CN116565200A - Additive for positive electrode slurry of lithium ion battery, preparation method and application thereof - Google Patents

Abstract

The invention relates to the field of lithium ion battery anode slurry, in particular to an additive for lithium ion battery anode slurry, a preparation method and application thereof. The additive for a positive electrode slurry for a lithium ion battery comprises a diblock copolymer comprising a first block having a nitrogen-containing group and a second block having an oxygen-containing group. The additive for the lithium ion battery anode slurry can reduce the viscosity of the slurry and improve the solid content of the slurry, thereby reducing the baking energy consumption and improving the manufacturing efficiency of the pole piece; the additive can also endow the slurry with higher stability, reduce the crystallinity of PVDF, and make PVDF softer, thereby improving the softness of the pole piece; the diblock copolymer contained in the additive has electrochemical stability, and the residual diblock copolymer in the pole piece can not affect the performance of the battery.

Description

Additive for positive electrode slurry of lithium ion battery, preparation method and application thereof

technical field

The invention relates to the field of lithium-ion battery positive electrode slurry, in particular to an additive for lithium-ion battery positive electrode slurry and a preparation method and application thereof.

Background technique

Lithium-ion batteries have the advantages of high voltage, high specific energy density, long cycle life, small self-discharge, safety and no memory effect, and have been widely used in various portable electronic products, small power systems, and aerospace and other fields. With the development of science and technology, the requirements for lithium-ion batteries tend to be high energy density. The lithium-ion battery includes an electrode group and a non-aqueous electrolyte, which are sealed in a battery case; the electrode group includes a positive electrode, a negative electrode and a diaphragm; the positive electrode includes a conductive substrate and a positive electrode material loaded on the conductive substrate. When preparing the positive electrode of the battery, it is necessary to mix the positive active material of the lithium ion battery, the conductive agent, the binder and the solvent to prepare a positive electrode slurry, and then coat and/or fill the slurry on the conductive substrate and remove the solvent After that, get the positive electrode.

At present, the preparation of lithium-ion battery electrode slurry is mainly to make a certain viscosity slurry by stirring and mixing. Due to the large specific surface area of the particles of the positive electrode material and the large amount of carbon coating, the manufacturability of the material is poor in industrial production. Chips are brittle and hard, and many positive electrode materials with good electrical properties cannot be applied.

Contents of the invention

The problem to be solved by the invention: the prior art lacks a positive electrode slurry additive for lithium ion batteries that improves the processing properties of the positive electrode slurry. In view of the above problems, the object of the present invention is to provide an additive for positive electrode slurry of lithium ion batteries, which can significantly increase the solid content and stability of the slurry and improve the flexibility of the electrode sheet when applied to the positive electrode slurry.

In order to solve the problem, the technical solution of the present invention is as follows:

The invention provides an additive for positive electrode slurry of lithium ion battery, which comprises a diblock copolymer, and the diblock copolymer comprises a first block with a nitrogen-containing group and a second block with an oxygen-containing group. part.

Preferably, the nitrogen-containing group is one or more of amido, nitrile, amino, pyrrolyl, pyridyl, pyrimidinyl, imidazolyl and pyrazolyl; preferably amido or nitrile group; preferably, the first block is selected from the block formed by the polymerization of nitrogen-containing compounds containing C=C double bonds; more preferably, the first block is selected from the group containing vinyl or propenyl A block formed by polymerization of one or more compounds of amine compounds, amide compounds, nitrile compounds or nitrogen-containing heterocyclic compounds, preferably selected from nitrogen-containing heterocyclic compounds containing vinyl groups, containing acryl groups Blocks formed by polymerizing one or two or more of the amine compounds, amide compounds or nitrile compounds, more preferably the nitrogen-containing heterocyclic compound is selected from substituted or unsubstituted pyrroles, imidazoles, Any compound in pyrazoles, pyridines or pyrimidines; further preferably, the first block is selected from N-vinylpyrrolidone, acrylamide, acrylonitrile, vinylamine, vinylpyridine and vinylimidazole Any homopolymer or copolymer formed by one or more than two kinds.

Preferably, the oxygen-containing group is one or more of ether group, ester group, furyl group and pyranyl group, preferably ether group; preferably, the second block is selected from the group containing A block formed by the polymerization of an oxygen-containing compound with a C=C double bond; more preferably, the second block is one or both of ethers, esters, or oxygen-containing heterocyclic compounds containing vinyl or propenyl groups. A block formed by the above polymerization; more preferably, the ether is an ether formed by C1-4 alkyl alcohol containing vinyl; the ester is formed by a carboxylic acid containing a C=C bond and an alkanol or cycloalkanol ester, the alkyl or cycloalkyl is an alkyl or cycloalkyl with 1-10 carbon atoms, preferably the alkyl is 1-4 carbon atoms, and the cycloalkyl is selected from tetrahydrofuryl and / or tetrahydropyranyl; more preferably, the second block is selected from one of allyloxy polyoxyethylene ether, tetrahydrofuryl acrylate, methyl acrylate, vinyloxytetrahydropyran or Any homopolymer or copolymer formed by two or more; Still further preferably, the second block is an allyloxypolyoxyethylene ether homopolymer, and the first block is an N-vinylpyrrolidone homopolymer polymer, acrylamide homopolymer, vinylpyridine homopolymer or vinylimidazole homopolymer.

