Polyacrylic binder, method for its production and lithium-ion battery

Abstract

The application relates to the new energy technology field, in particular to a polyacrylic binder, a preparation method thereof and a lithium ion battery. The preparation method of the polyacrylic powder binder comprises the following steps: mixing polymerization monomers and an initiator, generating a polymerization reaction, and preparing a polyacrylic copolymer; under the condition that an alcohol solvent exists, the polyacrylic copolymer is subjected to neutralization treatment at a temperature of not more than 60 DEG C, and a polyacrylic powder binder is obtained. The neutralization treatment is carried out under the condition that the alcohol solvent exists and at a temperature of not more than 60 DEG C, the obtained powder binder can adapt to a subsequent dry homogenization process, has good adhesion, is beneficial to inhibiting the volume expansion of an electrode pole piece, and thus the cycle performance of the lithium ion battery is improved. Meanwhile, if the alcohol solvent can be retained, the flexibility of the binder is increased, and the processing yield of the electrode pole piece is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy, in particular to a polyacrylic binder, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in the fields of electronic products, electric vehicles and energy storage devices due to their high energy density, long cycle life and easy design. With the increasing richness of application scenarios and functional requirements of various products, the market has also put forward higher requirements for the energy density, reliability and cost of lithium ion batteries.

[0003] The binder is an important material in lithium ion batteries, which mainly functions to adhere electrode active materials and conductive agents to the current collector. Although the amount of binder is not large, the performance of the binder has an important influence on the performance of lithium batteries.

[0004] At present, styrene-butadiene rubber solution (SBR) is widely used as a binder, and carboxymethyl cellulose (CMC) is added as a thickening dispersant during use. However, the material composition determines that the SBR / CMC contains limited polar functional groups such as carboxyl, ester and cyano groups, and the interaction between the binder and the negative electrode material, especially the silicon-carbon negative electrode, is weak, so the comprehensive performance of the battery, especially the low-temperature performance, has gradually become difficult to meet the application requirements.

[0005] Polyacrylic acid (PAA) binders contain a high content of polar functional groups in the polymer. During charging and discharging, complexation and decomplexation occur between the polar functional groups and lithium ions, which can promote lithium ion conduction and reduce the internal resistance of the battery. However, polyacrylic acid itself has an ultra-high molecular weight, and its viscosity in water is very high, so it is difficult to increase the solid content, resulting in an increase in the transportation and packaging costs of polyacrylic acid solution binders. Compared with solution binders, powder binders have lower transportation and packaging costs, but the current powder binders cannot well adapt to the dry homogenization process during the preparation of electrode slurry, which affects the performance of the battery. SUMMARY

[0006] Therefore, the first aspect of the present application provides a preparation method of a polyacrylic acid powder binder.

[0007] The preparation method of the polyacrylic acid powder binder comprises the following steps:

[0008] polymerization of the mixed monomers and the initiator to prepare a polyacrylic acid copolymer;

[0009] neutralization of the polyacrylic acid copolymer at a temperature not higher than 60°C in the presence of an alcohol solvent to obtain a polyacrylic acid powder binder.

[0010] The present application has found through experiments that, in the preparation process of the polyacrylic powder binder, the neutralization operation has an important influence on the subsequent powder binder capable of adapting to the dry electrode homogenate. The present application carries out the neutralization treatment under the condition of the presence of an alcohol solvent at a temperature not exceeding 60 DEG C, the reaction is more moderate, and the problem that the powder binder is difficult to be redissolved in the aqueous slurry, homogenate is difficult to occur, and the electrode cannot be prepared due to the neutralization treatment at high temperature is avoided. Moreover, the alcohol solvent can also be used as a dissolution inhibitor of the polyacrylic copolymer, the hydration problem of the polyacrylic copolymer in the low-temperature neutralization process is improved, the powder binder is smoothly obtained, the powder binder obtained by forced drying does not interfere with the subsequent dry homogenate stability, and the adhesion and the swelling inhibition capacity are significantly improved, the volume expansion of the active material in the charge-discharge cycle can be effectively inhibited, and the cycle performance of the electrode sheet and the lithium ion battery is improved. At the same time, if the alcohol solvent can be retained in the polyacrylic powder binder, the flexibility of the binder is also increased, the hard and brittle characteristics of the binder are improved, the die cutting off material is improved, and the processing yield of the electrode sheet is improved.

[0011] Optionally, the number of carbon atoms of the alcohol solvent is not less than 3.

