Polytetrafluoroethylene composite binder and dry electrode prepared from same

Abstract

The invention discloses a polytetrafluoroethylene composite binder and a dry electrode prepared from the same, and relates to the technical field of binders. The preparation method of the polytetrafluoroethylene composite binder comprises the following steps: step 1, carrying out esterification reaction on polydopamine coated polytetrafluoroethylene micro powder and carboxyl-polyethylene glycol-silane to obtain modified polytetrafluoroethylene; step 2, carrying out amidation reaction on the acidified carbon nano tube and dopamine to obtain a modified carbon nano tube; step 3, (1) adding the modified polytetrafluoroethylene, the modified carbon nanotubes and sodium carboxymethyl cellulose into the polytetrafluoroethylene emulsion, and uniformly stirring and mixing to obtain a polytetrafluoroethylene composite solution; and (2) adding a demulsifier into the polytetrafluoroethylene composite solution, and carrying out stirring demulsification, condensation, separation and purification to obtain the polytetrafluoroethylene composite binder.

Description

Technical Field

[0001] The invention relates to the technical field of binders, in particular to a polytetrafluoroethylene composite binder and a dry-process electrode prepared therefrom. Background Art

[0002] With the widespread application of lithium-ion batteries in new energy vehicles, energy storage systems, and other fields, the limitations of traditional wet-process electrode preparation have become increasingly prominent. The wet process relies on organic solvents such as N-methylpyrrolidone, which not only poses safety risks such as high toxicity and flammability, but also consumes more than 51% of the total energy consumption of battery production, resulting in high production costs. Furthermore, the wet process is difficult to produce thicker electrodes, which undoubtedly limits further improvements in battery energy density.

[0003] Therefore, dry electrode technology has become a research hotspot due to its advantages such as no need for solvents and simplified process. Among them, polytetrafluoroethylene has become the mainstream binder for dry electrodes due to its excellent chemical stability and fiberization ability. Polytetrafluoroethylene can form a three-dimensional fiber network under the action of shear force, thereby anchoring the active material and conductive agent, and preparing a self-supporting electrode membrane. However, existing polytetrafluoroethylene-based dry electrodes still face the following key problems: (1) insufficient ion conductivity; (2) difficulty in balancing bonding and mechanical properties; (3) poor wettability in electrolyte; and (4) unstable binder performance.

[0004] Based on this, in order to solve the above problems, the present invention prepares a polytetrafluoroethylene composite binder, and uses it to prepare a dry-process electrode with excellent performance. Summary of the Invention

[0005] The object of the present invention is to provide a polytetrafluoroethylene composite binder and a dry electrode prepared therefrom, so as to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides the following technical solutions:

[0007] A polytetrafluoroethylene composite adhesive, and a preparation method thereof, comprising the following steps:

[0008] Step 1: (1) dopamine self-polymerizes and coats polytetrafluoroethylene micropowder to obtain polydopamine-coated polytetrafluoroethylene micropowder;

[0009] (2) carboxyl-polyethylene glycol-thiol undergoes a click reaction with vinyltrimethoxysilane to obtain carboxyl-polyethylene glycol-silane;

[0010] (3) Polydopamine-coated polytetrafluoroethylene micropowder undergoes esterification reaction with carboxyl-polyethylene glycol-silane to obtain modified polytetrafluoroethylene;

[0011] Step 2: (1) acidifying the carbon nanotubes to obtain acidified carbon nanotubes;

[0012] (2) Acidified carbon nanotubes undergo amidation reaction with dopamine to obtain modified carbon nanotubes;

[0013] Step 3: (1) adding modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose to a polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution;

[0014] (2) Adding a demulsifier to the polytetrafluoroethylene composite solution, stirring to demulsify, coagulating, separating and purifying, thereby obtaining a polytetrafluoroethylene composite binder.

[0015] Furthermore, the preparation method of the modified polytetrafluoroethylene is as follows: (1) adding polytetrafluoroethylene powder into a reaction vessel containing dopamine-Tris buffer solution, stirring at 15-25° C. and a stirring speed of 60-120 r / min for 3-12 hours, and obtaining polydopamine-coated polytetrafluoroethylene powder through separation and purification; (2) adding carboxyl-polyethylene glycol-thiol, vinyl trimethoxysilane, and a photoinitiator into the reaction vessel, stirring and mixing; The mixture was uniformly mixed, irradiated with ultraviolet light for 15 to 45 minutes, and separated and purified to obtain carboxyl-polyethylene glycol-silane; (3) polydopamine-coated polytetrafluoroethylene powder was added to N,N-dimethylformamide, ultrasonically dispersed for 5 to 15 minutes, and then carboxyl-polyethylene glycol-silane, 1-ethyl-(3-dimethylaminopropyl) carbodiimide, and 4-pyrrolidinopyridine were added thereto, stirred for reaction for 24 to 48 hours, and separated and purified to obtain modified polytetrafluoroethylene.

