CN114805804A

CN114805804A - Branched cross-linked polyamic acid solution, polyimide adhesive, and preparation method and application thereof

Info

Publication number: CN114805804A
Application number: CN202210465436.2A
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: 2022-07-29

Abstract

A branched cross-linked polyamic acid solution, a polyimide adhesive, a preparation method and an application thereof relate to the field of electrode materials, the polyamic acid molecular chain in the branched cross-linked polyamic acid solution contains a strong polar group, and the whole molecular chain is in a branched cross-linked form; the strong polar group is at least one of a hydroxyl group, a carboxyl group, a sulfonic acid group, a trifluoromethyl group and a cyano group; the solid content of the branched cross-linked polyamic acid solution is 0.5-50 wt%, and the intrinsic viscosity is 0.1-6.63 dL/g. The polyimide adhesive prepared from the strong-polarity branched cross-linked polyamic acid solution provided by the invention has stronger binding power, so that the components of an electrode material 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 polyimide adhesive has more excellent cycle performance, rate capability and safety performance.

Description

Branched cross-linked polyamic acid solution, polyimide adhesive, and preparation method and application thereof

Technical Field

The invention relates to the field of electrode materials, in particular to a branched cross-linked polyamic acid solution, a polyimide adhesive, and a preparation method and application thereof.

Background

Since the 21 st century, Lithium Ion Batteries (LIBs) have been widely used in the fields of various portable electronic devices, power cars, energy storage power stations, electric tools, and the like because of their advantages of high energy density, high rate capability, environmental friendliness, and the like. However, in recent years, LIBs are frequently used, the safety problem of LIBs becomes a hot issue of social concern, and the development of LIBs towards high capacity, high specific energy and high safety is an inevitable trend.

The LIBs mainly comprise four major parts, namely an anode, a cathode, electrolyte and a diaphragm, wherein the anode and the cathode consist of powdery active substances, a conductive agent, an adhesive and a current collector; the adhesive is a main carrier for tightly connecting the active substance, the conductive agent and the current collector, and has the functions of uniformly dispersing the positive and negative electrode components, bearing the volume expansion of the electrode, reducing the side reaction of the interface of the active material and the electrolyte and the like. The high-performance adhesive should have various properties such as strong adhesion, resistance to swelling and corrosion of electrolyte, high tensile strength, good flexibility, excellent high-temperature resistance, good chemical and electrochemical stability, environmental friendliness and the like. However, most of the currently widely used binders, such as homopolymers or copolymers of polyvinylidene fluoride (PVDF), have the disadvantages of poor adhesion, excessive swelling in electrolyte, low mechanical strength, high-temperature softening, etc., and may cause problems of connection failure of electrode material components, collapse of electrode structure, poor battery safety performance, etc., after repeated charge and discharge cycles.

In order to solve the problems of the conventional adhesive, patent CN106220779A (application No. 201610677774.7) provides an acrylonitrile copolymer adhesive, which takes acrylonitrile as a main body, adds acrylate monomers, acrylamide monomers and acrylate monomers for copolymerization, improves the adhesive performance to a certain extent through strong intermolecular interaction, and has good flexibility and electrolyte wettability; however, the adhesive is prepared by polymerizing acrylonitrile, acrylate, acrylamide and acrylate monomers, so that the heat resistance, the adhesive strength and the mechanical properties of the adhesive still need to be further improved.

Disclosure of Invention

The invention provides a branched cross-linked polyamic acid solution, a polyimide adhesive, and preparation methods and applications thereof, aiming at one or more technical problems in the prior art. The invention firstly provides a strong-polarity polyamide acid solution with a branched cross-linked structure, and the polyimide adhesive prepared from the polyamide acid solution has stronger binding power, so that the components of the electrode material 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 polyimide adhesive has more excellent cycle performance, rate capability and safety performance.

The invention provides a branched cross-linked polyamic acid solution, wherein a polyamic acid molecular chain contains a strong polar group, and the whole molecular chain is in a branched cross-linked form;

the strong polar group is at least one of a hydroxyl group, a carboxyl group, a sulfonic acid group, a trifluoromethyl group and a cyano group;

the solid content of the polyamic acid solution is 0.5-50 wt%, and the intrinsic viscosity is 0.1-6.63 dL/g.

The present invention in its second aspect provides a method for producing a branched cross-linked polyamic acid solution as described in the above first aspect, comprising the steps of:

(1) carrying out polycondensation reaction on dicarboxylic anhydride and diamine in a polar solvent to obtain a linear polyamic acid solution; wherein the diamine comprises a general diamine and a functional diamine;

(2) and adding polyamine into the linear polyamic acid solution to react to obtain a branched crosslinking polyamic acid solution.

Preferably, in step (1), the dibasic acid anhydride is selected from at least one of pyromellitic dianhydride (PMDA), 4,4 ' -diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), 3 ', 4,4 ' -diphenylsulfone tetracarboxylic dianhydride (DSDA), hexafluoro dianhydride (6FDA), 3 ', 4,4 ' -Benzophenone Tetracarboxylic Dianhydride (BTDA), 4,4 ' - (4,4 ' -isopropylidenediphenoxy) diphthalic anhydride (BisADA), p-phenylene-bistrimellitic dianhydride (TAHQ).

The common diamine is selected from p-phenylenediamine (p-PDA), m-phenylenediamine (mPDA), 4 ' -diaminodiphenyl ether (4,4 ' -ODA), 3,4 ' -diaminodiphenyl ether (3,4 ' -ODA), 4 ' -diaminodiphenyl sulfone (DDS), 3 ' -diaminodiphenyl sulfone (3,3 ' -DDS), at least one of 2,2 ' -dimethyl-4, 4 ' -diaminobiphenyl (OTOL), 4 ' -diaminodiphenylmethane (MDA), 1, 3-bis (4 ' -aminophenoxy) benzene (TPE-R), 4 ' -diaminobenzophenone, 9-bis- (4-aminophenyl), 9-bis- (3-fluoro-4-aminophenyl) fluorene;

the polar solvent is at least one selected from the group consisting of N-methylpyrrolidone (NMP), N-dimethylformamide (DM F), N-dimethylacetamide (DMAc), N-ethylpyrrolidone (NEP), dimethyl sulfoxide (DMSO), Hexamethylphosphoramide (HMPA), and preferably, N-methylpyrrolidone (NMP).

Preferably, in step (1), the functional diamine is a diamine containing a strongly polar group;

preferably, the strongly polar group is selected from at least one of a hydroxyl group, a carboxyl group, a sulfonic acid group, a trifluoromethyl group, and a cyano group;

more preferably, the functional diamine containing the hydroxyl group is at least one selected from the group consisting of 3, 3' -dihydroxybenzidine (HAB), 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6 FAP); the functional diamine containing the carboxyl group is at least one selected from 3, 5-diaminobenzoic acid (DABA), 2, 3-diaminobenzoic acid, 3, 5-bis (4-aminophenoxy) benzoic acid, and 4,4 ' -diaminobiphenyl-2, 2 ' -dicarboxylic acid (2,2 ' -DCB); the functional diamine containing the sulfonic acid group is selected from at least one of 2, 4-diaminobenzene sulfonic acid, 2,4, 6-trimethyl-3, 5-diaminobenzene sulfonic acid and benzidine disulfonic acid (BDSA); the functional diamine containing trifluoromethyl is at least one selected from 2,2 ' -bis (trifluoromethyl) -4,4 ' -diaminophenyl ether (6FODA) and 4,4 ' -bis (4-amino-2-trifluoromethylphenoxy) biphenyl; the functional diamine containing the cyano group is at least one selected from 2, 5-diaminobenzonitrile and 4, 5-diaminoisophthalonitrile;

preferably, in the step (1), the molar ratio of the acid anhydride groups in the dibasic acid anhydride to the total amino groups in the diamine and the polyamine is 1-1.5: 1; the functional diamine accounts for 5-98% of the diamine by mole;

the temperature of the polycondensation reaction is-10 ℃, preferably the temperature of the polycondensation reaction is 0-4 ℃, and the time is 0.5-12 h.

