CN114773599B

CN114773599B - Block type polyamide acid solution, block type polyimide adhesive, preparation method and application thereof

Info

Publication number: CN114773599B
Application number: CN202210464927.5A
Authority: CN
Inventors: 贾南方; 王杰
Original assignee: Beijing Yucheng Technology Co ltd
Current assignee: Beijing Yucheng Technology Co ltd
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2024-05-03
Anticipated expiration: 2042-04-29
Also published as: CN114773599A

Abstract

The invention provides a block type polyamic acid solution, a block type polyimide adhesive and a preparation method and application thereof, and relates to the field of electrode materials; the molar ratio of the rigid polyamide acid chain segment to the flexible polyamide acid chain segment is (0.05-20): 1; the solid content of the polyamic acid solution is 0.5 to 40 weight percent; the intrinsic viscosity of the polyamic acid solution is 0.5 to 6.0dL/g. The polyimide adhesive prepared from the block type polyamide acid has stronger cohesive force, so that the electrode material components have stronger interaction, better adhesive property and coating property, and more uniform slurry dispersion; the lithium ion battery assembled by the lithium ion battery pole piece containing the block type polyimide adhesive has higher specific discharge capacity, higher capacity retention rate and better high-temperature safety performance.

Description

Block type polyamide acid solution, block type polyimide adhesive, preparation method and application thereof

Technical Field

The invention relates to the field of electrode materials, in particular to a block type polyamide acid solution, a block type polyimide adhesive, a preparation method and application thereof.

Background

Since the 90 th year of the 20 th century, lithium ion batteries have been developed by sony corporation, and have been widely paid attention to the academic world and industry because of their advantages of high energy density, long cycle life, high voltage, no memory effect, fast charge and discharge, green environmental protection, etc., and have been currently applied to the fields of 3C electronics, electric vehicles, energy storage facilities, etc.

The lithium ion battery mainly comprises four components of an anode, a cathode, electrolyte and a diaphragm. The positive electrode and the negative electrode generally consist of an active material, a conductive agent, an adhesive and a current collector, wherein the adhesive occupies smaller (generally 1.5-10 wt%) in the lithium ion battery pole piece, but plays a non-trivial role; the main function of the adhesive is to effectively connect all the components together and form a complete pole piece structure, and proper selection of the adhesive can also effectively inhibit cation mixing, irreversible reaction between electrolyte and the surface of active particles, volume expansion of pole piece materials caused by internal stress and the like; in addition, the pole piece can have good ion permeability through the structural design of the adhesive. Most of the existing widely used lithium ion battery pole piece adhesives use simple physical adhesion, and problems such as connection failure, electrolyte swelling and the like are easy to occur in the long-term use process of the battery, so that the situations such as capacity attenuation and service life shortening of the lithium ion battery are caused.

Polyimide is used as one of the polymer materials with the most excellent comprehensive performance, has excellent mechanical strength, heat stability, flame retardance, chemical stability and the like, and can improve the battery performance when being applied to the lithium ion battery adhesive; polyimide adhesives reported in recent years have more excellent heat resistance than conventional PVDF-type adhesives, and at the same time can more effectively suppress the volume change of the electrode active material during charge and discharge, and thus the corresponding lithium ion battery exhibits higher capacity retention. However, polyimide has high rigidity and high flexibility, so that the polyimide adhesive with single system has high tensile strength and high heat resistance.

Disclosure of Invention

Aiming at one or more technical problems in the prior art, the invention provides a block type polyamide acid solution, a block type polyimide adhesive, a preparation method and application thereof. According to the invention, the rigid precursor and the flexible precursor are synthesized by respectively selecting the rigid monomer and the flexible monomer, and the rigid precursor and the flexible precursor are subjected to polycondensation and heat treatment to obtain the block type polyimide with the rigid chain segment and the flexible chain segment, so that the lithium ion battery assembled by the block type polyimide lithium ion battery pole piece has higher capacity retention rate and discharge specific capacity and better high-temperature safety performance.

The first aspect of the invention provides a block type polyamic acid solution, wherein the block type polyamic acid in the block type polyamic acid solution consists of a rigid polyamic acid chain segment and a flexible polyamic acid chain segment in a block form; the molar ratio of the rigid polyamic acid segment to the flexible polyamic acid segment is (0.05-20): 1; the solid content of the block type polyamide acid solution is 0.5-40 wt%; the intrinsic viscosity of the polyamic acid solution is 0.5 to 6.0dL/g.

Preferably, the molar ratio of the rigid polyamic acid segment to the flexible polyamic acid segment in the block-type polyamic acid is (0.4 to 2.5): 1.

Preferably, the solid content of the polyamic acid solution is 10 to 25% by weight, and the intrinsic viscosity of the polyamic acid solution is 1.5 to 4dL/g.

Preferably, the average molecular weight of the block type polyamic acid is 10000 to 500000, and preferably, the average molecular weight of the block type polyamic acid is 50000 to 200000.

The second aspect of the present invention provides a method for preparing the block type polyamic acid solution according to the first aspect, comprising the steps of:

(1) Carrying out polycondensation reaction on rigid dibasic acid anhydride and rigid diamine in a polar solvent to generate a rigid polyamic acid precursor;

(2) Carrying out polycondensation reaction on flexible dibasic acid anhydride and flexible diamine in a polar solvent to generate a flexible polyamic acid precursor;

(3) Continuously carrying out polycondensation reaction on the rigid polyamic acid precursor obtained in the step (1) and the flexible polyamic acid precursor obtained in the step (2) to obtain a block type polyamic acid solution;

in step (1), the rigid polyamic acid precursor comprises an anhydride-terminated rigid polyamic acid precursor and/or an amine-terminated rigid polyamic acid precursor;

in step (2), the flexible polyamic acid precursor comprises an anhydride-terminated flexible polyamic acid precursor and/or an amine-terminated flexible polyamic acid precursor;

in the step (3) of the process,

When the rigid polyamic acid precursor is the anhydride-terminated rigid polyamic acid precursor, the flexible polyamic acid precursor comprises at least the amine-terminated flexible polyamic acid precursor; or (b)

When the rigid polyamic acid precursor is the amine-terminated rigid polyamic acid precursor, the flexible polyamic acid precursor comprises at least the anhydride-terminated flexible polyamic acid precursor; or (b)

When the rigid polyamic acid precursor comprises the anhydride-terminated rigid polyamic acid precursor and the amine-terminated rigid polyamic acid precursor, the flexible polyamic acid precursor comprises the amine-terminated flexible polyamic acid precursor and/or the anhydride-terminated flexible polyamic acid precursor.

Preferably, in step (1), the molar ratio of rigid dianhydride to rigid diamine employed in the synthesis of the anhydride-terminated rigid polyamic acid precursor is (1.01 to 1.50): 1, preferably (1.02 to 1.06): 1;

the molar ratio of the rigid dicarboxylic anhydride to the rigid diamine used in the synthesis of the amine-terminated rigid polyamic acid precursor is 1 (1.01-1.50), preferably 1 (1.02-1.06);

Preferably, in step (2), the molar ratio of flexible dicarboxylic anhydride to flexible diamine employed in synthesizing the anhydride-terminated flexible polyamic acid precursor is (1.01 to 1.50): 1, preferably (1.02 to 1.06): 1;

the molar ratio of flexible dicarboxylic anhydride to flexible diamine used in synthesizing the amine-terminated flexible polyamic acid precursor is 1 (1.01-1.50), preferably 1 (1.02-1.06).

