Electrode film, preparation method thereof, electrode sheet, and energy storage device

Abstract

The present invention relates to an electrode film, a preparation method thereof, an electrode sheet, and an energy storage device. The preparation method of the electrode film comprises the following steps: obtaining a binder emulsion; spray-drying the binder emulsion to prepare binder micropowder; in-situ online mixing the binder micropowder with an electrode matrix material to prepare a premix; and calendering the premix into a film. By using this preparation method to prepare the electrode film, the binder dosage can be effectively reduced, and the electrode film has good binding and film-forming effects, excellent electrical properties, and good mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage devices, and particularly to an electrode film, a preparation method thereof, an electrode sheet, and an energy storage device. Background Art

[0002] Energy storage devices, such as capacitors, batteries, lithium-ion capacitors, fuel cells, etc., can be used to power electronic devices. An energy storage device has an electrode including one or more electrode films, and the electrode can be divided into a negative electrode and a positive electrode. Generally speaking, the composition of the electrode film mainly includes a binder of a polymer material and one or more active electrode components. The electrical performance of the energy storage device mainly depends on the properties and preparation processes of the binder and the active electrode components.

[0003] In terms of the preparation process, the preparation of the electrode film of a traditional energy storage device includes a wet process and a dry process. Among them, the wet process refers to mixing a binder and active electrode components with a solvent to prepare a slurry, and then coating the slurry on a current collector, and forming a film on the current collector after drying to remove the solvent. The dry process refers to directly dry-mixing the binder and the active electrode components, and then forming a film layer by means of rolling the dry mixture, and then compounding it with the current collector. In view of the different film-forming principles, the requirements for the binder in the wet process and the dry process are also different. The binder commonly used in the wet process (usually called a wet binder) is usually a polymer material with thermoplasticity, and typically, such as polyvinylidene fluoride (PVDF). The binder in the dry process (usually called a dry binder) needs to be a polymer material that can be fibrillated, and typically, such as polytetrafluoroethylene (PTFE).

[0004] Compared with the wet process, the dry process does not need to use a solvent, effectively avoiding the environmental pollution caused by solvent volatilization and residue, excessive energy consumption, and the adverse effects on the electrical performance caused by the introduction of impurities inside the electrode. However, in order to maintain good film-forming properties, a relatively large amount of binder (such as not less than 8%) is usually required in the traditional dry process. Otherwise, it is difficult to ensure the mechanical properties of the electrode film, and even self-support cannot be achieved. And the increase in the amount of binder will lead to a decrease in the electrical performance of the electrode. Summary of the Invention

[0005] Based on this, the present invention provides a preparation method of an electrode film that can effectively reduce the amount of binder used, and has good binder film-forming effect, good electrical performance, and good mechanical properties.

[0006] In the first aspect of the present invention, a preparation method of an electrode film is provided, including the following steps:

[0007] Obtain a binder emulsion;

[0008] Perform spray drying on the binder emulsion to prepare binder micropowder;

[0009] In-situ online mixing of the binder fine powder and the electrode matrix material to prepare a premix;

[0010] Roll the premix into a film.

[0011] In one embodiment, the average particle size of the binder particles in the binder emulsion is 0.1 μm to 0.4 μm.

[0012] In one embodiment, the solid content of the binder emulsion is 10% to 60%.

[0013] In one embodiment, the conditions for spray drying include: the hot air inlet temperature is 150 °C to 300 °C, and the feeding rate of the binder emulsion is 4 kg / h to 12 kg / h.

[0014] In one embodiment, the conditions for mixing include: the tip speed of the stirring paddle blade is 0.2 m / s to 30 m / s, and the time is 5 min to 60 min.

[0015] In one embodiment, the method of rolling into a film is multi-pass rolling into a film, and the number of passes is 2 to 10 times

[0016] In one embodiment, the rolling temperature is 50 °C to 250 °C.

[0017] In one embodiment, by mass percentage, the premix contains the following components: 1% to 15% of the binder fine powder, 70% to 98% of the electrode active material, 1% to 15% of the conductive agent, 0% to 3% of the pore former, and 0% to 5% by weight of the binder enhancer.

[0018] In one embodiment, the electrode active material is a positive electrode active material or a negative electrode active material;

[0019] The positive electrode active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium cobalt oxide;

[0020] The negative electrode active material is selected from at least one of natural graphite, synthetic graphite, hard carbon, soft carbon, activated carbon, silicon, silicon oxide, silicon carbon, tin, tin oxide, and lithium titanate.

[0021] In one embodiment, the conductive agent is selected from at least one of conductive carbon black, graphene, carbon nanotubes, carbon fibers, acetylene black, and Ketjen black; and / or

[0022] The pore former is selected from at least one of citric acid, oxalic acid, ammonium hydrogen oxalate, ammonium bicarbonate, ammonium carbonate, and benzoic acid; and / or

[0023] The binder enhancer can be at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyethylene oxide, and styrene-butadiene rubber.

[0024] In the second aspect of the present invention, there is provided an electrode film prepared by the described preparation method.

[0025] In the third aspect of the present invention, there is provided an electrode sheet, including a current collector and the electrode film laminated on the surface of the current collector as described above.

