Manufacturing method of dry electrode for secondary battery

Abstract

The present invention relates to a dry electrode manufacturing method for a secondary battery, comprising the steps of: a. mixing an active material, a binder, and a conductive material and feeding the mixture into a screw mixer; b. heating and melting the mixture in a first step while moving it forward by rotating the screw; c. stirring the heated and melted mixture while moving it forward by rotating the screw; d. heating and stirring the stirred mixture in a second step while moving it forward by rotating the screw; e. pressing the second heated and stirred mixture forward by rotating the screw and advancing it to a nozzle end; f. a film manufacturing step in which the mixture discharged in a film shape through the nozzle is extruded by pressing it with rollers located above and below; and g. attaching the manufactured film to a metal foil to manufacture an electrode.

Description

Technology Field

[0001] The present invention relates to a manufacturing method for a secondary battery that omits a drying process, and more specifically, to a manufacturing method that applies a thermoplastic binder as a binding material for active materials, and creates voids between active materials to solve the problem in which electrolyte impregnation is impossible due to the non-creation of voids between active materials when the thermoplastic binder is used. Background Technology

[0002] Recently, secondary batteries have been experiencing rapid growth as electric vehicles replace internal combustion engines.

[0003] Nearly 100 million internal combustion engine vehicles are sold worldwide each year, and as carbon dioxide emitted from these vehicles causes global warming and various natural disasters around the world, electric vehicles using hydrogen fuel cells and electric vehicles using batteries are gaining prominence, and among these, electric vehicles using batteries are being adopted as a realistic alternative.

[0004] The batteries currently used in these electric vehicles are primarily lithium-ion batteries, and it is expected that solid-state batteries and the like will replace them in the future.

[0005] While lithium-ion batteries (LIBs) were previously dominated by small batteries used in laptops and mobile phones, the demand for large batteries capable of driving more than 500 km on a single charge is exploding with the spread of electric vehicles, and production facilities required for battery production are also becoming increasingly larger.

[0006] A lithium-ion battery is completed by manufacturing the positive and negative electrodes, combining them with a separator in between, stacking them, placing them in a case, filling the battery with electrolyte, and performing an initial charge.

[0007] The basic structure of the battery made in this way is as shown in Fig. 1.

[0008] Referring to Figure 1, the active material constituting the negative and positive electrodes is attached to the current collector with a specific thickness, there is a separator between the two electrode plates, and the electrolyte fills the voids between the active materials.

[0009] When charging and discharging, lithium ions on opposite plates gain electrons (charging) or lose electrons (discharging), moving to the opposite side through the separator to create a flow of electricity through the wire connected to the plates.

[0010] At this time, an electrolyte is required for lithium ions to smoothly pass through and move between active materials, and current lithium-ion batteries consist of this electrolyte in liquid form.

[0011] All-solid-state batteries, considered the batteries of the future, consist of a solid electrolyte and contain a film made of the electrolyte instead of a separator.

[0012] As described above, in order to manufacture a secondary battery, positive and negative electrode plates must be manufactured, and these plates consist of a current collector and active material powder.

[0013] The active materials are, respectively, the positive electrode is a powder of a lithium compound (Li, Ni, Co, Mn, Al, etc.) (diameter about 10 µm) and the negative electrode is a powder of graphite or silicon (diameter about 10 µm).

[0014] The electrodes are manufactured by laminating the positive active material to a thickness of about 100 µm on an aluminum foil with a thickness of about 10 µm for the positive electrode, and laminating the negative active material to a thickness of about 10 µm on a copper foil with a thickness of about 10 µm for the negative electrode.

[0015] The problem is that when manufacturing the electrode plates, the powders must be made to adhere to each other and to the current collector, and additionally, gaps must be formed between the active material powders to allow the electrolyte to be injected into those gaps.

[0016] If there are no pores, the electrolyte cannot be impregnated, and since ions cannot move through the separator, the battery does not operate. To solve this problem, the electrode fabrication methods currently in use are as follows.

[0017] First, binder solutions are prepared. For the anode, the binder solution is prepared by dissolving PVDF (polyvinylidene fluoride) in NMP (N-Methyl-2-Pyrrolidone) solution, and for the cathode, it is prepared by dissolving SBR (styrere = butadiene rubber) solution and CMC (carboxymethyl cellulose) in ultrapure water (DI).

[0018] Active material powder is added to the binder solution prepared in this way and stirred. The result is a slurry solution in which the active material powder is evenly stirred in the binder solution.

[0019] This slurry solution is supplied to a coating device, and when coated onto a current collector through a T-die, a primary electrode plate is obtained.