Preferably, in step (3), the ratio of the total number of moles of the anhydride-terminated rigid polyamic acid precursor and the anhydride-terminated flexible polyamic acid precursor to the total number of moles of the amine-terminated rigid polyamic acid precursor and the amine-terminated flexible polyamic acid precursor is 1:1.

Preferably, the rigid dibasic acid anhydride has a structure shown in a general formula 1:

formula 1, wherein Ar ₁ is an aromatic ring or an aromatic ring derivative;

Preferably, the rigid dicarboxylic anhydride is selected from the group consisting of pyromellitic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 3', 4' -diphenyl sulfone tetracarboxylic dianhydride, hexafluorodianhydride, 3', 4' -biphenyl tetracarboxylic dianhydride, 3', more preferably, the rigid dicarboxylic anhydride is selected from one or more of benzene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 3', 4' -biphenyl tetracarboxylic dianhydride, 3', 4' -benzophenone tetracarboxylic dianhydride;

Preferably, the flexible dibasic acid anhydride has a structure shown in a general formula 2:

formula 2, wherein Ar ₂ is an aromatic ring derivative containing an ether linkage or a thioether linkage;

Preferably, the flexible dicarboxylic anhydride is selected from one or more of 4,4 '-diphenyl ether dianhydride, bisphenol a type diether dianhydride, 4' - (3, 4-dicarboxyphenoxy) diphenyl sulfide dianhydride and 3,3', 4' -triphenyl diether tetracarboxylic dianhydride, more preferably, the flexible dicarboxylic anhydride is bisphenol a type diether dianhydride;

preferably, the rigid diamine has a structure as shown in a general formula 3:

Formula 3, wherein Ar ₃ is an aromatic ring or an aromatic ring derivative;

Preferably, the rigid diamine is selected from one or more of 1, 5-naphthalene diamine, 4 '-diaminodiphenylmethane, p-phenylenediamine, and 2,2' -bis (trifluoromethyl) diaminobiphenyl, more preferably, the rigid diamine is selected from at least one of 1, 5-naphthalene diamine and p-phenylenediamine;

Preferably, the flexible diamine has a structure as shown in a general formula 4:

General formula 4, wherein Ar ₄ is an aromatic ring derivative containing an ether linkage;

Preferably, the flexible diamine is selected from one or more of 1, 3-bis (4-aminophenoxy) benzene, 2-bis [4- (4-aminophenoxy) phenyl ] hexafluoropropane, 4 '-diaminodiphenyl ether, 2-bis [4- (4-aminophenoxy) phenyl ] propane, more preferably, the flexible diamine is 4,4' -diaminodiphenyl ether.

Preferably, the polar solvent is selected from one or more of N-methyl pyrrolidone, N-dimethylformamide and N, N-dimethylacetamide, and preferably, the polar solvent is N-methyl pyrrolidone.

Preferably, in step (1), step (2) and/or step (3), the temperature of the polycondensation reaction is-10 to 10 ℃, preferably the temperature of the polycondensation reaction is 0 to 4 ℃ for 0.5 to 12 hours.

The third aspect of the present invention provides a method for preparing a block type polyimide adhesive, comprising the steps of:

(i) Preparing a block polyamic acid solution according to the preparation method of any one of the second aspects;

(ii) Fully mixing and uniformly stirring the positive electrode active material or the negative electrode active material, the block type polyamide acid solution, the conductive agent and the polar solvent to obtain electrode slurry;

(iii) And uniformly coating the electrode slurry on a current collector, drying and rolling, and finally performing heat treatment to obtain the block type polyimide adhesive on the lithium ion battery pole piece.

Preferably, in step (ii), the solid content of the electrode slurry is 20 to 90wt%;

the non-solvent part of the electrode slurry comprises 80 to 99 weight percent of active substances, 0.5 to 10 weight percent of conductive agents and 0.5 to 10 weight percent of block polyamide acid;

the viscosity of the electrode paste is 500-20000 cP, preferably 3000-8500 cP;

Preferably, the positive electrode active material is at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt aluminate and lithium nickel cobalt manganate ternary material;

Preferably, the negative electrode active material is at least one of a carbon material, silicon and its oxide, tin and its oxide, a silicon-carbon composite material, a silicon-oxygen-carbon composite material, and a tin-carbon composite material;

Preferably, the conductive agent is at least one of conductive carbon black, conductive graphite, graphene and carbon nanotubes;

preferably, the polar solvent is selected from one or more of N-methylpyrrolidone, N-dimethylformamide and N, N-dimethylacetamide, and is preferably N-methylpyrrolidone.

Preferably, in step (iii), the thickness of the electrode slurry coating is 75-200 μm;

The current collector is aluminum foil, copper foil, carbon-containing aluminum foil or carbon-containing copper foil;

The compacted density of the rolling is 1.4-4 g/cm ³;

The heat treatment is carried out at the temperature of 200-450 ℃ for 1-120 min.

According to a fourth aspect of the present invention, there is provided a block polyimide adhesive prepared by the preparation method of the third aspect.

The fifth aspect of the invention provides a lithium ion battery pole piece comprising the block type polyimide adhesive prepared by the preparation method of the third aspect, wherein the lithium ion battery pole piece consists of an active material layer and a current collector;

The active material layer is composed of a positive electrode active material or a negative electrode active material, a conductive agent and a block type polyimide binder; preferably, the active material layer comprises the following components in percentage by mass: 80 to 99 weight percent of positive electrode or negative electrode active material, 0.5 to 10 weight percent of conductive agent and 1 to 10 weight percent of block polyimide binder.

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

(1) The rigid precursor and the flexible precursor are synthesized by respectively selecting rigid and flexible monomers, and the rigid precursor and the flexible precursor are subjected to polycondensation and heat treatment to obtain the segmented polyimide with the rigid chain segment and the flexible chain segment, wherein the flexible chain segment has excellent stretching resistance, can provide a good coating network, can inhibit the volume expansion problem of positive electrode or negative electrode material particles caused by internal stress in the charging and discharging process, so that the capacity retention rate of the lithium ion battery is obviously improved, and the service life is prolonged; the rigid polyimide chain segment can provide extremely excellent high temperature resistance, can still play a role of a binder under the condition of higher internal temperature of the battery, and further improves the use safety of the lithium ion battery, so that the lithium ion battery assembled by the block type polyimide lithium ion battery pole piece has higher capacity retention rate and discharge specific capacity, and simultaneously has better thermal stability and high-temperature safety performance.

(2) The block type polyamide acid and the block type polyimide prepared by the invention have extremely strong designability of molecular structures, can be specifically designed according to the problems which are required to be mainly solved in different application scenes, and can increase the proportion of rigid chain segments in the application scenes aiming at the application scenes with good temperature resistance; if it is required to address the scenario of high capacity retention/good lifetime performance after cycling, the ratio of the rigid segments to the flexible segments can be adjusted to a range close to 1:1 to improve the overall performance of the lithium ion battery binder and the lithium ion battery.

(3) In the process for preparing the lithium ion battery pole piece containing the block polyimide, the polyamide acid solution, the active component, the conductive agent, the polar solvent and the like are mixed, and compared with the traditional fluorine-based adhesive process and the process of directly mixing the polyimide adhesive with each electrode material component, the process has the advantages that the polyamide acid structure has a large number of polar amide groups and strong polar carboxyl groups, so that the interaction among the electrode material components in the slurry dispersing process is stronger, the dispersing is more uniform, the coating performance is better, and the formation of the complete pole piece with uniform and stable structure is facilitated.

