A hyperbranched polyamide binder, a preparation method and application of a positive electrode sheet

Abstract

The present invention relates to the technical field of positive electrode sheets for lithium batteries, and specifically relates to a hyperbranched polyamide binder, a preparation method and application of a positive electrode sheet. The hyperbranched polyamide binder is a high molecular polymer prepared by polycondensation reaction of diamine monomers, polyamine monomers and diacid monomers. The positive electrode sheet is obtained by mixing a positive electrode material, a conductive agent and a binder to make a slurry, coating and drying. The number average molecular weight of the hyperbranched polyamide binder is 15,000 to 150,000. The positive electrode sheet includes the hyperbranched polyamide binder of the present invention. The positive electrode sheet is applied to a lithium battery. The hyperbranched polyamide binder uses aliphatic raw materials for polycondensation, with low raw material costs, simple processes, easy production and good economic benefits; the electrode sheet has good flexibility, is not easy to crack in thick coating, has good slurry stability and is easy to process; the battery has high energy density and long cycle life, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to a hyperbranched polyamide binder, a preparation method and application of a positive electrode sheet, and belongs to the technical field of positive electrode sheets for lithium batteries. Background Art

[0002] At present, the new energy industry is developing rapidly. As the most important part of the industry, lithium-ion batteries (LIBs) have been commercialized in the field of new energy vehicles. However, based on the requirements for energy density, battery cost, cycle life and use safety, the optimization and modification of each component of lithium-ion batteries have been continuously carried out. The binder is an important guarantee for the mechanical properties of the electrode, which can tightly connect the active material, conductive agent, current collector, etc. into one body, maintain the stability of the electrode structure and the integrity of the electron channel, and directly affect the use safety and cycle stability of LIBs. Therefore, the design and optimization of the molecular structure of the binder are of great significance for improving the safety and service life of lithium batteries.

[0003] In order to adapt to the increasing application scenarios of current lithium-ion batteries, the exploration of binders is also continuously deepening. Polyvinylidene fluoride (PVDF) occupies a core position in the field of LIBs binders, and mainly binds the active material, conductive agent and current collector by the van der Waals force between molecules. PVDF has good electrochemical stability and electrolyte wettability. However, PVDF has many disadvantages: such as it is easy to degrade during the charge and discharge cycle process and high-temperature operation, resulting in an increase in internal resistance, a decrease in battery rate and cycle performance; gelation occurs during the pulping process, resulting in difficult coating; toxic fluorine-containing gases are generated during the high-temperature cutting process of the electrode sheet.

[0004] Both polyimide and polyamideimide contain aromatic groups and have strong rigidity, and there is a risk of cracking during coating, rolling and winding processes, reducing the use safety and capacity retention rate of the battery. When the coating layer thickness is increased, the cracking phenomenon is more significant, limiting the energy density of the battery. Therefore, finding a binder with good thermal stability and mechanical properties is one of the ways to solve the current problems of lithium-ion batteries.

[0005] The patent application with the publication number CN118496503A discloses a hyperbranched sulfonated polyimide, its preparation method and application, a positive electrode material, a positive electrode sheet and a lithium-ion battery. This patent proposes to first obtain a linear sulfonated polyamic acid by polycondensation reaction of a diamine containing a sulfonic acid group, a diamine containing a flexible structure and a dianhydride, then obtain a hyperbranched sulfonated polyamic acid by polycondensation reaction with a triamine, and finally obtain a hyperbranched sulfonated polyimide through imidization reaction. When used as a positive electrode binder, this hyperbranched sulfonated polyimide has high thermal stability and good liquid absorption capacity, which can improve the cycle stability of the battery. However, the raw material cost is high, the preparation process is complex, the flexibility of the binder is poor, it is easy to crack during use, it is impossible to thickly coat to improve the energy density, and there are certain safety hazards.

[0006] The patent application with the publication number CN118460169A discloses a positive electrode slurry, its preparation method, a positive electrode sheet and a lithium-ion battery, which are obtained by an ionization reaction of polyethyleneimine, ethylenediamine core dendrimeric polyamidoamine and succinic anhydride, 1,8-naphthalene sulfonic acid lactone, and propylene carbonate. The anions on the binder molecular chain have the function of transporting lithium ions, which can reduce the internal resistance of the electrode sheet, improve the charge and discharge rate, specific capacity and cycle performance. However, the molecular weight of the binder is low (<5000), the dosage is large, the adhesion of the electrode sheet is poor, it is easy to drop materials, and the practicability is poor, which cannot meet the use requirements of current high-energy density batteries.

[0007] In summary, the existing binders have poor adhesion and complex production processes; the positive electrode sheets have poor flexibility and are easy to crack when thickly coated; the batteries have problems such as low energy density, poor safety and low cycle life. Summary of the Invention

[0008] In view of the deficiencies of the existing technology, the present invention provides a preparation method and application of a hyperbranched polyamide binder and a positive electrode sheet. The hyperbranched polyamide binder is prepared by polycondensation of aliphatic raw materials, with low raw material cost, simple process, easy production, and good economic benefits; the electrode sheet has good flexibility, is not easy to crack when thickly coated, has good slurry stability, and is easy to process; the battery has high energy density and long cycle life, and has good application prospects.

