Composite binder and preparation method thereof, positive electrode slurry and preparation method thereof, and positive electrode plate

Abstract

The invention provides a composite binder and a preparation method thereof, positive electrode slurry and a preparation method thereof, and a positive electrode plate. The composite binder comprises a phenolic hydroxyl group and an anilino group. Wherein the phenolic hydroxyl group has hydrophilicity, and the anilino group also has certain hydrophilicity and can interact with hydrogen bonds in water molecules, so that the composite binder can form a stable dispersion system in water and is suitable for a water-based positive electrode formula.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a composite binder and a preparation method thereof, a positive electrode slurry and a preparation method thereof, and a positive electrode sheet. Background Art

[0002] Due to its excellent high adhesion, corrosion resistance and electrochemical stability, polyvinylidene fluoride (PVDF) is often used as a binder in the positive electrode formula of lithium iron phosphate (LFP). PVDF is a polymer composite material that is usually insoluble in water, so N-methylpyrrolidone (NMP) with a stronger polarity is usually used as a solvent to disperse the positive electrode LFP formula, that is, an oil-based positive electrode system. However, the recovery of NMP in the oil-based positive electrode system is time-consuming, labor-intensive and costly, so the development of a new positive electrode binder formula is urgent. Summary of the invention

[0003] Purpose of the invention: The embodiment of the present application provides a composite adhesive that is soluble in water and has a simple preparation process, high repeatability, and high conductivity.

[0004] A first aspect of the present application provides a composite adhesive, which contains a phenolic hydroxyl group and an aniline group.

[0005] In some embodiments, the composite binder includes a polyphenol compound and polyaniline, wherein the polyphenol compound includes the phenolic hydroxyl group and the polyaniline includes the aniline group;

[0006] The composite binder also includes a two-dimensional inorganic compound, and the mass ratio of the polyphenol compound, the polyaniline and the two-dimensional inorganic compound is 1:1.5-2.2:0.6-0.8.

[0007] A second aspect of the present application provides a method for preparing a composite adhesive, comprising:

[0008] Dissolving the polyphenol compound and the two-dimensional inorganic compound in deionized water, stirring and reacting to obtain a mixed solution;

[0009] Continue to add aniline and initiator to the mixed solution, stir and react to obtain a precipitate;

[0010] The precipitate is dried to obtain a composite adhesive.

[0011] In some embodiments, the mass ratio of the polyphenol compound, the two-dimensional inorganic compound and the aniline is 1:0.4-0.7:1.2-1.8.

[0012] In some embodiments, the mass ratio of the aniline to the initiator is 1:0.5-0.8.

[0013] In some embodiments, the polyphenol compound is selected from at least one of tannic acid and dopamine.

[0014] In some embodiments, the two-dimensional inorganic compound is selected from MXene-Ti3AlC2.

[0015] In some embodiments, the initiator is selected from at least one of anhydrous copper sulfate, ammonium sulfate, hydrogen peroxide, ammonium persulfate, benzoyl peroxide, and acetophenone peroxide.

[0016] The third aspect of the present application provides a positive electrode slurry, comprising a positive electrode material, a composite binder and an additive, wherein the composite binder comprises the composite binder as described above or a composite binder prepared by the method for preparing the composite binder as described above.

[0017] In some embodiments, the mass ratio of the composite binder, the positive electrode material and the additive is 97-98.6:1.2-2.5:0.2-0.5.

[0018] In some embodiments, the positive electrode material is selected from at least one of lithium iron phosphate and lithium iron manganese phosphate.

[0019] In some embodiments, the additive is selected from at least one of styrene-butadiene rubber, polyurethane, acrylate, and acrylonitrile.

[0020] A fourth aspect of the present application provides a method for preparing a positive electrode slurry, comprising:

[0021] Adding the composite binder and deionized water into a stirrer, wherein the stirrer performs a first stirring at a first speed;

[0022] Then, adding the positive electrode material and the deionized water into the stirrer, and stirring the stirrer for the second time at a second speed;

[0023] Adding additives into the stirrer, and stirring the stirrer for the third time at a third speed to obtain a positive electrode slurry;

[0024] Wherein, the composite adhesive includes the composite adhesive as described above or the composite adhesive prepared by the method for preparing the composite adhesive as described above.

