A dry electrode, a method of manufacturing the same, and a battery

Abstract

The application provides a dry electrode and a preparation method and a battery, and particularly relates to the technical field of batteries. The dry electrode comprises a current collector and a dry electrode film arranged on at least one side surface of the current collector, wherein the dry electrode film comprises an active material, a conductive agent, a first binder and a second binder, the first binder comprises polytetrafluoroethylene, and the second binder is selected from ionomers. The first binder and the second binder are simultaneously added in the dry electrode, so that the adhesion of the dry electrode is improved, and the electrical properties such as the initial efficiency, the rate, the cycle and the like of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a dry electrode, its preparation method, and a battery. Background Technology

[0002] Electrode production is the primary step in battery cell manufacturing and one of the factors affecting the basic performance of the battery cell. Currently, most electrode sheets are prepared using a wet coating method. This method is not only complex, but the evaporation of solvents during preparation can easily cause environmental pollution. Furthermore, the wet stirring coating process can easily lead to problems such as gelation, coating cracking, and binder floating. In addition, there is the issue of solvent residue in the coated electrode. Achieving effective solvent recovery during electrode sheet preparation requires high-capacity equipment, which also increases process costs.

[0003] Dry electrode technology, as a new production process for lithium-ion batteries, has the following advantages compared to conventional wet electrodes: the process is simple and there is no problem of solvent evaporation, resulting in significantly reduced equipment investment and energy consumption; at the same time, under conditions such as high temperature and electrolyte, dry electrodes prepared by the dry process have better bonding performance and adhesion, which can further improve the overall performance of the battery.

[0004] Existing dry processes mainly include the binder fibrillation method and the electrostatic spraying method. The electrostatic spraying method is inferior to the binder fibrillation method in terms of processability, adhesion stability, electrode flexibility, and durability. The binder fibrillation method involves mixing a fibrous binder with the active electrode material, drawing it into fibers, hot-pressing it into a film, and finally thermally bonding it with the current collector. Currently, the most common binder is polytetrafluoroethylene (PTFE), but PTFE is prone to lithium intercalation at low voltages, resulting in reduced initial efficiency, and PTFE-based electrodes have relatively low adhesion and cohesion.

[0005] Therefore, there is a need to provide a dry electrode, its preparation method, and a battery to solve the above problems. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the present invention provides a dry electrode, a method for preparing the same, and a battery, to improve the problems of reduced initial efficiency and low adhesion caused by lithium intercalation of the binder polytetrafluoroethylene under low pressure in dry electrodes.

[0007] To achieve the above and other related objectives, the present invention provides a dry electrode comprising: a current collector and a dry electrode film disposed on at least one side surface of the current collector, wherein the dry electrode film comprises an active material, a conductive agent, a first binder and a second binder, the first binder comprising polytetrafluoroethylene and the second binder selected from ionomers.

[0008] In one example of the present invention, the second adhesive is selected from at least one of the compounds shown in formula (1), formula (3) and formula (7):

[0009]

[0010] In equation (1), the value range of x1 is 1500 to 3000, the value range of y1 is 1400 to 2800, and the structural formula of R1 is shown in equation (2):

[0011]

[0012] In equation (2), the value of 'a' ranges from 1 to 3;

[0013]

[0014] In equation (3), x2 ranges from 1000 to 2000, y2 ranges from 1000 to 2300, b ranges from 4 to 8, and R2 is selected from any one of equations (4) to (6):

[0015]

[0016] In equation (4), the value of c ranges from 1 to 3; in equation (6), the value of d ranges from 1 to 4.

[0017]

[0018] In equation (7), the value range of x3 is 900 to 1700; the value range of y3 is 800 to 1600; the value range of z is 900 to 1900; and the value range of e is 4 to 8.

[0019] In one example of the present invention, the dry electrode is a positive electrode sheet, and based on the total mass of the dry electrode film, the content of the active material is 91.0 to 98.6 wt%, the content of the conductive agent is 0.4 to 5 wt%, the content of the first binder is 0.2 to 1 wt%, and the content of the second binder is 0.8 to 3 wt%.

[0020] In one example of the present invention, the dry electrode is a negative electrode sheet, and based on the total mass of the dry electrode film, the content of the active material is 91.7-98.5 wt%, the content of the conductive agent is 0.2-5 wt%, the content of the first binder is 0.1-0.3 wt%, and the content of the second binder is 1.2-5 wt%.

[0021] Another aspect of the present invention provides a method for preparing a dry electrode, the method comprising: a dry powder mixing step, wherein an active material, a conductive agent, a first binder, and a second binder are mixed uniformly to obtain a first mixture; a fiberization step, wherein the first mixture is subjected to fiberization treatment under shearing to obtain a second mixture; a film forming step, wherein the second mixture is extruded to form a dry electrode film; and a composite step, wherein the dry electrode film is rolled thinned and composited with a current collector to obtain a dry electrode.