(4) The lithium ion battery assembled by the lithium ion battery pole piece containing the polyimide adhesive prepared by the invention has better coating performance, mechanical performance and thermal stability, so that the corresponding lithium battery has better capacity retention rate and high-temperature safety performance.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a thermal weight loss (TGA) curve for the preparation of a block polyimide adhesive from example 5 and a PVDF adhesive from comparative example 1;

FIG. 2 is a DSC curve of the preparation of a block polyimide adhesive from example 5 and a PVDF adhesive from comparative example 1;

FIG. 3 is an SEM topography of a positive electrode sheet comprising the block polyimide prepared according to example 5, at 500 x magnification;

FIG. 4 is an SEM topography of a positive electrode sheet comprising the block polyimide prepared according to example 5, magnified 10000 times;

FIG. 5 is a SEM topography of a positive electrode sheet (comparative example 1) comprising PVDF binder prepared in comparative example 1, shown at 500 x magnification;

FIG. 6 is an SEM topography of a positive electrode sheet (comparative example 1) comprising PVDF binder prepared in comparative example 1, shown at 10000 times magnification;

fig. 7 is a charge and discharge curve at 0.1C rate for a button cell assembled with a positive electrode tab of a lithium ion battery comprising the binders prepared in example 5 and comparative example 1.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments described below will be clearly and completely described in conjunction with the technical solutions of the embodiments of the present invention, and it is apparent that the described embodiments are some, but not all, embodiments of the present invention, and all other embodiments obtained by persons of ordinary skill in the art without making any inventive effort based on the embodiments of the present invention are within the scope of protection of the present invention.

The first aspect of the invention provides a block type polyamic acid solution, wherein the block type polyamic acid in the block type polyamic acid solution consists of a rigid polyamic acid chain segment and a flexible polyamic acid chain segment in a block form; the molar ratio of the rigid polyamic acid segment to the flexible polyamic acid segment is (0.05 to 20): 1 (e.g., may be 0.05:1、0.1:1、0.5:1、0.8:1、1:1、2:1、3:1、4:1、5:1、6:1、7:1、8:1、9:1、10:1、11:1、12:1、13:1、14:1、15:1、16:1、17:1、18:1、19:1 or 20:1); the polyamic acid solution has a solid content of 0.5 to 40wt% (for example, may be 0.5wt%, 2wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt%, 30wt%, 32wt%, 35wt%, 38wt% or 40 wt%); the intrinsic viscosity of the block type polyamic acid solution is 0.5 to 6.0dL/g (for example, 0.5dL/g、0.8dL/g、1dL/g、1.5dL/g、1.8dL/g、2dL/g、2.5dL/g、3dL/g、3.5dL/g、4dL/g、4.5dL/g、4.8dL/g、5dL/g、5.5dL/g、5.8dL/g or 6dL/g may be used).

According to some preferred embodiments, the molar ratio of the rigid polyamic acid segment to the flexible polyamic acid segment in the block-type polyamic acid is (0.4 to 2.5): 1 (e.g., may be 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, or 2.5:1), the solid content of the polyamic acid solution is 10 to 25wt% (e.g., may be 10wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, or 25 wt%), and the intrinsic viscosity of the polyamic acid solution is 1.5 to 4dL/g (e.g., may be 1.5dL/g, 1.8 dL/dL, 2.8 dL/dL, 2.4 g, 3 g/dL, 3.3 g).

According to some preferred embodiments, the average molecular weight of the block-type polyamic acid is 10000 to 500000 (e.g., may be 10000, 50000, 80000, 100000, 150000, 200000, 250000, 300000, 350000, 400000, 450000, 480000, or 500000), and preferably, the average molecular weight of the block-type polyamic acid is 50000 to 200000 (e.g., may be 50000, 60000, 70000, 80000, 90000, 100000, 110000, 120000, 130000, 140000, 150000, 160000, 170000, 180000, 190000, or 200000);

The average molecular weight of the block type polyamic acid of the invention should be controlled in the above range, and the inventor finds that the average molecular weight of the block type polyamic acid is too small, and the chain of the block type polyamic acid is short, so that the coating performance of the block type polyamic acid is poor, and the mechanical performance and the heat resistance are poor; the average molecular weight of the block type polyamic acid is too large, and the viscosity is large, so that it is not easy to mix with the positive electrode active material or the negative electrode active material, the conductive agent and the polar solvent, thereby forming a positive electrode paste or a negative electrode paste.

in the step (3) of the process,

According to the invention, a rigid precursor and a flexible precursor are synthesized by respectively selecting rigid and flexible monomers, and the rigid precursor and the flexible precursor are subjected to polycondensation and heat treatment to obtain the block type polyimide with the rigid chain segment and the flexible chain segment, wherein the flexible chain segment has excellent tensile resistance, can provide a good coating network, can inhibit the volume expansion problem of positive electrode or negative electrode material particles caused by internal stress in the charge and discharge process, so that the capacity retention rate of the lithium ion battery is remarkably improved, and the service life is prolonged; the rigid polyimide chain segment can provide extremely excellent high temperature resistance, can still play a role of a binder under the condition of higher internal temperature of the battery, and further improves the use safety of the lithium ion battery, so that the lithium ion battery assembled by the block type polyimide lithium ion battery pole piece has higher capacity retention rate and discharge specific capacity, and simultaneously has better thermal stability and high-temperature safety performance.

When the rigid polyamic acid precursor is the rigid polyamic acid precursor with the end capped by anhydride, the rigid polyamic acid precursor with the end capped by amine and the flexible polyamic acid precursor with the end capped by anhydride can be selected according to the requirements on the premise that the flexible polyamic acid precursor is the flexible polyamic acid precursor with the end capped by amine, and the specific steps are as follows: when the rigid polyamic acid precursor is an anhydride-terminated rigid polyamic acid precursor, the flexible polyamic acid precursor may include an amine-terminated flexible polyamic acid precursor and an anhydride-terminated flexible polyamic acid precursor, or may be only an amine-terminated flexible polyamic acid precursor; when the rigid polyamic acid precursor is an amine-terminated rigid polyamic acid precursor, the anhydride-terminated rigid polyamic acid precursor and the amine-terminated flexible polyamic acid precursor may be selected as needed on the premise that the flexible polyamic acid precursor is an anhydride-terminated flexible polyamic acid precursor, specifically: when the rigid polyamic acid precursor is an amine-terminated rigid polyamic acid precursor, the flexible polyamic acid precursor may include an anhydride-terminated flexible polyamic acid precursor and an amine-terminated flexible polyamic acid precursor, or may be only an anhydride-terminated flexible polyamic acid precursor; when the rigid polyamic acid precursor includes an anhydride-terminated rigid polyamic acid precursor and an amine-terminated rigid polyamic acid precursor, the flexible polyamic acid precursor may include an amine-terminated flexible polyamic acid precursor and an anhydride-terminated flexible polyamic acid precursor, may be an anhydride-terminated flexible polyamic acid precursor alone, or may be an amine-terminated flexible polyamic acid precursor alone.

According to some preferred embodiments, in step (1), the molar ratio of rigid dianhydride to rigid diamine employed in synthesizing the anhydride-terminated rigid polyamic acid precursor is (1.01 to 1.50): 1 (e.g., may be 1.01:1、1.02:1、1.05:1、1.08:1、1.1:1、1.12:1、1.15:1、1.2:1、1.22:1、1.25:1、1.3:1、1.32:1、1.35:1、1.4:1、1.42:1、1.45:1 or 1.5:1), preferably (1.02 to 1.06): 1 (e.g., may be 1.02:1, 1.03:1, 1.04:1, 1.05:1 or 1.06:1);

The amine-terminated rigid polyamic acid precursor is synthesized using a molar ratio of rigid dianhydride to rigid diamine of 1 (1.01 to 1.50) (e.g., 1:1.01、1:1.02、1:1.05、1:1.08、1:1.1、1:1.12、1:1.15、1:1.2、1:1.22、1:1.25、1:1.3、1:1.32、1:1.35、1:1.4、1:1.42、1:1.45 or 1:1.5), preferably 1 (1.02 to 1.06) (e.g., 1:1.02, 1:1.03, 1:1.04, 1:1.05 or 1:1.06).

