrode sheet has the characteristics of a high proportion of active material, low internal resistance, and strong adhesion. Therefore, the prepared lithium-ion battery has the characteristic of high energy density.

[0047] The beneficial effects of the present application will be further described below in conjunction with specific embodiments. It should be noted that the active material, composite conductive agent, and composite binder in the following embodiments are the same and are all existing components.

[0048] Example 1

[0049] The implementation plan of positive electrode sheet C is as follows:

[0050] The positive electrode formula consists of the following components in parts by weight: active material, composite conductive agent, composite binder, and corresponding additive compound 2 = 98:1:1:0.02.

[0051] Polyvinylidene fluoride prepared by emulsion polymerization, PVDF prepared by suspension polymerization, and compound 3 are mixed to form a composite binder. Solvent N-methylpyrrolidone is added to the composite binder, and it is stirred at a vacuum degree of -95 KPa for 200 minutes, with a revolution speed of 15 r / min and a rotation speed of 800 r / min to form a glue solution; Conductive carbon black active material and lithium iron phosphate are successively added to the obtained glue solution, and it is stirred at a vacuum degree of -95 KPa for 240 minutes, with a revolution speed of 30 r / min and a rotation speed of 3000 r / min. Graphene and carbon nanotubes are added to the above slurry, and it is stirred at a vacuum degree of -95 KPa for 80 minutes, with a revolution speed of 20 r / min and a rotation speed of 2000 r / min to form a positive electrode slurry; The viscosity of the slurry is measured every 4 h in a beaker, and the viscosity range is 6000 - 8000 mPa·S. When the viscosity ≥ 10000 mPa·S and its fluidity is observed to become poor, it can be judged as gel. The obtained slurry is evenly coated on both sides of a carbon-coated aluminum foil with a conductive carbon black coating on both sides. Among them, the base thickness of the carbon-coated aluminum foil is 10 μm; The single-sided thickness of the conductive carbon black coating is 1 μm; It is dried in an oven and roll-pressed to form a positive electrode sheet. The coating speed is 8 m / min; The roll-pressing speed is 10 m / min. Subsequently, the resistivity and peel strength of the positive electrode sheet are measured respectively.

[0052] Example 2

[0053] The implementation scheme of the positive electrode sheet B is as follows:

[0054] The positive electrode formula consists of the following components in parts by weight: active material, composite conductive agent, and composite binder = 98:1:1.

[0055] Mix the polyvinylidene fluoride prepared by emulsion polymerization and the PVDF prepared by suspension polymerization to make a composite binder, add the solvent N-methylpyrrolidone to the composite binder, and stir at a vacuum degree of -95 KPa for 200 minutes with a revolution speed of 15 r / min and a rotation speed of 800 r / min to make a glue solution; add the conductive carbon black active material and lithium iron phosphate to the obtained glue solution in sequence, and stir at a vacuum degree of -95 KPa for 240 minutes with a revolution speed of 30 r / min and a rotation speed of 3000 r / min. Add graphene and carbon nanotubes to the above slurry, and stir at a vacuum degree of -95 KPa for 80 minutes with a revolution speed of 20 r / min and a rotation speed of 2000 r / min to make a positive electrode slurry; place the slurry in a beaker and measure its viscosity every 4 h. The viscosity range is 6000-8000 mPa·S. When the viscosity ≥ 10000 mPa·S and its fluidity becomes poor, it can be judged as gel. Coat the obtained slurry evenly on both sides of the carbon-coated aluminum foil with a conductive carbon black coating on both sides. Among them, the substrate thickness of the carbon-coated aluminum foil is 10 μm; the single-sided thickness of the conductive carbon black coating is 1 μm; dry in an oven and roll to make a positive electrode sheet. The coating speed is 8 m / min; the rolling speed is 10 m / min. Subsequently, measure the resistivity and peel strength of the positive electrode sheet respectively.