Preferably, the weight average molecular weight of the diblock copolymer is 1000-20000.

Preferably, the molar ratio of the nitrogen-containing groups to the oxygen-containing groups is 1:1˜1:1000.

The present invention also provides a preparation method for the above addition, comprising the following steps:

(1) mixing the solvent, the monomer containing nitrogen groups, the chain transfer agent and the initiator, and performing the first polymerization reaction to obtain a homopolymer;

(2) Adding an oxygen-containing monomer to the homopolymer in step (1) to carry out a second polymerization reaction to obtain an additive for lithium-ion battery cathode slurry.

Preferably, the aforementioned solvent is N-methylpyrrolidone.

Preferably, the chain transfer agent is a dithioester chain transfer agent; preferably, the dithioester chain transfer agent is diphenylethyl thioester hydrochloride, benzyl dithiobenzoate, dithioester One or more of phenethyl benzoate and cumyl dithiobenzoate.

Preferably, the initiator is azobisisobutyronitrile and/or dibenzoyl peroxide.

Preferably, the nitrogen-containing monomer is one or more of N-vinylpyrrolidone, acrylamide, acrylonitrile, vinylamine, vinylpyridine and vinylimidazole.

Preferably, the oxygen-containing monomer is one or more of allyloxy polyoxyethylene ether, tetrahydrofuryl acrylate, methyl acrylate, and ethyleneoxy tetrahydropyran.

Preferably, the temperature of the first polymerization reaction in step (1) is 60-90°C; preferably, the polymerization reaction time is 6-12h.

Preferably, the temperature of the second polymerization reaction in step (2) is 60-90°C; preferably, the polymerization reaction time is 6-12h.

The present invention also provides a positive electrode slurry for a lithium ion battery, which comprises the above-mentioned additive for the positive electrode slurry of the lithium ion battery or the additive for the positive electrode slurry for the lithium ion battery prepared by the above preparation method.

The present invention also provides a lithium-ion battery positive electrode, which comprises the above-mentioned additive for lithium-ion battery positive-electrode slurry or the additive for lithium-ion battery positive-electrode slurry prepared by the above-mentioned preparation method or the above-mentioned positive electrode slurry.

The present invention also provides a lithium ion battery, which comprises the above additive for positive electrode slurry of lithium ion battery or the additive for positive electrode slurry of lithium ion battery prepared by the above preparation method or the above positive electrode slurry or the above positive electrode of battery.

Compared with the prior art, the present invention has the following beneficial effects:

The additive for the positive electrode slurry of the lithium ion battery of the present invention contains a diblock copolymer, and the nitrogen-containing group of the diblock copolymer can be adsorbed on the surface of the positive electrode active material particles to help the particles separate from each other, reduce the viscosity of the slurry, and improve the solidity of the slurry. content, thereby reducing the baking energy consumption and improving the production efficiency of the pole piece; the steric hindrance of the oxygen-containing groups of the diblock copolymer can prevent the particles from re-agglomerating, thereby avoiding the flocculation and precipitation of the particles during storage, and endowing the slurry with Higher stability; the oxygen atoms of the oxygen-containing groups of the diblock copolymer can form hydrogen bonds with the hydrogen atoms of the binder PVDF, reducing the crystallinity of PVDF and making PVDF softer, thereby improving the softness of the pole piece degree; and the diblock copolymer has electrochemical stability, and the residue in the pole piece will not affect the performance of the battery.

Detailed ways

In this specification, unless otherwise specified, symbols, units, abbreviations, and terms have the following meanings. For example, when ~ or - is used to represent a numerical range, both endpoints are included, and the unit is common. For example, 1,000 to 20,000 means 1,000 or more and 20,000 or less.

In the present invention, the test of the flexibility of the positive electrode sheet is to cut the rolled positive electrode sheet into a 25cm*2cm long strip, and then spread the positive electrode sheet on a platform 2cm above the desktop, and place the electrode sheet perpendicular to the edge of the platform Push it out, and record the length of the remaining pole piece in the platform when the pole piece just touches the table. The longer the length of the remaining pole pieces in the platform, the better the flexibility.

In order to better understand the above technical solutions, the present invention will be further described in detail below.

The invention provides an additive for positive electrode slurry of lithium ion battery, which comprises a diblock copolymer, and the diblock copolymer comprises a first block with a nitrogen-containing group and a second block with an oxygen-containing group. part.