[0009] The technical solution of the present invention to solve the above technical problems is as follows: A hyperbranched polyamide binder, which is prepared by polycondensation reaction of diamine monomers, polyamine monomers and diacid monomers;

[0010] The diamine monomer is any one or a combination of several of C4-C12 aliphatic diamines, and the diamine monomer is straight-chain or branched; the polyamine monomer is C4-C10 aliphatic polyamine, and the C4-C10 aliphatic polyamine is any one or a combination of several of diethylenetriamine, 3,3'-diaminodipropylamine, bis(hexamethylenetriamine), triethylenetetramine or tetraethylenepentamine; the diacid monomer is any one or a combination of several of C4-C20 aliphatic diacids, and the diacid monomer is straight-chain or branched.

[0011] Furthermore, the C4-C12 aliphatic diamine is any one or a combination of several of butanediamine, pentanediamine, hexanediamine, heptanediamine, octanediamine, nonanediamine, decanediamine, 1,11-diaminoundecane, 1,12-diaminododecane, trimethylhexamethylenediamine;

[0012] The C4-C20 aliphatic diacid is any one or a combination of several of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, eicosanedioic acid, 3-tert-butyladipic acid.

[0013] Furthermore, the number-average molecular weight of the hyperbranched polyamide binder is 15,000-150,000.

[0014] The present invention also discloses a preparation method of a hyperbranched polyamide binder, and the preparation method is as follows:

[0015] The diamine monomer, polyamine monomer and diacid monomer carry out polycondensation reaction in an organic solvent, react at 150-230 °C for 8-96 h, continuously introduce an inert gas to carry out the generated water of reaction, cool to room temperature, maintain the inert gas atmosphere, and obtain a hyperbranched polyamide binder solution with a certain solid content;

[0016] The mass fraction of the solid content during the polycondensation reaction is 30%-90%.

[0017] Furthermore, the total molar amount of the diamine monomer and polyamine monomer and the molar ratio of the diacid monomer is 1.0:(0.8-1.3); the molar ratio of the diamine monomer and the polyamine monomer is 1.0:(3.0-30.0);

[0018] The organic solvent is a polar high-boiling solvent, and the boiling point of the organic solvent is 150-250 °C.

[0019] Further, the organic solvent is selected from any one or a combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol.

[0020] The present invention also discloses a positive electrode sheet, which contains the hyperbranched polyamide binder of the present invention.

[0021] The present invention also discloses a method for preparing a positive electrode sheet. By weight, the positive electrode sheet includes 85-98 parts of a positive electrode material, 1-10 parts of a conductive agent, and 1-10 parts of a hyperbranched polyamide binder. The method for preparing the positive electrode sheet is as follows:

[0022] S1. Pulp making: Mix the positive electrode material, conductive agent, binder, and solvent to obtain a positive electrode slurry with a certain solid content and viscosity;

[0023] S2. Coating: Uniformly coat the obtained slurry on a current collector aluminum foil;

[0024] S3. Drying: Remove the solvent and roll to obtain a positive electrode sheet.

[0025] Further, the positive electrode material is one or a combination of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and ternary materials; the ternary materials are one or a combination of NCM523, NCM622, and NCM811;

[0026] The conductive agent is one or a combination of conductive carbon black, conductive polymer, carbon fiber, carbon nanotube, conductive graphite, and graphene;

[0027] The solvent in step S1 is any one or a combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol;

[0028] The mass fraction of the solid content of the slurry in step S1 is 50%-70%, and the viscosity is 3000 cP-40000 cP;

[0029] The drying conditions in step S3 are: the drying temperature is 80-160°C, and the drying time is 5-12 h; the thickness of the electrode sheet is 50-120 μm.

[0030] The present invention also discloses an application of a positive electrode sheet, and the positive electrode sheet is applied to a lithium battery.

[0031] The beneficial effects of the present invention are as follows:

[0032] (1) The raw materials used in the hyperbranched polyamide binder of the present invention do not contain fluorine, avoiding gelation caused by the generation of hydrogen fluoride during the pulping process, and no toxic fluorine-containing gas is generated during the electrode sheet cutting process; the use of aliphatic raw materials for polymerization results in a molecular structure without aromatic groups, having good flexibility; the carbonyl groups in the structure can form intermolecular hydrogen bonds, improving the adhesion between the current collector and the coating layer, enhancing the stability of the electrode sheet, reducing the shedding of active substances during the charge and discharge process of the electrode sheet, and improving the capacity retention rate, safety, and service life of the battery.

[0033] (2) By adjusting the reaction temperature and the material ratio, reasonably controlling the degree of hyperbranching, ensuring good solubility of the product, the electrode sheet has good flexibility, low cracking risk, and is not easy to crack even with thick coating, and the battery energy density can be increased by using thick coating. The binder has good stability, can maintain the structural and volume changes of the active material during the charge and discharge process, and during the continuous charge and discharge process of the battery, the binder is not easily degraded, the shedding of the coating layer is reduced, and the battery capacity retention rate is further improved.