[0025] In some embodiments, the mass ratio of the composite binder, the positive electrode material and the additive is 97-98.6:1.2-2.5:0.2-0.5.

[0026] In some embodiments, the mass ratio of the composite binder to the deionized water is 1:9-19.

[0027] In some embodiments, the first speed is V1, the second speed is V2, and the third speed is V3, satisfying: V3 <V1<V2。

[0028] In some embodiments, the first stirring time is t1, satisfying: 1h≤t1≤2h, the second stirring time is t2, satisfying: 3h≤t2≤5h, and the third stirring time is t3, satisfying: 0.5h≤t3≤1h.

[0029] In some embodiments, during the second stirring, the deionized water is continuously added into the stirrer to adjust the viscosity of the positive electrode slurry.

[0030] A fifth aspect of the present application provides a positive electrode plate, comprising a current collector and a positive electrode slurry disposed on at least one side of the current collector, wherein the positive electrode slurry comprises the positive electrode slurry as described above or is prepared by the preparation method of the composite binder as described above.

[0031] The present application provides a composite binder comprising phenolic hydroxyl groups and aniline groups; wherein the phenolic hydroxyl groups are hydrophilic, and the aniline groups also have a certain degree of hydrophilicity, and can interact with hydrogen bonds in water molecules, so the composite binder can form a stable dispersion system in water, which is suitable for aqueous positive electrode formulations.

[0032] The present application provides a method for preparing a composite binder, by dissolving a polyphenol compound and a two-dimensional inorganic compound in deionized water, wherein the polyphenol compound can improve the agglomeration of the two-dimensional inorganic compound caused by stacking, thereby improving the conductive properties of the two-dimensional inorganic compound. The composite binder provided in the present application is suitable for an aqueous positive electrode formulation, and has a simple preparation process, high repeatability, and good conductivity, and can improve the positive electrode capacity of the battery. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0034] In the present specification, a numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the minimum value and the maximum value, respectively.

[0035] The first aspect of the present application provides a composite adhesive, which will be described in detail below in conjunction with specific embodiments.

[0036] A composite binder contains phenolic hydroxyl groups and aniline groups.

[0037] It can be understood that the phenolic hydroxyl group is hydrophilic and the aniline group is also hydrophilic to a certain extent, and can interact with the hydrogen bonds in the water molecules. Therefore, the composite binder can form a stable dispersion system in water and is suitable for water-based positive electrode formulations.

[0038] In some embodiments, the composite binder includes a polyphenol compound and polyaniline, wherein the polyphenol compound includes a phenolic hydroxyl group and the polyaniline includes an aniline group;

[0039] The composite binder further comprises a two-dimensional inorganic compound, and the mass ratio of the polyphenol compound, polyaniline and the two-dimensional inorganic compound is 1:1.5 to 2.2:0.6 to 0.8. Specifically, the mass ratio of the polyphenol compound, polyaniline and the two-dimensional inorganic compound can be any one of 1:1.5:0.6, 1:1.5:0.7, 1:1.5:0.8, 1:2:0.6, 1:2:0.7, 1:2:0.8, 1:2.2:0.6, 1:2.2:0.7, 1:2.2:0.8 or any two of the ratios.

[0040] It can be understood that polyphenol compounds have adhesive properties, two-dimensional inorganic compounds have excellent conductive properties, polyaniline has conductivity and adhesive properties, and the composite binder provided in this application is suitable for aqueous positive electrode formulations, and has a simple preparation process, high repeatability, and good conductivity, which can improve the positive electrode capacity of the battery.

[0041] In some embodiments, the polyphenol compound is selected from at least one of tannic acid and dopamine.

[0042] It is understandable that tannic acid and dopamine are hydrophilic and can form a stable dispersion system in water. In addition, tannic acid and dopamine can self-polymerize in aqueous solution, and thus have good adhesion, and can interact with various surfaces to form a uniform coating.

[0043] In some embodiments, the two-dimensional inorganic compound is selected from MXene-Ti3AlC2.

[0044] It can be understood that MXene-Ti3AlC2 is a two-dimensional structured material with excellent conductive properties.

[0045] A second aspect of the present application provides a method for preparing a composite adhesive, comprising:

[0046] Dissolving the polyphenol compound and the two-dimensional inorganic compound in deionized water, stirring and reacting to obtain a mixed solution;

[0047] Continue to add aniline and initiator to the mixed solution, stir and react to obtain a precipitate;

[0048] The precipitate is dried to obtain a composite adhesive.