[0026] In one embodiment, the current collector is aluminum foil coated with a conductive carbon layer, copper foil coated with a conductive carbon layer, nickel foil coated with a conductive carbon layer, stainless steel foil coated with a conductive carbon layer, porous aluminum foil coated with a conductive carbon layer, porous copper foil coated with a conductive carbon layer, porous nickel foil coated with a conductive carbon layer, porous stainless steel foil coated with a conductive carbon layer, or etched aluminum foil coated with a conductive carbon layer.

[0027] In the fourth aspect of the present invention, there is provided a method for preparing the electrode sheet as described above, including the step of thermally compounding the current collector and the electrode film.

[0028] In one embodiment, the temperature of the thermal compounding is 100°C to 300°C.

[0029] In the fifth aspect of the present invention, there is provided an energy storage device including the electrode sheet as described above.

[0030] It has been found through research that during the preparation of the electrode film using the dry process, the main reason for the large amount of binder used is the control of the particle size of the dry binder. The traditional dry binder is obtained by coagulating and drying the binder emulsion, with a relatively large particle size (about 500 μm), which is 1 to 4 orders of magnitude larger than the particle size of the electrode active material, which accounts for the largest proportion in the electrode matrix material (the average particle size of the electrode active material is generally 0.5 to 20 μm). When applied to the dry process, its mixing state with the electrode active material can be as shown in Figure 1 (a), resulting in a large amount of additive required, increased electrode surface resistance, and increased internal resistance of the fabricated device.

[0031] Based on this discovery, the above preparation method of the electrode film first introduces spray drying in the dry process of the electrode film to prepare dry binder micropowders with smaller particle sizes (the particle size range can be 0.5 to 50 μm). At the same time, the binder micropowders are immediately mixed with the electrode matrix material through in-situ online mixing to minimize the secondary aggregation of the binder micropowders, making the particle size of the binder micropowders in the mixing process at the same order of magnitude as that of the electrode active material. Its mixing state with the electrode active material can be as shown in Figure 1As shown in (b), this can more effectively utilize the properties of the binder, reduce the addition amount, and simultaneously take into account the film-forming property, mechanical property, and electrical property of the electrode film. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram comparing the state of the traditional dry binder in the premix with the state of the binder fine powder after spray drying in the premix of the present invention;

[0033] Figure 2 It is a device flowchart of the preparation method of the electrode film according to an embodiment of the present invention;

[0034] Figure 3 It is a process flowchart of the preparation method of the electrode film according to an embodiment of the present invention;

[0035] Figure 4 It is the electrode film prepared in Example 1 (6%) of the present invention;

[0036] Figure 5 It is the electrode film prepared in Example 6-1 (2%) of the present invention;

[0037] Figure 6 It is the electrode film prepared in Example 6-4 (15%) of the present invention;

[0038] Figure 7 It is the electrode film prepared in the comparative example (6%) of the present invention;

[0039] Figure 8 It is the electrode film prepared in Example 7-1 (graphite) of the present invention;

[0040] Figure 9 It is the electrode film prepared in Example 7-2 (silicon carbide) of the present invention;

[0041] Figure 10 It is the electrode film prepared in Example 7-3 (lithium iron phosphate) of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The following further describes the electrode film of the present invention, its preparation method, electrode sheet, and energy storage device in detail with specific embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present invention more thorough and comprehensive.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0044] As used herein, the optional scope of the terms "and / or", "or / and", "and / or" includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The any and all combinations include combinations of any two related listed items, any more related listed items, or all related listed items.

[0045] As used herein, "at least one kind" means any one kind, any two kinds or any two or more kinds of the listed items.

[0046] In the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", "the fifth aspect", etc. are only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", "the fifth", etc. only serve the purpose of non-exhaustive enumerative description and should be understood not to constitute a closed limitation on quantity.

[0047] In the present invention, among the technical features described in an open-ended manner, there are included closed technical solutions composed of the listed features, and also open technical solutions including the listed features.

[0048] In the present invention, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum value and the maximum value of the range, as well as each value between such minimum value and maximum value. Further, when the range refers to integers, it includes each integer between the minimum value and the maximum value of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0049] In the present invention, for the percentage content involved, unless otherwise specified, for solid-liquid mixing and solid-solid mixing, it refers to the mass percentage, and for liquid-liquid mixing, it refers to the volume percentage.

[0050] In the present invention, for the percentage concentration involved, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after adding the component.

[0051] In the present invention, for the temperature parameters, unless otherwise specified, it is allowed to be isothermal treatment, and it is also allowed to be treated within a certain temperature range. The isothermal treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.

[0052] In the present invention, the meaning of "in-situ online mixing" refers to directly feeding the binder micropowder for mixing with the electrode matrix material after the preparation of the binder micropowder is completed, without other steps including transfer, storage, etc. in the middle, and the production line is continuous and uninterrupted.

[0053] The present invention provides a method for preparing an electrode film, comprising the following steps (the equipment and process flow chart is as Figure 2 shown):

[0054] S1: Obtain a binder emulsion;

[0055] S2: Spray-dry the binder emulsion to prepare binder micropowder;

[0056] S3: In-situ online mix the binder micropowder with the electrode matrix material to prepare a premix;

[0057] S4: Roll the premix into a film.