[0034] (3) Using high-boiling solvents for polymerization and pulping, which can be polar solvents such as hexanol, ethylene glycol, propylene glycol, and butanediol, not limited to solvents such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. The solvent has low cost and low toxicity, the slurry has moderate viscosity, good dispersibility and stability, the suspension is not easy to settle, and it is easy to process and coat.

[0035] (4) In the preparation process of the hyperbranched polyamide binder, the process is simple, no catalyst is used, reducing the raw material cost, and at the same time eliminating the step of post-treatment to remove the catalyst, avoiding the influence of catalyst residues on the battery performance; the product does not require precipitation and purification, avoiding waste of solvents, not generating waste gas and waste solid, and reducing the production cost. It can be applied to the field of lithium battery materials, having good economic benefits and broad application prospects.

[0036] In summary, in the preparation method of the hyperbranched polyamide binder of the present invention, the raw material cost is low, the process is simple, it is easy to produce, has strong applicability, and has good economic benefits. When the hyperbranched polyamide binder is applied, the electrode sheet has good flexibility, high thermal stability, and is not easy to crack with thick coating; the battery has high energy density and long cycle life, and has good application prospects. Detailed implementation manners

[0037] The following is a detailed description of the specific embodiments of the present invention. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0039] A hyperbranched polyamide binder, wherein the hyperbranched polyamide binder is prepared by polycondensation reaction of diamine monomers, polyamine monomers and diacid monomers;

[0040] The diamine monomers are any one or a combination of several of C4-C12 aliphatic diamines, and the diamine monomers are straight-chain or branched-chain; the polyamine monomers are C4-C10 aliphatic polyamines, and the C4-C10 aliphatic polyamines are any one or a combination of several of diethylenetriamine, 3,3'-diaminodipropylamine, bis(hexamethyl)triamine, triethylenetetramine or tetraethylenepentamine; the diacid monomers are any one or a combination of several of C4-C20 aliphatic diacids, and the diacid monomers are straight-chain or branched-chain.

[0041] Specifically, the C4-C12 aliphatic diamines are any one or a combination of several of butanediamine, pentanediamine, hexanediamine, heptanediamine, octanediamine, nonanediamine, decanediamine, 1,11-diaminoundecane, 1,12-diaminododecane, trimethylhexamethylenediamine;

[0042] The C4-C20 aliphatic diacids are any one or a combination of several of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, eicosanedioic acid, 3-tert-butyladipic acid.

[0043] Specifically, the number-average molecular weight of the hyperbranched polyamide binder is 15,000-150,000.

[0044] A preparation method of a hyperbranched polyamide binder, the preparation method being:

[0045] The diamine monomers, polyamine monomers and diacid monomers are subjected to polycondensation reaction in an organic solvent, reacting at 150-230 °C for 8-96 h, continuously introducing an inert gas to carry out the water generated by the reaction, cooling to room temperature, and maintaining an inert gas atmosphere to obtain a hyperbranched polyamide binder solution with a certain solid content;

[0046] The mass fraction of the solid content during the polycondensation reaction is 30% - 90%.

[0047] Specifically, the molar ratio of the total moles of the diamine monomers and polyamine monomers to the diacid monomers is 1.0:(0.8 - 1.3); the molar ratio of the diamine monomers to the polyamine monomers is 1.0:(3.0 - 30.0);

[0048] The organic solvent is a polar high-boiling solvent, and the boiling point of the organic solvent is 150 - 250 °C.

[0049] Specifically, the organic solvent is selected from any one or a combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol.

[0050] A positive electrode sheet, wherein the hyperbranched polyamide binder of the present invention is in the positive electrode sheet.

[0051] Specifically, by weight, the positive electrode sheet comprises 85 - 98 parts of positive electrode material, 1 - 10 parts of conductive agent, and 1 - 10 parts of hyperbranched polyamide binder. The preparation method of the positive electrode sheet is as follows:

[0052] S1. Pulp making: Mix the positive electrode material, conductive agent, binder, and solvent to obtain a positive electrode slurry with a certain solid content and viscosity;

[0053] S2. Coating: Uniformly coat the obtained slurry on the current collector aluminum foil;

[0054] S3. Drying: Remove the solvent and roll press to obtain the positive electrode sheet.

[0055] Specifically, the positive electrode material is one or a combination of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and ternary materials; the ternary materials are one or a combination of NCM523, NCM622, and NCM811;

[0056] The conductive agent is one or a combination of conductive carbon black, conductive polymer, carbon fiber, carbon nanotube, conductive graphite, and graphene;

[0057] The solvent described in step S1 is any one or a combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol; the solvent can be the same as or different from the organic solvent used in the preparation of the hyperbranched polyamide binder, as long as they are mutually soluble.

[0058] The mass fraction of the solid content of the slurry in step S1 is: 50% - 70%, and the viscosity is 3000 cP - 40000 cP;

[0059] The drying conditions in step S3 are: the drying temperature is: 80 - 160 °C, and the drying time is 5 - 12 h; the thickness of the electrode sheet is 50 - 120 μm.

[0060] The positive electrode sheet is applied to a lithium battery.