[0049] It is understandable that two-dimensional inorganic compounds are easily oxidized and easily stacked to cause agglomeration. By first dissolving the polyphenol compounds and the two-dimensional inorganic compounds in deionized water, the problem of the two-dimensional inorganic compounds being difficult to disperse and easy to agglomerate can be improved. At the same time, the polyphenol compounds are dissolved in deionized water and undergo self-polymerization reaction by stirring to form polyphenol compounds with certain adhesion. Aniline monomer and initiator are then added. The aniline monomer undergoes polymerization reaction under the action of the initiator to form polyaniline. The polyphenol compounds and the two-dimensional inorganic compounds are composited with polyaniline to further improve the conductivity of polyaniline, thereby preparing a composite binder, which is suitable for water-based positive electrode formulations, and has a simple preparation process, high repeatability, and good conductivity, and can increase the positive electrode capacity of the battery.

[0050] In some embodiments, the present application also provides a method for preparing a two-dimensional inorganic compound, comprising:

[0051] Dissolve the fluoride salt in an acid solution, add MAX-Ti3AlC2, stir, filter, wash the precipitate to a preset pH value, and ultrasonically disperse it in deionized water to obtain a dispersion;

[0052] The dispersion is centrifuged and the precipitate is dried to obtain a two-dimensional inorganic compound.

[0053] It can be understood that the acid solution can provide an acidic environment to activate the surface of MAX-Ti3AlC2, which is helpful to remove the oxide layer, impurities and surface functional groups. By dissolving fluoride salt in the acid solution, fluoride ions (F - ), fluorination treatment can change the electronic structure and conductive properties of MAX-Ti3AlC2, which helps to improve its electrical conductivity, energy storage capacity and electrode performance.

[0054] In some embodiments, the fluoride salt is selected from at least one of lithium fluoride and sodium fluoride.

[0055] In some embodiments, the acid is selected from at least one of hydrochloric acid, hydrofluoric acid, and sulfuric acid.

[0056] In some embodiments, the pH value may be any one of 5, 6, 7, 8, or a range consisting of any two values.

[0057] In some embodiments, during the process of dissolving the polyphenol compound and the two-dimensional inorganic compound in deionized water, stirring and reacting, the stirring temperature is 23 to 26° C., and the stirring time is 5 to 6 hours. Specifically, the stirring temperature can be any one of 23° C., 24° C., 25° C., and 26° C., or a range consisting of any two values; the stirring time can be any one of 5 hours, 5.5 hours, and 6 hours, or a range consisting of any two values.

[0058] It can be understood that the polyphenol compounds are dissolved in deionized water and undergo a self-polymerization reaction through stirring to form polyphenol compounds. The stirring temperature is also the reaction temperature, and the stirring time is also the reaction time.

[0059] In some embodiments, during the process of adding aniline and initiator to the mixed solution, stirring and reacting, the reaction temperature is 0 to 5°C and the reaction time is 7 to 9 hours. Specifically, the reaction temperature can be any one of 0°C, 1°C, 2°C, 3°C, 4°C, and 5°C, or a range consisting of any two values, and the reaction time can be any one of 7h, 8h, and 9h, or a range consisting of any two values.

[0060] In some embodiments, during the drying of the precipitate, the drying temperature is 80 to 120° C., and the drying time is 8 to 12 hours. Specifically, the drying temperature can be any one of 80° C., 90° C., 100° C., 110° C., and 120° C., or a range consisting of any two values; the drying time can be any one of 8 hours, 9 hours, 10 hours, 11 hours, and 12 hours, or a range consisting of any two values.

[0061] In some embodiments, the mass ratio of the polyphenol compound, the two-dimensional inorganic compound and aniline is 1:0.4-0.7:1.2-1.8. Specifically, the mass ratio of the polyphenol compound, the two-dimensional inorganic compound and aniline can be any one of 1:0.4:1.2, 1:0.4:1.8, 1:0.5:1.2, 1:0.5:1.8, 1:0.7:1.2, 1:0.7:1.8 or any two of the ratios.