[0022] In one example of the present invention, the dry powder mixing step includes: mixing the active material, the conductive agent, the first binder and the second binder at a temperature of -40 to 0°C for 15 to 30 minutes.

[0023] In one example of the present invention, the fiberization step includes: pre-fiberizing the first mixture at 60-120°C for 30 minutes, and then dispersing it under shear force for 15-60 minutes.

[0024] In one example of the present invention, the film-forming step includes: mixing and conveying the second mixture by a screw and extruding it through a die to form a dry electrode film, wherein the temperature of the screw is 120-160°C and the thickness of the dry electrode film is 2-7 μm.

[0025] In one example of the present invention, the composite step includes: thinning the dry electrode film to 0.5-2 mm by rolling, and then hot rolling composite with the current collector to form a dry electrode, wherein the rolling pressure of the hot rolling composite is 3-50T and the rolling temperature is 80-160℃.

[0026] The present invention also provides a battery comprising the dry electrode described above.

[0027] This invention simultaneously incorporates a first binder, polytetrafluoroethylene (PTFE), and a second binder into a dry electrode. PTFE, acting as a binder, undergoes fibrosis under shear force to form a network structure, which is used to bond the active material and the conductive agent. The second binder is selected from an ionomer; during the high-temperature mixing and extrusion film formation process, this ionomer achieves in-situ crosslinking, resulting in a more uniform distribution within the electrode and promoting Li... + Transmission ensures good interface contact; Li + Electrostatic coupling between the sulfonate terminus and the quaternary ammonium cation is beneficial for promoting Li + The conductive properties of the dynamic cross-linked network binder, composed of hydrogen bonds and electrostatic interactions, enable it to repair cracks in the electrode and maintain structural integrity during long-term cycling, thereby improving the cycle performance of the battery.

[0028] This invention employs a dry process that eliminates the need for solvents, thus avoiding solvent residue in the electrodes, reducing equipment investment, energy consumption, and costs. Furthermore, the use of high-temperature multi-stage rolling improves the consistency of the electrode sheets, enabling the production of thicker electrodes. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the dry electrode of the present invention in one embodiment;

[0031] Figure 2 This is a flowchart of one embodiment of the dry electrode preparation method of the present invention;

[0032] Figure 3 This is a schematic diagram illustrating a method for preparing the dry electrode of the present invention, which employs single-screw extrusion film formation and roll pressing in one embodiment.

[0033] Figure 4 This is a schematic diagram illustrating the preparation method of the dry electrode of the present invention in one embodiment, which employs twin-screw extrusion film formation and roll pressing for composite deposition.

[0034] Figure 5 This is a schematic diagram of a four-roller compounding process used in one embodiment of the dry electrode preparation method of the present invention.

[0035] Figure 6 This is a schematic diagram illustrating the extrusion film formation, thinning, and composite processes in one embodiment of the dry electrode preparation method of the present invention.

[0036] Figure Labels

[0037] 10. Dry electrode; 11. Current collector; 12. Dry electrode film; 20. Single screw extruder; 21. Die head; 30. Winding mechanism; 40. Unwinding mechanism; 50. Compounding mechanism; 60. Twin screw extruder; 70. Double rollers. Detailed Implementation

[0038] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0041] In this article, the terms "multiple," "various," and "multiple times" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0042] In this document, terms such as "preferred," "better," and "more effective" are merely descriptions of more effective implementation methods or embodiments, and should be understood not to limit the scope of protection of this invention. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0043] In this document, terms such as "further," "even further," and "particularly" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0044] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0045] Please see Figure 1This invention provides a dry electrode 10, which includes a current collector 11 and a dry electrode film 12. The dry electrode film 12 is disposed on at least one side of the current collector 11, meaning the current collector 11 has two opposing first and second surfaces along its thickness direction. The dry electrode film 12 can be disposed on either the first or second surface, or it can be disposed on both the first and second surfaces. The dry electrode film 12 includes an active material, a conductive agent, a first binder, and a second binder. The first binder includes polytetrafluoroethylene (PTFE), and the second binder is selected from ionomers.

[0046] Please see Figure 1 The material of the current collector 11 can be selected according to the type of dry electrode 10. For example, if the dry electrode is a positive electrode sheet, the current collector 11 can be aluminum foil with a thickness of 5 to 20 μm, or 10 to 15 μm, or even 12 μm. The current collector 11 can also be a composite current collector, which uses a polymer insulating resin material as a "sandwich" layer, with aluminum deposited on its upper and lower surfaces. The polymer resin can be polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polystyrene (PS), polyamide (PA), etc. If the electrode is a negative electrode, the current collector 11 can be a copper foil with a thickness of 4-15 μm, or even 5-10 μm, or 8 μm. The current collector 11 can also be a composite current collector, which uses a polymer insulating resin material as a "sandwich" layer with copper deposited on both the top and bottom surfaces. The polymer resin can be selected from polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polystyrene (PS), polyamide (PA), etc.