[0020] However, in this case, the solvent (NMP for the anode and ultrapure water for the cathode) remains between the active material powders contained within the coated active material film, and therefore, the electrolyte cannot be impregnated, so a battery cannot be manufactured in this state.

[0021] The solvent between these active material powders is removed through a drying process after the coating process.

[0022] The electrode, having undergone the drying process, is compressed to about 20% of its thickness through a press and then manufactured into a battery.

[0023] At this stage, if the solvent between the active material powders evaporates during the drying process, the corresponding space becomes empty, and voids are created that can be filled with electrolyte.

[0024] The most expensive process in the manufacturing of these secondary batteries is the drying process.

[0025] As illustrated in Figure 2, the drying process takes about 1 minute at approximately 150 degrees, and since the maximum electrode plate production speed of current battery manufacturers is about 100m per minute, a drying furnace of 100m is also required.

[0026] The solvent evaporated from the drying oven must be recovered, and an additional solvent recovery device is required.

[0027] Since the cost required for this is known to be approximately 30 to 50 billion won per electrode manufacturing facility, battery companies that must have at least one line each for negative and positive electrode manufacturing facilities face the problem of incurring facility investments of up to 100 billion won per battery line (positive and negative electrode manufacturing facilities) just for drying-related facility costs.

[0028] Furthermore, the electricity costs for operating drying ovens and solvent recovery devices are enormous. Due to this drying oven issue, there is a contradictory problem in the battery manufacturing stage of electric vehicles—which are being adopted to replace internal combustion engine cars and reduce carbon dioxide emissions—where power plants must generate electricity while emitting carbon dioxide due to the massive electricity consumption required.

[0029] As shown in Figure 2, it can be seen that a large-scale drying device is required to recover the solvent in the drying device used in the wet-based electrode manufacturing process.

[0030] To solve this problem, there is a method to create an electrode plate by making an active material film without a solvent and adhering this film to a current collector.

[0031] Figure 3 explains the method of making an electrode plate by creating an active material film and attaching this film to a current collector. In this method, a binder and an active material are supplied and heated (melted) and stirred in a twin-screw stirrer, then extruded through a nozzle to form a film, and then the film and the thin plate of the current collector are passed between heated rollers to bond (laminate).

[0032] As shown in Figure 3, during the process of heating and stirring in a twin-screw stirrer, the binder melts due to heat and connects the active material powders, allowing them to be formed into a film after extrusion.

[0033] However, there is a problem with the method of Figure 3 as well, because if the binder used melts due to heat and completely surrounds the active material, the binder fills the space between the active material particles and cannot form voids, so the electrolyte cannot be impregnated.

[0034] Therefore, in the method of Figure 3, fluorine compound polymer resins such as PTFE (Polytetrafluoroethylene) are currently used as binder materials.

[0035] PTFE (trade name Teflon) has a very high melting point and extremely high lubricity, so it does not adhere to the surface of the active material.

[0036] Using this property, the PTFE powder is mixed with an active material and heated appropriately (about 130 degrees. The melting point of PTFE is 327 degrees), and then the PTFE is stretched into a thread using a kneader.

[0037] PTFE, stretched into a thread-like shape when mixed with the active material, mechanically holds the active material, enabling it to maintain its film shape after extrusion.

[0038] However, stretching PTFE into a thread at low temperatures requires a powerful kneader, and since it is difficult to implement in a continuous manner, it is difficult to mass-produce active material films in a continuous manner.

[0039] The method currently being used experimentally involves mixing a binder (PTFE) with an active material and stirring it in a powder state, then placing it into a heated kneader to fiberize the binder to create a pellet of the active material and binder mixture, and then crushing the pellet as it cools out of the kneader and placing the crushed powder between two rollers to form a film.

[0040] All of these processes are currently carried out using a batch method, which is an intermittent operation, and since the equipment for each process is difficult to operate continuously, dry electrodes cannot be mass-produced using this manufacturing method.

[0041] Nevertheless, the reason for using this method to manufacture batteries is that PTFE has no adhesive properties, allowing the voids between active materials to be maintained without being filled.

[0042] For this reason, an electrode manufacturing method using a PTFE-based binder is currently proposed as a dry electrode manufacturing method; however, limitations in mass production are arising due to the use of PTFE.

[0043] This method is patented by Maxwell of the United States, and although Tesla, also of the United States, acquired the company to mass-produce batteries for electric vehicles using this method, it ultimately failed to overcome the hurdle of mass production and was sold to another company in July 2021, just two years later, indicating that this method is difficult to apply to mass production.