[0062] It is understandable that too little polyphenol compound may not be able to disperse the two-dimensional inorganic compound and cannot improve the adhesion of the composite binder, and too much polyphenol compound will affect the conductivity; too little two-dimensional inorganic compound cannot improve the conductivity of the composite binder, and too much two-dimensional inorganic compound will cause agglomeration; too little aniline cannot improve the adhesion, and too much aniline will affect the conductivity of the composite binder; by controlling the mass ratio of polyphenol compounds, two-dimensional inorganic compounds and aniline to 1:0.4~0.7:1.2~1.8, a composite binder is prepared, which is suitable for water-based positive electrode formulations, and has a simple preparation process, high repeatability, good conductivity, and can improve the positive electrode capacity of the battery.

[0063] In some embodiments, the mass ratio of aniline to initiator is 1:0.5 to 0.8. Specifically, the mass ratio of aniline to initiator can be any one of 1:0.5, 1:0.6, 1:0.7, 1:0.8 or any two of the ratios.

[0064] It can be understood that by controlling the mass ratio of aniline to initiator to be 1:0.5-0.8, so that the initiator is excessive, it can be ensured that aniline is completely initiated to polymerize to form polyaniline.

[0065] In some embodiments, the polyphenol compound is selected from at least one of tannic acid and dopamine.

[0066] It can be understood that polytannic acid and polydopamine are hydrophilic and can form a stable dispersion system in water. In addition, polytannic acid and polydopamine have good adhesion and can interact with various surfaces to form a uniform coating.

[0067] In some embodiments, the two-dimensional inorganic compound is selected from MXene-Ti3AlC2.

[0068] It can be understood that MXene-Ti3AlC2 is a two-dimensional structured material with excellent conductive properties.

[0069] In some embodiments, the initiator is selected from at least one of anhydrous copper sulfate, ammonium sulfate, hydrogen peroxide, ammonium persulfate, benzoyl peroxide, and acetophenone peroxide.

[0070] It is understood that aniline undergoes an oxidation reaction under the action of an initiator to form free radicals, and these free radicals react with other aniline molecules to form polyaniline.

[0071] The third aspect of the present application provides a positive electrode slurry, including a positive electrode material, a composite binder and an additive, wherein the composite binder includes the composite binder as described above or a composite binder prepared by the method for preparing the composite binder as described above.

[0072] It can be understood that the positive electrode slurry provided in the present application has good dispersibility, good film-forming property and is not easy to detach.

[0073] In some embodiments, the mass ratio of the composite binder, the positive electrode material and the additive is 97-98.6:1.2-2.5:0.2-0.5. Specifically, the mass ratio of the composite binder, the positive electrode material and the additive is any one of 97:2.5:0.5, 97.3:2.5:0.2, 98:1.5:0.5, 98.6:1.2:0.2, 98.3:1.2:0.5, 98.5:2.2:0.3 or any two of the ratios.

[0074] It can be understood that by controlling the mass ratio of the composite binder, the positive electrode material and the additive to be 97-98.6:1.2-2.5:0.2-0.5, the prepared positive electrode slurry has good dispersibility, good film-forming property and is not easy to detach.

[0075] In some embodiments, the positive electrode material is selected from at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0076] In some embodiments, the additive is selected from at least one of styrene-butadiene rubber, polyurethane, acrylate, and acrylonitrile.

[0077] It is understandable that the flexibility of the prepared positive electrode sheet can be improved by adding additives.

[0078] A fourth aspect of the present application provides a method for preparing a positive electrode slurry, comprising:

[0079] Adding the composite binder and deionized water into the stirrer, and stirring the mixture for the first time at a first speed;

[0080] Then, the positive electrode material and deionized water are added into the stirrer, and the stirrer performs a second stirring at a second speed;

[0081] Adding additives to the stirrer, and stirring the stirrer for the third time at a third speed to obtain a positive electrode slurry;

[0082] The composite adhesive includes the composite adhesive as described above or a composite adhesive prepared by the method for preparing the composite adhesive as described above.

[0083] It can be understood that by first adding the composite binder and deionized water and then adding the positive electrode material and additives, the preparation time of the positive electrode slurry is shortened, and the prepared positive electrode slurry has good dispersibility.

[0084] In some embodiments, the mass ratio of the composite binder, the positive electrode material and the additive is 97-98.6:1.2-2.5:0.2-0.5. Specifically, the mass ratio of the composite binder, the positive electrode material and the additive is any one of 97:2.5:0.5, 97.3:2.5:0.2, 98:1.5:0.5, 98.6:1.2:0.2, 98.3:1.2:0.5 or any two of the ratios.

