Dry electrode film and method for manufacturing same

Abstract

A dry electrode film. The dry electrode film comprises an active material and a binder. The binder comprises a polymer, and carbon nanotubes and carbon black which are dispersed in the polymer, wherein the average diameter of the carbon nanotubes is 13 nm to 100 nm, and the D / G ratio of the carbon nanotubes is 0.5 to 1.4. Also provided is a method for manufacturing the dry electrode film. On the basis of the total weight of the binder, the sum of the content of the carbon nanotubes and the content of the carbon black is greater than 5 wt%, and the content of the polymer is greater than 40 wt%; and the weight ratio of the carbon black to the carbon nanotubes is 8: 1 to 1: 8.

Description

A dry electrode film and method for preparing the same

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 20, 2023, with application number 202311764529.6 and application name “A dry electrode membrane and a method for preparing the same”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of secondary batteries, and specifically provides a dry electrode film and a method for preparing the same. Background Art

[0003] Secondary batteries are widely used in consumer batteries and new energy vehicle power batteries due to their high energy density and wide usage scenarios. In the current traditional lithium battery manufacturing process, it is necessary to use organic solvents to prepare a stable electrode slurry and coat it on the current collector. However, the classic slurry-coated wet battery electrodes have some undesirable problems, such as cracking, delamination, poor flexibility and low energy density, which are exacerbated in thicker electrode films. As the electrode film becomes thicker (usually corresponding to a higher electrode material load), a loss of electrochemical performance and reliability occurs in the wet-coated electrode. Wet-coated electrode films may also suffer from uneven dispersion of components (such as active materials). As the film thickness and / or density increases, the unevenness may increase and may lead to poor ionic conductivity and / or electronic conductivity. The wet method also generally requires an expensive and time-consuming drying step, and the drying process becomes more difficult as the film becomes thicker.

[0004] To address these challenges, researchers have begun researching dry electrode technology. This involves mixing active materials, conductive agents, and binders to create a mixed powder. This is then rolled into a continuous, self-supporting film, which is then bonded to a current collector to form a complete electrode sheet. Dry electrode production eliminates the use of organic solvents, saving costs and enabling the production of thicker electrodes, thereby increasing battery energy density and lifespan.

[0005] However, since the dry electrode process does not use organic solvents, the conductive agent in the electrode is affected by the binder and cannot be fully dispersed, which has a negative effect on the electrode performance.

[0006] Summary of the Invention

[0007] In order to solve the above problems, the purpose of the present application is to provide a dry electrode film, which includes an active material and a binder, the binder including a polymer and carbon nanotubes and carbon black dispersed in the polymer, wherein the average diameter of the carbon nanotubes is 13nm to 100nm, the D / G ratio of the carbon nanotubes is 0.5 to 1.4, and wherein, based on the total weight of the binder, the sum of the contents of the carbon nanotubes and carbon black is greater than 5% by weight, and the content of the polymer is greater than 40% by weight, wherein the weight ratio of carbon black to the carbon nanotubes is 8:1 to 1:8.

[0008] The battery electrode sheet of the present application achieves uniform dispersion of the conductive agent in the binder in a dry electrode film prepared using a dry process. Because the conductive agent is dispersed within the polymer, even when the electrode film is prepared using a dry process, the conductive agent in the electrode film can fully function, resulting in optimized conductivity and, consequently, improved electrochemical performance of the secondary battery. The inventors of the present application have discovered that the average diameter and D / G ratio of the carbon nanotubes dispersed in the polymer significantly affect the electrode sheet conductivity. An average diameter of the carbon nanotubes less than 13 nm or greater than 100 nm, or a D / G ratio less than 0.5 or greater than 1.4, negatively impacts the electrode sheet conductivity. When the combined content of carbon nanotubes and carbon black in the binder is below 5 wt%, the electrode sheet conductivity is not effectively improved. When the polymer content in the binder is too low, the desired dry electrode film strength cannot be achieved. Furthermore, the inventors have discovered that even when the combined content of carbon nanotubes and carbon black is the same, the carbon nanotubes and carbon black must meet the ratio specified in the present application to achieve the desired conductivity.