[0016] Furthermore, the dopamine-Tris buffer solution comprises the following components: 0.1-5 g / L dopamine, 1-10 mM tris(hydroxyaminomethane) hydrochloride, deionized water as the solvent, and a pH of 8-8.5.

[0017] Furthermore, the ratio of the polytetrafluoroethylene powder to the dopamine-Tris buffer solution is (5-20) g:1 L.

[0018] Furthermore, the mass ratio of the carboxyl-polyethylene glycol-mercapto group, vinyltrimethoxysilane and photoinitiator is 10:(1.5-2):(0.25-0.5).

[0019] Furthermore, the raw materials required for preparing the modified polytetrafluoroethylene include the following components: 10 parts by mass of polydopamine-coated polytetrafluoroethylene micropowder, 2 to 4 parts of carboxyl-polyethylene glycol-silane, 1 to 2 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 1 to 2 parts of 4-pyrrolidinopyridine, and 25 parts of N,N-dimethylformamide.

[0020] Furthermore, the preparation method of the modified carbon nanotubes is as follows: (1) adding carbon nanotubes into a reaction vessel filled with an acid solution, stirring and heating to 50-80° C., soaking and acidifying for 1-6 hours, and obtaining acidified carbon nanotubes through separation and purification; (2) adding acidified carbon nanotubes, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 4-pyrrolidinopyridine into a reaction vessel filled with deionized water, stirring and mixing uniformly, then adjusting the temperature of the reaction system to 5-20° C., adding dopamine, stirring and reacting for 12-48 hours, and obtaining modified carbon nanotubes through separation and purification.

[0021] Furthermore, the ratio of the carbon nanotubes to the acid solution is (1-5) g:100 mL.

[0022] Furthermore, the carbon nanotubes include but are not limited to multi-walled carbon nanotubes or single-walled carbon nanotubes, or a combination of the two.

[0023] Furthermore, the acid solution is obtained by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, wherein the concentration of the concentrated sulfuric acid is ≥96wt%, and the concentration of the concentrated nitric acid is ≥68wt%.

[0024] Preferably, in an embodiment of the present invention, the carbon nanotubes are composed of a mixture of multi-walled carbon nanotubes and single-walled carbon nanotubes in a mass ratio of 1:(1-2).

[0025] Furthermore, the raw materials required for preparing the modified carbon nanotubes include the following components: 10 parts by mass of acidified carbon nanotubes, 2 to 4 parts of dopamine, 1 to 2 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 1 to 2 parts of 4-pyrrolidinopyridine, and 25 parts of deionized water.

[0026] Furthermore, the raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: by mass percentage, 60-78% polytetrafluoroethylene emulsion, 10.4-19.8% modified polytetrafluoroethylene, 5.4-9.8% modified carbon nanotubes, 5.4-9.8% sodium carboxymethyl cellulose, and 0.6-0.8% demulsifier.

[0027] In order to enhance the related properties of polytetrafluoroethylene binder, the present invention is designed to make dopamine undergo self-polymerization reaction on the surface of polytetrafluoroethylene micropowder, and then coat a layer of polydopamine on the surface of polytetrafluoroethylene to obtain polydopamine-coated polytetrafluoroethylene micropowder; then the polydopamine-coated polytetrafluoroethylene micropowder is esterified and grafted with carboxyl-polyethylene glycol-silane to prepare modified polytetrafluoroethylene.

[0028] The incorporation of carbon nanotubes into polytetrafluoroethylene can effectively enhance its electrical conductivity, mechanical properties, wettability and other related properties. In order to further enhance the related properties of the polytetrafluoroethylene composite binder, the carbon nanotubes are further acidified and then grafted with dopamine through amidation to obtain modified carbon nanotubes.

[0029] The second aspect of the present invention provides the following technical solutions:

[0030] A dry-process electrode prepared from a polytetrafluoroethylene composite binder, wherein the preparation method comprises the following steps: (1) adding an electrode active material, a conductive agent, and a polytetrafluoroethylene composite binder into a mixer in a certain proportion, and stirring and mixing the mixture at a stirring speed of 1000 to 1200 r / min for 1 to 5 hours to obtain a mixture A; (2) adding the mixture A into a roller press, and rolling the mixture at 100 to 180° C. to obtain an electrode film with a thickness of 100 to 200 μm; and (3) covering the electrode film on both sides of a copper foil or an aluminum foil, and hot-pressing the composite film at 100 to 180° C. on a roller press to obtain a dry-process electrode.

[0031] Furthermore, the mass ratio of the electrode active material, the conductive agent, and the polytetrafluoroethylene composite binder is (82-90):(5-10):(3-10).