[0085] In some embodiments, the mass ratio of the composite binder to deionized water is 1:9 to 19. Specifically, the mass ratio of the composite binder to deionized water can be any one of 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or any two of the ratios.

[0086] It can be understood that by controlling the mass ratio of the composite binder to deionized water to be 1:9-19, the solid content of the composite binder can be controlled to be 5-10%, thereby increasing the solid content of the positive electrode slurry.

[0087] In some embodiments, the first speed is V1, the second speed is V2, and the third speed is V3, satisfying: V3 <V1<V2。

[0088] It can be understood that after adding the composite binder and deionized water to the agitator, the composite binder can be evenly dispersed in the deionized water by stirring at the first speed V1; after adding the positive electrode material, due to the increase in the solid content in the slurry, it is necessary to stir at the second speed V2 so that the positive electrode material and the composite binder can be mixed more quickly and evenly; finally, after adding the additive, stirring at the third speed V3 can obtain a uniformly dispersed positive electrode slurry.

[0089] In some embodiments, the first speed is V1, which satisfies: 1500 rpm≤V1≤2500 rpm. Specifically, the first speed V1 can be any one of 1500 rpm, 1800 rpm, 2000 rpm, 2300 rpm, and 2500 rpm, or a range consisting of any two of the values.

[0090] In some embodiments, the second speed is V2, which satisfies: 3500 rpm≤V2≤4500 rpm. Specifically, the second speed V2 can be any one of 3500 rpm, 3800 rpm, 4000 rpm, 4300 rpm, and 4500 rpm, or a range consisting of any two of the values.

[0091] In some embodiments, the third speed is V3, which satisfies: 500 rpm≤V3≤1000 rpm. Specifically, the third speed V3 can be any one of 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, and 1000 rpm, or a range consisting of any two values.

[0092] In some embodiments, the first stirring time is t1, which satisfies: 1h≤t1≤2h, the second stirring time is t2, which satisfies: 3h≤t2≤5h, and the third stirring time is t3, which satisfies: 0.5h≤t3≤1h. Specifically, the first stirring time t1 can be any one of 1h, 1.5h, and 2h, or a range consisting of any two values; the second stirring time t2 can be any one of 3h, 4h, and 5h, or a range consisting of any two values; the third stirring time t3 can be any one of 0.5h, 0.8h, and 1h, or a range consisting of any two values.

[0093] It can be understood that after adding the composite binder and deionized water to the agitator, by controlling the time of the first stirring to t1 and satisfying: 1h≤t1≤2h, the composite binder can be evenly dispersed in the deionized water. After adding the positive electrode material, by controlling the time of the second stirring to t2 and satisfying: 3h≤t2≤5h, the positive electrode material and the composite binder can be mixed more quickly and evenly. Finally, after adding the additive, by controlling the time of the third stirring to t3 and satisfying: 0.5h≤t3≤1h, a uniformly dispersed positive electrode slurry can be obtained.

[0094] In some embodiments, during the second stirring, deionized water is continuously added into the stirrer to adjust the viscosity of the positive electrode slurry.

[0095] A fifth aspect of the present application provides a positive electrode plate, comprising a current collector and a positive electrode slurry arranged on at least one side of the current collector, wherein the positive electrode slurry comprises the positive electrode slurry as above or is prepared by the preparation method of the composite binder as above.

[0096] It can be understood that the positive electrode plate provided in the present application has the advantages of high peel strength and low resistivity due to the use of a composite binder including polyphenol compounds, two-dimensional inorganic compounds and aniline. At the same time, due to the addition of additives, the positive electrode plate has good flexibility and is not easy to fall off.

[0097] A sixth aspect of the present application provides a method for preparing a positive electrode sheet, comprising:

[0098] The positive electrode slurry is coated on at least one side of the current collector and baked to obtain a positive electrode sheet. The positive electrode slurry includes the slurry as described above.

[0099] In some embodiments, the current collector is selected from any one of aluminum foil and carbon-coated aluminum foil.

[0100] In some embodiments, the coating method is selected from any one of transfer coating and extrusion coating.

[0101] In some embodiments, the baking temperature is 100-130° C. Specifically, the baking temperature can be any one of 100° C., 105° C., 110° C., 115° C., 120° C., 125° C., and 130° C., or a range consisting of any two of the values.