[0009] According to one embodiment of the present application, the active material is a negative electrode active material, and the dry electrode film is provided in a negative electrode sheet.

[0010] According to one embodiment of the present application, the active material is a positive electrode active material, and the dry electrode film is provided in a positive electrode sheet.

[0011] According to one embodiment of the present application, the average diameter of the carbon nanotubes is, for example, 13 nm, 20 nm, 30 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any range thereof.

[0012] According to one embodiment of the present application, the D / G ratio of the carbon nanotubes is, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or any range thereof.

[0013] According to one embodiment of the present application, the dry electrode film is a solvent-free electrode film, and in particular, the dry electrode film does not contain N-methylpyrrolidone.

[0014] According to one embodiment of the present application, the polymer includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, styrene, polyacrylonitrile, polyvinyl chloride, polyacrylic acid, polychlorotrifluoroethylene and polyacrylate.

[0015] According to one embodiment of the present application, the polymer includes polytetrafluoroethylene, and the content of polytetrafluoroethylene is greater than 90 wt % based on the total mass of the polymer. According to one embodiment of the present application, the polymer is polytetrafluoroethylene.

[0016] According to one embodiment of the present application, the average diameter of the carbon nanotubes is 15 nm to 80 nm.

[0017] According to one embodiment of the present application, the D / G ratio of the carbon nanotubes is 0.6 to 1.3.

[0018] According to one embodiment of the present application, the length of the carbon nanotubes is 0.8 μm to 17 μm, preferably 8 μm to 15 μm.

[0019] In some embodiments, the length of the carbon nanotubes is, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, or any interval thereof.

[0020] According to one embodiment of the present application, the content of the binder is 0.5 wt % to 4.0 wt % based on the total weight of the dry electrode film. In some embodiments, the content of the binder is 0.5 wt %, 1.0 wt %, 1.5 wt %, 2.0 wt %, 2.5 wt %, 3.0 wt %, 3.5 wt %, 4.0 wt %, or any range thereof.

[0021] According to one embodiment of the present application, the carbon nanotubes are present in an amount of 1 to 30 wt % based on the total weight of the binder. In some embodiments, the carbon nanotubes are present in an amount of 1 wt %, 5 wt %, 10 wt %, 15 wt %, 25 wt %, 30 wt %, or any range thereof based on the total weight of the binder.

[0022] According to one embodiment of the present application, the carbon black content is 5 wt % to 35 wt % based on the total weight of the binder. In some embodiments, the carbon black content is 5 wt %, 10 wt %, 15 wt %, 25 wt %, 30 wt %, 50 wt %, or any interval thereof, based on the total weight of the binder.

[0023] According to one embodiment of the present application, the content of the polymer is 50 wt % to 92 wt % based on the total weight of the binder. In some embodiments, the content of the polymer is 50 wt %, 60 wt %, 70 wt %, 80 wt %, 90 wt %, 92 wt % or any interval thereof based on the total weight of the binder.

[0024] According to one embodiment of the present application, the average particle size of the carbon black is 35 nm to 60 nm.

[0025] According to one embodiment of the present application, the average particle size of the carbon black is 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm or any range thereof.

[0026] According to one embodiment of the present application, if the oil absorption value of carbon black is too large or too small, it will negatively affect the electrode conductivity and charge transfer impedance. Therefore, the oil absorption value of carbon black is limited to 120mL / 100g to 300mL / 100g, for example, 120mL / 100g, 140mL / 100g, 160mL / 100g, 180mL / 100g, 200mL / 100g, 220mL / 100g, 240mL / 100g, 260mL / 100g, 280mL / 100g, 300mL / 100g or any interval thereof.

[0027] According to one embodiment of the present application, if the specific surface area of ​​carbon black is too large or too small, it will negatively affect the conductivity and charge transfer impedance of the electrode. Therefore, the specific surface area of ​​carbon black is limited to 40m 2 / g to 90m 2 / g, for example 40m 2 / g, 50m 2 / g, 60m 2 / g、70m 2 / g、80m 2 / g、90m 2 / g or any interval formed by them.