In a preferred embodiment of the present invention, the nitrogen-containing group is one or more of amido, nitrile, amine, pyrrolyl, pyridyl, pyrimidinyl, imidazolyl and pyrazolyl, It is preferably an amide group or a nitrile group; preferably, the first block is a block selected from the polymerization of a nitrogen-containing compound containing a C=C double bond; more preferably, the first block is a block selected from a group containing Vinyl or propenyl amine compounds, amide compounds, nitrile compounds or nitrogen-containing heterocyclic compounds polymerized block formed by one or two or more compounds, preferably selected from vinyl-containing nitrogen-containing heterocyclic compounds Cyclic compound, a block formed by polymerization of one or two or more of amine compounds, amide compounds or nitrile compounds containing acrylic groups, more preferably the nitrogen-containing heterocyclic compound is selected from substituted or unsubstituted Any compound in pyrroles, imidazoles, pyrazoles, pyridines or pyrimidines; more preferably, the first block is selected from N-vinylpyrrolidone, acrylamide, acrylonitrile, vinylamine, ethylene Any homopolymer or copolymer formed by one or more of pyridine and vinylimidazole.

In a preferred embodiment of the present invention, the oxygen-containing group is one or more of ether group, ester group, furyl group and pyryl group, preferably ether group; preferably, the second The block is a block formed by polymerization of oxygen-containing compounds containing C=C double bonds; more preferably, the second block is selected from ethers, esters or oxygen-containing heterocyclic compounds containing vinyl or propenyl groups One or more blocks formed by polymerization; more preferably, the ether is an ether formed by a vinyl-containing C1-4 alkyl alcohol; the ester is a carboxylic acid and an alkane containing a C=C bond An ester formed of alcohol or cycloalkanol, the alkyl or cycloalkyl is an alkyl or cycloalkyl group with 1-10 carbon atoms, preferably the alkyl group has 1-4 carbon atoms, and the cycloalkane The group is selected from tetrahydrofuryl and/or tetrahydropyranyl; more preferably, the first block is selected from allyloxy polyoxyethylene ether, tetrahydrofuryl acrylate, methyl acrylate, vinyloxytetrahydropyryl Any homopolymer or copolymer formed by one or more than two kinds of furans; Still further preferably, the second block is an allyloxy polyoxyethylene ether homopolymer, and the first block is One of N-vinylpyrrolidone homopolymer, acrylamide homopolymer, vinylpyridine homopolymer or vinylimidazole homopolymer.

In yet another preferred embodiment of the present invention, the weight average molecular weight of the diblock copolymer is 1,000-20,000. Too high or too low molecular weight will reduce the dispersion effect of the copolymer.

In yet another preferred embodiment of the present invention, the molar ratio of the nitrogen-containing groups to the oxygen-containing groups is 1:1˜1:1000. When the nitrogen-containing groups are insufficient, the adsorption is weak, which is not conducive to dispersion. When the oxygen-containing groups are insufficient, the steric hindrance effect is weak and it is not conducive to dispersion.

The present invention also provides a method for preparing the additive for the positive electrode slurry of the above-mentioned lithium ion battery, which comprises the following steps:

(1) Mix solvent, nitrogen-containing group monomer, chain transfer agent and initiator, and carry out the first polymerization reaction to obtain homopolymer;

(2) Adding an oxygen-containing monomer to the homopolymer in step (1), performing a second polymerization reaction to obtain an additive for lithium-ion battery cathode slurry.

The solvent described in the step (1) is N-methylpyrrolidone; the chain transfer agent is a dithioester chain transfer agent, preferably, the dithioester chain transfer agent is diphenylethyl thioester hydrochloride, dithioester One or more of benzyl thiobenzoate, phenylethyl dithiobenzoate and cumyl dithiobenzoate; the initiator is azobisisobutyronitrile and/or or dibenzoyl peroxide; the nitrogen-containing monomer is one or more of N-vinylpyrrolidone, acrylamide, acrylonitrile, vinylamine, vinylpyridine and vinylimidazole; The first polymerization reaction temperature is 60-90° C., and the polymerization reaction time is 6-12 hours.

The oxygen-containing monomer in the step (2) is one or more of allyloxy polyoxyethylene ether, tetrahydrofuryl acrylate, methyl acrylate, and vinyloxytetrahydropyran; the The second polymerization reaction temperature is 60-90° C., and the polymerization reaction time is 6-12 hours.

The present invention also provides a positive electrode slurry for a lithium ion battery, which comprises the above-mentioned additive for the positive electrode slurry of the lithium ion battery or the additive for the positive electrode slurry for the lithium ion battery prepared by the above preparation method.

The present invention also provides a positive electrode of a lithium ion battery, which comprises the above additive for the positive electrode slurry of the lithium ion battery or the above positive electrode slurry of the lithium ion battery. The initial viscosity of the positive electrode slurry prepared by using the additive of the present invention is 10500-14500mPa·s, and after standing for 24 hours, the viscosity is 13000-37000mPa·s, and the length of the remaining electrode sheet in the positive electrode sheet flexibility test platform is 17-22cm. The capacity retention rate after 100 cycles is 97.7-98.5%.

The present invention also provides a lithium-ion battery, which comprises the above-mentioned additive for the positive electrode slurry of the lithium-ion battery or the above-mentioned positive electrode slurry of the lithium-ion battery or the above-mentioned positive electrode of the lithium-ion battery.