[0102] In some embodiments, the baking time is 3 to 5 minutes. Specifically, the baking time can be any one of 3 minutes, 4 minutes, and 5 minutes, or a range consisting of any two values.

[0103] The following describes the invention in conjunction with specific embodiments.

[0104] Example 1

[0105] (1) Preparation of composite adhesive:

[0106] The mass ratio of tannic acid, MXene-Ti3AlC2, and aniline is 1:0.5:1.6;

[0107] Dissolve 100 g of tannic acid in 1 L of deionized water, add 50 g of MXene-Ti3AlC2, stir and react at 25 °C for 6 h to obtain a mixed solution;

[0108] Continue to add 160g of aniline to the mixed solution, precool it in an ice-water bath for 30min, then add 80g of anhydrous copper sulfate, stir and react at 0℃ for 8h to obtain a precipitate;

[0109] The precipitate is dried and crushed to obtain a composite adhesive.

[0110] (2) Preparation of positive electrode slurry:

[0111] The mass ratio of LFP, composite binder and SBR is 98.2:1.5:0.3;

[0112] The composite binder and deionized water are added into a double planetary stirrer and stirred for 5 hours at a first speed V1, wherein the first speed V1 is 2000 rpm and the mass ratio of the composite binder to the deionized water is 1:14;

[0113] Then, LFP and deionized water were added into the double planetary mixer and stirred for 4 h at a second speed V2 of 3500 rpm;

[0114] Finally, SBR was added into the double planetary mixer and stirred for 0.5 h at the third speed V3, where the third speed V3 was 800 rpm, to obtain positive electrode slurry.

[0115] Example 2

[0116] The preparation method of Example 2 is the same as that of Example 1, except that the mass ratio of LFP, composite binder and SBR is 98.3:1.2:0.5.

[0117] Example 3

[0118] The preparation method of Example 3 is the same as that of Example 1, except that the mass ratio of LFP, composite binder and SBR is 97.7:2:0.3.

[0119] Example 4

[0120] The preparation method of Example 4 is the same as that of Example 1, except that the mass ratio of LFP, composite binder and SBR is 97.3:2.5:0.2.

[0121] Comparative Example 1

[0122] The mass ratio of LFP, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) is 96.5:1.5:2;

[0123] Add SP, PVDF and N-methylpyrrolidone (NMP) into a double planetary stirrer and stir for 4 h at a first speed V1 of 2000 rpm, with a mass ratio of SP and PVDF to deionized water of 3:2;

[0124] Then, LFP and NMP were added into the double planetary stirrer and stirred for 5 h at a second speed V2 of 3500 rpm to obtain a positive electrode slurry.

[0125] Comparative Example 2

[0126] The preparation method of Comparative Example 2 is the same as that of Example 1, except that the mass ratio of LFP to the composite binder is 98.5:1.5.

[0127] Comparative Example 3

[0128] The preparation method of Comparative Example 3 is the same as that of Example 1, except that the mass ratio of LFP, SP and SBR is 97.9:1.8:0.3.

[0129] A method for preparing a positive electrode sheet comprises:

[0130] Providing positive electrode slurry: positive electrode slurry prepared in Examples 1 to 4 and Comparative Examples 1 to 3;

[0131] The positive electrode slurry was coated on one side of the aluminum foil by transfer coating and baked at 120° C. for 3 minutes to obtain a positive electrode sheet.

[0132] Positive electrode performance test:

[0133] (1) Surface density: Use a sampler to take a small sample from the positive electrode. The sample area is s, in m 2 ; The sample is weighed on an electronic balance, the sample weight is M, unit is g; the weight of the copper foil of the same area is recorded as m, unit is g; the surface density X is: Unit: g / m 2 .

[0134] (2) Peel strength: refer to GB / T2792-2014 standard.

[0135] (3) Electrode resistivity: Two-probe method, the terminals are placed at both ends of the sample, and the current at both ends of the sample is collected by inputting an AC voltage signal to obtain the sample resistance, and the sample resistivity is obtained through the conversion relationship.