[0012] Optionally, the number of carbon atoms of the alcohol solvent is between 3 and 6. For example, the number of carbon atoms of the alcohol solvent is 3, 4, 5 or 6.

[0013] Optionally, the alcohol solvent is selected from one or more of 1,3-butanediol, 1,4-butanediol, 1,2-propanediol, 1,2-pentanediol, pentaerythritol, isopropyl alcohol, glycerol, 1-butanol, 1-pentanol, 2-butanol and 1-hexanol.

[0014] Optionally, the mass of the alcohol solvent is not less than the total mass of the polymerized monomers. If the amount of the alcohol solvent added is less than the total mass of the polymerized monomers, the dissolution inhibition effect of the polyacrylic copolymer is relatively poor, the polyacrylic copolymer is hydrated in the neutralization treatment, a thick paste is formed, the difficulty of obtaining the powder binder by drying is increased, if the powder binder is forced to dry, the drying time needs to be prolonged, a small amount of insoluble substances will be produced, the homogenate instability will be aggravated, the adhesion and the swelling inhibition capacity will be affected, and the battery performance will be affected. Optionally, the mass of the alcohol solvent is 1 to 3 times the total mass of the polymerized monomers. For example, the mass of the alcohol solvent is 1, 2 or 3 times the total mass of the polymerized monomers. If the amount of the alcohol solvent added is too much, the energy consumption cost of recovery will be increased.

[0015] In the present application, the temperature of the neutralization treatment is not more than 60℃. For example, the temperature of the neutralization treatment is 10℃, 20℃, 30℃, 40℃, 50℃, 60℃. When the temperature of the neutralization treatment is too high, the PAA will be self-crosslinked, and when the dry homogenization is performed, the powder binder is difficult to be re-dissolved in the aqueous slurry, and gel or insoluble matter will be generated, which will affect the preparation of the electrode.

[0016] Optionally, after the neutralization treatment, the following step is further included: solid-liquid separation is performed on the reaction system after the neutralization treatment is completed, and the obtained solid is incompletely dried. In order to cooperate with the subsequent dry homogenization process, the solid is incompletely dried.

[0017] Optionally, the temperature of the incomplete drying is not more than 80℃. For example, the temperature of the incomplete drying is 40℃, 50℃, 60℃, 70℃, 80℃. Controlling the temperature of the incomplete drying is beneficial to obtain a powder binder that is more suitable for the dry homogenization process.

[0018] Optionally, the conditions of the incomplete drying are controlled so that the solid content of the polyacrylic powder binder is 90wt%-99wt%. For example, the solid content of the polyacrylic powder binder is 90wt%, 92wt%, 95wt%, 98wt%, 99wt%. The above-mentioned solid content is beneficial to the subsequent dry homogenization.

[0019] When the alcohol solvent has a large number of carbon atoms, for example, the number of carbon atoms is 6, in the subsequent incomplete drying process, the alcohol solvent is not easy to volatilize, and the content of the alcohol solvent remaining in the polyacrylic powder binder is large. Optionally, the content of the residual alcohol solvent in the polyacrylic powder binder is greater than or equal to 0.3wt%. Optionally, the content of the residual alcohol solvent in the polyacrylic powder binder is 0.3wt%-8wt%. For example, the content of the residual alcohol solvent in the polyacrylic powder binder is 0.3wt%, 0.5wt%, 2wt%, 5wt%, 8wt%. The residual alcohol solvent can act as a plasticizer, which is beneficial to increase the flexibility of the binder, improve the hard and brittle characteristics of the binder, improve the die cutting scrap, and improve the processing yield rate of the electrode plate.

[0020] When the alcohol solvent has a small number of carbon atoms, for example, 3, the alcohol solvent is easy to volatilize in the subsequent incomplete drying process, and the alcohol solvent content in the polyacrylic powder binder is small. In order to improve the flexibility of the binder, after incomplete drying, the following steps are optionally included: supplementing the alcohol solvent to the polyacrylic powder binder to make the alcohol solvent content greater than or equal to 0.3wt%; optionally, supplementing the alcohol solvent to the polyacrylic powder binder to make the alcohol solvent content 0.3wt%-8wt%. For example, supplementing the alcohol solvent to the polyacrylic powder binder to make the alcohol solvent content 0.3wt%, 0.5wt%, 2wt%, 5wt%, 8wt%. By supplementing the alcohol solvent, it is beneficial to increase the flexibility of the binder, improve the hard and brittle characteristics of the binder, improve the die cutting scrap, and improve the processing yield rate of the electrode sheet.