[0047] Please see Figure 1 The active material in the dry electrode film 12 is the main substance participating in the electrochemical reaction. The selection of the active material is related to the battery type and the type of dry electrode 10. Taking a lithium-ion battery as an example, when the dry electrode is a positive electrode sheet, the active material is selected from one or more of lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), ternary materials, lithium-rich materials, polyanionic materials, and lithium-sulfur positive electrode materials. Among them, ternary materials include, but are not limited to, LiNi 0.5 Mn 1.5 O4, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNiCoAlO2; polyanionic materials such as lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), or borate, sulfate, and other polyanionic cathode materials. That is, the active material can be any one of the materials listed above, or any combination of two or more, without limitation. Of course, the active material can also be a cathode material not listed above. When the dry electrode 10 is a negative electrode, the active material is selected from one or more mixtures of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, silicon, silicon suboxide, silicon-carbon composite materials, silicon / germanium composite materials, lithium titanate, and lithium. For example, the active material is artificial graphite, or a mixture of artificial graphite and silicon, etc. When the active material is a composition of two or more materials, there is no limitation on the ratio between the components in the composition; they can be mixed in any proportion.

[0048] The conductive agent in the dry electrode film 12 can improve electronic conductivity. To ensure good charge and discharge performance of the battery, it collects micro-currents between active materials and between active materials and current collectors, thereby reducing battery contact resistance and accelerating electron mobility. Additionally, the conductive agent can improve electrode processability, promote electrolyte wetting of the electrode, and effectively increase the migration rate of lithium ions in the battery materials, thus improving battery charge and discharge efficiency and battery life. The conductive agent includes, but is not limited to, carbon black, acetylene black, carbon nanotubes, carbon fibers, graphene, and Ketjen black. The conductive agent can be any one of the materials listed above, or any combination of two or more of the materials listed above. For example, the conductive agent can be carbon black; or carbon nanotubes; or a combination of carbon black and acetylene black; or a combination of carbon fibers, acetylene black, and graphene, etc. It should be noted that when the conductive agent is a combination of multiple components, there are no restrictions on the proportions of the components within the composition; they can be mixed in any proportion.

[0049] The binder in the dry electrode film 12 is used to bond the active material and the conductive agent. The inventors found that using polytetrafluoroethylene (PTFE) as a binder easily leads to lithium intercalation at low voltages, resulting in reduced battery efficiency and low adhesion. Therefore, the binder of this invention includes a first binder and a second binder. The first binder includes PTFE, which undergoes fibrosis under high shear force to form a rich fibrous network between the active material and the conductive agent. In this invention, the molecular weight of PTFE is 60W to 120W, for example, 60W, 80W, 700W, or 120W, and the relative standard density (SSG) is 2.1 to 2.3, for example, 2.1, 2.2, or 2.3. In other embodiments, the first binder may also be carboxymethyl cellulose (CMC) or polyvinylidene fluoride (PVDF). The second binder is selected from ionomers. Ionomers can achieve in-situ crosslinking at high temperatures, resulting in a more uniform distribution of the ionomer in the dry electrode film 12 and promoting Li-ionization. + The transport of these components ensures good interfacial contact; secondly, the sulfonate ions and quaternary ammonium cations in the ionomer react with Li... + Electrostatic coupling between them is beneficial to promoting Li + The conductive properties of the dynamic cross-linked network binder, composed of hydrogen bonds and electrostatic interactions, enable it to repair cracks in the electrode and maintain structural integrity during long-term cycling, thereby improving the cycle performance of the battery.

[0050] In some embodiments, the second adhesive may be selected from any one of the compounds shown in structural formula (1), structural formula (3) and structural formula (7) below, or may be any combination of two or more:

[0051]

[0052] In equation (1), the value of x1 ranges from 1500 to 3000, meaning x1 can be any value within this range, such as 1500, 2000, 2500, or 3000; the value of y1 ranges from 1400 to 2800, meaning y1 can be any value within this range, such as 1400, 2000, 2500, or 2800; the structure of R1 is shown in equation (2):

[0053]

[0054] The value of a in equation (2) is 1 to 3. For example, a can be 1, 2, or 3.

[0055] The second binder shown in formula (1) can be prepared by conventional methods in the art, for example: CF2=CF2 and CF2=CFR1 are mixed in a certain molar ratio and polymerized under the action of an initiator and a catalyst at 50~140℃ and 2~6MPa to form the above binder. The molar ratio of CF2=CF2 to CF2=CFR1 can be 1:1. The initiator can be selected from perfluoroalkyl sulfonate, and the catalyst can be ammonium persulfate. The specific reaction temperature and reaction pressure can be selected within the above range. For example, the reaction temperature can be 50℃, 80℃, 100℃, 140℃, etc., and the reaction pressure can be 2MPa, 4MPa or 6MPa, etc.

[0056]

[0057] In equation (3), the value of x2 ranges from 1000 to 2000, further from 1300 to 1700, and even further from 1500; the value of y2 ranges from 1000 to 2300, further from 1500 to 2000, and even further from 1800; the value of b ranges from 4 to 8, and further from 4, 6, or 8, etc. R2 is selected from any one of equations (4) to (6):

[0058]

[0059] In equation (4), the value of c ranges from 1 to 3. For example, c can take the values ​​1, 2 or 3, etc.