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The modified polytetrafluoroethylene prepared by the present invention has a polydopamine layer structure, polyethylene glycol chain ends, and a silane structure, and exhibits good dispersibility in polytetrafluoroethylene emulsions. Because the polydopamine layer structure and polyethylene glycol chain ends provide abundant phenolic hydroxyl groups, they improve the interfacial bonding strength between the polytetrafluoroethylene composite binder and the electrode active material and conductive agent, enhancing the binder's stability while significantly reducing the volume expansion caused by the electrode during cycling, thereby helping to improve the electrode's cycling stability. Furthermore, the polydopamine structure can form a synergistic conductive network with the conductive agent, which can, to a certain extent, improve the insufficient ion conductivity of traditional dry-process electrodes. The polyethylene glycol chain ends can also improve the processing performance of the polytetrafluoroethylene composite binder, simplifying the dry-process electrode preparation process.

[0034] 2. In the present invention, considering that the use of only single-walled carbon nanotubes will result in poor dispersion of the carbon nanotubes, easy agglomeration and high cost, the carbon nanotubes are introduced into the polytetrafluoroethylene composite binder by combining multi-walled carbon nanotubes and single-walled carbon nanotubes, and dopamine is grafted on the surface of the carbon nanotubes to obtain modified carbon nanotubes with good dispersion performance.

[0035] 3. In addition, since the modified polytetrafluoroethylene also contains a silane structure, it can further disperse the modified carbon nanotubes in the polytetrafluoroethylene composite solution.

[0036] 4. The present invention adds an appropriate amount of sodium carboxymethyl cellulose, which can synergistically modify polytetrafluoroethylene and modified carbon nanotubes, comprehensively make up for the defects of the existing technology, and finally obtain a polytetrafluoroethylene composite adhesive with excellent ion conductivity, excellent bonding performance, excellent mechanical properties, excellent wettability and stable performance. DETAILED DESCRIPTION

[0037] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0038] It should be noted that the following parts are calculated by weight, and the purchasers of all raw materials involved in the present invention include, without any special restrictions, the following examples:

[0039] In the following examples, polytetrafluoroethylene powder, purity of 98%, CAS number: 9002-84-0, particle size of 10-15 μm, dopamine, purity of 98%, vinyltrimethoxysilane, purity of 98%, N,N-dimethylformamide, purity of 98%, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, purity of 98%, and 4-pyrrolidinopyridine, purity of 98%, were all purchased from JACS-Zhengzhou Jacks Chemical Products Co., Ltd.

[0040] Trishydroxyaminomethane hydrochloric acid, purity 99%, photoinitiator, model: IHT-PIMBF, sodium carboxymethyl cellulose, purity 99.5%, ammonium carbonate, purity 99%, lithium iron phosphate, purity 99%, product number: GA0963, conductive carbon black, purity 99.5%, all purchased from Hubei Guangao Biotechnology Co., Ltd.

[0041] Carboxyl-polyethylene glycol-thiol, purity 95%, molecular weight 2000, purchased from Chongqing Yusi Pharmaceutical Technology Co., Ltd.

[0042] Multi-walled carbon nanotubes, 99% purity, 50 nm diameter, 10 μm length, catalog number 100288, purchased from Xianfeng Nano Co., Ltd.

[0043] Single-walled carbon nanotubes, purity 99.99%, product number: AM-C6-067-1, tube diameter 5 nm, purchased from Yamei Nano Technology Co., Ltd.

[0044] Polytetrafluoroethylene emulsion, with a concentration of 60%, was purchased from Wuhan Rongcan Biotechnology Co., Ltd.

[0045] Example 1: A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0046] 1. Preparation of polytetrafluoroethylene composite binder:

[0047] Step 1: (1) adding polytetrafluoroethylene powder to a reaction vessel containing dopamine-Tris buffer solution (the dopamine-Tris buffer solution comprises the following components: 2 g / L dopamine, 5 mM trishydroxyaminomethane hydrochloride, deionized water as solvent, and pH 8), stirring at 20°C and a stirring speed of 100 r / min for 9 h, and obtaining polydopamine-coated polytetrafluoroethylene powder after separation and purification, wherein the ratio of polytetrafluoroethylene powder to dopamine-Tris buffer solution is 10 g:1 L; (2) adding carboxyl-polyethylene glycol-thiol, vinyl trimethylol Oxysilane and photoinitiator were added into the reaction vessel in a mass ratio of 10:1.8:0.4, stirred and mixed evenly, irradiated with ultraviolet light for 30 minutes, and separated and purified to obtain carboxyl-polyethylene glycol-silane; (3) 10 parts of polydopamine-coated polytetrafluoroethylene powder were added to 25 parts of N,N-dimethylformamide, ultrasonically dispersed for 10 minutes, and then 3 parts of carboxyl-polyethylene glycol-silane, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine were added thereto, stirred and reacted for 36 hours, and separated and purified to obtain modified polytetrafluoroethylene.