[0058] The above method for preparing an electrode film introduces spray drying into the dry process of the electrode film for the first time, prepares the dry binder into micropowder, and immediately mixes the binder micropowder with the electrode matrix material through in-situ online mixing, minimizing the secondary aggregation of the binder micropowder, thereby effectively reducing the amount of binder used in the electrode film, and having good film-forming and electrical properties.

[0059] Further, in steps S1-S2, by controlling the solid content of the binder emulsion and the feeding rate during the spray drying process, the particle size of the obtained binder micropowder can be controlled within a certain range, optimizing the dispersion of the binder micropowder in the electrode matrix material. Specifically, please refer to Figure 2 , the binder emulsion is pumped into an atomizer for atomization, and binder micropowder is formed in a drying chamber, and then is carried by an air flow to a cyclone separator, where gas-solid separation is achieved at the bottom, and enters the transition bin at the bottom of the cyclone separator.

[0060] It can be understood that the binder emulsion in step S1 is a binder emulsion prepared from a dry binder, which can be obtained commercially or prepared by oneself.

[0061] In some examples, the dry binder in the binder emulsion is selected from polytetrafluoroethylene (PTFE).

[0062] In some examples, the solid content of the binder emulsion is 10% - 60%. Specifically, the solid content of the binder emulsion includes but is not limited to: 10%, 13%, 15%, 17%, 20%, 25%, 28%, 30%, 32%, 35%, 40%, 45%, 50%, 55%, 60%. Preferably, the solid content of the binder emulsion is 20% - 40%.

[0063] In some of these examples, the average particle size of the binder particles in the binder emulsion is 0.1 μm to 0.4 μm. Specifically, the average particle size of the binder particles in the binder emulsion includes, but is not limited to, the range between the following endpoint values (including the endpoint values): 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm.

[0064] In addition, the spray drying in step S2 is mainly divided into three steps: atomization, drying, and separation. The specific description is as follows (but should not be construed as a limitation of the present invention):

[0065] (1) Atomization of the feed liquid: The feed liquid is dispersed into fine droplets with a small diameter through an atomizer, increasing its heat transfer area;

[0066] (2) Drying: The fine droplets with a small diameter are evenly sprayed in the drying chamber through a nozzle, and are in full contact with the high-temperature hot air generated by the heating device. The moisture in the droplets evaporates within a few seconds or more than ten seconds to obtain dry binder micropowder;

[0067] (3) Gas-solid separation: The material after drying is powdery material and water vapor, which is separated by the method of a cyclone separator plus a bag filter. The vast majority of the binder micropowder accumulates at the bottom of the cyclone separator and is discharged by a discharge valve.

[0068] It can be understood that the type of the atomizer is not limited, and it can be a traditional atomizer in the art. For example, it can be a pneumatic atomizer, a centrifugal atomizer, or a pressure atomizer.

[0069] The pneumatic atomizer uses the velocity difference between the high-speed air flow (compressed air) and the solution to generate frictional force and shear force between the solution, so that the solution instantly forms tiny droplets. The middle of the pneumatic atomizer is the material channel, and the outer edge is the gas channel. The gas flow velocity is generally between 200 and 340 m / s, and the feed liquid flow velocity is generally less than 2 m / s. There is a huge velocity difference between the gas phase and the liquid phase at the outlet of the atomizer, thus generating huge frictional force and shear force to atomize the feed liquid. This atomizer has a simple structure, small wear, large operating flexibility, and is not easily blocked. It is suitable for atomizing high-viscosity materials and can obtain droplets with a size of 5 to 30 μm, with a wide range of applications.

[0070] The atomizer of the centrifugal spray drying equipment is a high-speed rotating atomizer. During the process of the feed liquid contacting the high-speed rotating atomizer, due to the action of centrifugal force, it is horizontally thrown out to form fine droplets with a small diameter. During the falling process, it is in contact with the rising high-temperature hot air, and there is frictional force to promote further atomization of the liquid, and finally a dry product is obtained.

[0071] The pressure atomizer consists of a liquid tangential inlet, a fluid swirl chamber, and a nozzle orifice. In the pressure atomizer, the material is pressured into the atomizer by a high-pressure pump at a pressure of 70 - 200 atmospheres, causing the liquid material to disperse into mist-like particles and come into contact with hot air.

[0072] The orientation of the nozzle can be upward, downward, lateral, or other orientations; thus, the direction of the spray can be top spray, bottom spray, lateral spray, or other spray orientations.

[0073] Mixing flow mode: It can be co-current, counter-current, or mixed flow.

[0074] Co-current: The spray is directed into the hot air in the drying chamber and passes through the drying chamber in the same direction;

[0075] Counter-current: The spray and the hot air are introduced at both ends of the dryer respectively. The nozzle is located at the top and the hot air enters from the bottom;

[0076] Mixed flow: The nozzle is located at the bottom of the dryer and the hot air enters from the top. This mixed flow mode has both co-current and counter-current.

[0077] In some of these examples, the conditions for spray drying include: the hot air inlet temperature is 150°C - 300°C, and the feeding rate of the binder emulsion is 4 kg / h - 12 kg / h.