[0060]

[0061] In equation (6), the value of d ranges from 1 to 4. For example, d can be 1, 2, 3 or 4.

[0062] The second binder shown in formula (3) can be prepared using methods conventional in the art, for example, by using CH2=CHCOO(CH2CH2O). b The binder was synthesized by mixing CH2=CHR2 at a specific molar ratio and under tert-butyl peroxide catalysis at 120–180 °C and 15–25 MPa. CH2=CHCOO(CH2CH2O) b The molar ratio of CH2=CHR2 can be 1:1, and the reaction temperature and pressure can be any value within the range listed above. For example, the reaction temperature can be 120℃, 150℃ or 180℃, etc.; the reaction pressure can be 15MPa, 20MPa or 25MPa, etc. The R2 group in formula (3) is the same as the R2 in the reactant CH2=CHR2.

[0063]

[0064] In equation (7), the value range of x3 is 900 to 1700, and further, the value range of x3 is 1000 to 1500, such as 1200 or 1400; the value range of y3 is 800 to 1600, and further, the value range of y3 is 1000 to 1500, such as 1200, 1300 or 1500; the value range of z is 900 to 1900, and further, the value range of z is 1200 to 1700, and even further, z can be 1400 or 1600; the value range of e is 4 to 8, for example, e can be 4, 6 or 8.

[0065] The second binder shown in formula (7) can be prepared using methods conventional in the art. For example, CH2=CHCOO(CH2CH2O) can be used as a binder. e CH2=CHCOOCH2CH2OH and CH2=CHCOOCH2CH2N + (CH3)2CH2CH2CH2SO3Li is mixed in a certain molar ratio and synthesized by catalysis with tert-butyl peroxide at 130-200℃ and 25-30MPa. The molar ratio of the reactants is 1:1:1. The reaction temperature and reaction pressure can be any values ​​within the above range. For example, the reaction temperature can be 130℃, 150℃, 180℃ or 200℃, etc., and the reaction pressure can be 25MPa, 28MPa or 300MPa, etc.

[0066] The ratio of active material, conductive agent, first binder, and second binder in the aforementioned dry electrode is related to the type of dry electrode. When the dry electrode is a positive electrode sheet, based on the total mass of the dry electrode film, the active material accounts for 91.0–98.6 wt% of the dry electrode film, for example, 93 wt%, 95 wt%, 98 wt%, etc.; the conductive agent accounts for 0.4–5 wt% of the dry electrode film, for example, 0.4 wt%, 1 wt%, 3 wt%, or 5 wt%, etc.; the first binder accounts for 0.2–1 wt% of the dry electrode film, for example, 0.2 wt%, 0.5 wt%, 0.8 wt%, or 1 wt%; and the second binder accounts for 0.8–3 wt% of the dry electrode film, for example, 0.8 wt%, 1 wt%, 2 wt%, or 3 wt%, etc. When the dry electrode is the negative electrode sheet, based on the total mass of the dry electrode film, the active material accounts for 91.7 to 98.5 wt% of the dry electrode film, for example, 91.7 wt%, 93 wt%, 95 wt%, or 98.5 wt%; the conductive agent accounts for 0.2 to 5 wt% of the dry electrode film, for example, 0.2 wt%, 2 wt%, 3 wt%, or 5 wt%; the first binder accounts for 0.1 to 0.3 wt% of the dry electrode film, for example, 0.1 wt%, 0.2 wt%, or 0.3 wt%; and the second binder accounts for 1.2 to 5 wt% of the dry electrode film, for example, 1.2 wt%, 2 wt%, 3 wt%, or 5 wt%.

[0067] Please see Figure 1 and Figure 2 In another aspect, the present invention provides a method for preparing the above-mentioned dry electrode, comprising at least the following steps:

[0068] S1. Dry powder mixing step: The active material, conductive agent, first binder and second binder are mixed evenly to obtain the first mixture.

[0069] S2, Fiberization step: The first mixture is fiberized under shear force to obtain the second mixture;

[0070] S3, film forming step: extruding the second mixture to obtain the dry electrode film 12;

[0071] S4. Composite step: The dry electrode film 12 and the current collector 11 are hot-rolled and composited to obtain the dry electrode 10.

[0072] Please see Figure 2In step S1, the types of active material, conductive agent, first binder, and second binder are related to the battery type and electrode type, as detailed above. The proportions of each component are related to the electrode type: when the dry electrode is a positive electrode, the active material accounts for 91.0–98.6 wt% of the dry electrode film, the conductive agent accounts for 0.4–5 wt%, the first binder accounts for 0.2–1 wt%, and the second binder accounts for 0.8–3 wt%; when the dry electrode is a negative electrode, the active material accounts for 91.7–98.5 wt%, the conductive agent accounts for 0.2–5 wt%, the first binder accounts for 0.1–0.3 wt%, and the second binder accounts for 1.2–5 wt%. Specific proportions can be selected within the above ranges according to actual needs.