According to some preferred embodiments, in step (2), the molar ratio of flexible dicarboxylic anhydride to flexible diamine employed in synthesizing the anhydride-terminated flexible polyamic acid precursor is (1.01 to 1.50): 1 (e.g., may be 1.01:1、1.02:1、1.05:1、1.08:1、1.1:1、1.12:1、1.15:1、1.2:1、1.22:1、1.25:1、1.3:1、1.32:1、1.35:1、1.4:1、1.42:1、1.45:1 or 1.5:1), preferably (1.02 to 1.06): 1 (e.g., may be 1.02:1, 1.03:1, 1.04:1, 1.05:1 or 1.06:1);

The molar ratio of flexible dicarboxylic anhydride to flexible diamine employed in synthesizing the amine-terminated flexible polyamic acid precursor is 1 (1.01 to 1.50) (e.g., may be 1:1.01、1:1.02、1:1.05、1:1.08、1:1.1、1:1.12、1:1.15、1:1.2、1:1.22、1:1.25、1:1.3、1:1.32、1:1.35、1:1.4、1:1.42、1:1.45 or 1:1.5), preferably 1 (1.02 to 1.06) (e.g., may be 1:1.02, 1:1.03, 1:1.04, 1:1.05 or 1:1.06).

The molar ratio of the rigid/flexible dicarboxylic anhydride to the rigid/flexible diamine adopted in the synthesis of the anhydride-terminated rigid/flexible polyamic acid precursor is controlled in the above range, and the inventor finds that when the molar ratio of the rigid/flexible dicarboxylic anhydride to the rigid/flexible diamine is too small, the obtained anhydride-terminated rigid/flexible polyamic acid precursor chain is too long, the obtained block-type polyamic acid has too large average molecular weight and large viscosity, and is not easy to mix with the positive electrode active material or the negative electrode active material, the conductive agent and the polar solvent to form positive electrode slurry or negative electrode slurry; when the molar ratio of the rigid/flexible diamine to the rigid/flexible diamine is too large, the obtained anhydride end-capped rigid/flexible polyamic acid precursor chain is too short, and the average molecular weight of the obtained block type polyamic acid is too small, so that the block type polyamic acid has poor coating performance, mechanical performance and heat resistance.

The molar ratio of the rigid/flexible diamine to the rigid/flexible diamine adopted in the synthesis of the amine-terminated rigid/flexible polyamic acid precursor is controlled in the above range, and the inventor finds that when the molar ratio of the rigid/flexible diamine to the rigid/flexible diamine anhydride is too small, the obtained amine-terminated rigid/flexible polyamic acid precursor chain is too long, the obtained block-type polyamic acid has too large average molecular weight and large viscosity, and is not easy to mix with the positive electrode active material or the negative electrode active material, the conductive agent and the polar solvent to form positive electrode slurry or negative electrode slurry; when the molar ratio of the rigid/flexible diamine to the rigid/flexible dicarboxylic anhydride is too large, the obtained amine-terminated rigid/flexible polyamic acid precursor chain is too short, and the average molecular weight of the obtained block type polyamic acid is too small, so that the obtained block type polyimide adhesive has poor coating performance, mechanical performance and heat resistance.

According to some preferred embodiments, the amine-terminated flexible polyamic acid precursor is synthesized using a molar ratio of flexible dicarboxylic anhydride to flexible diamine of 1 (1.01 to 1.50) (e.g., 1:1.01、1:1.02、1:1.05、1:1.08、1:1.1、1:1.12、1:1.15、1:1.2、1:1.22、1:1.25、1:1.3、1:1.32、1:1.35、1:1.4、1:1.42、1:1.45 or 1:1.5), preferably 1 (1.02 to 1.06) (e.g., 1:1.02, 1:1.03, 1:1.04, 1:1.05, or 1:1.06).

According to some preferred embodiments, the rigid dibasic acid anhydride has a structure as shown in formula 1:

General formula 1, wherein Ar ₁ is an aromatic ring or an aromatic ring derivative;

Preferably, the rigid dicarboxylic anhydride is selected from the group consisting of pyromellitic dianhydride (PMDA), 1,4,5, 8-naphthalene tetracarboxylic anhydride (NTDA), 3', 4' -diphenyl sulfone tetracarboxylic dianhydride (DSDA), hexafluorodianhydride (6 FDA), 3', 4' -biphenyl tetracarboxylic dianhydride (BPDA) and 3,3', one or more of 4,4' -Benzophenone Tetracarboxylic Dianhydride (BTDA), more preferably, the rigid dicarboxylic anhydride is selected from one or more of benzene tetracarboxylic dianhydride (PMDA), 1,4,5, 8-naphthalene tetracarboxylic anhydride (NTDA), 3', 4' -biphenyl tetracarboxylic dianhydride (BPDA), 3', 4' -Benzophenone Tetracarboxylic Dianhydride (BTDA);

According to some preferred embodiments, the flexible dibasic acid anhydride has a structure as shown in formula 2:

Preferably, the flexible dicarboxylic anhydride is selected from one or more of 4,4 '-diphenyl ether dianhydride (ODPA), bisphenol a type diether dianhydride (BPADA), 4' - (3, 4-dicarboxyphenoxy) diphenyl sulfide dianhydride (BDSDA) and 3,3', 4' -triphenyl diether tetracarboxylic dianhydride (HQDA), more preferably, the flexible dicarboxylic anhydride is bisphenol a type diether dianhydride (BPADA);

according to some preferred embodiments, the rigid diamine has a structure as shown in formula 3:

Formula 3, wherein Ar ₃ is an aromatic ring or an aromatic ring derivative;

Preferably, the rigid diamine is selected from one or more of 1, 5-Naphthalene Diamine (NDA), 4 '-diaminodiphenylmethane (MDA), p-Phenylenediamine (PDA), and 2,2' -bis (trifluoromethyl) diaminobiphenyl (TFDB), and more preferably, the rigid diamine is selected from at least one of 1, 5-Naphthalene Diamine (NDA) and p-Phenylenediamine (PDA).

According to some preferred embodiments, the flexible diamine has a structure as shown in formula 4:

Preferably, the flexible diamine is selected from one or more of 1, 3-bis (4-aminophenoxy) benzene (1, 3, 4-APB), 2-bis [4- (4-aminophenoxy) phenyl ] Hexafluoropropane (HFBAPP), 4 '-diaminodiphenyl ether (ODA), 2-bis [4- (4-aminophenoxy) phenyl ] propane (BAPP), more preferably, the flexible diamine is 4,4' -diaminodiphenyl ether (ODA).

The rigid dicarboxylic anhydride, the flexible dicarboxylic anhydride, the rigid diamine and the flexible diamine are not particularly limited in source, and can be directly purchased products or can be obtained by self-synthesis through the existing method.

According to some preferred embodiments, the polar solvent is selected from one or more of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), preferably N-methylpyrrolidone (NMP).

According to some preferred embodiments, in step (1), step (2) and/or step (3), the temperature of the polycondensation reaction is from-10 to 10 ℃ (e.g. may be-10 ℃, -8 ℃, -6 ℃, -4 ℃, -2 ℃,0 ℃,2 ℃,4 ℃,6 ℃,8 ℃ or 10 ℃), preferably the temperature of the polycondensation reaction is from 0 to 4 ℃ (e.g. may be 0 ℃,1 ℃,2 ℃,3 ℃ or 4 ℃), for a time of from 0.5 to 12 hours (e.g. may be 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours).