[0044] This patent was filed in the United States on December 9, 2016, under application number 15374043 and registered on January 28, 2020, under registration number 10547057.

[0045] Claims 1, 6, and 7 are as follows.

[0046]

[0047]

[0048] That is, claim 1 provides a method for manufacturing an energy storage device comprising: providing conductive particles; providing dry binder particles constituting a single fibrillizable bonding material in the absence of essentially other bonding materials; mixing the conductive and dry binder particles; and forming a film on the mixed conductive and dry binder particles, wherein the mutual mixing and forming is performed without substantial use of process agents and lubricants.

[0049] Claim 6 describes the method of Claim 1, wherein the fibrillizable binding material comprises a fluorinated polymer.

[0050] Claim 7 describes the method of Claim 6, wherein the fluorinated polymer comprises PTFE.

[0051] As described above, the patent for using a material capable of fiberization as a binder is claimed as Claim 1, and the scope of rights is broad. Therefore, if one intends to make a battery by using PTFE, fiberizing it through a kneader, and then making an active material film, even by a batch method, it conflicts with the said patent.

[0052] Due to these problems, the currently proposed PTFE-based dry electrode manufacturing method is difficult to replace the existing wet electrode manufacturing method.

[0053] Current wet electrode manufacturing methods continuously produce photovoltaic electrodes with a width of 1 m at a speed of more than 100 m per minute, but PTFE binder-based dry electrode manufacturing methods are produced intermittently at a lab scale and in a batch manner.

[0054] The batteries currently used in these electric vehicles are primarily lithium-ion batteries, and it is expected that solid-state batteries and the like will replace them in the future.

[0055] While lithium-ion batteries were previously dominated by small batteries used in laptops and mobile phones, with the proliferation of electric vehicles, the demand for large batteries capable of driving over 500 km on a single charge is exploding, and production facilities required for battery production are also becoming increasingly larger.

[0056] However, since lithium-ion batteries require drying the binder during the manufacturing process, large-capacity dryers are necessary to meet production volume, and such large-capacity dryers cause many problems in terms of production costs and operation.

[0057] Furthermore, the dry electrode manufacturing process also involves fiberizing PTFE, which does not adhere to the active material, to create a film for pore formation; however, mass production is difficult due to the high-temperature characteristics of PTFE. To overcome this problem and enable continuous production, a thermoplastic binder and active material are fed into a twin-screw system, the binder is melted and agit with the active material, and then extruded through a nozzle to continuously produce active material films. However, in this case, the binder completely fills the spaces between the active materials, leaving no pores, which results in a problem where the electrolyte cannot be impregnated. The problem to be solved

[0058] The present invention aims to solve the aforementioned problems, and the purpose of the present invention is to propose a method for manufacturing a dry electrode of a secondary battery that omits the drying process in the manufacture of a secondary battery.

[0059] To this end, the present invention proposes a method for manufacturing dry electrodes in large quantities without using a solvent and an electrode for a secondary battery manufactured through such a manufacturing process.

[0060] Accordingly, the present invention applies a thermoplastic binder as a material for binding active materials, and proposes a manufacturing method that creates voids between active materials to solve the problem of being unable to impregnate the electrolyte due to the absence of voids between active materials when the thermoplastic binder is used.

[0061] However, the purpose of the present invention is not limited to the purposes mentioned above, and other unmentioned purposes will be clearly understood by those skilled in the art from the description below. means of solving the problem

[0062] To achieve the above objective, the present invention proposes a method for manufacturing a dry electrode for a secondary battery, wherein a solvent-free binder is used, and a foaming process is applied to solve the problem of no voids being formed due to the absence of a solvent in the binder.

[0063] Here, a dry electrode for secondary batteries refers to an electrode manufactured by proceeding with the process without using a solvent in the binder, thereby omitting the drying process due to the absence of solvent application, and by using a foaming agent to form pores to solve the problem of non-pores (a problem where the electrolyte cannot be impregnated due to the lack of pores) resulting from the absence of a solvent in the binder.

[0064] In addition, the foaming agent used to introduce foaming into the binder can be implemented in various ways, such as chemical foaming agents or gases.

[0065] First, I will explain the case where chemical foaming agents are used.