[0021] Optionally, the method of supplementing the alcohol solvent is to spray the alcohol solvent onto the powder in the form of spray.

[0022] Optionally, the conditions of the polymerization reaction and the neutralization treatment are controlled to make the weight average molecular weight (Mw) of the polyacrylic powder binder between 600,000 and 2,500,000. For example, the weight average molecular weight of the polyacrylic powder binder is 600,000, 700,000, 900,000, 1,200,000, 1,500,000, 2,000,000, 2,400,000, 2,500,000.

[0023] Optionally, the conditions of the polymerization reaction and the neutralization treatment are controlled to make the molecular weight distribution of the polyacrylic powder binder between 1.5 and 6. For example, the molecular weight distribution of the polyacrylic powder binder is 1.5, 1.8, 2, 3, 5, 6.

[0024] Optionally, the pH value of the system of the neutralization treatment is 6-9. For example, the pH value of the system of the neutralization treatment is 6, 7, 8, 9.

[0025] Optionally, the neutralizing agent of the neutralization treatment includes an alkaline substance. Optionally, the alkaline substance includes an inorganic base. Optionally, the inorganic base includes one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, lithium carbonate, sodium carbonate, and potassium carbonate.

[0026] Optionally, the polymerizable monomers include carboxyl-containing polymerizable monomers, amide-containing polymerizable monomers, and nitrile-containing polymerizable monomers. Optionally, the polymerizable monomers further include phosphorus-containing polymerizable monomers. In some examples, the polymerizable monomers include carboxyl-containing polymerizable monomers, amide-containing polymerizable monomers, nitrile-containing polymerizable monomers, and phosphorus-containing polymerizable monomers.

[0027] Optionally, the carboxyl-containing polymerizable monomer accounts for 20wt%-40wt% of the total amount of the polymerizable monomers, the amide-containing polymerizable monomer accounts for 10-35wt% of the total amount of the polymerizable monomers, the nitrile-containing polymerizable monomer accounts for 40-50wt% of the total amount of the polymerizable monomers, and the phosphorus-containing polymerizable monomer accounts for 0.1wt%-5wt% of the total amount of the polymerizable monomers.

[0028] Optionally, the carboxyl-containing polymerizable monomer is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, maleic acid, sodium maleate, and lithium maleate.

[0029] Optionally, the amide-containing polymerizable monomer is selected from one or more of acrylamide, methacrylamide, N,N-methylenebisacrylamide, N-isopropyl acrylamide, and N-ethyl acrylamide.

[0030] Optionally, the nitrile-containing polymerizable monomer is selected from one or more of acrylonitrile and methacrylonitrile.

[0031] Optionally, the phosphorus-containing polymerizable monomer is selected from one or more of a phosphate-containing acrylate, an allyl phosphate, and a phosphate-containing methacrylate. For example, the phosphorus-containing polymerizable monomer is selected from one or more of PAM 100, PAM 200, COPS-3, etc. from Solvay.

[0032] Optionally, the initiator includes one or more of sodium persulfate and sodium metabisulfite.

[0033] Optionally, the temperature of the polymerization reaction is 30°C-80°C.

[0034] Optionally, the time of the polymerization reaction is 3h-7h.

[0035] After the polymerization reaction is completed, the solid product is filtered, and the solid product is washed to obtain the polyacrylic copolymer.

[0036] Optionally, after the incomplete drying, the following step is further included: crushing to a particle size D 50 of the polyacrylic powder binder is 20μm-300μm. For example, the particle size D 50 of the polyacrylic powder binder is 20μm, 30μm, 50μm, 80μm, 100μm, 150μm, 200μm, or 300μm. The particle size D 50 is too low, the energy consumption of the crushing is high, and the size is too high, and the speed of the dry homogenate dissolution is slow. The crushing method can be grinding or milling, and after the crushing, a sieving step is further included.

[0037] The polyacrylic powder binder prepared by the method can be used for subsequent dry homogenization, has high homogenization efficiency, is beneficial to the preparation of electrode sheets with high peeling strength and less volume expansion during charging and discharging, and is beneficial to the preparation of lithium ion batteries with good cycle performance.

[0038] The second aspect of the application provides a polyacrylic powder binder prepared by the preparation method.

[0039] Optionally, the weight average molecular weight of the polyacrylic powder binder is between 600,000 and 2,500,000.

[0040] Optionally, the molecular weight distribution of the polyacrylic powder binder is between 1.5 and 6.

[0041] Optionally, the particle size D 50 of the polyacrylic powder binder is between 20 μm and 300 μm.