In the process for preparing the lithium ion battery pole piece containing the block polyimide, the polyamide acid solution, the active component, the conductive agent, the polar solvent and the like are mixed, and compared with the traditional fluorine-based adhesive process and the process of directly mixing the polyimide adhesive with each electrode material component, the process has the advantages that the polyamide acid structure has a large number of polar amide groups and strong polar carboxyl groups, so that the interaction among the electrode material components in the slurry dispersing process is stronger, the dispersing is more uniform, the coating performance is better, and the formation of the complete pole piece with uniform and stable structure is facilitated.

According to some preferred embodiments, in step (ii), the solid content of the electrode slurry is 20 to 90wt% (e.g., may be 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85% or 90 wt%);

According to some preferred embodiments, in step (ii), the non-solvent portion of the electrode slurry comprises 80 to 99wt% (e.g., may be 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, 96wt%, or 99 wt%), 0.5 to 10wt% (e.g., may be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10 wt%) of the block-type polyamic acid;

According to some preferred embodiments, in step (ii), the viscosity of the electrode paste is 500-20000 cP (e.g. 500cP、1000cP、2000cP、3000cP、4000cP、5000cP、6000cP、7000cP、8000cP、9000cP、10000cP、11000cP、12000cP、13000cP、14000cP、15000cP、16000cP、17000cP、18000cP、19000cP or 20000 cP), preferably 3000-8500 cP (e.g. 3000cP, 3500cP, 4000cP, 4500cP, 5000cP, 5500cP, 6000cP, 6500cP, 7000cP, 7500cP, 8000cP or 8500 cP);

According to some preferred embodiments, in step (ii), the positive electrode active material is at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt aluminate and lithium nickel cobalt manganate ternary material;

According to some preferred embodiments, in step (ii), the negative electrode active material is at least one of a carbon material, silicon and its oxide, tin and its oxide, a silicon-carbon composite, a silicon-oxygen-carbon composite, and a tin-carbon composite;

according to some preferred embodiments, in step (ii), the conductive agent is at least one of conductive carbon black, conductive graphite, graphene and carbon nanotubes;

preferably, the polar solvent is selected from one or more of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), preferably N-methylpyrrolidone (NMP);

according to some preferred embodiments, in step (iii), the electrode slurry is coated with a thickness of 75 to 200 μm (e.g. may be 75μm、80μm、85μm、90μm、95μm、100μm、105μm、110μm、115μm、120μm、125μm、130μm、135μm、140μm、145μm、150μm、155μm、160μm、165μm、170μm、175μm、180μm、185μm、190μm、195μm or 200 μm); the thickness of the electrode paste coating is 75-200 mu m, and too small thickness of the electrode paste coating can lead to low active material content of the electrode, and the battery capacity after the battery is assembled is low;

According to some preferred embodiments, the rolled compacted density is 1.4-4 g/cm ³ (e.g., 1.4g/cm³、1.5g/cm³、1.8g/cm³、2g/cm³、2.2g/cm³、2.5g/cm³、2.8g/cm³、3g/cm³、3.2g/cm³、3.5g/cm³、3.8g/cm³ or 4g/cm ³); the compaction density of the rolling is 1.4-4 g/cm ³, so that the electrode plate can be compacted, the stripping strength is higher, and the bonding performance is better; too small a density of electrode sheets will result in less peel strength of the electrodes and less adhesive strength of the electrode sheets.

According to some preferred embodiments, the heat treatment is carried out at a temperature of 200-450 ℃ for a time of 1-120 min, preferably the heat treatment is carried out by heating from room temperature to 135 ℃ over 60min, incubating at 135 ℃ for 60min, heating from 135 ℃ to 300 ℃ over 60min, incubating at 300 ℃ for 60min.

The polyimide adhesive prepared from the block type polyamide acid provided by the invention simultaneously comprises a rigid chain segment and a flexible chain segment, has stronger binding force, and has the advantages of stronger interaction between electrode material components, better binding property and cladding property, more uniform slurry dispersion, and better heat stability and high-temperature safety.

The active material layer is composed of a positive electrode active material or a negative electrode active material, a conductive agent and a block type polyimide binder; preferably, the active material layer comprises the following components in percentage by mass: the positive or negative electrode active material 80 to 99wt% (for example, may be 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 94wt%, 96wt%, or 99 wt%), the conductive agent 0.5 to 10wt% (for example, may be 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10 wt%), and the block type polyimide binder 1 to 10wt% (for example, may be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10 wt%).

The lithium ion battery pole piece containing the block type polyimide adhesive has stronger binding force because the polyimide adhesive contains the rigid chain segment and the flexible chain segment, so that the electrode material components have stronger interaction, better binding performance and cladding performance, and more uniform slurry dispersion, so that the lithium ion battery pole piece has better mechanical performance, thermal stability and high-temperature safety performance, and higher specific discharge capacity and capacity retention rate.

In order to more clearly illustrate the technical scheme and advantages of the present invention, the present invention will be further described below with reference to examples.

The electrochemical performance test and the thermal stability test in the present invention are described below.

Electrochemical performance test: drying the positive electrode plate, putting the positive electrode plate into a glove box, and assembling the button cell by using 2032 button cell shells: the negative electrode shell, the lithium sheet, the diaphragm, the positive electrode sheet, the gasket and the elastic sheet are placed in sequence, 200 mu L of electrolyte is dripped, the positive electrode shell is covered, the button cell is sealed on a sealing machine, the voltage range is set to be 2.5-4.3V, and the test is carried out under the multiplying power of 0.1C. The battery assembly was applicable to all of the following examples and comparative examples.

Thermal stability test: (1) The block type polyamide acid solution prepared in the example and the PVDF glue solution prepared in the comparative example 1 are coated into films, and after thermal imidization treatment, DSC test is carried out to characterize the thermal stability of the block type polyimide.

(2) After the electrode plates containing the polyimide binders prepared in examples and comparative examples were assembled into a battery cell and cycled at 0.1C for three weeks, the battery cell was disassembled by charging to 4.3V at 0.1C, the positive electrode plate was sonicated in DMAc for 10min, dried in a vacuum oven at 80 ℃ for 12h, and after scraping the material on the substrate, DSC testing was performed to characterize the thermal stability of the plate.

NCM811 is a LiNi _0.8Co_0.1Mn_0.1O₂ positive electrode material, and PVDF is polyvinylidene fluoride.

The materials and the reagents in the invention can be obtained by direct purchase or self-synthesis in the market, and the specific model is not limited.

Example 1

Preparation of a Block Polyamic acid solution with a molar ratio of the soft segment to the rigid segment of 9:1:

(i) Preparation of anhydride-terminated flexible polyamic acid precursor a: 2.14g of flexible diamine (ODA) is weighed, 30mL of NMP solvent is added for dissolution, 5.85g of flexible dicarboxylic anhydride (BPADA) is added, and the mixture is stirred for 4 hours under the nitrogen protection condition at the temperature of 0 ℃ to obtain anhydride end-capped flexible polyamic acid precursor A;

(ii) Preparation of amine-terminated flexible polyamic acid precursor B: 2.25g of flexible diamine (ODA) is weighed, 30mL of NMP solvent is added for dissolution, 5.57g of flexible dicarboxylic anhydride (BPADA) is added, and the mixture is stirred for 4 hours under the nitrogen protection condition at the temperature of 0 ℃ to obtain an amine-terminated flexible polyamic acid precursor B;

(iii) Preparation of amine-terminated rigid polyamic acid precursor D: 2.18g of rigid diamine (PDA) is weighed, 30mL of NMP solvent is added for dissolution, 5.64g of rigid dicarboxylic anhydride (BPDA) is added, and the mixture is stirred for 4 hours under the nitrogen protection condition at the temperature of 0 ℃ to obtain an amine-terminated rigid polyamic acid precursor D;

(iv) Preparation of a blocked polyamic acid solution: and mixing A, B and D according to a molar ratio of 5:4:1, and continuing to stir at 0 ℃ under nitrogen protection for 6 hours to obtain the block type polyamide acid solution with the solid content of 20 wt%.