Preferably, in the step (2), the polyamine has a molecular structure containing at least three amino groups, and preferably, the polyamine is a triamine or a tetramine;

more preferably, the triamine is at least one selected from the group consisting of tris (2-aminoethyl) amine (TAA), 1,3, 5-Triaminobenzene (TAB), tris (4-aminophenyl) amine (TAP), 1,3, 5-tris (4-aminophenyl) benzene (TPP), and 1,3, 5-tris (4-aminophenoxy) benzene (TAPOB); the tetraamine is at least one selected from Pentamine (PETA), 1,2,4, 5-benzene tetramine (PTA), 3' -Diaminobenzidine (DBA) and 3,3,4, 4-tetraaminodiphenyl ether (TDE);

preferably, the polyamine accounts for 1 to 20 percent of the total molar amount of the dibasic acid anhydride, the diamine and the polyamine.

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

(i) preparing a branched cross-linked polyamic acid solution according to the preparation method described in the second aspect;

(ii) fully mixing and uniformly stirring a positive electrode active substance or a negative electrode active substance, a conductive agent, the branched cross-linked polyamic acid solution and a polar solvent to obtain electrode slurry;

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

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

the non-solvent part in the electrode slurry comprises 80-98 wt% of active substances, 1-10 wt% of conductive agents and 1-10 wt% of polyamide acid;

the viscosity of the electrode paste is 500-20000 cP;

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

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

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

preferably, the polar solvent is at least one selected from the group consisting of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), N-ethylpyrrolidone (NEP), dimethyl sulfoxide (DMSO), Hexamethylphosphoramide (HMPA), preferably, the polar solvent is N-methylpyrrolidone (NMP);

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

the current collector is a carbon-containing aluminum foil or a carbon-containing copper foil;

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

The temperature for carrying out the heat treatment is 200-450 ℃, and the time is 1-120 min.

The fourth aspect of the present invention provides a polyimide adhesive prepared by the preparation method of the third aspect, wherein a polyimide molecular chain in the polyimide adhesive contains a strong polar group, and the whole molecular chain is in a branched cross-linked form;

preferably, the strongly polar group is at least one of a hydroxyl group, a carboxyl group, a sulfonic acid group, a trifluoromethyl group and a cyano group.

The fifth aspect of the invention provides a lithium ion battery pole piece containing the 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;

preferably, the active material layer is composed of a positive electrode active material or a negative electrode active material, a conductive agent, and a polyimide binder; more preferably, the active material layer comprises the following components in percentage by mass: 80-98 wt% of positive electrode or negative electrode active material, 1-10 wt% of conductive agent and 1-10 wt% of polyimide binder;

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

(1) the polyimide adhesive prepared by the invention has more excellent temperature resistance because the molecular chain contains a large amount of rigid and stable imide ring and benzene ring structures; the adhesive can exist stably at the temperature below 300 ℃, and is not softened and decomposed.

(2) In the branched cross-linked polyimide adhesive prepared by the invention, the polyimide molecular chain is in a cross-linked network structure, and the polyimide molecular chain contains strong polar groups, so that the polyimide molecular chain can be combined with an electrode material through strong hydrogen bond effect and bonding effect, the bonding performance among electrode material components is greatly enhanced, and the integrity of the electrode components is effectively ensured; meanwhile, a uniform and continuous protective coating is formed on the surface of the active material, so that the coating performance of the adhesive is greatly improved, and the stability of an electrode-electrolyte interface is effectively ensured.

(3) The preparation method adopts a mixing mode of a polyamic acid solution, an active component, a conductive agent and the like to prepare electrode slurry, and the electrode slurry is uniformly coated on a current collector and is subjected to dehydration condensation to prepare a polyimide adhesive and a lithium ion battery pole piece containing the polyimide adhesive; because a large amount of polar amide groups and strong polar groups exist in the polyamic acid structure, compared with the traditional fluorine adhesive only with weak van der waals force, the polyimide adhesive prepared by the invention can provide stronger bonding force, so that the interaction among electrode material components is stronger, the adhesive property and the coating property are better, the slurry is more uniformly dispersed, and the complete pole piece with the optimal conductive network structure is more favorably formed.

(4) The lithium ion battery assembled by the lithium ion battery pole piece containing the polyimide adhesive prepared by the invention has more excellent cycle performance, rate capability and 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 used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is an SEM topography at 5000 magnification of a positive electrode sheet containing PI (ODPA-mPDA7-DABA3-TAPOB 2%) adhesive prepared in example 2;

FIG. 2 is an SEM topography of a positive electrode sheet containing the PI (ODPA-mPDA7-DABA3-TAPOB 2%) adhesive prepared in example 2, at a magnification of 10000 times;

FIG. 3 is an SEM topography of a positive electrode sheet containing the PVDF binder prepared in comparative example 1, at 5000 Xmagnification;

FIG. 4 is an SEM topography of a positive electrode sheet comprising the PVDF binder prepared in comparative example 1, at a magnification of 10000 times;

FIG. 5 is an SEM topography for a positive electrode sheet containing PI (ODPA-mPDA7-DABA3) adhesive prepared in comparative example 5, at 5000 Xmagnification;

FIG. 6 is an SEM topography of a positive electrode sheet containing PI (ODPA-mPDA7-DABA3) adhesive prepared in comparative example 5, at 10000 times magnification;

fig. 7 is a graph of rate performance of coin cell assembled lithium ion positive electrode sheets comprising binders prepared according to example 2, comparative example 1 and comparative example 5;

fig. 8 is a charge and discharge graph at a high rate (5C) of a coin cell assembled with the adhesives prepared in example 2, comparative example 1, and comparative example 5;

fig. 9 is a graph of cycle performance of a coin cell assembled with adhesives prepared in example 2, comparative example 1, and comparative example 5.

Detailed Description

To make the objects, technical solutions and advantages of the embodiments of the present invention clearer and more complete, the following will clearly and completely describe the technical solutions in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments, and all other embodiments obtained by a person of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the protection scope of the present invention.

the polyamic acid solution has a solid content of 0.5 to 50 wt% (e.g., can be 0.5 wt%, 2 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, 42 wt%, 45 wt%, 48 wt%, or 50 wt%), and an intrinsic viscosity of 0.1 to 6.63dL/g (e.g., can be 0.1dL/g, 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, 6.5dL/g, 6.63dL/g, or 6.63 dL/g).