[0073] Step S1 involves mixing the above-mentioned active material, conductive agent, first binder, and second binder uniformly according to a certain ratio. The specific mixing method is not limited here; any method that can uniformly mix the components can be used. For example, the active material, conductive agent, first binder, and second binder are placed in a premixing device, such as a high-speed disperser, according to a certain ratio, and premixed at a low temperature of -40℃ to 0℃ for 15 to 30 minutes to ensure thorough dispersion. The premixing temperature and time can be any value within the above range; for example, the premixing temperature can be -40℃, -20℃, or 0℃, and the premixing time can be 15 minutes, 20 minutes, 25 minutes, or 30 minutes. Mixing under low-temperature conditions can effectively inhibit premature fiberization of polytetrafluoroethylene (PTFE), and at low temperature and high speed, the fine binder powder can fully contact the active material and conductive agent, resulting in more uniform mixing.

[0074] Please see Figure 2 Step S2 involves fiberizing the first mixture obtained in step S1 under high shear force, causing the first binder to form a rich fibrous network between the active material and the conductive agent, significantly improving the adhesion strength of the dry film. The specific fiberization process is as follows: First, the first mixture obtained in step S1 is pre-fiberized at 60–120°C for 30 minutes, softening and loosening the polytetrafluoroethylene (PTFE) binder, which is beneficial for subsequent fiberization. Then, it is dispersed at high speed for 15–60 minutes to allow the PTFE to fiberize under shear force, forming a rich network structure. The pre-fiberization temperature can be 60°C, 80°C, 100°C, or 120°C, etc., and the fiberization time can be 15 minutes, 25 minutes, 40 minutes, or 60 minutes, etc.

[0075] Please see Figure 2 , Figure 3 and Figure 4 In step S3, the second mixture obtained in step S2 is extruded to form a dry electrode film. Specifically, the second mixture is placed in a screw extruder, and the dry electrode film 12 is formed by screw mixing and conveying, and die extrusion. The screw extruder can be a single-screw extruder 20 or a twin-screw extruder 60. The die 21 of the screw extruder can be either a coat hanger type or a plunger type, without limitation. The screw extrusion temperature is 120–160℃, for example, 120℃, 140℃, or 160℃. At this temperature, the second mixture is mixed and extruded, and the second binder achieves in-situ crosslinking, resulting in a more uniform distribution of the second binder in the electrode and promoting Li... + The transmission ensures good interface contact; at the same time, Li + The electrostatic coupling between the sulfonate terminals and the quaternary ammonium cations in the second binder is beneficial for promoting Li + The conductive properties, along with the self-healing function of the dynamic cross-linked network binder composed of hydrogen bonds and electrostatic interactions, enable it to repair cracks in the electrode and maintain structural integrity during long-term cycling. The thickness of the extruded dry electrode film 12 is 2–7 mm, for example, 2 mm, 5 mm, or 7 mm, etc.

[0076] Please see Figures 2 to 4 In step S4, the dry electrode film 12 obtained in step S3 is combined with the current collector 11 to form the dry electrode 10. The material of the current collector is related to the type of dry electrode. When the dry electrode is a positive electrode sheet, the current collector 11 can be aluminum foil with a thickness of 5-20 μm, further, the thickness of the aluminum foil is 10-15 μm, and even further, the thickness of the aluminum foil is 12 μm. The current collector 11 can also be a composite current collector, which uses a polymer insulating resin material as a "sandwich" layer, with aluminum deposited on its upper and lower surfaces. The polymer resin can be polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polystyrene (PS), or polyamide (PA). When the dry electrode is the negative electrode, the current collector 11 can be a copper foil with a thickness of 4-15 μm, further, the thickness of the copper foil is 5-10 μm, and even further, the thickness of the copper foil is 8 μm; the current collector 11 can also be a composite current collector, which uses a polymer insulating resin material as a "sandwich" layer, with copper deposited on both the top and bottom surfaces. The polymer resin can be selected from polyethylene terephthalate PET, polypropylene PP, polyimide PI, polystyrene PS, polyamide PA, etc.

[0077] Please see Figures 2 to 6The specific steps of step S4 are as follows: the extruded dry electrode film 12 is conveyed to the composite mechanism 50, and at the same time the unwinding mechanism 40 sends the current collector 11 into the composite mechanism 50. The dry electrode film 12 and the current collector 11 are rolled together by the composite mechanism 50 to form a dry electrode 10, which is then collected and stored by the winding mechanism 30. The aforementioned composite mechanism 50 can be a three-roller press or a four-roller press. In the three-roller mode, the roller speed ratio A:B:C = 1:1:1.5 to 1:2.5:5.5, for example, 1:1:1.5, 1:1.5:3.5, or 1:2.5:5.5, etc. In the four-roller mode, the roller speed ratio A:B:C:D = 1:1:1:1.5 to 1:2.5:2.5:5, for example, 1:1:1:1.5, 1:1.5:1.5:3, or 1:2.5:2.5:5, etc. The rolling pressure can be any value from 3 to 50T, such as 3T, 10T, 30T or 50T, etc., and the rolling temperature can be any value from 80 to 160℃, such as 80℃, 120℃ or 160℃, etc.; preferably, before rolling composite, the dry electrode film 12 can be thinned to 0.5 to 2mm using the rollers 70, such as 0.5mm, 1mm, 1.5mm or 2mm, etc., and then hot-rolled composite with the current collector 11 to form the dry electrode 10.