Below in conjunction with embodiment, further elaborate the present application. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

The raw materials or reagents used in the present invention are all purchased from mainstream manufacturers in the market, and those who do not indicate the manufacturer or the concentration are all analytically pure grade raw materials or reagents that can be routinely obtained. As long as they can play the expected role, There are no particular restrictions. The instruments and equipment used in this example are all purchased from major manufacturers in the market, and there are no special limitations as long as they can play the expected role. If no specific technique or condition is indicated in this example, the technique or condition described in the literature in this field or the product manual shall be followed.

instrument:

The DSC analyzer is a differential scanning calorimeter DSC-600 from Nanjing Huicheng Instrument Co., Ltd.

GPC gel chromatograph adopts GPC gel chromatograph from Shimadzu Corporation of Japan.

Example 1

1. Preparation of additives for lithium-ion battery cathode slurry

Add 80g solvent N-methylpyrrolidone (NMP), 20g nitrogen-containing group monomer N-vinylpyrrolidone, 0.1g chain transfer agent bisphenylethyl thioester hydrochloride and 0.2g initiator azobisiso A mixture of nitriles, after the first polymerization reaction at 60°C for 10 hours, a nitrogen-containing group homopolymer was obtained, and an oxygen-containing group monomer allyloxypolyoxyethylene ether (n=15) was added, N- The molar ratio of the pyrrolidone group in the vinylpyrrolidone to the ether group in the allyloxy polyoxyethylene ether is 1:1, and the second polymerization reaction is carried out at 60° C. for 10 hours to obtain the additive for the positive electrode slurry of the lithium ion battery.

Utilize gel chromatography (GPC) to record the weight-average molecular weight of the above-mentioned lithium-ion battery cathode slurry additive, and the test method is as follows:

Weigh an appropriate amount of sample and adjust the pH value to 7-9 with NaOH or KOH; drop the sample dropwise into the precipitant while stirring, the precipitated solid is viscous at first, and then gradually becomes powdery, repeated purification three times; Dry to constant weight, cool down and prepare the sample to be tested; use NaNO ₃ aqueous solution as the mobile phase, and perform gel chromatography analysis with an injection volume of 50-100 μL.

Utilize DSC to measure the glass transition temperature Tg of the additive for the positive electrode slurry of the above-mentioned lithium ion battery, the test method is as follows:

Weigh 5-10 mg film in an aluminum crucible, put it into the DSC sample chamber, and use a blank aluminum crucible (with cover) for reference. Temperature program: the initial temperature is 40°C; the temperature is raised to 100°C at 10°C/min, and kept for 30 minutes; the temperature is then lowered to -40°C at 10°C/min; Cool down to -40°C (1st-run); heat up to 160°C at 10°C/min (2nd-run). High-purity nitrogen purging, flow rate 50ml/min, nitrogen protection flow rate 20ml/min. Baseline correction was used. Read the glass transition midpoint temperature for the second run.

The weight-average molecular weight of the above-mentioned additive for the positive electrode slurry of the lithium ion battery is 1000; the glass transition temperature of the additive for the positive electrode slurry of the above lithium ion battery is Tg1=130°C; Tg2=-30°C, indicating that the lithium ion The additive for battery cathode slurry is a diblock polymer.

2. Preparation of cathode slurry

Mix the positive electrode active material lithium iron phosphate material, conductive carbon black SP, binder polyvinylidene fluoride (PVDF) and the above additives for lithium ion battery positive electrode slurry in a mass ratio of 95:2:2.5:0.5, and add an appropriate amount of solvent N -Methylpyrrolidone (NMP) is fully stirred and mixed, and the viscosity is adjusted to 10000-15000mPa·s to prepare a uniform positive electrode slurry.

Example 2

1. Preparation of additives for lithium-ion battery cathode slurry

Add the mixture of the monomer N-vinylpyrrolidone of 80g solvent NMP, 20g nitrogen-containing group, 0.1g chain transfer agent bisphenylethyl thioester hydrochloride and 0.2g initiator dibenzoyl peroxide in reactor, at 90 After the first polymerization reaction at ℃ for 8 hours, a nitrogen-containing group homopolymer was obtained, and an oxygen-containing monomer allyloxypolyoxyethylene ether (n=15) was added, and the pyrrolidone group in N-vinylpyrrolidone The molar ratio of the group to the ether group in the allyloxy polyoxyethylene ether was 1:10, and the second polymerization reaction was carried out at 90° C. for 8 hours to obtain the additive for the positive electrode slurry of the lithium ion battery.

According to the method in Example 1, the weight-average molecular weight of the additive used in the positive electrode slurry of lithium ion batteries recorded by GPC is 5000; according to the method in Example 1, the glass transition of the additives used in the positive electrode slurry of lithium ion batteries is recorded by DSC The temperature is Tg1=130°C; Tg2=-30°C, indicating that the additive for the positive electrode slurry of the lithium ion battery is a diblock polymer.

2. Preparation of cathode slurry

The additive for the positive electrode slurry of the lithium ion battery prepared in Example 2 was used, and the other preparation methods of the positive electrode slurry in Example 1 were the same.