[0042] Optionally, the solid content of the polyacrylic powder binder is between 90 wt% and 99 wt%.

[0043] Optionally, the content of the alcohol solvent in the polyacrylic powder binder is between 0.3 wt% and 8 wt%.

[0044] The polyacrylic powder binder can be used for the preparation of electrode sheets by dry homogenization process, is beneficial to the preparation of electrode sheets with high peeling strength, can exert high adhesive force with less addition amount, is beneficial to the improvement of battery energy density, and the prepared electrode sheets are less likely to expand in volume during charging and discharging, which is beneficial to the preparation of lithium ion batteries with good cycle performance.

[0045] The third aspect of the application provides a lithium ion battery comprising a positive electrode sheet and a negative electrode sheet, and the raw material for the preparation of at least one of the positive electrode sheet and the negative electrode sheet comprises the polyacrylic powder binder.

[0046] Optionally, the raw material for the preparation of the negative electrode sheet comprises the polyacrylic powder binder. Optionally, the raw material for the preparation of the negative electrode sheet further comprises a negative active material, and the negative active material comprises one or more of artificial graphite, natural graphite, hard carbon and silicon-carbon. The polyacrylic powder binder can form hydrogen bonds with the surface of the silicon negative electrode, improve the dispersion and adhesion of the negative active material, thereby inhibiting the volume expansion of the negative active material during charging and discharging, improving the performance of the SEI film to prevent the decomposition of the electrolyte during the electrochemical cycle process. In the process of pursuing high energy density of lithium batteries, the demand for silicon-carbon materials is increasing, and such materials have more stringent requirements for binders. The polyacrylic powder binder can be used as a binder for silicon-carbon negative electrodes and has good adhesion.

[0047] Optionally, the raw material for preparing the positive electrode plate comprises the polyacrylic powder binder described above. Optionally, the raw material for preparing the positive electrode plate further comprises a positive electrode active material, and the positive electrode active material comprises one or more of ternary positive electrode material, lithium cobaltate positive electrode material, lithium iron phosphate positive electrode material, and lithium manganate positive electrode material. DETAILED DESCRIPTION

[0048] The present application is further described in detail by the following specific examples. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing specific embodiments only and is not intended to be limiting of the application.

[0050] Terminology

[0051] Unless otherwise indicated or contradictory, the terms or phrases used herein have the following meanings:

[0052] In the present application, the terms “plurality”, “multiple”, “multiple times”, “poly-” and the like, if not specifically limited, refer to greater than or equal to 2 in number. For example, “one or more” means one or more than two.

[0053] In the present application, the terms “optionally”, “optional” and “optional” refer to the fact that it can or can not be present, i.e. it refers to any one of the two parallel schemes “yes” or “no”. If there are multiple “optional” in a technical solution, if there is no special description and no contradictory or mutually restrictive relationship, each “optional” is independent.

[0054] In the present application, in the terms “first aspect”, “second aspect”, “third aspect”, “fourth aspect” and the like, the terms “first”, “second”, “third”, “fourth” and the like are only used for description purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implying the importance or quantity of the indicated technical features. Moreover, “first”, “second”, “third”, “fourth” and the like only serve the purpose of non-exhaustive enumeration and description, and should be understood as not constituting a closed limitation on the quantity.

[0055] In the present application, with respect to the numerical interval (i.e. the numerical range), if not specifically stated, the optional numerical distribution within the above numerical interval is considered to be continuous, and includes the two numerical endpoints (i.e. the minimum value and the maximum value) of the numerical range, as well as each numerical value between the two numerical endpoints.

[0056] The temperature parameters in the present application, if not particularly limited, allow for constant temperature treatment, and also allow for fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for fluctuations within the accuracy range controlled by the instrument. Fluctuations within a range such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C are allowed.

[0057] In the present application, when percentages are involved, if not particularly specified, mass percentages are meant for solid-liquid mixing and solid-solid mixing, and volume percentages are meant for liquid-liquid mixing.

[0058] In the present application, when percentage concentrations are involved, if not particularly specified, final concentrations are meant.

[0059] In the present application, %(w / w) and wt% both represent weight percentages, %(v / v) represents volume percentages, and %(w / v) represents mass-volume percentages.

[0060] In the present application, the test method for the solid content of the polyacrylic powder binder is as follows: 2-3 g of the polyacrylic powder binder to be tested is placed in a blast oven at 150°C and baked for 1 h, and the mass m0 before baking and the mass m1 after baking are recorded, and the solid content = m1 / m0 x 100%.