Preparation of block polyimide adhesive and positive electrode plate applying the adhesive:

Mixing an anode active material NCM811, conductive carbon black and a block type polyamide acid solution (calculated according to the solute mass) according to a mass ratio of 94:3:3, adding an NMP solvent, and stirring for 20min to prepare anode slurry with a solid content of 40 wt%; and 8.50g of positive electrode slurry is coated on aluminum foil (10 cm multiplied by 12 cm) and placed in an ultra-clean bench to be dried at room temperature for 12 hours, then the aluminum foil is cut into round pole pieces with the diameter of 14mm, the round pole pieces are rolled, the rolling density is 3g/cm ³, the rolled pole pieces are placed in an oven to be subjected to heat treatment, and the block type polyimide adhesive and the positive electrode pieces of the lithium ion battery containing the adhesive are obtained, wherein the temperature rise program of the heat treatment is that the temperature rises from the room temperature to 135 ℃ for 30 minutes, the temperature rises to 300 ℃ for 90 minutes, and the heat preservation is carried out for 2 hours.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 1 are shown in table 2.

According to the pole piece preparation, battery assembly and test methods, the NCM811 has a 0.1C discharge specific capacity of 211mAh/g in the system, and the initial efficiency is 86.3%.

Example 2

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 8:2:

(i) Preparation of anhydride-terminated flexible polyamic acid precursor (a): as in example 1;

(ii) Preparation of amine-terminated flexible polyamic acid precursor (B): as in example 1;

(iii) Preparation of amine-terminated rigid polyamic acid precursor (D): as in example 1;

(iv) Preparation of a blocked polyamic acid solution: and mixing A, B and D according to a molar ratio of 5:3:2, and continuing to stir at 0 ℃ under nitrogen protection for 6 hours to obtain the block type polyamide acid solution with the solid content of 20 wt%.

Preparation of block polyimide adhesive and positive electrode plate applying the adhesive: as in example 1.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 2 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the 0.1C discharge specific capacity of NCM811 in the system is 214mAh/g, and the first efficiency is 87.8%.

Example 3

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 7:3:

(iv) Preparation of a blocked polyamic acid solution: and mixing A, B and D according to a molar ratio of 5:2:3, and continuing to stir at 0 ℃ under nitrogen protection for 6 hours to obtain the block type polyamide acid solution with the solid content of 20 wt%.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 3 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the specific capacity of 0.1C discharge of NCM811 in the system is 220mAh/g, and the first efficiency is 87.1%.

Example 4

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 6:4:

(iv) Preparation of a blocked polyamic acid solution: and mixing A, B and D according to a molar ratio of 5:1:4, and continuing to stir at 0 ℃ under nitrogen protection for 6 hours to obtain the block type polyamide acid solution with the solid content of 20 wt%.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 4 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the specific capacity of 0.1C discharge of NCM811 in the system is 222mAh/g, and the initial efficiency is 86.8%.

Example 5

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 5:5:

(ii) Preparation of amine-terminated rigid polyamic acid precursor (D): as in example 1;

(iii) Preparation of a blocked polyamic acid solution: mixing A and D according to a molar ratio of 5:5, and continuing to stir at 0 ℃ under nitrogen protection for 6 hours to obtain the block type polyamic acid solution with the solid content of 20 weight percent.

The thermal weight loss (TGA) curve and DSC curve of the block polyimide adhesive prepared in example 5 are shown in fig. 1 and fig. 2, and the thermal stability data are shown in table 1.

The morphology of the positive electrode sheet containing the block polyimide binder prepared in example 5 is shown in fig. 3 and 4.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 5 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the specific capacity of 0.1C discharge of NCM811 in the system is 226mAh/g, and the initial efficiency is 89.1%.

Example 6

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 4:6:

(i) Preparation of anhydride-terminated flexible polyamic acid precursor (a): 2.14g of rigid diamine (ODA) is weighed, 30mL of NMP solvent is added for dissolution, 5.85g of flexible dicarboxylic anhydride (BPADA) is added, and the mixture is stirred for 4 hours under the nitrogen protection condition at the temperature of 0 ℃ to obtain an anhydride end-capped flexible polyamic acid precursor (A);

(ii) Preparation of anhydride-terminated rigid polyamic acid precursor (C): 2.07g of rigid diamine (PDA) is weighed, 30mL of NMP solvent is added for dissolution, 5.92g of rigid dicarboxylic anhydride (BPDA) is added, and the mixture is stirred for 4 hours under the nitrogen protection condition at the temperature of 0 ℃ to obtain an anhydride end-capped rigid polyamic acid precursor (C);

(iii) Preparation of amine-terminated rigid polyamic acid precursor (D): 2.18g of rigid diamine (PDA) is weighed, 30mL of NMP solvent is added for dissolution, 5.64g of rigid dicarboxylic anhydride (BPDA) is added, and the mixture is stirred for 4 hours under the nitrogen protection condition at the temperature of 0 ℃ to obtain an amine-terminated rigid polyamide acid precursor (D);

(iv) Preparation of a blocked polyamic acid solution: and mixing A, C and D according to a molar ratio of 4:1:5, and continuing to stir at 0 ℃ under nitrogen protection for 6 hours to obtain the block type polyamide acid solution with the solid content of 20 wt%.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 6 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the specific capacity of 0.1C discharge of NCM811 in the system is 210mAh/g, and the first efficiency is 84.7%.

Example 7

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 3:7:

(i) Preparation of anhydride-terminated flexible polyamic acid precursor (a): same as in example 6;

(ii) Preparation of anhydride-terminated rigid polyamic acid precursor (C): same as in example 6;

(iii) Preparation of amine-terminated rigid polyamic acid precursor (D): same as in example 6;

(iv) Preparation of a blocked polyamic acid solution: and mixing A, C and D according to the molar ratio of 3:2:5, and continuing to stir at the temperature of 0 ℃ under the protection of nitrogen for 6 hours to obtain the block type polyamide acid solution with the solid content of 20 wt%.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 7 are shown in table 2.

According to the pole piece preparation, battery assembly and test methods, the specific capacity of 0.1C discharge of NCM811 in the system is 207mAh/g, and the initial efficiency is 82.9%.

Example 8

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 2:8:

(iv) Preparation of a blocked polyamic acid solution: and mixing A, C and D according to the molar ratio of 2:3:5, and continuing to stir at the temperature of 0 ℃ under the protection of nitrogen for 6 hours to obtain the block type polyamide acid solution with the solid content of 20 wt%.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 8 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the 0.1C discharge specific capacity of NCM811 in the system is 205mAh/g, and the initial efficiency is 81.3%.

Example 9

Preparing a block type polyamic acid solution with a molar ratio of a soft segment to a rigid segment of 1:9:

(iv) Preparation of a blocked polyamic acid solution: a, C and D are mixed according to the mol ratio of 1:4:5, and then stirring is continued for 6 hours at the temperature of 0 ℃ under the protection of nitrogen, so that the block type polyamide acid solution with the solid content of 20wt% is obtained.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in example 9 are shown in table 2.