[0028] According to one embodiment of the present application, if the ratio of the weight of the polymer to the sum of the weights of the carbon nanotubes and carbon black is too large or too small, it will negatively affect the strength of the dry electrode film, the electrode conductivity, and the charge transfer impedance. In addition, when the weight of the polymer is less than the sum of the weights of the carbon nanotubes and carbon black, the strength of the dry electrode film cannot meet the self-supporting requirements. Therefore, the ratio of the weight of the polymer to the sum of the weights of the carbon nanotubes and carbon black is limited to 9:1 to 1:1, for example, 9:1 to 1:1, 8:1 to 1:1, 7:1 to 1:1, 6:1 to 1:1, 5:1 to 1:1, 4:1 to 1:1, 3:1 to 1:1, and 2:1 to 1:1.

[0029] According to one embodiment of the present application, if the weight ratio of carbon black to carbon nanotubes in the binder is too large or too small, the synergistic effect of carbon black and carbon nanotubes acting as conductive agents cannot be achieved, which will negatively affect the electrode conductivity and charge transfer impedance. Therefore, the weight ratio of carbon black to carbon nanotubes is limited to 4:1 to 1:4. Surprisingly, the conductive properties of the dry electrode film can be significantly improved by adjusting the weight ratio of carbon black to carbon nanotubes to a range of 4:1 to 1:4, while keeping the total content of carbon black and carbon nanotubes unchanged.

[0030] According to one embodiment of the present application, in addition to the carbon black and carbon nanotubes in the binder, the dry electrode film further comprises an additional conductive agent, and the content of the additional conductive agent is no more than 1.5%, such as no more than 1.4%, 1.3%, 1.2%, 1.1%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1%, based on the total weight of the dry electrode film. According to one embodiment of the present application, the additional conductive agent is not dispersed in the binder. According to one embodiment of the present application, the additional conductive agent is dispersed in the active material.

[0031] The present application also aims to provide a method for preparing a dry electrode film according to the present application, the method comprising the following steps:

[0032] (a) providing a polymer emulsion, wherein the polymer comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, styrene, polyacrylonitrile, polyvinyl chloride, polyacrylic acid, polychlorotrifluoroethylene, and polyacrylate, and the solid content of the emulsion is less than 5%;

[0033] (b) adding carbon nanotubes and carbon black to the emulsion obtained in step (a) under stirring, wherein the average diameter of the carbon nanotubes is 13 nm to 100 nm and the D / G ratio of the carbon nanotubes is 0.5 to 1.4 to obtain an emulsion in which the carbon nanotubes and carbon black are dispersed;

[0034] (c) drying the emulsion obtained from step (b) to obtain a dry binder;

[0035] (d) mixing the active material and the dry binder obtained in step (c), and rolling to obtain the dry electrode film.

[0036] According to one embodiment of the present application, the polymer emulsion in step (a) is obtained by mixing the polymer with water (eg, deionized water).

[0037] According to one embodiment of the present application, the polymer in step (a) comprises polytetrafluoroethylene, and in particular, the content of polytetrafluoroethylene is greater than 90 wt % based on the total mass of the polymer.

[0038] According to one embodiment of the present application, the polymer in step (a) is polytetrafluoroethylene.

[0039] According to one embodiment of the present application, the polymer emulsion in step (a) has a solid content of 50% to 70%.

[0040] According to one embodiment of the present application, the emulsion of the polymer in step (a) has 3 wt % to 8 wt % of an emulsifier. In some embodiments, the emulsifier is selected from cationic surfactants such as perfluoroalkyl quaternary ammonium salts, anionic surfactants such as perfluoroalkyl carboxylates, and nonionic surfactants such as PEO, PPO, and PEO-PPO copolymers.

[0041] According to one embodiment of the present application, the polymer in step (a), such as polytetrafluoroethylene, has an average particle size of 170 nm to 250 nm. In some embodiments, the polymer in step (a) is polytetrafluoroethylene with an average particle size ranging from 200 nm to 240 nm.

[0042] The present application also aims to provide a secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein at least one of the positive electrode sheet and the negative electrode sheet comprises the dry electrode film described in the present application.