[0061] In the present application, D 50 The test method for particle size is as follows: a Bettersize 2600 model laser particle size instrument from Dandong Baite is used for testing.

[0062] In the present application, the test method for weight average molecular weight and molecular weight distribution is as follows: a Shimadzu 20A GPC instrument is used, and the method of GB / T 31816-2015 is referred to for testing.

[0063] In the present application, the test method for the alcohol solvent in the polyacrylic powder binder is as follows: the solid content s1% of the polyacrylic powder binder is first tested, then the water content s2% in the polyacrylic powder binder is tested by using a Karl Fischer moisture tester, and the content of the alcohol solvent is 100%-s1%-s2%.

[0064] The following is further illustrated by specific examples and comparative examples. The raw materials involved in the following specific examples and comparative examples, if not particularly specified, can be sourced from the market, the instruments used, if not particularly specified, can be sourced from the market, and the processes involved, if not particularly specified, are conventional choices for those skilled in the art. The compounds used in the following specific examples and comparative examples and their sources are shown in Table 1.

[0065] Table 1

[0066]

[0067] Example 1

[0068] The present embodiment provides a polyacrylic powder binder and a preparation method thereof, and the steps are as follows:

[0069] Step 1, add 300 parts of deionized water in a reaction bottle, stir at 200 rpm, add polymerization monomers AA, AM, AN and PAM100 according to the mass parts shown in Table 2, continuously pass nitrogen for 1 h, obtain a monomer aqueous solution; heat to 70℃, add 1 part of ammonium persulfate aqueous solution (mass fraction of 5%) to the monomer aqueous solution, react at 70℃ for 5 h, after the reaction is completed, wash the product with water of the same mass as the obtained product twice at room temperature, and obtain a polyacrylic copolymer.

[0070] Step 2, add 300 parts of 1,3-butanediol to the polyacrylic copolymer obtained in step 1, add sodium carbonate aqueous solution at 40℃ until the pH of the system is 7.8, and perform neutralization treatment, stir and disperse for 1 h, then collect the solid by filtering through a filter screen, and perform incomplete drying in a 60℃ oven, then perform crushing and sieving, and add 0.5 parts of 1,3-butanediol in the form of spraying to obtain a water-soluble polyacrylic powder binder.

[0071] Referring to Table 3, the solid content of the polyacrylic powder binder obtained in the present embodiment is 93wt%, the alcohol solvent content is 0.7wt%, the D 50 The particle size is 105μm, the Mw is 1.09 million, and the molecular weight distribution is 3.35.

[0072] Example 2

[0073] The present embodiment provides a polyacrylic powder binder and a preparation method thereof, which are basically the same as those of Example 1, and the main differences are as follows: 1) add each raw material according to the mass parts shown in Table 2; 2) the polymerization temperature of step 1 is 50℃; and 3) the pH of the neutralization treatment system of step 2 is 7.2.

[0074] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0075] Example 3

[0076] The present embodiment provides a polyacrylic powder binder and a preparation method thereof, which are basically the same as those of Example 1, and the main differences are as follows: 1) the polymerization monomers are shown in Table 2; 2) add each raw material according to the mass parts shown in Table 2; 3) the polymerization temperature of step 1 is 30℃; 3) the temperature of the neutralization treatment of step 2 is 20℃; and 4) the oven temperature of step 2 is 50℃.

[0077] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0078] Example 4

[0079] The present embodiment provides a polyacrylic powder binder and a preparation method thereof, which is basically the same as that of Example 1, and the main difference lies in that: 1) the polymerization monomers are shown in Table 2; 2) each raw material is added according to the mass parts shown in Table 2.

[0080] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0081] Example 5

[0082] The present embodiment provides a polyacrylic powder binder and a preparation method thereof, which is basically the same as that of Example 1, and the main difference lies in that: 1) the polymerization monomers are shown in Table 2; 2) each raw material is added according to the mass parts shown in Table 2.

[0083] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0084] Example 6

[0085] The present embodiment provides a polyacrylic powder binder and a preparation method thereof, which is basically the same as that of Example 1, and the main difference lies in that: 1) the polymerization monomers are shown in Table 2; 2) each raw material is added according to the mass parts shown in Table 2.

[0086] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0087] Example 7

[0088] The present embodiment provides a polyacrylic powder binder and a preparation method thereof, which is basically the same as that of Example 1, and the main difference lies in that: 1) the polymerization monomers are shown in Table 2; 2) each raw material is added according to the mass parts shown in Table 2.