Comparative example 1

2.68G of powdered PVDF was weighed and dissolved in 30mL of NMP to obtain a PVDF dope having a solid content of 5 wt%. The positive electrode active material NCM811, conductive carbon black and PVDF glue solution (calculated according to the solute thereof) are mixed according to the mass ratio of 94:3:3, and 0.83g of NMP solvent is added and stirred for 20min, so as to prepare the positive electrode slurry. 8.50g of PVDF-containing slurry was coated on aluminum foil (10 cm. Times.12 cm) and dried in a vacuum oven at 80℃for 4h. Cutting into 14mm diameter discs, rolling, and weighing.

The thermal weight loss (TGA) curve and DSC curve of the PVDF binder prepared in comparative 1 are shown in fig. 1 and fig. 2, and the thermal stability data are shown in table 1.

The morphology of the positive electrode sheet containing the PVDF binder prepared in comparative example 1 is shown in FIGS. 5 and 6.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in comparative example 1 are shown in table 2.

According to the pole piece preparation, battery assembly and testing methods, NCM811 has a specific capacity of 161mAh/g at 0.1C discharge in the system, and a first time efficiency of 67.4%.

Comparative example 2

BPADA 5.62g was weighed and placed in a feed bottle and sealed for further use. Weighing ODA 2.14g, dissolving in 30mL NMP solvent, and stirring for 4 hours under the protection of nitrogen at 0 ℃ to obtain polyamic acid glue solution with the solid content of 20 wt%;

Mixing an anode active material NCM811, conductive carbon black and polyamide acid solution (calculated according to the mass of solute) according to the mass ratio of 94:3:3, adding an NMP solvent, and stirring for 20min to prepare anode slurry with the solid content of 40 wt%; and 8.50g of positive electrode slurry is coated on aluminum foil (10 cm multiplied by 12 cm) and placed in an ultra-clean bench to be dried for 12 hours at room temperature, then the aluminum foil is cut into round pole pieces with the diameter of 14mm, the round pole pieces are rolled, the rolling density is 3g/cm ³, the rolled pole pieces are placed in an oven to be subjected to thermal imidization treatment, and a polyimide adhesive and a positive electrode plate of a lithium ion battery containing the adhesive are obtained, wherein the temperature rise program of the thermal imidization treatment is that the temperature rises from the room temperature to 135 ℃ for 30 minutes, and then the temperature rises to 300 ℃ for 90 minutes, and the thermal insulation treatment is carried out for 2 hours.

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in comparative example 2 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the 0.1C discharge specific capacity of NCM811 in the system is 211mAh/g, and the initial efficiency is 85.2%.

Comparative example 3

Weigh BPDA 5.69g and place in the addition bottle to seal for future use. 2.07g of PDA is weighed and fully dissolved in 30mL of NMP solvent, and stirred for 4 hours under the protection of nitrogen at the temperature of 0 ℃ to obtain polyamic acid glue solution with the solid content of 20 wt%;

The test results of capacity retention after 100 cycles at normal temperature (25 ℃) and 100 weeks at high temperature (60 ℃) and full state thermal stability (characterization safety) of the positive electrode sheet of lithium ion battery comprising the block type polyimide binder prepared in comparative example 3 are shown in table 2.

According to the pole piece preparation, battery assembly and testing method, the NCM811 has a specific capacity of 195mAh/g at 0.1C discharge in the system, and the initial efficiency is 73.9%.

Table 1 thermal stability of the adhesives prepared in comparative example 1 and example 1

Sample name	T_d5(℃)
		Comparative example 1	450
Example 5	532

Table 2 electrochemical properties of the positive electrode sheets prepared in examples and comparative examples

As can be seen from table 1, the block type polyimide adhesive prepared in example 5 has better thermal stability than the PVDF adhesive prepared in comparative example 1.

From table 2 it can be seen that:

(1) From example 1 to example 9, the thermal stability of the full-charged battery gradually increased with increasing content of the rigid segment, mainly because the thermal stability of the rigid polyimide was better than that of the flexible polyimide, and under the same conditions, the thermal stability of the battery and that of the binder were positively correlated, and thus the thermal stability of the lithium battery containing the rigid-chain polyimide binder was also better.

(2) Comparison of comparative example 2 and comparative example 3 shows that the fully flexible chain polyimide adhesive prepared in comparative example 2 provides a higher capacity retention after 100 weeks than a fully rigid chain assembled battery at 25 ℃, mainly because the flexible chain can be better bent by rotation, providing better coating properties; in contrast, the polyimide with the full rigid segment prepared in comparative example 3 provides better mechanical properties and thermal stability during the cycle (so-called high temperature cycle), and thus has a higher capacity retention rate after 100 weeks, because side reactions are easily generated inside the battery to cause gas generation, heat generation, and the like.

(3) From examples 1 to 9, as the content of the rigid segment increases, the soft segment decreases, and the capacity retention rates at 25 ℃ and 60 ℃ overall show a tendency to increase and decrease after one another, because the capacity retention rate of the battery is simultaneously affected by multiple factors, and the polyimide-type binder containing both the soft segment and the rigid segment can provide both good coating properties and good mechanical and thermal stability (to resist gas and heat generation due to weak side reactions in the battery), and thus the corresponding lithium battery has a more excellent capacity retention rate.

As can be seen from fig. 1, the PVDF adhesive of comparative example 1 has a 5% weight loss temperature and a 10% weight loss temperature of about 450 ℃ and 465 ℃ respectively, while the block polyimide adhesive of example 5 has a 5% weight loss temperature and a 10% weight loss temperature of about 532 ℃ and 575 ℃ respectively, i.e., the block polyimide adhesive of example 5 has a 5% weight loss temperature and a 10% weight loss temperature significantly higher; meanwhile, the thermal weight loss rate of PVDF after the initial weight loss is larger, which shows that the thermal stability of the polyimide type adhesive is far higher than that of PVDF.

As can be seen from fig. 2, the endothermic peak (melting peak) of the PVDF adhesive in comparative example 1 is 158 ℃, while the curve of the block polyimide adhesive in example 5 is kept flat throughout the temperature scan interval, and no thermodynamic state transition occurs at 100 to 300 ℃, which means that the block polyimide adhesive in example 5 can maintain the original thermodynamic state at high temperature operation, and has better thermal stability.

As can be seen from fig. 3 to 6, compared with the positive electrode sheet using the PVDF adhesive of comparative example 1, the block-type polyimide adhesive in the battery sheet using the block-type polyimide adhesive of example 5 of the present application makes effective connection between the positive electrode active particles and the conductive agent, uniformly coats the surface of the positive electrode active material, has a good coating effect, and adheres a large amount of conductive agent to the surface and the periphery of the active material, thereby forming a good conductive network. While the positive electrode sheet using the PVDF binder of comparative example 1, although the PVDF binder can connect the active material and the conductive agent together, the connection effect is poor, the surface of the positive electrode active particles is substantially free from the conductive agent, the surrounding connection condition is not ideal, and the bonding effect between the positive electrode components is significantly worse than that of example 5.

As can be seen from fig. 7, the lithium ion battery using the block type polyimide binder of example 5 has a higher specific discharge capacity (226 mAh/g) than the lithium ion battery using the general type PVDF binder of comparative example 1 (161 mAh/g).