[0043] The present application also aims to provide an electronic device comprising the secondary battery according to the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 shows an SEM image of a binder in a dry electrode film according to Example 1 of the present application;

[0045] FIG2 shows the Raman spectrum of the carbon nanotubes used in Example 1 of the present application. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application. All other embodiments obtained by those skilled in the art based on the technical solutions and embodiments provided in the present application fall within the scope of protection of the present application.

[0047] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0048] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.

[0049] As used herein, a "solvent-free" dry electrode film is an electrode film that is completely free of organic solvents, i.e., contains no detectable organic solvents, organic solvent residues, or organic solvent impurities. The organic solvent, for example, N-methylpyrrolidone (NMP), is because no organic solvent is used in the production process of the dry electrode film. However, due to the use of an aqueous dispersion of a binder during the production process, trace amounts of water may remain in the solvent-free dry electrode film. The content of the trace amounts of water is less than 0.1% by weight, in particular, less than 0.09% by weight, 0.08% by weight, 0.07% by weight, 0.06% by weight, 0.05% by weight, 0.04% by weight, 0.03% by weight, 0.02% by weight, or 0.01% by weight.

[0050] As used herein, "wet" electrodes, "wet process," and "wet-coated" electrodes refer to electrodes prepared by at least one step involving a slurry of active material, binder, and optional additives. Wet electrodes typically contain organic solvents, organic solvent residues, and / or organic solvent impurities. Wet coating is performed by applying a positive electrode slurry or a negative electrode slurry to a positive electrode current collector or a negative electrode current collector to form a positive electrode active coating or a negative electrode active coating.

[0051] As used herein, "electrode dry material" refers to a material that is completely free of organic solvents, substantially free of water, and comprises an active material, a binder, and a conductive agent. The electrode dry material may be in powder or granular form. The electrode dry material may be arranged on an electrode by mechanical processing methods such as pressing or rolling to form a high-strength, self-supporting membrane.

[0052] "Dry manufacturing process", "dry method" and "dry coating" described in the context of this application refer to a process in which no solvent is used or substantially no solvent is used in the formation of the electrode film. In some embodiments, the dry manufacturing process does not use a solvent and there is no solvent residue resulting therefrom. In some embodiments, the dry electrode film is a self-supporting film formed from an electrode dry material by a dry manufacturing process. In some embodiments, the method for forming the dry electrode film may include initially fiberizing an initially fiberizable binder component so that the film contains an initially fiberized binder. In a further embodiment, the dry electrode film may be formed in the absence of a current collector. In a still further embodiment, the dry electrode film may contain an initially fiberized polymer matrix so that the dry electrode film is self-supporting.

[0053] The "D / G ratio of carbon nanotubes" in the context of this application refers to the D / G ratio of carbon nanotubes determined by Raman spectroscopy at 1360±50 cm -1 The maximum peak intensity of the D band at 1580±50cm -1 The average value of the ratio of the maximum peak intensity of the G band at .

[0054] 1. Negative electrode

[0055] According to some embodiments of the present application, the negative electrode includes a negative electrode current collector and a dry electrode film, wherein the dry electrode film includes a negative electrode active material, a conductive agent, and a binder.

[0056] According to some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active coating, wherein the negative electrode active coating includes a negative electrode active material, a conductive agent, and a binder.

[0057] In some embodiments, the negative electrode active material may be a commonly used negative electrode active material, including but not limited to carbon-based materials, silicon-based materials, metal oxides, and tin-based materials. For example, silicon-based composite materials include but are not limited to silicon-carbon composites, silicon-oxygen composites, silicon-metal oxide composites, and silicon alloy composites. For example, metal oxides include but are not limited to iron oxide, lithium titanate, copper oxide, and the like, and are considered to be any metal oxide capable of lithium intercalation, deintercalation, and storage.

[0058] In some embodiments, the conductive agent can be a commonly used conductive agent, including but not limited to: metal-based materials, carbon-based materials, conductive polymers, and mixtures thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, nickel, copper, aluminum, or silver. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, acetylene black, Ketjen black, carbon black, carbon fiber, or any combination thereof.