[0048] Step 2: (1) adding carbon nanotubes (multi-walled carbon nanotubes and single-walled carbon nanotubes in a mass ratio of 1:1.5) into a reaction vessel containing an acid solution (the acid solution is obtained by mixing 98wt% concentrated sulfuric acid and 68wt% concentrated nitric acid in a volume ratio of 3:1), stirring and heating to 60°C, soaking and acidifying for 4h, separating and purifying to obtain acidified carbon nanotubes, wherein the ratio of carbon nanotubes to acid solution is 4g:100mL; (2) adding 10 parts of acidified carbon nanotubes, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine into a reaction vessel containing 25 parts of deionized water, stirring and mixing evenly, then adjusting the reaction system temperature to 10°C, adding 3 parts of dopamine, stirring and reacting for 24h, separating and purifying to obtain modified carbon nanotubes.

[0049] Step 3: (1) adding modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose to a polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution;

[0050] (2) adding ammonium carbonate to the polytetrafluoroethylene composite solution, stirring to break the emulsion, coagulating, separating and purifying, and obtaining a polytetrafluoroethylene composite binder;

[0051] The raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: calculated by mass percentage, 69.3% polytetrafluoroethylene emulsion, 15% modified polytetrafluoroethylene, 7.5% modified carbon nanotubes, 7.5% sodium carboxymethyl cellulose, and 0.7% ammonium carbonate.

[0052] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0053] Example 2: A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0054] 1. Preparation of polytetrafluoroethylene composite binder:

[0055] Step 1: (1) adding polytetrafluoroethylene powder to a reaction vessel containing dopamine-Tris buffer solution (the dopamine-Tris buffer solution comprises the following components: 2 g / L dopamine, 5 mM trishydroxyaminomethane hydrochloride, deionized water as solvent, and pH 8), stirring at 20°C and a stirring speed of 100 r / min for 9 h, and obtaining polydopamine-coated polytetrafluoroethylene powder after separation and purification, wherein the ratio of polytetrafluoroethylene powder to dopamine-Tris buffer solution is 20 g:1 L; (2) adding carboxyl-polyethylene glycol-thiol, vinyl trimethylolpropane, and thiol as solvent to a reaction vessel; Oxysilane and photoinitiator were added into the reaction vessel in a mass ratio of 10:1.8:0.4, stirred and mixed evenly, irradiated with ultraviolet light for 30 minutes, and separated and purified to obtain carboxyl-polyethylene glycol-silane; (3) 10 parts of polydopamine-coated polytetrafluoroethylene powder were added to 25 parts of N,N-dimethylformamide, ultrasonically dispersed for 10 minutes, and then 2 parts of carboxyl-polyethylene glycol-silane, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine were added thereto, stirred and reacted for 36 hours, and separated and purified to obtain modified polytetrafluoroethylene.

[0056] Step 2: (1) adding carbon nanotubes (multi-walled carbon nanotubes and single-walled carbon nanotubes in a mass ratio of 1:2) into a reaction vessel containing an acid solution (the acid solution is obtained by mixing 98wt% concentrated sulfuric acid and 68wt% concentrated nitric acid in a volume ratio of 3:1), stirring and heating to 60°C, soaking and acidifying for 4h, separating and purifying to obtain acidified carbon nanotubes, wherein the ratio of carbon nanotubes to acid solution is 4g:100mL; (2) adding 10 parts of acidified carbon nanotubes, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine into a reaction vessel containing 25 parts of deionized water, stirring and mixing evenly, then adjusting the reaction system temperature to 10°C, adding 2 parts of dopamine, stirring and reacting for 24h, separating and purifying to obtain modified carbon nanotubes.

[0057] Step 3: (1) adding modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose to a polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution;

[0058] (2) adding ammonium carbonate to the polytetrafluoroethylene composite solution, stirring to break the emulsion, coagulating, separating and purifying, and obtaining a polytetrafluoroethylene composite binder;

[0059] The raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: calculated by mass percentage, 78% polytetrafluoroethylene emulsion, 10.4% modified polytetrafluoroethylene, 5.4% modified carbon nanotubes, 5.4% sodium carboxymethyl cellulose, and 0.8% ammonium carbonate.

[0060] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0061] Example 3: A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0062] 1. Preparation of polytetrafluoroethylene composite binder:

[0063] Step 1: (1) adding polytetrafluoroethylene powder to a reaction vessel containing dopamine-Tris buffer solution (the dopamine-Tris buffer solution comprises the following components: 2 g / L dopamine, 5 mM trishydroxyaminomethane hydrochloride, deionized water as solvent, and pH 8), stirring at 20°C and a stirring speed of 100 r / min for 9 h, and obtaining polydopamine-coated polytetrafluoroethylene powder after separation and purification, wherein the ratio of polytetrafluoroethylene powder to dopamine-Tris buffer solution is 5 g:1 L; (2) adding carboxyl-polyethylene glycol-thiol, vinyl trimethylol Oxysilane and photoinitiator were added into the reaction vessel in a mass ratio of 10:1.5:0.3, stirred and mixed evenly, irradiated with ultraviolet light for 30 minutes, and separated and purified to obtain carboxyl-polyethylene glycol-silane; (3) 10 parts of polydopamine-coated polytetrafluoroethylene powder were added to 25 parts of N,N-dimethylformamide, ultrasonically dispersed for 10 minutes, and then 4 parts of carboxyl-polyethylene glycol-silane, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine were added thereto, stirred and reacted for 36 hours, and separated and purified to obtain modified polytetrafluoroethylene.