[0056] Examples 3-13

[0057] The implementation schemes of the remaining positive electrode sheets A / D / E / F / G / H / I / J / K / L / M are the same as those of the positive electrode sheet C in Example 1 except for the following content, and the remaining steps are as follows: The addition amounts of the additives in each example are shown in Table 1, and the formulas of each example are as follows:

[0058] The positive electrode sheet corresponding to Example 3 is A, and its formula component composition: active material, composite conductive agent, composite binder, and the corresponding additive compound 1 = 98:1:1:0.02.

[0059] The positive electrode sheet corresponding to Example 4 is D, and its formula component composition: active material, composite conductive agent, composite binder, and the corresponding additive compound 3 = 98:1:1:0.02.

[0060] The positive electrode sheet corresponding to Example 5 is E, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 4 = 98:1:1:0.03.

[0061] The positive electrode sheet corresponding to Example 6 is F, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 5 = 95.5:2.3:2.2:0.02.

[0062] The positive electrode sheet corresponding to Example 7 is G, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 6 = 98:1:1:0.03.

[0063] The positive electrode sheet corresponding to Example 8 is H, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 7 = 98:1:1:0.03.

[0064] The positive electrode sheet corresponding to Example 9 is I, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 8 = 95.5:2.3:2.2:0.03.

[0065] The positive electrode sheet corresponding to Example 10 is J, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 9 = 98:1:1:0.03.

[0066] The positive electrode sheet corresponding to Example 11 is K, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 10 = 98:1:1:0.03.

[0067] The positive electrode sheet corresponding to Example 12 is L, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 11 = 98:1:1:0.01.

[0068] The positive electrode sheet corresponding to Example 13 is M, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 12 = 98:1:1:0.03.

[0069] The positive electrode sheet corresponding to Example 14 is N, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 12 = 98:1:1:0.001.

[0070] The positive electrode sheet corresponding to Example 15 is O, and its composition of formula components: active material, composite conductive agent, composite binder and corresponding additive compound 13 (p-chlorophenylacetic acid) = 98:1:1:0.02.

[0071] Table 1 Parameters of the slurry and its pole piece after rolling

[0072]

[0073] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: In the preparation method of the lithium battery positive electrode slurry and its electrode sheet provided by the present invention, the slurry improves its fluidity by adding additives, and the positive electrode sheet is obtained by coating a positive electrode slurry obtained by uniformly mixing an active material, a composite conductive agent, a composite binder and corresponding additives on a current collector and then roll-pressing, and the current collector is a carbon-coated aluminum foil with conductive carbon black coatings on both sides; the positive electrode sheet of the present invention has the characteristics of a high proportion of active material, low internal resistance, and strong adhesion.

[0074] The foregoing is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A cathode slurry for a lithium-ion battery, characterized in that, The slurry includes an active material, a composite conductive agent, a composite binder, and an additive that competes with the composite binder. Among them, the composite conductive agent includes a first conductive agent, a second conductive agent, and a third conductive agent. The first conductive agent is selected from one or more of acetylene black, conductive carbon black, and conductive graphite. The second conductive agent is carbon nanotubes, and the third conductive agent is graphene. The composite binder includes a first binder and a second binder. The first binder is PVDF prepared by emulsion polymerization; the second binder is PVDF prepared by suspension polymerization. The additive is selected from any one of the following compounds: Compound 2 and Compound 3.

2. The slurry according to claim 1, wherein By weight, the ratio of the active material: the composite conductive agent: the composite binder: the additive is: 98~95.5: 1~2.3: 1~2.2: 0.005~0.

03.

3. The slurry according to claim 2, wherein, The ratio of the active material: the composite conductive agent: the composite binder: the additive is: 98~95.5: 1~2.3: 1~2.2: 0.01~0.

03.