[0059] In some embodiments, the binder includes carbon nanotubes dispersed in the binder, whereby the content of the additional conductive agent in the negative dry electrode film, excluding the conductive agent in the binder, does not exceed 0.5 wt %.

[0060] In some embodiments, the binder includes carbon nanotubes dispersed in the binder, whereby no additional conductive agent is added to the negative dry electrode film except for the conductive agent in the binder.

[0061] 2. Positive electrode

[0062] The materials, compositions and manufacturing methods of the positive electrode that can be used in the embodiments of the present application include any technology disclosed in the prior art.

[0063] According to some embodiments of the present application, the positive electrode includes a positive electrode current collector and a dry electrode film, wherein the dry electrode film includes a positive electrode active material, a conductive agent, and a binder.

[0064] According to some embodiments of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active coating layer, wherein the positive electrode active coating layer includes a positive electrode active material, a conductive agent, and a binder.

[0065] According to some embodiments of the present application, the positive electrode active material includes, but is not limited to: lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium vanadate (LiVO2), lithium titanate (LiTi5O 12 ), lithium nickel cobalt manganese (NCM) ternary material, lithium nickel cobalt aluminum (NCA) ternary material, lithium iron phosphate (LiFePO4), lithium iron manganese phosphate (LiMn x Fe 1-x PO4), lithium manganese phosphate (LiMnPO4), lithium nickel phosphate (LiNiPO4), lithium cobalt phosphate (LiCoPO4), lithium niobium phosphate or lithium manganate (LiMn2O4).

[0066] According to one embodiment of the present application, the positive electrode active material is Li[Ni 1-x-y Co x M y ]O2(M=Mn, Al, etc., such as lithium nickel cobalt manganese oxide Li[Ni 1-x-y Co x Mn y ]O2, 1-xy≥0.5, lithium nickel cobalt aluminum oxide Li[Ni 1-x-y Co x Al y ]O2, 1-xy≥0.5).

[0067] According to one embodiment of the present application, the positive electrode active material includes LiMn k X (1-k)At least one phosphate-based material in PO4, wherein 0≤k≤1, and the X element is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, or lead. In some embodiments, the positive electrode active material includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0068] According to some embodiments of the present application, the conductive agent includes, but is not limited to: a carbon-based material, a metal-based material, a conductive polymer, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.

[0069] In some embodiments, the binder includes carbon nanotubes dispersed in the binder, whereby the content of the additional conductive agent in the positive dry electrode film, excluding the conductive agent in the binder, does not exceed 0.6 wt %.

[0070] In some embodiments, the binder includes carbon nanotubes dispersed in the binder, whereby no additional conductive agent is added to the positive dry electrode film except for the conductive agent in the binder.

[0071] 3. Diaphragm

[0072] The material and shape of the separator used in the embodiments of the present application are not particularly limited and can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0073] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, and polyethylene terephthalate. Specifically, polypropylene porous membrane, polyethylene porous membrane, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0074] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0075] In a preferred embodiment of the present application, the separator is a polyethylene (PE) separator coated with ceramic layers on both sides, wherein the PE layer thickness is in the range of 5 to 20 μm, and the coating thickness of each ceramic layer is in the range of 0 to 5 μm.

[0076] 4. Electrolyte

[0077] In some embodiments, the electrolyte includes a lithium salt and a solvent.

[0078] In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalatoborate), or lithium difluorooxalatoborate.

[0079] In some embodiments, the solvent can be selected from one or more of ethylene carbonate (EC), propylene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0080] In a preferred embodiment of the present application, the electrolyte is LiPF6 / EC+DMC+EMC.

[0081] 5. Secondary Batteries

[0082] The secondary battery according to the present application is, for example, a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In some embodiments, the secondary battery of the present application includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0083] The secondary battery according to the present application can be used in electronic devices, including but not limited to laptop computers, motors, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, motorcycles, power-assisted bicycles, bicycles, lithium-ion capacitors, etc.