[0078] Specifically, the hot air inlet temperature includes but is not limited to: 150°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 250°C, 270°C, 300°C.

[0079] The feeding rate of the binder emulsion includes but is not limited to: 4 kg / h, 5 kg / h, 6 kg / h, 7 kg / h, 8 kg / h, 9 kg / h, 10 kg / h, 11 kg / h, 12 kg / h.

[0080] In some of these examples, after spray drying, the particle size of the obtained binder micropowder is 0.5 μm - 50 μm. Preferably, the particle size of the binder micropowder is 1 μm - 10 μm.

[0081] Furthermore, in step S3, the binder micropowder is mixed with the electrode matrix material in situ online to prepare a premix. Reasonable control of the mixing steps and processes can optimize the mechanical and electrical properties of the electrode film. Specifically, please refer to Figure 2, The binder fine powder (the first component) in the transition silo at the bottom of the cyclone separator is directly metered and then added to a mixer to be mixed with the electrode matrix material (the second component) to prepare a premix (the third component). Through in-situ online feeding and mixing, the binder fine powder and the electrode matrix material are immediately mixed, which can avoid the secondary agglomeration of the binder fine powder during storage and transportation. At the same time, if the environmental humidity is high, long-term storage or transportation will cause the binder powder to absorb moisture and even cake, and in-situ mixing can effectively avoid this problem.

[0082] Understandably, the components in the electrode matrix material can be mixed first and then mixed with the binder fine powder, or the components in the electrode matrix material and the binder fine powder can be fed and mixed synchronously at the same time.

[0083] In some examples, the mixing method is as follows: the binder fine powder and the electrode matrix material are metered separately and then mixed. Metering can be carried out using a metering feeding device, such as a screw loss-in-weight feeder.

[0084] Without limitation, the mixing method can adopt a container rotary mixer. The materials are in a container rotating around an axis and mainly undergo complex movements under the action of gravity to mix with each other. According to the shape of the container, it can be cylindrical, drum-shaped, vertical, double-cone-shaped, V-shaped, etc.

[0085] Without limitation, the mixing method can adopt a forced stirring mixer. According to the shape of the blades, it can be paddle-shaped, spiral ribbon-shaped, spiral blade-shaped, etc.

[0086] Without limitation, the mixing method can adopt a pneumatic mixer. The materials are strongly agitated by a pulsed high-speed air flow or the materials are mixed due to the convective movement formed by the high-pressure air flow in the container, such as fluidized type and pulsed swirl type, etc.

[0087] In some examples, the mixing conditions include: the end speed of the stirring paddle blade is 0.2 m / s to 30 m / s, and the time is 5 min to 60 min. Specifically, the end speed of the stirring paddle blade includes but is not limited to: 0.2 m / s, 0.5 m / s, 1 m / s, 1.5 m / s, 1.7 m / s, 1.8 m / s, 1.9 m / s, 2 m / s, 5 m / s, 8 m / s, 10 m / s, 15 m / s, 20 m / s, 25 m / s, 30 m / s. The mixing time includes but is not limited to: 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, 30 min, 32 min, 35 min, 38 min, 40 min, 50 min, 60 min. Preferably, the mixing time is 10 min to 30 min.

[0088] In some of these examples, the electrode matrix material comprises at least the electrode active material. Further, the electrode matrix material may further comprise at least one of a conductive agent, a pore-forming agent, and a binder enhancer.

[0089] In some of these examples, by mass percentage, the premix comprises the following components: 1% - 15% of binder fine powder, 70% - 98% of electrode active material, 1% - 15% of conductive agent, 0% - 3% of pore-forming agent, and 0% - 5% of binder enhancer by weight fraction.

[0090] Specifically, in the premix, the mass percentage of the binder fine powder includes but is not limited to: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%. Preferably, the mass percentage of the binder fine powder is 2% - 6%.

[0091] Specifically, in the premix, the mass percentage of the electrode active material includes but is not limited to: 70%, 73%, 75%, 78%, 80%, 81%, 82%, 85%, 88%, 90%, 92%, 94%, 96%, 98%. Preferably, the mass percentage of the electrode active material is 80% - 94%.

[0092] It can be understood that the electrode active material is a positive electrode active material or a negative electrode active material.

[0093] In some of these examples, the positive electrode active material is selected from at least one of lithium nickel cobalt manganese oxide (NCM), lithium iron phosphate (LFP), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), and lithium cobalt oxide (LCO).

[0094] In some of these examples, the negative electrode active material is selected from at least one of natural graphite, synthetic graphite, hard carbon, soft carbon, activated carbon, silicon, silicon oxide, silicon carbon, tin, tin oxide, and lithium titanate.

[0095] Specifically, in the premix, the mass percentage of the conductive agent includes but is not limited to: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%. Preferably, the mass percentage of the conductive agent is 3% - 8%.

[0096] In some of these examples, the conductive agent is selected from at least one of conductive carbon black, graphene, carbon nanotubes, carbon fibers, acetylene black, and Ketjen black.

[0097] Specifically, in the premix, the mass percentage of the pore-forming agent includes but is not limited to: 0% (i.e., not used), 0.5%, 1%, 1.5%, 2%, 3%. Preferably, the mass percentage of the pore-forming agent is 0.5% - 1.5%.