[0061] Example 1

[0062] Preparation of hyperbranched polyamide binder:

[0063] At room temperature, 5.969 g of glutaric acid, 33.084 g of octadecanedioic acid, and 83.402 g of N-methylpyrrolidone were successively added to a three-necked flask, 2.592 g of decanediamine and 13.956 g of diethylenetriamine were added with stirring, the temperature was slowly raised, and an inert gas was continuously introduced to carry out the reaction-generated water. After reacting at 160 - 165 °C for 90 h, the viscosity and molecular weight of the hyperbranched polyamide were sampled and tested. After meeting the standards, the reaction was stopped, and the inert gas atmosphere was maintained and cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0064] Preparation of positive electrode sheet:

[0065] By weight, 92 parts of lithium iron phosphate, 4 parts of conductive carbon black, and 4 parts of hyperbranched polyamide binder were added to a closed container, and then N-methylpyrrolidone solvent was added to adjust the solid content of the slurry to 54%. After high-speed stirring and mixing evenly, it was sieved and then coated on aluminum foil. It was dried in vacuum at 100 °C for 12 h, and then roll-pressed to obtain a positive electrode sheet.

[0066] Example 2

[0067] Preparation of hyperbranched polyamide binder:

[0068] At room temperature, 11.738 g of adipic acid, 34.438 g of hexadecanedioic acid, and 18.905 g of N,N-dimethylacetamide were successively added to a three-necked flask. While stirring, 2.538 g of nonanediamine and 26.906 g of triethylenetetramine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 160 - 165 °C for 72 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. After reaching the standard, the reaction was stopped, and the inert gas atmosphere was maintained. It was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0069] Preparation of the positive electrode plate:

[0070] By weight, 95 parts of lithium cobalt oxide, 2.4 parts of conductive carbon black, 0.1 g of carbon nanotubes, and 2.5 parts of hyperbranched polyamide binder were added to a sealed container. Then, N,N-dimethylacetamide solvent was added to adjust the solid content of the slurry to 63%. After high-speed stirring and mixing evenly, it was sieved and then coated on aluminum foil. It was vacuum dried at 80 °C for 12 h and roll-pressed to obtain the positive electrode plate.

[0071] Example 3

[0072] Preparation of the hyperbranched polyamide binder:

[0073] At room temperature, 12.061 g of pimelic acid, 25.766 g of icosanedioic acid, and 59.731 g of dimethyl sulfoxide were successively added to a three-necked flask. While stirring, 2.602 g of octanediamine and 19.302 g of triethylenetetramine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 180 - 185 °C for 46 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. After reaching the standard, the reaction was stopped, and the inert gas atmosphere was maintained. It was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0074] Preparation of the positive electrode plate:

[0075] By weight, 97 parts of lithium nickel oxide, 1.5 parts of conductive carbon black, and 1.5 parts of hyperbranched polyamide binder were added to a sealed container. Then, N-methylpyrrolidone solvent was added to adjust the solid content of the slurry to 69%. After high-speed stirring and mixing evenly, it was sieved and then coated on aluminum foil. It was vacuum dried at 150 °C for 8 h and roll-pressed to obtain the positive electrode plate.

[0076] Example 4

[0077] Preparation of the hyperbranched polyamide binder:

[0078] At room temperature, 17.507 g of suberic acid, 21.714 g of undecanedioic acid, and 40.449 g of ethylene glycol were successively added to a three-necked flask. While stirring, 3.915 g of heptanediamine and 17.539 g of diethylenetriamine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 185 - 190 °C for 36 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. After reaching the standard, the reaction was stopped, and the inert gas atmosphere was maintained. It was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0079] Preparation of the positive electrode plate:

[0080] By weight, 89 parts of lithium manganese oxide, 5 parts of Ketjenblack, and 6 parts of hyperbranched polyamide binder were added to a sealed container, and then ethylene glycol solvent was added. The solid content of the slurry was adjusted to 67%, and it was stirred at high speed and mixed evenly. After sieving, it was coated on aluminum foil. It was vacuum dried at 150 °C for 10 h and roll-pressed to obtain the positive electrode plate.

[0081] Example 5

[0082] Preparation of the hyperbranched polyamide binder:

[0083] At room temperature, 13.606 g of azelaic acid, 13.100 g of pentadecanedioic acid, and 101.578 g of butanediol were successively added to a three-necked flask. While stirring, 2.789 g of hexanediamine and 14.038 g of triethylenetetramine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 220 - 225 °C for 10 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. After reaching the standard, the reaction was stopped, and the inert gas atmosphere was maintained. It was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0084] Preparation of the positive electrode plate:

[0085] By weight, 90 parts of NCM811, 4.5 parts of acetylene black, and 5.5 parts of hyperbranched polyamide binder were added to a sealed container, and then butanediol solvent was added. The solid content of the slurry was adjusted to 63%, and it was stirred at high speed and mixed evenly. After sieving, it was coated on aluminum foil. It was vacuum dried at 160 °C for 8 h and roll-pressed to obtain the positive electrode plate.