[0084] 6. Test Method

[0085] Pole conductivity test: Use HIOKI pole piece resistance meter to test the conductivity of the pole piece. 2 Place the electrode under the probe, release the limit device, and make the probe touch the electrode surface by its own weight to read the electrode resistance value. Take 3 points for each electrode to measure, and take the average value of the volume resistance of 12 points after measurement.

[0086] Determination of carbon nanotube diameter: Disperse the carbon nanotube sample and place it on a microgrid dedicated to a transmission electron microscope and store it properly; use a transmission electron microscope to observe the hollow structure of the carbon nanotube and obtain a certain number of TEM effective field of view images; by analyzing all effective field of view images of the same carbon nanotube sample, measure and calculate the diameter of the carbon nanotube sample and take the average value.

[0087] Determination of carbon nanotube length: Disperse the carbon nanotube sample and place it on aluminum foil and store it properly. Use a scanning electron microscope to observe the tubular structure of the carbon nanotube and obtain a certain number of SEM effective field of view images. By analyzing all effective field of view images of the same carbon nanotube sample, measure and calculate the length of the carbon nanotube sample from beginning to end and take the average value.

[0088] Determination of the D / G ratio of carbon nanotubes: Testing was performed using a 50x microscope objective and a 532nm laser. Nine valid spectra were collected by scanning the sample area. The peak areas of the D and G peaks were obtained using Lorentzian line fitting. The nine values ​​were then divided and averaged.

[0089] Determination of primary particle size of carbon black: see GB / T19077-2016.

[0090] Determination of specific surface area of ​​carbon black: refer to BET method.

[0091] Determination of oil absorption value of carbon black: See GB / T 3780.2-2007-Carbon black-Part 2: Determination of oil absorption value.

[0092] Dry electrode film strength test: The dry electrode film was cut into sheets with a width of 15 mm and a length of more than 10 cm. The tensile strength was tested on a universal testing machine in the pull-up mode at a stretching speed of 5 mm / min.

[0093] Charge transfer impedance was measured using a blue electrochemical test cabinet at 25°C, with the battery discharged at 0.1C to 0.005V over the voltage range of 0.005V-1.5V. After a 5-minute rest, the battery was discharged at 0.05C to 0.005V. After a 5-minute rest, the battery was charged at 0.1C to 1.5V. After two cycles, the battery was discharged at 0.1C to 50% SOC. The battery was transferred to an Autolab electrochemical workstation and tested with an amplitude of 10mV and a frequency range of 100,000Hz-0.01Hz.

[0094] 2C capacity retention rate test method: The battery is charged and discharged at 0.1C for the first time, and then charged and discharged at 0.33C, 0.5C, 1C, and 2C for 3 weeks, and the ratio of the capacity at 2C rate to the capacity at 0.1C is calculated.

[0095] Example 1

[0096] Preparation of binder:

[0097] -Select polytetrafluoroethylene emulsion (DF-301 commercially available from Dongyue) according to Table 1, and add deionized water to reduce the solid content of the emulsion to below 5% based on the initial solid content of the emulsion;

[0098] - adding carbon nanotubes and carbon black according to Table 1 (the contents shown in Table 1 are calculated based on the total weight of the binder) to the polymer emulsion under stirring, wherein the carbon nanotubes are added in the form of a dispersion, and continuously stirring to fully disperse the carbon nanotubes and carbon black;

[0099] - Collect the adhesive after drying.

[0100] The SEM image of the binder obtained in Example 1 is shown in FIG1 , from which it can be seen that small particles of carbon black and linear carbon nanotubes are dispersed inside the polymer.

[0101] The Raman spectrum of the carbon nanotubes used in Example 1 is shown in FIG2 , and it can be seen that the D / G ratio of the carbon nanotubes is 0.6.

[0102] Preparation of positive electrode:

[0103] - A commercially available lithium iron phosphate positive electrode material and the binder prepared in this example were mixed to form an electrode mixture, wherein the content of the binder in the electrode mixture was 3 parts by weight and the content of the lithium iron phosphate positive electrode material was 100 parts by weight.