[0136] A method for preparing a lithium-ion battery, comprising:

[0137] Positive electrode sheet: the positive electrode sheet prepared in Examples 1 to 4 and Comparative Examples 1 to 2;

[0138] Negative electrode sheet: The negative electrode slurry includes artificial graphite, SP, carboxymethyl cellulose (CMC) and SBR in a mass ratio of 93.7-97.2:0.8-2.0:1.0-1.8:1.0-2.5, the solvent is deionized water, and the solid content is controlled to be 45-60%; the negative electrode slurry is applied on one side of the copper foil by transfer coating, and baked at 80°C for 3-5 minutes to obtain the negative electrode sheet.

[0139] Electrolyte: The electrolyte includes lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC); wherein the volume ratio of EC, DMC and EMC is 1:1:1, and a lithium ion battery electrolyte is obtained, and the concentration of LiPF6 is 1 mol / L;

[0140] Diaphragm: polyethylene film;

[0141] Rolling and die-cutting the positive electrode sheet and the negative electrode sheet;

[0142] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, thereby obtaining a stack;

[0143] The laminate is wound to obtain a bare cell, which is placed in an outer packaging shell, dried and injected with electrolyte, and then subjected to vacuum packaging, standing, forming, shaping and other processes to obtain a lithium-ion battery.

[0144] Lithium-ion battery performance test

[0145] (1) Basic electrical performance test: At 25°C, the lithium-ion battery is first pre-charged with a small current for 180 minutes, fully charged at a constant current of 0.33C to 3.65V, and then fully discharged at a constant voltage of 0.05C to 2.5V at 0.33C. The ratio of the discharge capacity to the charge capacity is calculated to obtain the initial efficiency.

[0146] (2) Dynamic performance test: The lithium-ion battery is tested at 25°C and -20°C using the standard HPPC (Hybrid Pulse Power Characteristic) test method to measure the charge and discharge DCR (Direct Current Resistance) at different SOCs (State of Charge). The DCR at 50% is mainly evaluated.

[0147] (3) Cycle performance test: At 25°C, the lithium-ion battery was charged at a rate of 3C and discharged at a rate of 1C, and a full charge and discharge cycle test was performed until the capacity of the lithium-ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.

[0148] Table 1 shows the performance test results of the positive electrode slurries and positive electrode sheets prepared in Examples 1 to 4 and Comparative Examples 1 to 3

[0149]

[0150] Result analysis:

[0151] It can be seen from the test results in Table 1 that the slurry discharge state and coating state of Examples 1 to 4 and Comparative Example 1 are normal, and the positive electrode sheets prepared in Examples 1 to 4 have higher sheet peeling strength and lower sheet resistivity. Compared with Comparative Example 1, the peeling strength of the positive electrode sheets in Examples 1 to 4 is increased by 10% to 20%, and the resistivity of the positive electrode sheets is reduced by 14% to 20%.

[0152] The slurry discharge and coating states of Examples 1 to 4 and Comparative Example 2 are normal, but the die-cut edge of Comparative Example 2 has slight chipping, and the peel strength of the positive electrode sheet of Comparative Example 2 is also slightly lower than that of Examples 1 to 4. The reason is that the lack of SBR in the positive electrode slurry formula of Comparative Example 2 makes the prepared positive electrode sheet brittle, and even if the peel strength is within the qualified range, it is still easy to cause edge chipping.

[0153] Compared with Example 3, Example 3 uses SP instead of the polytannic acid / MXene-Ti3AlC2 / polyaniline composite binder in Examples 1 to 4. Only 0.3% SBR cannot disperse the slurry normally, and the slurry settles and cannot be coated.

[0154] Table 2 shows the test results of lithium ion batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 3

[0155]

[0156] Result analysis:

[0157] From the test results in Table 2, it can be seen that compared with Comparative Example 1, Examples 1 to 4 have an increase of about 2% in the first efficiency of the battery, a decrease of 10% to 18% in the internal resistance of the battery, a significant decrease in the DCR at both room temperature and low temperature, and an increase of about 10% in the number of cycles at room temperature 3C / 1C. The reason is that the positive electrode formula in Comparative Example 1 is an oil-based positive electrode formula, in which PVDF is an electronic insulating compound, and adding it to the positive electrode sheet will affect electron transmission, thereby affecting the first efficiency and internal resistance of the battery.