The method specifically comprises the following steps: (1) completely dissolving diamine in a polar solvent under the protection of nitrogen at 0 ℃, uniformly stirring, adding dibasic acid anhydride, and continuously reacting for 0.5-12 h to obtain a linear polyamide acid solution; wherein the molar ratio of an anhydride group in the dibasic acid anhydride to the total amino groups in the diamine and the polyamine is 1-1.5: 1; the functional diamine accounts for 5-98% of the diamine by mole; (2) dissolving all polyamine in a polar solvent, slowly dropwise adding the polar solvent into a linear polyamic acid solution, and continuously reacting to obtain a branched cross-linked polyamic acid solution with the solid content of 0.5-50 wt% and the intrinsic viscosity of 0.1-6.63 dL/g; wherein the polyamine accounts for 0.1-20% of the total molar amount of the dibasic acid anhydride, the diamine and the polyamine.

The invention prepares the polyamic acid solution with strong polarity and a branched crosslinking structure by introducing functional diamine and polyamine monomers containing strong polar groups (at least one of hydroxyl groups, carboxyl groups, sulfonic acid groups, trifluoromethyl groups and cyano groups), and further obtains the polyimide adhesive with strong polarity and a branched crosslinking structure by dehydration condensation reaction.

According to some preferred embodiments, in step (1), the dibasic acid anhydride is selected from at least one of pyromellitic dianhydride (PMDA), 4,4 ' -diphenyl ether dianhydride (ODPA), biphenyl dianhydride (BPDA), 3 ', 4,4 ' -diphenylsulfone tetracarboxylic dianhydride (DSDA), hexafluoro dianhydride (6FDA), 3 ', 4,4 ' -Benzophenone Tetracarboxylic Dianhydride (BTDA), 4,4 ' - (4,4 ' -isopropylidenediphenoxy) bisphthalic anhydride (bissda), p-phenylene-bistrimellitic acid ester dianhydride (TAHQ).

the polar solvent is at least one selected from the group consisting of N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), N-ethylpyrrolidone (NEP), dimethyl sulfoxide (DMSO), Hexamethylphosphoramide (HMPA), and preferably, N-methylpyrrolidone (NMP).

According to some preferred embodiments, in step (1), the functional diamine is a diamine containing a strongly polar group;

more preferably, the functional diamine containing the hydroxyl group is at least one selected from the group consisting of 3, 3' -dihydroxybenzidine (HAB), 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6 FAP); the functional diamine containing the carboxyl group is at least one selected from 3, 5-diaminobenzoic acid (DABA), 2, 3-diaminobenzoic acid, 3, 5-bis (4-aminophenoxy) benzoic acid, and 4,4 ' -diaminobiphenyl-2, 2 ' -dicarboxylic acid (2,2 ' -DCB); the functional diamine containing the sulfonic acid group is selected from at least one of 2, 4-diaminobenzene sulfonic acid, 2,4, 6-trimethyl-3, 5-diaminobenzene sulfonic acid and benzidine disulfonic acid (BDSA); the functional diamine containing trifluoromethyl is at least one selected from 2,2 ' -bis (trifluoromethyl) -4,4 ' -diaminophenyl ether (6FODA) and 4,4 ' -bis (4-amino-2-trifluoromethylphenoxy) biphenyl; the functional diamine containing the cyano group is at least one selected from 2, 5-diaminobenzonitrile and 4, 5-diaminophthalimide.

According to some preferred embodiments, in step (1), the molar ratio of anhydride groups in the dibasic acid anhydride to the total amino groups in the diamine and the polyamine is 1 to 1.5:1 (e.g., may be 1:1, 1.01:1, 1.02:1, 1:05, 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); the percentage of the functional diamine in the diamine is 5-98% (e.g., 5%, 8%, 10%, 12%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98%);

the polycondensation reaction is carried out at a temperature of-10 to 10 ℃ (for example, -10 ℃, -9 ℃, -8 ℃, -7 ℃, -6 ℃, -5 ℃, -4 ℃, -3 ℃, -2 ℃, -1 ℃, 0 ℃, 1 ℃,2 ℃,3 ℃,4 ℃,5 ℃,6 ℃, 7 ℃, 8 ℃,9 ℃ or 10 ℃), preferably at a temperature of 0 to 4 ℃ (for example, 0 ℃, 1 ℃,2 ℃,3 ℃, or 4 ℃) for a period of 0.5 to 12 hours (for example, 0.5 hour, 1 hour, 1.5 hour, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, 9.5 hours, 10 hours, 10.5 hours, 11 hours, 11.5 hours, or 12 hours).

According to some preferred embodiments, in step (2), the polyamine has a molecular structure containing at least three amino groups, and preferably, the polyamine is a triamine or a tetramine;

preferably, the polyamine comprises 0.1 to 20% (e.g., can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%) of the total molar amount of the dibasic anhydride, the diamine, and the polyamine.

The functional diamine with strong polar group (at least one of hydroxyl group, carboxyl group, sulfonic acid group, trifluoromethyl group and cyano group) is adopted to ensure that the prepared polyimide adhesive has strong polarity, and the polyamine is added to ensure that the prepared polyimide adhesive has a branched crosslinking structure; the polyimide adhesive with strong polarity and a branched crosslinking structure, which is obtained by adding functional diamine and polyamine, has strong hydrogen bond effect and bonding effect with an active material, so that the adhesive property among electrode material components is greatly enhanced, and the integrity of the electrode components is effectively ensured; meanwhile, a uniform and continuous protective coating is formed on the surface of the active material, so that the coating performance of the adhesive is greatly improved, and the stability of an electrode-electrolyte interface is effectively ensured.

(i) preparing a branched cross-linked polyamic acid solution according to the method of the second aspect;

The preparation method comprises the steps of mixing a polyamic acid solution with strong polarity and a branched cross-linked structure, a positive electrode active substance or a negative electrode active substance, a conductive agent and a polar solvent to obtain an electrode slurry, uniformly coating the electrode slurry on a current collector, drying, rolling, and finally performing heat treatment to obtain the polyimide adhesive with the strong polarity and the branched cross-linked structure and the lithium ion battery pole piece containing the polyimide adhesive.

The polyimide adhesive with the branched cross-linked structure prepared by the method improves the bonding strength and the mechanical strength of the polyimide adhesive and the coating performance of the polyimide adhesive on electrode material components, can uniformly coat the electrode material and the conductive agent, has strong adhesion performance among the electrode components and good coating and adhesion effects, is tightly connected to form a complete and compact conductive structure, and is favorable for forming a complete and firm electrode structure.

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

the non-solvent part in the electrode paste comprises 80-98 wt% (for example, 80 wt%, 82 wt%, 84 wt%, 86 wt%, 88 wt%, 90 wt%, 92 wt%, 94 wt%, 96 wt% or 98 wt%) of an active material, 1-10 wt% (for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%) of a conductive agent, 1-10 wt% (for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%) of a polyamic acid;

the viscosity of the electrode paste is 500-20000 cP (for example, 500cP, 1000cP, 2000cP, 3000cP, 4000cP, 5000cP, 6000cP, 7000cP, 8000cP, 9000cP, 10000cP, 11000cP, 12000cP, 13000cP, 14000cP, 15000cP, 16000cP, 17000cP, 18000cP, 19000cP, or 20000cP can be obtained);

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

the compacted density of the rolling is 1.4-4 g/cm ³ (e.g., it may be 1.4 g/cm) ³ 、1.5g/cm ³ 、1.8g/cm ³ 、2g/cm ³ 、2.2g/cm ³ 、2.5g/cm ³ 、2.8g/cm ³ 、3g/cm ³ 、3.2g/cm ³ 、3.5g/cm ³ 、3.8g/cm ³ Or 4g/cm ³ ) (ii) a The compacted density of the rolled steel sheet is 1.4-4 g/cm ³ The electrode plate can be compacted, and the electrode plate has higher peel strength and better adhesive property; the electrode slice with too low density is not compacted, so that the peeling strength of the electrode is low, and the adhesive strength of the electrode slice is low.