[0086] Example 6

[0087] Preparation of the hyperbranched polyamide binder:

[0088] At room temperature, 28.457 g of sebacic acid, 14.719 g of tridecanedioic acid, and 33.016 g of N-methylpyrrolidone were successively added to a three-necked flask. While stirring, 4.710 g of pentamethylenediamine and 29.152 g of tetraethylenepentamine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 195 - 200 °C for 16 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. After reaching the standard, the reaction was stopped, and the inert gas atmosphere was maintained. It was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0089] Preparation of the positive electrode sheet:

[0090] By weight, 91 parts of lithium nickel manganese oxide, 4 parts of conductive carbon black, 0.5 part of Ketjenblack, and 4.5 parts of hyperbranched polyamide binder were added to a sealed container. Then, N-methylpyrrolidone solvent was added to adjust the solid content of the slurry to 62%. After high-speed stirring and mixing evenly, it was sieved and then coated on aluminum foil. It was vacuum dried at 120 °C for 12 h and roll-pressed to obtain the positive electrode sheet.

[0091] Example 7

[0092] Preparation of the hyperbranched polyamide binder:

[0093] At room temperature, 57.915 g of dodecanedioic acid and 56.531 g of diethylene glycol monomethyl ether were successively added to a three-necked flask. While stirring, 2.329 g of 1,11-diaminoundecane and 24.552 g of diethylenetriamine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 175 - 180 °C for 60 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. After reaching the standard, the reaction was stopped, and the inert gas atmosphere was maintained. It was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0094] Preparation of the positive electrode sheet:

[0095] By weight, 94 parts of lithium nickel manganese oxide, 2.5 parts of conductive carbon black, 0.5 part of graphene, and 3 parts of hyperbranched polyamide binder were added to a sealed container. Then, diethylene glycol monomethyl ether solvent was added to adjust the solid content of the slurry to 58%. After high-speed stirring and mixing evenly, it was sieved and then coated on aluminum foil. It was vacuum dried at 150 °C for 6 h and roll-pressed to obtain the positive electrode sheet.

[0096] Example 8

[0097] Preparation of the hyperbranched polyamide binder:

[0098] At room temperature, 51.930 g of tetradecanedioic acid and 74.920 g of diethylene glycol monoethyl ether were successively added to a three-necked flask. While stirring, 4.833 g of 1,12-diaminododecane and 18.158 g of diethylenetriamine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated in the reaction. After reacting at 185 - 190 °C for 48 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. After reaching the standard, the reaction was stopped, and the inert gas atmosphere was maintained. It was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0099] Preparation of the positive electrode plate:

[0100] By weight, 86.5 parts of lithium nickel manganese oxide, 6.8 parts of conductive carbon black, 0.2 part of graphite, and 6.5 parts of hyperbranched polyamide binder were added to a closed container. Then, diethylene glycol monoethyl ether solvent was added, and the solid content of the slurry was adjusted to 51%. After high-speed stirring and mixing evenly, it was sieved and coated on aluminum foil. It was vacuum dried at 140 °C for 10 h and roll-pressed to obtain the positive electrode plate.

[0101] Comparative Example 1

[0102] The hyperbranched polyamide binder was prepared by the same method as in Example 1, except that in this Comparative Example 1, the feed ratio of the diacid monomer was increased. The specific preparation process was as follows:

[0103] At room temperature, 8.953 g of glutaric acid, 49.627 g of octadecanedioic acid, and 112.692 g of N-methylpyrrolidone were successively added to a three-necked flask. While stirring, 2.592 g of decanediamine and 13.956 g of diethylenetriamine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated in the reaction. After reacting at 160 - 165 °C for 90 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. The inert gas atmosphere was maintained, and it was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0104] Preparation of the positive electrode plate:

[0105] By weight, 92 parts of lithium iron phosphate, 4 parts of conductive carbon black, and 4 parts of hyperbranched polyamide binder were added to a closed container. Then, N-methylpyrrolidone solvent was added, and the solid content of the slurry was adjusted to 54%. After high-speed stirring and mixing evenly, it was sieved and coated on aluminum foil. It was vacuum dried at 100 °C for 12 h and roll-pressed to obtain the positive electrode plate.

[0106] Comparative Example 2

[0107] The hyperbranched polyamide binder was prepared by the same method as in Example 1, except that in this Comparative Example 2, the amount of organic solvent was increased, and the solid content of the polycondensation reaction was changed from 40% to 20%. The specific preparation process was as follows:

[0108] At room temperature, 5.969 g of glutaric acid, 33.084 g of octadecanedioic acid, and 222.406 g of N-methylpyrrolidone were successively added to a three-necked flask. While stirring, 2.592 g of sebac diamine and 13.956 g of diethylenetriamine were added. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 160 - 165 °C for 90 h, samples were taken to detect the viscosity and molecular weight of the hyperbranched polyamide. Maintaining the inert gas atmosphere, it was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0109] Preparation of the positive electrode plate:

[0110] By weight, 92 parts of lithium iron phosphate, 4 parts of conductive carbon black, and 4 parts of hyperbranched polyamide binder were added to a closed container, and then N-methylpyrrolidone solvent was added. The solid content of the slurry was adjusted to 54%, and it was stirred at high speed and mixed evenly. After passing through a sieve, it was coated on aluminum foil. It was dried in vacuum at 100 °C for 12 h, and the positive electrode plate was obtained by rolling.