[0078] The present invention also provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is disposed between the positive and negative electrode and serves as an isolation agent; the electrolyte permeates the positive and negative electrode within the casing and serves to conduct lithium ions; the positive and / or negative electrode is a dry electrode as described above, or is prepared using the preparation method described above.

[0079] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0080] Example 1

[0081] Cathode preparation: The cathode active material LiNi is prepared... 0.6 Co 0.2 Mn 0.2O2:SP:first binder PTFE:second binder are premixed at -10℃ for 20 min by mass ratio of 96.0%:2.0%:0.5%:1.5%, then kept at 80℃ for 30 min and dispersed at high speed for 30 min. The mixture is then extruded at 100℃ using a single-screw extruder to form a 5 mm dry electrode film, which is then thinned and laminated to form the positive electrode sheet. The current collector is made of 12 μm aluminum foil.

[0082] Negative electrode preparation: The negative electrode active material, artificial graphite:SP:first binder PTFE:second binder, was premixed at -10℃ for 20 min at a mass ratio of 97.45%:0.4%:0.15%:2%, then kept at 80℃ for 30 min, and dispersed at high speed for 30 min. The mixture was then extruded at 100℃ using a single-screw extruder to form a 6 mm dry electrode film. The film was then thinned and laminated to form the negative electrode sheet. An 8 μm copper foil was used as the current collector.

[0083] Cell fabrication: The positive and negative electrode sheets are rolled and die-cut, and then wound, packaged, injected with liquefaction and other processes to complete the cell fabrication.

[0084] The structural formula of the second binder in the positive and negative electrode plates is as follows:

[0085]

[0086] In the formula, x is 2250 and y is 2100.

[0087] Example 2

[0088] The difference between this embodiment and Embodiment 1 is that the second binder in the positive and negative electrode sheets is replaced with a compound shown in the following structural formula:

[0089]

[0090] In the formula, x is 1500 and y is 1500.

[0091] Example 3

[0092] The difference between this embodiment and Embodiment 1 is that the second binder in the positive and negative electrode sheets is replaced with a compound shown in the following structural formula:

[0093]

[0094] In the formula, x is 1500 and y is 1905.

[0095] Example 4

[0096] The difference between this embodiment and Embodiment 1 is that the second binder in the positive and negative electrode sheets is replaced with a compound shown in the following structural formula:

[0097]

[0098] In the formula, x is 1500 and y is 1283.

[0099] Example 5

[0100] The difference between this embodiment and Embodiment 1 is that the second binder in the positive and negative electrode sheets is replaced with a compound shown in the following structural formula:

[0101]

[0102] In the formula, x is 1250, y is 1100, z is 1150, and e is 5.

[0103] Example 6

[0104] The difference between this embodiment and Embodiment 1 is that the proportions of the materials in the positive electrode are adjusted to: LiNi 0.6 Co 0.2 Mn 0.2 O2:SP: First binder PTFE: Second binder = 95%: 2.0%: 0.5%: 2.5%.

[0105] Example 7

[0106] The difference between this embodiment and Embodiment 1 is that the proportions of the materials in the positive electrode are adjusted to: LiNi 0.6 Co 0.2 Mn 0.2 O2:SP: First binder PTFE: Second binder = 96%: 2.0%: 1%: 1%.

[0107] Example 8

[0108] The difference between this embodiment and Embodiment 1 is that the proportions of the materials in the negative electrode sheet are adjusted to: artificial graphite: SP: first binder PTFE: second binder = 96.45%: 0.4%: 0.15%: 3%.

[0109] Example 9

[0110] The difference between this embodiment and Embodiment 1 is that the proportions of the materials in the negative electrode sheet are adjusted to: artificial graphite: SP: first binder PTFE: second binder = 97.8%: 0.4%: 0.3%: 1.5%.

[0111] Comparative Example 1

[0112] Cathode preparation: The cathode active material LiNi is prepared... 0.6 Co 0.2 Mn 0.2O2:CNT:SP:binder PVDF:dispersant PVP are uniformly dispersed in a mass ratio of 96.9%:0.8%:1.0%:1.0%:0.3%, with NMP as the solvent and a solid content of 75%. The mixture is coated on the current collector and then dried, rolled, and slit to form a positive electrode sheet.