[0064] Step 2: (1) adding carbon nanotubes (multi-walled carbon nanotubes and single-walled carbon nanotubes mixed in a mass ratio of 1:1) into a reaction vessel filled with an acid solution (the acid solution is obtained by mixing 98wt% concentrated sulfuric acid and 68wt% concentrated nitric acid in a volume ratio of 3:1), stirring and heating to 60°C, soaking and acidifying for 4h, separating and purifying to obtain acidified carbon nanotubes, wherein the ratio of carbon nanotubes to acid solution is 4g:100mL; (2) adding 10 parts of acidified carbon nanotubes, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine into a reaction vessel filled with 25 parts of deionized water, stirring and mixing evenly, then adjusting the reaction system temperature to 10°C, adding 4 parts of dopamine, stirring and reacting for 24h, separating and purifying to obtain modified carbon nanotubes.

[0065] Step 3: (1) adding modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose to a polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution;

[0066] (2) adding ammonium carbonate to the polytetrafluoroethylene composite solution, stirring to break the emulsion, coagulating, separating and purifying, and obtaining a polytetrafluoroethylene composite binder;

[0067] The raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: calculated by mass percentage, 60% polytetrafluoroethylene emulsion, 19.8% modified polytetrafluoroethylene, 9.8% modified carbon nanotubes, 9.8% sodium carboxymethyl cellulose, and 0.6% ammonium carbonate.

[0068] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0069] The following control experiments are conducted based on Example 1, and comparative examples 1 to 5 are set as follows:

[0070] Comparative Example 1: Comparative Example 1 is based on Example 1, with the following modifications: only dopamine is self-polymerized to coat polytetrafluoroethylene powder, and other processes remain unchanged, specifically:

[0071] A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0072] 1. Preparation of polytetrafluoroethylene composite binder:

[0073] Step 1: (1) adding polytetrafluoroethylene powder to a reaction vessel containing a dopamine-Tris buffer solution (the dopamine-Tris buffer solution comprises the following components: 2 g / L dopamine, 5 mM trishydroxyaminomethane hydrochloride, deionized water as solvent, and a pH of 8), stirring the mixture at 20° C. and a stirring speed of 100 r / min for 9 h, and obtaining polydopamine-coated polytetrafluoroethylene powder (modified polytetrafluoroethylene) after separation and purification, wherein the ratio of polytetrafluoroethylene powder to dopamine-Tris buffer solution is 10 g:1 L.

[0074] Step 2: (1) adding carbon nanotubes (multi-walled carbon nanotubes and single-walled carbon nanotubes in a mass ratio of 1:1.5) into a reaction vessel containing an acid solution (the acid solution is obtained by mixing 98wt% concentrated sulfuric acid and 68wt% concentrated nitric acid in a volume ratio of 3:1), stirring and heating to 60°C, soaking and acidifying for 4h, separating and purifying to obtain acidified carbon nanotubes, wherein the ratio of carbon nanotubes to acid solution is 4g:100mL; (2) adding 10 parts of acidified carbon nanotubes, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine into a reaction vessel containing 25 parts of deionized water, stirring and mixing evenly, then adjusting the reaction system temperature to 10°C, adding 3 parts of dopamine, stirring and reacting for 24h, separating and purifying to obtain modified carbon nanotubes.

[0075] Step 3: (1) adding modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose to a polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution;

[0076] (2) adding ammonium carbonate to the polytetrafluoroethylene composite solution, stirring to break the emulsion, coagulating, separating and purifying, and obtaining a polytetrafluoroethylene composite binder;

[0077] The raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: calculated by mass percentage, 69.3% polytetrafluoroethylene emulsion, 15% modified polytetrafluoroethylene, 7.5% modified carbon nanotubes, 7.5% sodium carboxymethyl cellulose, and 0.7% ammonium carbonate.