[0111] Comparative Example 3

[0112] The hyperbranched polyamide binder was prepared by the same method as in Example 1, except that: in the polycondensation reaction process of this Comparative Example 3, no solvent was added, that is, the solid content was changed from 40% to 100%. The specific preparation process was as follows:

[0113] At room temperature, 5.969 g of glutaric acid, 33.084 g of octadecanedioic acid, 2.592 g of sebac diamine, and 13.956 g of diethylenetriamine were successively added to a three-necked flask. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 160 - 165 °C for 90 h, a hyperbranched polyamide semi-solid was obtained. The reaction solution was clear, and it was in a semi-solid state after cooling. N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol could not dissolve it.

[0114] Comparative Example 4

[0115] The hyperbranched polyamide binder was prepared by the same method as in Example 5, except that: in the preparation process of this Comparative Example 4, the polycondensation reaction temperature was lowered. The specific preparation process was as follows:

[0116] At room temperature, 13.606 g of azelaic acid, 13.100 g of pentadecanedioic acid, and 101.578 g of butanediol were successively added to a three-necked flask. 2.789 g of hexamethylenediamine and 14.038 g of triethylenetetramine were added with stirring. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 125 - 130 °C for 10 h, the viscosity and molecular weight of the hyperbranched polyamide were sampled and measured. While maintaining the inert gas atmosphere, it was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0117] Preparation of the positive electrode plate:

[0118] By weight, 90 parts of NCM811, 4.5 parts of acetylene black, and 5.5 parts of the hyperbranched polyamide binder were added to a closed container, and then butanediol solvent was added. The solid content of the slurry was adjusted to 63%, and it was stirred at high speed and mixed evenly. After sieving, it was coated on aluminum foil. It was vacuum dried at 160 °C for 8 h, and the positive electrode plate was obtained by rolling.

[0119] Comparative Example 5

[0120] The hyperbranched polyamide binder was prepared by the same method as in Example 5, except that: during the preparation of the hyperbranched polyamide binder in this Comparative Example 5, the polymerization reaction temperature was increased. The specific preparation process was as follows:

[0121] At room temperature, 13.606 g of azelaic acid, 13.100 g of pentadecanedioic acid, and 101.578 g of butanediol were successively added to a three-necked flask. 2.789 g of hexamethylenediamine and 14.038 g of triethylenetetramine were added with stirring. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 240 - 245 °C for 4 h, it gelled and agglomerated into a jelly-like state, and it was in a semi-solid state after cooling. It could not be dissolved in N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butanediol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol.

[0122] Comparative Example 6

[0123] The hyperbranched polyamide binder was prepared by the same method as in Example 5, except that: during the preparation of the hyperbranched polyamide binder in this Comparative Example 6, the feed ratio of the diamine monomer was increased. The specific preparation process was as follows:

[0124] At room temperature, 13.606 g of azelaic acid, 13.100 g of pentadecanedioic acid, and 100.738 g of butanediol were successively added to a three-necked flask. 4.183 g of hexamethylenediamine and 12.283 g of triethylenetetramine were added with stirring. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 220 - 225 °C for 10 h, the reaction solution became clear. After cooling, it was in a turbid semi-solid state, and N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butanediol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol could not dissolve it.

[0125] Comparative Example 7

[0126] The hyperbranched polyamide binder was prepared by the same method as in Example 5, except that: in the preparation process of the hyperbranched polyamide binder of this Comparative Example 7, diamine monomers were not added, and only polyamine monomers were added. The specific preparation process was as follows:

[0127] At room temperature, 13.606 g of azelaic acid, 13.100 g of pentadecanedioic acid, and 103.26 g of butanediol were successively added to a three-necked flask. 17.548 g of triethylenetetramine was added with stirring. The temperature was slowly raised, and an inert gas was continuously introduced to carry out the water generated by the reaction. After reacting at 220 - 225 °C for 10 h, the viscosity and molecular weight of the hyperbranched polyamide were sampled and detected. Maintaining an inert gas atmosphere, it was cooled to room temperature to obtain a hyperbranched polyamide binder solution with a certain solid content.

[0128] Preparation of the positive electrode sheet:

[0129] The positive electrode sheet was prepared by the same method as in Example 5.

[0130] Comparative Example 8

[0131] The hyperbranched polyamide binder prepared in Example 7 was used, except that: in this Comparative Example 8, the solid content in the pulping process was reduced. The specific electrode sheet preparation process was as follows:

[0132] Preparation of the positive electrode sheet:

[0133] By weight, 94 parts of lithium nickel manganese oxide, 2.5 parts of conductive carbon black, 0.5 part of graphene, and 3 parts of hyperbranched polyamide binder were added to a closed container, and then diethylene glycol monomethyl ether solvent was added to adjust the solid content of the slurry to 47%. After high-speed stirring and mixing evenly, it was sieved and then coated on aluminum foil. It was vacuum-dried at 150 °C for 6 h and roll-pressed to obtain the positive electrode sheet.

[0134] Comparative Example 9

[0135] Using the purchased Solvay PVDF 5130 as the binder, prepare the positive electrode sheet according to the steps and methods of Example 1 and test its performance.

[0136] Performance test:

[0137] I. Method for measuring the performance of the hyperbranched polyamide binder obtained in the above examples and comparative examples:

[0138] (1) Use gel permeation chromatography (GPC) to test the number average molecular weight Mw;

[0139] (2) Use a cone plate viscometer to test the viscosity of the binder with a solid content of 10%.