The heat treatment is carried out at the temperature of 200-450 ℃ for 1-120 min, preferably, the heat treatment is carried out at the temperature of 60min to 135 ℃ from room temperature, the heat preservation is carried out at the temperature of 135 ℃ for 60min, the temperature is carried out at the temperature of 60min to 300 ℃ from 135 ℃ for 60 min.

preferably, the strongly polar group is at least one of a hydroxyl group, a carboxyl group, a sulfonic acid group, a trifluoromethyl group, and a cyano group.

The polyimide adhesive prepared by the invention is a strong-polarity polyimide adhesive with a branched cross-linked structure, the formation of the branched cross-linked structure increases the free volume of the polyimide adhesive, enhances the wettability of the polyimide adhesive on electrolyte, improves the diffusion migration rate of lithium ions, and effectively overcomes the defect of poor ion conductivity caused by strong insulation of polyimide.

preferably, the active material layer is composed of a positive electrode active material or a negative electrode active material, a conductive agent, and a polyimide binder; more preferably, the active material layer comprises the following components in percentage by mass: 80-98 wt% (e.g., may be 80 wt%, 82 wt%, 84 wt%, 86 wt%, 88 wt%, 90 wt%, 92 wt%, 94 wt%, 96 wt%, or 98 wt%), 1-10 wt% (e.g., may be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%) of a polyimide binder;

the polyimide adhesive with strong polarity and a branched crosslinking structure, which is prepared by the invention, has excellent adhesive property, excellent coating effect and outstanding high-temperature and high-pressure resistance, can greatly improve the stability of an electrode structure, and a battery assembled by a battery pole piece containing the adhesive has excellent cycle performance, rate capability and safety performance, and has wide application prospect in the field of high-specific energy lithium ion batteries.

In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention is further described below with reference to the following embodiments.

In the present invention, the electrochemical performance test, the thermal stability test and the peel strength test are performed by the following methods.

And (3) electrochemical performance testing: the voltage range is set to be 2.5-4.3V, the test is carried out under the multiplying power of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C, and the cycle performance and the multiplying power performance of the batteries of the embodiment and the comparative example are tested.

And (3) testing thermal stability: and (3) carrying out three-cycle circulation on the electricity-detained battery at the voltage of 2.5-4.5V and the current density of 0.1C, and finally keeping the fully charged state. And (3) disassembling the battery, cleaning the positive pole piece in dimethyl carbonate (DMC), drying in a vacuum oven, and finally scraping the positive pole material (3-7 mg) to perform a full-electric-state DSC test to represent the thermal stability of the pole piece.

And (3) testing the peel strength: the positive electrode sheet was cut into rectangular specimens and tested according to the test standards described in GB/T2790-1995.

NCM811 is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ And (3) a positive electrode material.

The materials and reagents in the invention can be purchased directly from the market, and the specific model is not limited.

Example 1

Preparation of ODPA-mPDA7-DABA3-TAPOB 1% System polyamic acid solution, PI (ODPA-mPDA7-DABA3- TAPOB 1%) type adhesive and positive electrode sheet comprising the same:

(i) weighing 5.487g of dicarboxylic anhydride (ODPA), 1.299g of common diamine (mPDA), 0.783g of functional Diamine (DABA) and 0.14g of Triamine (TAPOB) according to the molar ratio of an anhydride group in the dicarboxylic anhydride to a total amino group in the diamine and the polyamine of 1:1, the molar ratio of the common diamine (mPDA) to the functional Diamine (DABA) in the diamine and the molar amount of the Triamine (TAPOB) accounting for 1 percent of the total molar amount of the dicarboxylic anhydride, the diamine and the triamine, weighing 30mL of NMP, completely dissolving the mPDA and the DABA in 25mL of NMP under the protection of nitrogen at 0 ℃, adding the ODPA after completely dissolving and uniformly stirring for reaction, and continuously and fully stirring for reaction for 8 hours to obtain a linear polyamic acid solution; after the whole amount of TAPOB was dissolved in 5mL of NMP, it was slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched crosslinking type polyamic acid solution having a solid content of 20% by weight.

(ii) Fully and uniformly mixing a polyamide acid solution (calculated according to the mass of a solute) obtained in a positive electrode active material NCM811 (i) and conductive carbon black according to a mass ratio of 90:5:5 to obtain positive electrode slurry with the solid content of 40 wt%, coating the positive electrode slurry on a current collector (carbon-containing aluminum foil), and drying for 8 hours at room temperature in a superclean bench; then cutting the sheet into small round pole pieces with the diameter of 14mm, and rolling the round pole pieces with the rolling density of 3g/cm ³ (ii) a Putting the rolled pole piece into a high-temperature oven for heat treatment to enable a polyamide acid solution to be subjected to dehydration condensation to obtain a polyimide adhesive and a lithium ion battery positive pole piece containing the adhesive, wherein the temperature rise procedure of the heat treatment is to rise from room temperature to 135 ℃ over 60min, preserve the temperature at 135 ℃ for 60min, rise from 135 ℃ to 300 ℃ over 60min and keep the temperature at 300 DEG CAnd preserving the temperature for 60 min.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention rate after 100 cycles of the positive electrode sheet of the lithium ion battery comprising the polyimide adhesive prepared in example 1 are shown in table 1.

The lithium ion battery positive electrode plate containing the polyimide adhesive prepared in the example 1 and the battery assembling and testing method have the specific discharge capacity of 0.1C of the NCM811 in the system of 211mAh/g and the primary efficiency of 87.3 percent.

Example 2

Preparation of ODPA-mPDA7-DABA3-TAPOB 2% System polyamic acid solution, PI (ODPA-mPDA7-DABA3- TAPOB 2%) type adhesive and positive electrode sheet comprising the same:

(i) weighing 5.449g of dicarboxylic anhydride (ODPA), 1.237g of common diamine (mPDA), 0.746g of functional Diamine (DABA) and 0.278g of Triamine (TAPOB) and measuring 30mL of NMP according to the molar ratio of an anhydride group in the dicarboxylic anhydride to a total amino group in the diamine and the polyamine of 1.01:1, the molar ratio of the common diamine (mPDA) to the functional Diamine (DABA) in the diamine of 7:3 and the molar amount of the Triamine (TAPOB) accounting for 2 percent of the total molar amount of the dicarboxylic anhydride, the diamine and the triamine, completely dissolving the mPDA and the DABA in 25mL of NMP under the protection of nitrogen at 0 ℃, adding the ODPA after completely dissolving and uniformly stirring for reaction, and continuously and fully stirring for reaction for 8 hours to obtain a linear polyamic acid solution; after the whole amount of TAPOB was dissolved in 5mL of NMP, it was slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched crosslinking type polyamic acid solution having a solid content of 20% by weight.