[0078] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0079] Comparative Example 2: Comparative Example 2 is based on Example 1, with the following modifications: only single-walled carbon nanotubes are used, and other processes remain unchanged, specifically:

[0080] A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0081] 1. Preparation of polytetrafluoroethylene composite binder:

[0082] Step 1: (1) adding polytetrafluoroethylene powder to a reaction vessel containing dopamine-Tris buffer solution (the dopamine-Tris buffer solution comprises the following components: 2 g / L dopamine, 5 mM trishydroxyaminomethane hydrochloride, deionized water as solvent, and pH 8), stirring at 20°C and a stirring speed of 100 r / min for 9 h, and obtaining polydopamine-coated polytetrafluoroethylene powder after separation and purification, wherein the ratio of polytetrafluoroethylene powder to dopamine-Tris buffer solution is 10 g:1 L; (2) adding carboxyl-polyethylene glycol-thiol, vinyl trimethylol Oxysilane and photoinitiator were added into the reaction vessel in a mass ratio of 10:1.8:0.4, stirred and mixed evenly, irradiated with ultraviolet light for 30 minutes, and separated and purified to obtain carboxyl-polyethylene glycol-silane; (3) 10 parts of polydopamine-coated polytetrafluoroethylene powder were added to 25 parts of N,N-dimethylformamide, ultrasonically dispersed for 10 minutes, and then 3 parts of carboxyl-polyethylene glycol-silane, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine were added thereto, stirred and reacted for 36 hours, and separated and purified to obtain modified polytetrafluoroethylene.

[0083] Step 2: (1) adding single-walled carbon nanotubes to a reaction vessel containing an acid solution (the acid solution is obtained by mixing 98wt% concentrated sulfuric acid and 68wt% concentrated nitric acid in a volume ratio of 3:1), stirring and heating to 60°C, soaking and acidifying for 4h, separating and purifying to obtain acidified carbon nanotubes, wherein the ratio of carbon nanotubes to acid solution is 4g:100mL; (2) adding 10 parts of acidified carbon nanotubes, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine to a reaction vessel containing 25 parts of deionized water, stirring and mixing evenly, then adjusting the reaction system temperature to 10°C, adding 3 parts of dopamine, stirring and reacting for 24h, separating and purifying to obtain modified carbon nanotubes.

[0084] Step 3: (1) adding modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose to a polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution;

[0085] (2) adding ammonium carbonate to the polytetrafluoroethylene composite solution, stirring to break the emulsion, coagulating, separating and purifying, and obtaining a polytetrafluoroethylene composite binder;

[0086] The raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: calculated by mass percentage, 69.3% polytetrafluoroethylene emulsion, 15% modified polytetrafluoroethylene, 7.5% modified carbon nanotubes, 7.5% sodium carboxymethyl cellulose, and 0.7% ammonium carbonate.

[0087] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0088] Comparative Example 3: Comparative Example 3 is based on Example 1, with the following adjustments: no modified polytetrafluoroethylene is added, and other processes remain unchanged, specifically:

[0089] A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0090] 1. Preparation of polytetrafluoroethylene composite binder:

[0091] Step 1: (1) adding carbon nanotubes (multi-walled carbon nanotubes and single-walled carbon nanotubes in a mass ratio of 1:1.5) into a reaction vessel containing an acid solution (the acid solution is obtained by mixing 98wt% concentrated sulfuric acid and 68wt% concentrated nitric acid in a volume ratio of 3:1), stirring and heating to 60°C, soaking and acidifying for 4h, separating and purifying to obtain acidified carbon nanotubes, wherein the ratio of carbon nanotubes to acid solution is 4g:100mL; (2) adding 10 parts of acidified carbon nanotubes, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine into a reaction vessel containing 25 parts of deionized water, stirring and mixing evenly, then adjusting the reaction system temperature to 10°C, adding 3 parts of dopamine, stirring and reacting for 24h, separating and purifying to obtain modified carbon nanotubes.

[0092] Step 2: (1) adding the modified carbon nanotubes and sodium carboxymethyl cellulose to the polytetrafluoroethylene emulsion, stirring and mixing them uniformly to obtain a polytetrafluoroethylene composite solution;

[0093] (2) adding ammonium carbonate to the polytetrafluoroethylene composite solution, stirring to break the emulsion, coagulating, separating and purifying, and obtaining a polytetrafluoroethylene composite binder;

[0094] The raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: 84.3% of polytetrafluoroethylene emulsion, 7.5% of modified carbon nanotubes, 7.5% of sodium carboxymethyl cellulose, and 0.7% of ammonium carbonate, calculated by mass percentage.

[0095] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0096] Comparative Example 4: Comparative Example 4 is based on Example 1, with the following adjustments: no modified carbon nanotubes are added, and other processes remain unchanged, specifically:

[0097] A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0098] 1. Preparation of polytetrafluoroethylene composite binder:

[0099] Step 1: (1) adding polytetrafluoroethylene powder to a reaction vessel containing dopamine-Tris buffer solution (the dopamine-Tris buffer solution comprises the following components: 2 g / L dopamine, 5 mM trishydroxyaminomethane hydrochloride, deionized water as solvent, and pH 8), stirring at 20°C and a stirring speed of 100 r / min for 9 h, and obtaining polydopamine-coated polytetrafluoroethylene powder after separation and purification, wherein the ratio of polytetrafluoroethylene powder to dopamine-Tris buffer solution is 10 g:1 L; (2) adding carboxyl-polyethylene glycol-thiol, vinyl trimethylol Oxysilane and photoinitiator were added into the reaction vessel in a mass ratio of 10:1.8:0.4, stirred and mixed evenly, irradiated with ultraviolet light for 30 minutes, and separated and purified to obtain carboxyl-polyethylene glycol-silane; (3) 10 parts of polydopamine-coated polytetrafluoroethylene powder were added to 25 parts of N,N-dimethylformamide, ultrasonically dispersed for 10 minutes, and then 3 parts of carboxyl-polyethylene glycol-silane, 1.5 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 1.5 parts of 4-pyrrolidinopyridine were added thereto, stirred and reacted for 36 hours, and separated and purified to obtain modified polytetrafluoroethylene.