[0158] Compared with Comparative Example 2, Examples 1 to 4 have little difference in the first efficiency, internal resistance, and DCR at room temperature and low temperature, but the number of cycles at room temperature 3C / 1C of Examples 1 to 4 is much higher than that of Comparative Example 2. The reason is that the positive electrode sheet with only polytannic acid / MXene-Ti3AlC2 / polyaniline composite binder and positive electrode material formula has low peeling force and is brittle. At the end of the cycle, the interface of the positive electrode sheet is poor and easy to fall off, thus affecting the number of cycles.

[0159] In summary, although the embodiments of the present application are described in detail above, the above embodiments are not intended to limit the present application, and ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and 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 application.

Claims

1. A composite adhesive, characterized in that: The composite binder contains phenolic hydroxyl groups and aniline groups.

2. The composite adhesive according to claim 1, characterized in that: The composite binder includes polyphenolic compounds and polyaniline. Among them, the polyphenolic compounds contain the phenolic hydroxyl groups, and the polyaniline contains the aniline groups; The composite binder further includes two-dimensional inorganic compounds, and the mass ratio of the polyphenolic compounds, the polyaniline, and the two-dimensional inorganic compounds is 1:1.5 - 2.2:0.6 - 0.

8.

3. A method for preparing a composite adhesive, characterized in that: It includes: Dissolve polyphenolic compounds and two-dimensional inorganic compounds in deionized water, stir and react to obtain a mixed solution; Continue to add aniline and an initiator to the mixed solution, stir and react to obtain a precipitate; Dry the precipitate to obtain a composite binder.

4. The preparation method of the composite binder according to claim 3, characterized in that The mass ratio of the polyphenolic compounds, the two-dimensional inorganic compounds, and the aniline is 1:0.4 - 0.7:1.2 - 1.8; and / or, The mass ratio of the aniline and the initiator is 1:0.5 - 0.

8.

5. The method for preparing the composite adhesive according to claim 3, characterized in that: The polyphenolic compounds are selected from at least one of tannic acid and dopamine; and / or, The two-dimensional inorganic compounds are selected from MXene-Ti3AlC2; and / or, The initiator is selected from at least one of anhydrous copper sulfate, ammonium sulfate, hydrogen peroxide, ammonium persulfate, benzoyl peroxide, and acetophenone peroxide.

6. A positive electrode slurry, characterized in that: It includes a cathode material, a composite binder, and an additive. The composite binder includes the composite binder according to any one of claims 1 - 2 or the composite binder prepared by the preparation method of the composite binder according to any one of claims 3 - 5.

7. The positive electrode slurry according to claim 6, characterized in that The mass ratio of the composite binder, the cathode material, and the additive is 97 - 98.6:1.2 - 2.5:0.2 - 0.5; and / or, The cathode material is selected from at least one of lithium iron phosphate and lithium manganese iron phosphate; and / or, The additive is selected from at least one of styrene-butadiene rubber, polyurethane, acrylate, and acrylonitrile.

8. A method for preparing a positive electrode slurry, characterized in that: It includes: Add the composite binder and deionized water to a stirrer, and the stirrer performs the first stirring at a first speed; Then add the cathode material and the deionized water to the stirrer, and the stirrer performs the second stirring at a second speed; Then add the additive to the stirrer, and the stirrer performs the third stirring at a third speed to obtain a cathode slurry; Among them, the composite binder includes the composite binder according to any one of claims 1 - 2 or the composite binder prepared by the preparation method of the composite binder according to any one of claims 3 - 5.

9. The method for preparing positive electrode slurry according to claim 8, characterized in that: The mass ratio of the composite binder, the cathode material, and the additive is 97 - 98.6:1.2 - 2.5:0.2 - 0.5; and / or, The mass ratio of the composite binder to the deionized water is 1:9 - 19; and / or, The first speed is V1, the second speed is V2, and the third speed is V3, satisfying: V3 < V1 < V2; and / or, The first stirring time is t1, which satisfies: 1h≤t1≤2h, the second stirring time is t2, which satisfies: 3h≤t2≤5h, and the third stirring time is t3, which satisfies: 0.5h≤t3≤1h; and / or, During the second stirring process, the deionized water is continuously added into the stirrer to adjust the viscosity of the positive electrode slurry.

10. A positive electrode sheet, characterized in that: It comprises a current collector and a positive electrode slurry arranged on at least one side of the current collector, wherein the positive electrode slurry comprises the positive electrode slurry as claimed in any one of claims 6 to 7 or is prepared by the preparation method of the composite binder as claimed in any one of claims 8 to 9.

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