(ii) The same as in example 1.

The morphology of the positive electrode plate of the lithium ion battery comprising the polyimide binder prepared in example 2 is shown in fig. 1 and 2. The figure shows that the polyimide adhesive uniformly coats the positive electrode material NCM811 and the conductive carbon black, the positive electrode components are tightly connected to form a complete and tight conductive structure, the adhesion performance of the positive electrode components is very strong, and the coating and adhesion effects are best.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention rate after 100 cycles of the positive electrode plate of the lithium ion battery comprising the polyimide adhesive prepared in example 2 are shown in table 1.

The lithium ion battery positive electrode sheet containing the polyimide binder prepared in example 2 and the battery assembly and test method, the 0.1C specific discharge capacity of the NCM811 in the system is 214mAh/g, and the primary efficiency is 88.4%.

Example 3

Preparation of ODPA-mPDA7-DABA3-TAPOB 3% System polyamic acid solution, PI (ODPA-mPDA7-DABA3- TAPOB 3%) type adhesive and positive electrode sheet comprising the same:

(i) weighing 5.381g of dicarboxylic anhydride (ODPA), 1.196g of common diamine (mPDA), 0.721g of functional Diamine (DABA) and 0.412g of Triamine (TAPOB) according to the molar ratio of an anhydride group in the dicarboxylic anhydride to the total amino groups in the diamine and the polyamine of 1:1, the molar ratio of the common diamine (mPDA) to the functional Diamine (DABA) in the diamine of 7:3 and the molar amount of the Triamine (TAPOB) accounting for 3 percent of the total molar amount of the dicarboxylic anhydride, the diamine and the triamine, weighing 30mLNMP, completely dissolving the mPDA and the DABA in 25mL of NMP under the protection of nitrogen at 0 ℃, adding the ODPA after completely dissolving and uniformly stirring for reaction, and continuously and fully stirring for reaction for 8 hours to obtain a linear polyamic acid solution; after the whole amount of TAPOB was dissolved in 5mL of NMP, it was slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched crosslinking type polyamic acid solution having a solid content of 20% by weight.

(ii) The same as in example 1.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention rate after 100 cycles of the positive electrode plate of the lithium ion battery comprising the polyimide adhesive prepared in example 3 are shown in table 1.

The lithium ion battery positive electrode sheet containing the polyimide binder prepared in example 3 and the battery assembly and testing method, the 0.1C specific discharge capacity of NCM811 in the system was 207mAh/g, and the primary efficiency was 87.2%.

Example 4

Preparation of ODPA-mPDA7-DABA3-TDE 2% System polyamic acid solution, PI (ODPA-mPDA7-DABA3- TDE 2%) type adhesive and positive electrode sheet comprising the adhesive:

(i) according to the mole ratio of an anhydride group in dibasic acid anhydride to a total amino group in diamine and polyamine of 1:1, the mole ratio of common diamine (mPDA) and functional Diamine (DABA) in diamine of 7:3, and the mole amount of a Tetraamine (TDE) accounting for 2% of the total monomer mole amount, 5.548g of dibasic acid anhydride (ODPA), 1.247g of common diamine (mPDA), 0.752g of functional Diamine (DAB) and 0.163g of Tetraamine (TDE) are weighed, 30mLNMP is weighed, under the protection of nitrogen at 0 ℃, mPDA and DABA are all dissolved in 25mLNMP, and are added into ODPA for reaction after being completely dissolved and uniformly stirred, and linear polyamic acid solution is obtained after being continuously stirred for 8 hours. After all of the TDE was dissolved in 5mL of NMP, it was slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched crosslinking polyamic acid solution having a solid content of 20 wt%.

(ii) The same as in example 1.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention rate after 100 cycles of the positive electrode plate of the lithium ion battery comprising the polyimide adhesive prepared in example 4 are shown in table 1.

The lithium ion battery positive electrode sheet containing the polyimide binder prepared in example 4 and the battery assembly and testing method, the 0.1C specific discharge capacity of NCM811 in the system was 204mAh/g, and the primary efficiency was 83.4%.

Example 5

Preparation of ODPA-mPDA5-DABA5-TAPOB 2% System polyamic acid solution, PI (ODPA-mPDA5-DABA5- TAPOB 2%) type bondThe adhesive and the pole piece containing the adhesive are as follows:

(i) according to the mole ratio of an anhydride group in a dibasic acid anhydride to a total amino group in diamine and polyamine of 1:1, the mole ratio of common diamine (mPDA) and functional Diamine (DABA) in diamine of 5:5, the mole amount of a Triamine (TAPOB) accounts for 2% of the total monomer mole amount, 5.336g of dibasic acid anhydride (ODPA), 0.873g of common diamine (mPDA), 1.228g of functional Diamine (DABA) and 0.272g of Triamine (TAPOB) are weighed to obtain 30mL of NMP, all the mPDA and the DABA are dissolved in 25mL of NMP under the protection of nitrogen at 0 ℃, the ODPA is added after complete dissolution and uniform stirring for reaction, and the linear polyamic acid solution is obtained after continuous stirring and reaction for 8 hours. After the whole amount of TAPOB was dissolved in 5mL of NMP, it was slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched crosslinking type polyamic acid solution having a solid content of 20% by weight.

(ii) The same as in example 1.

The peel strength test result (representing the adhesive property of the adhesive), the full electrical thermal stability test result (representing the safety), and the capacity retention rate after 100 cycles of the lithium ion battery positive electrode sheet including the polyimide adhesive prepared in example 5 are shown in table 1.

The lithium ion battery positive electrode sheet containing the polyimide binder prepared in example 5 and the battery assembly and testing method, the 0.1C specific discharge capacity of NCM811 in the system was 213mAh/g, and the primary efficiency was 86.2%.

Example 6

Preparation of ODPA-mPDA3-DABA7-TAPOB 2% System polyamic acid solution, PI (ODPA-mPDA3-DABA7- TAPOB 2%) type adhesive and pole piece using the adhesive:

(i) according to the method, 5.240g of dibasic acid anhydride (ODPA), 0.514g of ordinary diamine (mPDA), 1.689g of functional Diamine (DABA) and 0.267g of Triamine (TAPOB) are weighed according to the molar ratio of an anhydride group in dibasic acid anhydride to total amino groups in diamine and polyamine of 1:1, the molar ratio of ordinary diamine (mPDA) to functional Diamine (DABA) in diamine is 3:7, the molar amount of the Triamine (TAPOB) accounts for 2% of the total monomer molar amount, 30mL of NMP is weighed, all the mPDA and the DABA are dissolved in 25mL of NMP under the condition of 0 ℃ nitrogen protection, the NMP is added after complete dissolution and uniform stirring for reaction, and the linear solution is obtained after continuous stirring reaction for 8 hours. After the whole amount of TAPOB was dissolved in 5mL of NMP, it was slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched crosslinking type polyamic acid solution having a solid content of 20% by weight.

(ii) The same as in example 1.

The peel strength test result (representing the adhesive property of the adhesive), the full electrical thermal stability test result (representing the safety), and the capacity retention rate after 100 cycles of the lithium ion battery positive electrode sheet including the polyimide adhesive prepared in example 6 are shown in table 1.