[0100] Step 2: (1) adding modified polytetrafluoroethylene and sodium carboxymethyl cellulose to polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution;

[0101] (2) adding ammonium carbonate to the polytetrafluoroethylene composite solution, stirring to break the emulsion, coagulating, separating and purifying, and obtaining a polytetrafluoroethylene composite binder;

[0102] The raw materials required for preparing the polytetrafluoroethylene composite binder include the following components: calculated by mass percentage, 76.8% of polytetrafluoroethylene emulsion, 15% of modified polytetrafluoroethylene, 7.5% of sodium carboxymethyl cellulose, and 0.7% of ammonium carbonate.

[0103] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0104] Comparative Example 5: Comparative Example 5 is based on Example 1, with the following adjustments: modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose are not added, and other processes remain unchanged, specifically:

[0105] A polytetrafluoroethylene composite binder and a dry electrode prepared therefrom:

[0106] 1. Preparation of polytetrafluoroethylene binder: adding ammonium carbonate to polytetrafluoroethylene emulsion, stirring to break the emulsion, coagulation, separation and purification to obtain polytetrafluoroethylene binder;

[0107] The raw materials required for preparing the polytetrafluoroethylene binder include the following components: 99% polytetrafluoroethylene emulsion and 1% ammonium carbonate, calculated by mass percentage.

[0108] 2. Preparation of dry electrode: (1) Lithium iron phosphate, conductive carbon black, and polytetrafluoroethylene composite binder were added into a blender in a mass ratio of 88:7:5, and stirred at a stirring speed of 1100 r / min for 3 h to obtain a mixture A; (2) Mixture A was added into a roller press, and rolled at 150°C to obtain an electrode film with a thickness of 120 μm; (3) The electrode film was covered on both sides of aluminum foil, and hot-pressed at 150°C on a roller press to obtain a dry electrode.

[0109] Performance test: The dry-process electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were subjected to relevant performance tests. The specific test methods are as follows:

[0110] (1) Peel strength test: The dry-process electrodes prepared in each example were cut into 20 mm × 100 mm strips, 3M tape was affixed to the surface of the electrode, and then a 180° peel test was performed on the electrode using a multifunctional tensile testing machine at a tensile speed of 100 mm / min.

[0111] (2) Cycling performance test: Using a Neware battery tester, the capacity retention rate of each dry-process electrode after 100 cycles was tested at 25°C, a voltage range of 2.5 to 4.0 V, and a current density of 1C.

[0112] The test results of the above test contents are shown in Table 1 below:

[0113] Table 1

[0114]

[0115]

[0116] Results Analysis: The data from the Examples and Comparative Examples in Table 1 above demonstrate that the dopamine coating of polytetrafluoroethylene micropowder, the further grafting of polyethylene glycol chain ends onto its surface, and the selection and modification of carbon nanotubes are all crucial technical aspects of the present invention. Ultimately, the synergistic effects of modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethylcellulose resulted in the preparation of a polytetrafluoroethylene composite binder with excellent performance.

[0117] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A polytetrafluoroethylene composite adhesive, characterized in that: The preparation method comprises the following steps: Step 1: (1) dopamine self-polymerizes and coats polytetrafluoroethylene micropowder to obtain polydopamine-coated polytetrafluoroethylene micropowder; (2) carboxyl-polyethylene glycol-thiol undergoes a click reaction with vinyltrimethoxysilane to obtain carboxyl-polyethylene glycol-silane; (3) Polydopamine-coated polytetrafluoroethylene micropowder undergoes esterification reaction with carboxyl-polyethylene glycol-silane to obtain modified polytetrafluoroethylene; Step 2: (1) acidifying the carbon nanotubes to obtain acidified carbon nanotubes; (2) Acidified carbon nanotubes undergo amidation reaction with dopamine to obtain modified carbon nanotubes; Step 3: (1) adding modified polytetrafluoroethylene, modified carbon nanotubes, and sodium carboxymethyl cellulose to a polytetrafluoroethylene emulsion, stirring and mixing uniformly to obtain a polytetrafluoroethylene composite solution; (2) Adding a demulsifier to the polytetrafluoroethylene composite solution, stirring to demulsify, coagulating, separating and purifying, thereby obtaining a polytetrafluoroethylene composite binder.