[0098] In some of these examples, the pore-forming agent is selected from pore-forming agents with a thermal decomposition temperature of less than 200 °C. Further, the pore-forming agent is selected from at least one of citric acid, oxalic acid, ammonium hydrogen oxalate, ammonium bicarbonate, ammonium carbonate, and benzoic acid. Preferably, the pore-forming agent is citric acid.

[0099] In some of these examples, the particle size of the pore-forming agent is 5 μm to 20 μm.

[0100] Specifically, in the premix, the mass percentage of the binder enhancer includes but is not limited to: 0%, 1%, 2%, 3%, 4%, 5%. Preferably, the mass percentage of the binder enhancer is 0% to 3%.

[0101] In some of these examples, the binder enhancer can be at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), polyethylene oxide (PEO), and styrene-butadiene rubber (SBR).

[0102] Further, in step S4, the premix is rolled into a film. Specifically, the rolling is carried out under heating, and the heating causes the binder micropowder to soften sufficiently to generate thermal viscosity, and finally the premix becomes a self-supporting electrode film with a certain thickness.

[0103] In some of these examples, the rolling temperature is 50 °C to 250 °C. Specifically, the rolling temperature includes but is not limited to: 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 95 °C, 100 °C, 105 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 220 °C, 250 °C. Preferably, the rolling temperature is 100 °C to 200 °C.

[0104] It can be understood that the number of rolling passes can be one, two, or multiple.

[0105] In some of these examples, the method of rolling into a film is multiple rolling into a film. Preferably, the number of rolling passes is 2 to 10 times. More preferably, the number of rolling passes is 4 to 8 times. By rolling within a certain number of times, it is beneficial to optimize the mechanical properties and electrical properties of the electrode film.

[0106] In some of these examples, after the rolling into a film is completed, the thickness of the obtained electrode film is 50 μm to 300 μm.

[0107] The present invention also provides an electrode film prepared by the above preparation method.

[0108] The present invention also provides an electrode sheet, which includes a current collector and the above-mentioned electrode film laminated on the surface of the current collector.

[0109] In some of these examples, the current collector is aluminum foil coated with a conductive carbon layer, copper foil coated with a conductive carbon layer, nickel foil coated with a conductive carbon layer, stainless steel foil coated with a conductive carbon layer, porous aluminum foil coated with a conductive carbon layer, porous copper foil coated with a conductive carbon layer, porous nickel foil coated with a conductive carbon layer, porous stainless steel foil coated with a conductive carbon layer, or etched aluminum foil coated with a conductive carbon layer. Further, the thickness of the current collector can be 5 μm to 30 μm.

[0110] The present invention also provides a method for preparing the electrode sheet, including the step of thermally laminating the current collector and the electrode film.

[0111] Specifically, thermal lamination is to laminate the electrode film and the current collector at a high temperature, so that the film adheres firmly to the current collector to form an electrode sheet. At the same time, when the electrode film contains a pore-forming agent, the high temperature of thermal lamination can also cause the pore-forming agent to decompose by heating, leaving pores to form a porous electrode sheet. In the presence of a pore-forming agent, an electrode sheet with tiny holes on the surface is formed after thermal lamination, and the electrolyte can directly enter the deep layer of the electrode sheet, improving the liquid absorption property of the electrode sheet. If the electrode sheet does not absorb the electrolyte sufficiently, it will cause an increase in internal resistance and a reduction in effective capacity. In addition, first form the electrode film, and then form a porous electrode sheet through thermal lamination with the current collector. At this time, the strength is borne by the current collector, and the pores do not affect the mechanical properties of the electrode sheet.

[0112] It can be understood that according to the structural requirements of the electrode sheet, thermal lamination can be single-sided thermal lamination, double-sided thermal lamination, or multi-layer thermal lamination.

[0113] In some of these examples, the temperature of thermal lamination is 100°C to 300°C. Specifically, the temperature of thermal lamination includes but is not limited to: 100°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 300°C. Preferably, the temperature of thermal lamination is 150°C to 250°C. It can be understood that when the electrode film contains a pore-forming agent, the temperature of thermal lamination is not lower than the thermal decomposition temperature of the pore-forming agent.

[0114] The present invention also provides an energy storage device, including the electrode sheet as described above. Specifically, the energy storage device can be a capacitor, a battery, a lithium-ion capacitor, a fuel cell, etc.

[0115] The following are specific examples. Unless otherwise specified, the raw materials used in the examples are all commercially available products.

[0116] Activated carbon, YP-50 activated carbon from Kuraray Co., Ltd.

[0117] Conductive carbon black, Super P conductive carbon black from Timcal.