Example 3

1. Preparation of additives for lithium-ion battery cathode slurry

Add the mixture of 80g solvent NMP, 20g nitrogen-containing group monomer acrylamide, 0.1g chain transfer agent benzyl dithiobenzoate and 0.2g initiator azobisisobutyronitrile to the reaction kettle, at 80°C After the first polymerization reaction was carried out for 10 hours, the homopolymer of the nitrogen-containing group was obtained, and then the monomer allyloxy polyoxyethylene ether (n=15) containing the oxygen group was added, and the moles of the amide group and the ether group The ratio is 1:1000, and the second polymerization reaction is carried out at 80°C for 10 hours to obtain the additive for the positive electrode slurry of the lithium ion battery.

According to the method in Example 1, the weight-average molecular weight of the additive used in the positive electrode slurry of lithium ion batteries recorded by GPC is 10000; according to the method in Example 1, the glass transition of the additives used in the positive electrode slurry of lithium ion batteries is recorded by DSC The temperature is Tg1=150°C; Tg2=-30°C, indicating that the additive for the positive electrode slurry of the lithium ion battery is a diblock polymer.

2. Preparation of cathode slurry

The additive for the positive electrode slurry of the lithium ion battery prepared in Example 3 was used, and the other preparation methods of the positive electrode slurry in Example 1 were the same.

Example 4

1. Preparation of additives for lithium-ion battery cathode slurry

Add the mixture of 80g solvent NMP, 20g nitrogen-containing group monomer acrylamide, 0.1g chain transfer agent benzyl dithiobenzoate and 0.2g initiator dibenzoyl peroxide to the reaction kettle, at 80°C After the first polymerization reaction for 10 hours, a homopolymer of nitrogen-containing groups was obtained, and then tetrahydrofuryl acrylate, a monomer containing oxygen groups, was added. The molar ratio of amide groups to furan groups was 1:100, and carried out at 80°C After the second polymerization reaction for 10 hours, the additive for the positive electrode slurry of the lithium ion battery was obtained.

According to the method in Example 1, the weight-average molecular weight of the additive for the positive electrode slurry of lithium ion batteries recorded by GPC is 20000; according to the method in Example 1, the glass transition of the additives for the positive electrode slurry of lithium ion batteries is recorded by DSC The temperature is Tg1=150°C; Tg2=-20°C, indicating that the additive for the positive electrode slurry of the lithium ion battery is a diblock polymer.

2. Preparation of cathode slurry

The additive for the positive electrode slurry of the lithium ion battery prepared in Example 4 was used, and the other preparation methods of the positive electrode slurry in Example 1 were the same.

Example 5

1. Preparation of additives for lithium-ion battery cathode slurry

Add the mixture of 80g solvent NMP, 20g nitrogen-containing group monomer acrylonitrile, 0.1g chain transfer agent phenylethyl dithiobenzoate and 0.2g initiator azobisisobutyronitrile to the reaction kettle, at 80°C The homopolymer of nitrogen-containing groups was obtained after the first polymerization reaction for 10 hours, and the monomer methyl acrylate containing oxygen groups was added. The molar ratio of nitrile groups and ester groups was 1:10, at 80°C After performing the second polymerization reaction for 10 hours, the additive for the positive electrode slurry of the lithium ion battery is obtained.

According to the method in Example 1, the weight-average molecular weight of the additive used in the positive electrode slurry of lithium ion batteries recorded by GPC is 15000; according to the method in Example 1, the glass transition of the additives used in the positive electrode slurry of lithium ion batteries is recorded by DSC The temperature is Tg1 = 100° C.; Tg2 = 10° C., indicating that the additive for the positive electrode slurry of the lithium ion battery is a diblock polymer.

2. Preparation of cathode slurry

The additive for the positive electrode slurry of the lithium ion battery prepared in Example 5 was used, and the other preparation methods of the positive electrode slurry in Example 1 were the same.

Example 6

1. Preparation of additives for lithium-ion battery cathode slurry

Add the mixture of 80g solvent NMP, the monomer vinylamine of 20g nitrogen-containing group, 0.1g chain transfer agent cumyl dithiobenzoate and 0.2g initiator dibenzoyl peroxide in the reactor, 90 Perform the first polymerization reaction at ℃ for 6 hours to obtain a homopolymer containing nitrogen groups, and then add monomer ethyleneoxytetrahydropyran containing oxygen groups, and the molar ratio of amine groups to pyran groups is 1 : 10, after the second polymerization reaction was carried out at 90° C. for 6 hours, an additive for lithium-ion battery cathode slurry was obtained.

According to the method in Example 1, the weight-average molecular weight of the additive used in the positive electrode slurry of lithium ion batteries recorded by GPC is 15000; according to the method in Example 1, the glass transition of the additives used in the positive electrode slurry of lithium ion batteries is recorded by DSC The temperature is Tg1=-30°C; Tg2=-20°C, indicating that the additive for the positive electrode slurry of the lithium ion battery is a diblock polymer.