[0089] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0090] Example 8

[0091] The embodiment provides a polyacrylic powder binder and a preparation method thereof, which are basically the same as those in Embodiment 1, and the main difference is that 30 parts of 1,3-butanediol is added in step 2.

[0092] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0093] Embodiment 9

[0094] The embodiment provides a polyacrylic powder binder and a preparation method thereof, which are basically the same as those in Embodiment 1, and the main difference is that 1) each raw material is added according to the mass parts shown in Table 2; and 3) 300 parts of 1-hexanol is added in step 2.

[0095] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0096] Embodiment 10

[0097] The embodiment provides a polyacrylic powder binder and a preparation method thereof, which are basically the same as those in Embodiment 1, and the main difference is that 1) the polymerization monomers are shown in Table 2; 2) each raw material is added according to the mass parts shown in Table 2; and 3) 300 parts of pentaerythritol is added in step 2, and the pentaerythritol is not added again after incomplete drying.

[0098] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0099] Comparative Example 1

[0100] The comparative example provides a polyacrylic binder and a preparation method thereof, which are basically the same as those in Embodiment 1, and the main difference is that 1) no alcohol solvent is added; and 2) no alcohol solvent is added again, and step 2 is as follows:

[0101] In step 2, a sodium carbonate aqueous solution is added to the polyacrylic copolymer obtained in step 1 at 40 DEG C until the pH of the system is 7.8, neutralization treatment is performed, and after stirring and dispersing for 1 h, the system is filtered through a filter screen, no solid is collected, and a solution type polyacrylic binder is obtained.

[0102] The solid content, Mw and molecular weight distribution of the solution type polyacrylic binder obtained in the comparative example are shown in Table 3.

[0103] Comparative Example 2

[0104] The comparative example provides a polyacrylic powder binder and a preparation method thereof, which is basically the same as example 1, and the main difference is that the neutralization temperature is 80°C.

[0105] The solid content, alcohol solvent content, D 50 The particle size, Mw and molecular weight distribution are shown in Table 3.

[0106] Table 2

[0107]

[0108] Table 3

[0109]

[0110] The polyacrylic powder binder prepared in each of the above examples and comparative examples, and the solution type polyacrylic binder of comparative example 1 were applied to the preparation of lithium ion battery negative electrode sheets, and the steps were as follows:

[0111] In a stirring tank at room temperature, 1 part of conductive carbon black sp and 97.2 parts of negative electrode active material (graphite) were mixed, then 1.8 parts of the polyacrylic powder binder prepared in each of the examples and comparative examples and 30 parts of the solution type polyacrylic binder prepared in comparative example 1 were added, and the system was added to deionized water in a proportion of 50wt% solid content and stirred thoroughly to form a uniform negative electrode slurry, which was coated on a negative electrode current collector Cu foil, dried, rolled, and a negative electrode sheet was obtained.

[0112] The prepared negative electrode sheet was tested for peel strength and electrochemical performance.

[0113] Peel strength test: tested by a special adhesion tester, the test method of peel strength refers to the American Society for Testing and Materials standard ASTM D3330, and the instrument is a Jianjian tensile testing machine, as follows: the negative electrode sheet was cut into a sheet with a length of 150mm and a width of 15mm along the rolling direction. A smooth stainless steel plate was pasted with a 3M double-sided tape with a length of 100mm and a width of 15mm, and the sheet was pasted flat on the double-sided tape, and a 2kg rubber roller was rolled back and forth 10 times. Then the stainless steel plate was fixed on the tensile testing machine, and the sheet not pasted on the tape was clamped on the probe of the tensile testing machine in the opposite direction, and the base of the tensile testing machine was pulled at a speed of 5cm / min, and the sensor measured the peel force during the process. The average value of 5 parallel samples in each group was the final peel strength. Peel force = computer reading / 0.015, unit: N / m.

[0114] Electrochemical performance evaluation: the negative electrode prepared by the above method and the positive electrode with lithium iron phosphate as the positive electrode material are prepared and assembled into an aluminum plastic soft package according to the lithium ion battery production process familiar to the technical personnel in the industry, and electrochemical performance test is carried out. Specifically as follows:

[0115] Determination of 1000 cycle capacity retention rate: at 25℃, 3.5V voltage range, 0.5C charge, 1.0C discharge for charge-discharge cycle, the capacity retention rate after 1000 cycles is tested by constant current method, capacity retention rate = 1000th cycle discharge capacity / 1st cycle discharge capacity.