[0140] II. Method for testing the performance of the positive electrode sheet:

[0141] (1) Thickness test: Use a Mitutoyo digital thickness gauge made in Japan to test. Subtract the thickness of the uncoated current collector from the total thickness of the positive electrode sheet, and record it as the coating layer thickness.

[0142] (2) Flexibility test: Take the rolled electrode sheet, wind the electrode sheet around a stainless steel winding needle, align the part around the winding needle with force, align the microscope with the bending part, magnify it 100 times, and observe whether there are cracks. The diameter of the winding needle when cracks first appear is recorded as the flexibility of the electrode sheet.

[0143] (3) Peel strength test: Cut the obtained electrode sheet into a 10 cm × 2 cm spline, fix it on a 1 mm thick steel plate with double-sided tape on the current collector side, paste a transparent tape on the coating layer, and conduct a 180° directional pulling and peeling experiment with a peeling speed of 10 cm / min using a universal material testing machine.

[0144] III. Battery performance test:

[0145] Assemble a coin cell in a glove box, and then test the initial efficiency at a current density of 0.1C and the 1C cycle life.

[0146] Initial efficiency at 0.1C / % = Discharge specific capacity in the first cycle at 0.1C (mAh / g) ÷ Charge specific capacity in the first cycle at 0.1C (mAh / g) × 100%.

[0147] Cycle life: The number of cycles required for the capacity to drop to 80% of the initial capacity. The specific test results are shown in Table 1 below.

[0148] Table 1 Performance test results

[0149]

[0150] In Comparative Example 1, the feed ratio of the diacid monomer in the polycondensation reaction was high. Compared with Example 1, it was found that the molecular weight and viscosity of the binder in Comparative Example 1 were slightly higher. When the thickness of the electrode sheet was comparable, the flexibility was poor, the peel strength was 46 N / m lower, the initial efficiency of the battery changed little, and the cycle life decreased significantly. This shows that the feed ratio has a great influence on both the electrode sheet and battery performance. An appropriate feed ratio can adjust the structural stability of the hyperbranched polyamide, improve the flexibility of the electrode sheet, prevent the coating layer from cracking and peeling off, and ensure the chemical stability and safety of the battery during cycling.

[0151] In Comparative Example 2, the solid content in the polycondensation reaction was low. The molecular weight and viscosity of the hyperbranched polyamide binder were significantly lower than those in Example 1. There were also large differences in the flexibility and peel strength of the electrode sheet compared with Example 1. The cycle life of the battery was less than 50% of that in Example 1. This shows that the solid content has a great influence on the degree of polymerization of the binder. If the solid content is too low, below the required range of the present invention, it will lead to insufficient degree of polymerization, poor adhesion of the binder, and poor flexibility of the electrode sheet, thereby reducing the cycle life of the battery.

[0152] In Comparative Example 3, no solvent was added in the polycondensation reaction. The obtained hyperbranched polyamide binder was a semi-solid and insoluble in conventional solvents, and could not be used as a binder in liquid batteries. Without adding solvent for polymerization, the initial reaction was too violent, with obvious heat release, posing a safety hazard.

[0153] In Comparative Example 4, the polycondensation reaction temperature was low. The molecular weight and viscosity of the obtained hyperbranched polyamide binder were much lower than those in Example 5. There were also large differences in the flexibility and peel strength of the corresponding electrode sheet compared with Example 5. The cycle life of the battery was 64 times less than that in Example 5. This shows that when the polymerization reaction temperature is too low, the degree of polymerization of the binder is low, resulting in poor adhesion and flexibility of the electrode sheet, increasing the risk of cracking and shedding of the active material, thereby reducing the cycle life of the battery and affecting the use safety.

[0154] In Comparative Example 5, the polycondensation reaction temperature was high. The obtained hyperbranched polyamide binder was a gel-like semi-solid and insoluble in conventional solvents, and could not be used as a binder in liquid batteries. Increasing the reaction temperature can accelerate the reaction rate, but the degree of branching also increases accordingly. If the degree of branching is too high, it is easy to cause gel aggregation. This shows that the reaction temperature has a great influence on hyperbranched polyamide. Beyond the reaction temperature required by the present invention, a polyamide product with good adhesion cannot be obtained.

[0155] In Comparative Example 6, the feed ratio of the diamine monomer in the polycondensation reaction was high. The obtained hyperbranched polyamide was a turbid semi-solid and insoluble in conventional solvents, and could not be used as a binder in liquid batteries. When the feed ratio of the diamine monomer is too high, the degree of branching of the binder is low, resulting in poor solubility of the polyamide and being not conducive to exerting its binding effect.

[0156] In Comparative Example 7, the feed ratio of the polyamine monomer in the polycondensation reaction is high. Comparing with Example 5, it can be seen that the molecular weight and viscosity of the hyperbranched polyamide change little, the stripping strength of the electrode and the initial efficiency of the battery also have little difference, but the flexibility and cycle life are worse than those of Example 5. This shows that the feed ratio of the diamine monomer and the polyamine monomer will affect the flexibility of the electrode. Polymerization with an appropriate feed ratio can reduce the risks of cracking and shedding of the active material, and improve the cycle life and service safety of the battery.