The lithium ion battery positive electrode sheet containing the polyimide binder prepared in example 6 and the battery assembly and testing method, the 0.1C specific discharge capacity of NCM811 in the system was 210mAh/g, and the primary efficiency was 84.1%.

Example 7

Preparation of ODPA-mPDA7-BDSA3-TAPOB 2% System polyamic acid solution, PI (ODPA-mPDA7-BDSA3- TAPOB 2%) type adhesive and pole piece using the adhesive:

(i) according to the mole ratio of an anhydride group in a dibasic acid anhydride to a total amino group in diamine and polyamine of 1.01:1, the mole ratio of common diamine (mPDA) to functional diamine (BDSA) in diamine of 7:3, the mole amount of a Triamine (TAPOB) accounts for 2 percent of the total monomer mole amount, 5.449g of dibasic acid anhydride (ODPA), 1.237g of common diamine (mPDA), 1.679g of functional diamine (BDSA) and 0.267g of Triamine (TAPOB) are weighed, 30mL of NMP is weighed, all the mPDA and the DABA are dissolved in 25mL of NMP under the protection of nitrogen at 0 ℃, the ODPA is added after complete dissolution and uniform stirring for reaction, and the linear polyamic acid solution is obtained after continuous stirring and reaction for 8 hours. After the whole amount of TAPOB was dissolved in 5mL of NMP, it was slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched crosslinking type polyamic acid solution having a solid content of about 20% by weight.

(ii) The same as in example 1.

The results of the peel strength test (characterizing the adhesive properties of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention after 100 cycles for the positive electrode sheet of the lithium ion battery comprising the polyimide adhesive prepared in example 7 are shown in table 1.

The lithium ion battery positive electrode sheet containing the polyimide binder prepared in example 7 and the battery assembly and testing method, the 0.1C specific discharge capacity of NCM811 in this system was 204mAh/g, the primary efficiency was 84.8%.

Comparative example 1

Preparing a PVDF adhesive and a positive pole piece containing the adhesive:

a: weighing 0.526g of powdered PVDF (the molecular weight of PVDF is 50 ten thousand), dissolving the powdered PVDF in 10mL of NMP, and uniformly stirring to obtain PVDF glue solution with the solid content of 5 wt%;

b: and (B) fully and uniformly mixing the positive electrode material NCM811, the PVDF glue solution (calculated according to the mass of the solute) obtained in the step (A) and the conductive carbon black according to the mass ratio of 90:5:5 to obtain positive electrode slurry, wherein the solid content of the slurry is 40 wt%. Coating the positive electrode slurry on a carbon-containing aluminum foil and drying for 2 hours in a vacuum oven at the temperature of 80 ℃; then cutting the electrode into small circular pole pieces with the diameter of 14 mm; rolling the round pole piece with the rolling density of 3g/cm ³ And obtaining the polyimide adhesive and the lithium ion battery positive pole piece containing the adhesive.

The morphology of the positive electrode sheet of the lithium ion battery comprising the polyimide binder prepared in comparative example 1 is shown in fig. 3 and 4. It can be seen from the figure that the PVDF binder has poor adhesion to the positive electrode component, less adhesion of the active particle surface conductive agent, and poor coating properties.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention after 100 cycles of the positive electrode sheet of the lithium ion battery comprising the polyimide adhesive prepared in comparative example 1 are shown in table 1.

The lithium ion battery positive electrode plate containing the polyimide adhesive prepared in the example 1 and the battery assembling and testing method have the specific discharge capacity of 0.1C of the NCM811 in the system of 179mAh/g and the primary efficiency of 85.21%.

Comparative example 2

Preparation of an ODPA-mPDA system polyamic acid solution containing no polar group in the molecular chain, and PI (ODPA-mPDA) type adhesive Mixture and positive pole piece using same：

(i) 5.774g of dianhydride (4, 4' -diphenyl ether dianhydride, ODPA) and 1.993g of diamine (m-phenylenediamine, mPDA) are respectively weighed according to the molar ratio of 1.01:1, the mPDA is completely dissolved in NMP under the condition of nitrogen protection at 0 ℃, the weighed ODPA is added for reaction after the mPDA is completely dissolved and uniformly stirred, and the polyamic acid solution with the solid content of 20 wt% is obtained after the reaction is continuously and fully stirred for 8 hours.

(ii) The same as in example 1.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention after 100 cycles of the positive electrode sheet of the lithium ion battery comprising the polyimide adhesive prepared in comparative example 2 are shown in table 1.

The lithium ion battery positive pole piece containing the polyimide adhesive prepared in the comparative example 2 and the battery assembling and testing method have the specific discharge capacity of 0.1C of the NCM811 in the system of 195mAh/g and the primary efficiency of 86.1 percent.

Comparative example 3

Preparing soluble PI (6FDA-4, 4' -ODA7-DABA3) adhesive and a pole piece containing the adhesive:

(i) according to the technical scheme, 7.3207g of dicarboxylic anhydride (6FDA), 2.2870g of common diamine (4,4 ' -ODA) and 0.7447g of functional Diamine (DABA) and 30mL of NMP are weighed according to the molar ratio of an anhydride group in the dicarboxylic anhydride to the total amino groups in the diamine and the polyamine of 1.01:1 and the molar ratio of the common diamine (4,4 ' -ODA) to the functional Diamine (DABA) in the diamine of 7:3, the 4,4 ' -ODA and the DABA are all dissolved in 30mL of NMP under the protection of nitrogen at 0 ℃, the 6FDA is added for reaction after the complete dissolution and the uniform stirring, and then the polyamic acid solution with the solid content of 25 wt% is obtained after the full stirring reaction for 8 hours at low temperature; and (2) directly putting the polyamic acid solution after aging treatment into a high-temperature oven to carry out temperature programming heat treatment to dehydrate and condense the polyamic acid to obtain the polyimide adhesive, wherein the temperature programming is that the temperature is increased from room temperature to 135 ℃ for 60min after 60min, the temperature is kept at 135 ℃ for 60min, and the temperature is increased from 135 ℃ to 300 ℃ for 60min after 60 min.

(ii) Fully and uniformly mixing the polyimide adhesive obtained in the positive active material NCM811 (i) and the conductive carbon black according to the mass ratio of 90:5:5 to obtain positive slurry, wherein the solid content of the slurry is 40 wt%, coating the positive slurry on a carbon-containing aluminum foil, and drying for 8 hours at room temperature in an ultra-clean bench; then cutting the electrode into small circular pole pieces with the diameter of 14 mm; rolling the round pole piece with the rolling density of 3g/cm ³ And obtaining the lithium ion battery positive pole piece containing the polyimide adhesive.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention after 100 cycles of the positive electrode sheet of the lithium ion battery comprising the polyimide adhesive prepared in comparative example 3 are shown in table 1.