[0116] Flexibility test method: the negative electrode prepared by the above method is tested by winding with a winding needle in a low humidity room, the winding needle diameter is 1mm, the length of the electrode sheet cracking is tested, the shorter the length, the better the flexibility.

[0117] Physical rebound rate of electrode sheet: the thickness of the rolled negative electrode sheet is h0, and the thickness is measured again after 24h to obtain h1, the physical rebound rate is (h1-h0) / h0x100%.

[0118] The test results are shown in Table 4.

[0119] Table 4

[0120]

[0121] It can be seen from Comparative Example 1 that under the condition of not adding an alcohol solvent, the powder binder cannot be formed under neutralization treatment at 40℃. Compared with Example 7, the solution binder prepared in Comparative Example 1 has poorer adhesion than the powder binder prepared in Example 7, the prepared electrode has poor ability to inhibit swelling, and the prepared battery has poor cycle performance. It can be seen from Comparative Example 2 that if the temperature is increased to 80℃, it will be difficult for the powder binder to be redissolved in the aqueous slurry, and the problem of slurry uniformity will occur, and the electrode cannot be prepared. However, the alcohol solvent is added and the temperature of the neutralization treatment is controlled to be not more than 60℃ in each example of the present application, which shows better electrode sheet processability, higher peel strength, lower electrode sheet physical rebound and higher cycle capacity retention rate. It shows that the powder binder prepared under the above conditions has good adhesion and ability to inhibit swelling, which can effectively inhibit the volume expansion of the active material in the charge-discharge cycle, thereby improving the cycle performance of the electrode sheet and the lithium ion battery.

[0122] In addition, combined with Example 1 and Example 7, since the alcohol solvent volatilizes during incomplete drying, the content of the alcohol solvent in the final product is less, which leads to poor flexibility of the binder in Example 7, poor processability, and loss of adhesion and cycle performance.

[0123] In addition, in combination with Embodiment 1 and Embodiment 8, when the amount of alcohol solvent added is small, a part of the polyacrylic copolymer is still hydrated during the neutralization process, forming a small amount of viscous paste. After incomplete drying to the same solid content, insoluble substances appear in the dry homogenization stage of the powder binder, affecting the homogenization stability of the negative electrode slurry, leading to a decline in the adhesion and the ability of the electrode to inhibit swelling, and the cycle performance of the battery also declines.

[0124] The technical features of the above-described embodiments can be combined in any manner. For brevity, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict each other, they should be considered within the scope of the present disclosure.

[0125] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for producing a polyacryl powder binder, characterized by, The method comprises the following steps: mixing polymerization monomers and initiators to initiate polymerization reaction and prepare polyacrylic copolymer; neutralizing the polyacrylic copolymer at a temperature not exceeding 60℃ in the presence of an alcohol solvent to obtain polyacrylic powder binder.

2. The method of claim 1, wherein the polyacryl-based powder adhesive is prepared by mixing the polyacryl-based powder adhesive with a solvent, and then drying the mixture. The alcohol solvent has a carbon atom number not less than 3.

3. The method of claim 2, wherein the polyacryl powder binder is prepared by mixing the polyacryl binder powder and the water-soluble organic solvent at a ratio of 1 : 1 to 1 :

3. The alcohol solvent has a carbon atom number between 3 and 6.

4. The method of claim 3, wherein the polyacryl powder binder is prepared by mixing the polyacryl binder powder and the water-soluble organic solvent at a ratio of 1 : 1 to 1 :

3. The alcohol solvent is selected from one or more of 1,3-butanediol, 1,4-butanediol, 1,2-propanediol, 1,2-pentanediol, pentaerythritol, isopropyl alcohol, glycerol, 1-butanol, 1-pentanol, 2-butanol and 1-hexanol.

5. The method of claim 1, wherein the polyacrylic powder adhesive is prepared by mixing the polyacrylic powder adhesive with a solvent, and then drying the mixture. The mass of the alcohol solvent is not less than the total mass of the polymerization monomers.

6. The method of claim 5, wherein the polyacryl powder binder is prepared by mixing the polyacryl powder binder with the water-soluble organic solvent and the water-soluble inorganic salt. The mass of the alcohol solvent is 1-3 times the total mass of the polymerization monomers.

7. The method of claim 1, wherein the polyacrylic powder adhesive is prepared by mixing the polyacrylic powder adhesive with a solvent. After the neutralization treatment, the method further comprises the following steps: The method comprises the following steps: solid-liquid separation of the reaction system after the neutralization treatment, and incomplete drying of the obtained solid.