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A block type polyamic acid solution, characterized in that the block type polyamic acid in the block type polyamic acid solution is composed of a rigid polyamic acid segment and a flexible polyamic acid segment in a block form; the molar ratio of the rigid polyamic acid chain segment to the flexible polyamic acid chain segment is 6:4-5:5; the solid content of the polyamic acid solution is 0.5 to 40 weight percent; the intrinsic viscosity of the polyamic acid solution is 0.5 to 6.0dL/g;

The preparation method of the block type polyamic acid solution comprises the following steps:

S1, performing polycondensation reaction on rigid diamine and rigid dicarboxylic anhydride in a polar solvent to generate a rigid polyamic acid precursor;

s2, carrying out polycondensation reaction on flexible dibasic acid anhydride and flexible diamine in a polar solvent to generate a flexible polyamic acid precursor;

s3, continuing the polycondensation reaction of the rigid polyamic acid precursor and the flexible polyamic acid precursor to obtain a block type polyamic acid solution;

the rigid dicarboxylic anhydride is selected from one or more of pyromellitic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 3', 4' -diphenyl sulfone tetracarboxylic dianhydride, hexafluorodianhydride, 3', 4' -biphenyl tetracarboxylic dianhydride and 3,3', 4' -benzophenone tetracarboxylic dianhydride;

the flexible dibasic acid anhydride is selected from one or more of 4,4 '-diphenyl ether dianhydride, bisphenol A type diether dianhydride, 4' - (3, 4-dicarboxyphenoxy) diphenyl sulfide dianhydride and 3,3', 4' -triphenyl diether tetracarboxylic dianhydride;

the rigid diamine is selected from one or more of 1, 5-naphthalene diamine, 4 '-diaminodiphenyl methane, p-phenylenediamine and 2,2' -bis (trifluoromethyl) diaminobiphenyl;

The flexible diamine is selected from one or more of 1, 3-bis (4-aminophenoxy) benzene, 2-bis [4- (4-aminophenoxy) phenyl ] hexafluoropropane, 4' -diaminodiphenyl ether and 2, 2-bis [4- (4-aminophenoxy) phenyl ] propane.

2. The block type polyamic acid solution according to claim 1, wherein:

The solid content of the polyamic acid solution is 10 to 25 weight percent, and the intrinsic viscosity of the polyamic acid solution is 1.5 to 4dL/g; and/or

The average molecular weight of the block type polyamide acid is 10000-500000.

3. The block type polyamic acid solution according to claim 1, wherein:

The average molecular weight of the block type polyamide acid is 50000-200000.

4. A process for preparing the block polyamide acid solution according to any one of claims 1 to 3, comprising the steps of:

in the step (3) of the process,

5. The method of manufacturing according to claim 4, wherein:

in the step (1), the molar ratio of the rigid dibasic acid anhydride to the rigid diamine adopted in the synthesis of the anhydride-terminated rigid polyamic acid precursor is (1.01-1.50): 1;

the molar ratio of rigid dicarboxylic anhydride to rigid diamine used in the synthesis of the amine-terminated rigid polyamic acid precursor is 1 (1.01-1.50);

in the step (2), the molar ratio of flexible dicarboxylic anhydride to flexible diamine adopted in the synthesis of the anhydride-terminated flexible polyamic acid precursor is (1.01-1.50): 1;

The molar ratio of flexible dicarboxylic anhydride to flexible diamine adopted in the synthesis of the amine-terminated flexible polyamide acid precursor is 1 (1.01-1.50); and/or

In step (3), the ratio of the total number of moles of the anhydride-terminated rigid polyamic acid precursor and the anhydride-terminated flexible polyamic acid precursor to the total number of moles of the amine-terminated rigid polyamic acid precursor and the amine-terminated flexible polyamic acid precursor is 1:1.

6. The method of manufacturing according to claim 5, wherein:

in the step (1), the molar ratio of the rigid dibasic acid anhydride to the rigid diamine adopted in the synthesis of the anhydride-terminated rigid polyamic acid precursor is (1.02-1.06): 1;

the molar ratio of rigid dicarboxylic anhydride to rigid diamine adopted in the synthesis of the amine-terminated rigid polyamide acid precursor is 1 (1.02-1.06);

In the step (2), the molar ratio of flexible dicarboxylic anhydride to flexible diamine adopted in the synthesis of the anhydride-terminated flexible polyamic acid precursor is (1.02-1.06): 1;

the molar ratio of flexible dicarboxylic anhydride to flexible diamine adopted in the synthesis of the amine-terminated flexible polyamide acid precursor is 1 (1.02-1.06); and/or

7. The method of manufacturing according to claim 4, wherein:

the rigid dicarboxylic anhydride is selected from one or more of benzene tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 3', 4' -biphenyl tetracarboxylic dianhydride and 3,3', 4' -benzophenone tetracarboxylic dianhydride;

The flexible dicarboxylic anhydride is bisphenol A type diether dianhydride;

The rigid diamine is at least one selected from 1, 5-naphthalene diamine and p-phenylenediamine;

the flexible diamine is 4,4' -diaminodiphenyl ether.

8. The method according to claim 4, wherein the polar solvent is one or more selected from the group consisting of N-methylpyrrolidone, N-dimethylformamide, and N, N-dimethylacetamide; and/or

In the step (1), the step (2) and/or the step (3), the temperature of the polycondensation reaction is-10 ℃.

9. The method of claim 8, wherein the polar solvent is N-methylpyrrolidone; and/or

In the step (1), the step (2) and/or the step (3), the temperature of the polycondensation reaction is 0-4 ℃ and the time is 0.5-12 h.

10. A method for preparing a block polyimide adhesive, which is characterized by comprising the following steps:

(i) The block type polyamic acid solution according to the production method according to any one of claims 4 to 9;

11. The method of manufacturing according to claim 10, wherein:

In the step (ii), the solid content of the electrode slurry is 20-90 wt%;

the viscosity of the electrode slurry is 500-20000 cP; and/or

In the step (iii), the thickness of the electrode slurry coating is 75-200 mu m;

The compacted density of the rolling is 1.4-4 g/cm ³;

12. The method of manufacturing according to claim 11, wherein:

the viscosity of the electrode paste is 3000-8500 cP.

13. The method of manufacturing according to claim 11, wherein:

The positive electrode active material is at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt aluminate and lithium nickel cobalt manganate ternary materials.

14. The method of manufacturing according to claim 13, wherein:

the negative electrode active material is at least one of carbon material, silicon and oxide thereof, tin and oxide thereof, silicon-carbon composite material, silicon-oxygen-carbon composite material and tin-carbon composite material.

15. The method of manufacturing according to claim 11, wherein:

the conductive agent is at least one of conductive carbon black, conductive graphite, graphene and carbon nanotubes.

16. The method of manufacturing according to claim 11, wherein:

The polar solvent is selected from one or more of N-methyl pyrrolidone, N-dimethylformamide and N, N-dimethyl acetyl.

17. The method of manufacturing according to claim 16, wherein:

The polar solvent is N-methyl pyrrolidone.

18. A block polyimide adhesive prepared according to the preparation method of any one of claims 10 to 17.

19. A lithium ion battery pole piece comprising the polyimide binder prepared by the preparation method according to any one of claims 10 to 17, characterized in that:

the lithium ion battery pole piece consists of an active material layer and a current collector;

The active material layer is composed of a positive electrode active material or a negative electrode active material, a conductive agent, and a block type polyimide binder.

20. The polyimide adhesive lithium ion battery pole piece of claim 19, wherein:

the active material layer comprises the following components in percentage by mass: 80 to 99 weight percent of positive electrode or negative electrode active material, 0.5 to 10 weight percent of conductive agent and 1 to 10 weight percent of block polyimide binder.