2. Preparation of cathode slurry

The additive for the positive electrode slurry of the lithium ion battery prepared in Example 6 was used, and the other preparation methods of the positive electrode slurry in Example 1 were the same.

Example 7

1. Preparation of additives for lithium-ion battery cathode slurry

Add the mixture of 80g solvent NMP, 20g nitrogen-containing group monomer vinylpyridine, 0.1g chain transfer agent benzyl dithiobenzoate and 0.2g initiator azobisisobutyronitrile to the reaction kettle, at 90°C The homopolymer of the nitrogen-containing group is obtained after the first polymerization reaction under the following conditions for 6 hours, and then the monomer allyloxy polyoxyethylene ether containing the oxygen group is added, and the molar ratio of the pyridine group and the ether group is 1: After performing the second polymerization reaction at 500° C. and 90° C. for 6 hours, the additive for the positive electrode slurry of the lithium ion battery was obtained.

According to the method in Example 1, the weight-average molecular weight of the additive for the positive electrode slurry of lithium ion batteries recorded by GPC is 8500; according to the method in Example 1, the glass transition of the additives for the positive electrode slurry of lithium ion batteries is recorded by DSC The temperature is Tg1=130°C; Tg2=-30°C, indicating that the additive for the positive electrode slurry of the lithium ion battery is a diblock polymer.

2. Preparation of cathode slurry

The additive for the positive electrode slurry of the lithium ion battery prepared in Example 7 was used, and the other preparation methods of the positive electrode slurry in Example 1 were the same.

Example 8

1. Preparation of additives for lithium-ion battery cathode slurry

Add the mixture of the monomer vinylimidazole of 80g solvent NMP, 20g nitrogen-containing group, 0.1g chain transfer agent phenethyl dithiobenzoate and 0.2g initiator azobisisobutyronitrile in the reactor, 90 After the first polymerization reaction at ℃ for 6 hours, a nitrogen-containing group homopolymer was obtained, and oxygen-containing group monomer allyloxypolyoxyethylene ether (n=15), imidazole group and ether group were added The molar ratio is 1:200, and the second polymerization reaction is carried out at 90° C. for 6 hours to obtain the additive for the positive electrode slurry of the lithium ion battery.

According to the method in Example 1, the weight-average molecular weight of the additive for the positive electrode slurry of lithium ion batteries recorded by GPC is 8500; according to the method in Example 1, the glass transition of the additives for the positive electrode slurry of lithium ion batteries is recorded by DSC The temperature is Tg1=130°C; Tg2=-30°C, indicating that the additive for the positive electrode slurry of the lithium ion battery is a diblock polymer.

2. Preparation of cathode slurry

The additive for the positive electrode slurry of the lithium ion battery prepared in Example 8 was used, and the other preparation methods of the positive electrode slurry in Example 1 were the same.

Comparative example 1

The positive electrode slurry is prepared without using the additive for the positive electrode slurry of the lithium ion battery of the present invention, and the positive electrode active material lithium iron phosphate material, conductive carbon black and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95.5:2:2.5 , add an appropriate amount of solvent N-methylpyrrolidone (NMP) to stir and mix thoroughly, and adjust the viscosity to 10000-15000mPa·s to prepare a uniform positive electrode slurry.

The positive electrode slurry obtained above in Examples 1-8 and Comparative Example 1 is subjected to the following tests:

1. Positive electrode slurry viscosity test

Fix the measuring cup containing the positive electrode slurry at a constant temperature of 25° C. and let it stand for 5 minutes, and take the No. 4 rotor of a rotational viscometer (12 rpm) to measure the viscosity of the positive electrode slurry. The test results are shown in Table 1.

2. Positive electrode slurry solid content test

Put unused glass fiber paper in the aluminum foil, dry it in an oven at 105±2°C for 15 minutes, take it out, weigh it after cooling to room temperature in the desiccator, and record it as M1 (accurate to 0.0001g, the same below); Drop the sample (0.8-1.2g) on the glass fiber paper in the aluminum foil, ensure that the sample is fully spread out, and record the weight as M2; put the aluminum foil with the sample in an oven at 105±2°C, close the oven door, and dry Bake for 2 hours, take it out and put it in a desiccator to cool to room temperature, then take it out, and weigh it as M3; put the sample in the oven and bake it for 15 minutes, take it out, cool it in a desiccator to room temperature, and weigh it again as M4, if the difference between M4 and M3 is ≤ 0.0005g, the solid content can be calculated as:

Solid content (%)=(M3-M1)/(M2-M1)×100%

If the difference between M4 and M3 is >0.0005g, put it into the oven again and bake until the two adjacent weighings are ≤0.0005g. The test results are shown in Table 1.