Comparative example 4

Preparation of soluble PI (ODPA-4, 4' -ODA7-DABA3) adhesive and Pole piece comprising the adhesive:

(i) according to the technical scheme, 6.4933g of dicarboxylic anhydride (ODPA), 2.9049g of common diamine (4,4 ' -ODA) and 0.9460g of functional Diamine (DABA) and 30ml of LNMP are weighed according to the molar ratio of anhydride groups in dicarboxylic anhydride to total amino groups in diamine and polyamine of 1.01:1 and the molar ratio of common diamine (4,4 ' -ODA) to functional Diamine (DABA) in diamine of 7:3, the 4,4 ' -ODA and DABA are all dissolved in 30ml of LNMP under the condition of nitrogen protection at 0 ℃, the ODPA is added for reaction after the complete dissolution and the uniform stirring, and then the polyamic acid solution with the solid content of 25 wt% is obtained after the continuous full stirring reaction for 8 hours; and (2) directly putting the polyamic acid solution after aging treatment into a high-temperature oven to carry out temperature programming heat treatment to dehydrate and condense the polyamic acid to obtain the polyimide adhesive, wherein the temperature programming is that the temperature is increased from room temperature to 135 ℃ for 60min after 60min, the temperature is kept at 135 ℃ for 60min, and the temperature is increased from 135 ℃ to 300 ℃ for 60min after 60 min.

(ii) Fully and uniformly mixing the polyimide adhesive obtained in the positive active material NCM811 (i) and the conductive carbon black according to the mass ratio of 90:5:5 to obtain positive slurry, wherein the solid content of the slurry is 40 wt%, coating the positive slurry on a carbon-containing aluminum foil, and drying for 8 hours at room temperature in an ultraclean workbench; then cutting the electrode into small circular pole pieces with the diameter of 14 mm; rolling the round pole piece with the rolling density of 3g/cm ³ And obtaining the lithium ion battery positive pole piece containing the polyimide adhesive.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention after 100 cycles of the positive electrode sheet of the lithium ion battery comprising the polyimide adhesive prepared in comparative example 4 are shown in table 1.

Comparative example 5

Preparation of ODPA-mPDA7-DABA3 System polyamic acid solution, PI (ODPA-mPDA7-DABA3) type adhesive and Package The positive pole piece containing the adhesive comprises the following components:

(i) according to the technical scheme, 7.463g of dicarboxylic anhydride (ODPA), 1.803g of ordinary diamine (mPDA) and 1.087g of functional Diamine (DABA) are weighed according to the molar ratio of anhydride groups in dicarboxylic anhydride to total amino groups in diamine and polyamine of 1.01:1 and the molar ratio of ordinary diamine (mPDA) to functional Diamine (DABA) of diamine of 7:3, 30mL of NMP is weighed, mPDA and DABA are completely dissolved in 30mL of NMP under the condition of nitrogen protection at 0 ℃, ODPA is added for reaction after complete dissolution and uniform stirring, and a polyamic acid solution with the solid content of 25 wt% is obtained after continuous full stirring reaction for 8 hours.

(ii) The same as in example 1.

The morphology of the positive electrode sheet of the lithium ion battery comprising the polyimide binder prepared in comparative example 5 is shown in fig. 5 and 6. It can be seen from the figure that the polyimide adhesive uniformly coats the positive electrode material NCM811 and the conductive carbon black, and the positive electrode components are tightly connected to form a complete and tight conductive structure.

The results of the peel strength test (characterizing the adhesive property of the adhesive), the full electrical thermal stability test (characterizing the safety), and the capacity retention after 100 cycles of the positive electrode sheet of the lithium ion battery comprising the polyimide adhesive prepared in comparative example 5 are shown in table 1.

The lithium ion battery positive pole piece containing the polyimide adhesive prepared in the comparative example 5 and the battery assembling and testing method have the specific discharge capacity of 0.1C of the NCM811 in the system of 208mAh/g and the primary efficiency of 85.8 percent.

Example 8

Preparation of ODPA-mPDA7-DABA3-TAPOB 2% System polyamic acid solution, PI (ODPA-mPDA7-DABA3- TAPOB 2%) type binder and negative electrode sheet using the binder:

(i) 5.449g of dicarboxylic anhydride (ODPA), 1.237g of common diamine (mPDA), 0.746g of functional Diamine (DABA), 0.278g of Ternary Amine (TAPOB) and 30mL of weighed amount of 30mL of NMP are weighed according to the molar ratio of anhydride groups in the dicarboxylic anhydride to total amino groups in the diamine and the polyamine of 7:3, the molar ratio of the common diamine (mPDA) to the functional Diamine (DABA) in the diamine accounts for 2% of the total monomer molar amount, the mPDA and the DABA are all dissolved in 25mL of NMP under the protection of nitrogen at 0 ℃, the NMP is added into the polyamide acid after the mPDA and the DABA are completely dissolved by mechanical stirring for reaction, and the polyamide acid is obtained after continuous and full stirring for reaction for 8 h. All of the Triamine (TAPOB) monomer was dissolved in 5mL of NMP, and slowly added dropwise to the linear polyamic acid solution to continue the reaction to obtain a branched cross-linked polyamic acid solution.

(ii) And (3) fully and uniformly mixing the polyamic acid solution (calculated according to the mass of the solute) obtained in the negative electrode material (carbon material) and the conductive carbon black according to the mass ratio of 80:10:10 to obtain negative electrode slurry, wherein the solid content of the slurry is 40 wt%. Coating the negative electrode slurry on a current collector (carbon-containing copper foil), drying at room temperature in an ultra-clean workbench, cutting into pieces, rolling to obtain a negative electrode piece, putting the negative electrode piece into a high-temperature oven for programmed heating treatment to dehydrate and condense polyamic acid to obtain the polyimide adhesive and the lithium ion battery negative electrode piece containing the adhesive, wherein the temperature raising program is to raise the temperature from room temperature to 135 ℃ for 60min, preserve the temperature from 135 ℃ for 60min, raise the temperature from 135 ℃ to 300 ℃ for 60min, and preserve the temperature from 300 ℃ for 60 min.

The lithium ion battery negative electrode sheet containing the polyimide binder prepared in example 8 was good in flexibility, and the sheet did not fall off after being bent for 5 times, as shown in table 2.

Comparative example 6

Preparing a PVDF adhesive and a negative pole piece applying the adhesive:

(i) weighing 0.526g of powdered PVDF (the molecular weight of PVDF is 50 ten thousand), dissolving the powdered PVDF in 10mL of NMP, and uniformly stirring the powdered PVDF by using a magnetic stirrer to obtain PVDF glue solution with the solid content of 5 wt%;

(ii) and (3) fully and uniformly mixing the carbon material, the PVDF glue solution (calculated according to the mass of the solute) obtained in the step (i) and the conductive carbon black according to the mass ratio of 80:10:10 to obtain the negative electrode slurry, wherein the solid content of the slurry is 40 wt%. And coating the negative electrode slurry on a carbon-containing copper foil, drying for 2h in a vacuum oven at 80 ℃, and rolling the cut pieces to obtain the PVDF adhesive and the lithium ion battery negative electrode piece containing the adhesive.

The negative electrode sheet comprising the PVDF binder prepared in comparative example 6 was poor in flexibility, and the sheet had an obvious powder falling phenomenon after being bent 5 times, as shown in table 2.