[0118] Example 1

[0119] This example is a method for preparing an electrode film, and the steps are as follows (see the process flow chart in Figure 3 ):

[0120] (1) Preparation of PTFE micropowder:

[0121] The PTFE emulsion (PTFE emulsion from DAIKIN Co., Ltd., Japan, with a solid content of 30% and an average particle size of 0.22 μm of the emulsion particles) is fed at a rate of 8 kg / h, formed into droplets through an atomizer, and enters the drying chamber for spray drying. The hot air inlet temperature is 200 °C, and then gas-solid separation is carried out through a cyclone separator to obtain dry PTFE micropowder, D50 = 7.2 μm. This is the first component;

[0122] (2) Mix the activated carbon and conductive carbon black in proportion to obtain a uniform mixture. This is the second component;

[0123] (3) After gas-solid separation in step (1), the first component is metered into a V-type mixer through a screw loss-in-weight feeder; at the same time, the second component in step (2) is also metered into the V-type mixer for in-situ mixing. The end speed of the stirring paddle blade is 1.8 m / s, and the mixing time is 20 min. This is the third component; In the third component, by mass percentage, it is composed of 89% activated carbon, 5% conductive carbon black, and 6% PTFE micropowder.

[0124] (4) Roll the premix in step (3) into a self-supporting electrode film, and the rolling temperature is 100 °C; the number of rolling times is 5 times.

[0125] The thickness of the self-supporting electrode film is 120 μm. Perform performance tests:

[0126] a) Test its tensile strength according to the standard of GB / T 1040.3—2006 / ISO 527-3:2018 (the standard width of the test strip is a long strip specimen of 10 - 25 mm and the length is not less than 150 mm): The tensile strength in the length direction (longitudinal) is 0.208 MPa; the tensile strength in the width direction (transverse) is 0.135 MPa.

[0127] b) Measure the volume resistivity of the electrode film with multiple probes, and the result is 0.52 Ω·cm.

[0128] c) Clamp the electrode film up and down with two cylindrical metal fixtures with a diameter of 14 mm and apply a certain pressure to measure its through-resistance, and the result is 31 mΩ.

[0129] Example 2-1

[0130] This embodiment is a method for preparing an electrode film. The steps are the same as those in Embodiment 1, and the main difference is that the solid content of the PTFE emulsion is 15%.

[0131] The performance of the electrode film was tested according to the testing method in Embodiment 1. The results are shown in Table 1.

[0132] Embodiment 2-2

[0133] This embodiment is a method for preparing an electrode film. The steps are the same as those in Embodiment 1, and the main difference is that the solid content of the PTFE emulsion is 60%.

[0134] The performance of the electrode film was tested according to the testing method in Embodiment 1. The results are shown in Table 1.

[0135] Embodiment 3-1

[0136] This embodiment is a method for preparing an electrode film. The steps are the same as those in Embodiment 1, and the main difference is that the average particle size of the emulsion particles is 0.10 μm.

[0137] The performance of the electrode film was tested according to the testing method in Embodiment 1. The results are shown in Table 1.

[0138] Embodiment 3-2

[0139] This embodiment is a method for preparing an electrode film. The steps are the same as those in Embodiment 1, and the main difference is that the average particle size of the emulsion particles is 0.35 μm.

[0140] The performance of the electrode film was tested according to the testing method in Embodiment 1. The results are shown in Table 1.

[0141] Embodiment 4-1

[0142] This embodiment is a method for preparing an electrode film. The steps are the same as those in Embodiment 1, and the main difference is that during the spray drying process, the feeding rate of the PTFE emulsion is 4 kg / h.

[0143] The performance of the electrode film was tested according to the testing method in Embodiment 1. The results are shown in Table 1.

[0144] Embodiment 4-2

[0145] This embodiment is a method for preparing an electrode film. The steps are the same as those in Embodiment 1, and the main difference is that during the spray drying process, the feeding rate of the PTFE emulsion is 12 kg / h.

[0146] The performance of the electrode film was tested according to the testing method in Embodiment 1. The results are shown in Table 1.

[0147] Embodiment 5-1

[0148] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that the mixing time is 10 min.

[0149] The electrode film was tested for performance according to the same testing method as in Example 1. The results are shown in Table 1.

[0150] Example 5-2

[0151] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that the mixing time is 5 min.

[0152] The electrode film was tested for performance according to the same testing method as in Example 1. The results are shown in Table 1.

[0153] Example 5-3

[0154] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that the mixing time is 60 min.

[0155] The electrode film was tested for performance according to the same testing method as in Example 1. The results are shown in Table 1.

[0156] Example 6-1

[0157] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that the mass percentage of the binder micropowder is 2%, and the mass of the activated carbon is correspondingly increased or decreased.

[0158] The electrode film was tested for performance according to the same testing method as in Example 1. The results are shown in Table 1.

[0159] Example 6-2

[0160] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that the mass percentage of the binder micropowder is 4%, and the mass of the activated carbon is correspondingly increased or decreased.

[0161] The electrode film was tested for performance according to the same testing method as in Example 1. The results are shown in Table 1.

[0162] Example 6-3

[0163] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that the mass percentage of the binder micropowder is 8%, and the mass of the activated carbon is correspondingly increased or decreased.

[0164] The electrode film was tested for performance according to the same testing method as in Example 1. The results are shown in Table 1.

[0165] Example 6-4

[0166] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that the mass percentage of the binder micropowder is 15%, and the mass of the activated carbon is increased or decreased accordingly.

[0167] The performance of the electrode film was tested according to the same test method as in Example 1. The results are shown in Table 1.

[0168] Example 7-1

[0169] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that synthetic graphite is used to replace the activated carbon.

[0170] The performance of the electrode film was tested according to the same test method as in Example 1. The results are shown in Table 1.