[0113] Negative electrode preparation: The negative electrode active material artificial graphite: SP: thickener CMC: binder SBR is dispersed evenly in a mass ratio of 97.1%: 0.4%: 1.0%: 1.5%, with water as the solvent and a solid content of 55%. The mixture is coated on the current collector and then dried, rolled, and slit to form the positive electrode sheet.

[0114] The positive and negative electrode sheets are rolled and die-cut, and then wound, packaged, injected with liquefaction and other processes to complete the cell preparation.

[0115] Comparative Example 2:

[0116] Positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2:SP: binder PTFE, mixed in a mass ratio of 95.5%:2.0%:2.5% to form fibers, then thinned by roll forming to form a positive electrode sheet.

[0117] The negative electrode active material is artificial graphite: SP: binder PTFE, which are mixed in a mass ratio of 97.1%:0.4%:2.5% to form a fiber. After being thinned by roll pressing, the fiber is formed into a negative electrode sheet.

[0118] The positive and negative electrode sheets are rolled and die-cut, and then wound, packaged, injected with liquefaction and other processes to complete the cell preparation.

[0119] The electrode sheets and cells prepared in Examples 1 to 9 and Comparative Examples 1 to 2 were subjected to performance tests. The test methods are shown below, and the test results are shown in Table 1.

[0120] (1) Adhesion test:

[0121] The prepared electrode sheet is cut to 20*100mm. The side to be tested is glued to the stainless steel plate with double-sided tape and pressed with a pressure roller to make it completely adhere to the electrode sheet. One end of the stainless steel plate is fixed to the lower clamp of the tensile testing machine, and the bent end of the sample is fixed to the upper clamp. The tensile speed is 50mm / min.

[0122] (2) Ratio Test:

[0123] The battery cell was charged at 1 / 3C constant current to 4.2V, then charged at constant voltage to 0.05C, and left to rest for 30 minutes. 1 / 3C0 was then discharged to 3V, and left to rest for 30 minutes. The discharge capacity C0 was recorded. 1 / 3C0 was charged at 1 / 3C constant current to 4.2V, then charged at constant voltage to 0.05C0, and left to rest for 30 minutes. 1 / 3C0 was then discharged to 3V, and left to rest for 30 minutes. The discharge capacity C1 was recorded. 1 / 3C0 was charged at 1 / 3C constant current to 4.2V, then charged at constant voltage to 0.05C0, and left to rest for 30 minutes. 3C discharge was then discharged to 3V, and left to rest for 30 minutes. The discharge capacity Cn was recorded. The 3C capacity retention rate was Cn / C1*100%.

[0124] (3) DCR (Direct Current Impedance) Test:

[0125] Charge the battery cell with 1 / 3C constant current to 4.2V, then constant voltage to 0.05C, let it rest for 30 minutes, discharge 1 / 3C0 to 3V, let it rest for 30 minutes, and record the discharge capacity C0. Charge 1 / 3C0 with constant current to 4.2V, then constant voltage to 0.05C0, let it rest for 30 minutes, discharge 1 / 3C0 for 180 minutes, let it rest for 10 minutes, and record the resting end voltage V0. Discharge 2C for 30 seconds, and record the discharge end voltage V1. The discharge DCR = (V0 - V1) / I.

[0126] (4) First-efficacy and cycle tests:

[0127] Charge the battery cell with a constant current of 1 / 3C to 4.2V, then charge with a constant voltage of 0.05C, and record the charging capacity C0. Let it rest for 30 minutes, then discharge 1 / 3C0 to 3V, let it rest for 30 minutes, and record the discharge capacity D0. Charge 1 / 3D0 with a constant current of 4.2V, then charge with a constant voltage of 0.05D0, let it rest for 30 minutes, then discharge 1 / 3D0 to 3V, let it rest for 30 minutes, and record the discharge capacity D1. Repeat this cycle and record the discharge capacity Dn at the end of each cycle. The cycle capacity retention rate is Dn / D1*100%. Record the number of cycles N when the retention rate is 80%, and the first effect is D0 / C0*100%.

[0128] Table 1: Performance comparison of dry electrodes and cells prepared in Examples 1 to 9 and Comparative Examples 1 to 2

[0129]

[0130]

[0131] Comparing Examples 1 to 5 with Comparative Examples 1 and 2: Examples 1 to 5 added different types of second binders in the same proportion. The positive electrode sheets prepared in these examples showed a significant improvement in adhesion compared to the positive electrode sheets prepared in Comparative Example 2 (without adding a second binder) and Comparative Example 1 (wet process). At the same time, the battery cells assembled in Examples 1 to 5 showed improvements in first efficiency, rate performance, DCR performance, and cycle performance compared to the battery cells assembled in Comparative Example 2, especially in cycle performance, where the improvement was more significant.

[0132] Comparing Examples 1, 6, and 7, it can be concluded that: within a certain range, increasing the proportion of the second binder in the positive electrode sheet can improve the adhesion of the positive electrode sheet, and the first efficiency, rate performance, DCR performance, and cycle performance of the battery cell will also be improved to a certain extent; when the amount of the second binder added is large, although the adhesion of the electrode sheet is improved, the electrical performance of the battery cell is not significantly improved because the proportions of the active material, conductive agent, and first binder will also change.