TABLE 1 electrochemical Properties of examples and comparative examples (adhesive applied to Positive electrode sheet)

As can be seen from table 1, the peel strength of examples 1 to 7 is higher than that of comparative examples 3 and 4, and it can be seen that the method for preparing the slurry from the polyimide precursor (polyamic acid) according to the present invention is more favorable for improving the adhesion strength of the electrode sheet, and the formed positive electrode slurry is more uniformly dispersed due to the strong interaction between the polyamic acid and the positive electrode component. Compared with the conventional PVDF-type adhesive in comparative example 1 and the common PI-system adhesive in comparative example 2, the strong-polarity branched cross-linked polyimide adhesives provided in examples 1 to 7 of the present invention can provide significantly higher peel strength (i.e., better adhesive properties) for the lithium ion battery electrode sheet; the lithium ion battery assembled by the pole piece containing the polyimide adhesive has more excellent capacity retention rate and full-state thermal stability.

TABLE 2 electrochemical Properties of examples and comparative examples (Binder applied to negative electrode sheet)

As can be seen from Table 2, the negative electrode sheet prepared using the PI binder of type ODPA-mPDA7-DABA3-TAPOB 2% in example 8 has better adhesion than the PVDF binder of the conventional type in comparative example 6.

The positive electrode sheets prepared in example 2, comparative example 1 and comparative example 5 were assembled into button cells, and the test results were shown in fig. 7, fig. 8 and fig. 9. As can be seen from fig. 7 and 8, the lithium ion battery of example 2 using the PI (ODPA-mPDA7-DABA3-TAPOB 2%) type binder having strong polarity and cross-linking branching characteristics has higher specific discharge capacity than the lithium ion battery of comparative example 1 using the PVDF type binder at different rates of 0.1C, 0.2C, 0.5C, 1C, 2C and 5C. As can be seen from FIG. 9, the lithium ion battery using the PI (ODPA-mPDA7-DABA3-TAPOB 2%) type binder has a higher capacity retention rate after 100 cycles than the lithium ion battery using the general PVDF type binder.

As can be seen from fig. 1-6, the polyimide adhesive of example 2 uniformly coats the positive electrode material NCM811 and the conductive carbon black, the positive electrode components are tightly connected to form a complete and tight conductive structure, the adhesion performance of the positive electrode components is very strong, and the coating and adhesion effects are the best; comparative example 5 the polyimide adhesive uniformly coats the positive electrode material NCM811 and the conductive carbon black, and the positive electrode components are tightly connected to form a complete and tight conductive structure; comparative example 1PVDF binder has poor adhesion to the positive electrode component, less active particle surface conductive agent adhesion, and poor coating properties.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present 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 solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A branched cross-linked polyamic acid solution is characterized in that a polyamic acid molecular chain contains a strong polar group, and the whole molecular chain is in a branched cross-linked form;

2. A preparation method of a branched cross-linked polyamic acid solution, characterized by comprising the steps of:

3. The production method according to claim 2, wherein in step (1):

the dibasic acid anhydride is selected from at least one of pyromellitic dianhydride, 4,4 ' -diphenyl ether dianhydride, biphenyl dianhydride, 3 ', 4,4 ' -diphenyl sulfone tetracarboxylic dianhydride, hexafluoro dianhydride, 3 ', 4,4 ' -benzophenone tetracarboxylic dianhydride, 4,4 ' - (4,4 ' -isopropylidenediphenoxy) diphthalic anhydride and p-phenylene-bistrimellitic dianhydride;

the common diamine is at least one selected from p-phenylenediamine, m-phenylenediamine, 4 ' -diaminodiphenyl ether, 3,4 ' -diaminodiphenyl ether, 4 ' -diaminodiphenyl sulfone, 3 ' -diaminodiphenyl sulfone, 2 ' -dimethyl-4, 4 ' -diaminobiphenyl, 4 ' -diaminodiphenyl methane, 1, 3-bis (4 ' -aminophenoxy) benzene, 4 ' -diaminobenzophenone, 9-bis- (4-aminophenyl) and 9, 9-bis- (3-fluoro-4-aminophenyl) fluorene; and/or

The polar solvent is at least one selected from N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, N-ethylpyrrolidone, dimethyl sulfoxide and hexamethylphosphoramide, and preferably, the polar solvent is N-methylpyrrolidone.

4. The production method according to claim 2, wherein in step (1):

the functional diamine is diamine containing strong polar groups;

more preferably, the functional diamine containing the hydroxyl group is at least one selected from the group consisting of 3, 3' -dihydroxybenzidine and 2, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane; the functional diamine containing the carboxyl group is at least one selected from 3, 5-diaminobenzoic acid, 2, 3-diaminobenzoic acid, 3, 5-di (4-aminophenoxy) benzoic acid and 4,4 '-diaminobiphenyl-2, 2' -dicarboxylic acid; the functional diamine containing the sulfonic acid group is at least one selected from 2, 4-diaminobenzene sulfonic acid, 2,4, 6-trimethyl-3, 5-diaminobenzene sulfonic acid and benzidine disulfonic acid; the functional diamine containing trifluoromethyl is at least one selected from 2,2 ' -bis (trifluoromethyl) -4,4 ' -diaminophenyl ether and 4,4 ' -bis (4-amino-2-trifluoromethylphenoxy) biphenyl; the functional diamine containing the cyano group is at least one selected from 2, 5-diaminobenzonitrile and 4, 5-diaminophthalimide.

5. The production method according to claim 2,

the molar ratio of the anhydride groups in the dibasic acid anhydride to the total amino groups in the diamine and the polyamine is 1-1.5: 1; the functional diamine accounts for 5-98% of the diamine by mole percent;

the temperature of the polycondensation reaction is-10 ℃, preferably 0-4 ℃, and the time is 0.5-12 h.

6. The production method according to claim 2, wherein in step (2):

the molecular structure of the polyamine contains at least three amino groups, and preferably, the polyamine is a triamine or a tetramine;

more preferably, the triamine is at least one selected from the group consisting of tris (2-aminoethyl) amine, 1,3, 5-triaminobenzene, tris (4-aminophenyl) amine, 1,3, 5-tris (4-aminophenyl) benzene, and 1,3, 5-tris (4-aminophenoxy) benzene; the tetraamine is at least one selected from pentamine, 1,2,4, 5-benzene tetramine, 3' -diaminobenzidine and 3,3,4, 4-tetraaminodiphenyl ether;

the polyamine accounts for 0.1-20% of the total molar amount of the dibasic acid anhydride, the diamine and the polyamine.

7. A preparation method of a polyimide adhesive is characterized by comprising the following steps:

(i) preparing a branched cross-linked polyamic acid solution according to the preparation method described in any one of claims 2 to 6;

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

8. The method of claim 7, wherein:

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

the viscosity of the electrode paste is 500-20000 cP;

preferably, the polar solvent is at least one selected from the group consisting of N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, N-ethylpyrrolidone, dimethyl sulfoxide, and hexamethylphosphoramide, and preferably, the polar solvent is N-methylpyrrolidone; and/or

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

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

9. A polyimide adhesive prepared by the preparation method according to claim 7 or 8, characterized in that:

the polyimide molecular chain in the polyimide adhesive contains strong polar groups, and the whole molecular chain is in a branched crosslinking form;

10. A lithium ion battery electrode sheet comprising the polyimide adhesive prepared by the preparation method according to claim 7 or 8, characterized in that:

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

preferably, the active material layer is composed of a positive electrode active material or a negative electrode active material, a conductive agent, and a polyimide binder; more preferably, the active material layer comprises the following components in percentage by mass: 80-98 wt% of positive electrode or negative electrode active material, 1-10 wt% of conductive agent and 1-10 wt% of polyimide adhesive.