3. Full battery preparation and performance evaluation

3.1 Preparation of Li-ion battery

The positive electrode slurry obtained in Examples 1-8 and Comparative Example 1 were respectively coated on aluminum foil, dried, and rolled to obtain positive electrode sheets; Co., Ltd., silicon content 10%), conductive carbon black (SP), binder styrene-butadiene rubber (SBR), thickener sodium carboxymethylcellulose (CMC) according to the mass ratio 96.5:1.0:1.0:1.5 in After fully stirring and mixing in the deionized water solvent system, it is coated on copper foil, dried and cold-pressed to obtain a negative electrode sheet; a PE porous polymer film (Shenzhen Xingyuan Material Technology Co., Ltd.) is used as a diaphragm; the positive electrode sheet, The diaphragm and the negative electrode sheet are stacked in sequence and then wound along the same direction to obtain the bare cell. The bare cell is placed in the outer package, and the carbonate of LiPF6 with a concentration of 1mol/L is injected (volume ratio ethylene carbonate (EC)/carbonic acid Ethyl methyl ester (EMC)/diethyl carbonate (DEC)=3:5:2) is used as the electrolyte, and after vacuum packaging, shelving at 45°C, high-temperature fixture formation, secondary packaging, and volume separation, the positive electrode containing the above Slurry Li-ion batteries.

3.2 Positive sheet flexibility test

Cut the rolled positive electrode sheet into a 25cm*2cm long strip, spread it flat on the platform, the platform is 2cm higher than the tabletop, push the electrode sheet out perpendicular to the edge of the platform, and record when the electrode sheet just touches the tabletop. The length of the remaining pole piece inside, the test results are shown in Table 1.

3.3 Lithium-ion battery room temperature cycle performance test

Under the condition of normal temperature (25° C.), the above-mentioned lithium-ion battery was charged to 4.2V at 1C constant current and constant voltage, and then discharged to 2.5V at 1C constant current. After charging and discharging for 100 cycles, calculate the capacity retention rate after the 100th cycle according to the following formula:

The 100th cycle capacity retention rate (%)=(100th cycle discharge capacity/first cycle discharge capacity)×100%. The test results are shown in Table 1.

Table 1 Test results

It can be seen from Table 1 that the initial viscosity of the positive electrode slurry prepared in Examples 1-8 is 10500-14500mPa·s, and after standing for 24 hours, the viscosity is 13000-37000mPa·s. The length is 17-22cm, and the capacity retention rate after 100 cycles at room temperature is 97.7-98.5%. In Comparative Example 1, the positive electrode slurry prepared without adding the diblock copolymer, the viscosity increased by 458% compared with the initial viscosity after standing for 24 hours, and the positive electrode slurry obtained by adding the diblock copolymer prepared in Examples 1-8 of the present invention After standing for 24 hours, the viscosity increased by 25-155% compared with the initial viscosity, and the viscosity rebound was significantly reduced; Under the premise of meeting the viscosity of the positive electrode slurry, the solid content of the slurry can be increased, thereby reducing the baking energy consumption and improving the production efficiency of the electrode sheet. The test results of the flexibility of the positive pole piece show that the flexibility of the positive pole piece made by using the positive pole slurry obtained in Examples 1-8 is better than that of Comparative Example 1. The battery cycle performance test results show that the cycle performance of the battery made by using the positive electrode slurry obtained in Examples 1-8 is equivalent to that of the battery made by the positive electrode slurry obtained in Comparative Example 1.

In summary, the additive for the positive electrode slurry of lithium ion batteries of the present invention contains a diblock copolymer, and the nitrogen-containing groups of the diblock copolymer can be adsorbed on the surface of the positive electrode active material particles to help the particles separate from each other and reduce the viscosity of the slurry , increase the solid content of the slurry, thereby reducing the consumption of solvents, reducing the energy consumption of baking, and improving the efficiency of pole piece production; the steric hindrance of the oxygen-containing groups of the diblock copolymer can prevent the particles from reuniting, thereby avoiding storage The particle flocculation and precipitation during the process endow the slurry with higher stability; the oxygen atoms of the oxygen-containing groups of the diblock copolymer can hydrogen bond with the hydrogen atoms of the binder PVDF, reducing the crystallinity of PVDF, It makes PVDF softer, thereby improving the softness of the pole piece; and the diblock copolymer has electrochemical stability, and the residue in the pole piece will not affect the performance of the battery.

Although the present application is disclosed as above with preferred embodiments, it is not used to limit the claims. Any person skilled in the art can make some possible changes and modifications without departing from the concept of the present application. Therefore, the present application The scope of protection shall be based on the scope defined by the claims of the present application. The above is only a preferred embodiment for the implementation of the present invention, and does not limit the present invention in any form. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention need to be included in the within the protection scope of the present invention.

Claims (16)

1. An additive for a positive electrode slurry of a lithium ion battery, characterized in that it comprises a diblock copolymer comprising a first block having a nitrogen-containing group and a second block having an oxygen-containing group.