4. The slurry according to claim 2, wherein The active material is lithium iron phosphate.

5. A method for preparing a positive electrode sheet of a lithium-ion battery, characterized in that, The preparation method includes: Mix the active material, the composite conductive agent, the composite binder, and the additive that competes with the composite binder to obtain a positive electrode slurry. Coat the positive electrode slurry on a current collector to obtain a precursor of the electrode. Roll and form the precursor of the electrode to obtain the positive electrode of the lithium-ion battery. Among them, the composite conductive agent includes a first conductive agent, a second conductive agent, and a third conductive agent. The first conductive agent is selected from one or more of acetylene black, conductive carbon black, and conductive graphite. The second conductive agent is carbon nanotubes, and the third conductive agent is graphene. The composite binder includes a first binder and a second binder. The first binder is PVDF prepared by emulsion polymerization; the second binder is PVDF prepared by suspension polymerization. The additive is selected from any one of the following: Compound 2 and Compound 3.

6. The preparation method according to claim 5, characterized in that, The preparation method includes: Step S1: Mix the composite binder and the additive and add them to a solvent to make a glue solution. Step S2: Add the first conductive agent and lithium iron phosphate to the glue solution in sequence to obtain a mixed solution. Step S3: Add the second conductive agent and the third conductive agent to the mixed solution and mix further to obtain the positive electrode slurry. Step S4: Coat the positive electrode slurry on the current collector to obtain the precursor of the electrode. Step S5: Roll and form the precursor of the electrode to obtain the positive electrode of the lithium-ion battery.

7. The preparation method according to claim 6, characterized in that, Steps S1, S2, and S3 are all stirred under vacuum conditions, and the stirring includes both revolution and rotation.

8. The preparation method according to claim 7, characterized in that, The revolution speed in Step S1 is 13~16 r / min, the rotation speed is 600~1000 r / min, and the stirring time is 180~200 minutes.

9. The preparation method according to claim 7, characterized in that, The revolution speed in Step S2 is 25~30 r / min, the rotation speed is 2500~3500 r / min, and the stirring time is 200~250 minutes.

10. The preparation method according to claim 7, characterized in that, The revolution speed in step S3 is 18 - 22 r / min, the rotation speed is 1800 - 2200 r / min, and the stirring time is 75 - 90 minutes.

11. The preparation method according to claim 7, characterized in that, Control the system viscosity of step S1, step S2, and step S3 to be lower than 10000 mPa·S.

12. The preparation method according to claim 11, characterized in that, The system viscosity of each step is controlled within 6000 - 8000 mPa·S.

13. The preparation method according to any one of claims 5 to 12, characterized in that, By weight, the ratio of the active material: the composite conductive agent: the composite binder: the additive is: 98 - 95.5: 1 - 2.3: 1 - 2.2: 0.001 - 0.

03.

14. According to the preparation method described in claim 13, the ratio of the active material: the composite conductive agent: the composite binder: the additive is: 98 - 95.5: 1 - 2.3: 1 - 2.2: 0.01 - 0.

03.

15. According to the preparation method described in claim 13, the current collector is a carbon-coated aluminum foil with conductive carbon black coatings on both sides.

16. According to the preparation method described in claim 15, the substrate thickness of the carbon-coated aluminum foil is 9 - 11 μm, and the single-sided thickness of the conductive carbon black coating is 0.8 - 1.1 μm.

17. According to the preparation method described in claim 13, the positive electrode paste is coated on the current collector by means of coating.

18. According to the preparation method described in claim 17, the coating speed is 6 - 10 m / min.

19. According to the preparation method described in claim 13, the rolling speed is 8 - 12 m / min.

20. A positive electrode sheet of a lithium-ion battery, characterized in that, The positive electrode sheet is prepared from the paste described in any one of claims 1 to 4, or is prepared by the preparation method described in any one of claims 5 to 19.

21. A lithium-ion battery, the lithium-ion battery comprising a positive electrode tab, characterized in that, The positive electrode sheet is the positive electrode sheet described in claim 20.

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