[0171] Example 7-2

[0172] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that silicon oxide is used to replace the activated carbon.

[0173] The performance of the electrode film was tested according to the same test method as in Example 1. The results are shown in Table 1.

[0174] Example 7-3

[0175] This example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that lithium iron phosphate is used to replace the activated carbon.

[0176] The performance of the electrode film was tested according to the same test method as in Example 1. The results are shown in Table 1.

[0177] Comparative Example

[0178] This comparative example is a method for preparing an electrode film. The steps are the same as those in Example 1, and the main difference is that commercially available PTFE powder (D50 = 500 μm) is directly used for the mixing in step (3).

[0179] Summary of the performance test results of the examples and the comparative example (Table 1):

[0180] Table 1

[0181]

[0182]

[0183] As can be seen from Table 1, each example of the present invention can make the prepared electrode film have excellent mechanical properties and electrical properties with less binder usage. At the same time, further research can also find that:

[0184] (1) Emulsion solid content:

[0185] Referring to the comparison among Example 1, Example 2-1, and Example 2-2, at a constant feeding rate, a high solid content in the emulsion and a low evaporation load are beneficial to reducing the production energy consumption. However, when the solid content is too high, referring to the comparison between Example 2-2 and Example 1 and 2-1, the mechanical properties and electrical properties of the electrode film will both decline relatively significantly. While Example 1 can obtain mechanical properties and electrical properties equivalent to those of Example 2-1 while ensuring lower energy consumption.

[0186] (2) Average particle size of the binder emulsion particles:

[0187] Referring to the comparison among Example 1, Example 3-1, and Example 3-2, the smaller the particle size of the emulsion particles, the smaller the particle size of the obtained binder micropowder. However, when the particle size of the emulsion particles is too high or too low, referring to the comparison between Example 1 and Example 2-1 and 2-2, the electrical properties of the electrode film will both decline to a certain extent.

[0188] (3) Feeding rate:

[0189] Referring to the comparison among Example 1, Example 4-1, and Example 4-2, when the feeding rate is relatively large, the amount of emulsion passing through the atomizer per unit time is more, and at this time, the droplet size is also large. Therefore, under constant atomization and drying conditions, the micropowder particle size increases with the increase of the feeding rate. In other words, a lower feeding rate during the spray drying process helps to obtain binder micropowder with a smaller particle size, and is also beneficial to the properties such as the tensile strength, volume resistivity, and through-resistance of the membrane. However, if the feeding rate is too low, the production efficiency will be low. Generally speaking, it is preferred that the feeding rate is 4 kg / h to 12 kg / h, which can obtain better electrode film properties and higher production efficiency.

[0190] (4) Mixing time:

[0191] Referring to the comparison among Example 1, Example 5-1, Example 5-2, and Example 5-3, within a certain time range, increasing the mixing time is beneficial to the mixing of the binder micropowder and the electrode matrix material, and can improve the dispersion uniformity of the binder micropowder, thereby making both the mechanical properties and electrical properties of the membrane show an upward trend. However, when the mixing time is extended from 20 min to 60 min, it has little effect on the tensile strength, volume resistivity, and through-resistivity of the membrane, and even has a slight adverse effect.

[0192] (5) Binder content:

[0193] Referring to the comparison between Example 1 and Examples 6-1 to 6-4, the more the content of the binder, the stronger the adhesive force, and the tensile strength in the longitudinal and transverse directions of the diaphragm will increase. However, at the same time, the volume resistivity and through-resistance of the electrode film also increase rapidly, which is not conducive to the electrical performance of the device. In addition, too low a binder content will significantly reduce the tensile strength in the longitudinal and transverse directions of the electrode film, resulting in an increase in the serrated edge of the electrode film; it may even affect the progress of the thermal composite process. From Figures 4 to 8 the previous comparison, it can be seen that when the same 6% binder micropowder is used, the film-forming property of the electrode film of the comparative example ( Figure 7 ) is poor, and the serrated edge is significantly increased compared with Example 1 ( Figure 4 ). For Example 6-1 ( Figure 5 ), 2% binder micropowder is used. Although the serrated edge of the electrode film is increased compared with Example 1, it can still be comparable to or even better than the comparative example. For Example 6-3 ( Figure 6 ) and Example 6-4 ( Figure 7 ), 8% and 12% binder micropowder are used, and their electrical performance is lower than that of Example 1.

[0194] (6) Electrode active material:

[0195] Referring to Examples 7-1 to 7-3, it can be seen that the binder micropowder prepared by the present invention is applicable to different electrode active materials, and the prepared electrode film is shown in Figures 8 to 10 .

[0196] Application example:

[0197] Using the self-supporting electrode film prepared in Example 1 to prepare double-sided electrode sheets and capacitors.

[0198] The steps are as follows:

[0199] Perform double-sided thermal composite on the self-supporting electrode film and carbon-coated aluminum foil (electrode film - carbon-coated aluminum foil - electrode film), and the thermal composite temperature is 200 °C to obtain double-sided electrode sheets; use the double-sided electrode sheets to make cylindrical capacitor 60138.

[0200] In the same way, use the electrode film prepared in the comparative example to prepare double-sided electrode sheets and capacitors.