[0133] Comparing Examples 1, 8, and 9, it can be concluded that within a certain range, increasing the amount of the second binder added to the negative electrode sheet can improve the cell's initial efficiency, rate performance, DCR performance, and cycle performance. However, as the amount of the second binder increases, the cell's DCR value continuously increases. When the DCR value is high, the cell's initial efficiency, capacity retention, and cycle performance will decrease. Therefore, adding an appropriate amount of the second binder can improve the overall performance of the cell.

[0134] This invention simultaneously incorporates a first binder and a second binder into a dry electrode. Under high-temperature and high-speed dispersion conditions, the first binder fibroses to form a network structure that binds the active material and the conductive agent. Simultaneously, while the mixture is being mixed and extruded at high temperature to form a film, the second binder achieves in-situ crosslinking, resulting in a more uniform distribution of the ionomer within the electrode and promoting Li... + Transmission ensures good interface contact; Li + Electrostatic coupling between the sulfonate terminus and the quaternary ammonium cation is beneficial for promoting Li + The conductive properties of the polymer, combined with the self-healing function of the dynamic cross-linked network binder composed of hydrogen bonds and electrostatic interactions, enable it to repair cracks in the electrode and maintain structural integrity during long-term cycling, thereby improving the cycle performance of the battery. The dry process of this invention eliminates the need for solvents, reducing the use of equipment such as ovens during coating, thus lowering energy consumption and factory costs. Furthermore, the high-temperature multi-stage rolling process improves the consistency of the electrode sheets and allows for the production of thicker electrodes. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0135] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A dry electrode, characterized in that, include: current collector; A dry electrode film is disposed on at least one side of the current collector surface; The dry electrode film includes an active material, a conductive agent, a first binder, and a second binder. The first binder includes polytetrafluoroethylene, and the second binder is selected from ionomers. The second adhesive is selected from at least one of the compounds shown in formula (1), formula (3) and formula (7): In equation (1), the value range of x1 is 1500 to 3000, the value range of y1 is 1400 to 2800, and the structural formula of R1 is shown in equation (2): In equation (2), the value of a ranges from 1 to 3; In equation (3), x2 ranges from 1000 to 2000, y2 ranges from 1000 to 2300, b ranges from 4 to 8, and R2 is selected from any one of equations (4) to (6): In equation (4), the value of c ranges from 1 to 3; in equation (6), the value of d ranges from 1 to 4. In equation (7), the value range of x3 is 900 to 1700; the value range of y3 is 800 to 1600; the value range of z is 900 to 1900; and the value range of e is 4 to 8.

2. The dry electrode according to claim 1, characterized in that, The dry electrode is a positive electrode sheet. Based on the total mass of the dry electrode film, the content of the active material is 91.0-98.6 wt%, the content of the conductive agent is 0.4-5 wt%, the content of the first binder is 0.2-1 wt%, and the content of the second binder is 0.8-3 wt%.

3. The dry electrode according to claim 1, characterized in that, The dry electrode is a negative electrode sheet. Based on the total mass of the dry electrode film, the content of the active material is 91.7-98.5 wt%, the content of the conductive agent is 0.2-5 wt%, the content of the first binder is 0.1-0.3 wt%, and the content of the second binder is 1.2-5 wt%.

4. A method for preparing a dry electrode according to any one of claims 1 to 3, characterized in that, include: In the dry powder mixing step, the active material, conductive agent, first binder and second binder are mixed evenly to obtain the first mixture; In the fiberization step, the first mixture is subjected to fiberization under shearing action to obtain the second mixture; In the film-forming step, the second mixture is extruded and molded to obtain a dry electrode film; In the composite step, the dry electrode film is rolled thinned and then combined with a current collector to obtain a dry electrode.

5. The preparation method according to claim 4, characterized in that, The dry powder mixing step includes mixing the active material, the conductive agent, the first binder and the second binder at a temperature of -40 to 0°C for 15 to 30 minutes.

6. The preparation method according to claim 4, characterized in that, The fiberization step includes: pre-fiberizing the first mixture at 60-120°C for 30 minutes, and then dispersing it under shear force for 15-60 minutes.

7. The preparation method according to claim 4, characterized in that, The film-forming step includes: mixing and conveying the second mixture via a screw and extruding it through a die to form a dry electrode film, wherein the temperature of the screw is 120-160°C and the thickness of the dry electrode film is 2-7 μm.

8. The preparation method according to claim 4, characterized in that, The composite step includes: thinning the dry electrode film to 0.5-2 mm by rolling, and then hot rolling composite with the current collector to form a dry electrode, wherein the rolling pressure of the hot rolling composite is 3-50T and the rolling temperature is 80-160℃.

9. A battery, characterized in that, Includes the dry electrode as described in any one of claims 1 to 3.

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