[0104] - pre-fiberizing and re-fiberizing the electrode mixture to obtain a fiberized mixture;

[0105] - Roll-pressing the fiberized mixture at a temperature of 30° C. to 90° C. with a linear pressure of 0.01 t / cm to 1 t / cm to obtain a positive dry electrode film;

[0106] - At a temperature of 80°C to 120°C, the dry electrode film and aluminum foil are rolled to obtain the positive electrode sheet, with a linear pressure of 0.01t / cm to 10.5 and a composite roller diameter of more than 600mm.

[0107] Preparation of lithium-ion button batteries: Cut the positive electrode sheet with a diameter of 13 mm, and the counter electrode is a lithium sheet with a diameter of 13 mm; add LiPF6 to a solvent mixed with propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (PC:EC:DEC weight ratio of 1:1:1), and mix evenly to obtain an electrolyte with a LiPF6 molar concentration of 1M; package the positive electrode sheet, separator, negative electrode sheet (lithium sheet), electrolyte, battery shell and other accessories on a packaging machine to obtain a button battery.

[0108] Examples 2-9, 11-12

[0109] Examples 2-9, 11-12 were carried out with reference to Example 1, except that the contents and parameters of the polymer, carbon black, and carbon nanotubes were selected according to Table 1.

[0110] Example 10

[0111] Example 10 was carried out with reference to Example 1, except that the contents and parameters of the polymer, carbon black, and carbon nanotubes were selected according to Table 1, and the positive electrode was prepared by the following method:

[0112] - Mixing a commercially available lithium iron phosphate cathode material with carbon black to obtain an electrode premix, wherein the carbon black content is 0.6 parts by weight and the lithium iron phosphate cathode material content is 100 parts by weight;

[0113] - The electrode premix and the binder prepared in this embodiment are mixed to form an electrode mixture, wherein the content of the binder is 3 parts by weight and the content of the lithium iron phosphate positive electrode material is 100 parts by weight.

[0114] - pre-fiberizing and re-fiberizing the second mixture to obtain a fiberized second mixture;

[0115] - rolling the fiberized second mixture at a temperature of 30° C. to 90° C. with a linear pressure of 0.01 t / cm to 1 t / cm to obtain a positive dry electrode film;

[0116] - At a temperature of 80°C to 120°C, the dry electrode film and aluminum foil are rolled to obtain the positive electrode sheet, with a linear pressure of 0.01t / cm to 10.5 and a composite roller diameter of more than 600mm.

[0117] Comparative Examples 1-8

[0118] Comparative Examples 1-8 were carried out with reference to Example 1, except that the contents and parameters of the polymer, carbon black, and carbon nanotubes were selected according to Table 1.

[0119] Performance tests were performed on the carbon nanotubes, carbon black, binders, and button cells from Examples 1-12 and Comparative Examples 1-8. The test results are shown in Table 1.

[0120] Comparative Example 9

[0121] Preparation of positive electrode:

[0122] -A commercially available lithium iron phosphate positive electrode material (the same as in Example 1), a dry binder obtained by drying a polytetrafluoroethylene emulsion (DF-301 from Dongyue), carbon nanotubes (the same as in Example 1), and carbon black (the same as in Example 1) were mixed to form an electrode mixture, wherein the content of the polytetrafluoroethylene binder was 2.1 parts by weight, the content of the lithium iron phosphate positive electrode material was 100 parts by weight, the content of the carbon nanotubes was 0.225 parts by weight, and the content of the carbon black was 0.675 parts by weight.

[0123] - pre-fiberizing and re-fiberizing the electrode mixture to obtain a fiberized mixture;

[0124] - Roll-pressing the fiberized mixture at a temperature of 30° C. to 90° C. with a linear pressure of 0.01 t / cm to 1 t / cm to obtain a positive dry electrode film;

[0125] - At a temperature of 80°C to 120°C, the dry electrode film and aluminum foil are rolled to obtain the positive electrode sheet, with a linear pressure of 0.01t / cm to 10.5 and a composite roller diameter of more than 600mm.