2. A polytetrafluoroethylene composite adhesive according to claim 1, characterized in that: The preparation method of the modified polytetrafluoroethylene is: (1) adding polytetrafluoroethylene micropowder into a reaction vessel containing a dopamine-Tris buffer solution, stirring at 15-25° C. and a stirring speed of 60-120 r / min for 3-12 hours, and separating and purifying to obtain polydopamine-coated polytetrafluoroethylene micropowder; (2) adding carboxyl-polyethylene glycol-thiol, vinyl trimethoxysilane, and a photoinitiator into a reaction vessel, stirring and mixing uniformly, irradiating with ultraviolet light for 15 to 45 minutes, and separating and purifying to obtain carboxyl-polyethylene glycol-silane; (3) Add polydopamine-coated polytetrafluoroethylene powder to N,N-dimethylformamide and ultrasonically disperse it for 5 to 15 minutes. Then, add carboxyl-polyethylene glycol-silane, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 4-pyrrolidinopyridine. Stir and react for 24 to 48 hours. After separation and purification, modified polytetrafluoroethylene is obtained.

3. A polytetrafluoroethylene composite adhesive according to claim 2, characterized in that: The dopamine-Tris buffer solution comprises the following components: 0.1-5 g / L dopamine, 1-10 mM tris(hydroxyaminomethane) hydrochloride, deionized water as solvent, and a pH of 8-8.5; The ratio of the polytetrafluoroethylene powder to the dopamine-Tris buffer solution is (5-20) g:1 L; The mass ratio of the carboxyl group-polyethylene glycol-mercapto group, vinyltrimethoxysilane and photoinitiator is 10:(1.5-2):(0.25-0.5); The raw materials required for preparing the modified polytetrafluoroethylene include the following components: 10 parts by mass of polydopamine-coated polytetrafluoroethylene micropowder, 2 to 4 parts of carboxyl-polyethylene glycol-silane, 1 to 2 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 1 to 2 parts of 4-pyrrolidinopyridine, and 25 parts of N,N-dimethylformamide.

4. The polytetrafluoroethylene composite adhesive according to claim 1, characterized in that: The preparation method of the modified carbon nanotubes is: (1) adding carbon nanotubes into a reaction vessel containing an acid solution, stirring and heating to 50-80° C., soaking and acidifying for 1-6 hours, and separating and purifying to obtain acidified carbon nanotubes; (2) Add the acidified carbon nanotubes, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and 4-pyrrolidinopyridine into a reaction vessel filled with deionized water, stir and mix evenly, then adjust the temperature of the reaction system to 5-20°C, add dopamine, stir and react for 12-48 hours, and obtain modified carbon nanotubes after separation and purification.

5. The polytetrafluoroethylene composite adhesive according to claim 4, characterized in that: The ratio of the carbon nanotubes to the acid solution is (1-5) g:100 mL; The carbon nanotubes include multi-walled carbon nanotubes or single-walled carbon nanotubes, or a combination of the two; The acid solution is prepared by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, wherein the concentration of the concentrated sulfuric acid is ≥96wt%, and the concentration of the concentrated nitric acid is ≥68wt%; The raw materials required for preparing the modified carbon nanotubes include the following components: 10 parts by mass of acidified carbon nanotubes, 2-4 parts of dopamine, 1-2 parts of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 1-2 parts of 4-pyrrolidinopyridine, and 25 parts of deionized water.

6. The polytetrafluoroethylene composite adhesive according to claim 5, characterized in that: The carbon nanotubes are composed of multi-walled carbon nanotubes and single-walled carbon nanotubes mixed in a mass ratio of 1:(1-2).

7. The polytetrafluoroethylene composite adhesive according to claim 1, characterized in that: The raw materials required for preparing the polytetrafluoroethylene composite binder are The invention comprises the following components: calculated by mass percentage, 60-78% of polytetrafluoroethylene emulsion, 10.4-19.8% of modified polytetrafluoroethylene, 5.4-9.8% of modified carbon nanotube, 5.4-9.8% of sodium carboxymethyl cellulose and 0.6-0.8% of demulsifier.

8. A dry electrode, characterized in that: Its preparation method is: (1) adding an electrode active material, a conductive agent, and the polytetrafluoroethylene composite binder according to any one of claims 1 to 7 into a blender in a certain proportion, and stirring and mixing them at a stirring speed of 1000 to 1200 r / min for 1 to 5 hours to obtain a mixed material A; (2) adding the mixed material A into a roller press and rolling at 100-180° C. to obtain an electrode film with a thickness of 100-200 μm; (3) The electrode film is covered on both sides of copper foil or aluminum foil, and hot-pressed at 100-180°C by a roller press to obtain a dry electrode.

9. The dry electrode according to claim 8, characterized in that: The mass ratio of the electrode active material, the conductive agent and the polytetrafluoroethylene composite binder is (82-90):(5-10):(3-10).

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