8. The method of claim 7, wherein the polyacryl powder binder is prepared by mixing the polyacryl powder binder with the water-soluble organic solvent and the water-soluble inorganic salt. The method comprises at least one of the following features: (1) the temperature of the incomplete drying is not more than 80℃; (2) the conditions of the incomplete drying are controlled to make the solid content of the polyacrylic powder binder 90wt%-99wt%.

9. The method for preparing the polyacrylic acid powder binder according to claim 7, characterized in that, After the incomplete drying, the method further comprises the following steps: supplementing the alcohol solvent to make the alcohol solvent content in the polyacrylic powder binder greater than or equal to 0.3wt%.

10. The method of claim 9, wherein the polyacrylic powder adhesive is prepared by mixing the polyacrylic powder adhesive with the water-soluble organic solvent and the water-soluble inorganic salt. The alcohol solvent content in the polyacrylic powder binder is 0.3wt%-8wt%.

11. The method of producing a polyacrylic powder binder according to any one of claims 1 to 10, characterized by, The method comprises at least one of the following features: (1) the conditions of the polymerization reaction and the neutralization treatment are controlled to make the weight average molecular weight of the polyacrylic powder binder between 600,000 and 2,500,000; (2) the conditions of the polymerization reaction and the neutralization treatment are controlled to make the molecular weight distribution of the polyacrylic powder binder between 1.5 and 6.

12. The method of producing a polyacrylic powder binder according to any one of claims 1 to 10, characterized by, The method comprises at least one of the following features: (1) the pH value of the system of the neutralization treatment is 6-9; (2) the neutralizing agent of the neutralization treatment comprises an alkaline substance; (3) the polymerization monomers comprise carboxyl-containing polymerizable monomers, amide-containing polymerizable monomers and nitrile-containing polymerizable monomers; (4) the initiator comprises one or more of sodium persulfate and sodium metabisulfite; (5) the temperature of the polymerization reaction is 30℃-80℃; (6) the time of the polymerization reaction is 3h-7h.

13. The method of claim 12, wherein the polyacrylic powder adhesive is prepared by mixing the polyacrylic powder adhesive with a solvent, and then drying the mixture. The alkaline substance comprises an inorganic base.

14. The method of claim 13, wherein the polyacrylic powder adhesive is prepared by mixing the polyacrylic powder adhesive with the water-soluble organic solvent and the water-soluble inorganic salt. The inorganic base comprises one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, lithium carbonate, sodium carbonate and potassium carbonate.

15. The method of claim 12, wherein the polyacrylic powder adhesive is prepared by mixing the polyacrylic powder adhesive with a solvent, and then drying the mixture. The polymerization monomers further comprise phosphorus-containing polymerizable monomers.

16. The method of claim 15, wherein the polyacrylic powder adhesive is prepared by mixing the polyacrylic powder adhesive with a solvent, and then drying the mixture. The method comprises at least one of the following features: (1) the carboxyl-containing polymerizable monomers account for 20wt%-40wt% of the total amount of the polymerization monomers, the amide-containing polymerizable monomers account for 10-35wt% of the total amount of the polymerization monomers, the nitrile-containing polymerizable monomers account for 40-50wt% of the total amount of the polymerization monomers, and the phosphorus-containing polymerizable monomers account for 0.1wt%-5wt% of the total amount of the polymerization monomers; (2) the carboxyl-containing polymerizable monomers are selected from one or more of acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic acid sodium salt and maleic acid lithium salt; (3) the amide group-containing polymerizable monomer is selected from one or more of acrylamide, methacrylamide, N,N-methylenebisacrylamide, N-isopropyl acrylamide, and N-ethyl acrylamide; (4) the nitrile group-containing polymerizable monomer is selected from one or more of acrylonitrile and methacrylonitrile; (5) the phosphorus-containing polymerizable monomer is selected from one or more of a phosphorus-containing ester-containing acrylate, an allyl phosphate, and a phosphorus-containing ester-containing methacrylate.

17. The method of producing a polyacrylic powder binder according to any one of claims 7 to 10, 13 to 16, characterized in that, After incomplete drying, the following step is included: pulverization to a particle size D of the polyacrylic powder binder 50 20 μm to 300 μm.

18. A polyacrylic powder binder, characterized by, which is prepared by the preparation method of any one of claims 1 to 17.

19. A lithium-ion battery, characterized by The positive electrode sheet and the negative electrode sheet, and the raw material for preparing at least one of the positive electrode sheet and the negative electrode sheet comprises the polyacrylic powder binder of claim 18.

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