[0157] Comparative Example 8 uses the hyperbranched polyamide binder prepared in Example 7. By reducing the solid content in the pulping process, the viscosity of the slurry is low. When the electrode thickness is similar, the stripping strength is 30 N / m lower than that of Example 7, the flexibility is worse than that of Example 7, and the battery cycle life is 121 times less than that of Example 7. It is extremely easy to crack during thick coating. This shows that the solid content in the pulping process has a great influence on the performance of the electrode and the battery. Too thin slurry will increase the risks of electrode cracking and shedding, and affect the cycle life and service safety of the battery.

[0158] Comparative Example 9 uses commercial PVDF as the binder. Both the flexibility and stripping strength of the electrode are worse than those of Example 1. Although their initial efficiencies are similar, the cycle life of Example 1 is 154 times more than that of PVDF. This shows that the hyperbranched polyamide binder prepared by the present invention has good adhesiveness, the electrode has good flexibility and high stripping strength, the battery has good cycle performance and high safety, and has good application prospects.

[0159] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, all possible combinations of the various technical features in the above embodiments are not exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0160] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for preparing a hyperbranched polyamide binder, characterized in that: The hyperbranched polyamide binder is prepared by polycondensation reaction of diamine monomers, polyamine monomers and diacid monomers; The diamine monomer is any one or a combination of C4-C12 aliphatic diamines, and the diamine monomer is linear or branched; the polyamine monomer is C4-C10 aliphatic polyamine, and the C4-C10 aliphatic polyamine is any one or a combination of diethylenetriamine, 3,3'-diaminodipropylamine, hexamethyltriamine, triethylenetetramine or tetraethylenepentamine; the diacid monomer is any one or a combination of C4-C20 aliphatic diacids, and the diacid monomer is linear or branched; The preparation method is: The diamine monomer, the polyamine monomer and the diacid monomer are subjected to a condensation polymerization reaction in an organic solvent at 150-230° C. for 8-96 hours, an inert gas is continuously introduced to remove the reaction water, and the solution is cooled to room temperature while maintaining an inert gas atmosphere to obtain a hyperbranched polyamide binder solution with a certain solid content; The mass fraction of solid content in the polycondensation reaction process is 30% to 90%; The molar ratio of the total molar number of the diamine monomer and the polyamine monomer to the diacid monomer is 1.0:(0.8-1.3); the molar ratio of the diamine monomer to the polyamine monomer is 1.0:(3.0-30.0).

2. A method for preparing a hyperbranched polyamide binder according to claim 1, characterized in that: The C4-C12 aliphatic diamine is any one or a combination of butanediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octanediamine, nonamethylenediamine, decanediamine, 1,11-diaminoundecane, 1,12-diaminododecane, and trimethylhexamethylenediamine; The C4-C20 aliphatic diacid is one or a combination of glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid, hexadecanedioic acid, heptadecanedioic acid, octadecanedioic acid, eicosanedioic acid, and 3-tert-butyl adipic acid.

3. A method for preparing a hyperbranched polyamide binder according to any one of claims 1 to 2, characterized in that: The number average molecular weight of the hyperbranched polyamide binder is 15,000 to 150,000.

4. A method for preparing a hyperbranched polyamide binder according to claim 1, characterized in that: The organic solvent is a polar high boiling point solvent, and the boiling point of the organic solvent is 150-250°C.

5. A method for preparing a hyperbranched polyamide binder according to claim 1, characterized in that: The organic solvent is selected from any one or a combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol.

6. A method for preparing a positive electrode sheet, characterized in that: The positive electrode sheet comprises the hyperbranched polyamide binder prepared by the preparation method according to any one of claims 1 to 5; According to the weight percentage, the positive electrode sheet includes 85-98 parts of positive electrode material, 1-10 parts of conductive agent, and 1-10 parts of hyperbranched polyamide binder. The preparation method of the positive electrode sheet is: S1. Slurry preparation: mixing the positive electrode material, the conductive agent, the binder and the solvent to obtain a positive electrode slurry with a certain solid content and viscosity; the mass fraction of the solid content of the slurry is: 50%~70%, and the viscosity is 3000 cP~40000 cP; S2, coating: coating the obtained slurry evenly on the current collector aluminum foil; S3. Drying: removing the solvent and rolling to obtain the positive electrode sheet.

7. A method for preparing a positive electrode sheet according to claim 6, characterized in that: The positive electrode material is one or a combination of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and ternary materials; the ternary material is one or a combination of NCM523, NCM622, and NCM811; The conductive agent is one or a combination of conductive carbon black, conductive polymer, carbon fiber, carbon nanotube, conductive graphite, and graphene; The solvent in step S1 is any one or a combination of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether, hexanol, heptanol, octanol, nonanol, and decanol; The drying conditions in step S3 are: drying temperature: 80-160° C., drying time: 5-12 hours; the electrode thickness is 50-120 μm.

8. An application of a positive electrode sheet prepared by the preparation method according to claim 6 or 7, characterized in that: The positive electrode plate is used in a lithium battery.

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