[0201] Test according to the test method of electrical characteristics of double-layer capacitors for hybrid electric vehicles in IEC 62576-2018. The results are shown in Table 2 below.

[0202] Table 2

[0203] Capacitance (F) DC internal resistance (mΩ) Example 1 3380 0.21 Comparative example 3197 0.27

[0204] In summary, the embodiment of the present invention adopts spray drying technology. By controlling the solid content of the binder emulsion, the feeding speed, etc., dry binder micropowders with smaller particle sizes (particle size range 0.5 - 50 μm) are obtained. At the same time, the in-situ online mixing system enables the immediate mixing of the binder micropowders and the electrode matrix material, minimizing the secondary agglomeration of the binder micropowders to such an extent that the particle sizes of the binder micropowders during the mixing process are in the same order of magnitude as those of the electrode active materials. Therefore, the content can be reduced, ultimately reducing the DC internal resistance of the device and even enhancing the capacitance performance, thereby improving the overall performance of the device.

[0205] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as falling within the scope described in this specification.

[0206] The above-described embodiments merely represent several implementation manners of the present invention, facilitating the specific and detailed understanding of the technical solutions of the present invention. However, it should not be construed as a limitation on the protection scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning, or limited experiments based on the technical solutions provided by the present invention are all within the protection scope of the appended claims of the present invention. Therefore, the protection scope of the present invention patent should be determined by the content of the appended claims, and the description and drawings can be used to explain the content of the claims.

Claims

1. A method for preparing a dry electrode film, characterized in that, It includes the following steps: Obtain a binder emulsion; the binder in the binder emulsion is a fibrillatable polymer material; Perform spray drying on the binder emulsion to prepare binder micropowder; the conditions for spray drying include: the hot air inlet temperature is 150°C to 300°C, and the feeding rate of the binder emulsion is 4 kg / h to 12 kg / h; In-situ online mix the binder micropowder and the electrode matrix material to prepare a premix; Roll the premix into a film.

2. The preparation method of the dry electrode film according to claim 1, characterized in that The average particle size of the binder particles in the binder emulsion is 0.1 μm to 0.4 μm.

3. The preparation method of the dry electrode film according to claim 1, characterized in that, The solid content of the binder emulsion is 10% to 60%.

4. The method for preparing a dry electrode film according to claim 1, wherein After the spray drying is completed, the particle size of the obtained binder micropowder is 0.5 μm to 50 μm.

5. The preparation method of the dry electrode film according to claim 1, characterized in that, The conditions for mixing include: the end rate of the stirring paddle blade is 0.2 m / s to 30 m / s, and the time is 5 min to 60 min.

6. The preparation method of the dry electrode film according to claim 1, wherein The method of rolling into a film is multi-pass rolling into a film, and the number of passes is 2 to 10 times.

7. The method for preparing a dry electrode film according to claim 1, characterized in that, The temperature for rolling into a film is 50°C to 250°C.

8. The preparation method of the dry electrode film according to any one of claims 1 to 7, characterized in that, By mass percentage, the premix contains the following components: 1% to 15% of the binder micropowder, 70% to 98% of the electrode active material, 1% to 15% of the conductive agent, 0% to 3% of the pore former, and 0% to 5% by weight of the binder enhancer.

9. The method for preparing a dry electrode film according to claim 8, characterized in that, The electrode active material is a positive electrode active material or a negative electrode active material; The positive electrode active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium cobalt oxide; The negative electrode active material is selected from at least one of natural graphite, synthetic graphite, hard carbon, soft carbon, activated carbon, silicon, silicon oxide, silicon carbon, tin, tin oxide, and lithium titanate.

10. The preparation method of the dry electrode film according to claim 8, characterized in that, The conductive agent is selected from at least one of conductive carbon black, graphene, carbon nanotubes, carbon fiber, acetylene black, and Ketjen black; and / or The pore former is selected from at least one of citric acid, oxalic acid, ammonium hydrogen oxalate, ammonium bicarbonate, ammonium carbonate, and benzoic acid; and / or The binder enhancer is selected from at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyethylene oxide, and styrene-butadiene rubber.

11. A dry electrode film prepared by the preparation method according to any one of claims 1 to 10.

12. An electrode sheet, characterized in that, It includes a current collector and the dry electrode film according to claim 11 laminated on the surface of the current collector.

13. The electrode sheet according to claim 12, characterized in that, The current collector is aluminum foil coated with a conductive carbon layer, copper foil coated with a conductive carbon layer, nickel foil coated with a conductive carbon layer, stainless steel foil coated with a conductive carbon layer, porous aluminum foil coated with a conductive carbon layer, porous copper foil coated with a conductive carbon layer, porous nickel foil coated with a conductive carbon layer, porous stainless steel foil coated with a conductive carbon layer, or etched aluminum foil coated with a conductive carbon layer.

14. The method for preparing the electrode sheet according to claim 12 or 13, characterized in that, It includes the step of thermally compounding the current collector and the dry electrode film.

15. The preparation method of the electrode sheet according to claim 14, wherein The temperature for thermal compounding is 100°C to 300°C.

16. An energy storage device, characterized in that, It includes the electrode sheet according to claim 12 or 13.

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