2. The additive according to claim 1, wherein the nitrogen-containing group is one or more of an amide group, a nitrile group, an amine group, a pyrrole group, a pyridine group, a pyrimidine group, an imidazole group, and a pyrazole group; preferably an amide group or a nitrile group; preferably, the first block is a block formed by polymerization of a nitrogen-containing compound selected from the group consisting of c=c double bonds; more preferably, the first block is a block formed by polymerizing one or more compounds selected from the group consisting of an amine compound containing vinyl group or propenyl group, an amide compound, a nitrile compound, and a nitrogen-containing heterocyclic compound, preferably a block formed by polymerizing one or more compounds selected from the group consisting of an amine compound containing vinyl group, an amide compound, and a nitrile compound containing propenyl group, and more preferably, the nitrogen-containing heterocyclic compound is any one compound selected from the group consisting of substituted or unsubstituted pyrrole, imidazole, pyrazole, pyridine, and pyrimidine; further preferably, the first block is any homopolymer or copolymer formed from one or more selected from the group consisting of vinylpyrrolidone, acrylamide, acrylonitrile, vinylamine, vinylpyridine, and vinylimidazole.

3. Additive according to claim 1 or 2, wherein the oxygen containing group is one or more of an ether group, an ester group, a furan group and a pyran group, preferably an ether group; preferably, the second block is a block formed by polymerization of an oxygenate compound selected from the group consisting of c=c double bonds; more preferably, the second block is a block formed by polymerization of one or more selected from ethers, esters or oxygen-containing heterocyclic compounds containing vinyl or propenyl groups; further preferred, the ether is an ether formed from a C1-4 alkyl alcohol containing a vinyl group, the ester is an ester formed from a carboxylic acid containing a c=c bond and an alkanol or cycloalkyl alcohol, the alkyl or cycloalkyl group being an alkyl or cycloalkyl group having 1 to 10 carbon atoms, preferably the alkyl group being a C1-4 carbon atom, the cycloalkyl group being selected from tetrahydrofuranyl and/or tetrahydropyranyl; still more preferably, the second block is any homopolymer or copolymer formed from one or more selected from allyloxy polyoxyethylene ether, tetrahydrofuranyl acrylate, methyl acrylate, ethyleneoxy tetrahydropyran; still further preferably, the second block is an allyloxy polyoxyethylene ether homopolymer and the first block is one of an N-vinylpyrrolidone homopolymer, an acrylamide homopolymer, a vinylpyridine homopolymer, or a vinylimidazole homopolymer.

4. An additive according to any one of claims 1 to 3, wherein the diblock copolymer has a weight average molecular weight of from 1000 to 20000.

5. An additive according to any one of claims 1 to 4 wherein the molar ratio of nitrogen-containing groups to oxygen-containing groups is 1:1 to 1:1000.

6. the method for preparing an additive according to any one of claims 1 to 5, comprising the steps of:

(1) Mixing a solvent, a monomer containing nitrogen groups, a chain transfer agent and an initiator, and performing a first polymerization reaction to obtain a homopolymer;

(2) And (3) adding an oxygen group-containing monomer into the homopolymer in the step (1) to perform a second polymerization reaction to obtain the additive for the lithium ion battery anode slurry.

7. The method according to claim 6, wherein the solvent is N-methylpyrrolidone.

8. The production method according to claim 6 or 7, wherein the chain transfer agent is a dithioester chain transfer agent; preferably, the dithioesters chain transfer agent is one or more of diphenyl ethyl sulfate hydrochloride, benzyl dithiobenzoate, phenethyl dithiobenzoate and isopropyl dithiobenzoate.

9. The process according to any one of claims 6 to 8, wherein the initiator is azobisisobutyronitrile and/or dibenzoyl peroxide.

10. The method according to any one of claims 6 to 9, wherein the monomer containing a nitrogen group is one or more of N-vinylpyrrolidone, acrylamide, acrylonitrile, vinylamine, vinylpyridine and vinylimidazole.

11. The method according to any one of claims 6 to 10, wherein the oxygen group-containing monomer is one or more of allyloxy polyoxyethylene ether, tetrahydrofuranyl acrylate, methyl acrylate, and ethyleneoxy tetrahydropyran.

12. The method of any one of claims 6-11, wherein the temperature of the first polymerization reaction of step (1) is 60-90 ℃; preferably, the polymerization time is from 6 to 12 hours.

13. The process according to any one of claims 6 to 12, wherein the temperature of the second polymerization reaction of step (2) is 60 to 90 ℃; preferably, the polymerization time is from 6 to 12 hours.

14. A lithium ion battery positive electrode slurry, characterized in that it comprises the additive for lithium ion battery positive electrode slurry according to any one of claims 1 to 5 or the additive for lithium ion battery positive electrode slurry produced by the production method according to any one of claims 6 to 13.

15. A positive electrode for a lithium ion battery, characterized in that it comprises the additive for a positive electrode slurry for a lithium ion battery according to any one of claims 1 to 5 or the additive for a positive electrode slurry for a lithium ion battery produced by the production method according to any one of claims 6 to 13 or the positive electrode slurry according to claim 14.

16. A lithium ion battery comprising the additive for lithium ion battery positive electrode slurry according to any one of claims 1 to 5 or the additive for lithium ion battery positive electrode slurry produced by the production method according to any one of claims 6 to 13 or the positive electrode slurry according to claim 14 or the battery positive electrode according to claim 15.