[0126] Preparation of lithium-ion button batteries: Cut the positive electrode sheet with a diameter of 13 mm, and the counter electrode is a lithium sheet with a diameter of 13 mm; add LiPF6 to a solvent mixed with propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (PC:EC:DEC weight ratio of 1:1:1), and mix evenly to obtain an electrolyte with a LiPF6 molar concentration of 1M; package the positive electrode sheet, separator, negative electrode sheet (lithium sheet), electrolyte, battery shell and other accessories on a packaging machine to obtain a button battery.

[0127] The button cell of Comparative Example 9 was subjected to a performance test, and the test results are shown in Table 1.

[0128] Table 1

[0129] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that certain modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims, and such modifications and changes also fall within the scope of protection of the present application.

Claims

1. A dry electrode film, comprising an active material and a binder, characterized in that: The binder comprises a polymer and carbon nanotubes and carbon black dispersed in the polymer, wherein the average diameter of the carbon nanotubes is 13 nm to 100 nm, the D / G ratio of the carbon nanotubes is 0.5 to 1.4, and wherein, based on the total weight of the binder, the sum of the contents of the carbon nanotubes and the carbon black is greater than 5 wt %, and the content of the polymer is greater than 40 wt %, Wherein, the weight ratio of the carbon black to the carbon nanotubes is 8:1 to 1:

8.

2. The dry electrode film according to claim 1, characterized in that: The dry electrode film is an electrode film that does not contain a solvent, and in particular, the dry electrode film does not contain N-methylpyrrolidone.

3. The dry electrode film according to claim 1 or 2, characterized in that: The polymer includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, styrene, polyacrylonitrile, polyvinyl chloride, polyacrylic acid, polychlorotrifluoroethylene and polyacrylate.

4. The dry electrode film according to any one of claims 1 to 3, characterized in that: The average diameter of the carbon nanotubes is 15 nm to 80 nm, and / or the D / G ratio of the carbon nanotubes is 0.6 to 1.

3.

5. The dry electrode film according to any one of claims 1 to 4, characterized in that: The length of the carbon nanotubes is 0.8 μm to 17 μm, preferably 8 μm to 15 μm.

6. The dry electrode film according to any one of claims 1 to 5, characterized in that: Based on the total weight of the dry electrode film, the content of the binder is 0.5 wt % to 4.0 wt %, and / or Based on the total weight of the binder, the content of the polymer is 50 wt % to 92 wt %, the content of the carbon nanotube is 1 wt % to 30 wt %, and the content of the carbon black is 5 wt % to 35 wt %.

7. The dry electrode film according to any one of claims 1 to 6, characterized in that: At least one of the following conditions is met: (i) the average particle size of the carbon black is 35 nm to 60 nm; (ii) the carbon black has an oil absorption value of 120 mL / 100 g to 300 mL / 100 g; (iii) The specific surface area of ​​the carbon black is 40 m 2 / g to 90m 2 / g; (iv) the ratio of the weight of the polymer to the sum of the weights of the carbon nanotubes and the carbon black is 9:1 to 1:1; (v) The weight ratio of the carbon black to the carbon nanotubes is 4:1 to 1:

4.

8. A method for preparing a dry electrode film according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: (a) providing a polymer emulsion, wherein the polymer comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, styrene, polyacrylonitrile, polyvinyl chloride, polyacrylic acid, polychlorotrifluoroethylene and polyacrylate, and the solid content of the emulsion is less than 5%; (b) adding carbon nanotubes and carbon black to the emulsion obtained in step (a) under stirring, wherein the average diameter of the carbon nanotubes is 13 nm to 100 nm, and the D / G ratio of the carbon nanotubes is 0.5 to 1.4, to obtain an emulsion in which the carbon nanotubes and the carbon black are dispersed; (c) drying the emulsion obtained in step (b) to obtain a dry binder; (d) mixing the active material and the dry binder obtained in step (c), and obtaining the dry electrode film by rolling.

9. A secondary battery, characterized in that: The secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein at least one of the positive electrode sheet and the negative electrode sheet comprises the dry electrode film according to any one of claims 1 to 7.

10. An electronic device, characterized in that: The electronic device includes the secondary battery according to claim 9.

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