[0066] a. A step of feeding a mixture of active material, binder, and conductive material into a screw mixer; and

[0067] b. A step of primary heating and melting the above mixture while advancing it forward by rotating a screw; and

[0068] c. A step of stirring the heated and melted mixture while rotating the screw to advance it forward; and

[0069] d. A step of secondary heating and stirring the stirred mixture while moving it forward by rotating the screw; and

[0070] e. A step of advancing the mixture heated and stirred in the second time by rotating the screw to apply pressure forward and moving it toward the nozzle end; and

[0071] f. A film manufacturing step of extruding the mixture discharged in a film shape through the nozzle through upper and lower rollers; and

[0072] g. A step of manufacturing an electrode by attaching the above-mentioned manufactured film to a metal foil to manufacture an electrode; and a dry electrode manufacturing method for a secondary battery is proposed.

[0073] In addition, the active material, binder, and conductive material may be mixed in step a above and fed into a screw mixer, or they may be fed separately depending on the case.

[0074] The mixture is prepared by including an organic or inorganic foaming agent in the above mixture, and in step b, the first heating temperature is set higher than the melting temperature of the binder so that the binder melts and mixes with the active material, conductive material, and foaming agent.

[0075] Next, in step d above, the secondary heating temperature is raised higher than the vaporization temperature of the foaming agent so that the foaming agent vaporizes and mixes with the molten binder, and in step e above, as the stirred mixture advances while being pressurized, the vaporized gas mixes with the molten binder in a compressed state.

[0076] At this time, it is preferable that the foaming agent contains one or more of carbon monoxide, carbon dioxide, helium, butane, pentane, nitrogen, water vapor, and nitrogen compounds.

[0077] Subsequently, when the mixture is discharged through the nozzle in step f, the gas compressed in the molten binder expands to form bubbles, creating voids, and these voids are later utilized as spaces for impregnating the electrolyte when the electrolyte is injected.

[0078] In addition, the present invention is characterized by the fact that when the foaming material is foamed, it is converted into one or more of carbon monoxide, carbon dioxide, helium, butane, pentane, nitrogen, water vapor, and nitrogen compounds and evaporates, thereby creating open-cell pores in the binder.

[0079] Next, we would like to introduce another embodiment in which the above voids are created by introducing a gas or supercritical fluid.

[0080] a. A step of mixing the active material, binder, and conductive material and feeding the mixture into a screw mixer;

[0081] b. A step of heating and melting the above mixture while rotating the screw to move it forward;

[0082] c. A step of introducing one of carbon dioxide, nitrogen, helium, butane, pentane, or hydrocarbon gas into the screw mixer in a gaseous or supercritical fluid state,

[0083] d. A step of stirring the heated and melted mixture while moving it forward by rotating the screw.

[0084] e. A step of rotating the screw to apply pressure forward and advance the stirred mixture to the nozzle end.

[0085] f. A film manufacturing step of extruding the mixture, discharged in a film shape through the nozzle, through upper and lower rollers;

[0086] g. A step of manufacturing an electrode by attaching the above-mentioned manufactured film to a metal foil to manufacture an electrode; and a method for manufacturing a dry electrode for a secondary battery is proposed, characterized by comprising the above steps.

[0087] In addition, a method for manufacturing a dry electrode for a secondary battery is proposed, characterized in that, as the stirred mixture advances under pressure in step e, the gas or supercritical fluid is mixed with the molten binder, and when the mixture is discharged through the nozzle in step f, the gas or supercritical fluid mixed in the binder solution expands to form bubbles, and by adjusting the amount of gas or supercritical fluid and temperature conditions, the gas escapes and the bubbles connect to each other to form open voids, and the voids are filled with an electrolyte.

[0088] In this case, it is preferable to use one of the gases among nitrogen, helium, butane, pentane, carbon dioxide, and hydrocarbons as the supercritical fluid.

[0089] The core technology of the present invention is a manufacturing method for producing a dry electrode for a secondary battery, wherein it is preferable to use a thermoplastic resin as the binder in the manufacturing process described above, and since no solvent is used, the drying process is eliminated, while a foaming agent is applied to form pores in the binder to secure a space for impregnating the electrolyte.

[0090] The features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings.

[0091] Prior to this, terms and words used in this specification and claims should not be interpreted in their ordinary and dictionary senses, but should be interpreted in a sense and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention. Effects of the invention

[0092] As described above, according to the present invention, the advantage of being able to easily manufacture a dry electrode for a secondary battery is expected.

[0093] In addition, there is no need for a dryer with a length of about 100m, which is the standard for secondary batteries, and since the solvent does not evaporate, there is no need for a solvent recovery device, which can reduce electricity costs associated with operating the dryer and significantly reduce the factory site area by omitting the dryer.

[0094] Furthermore, since a 100m long solvent dryer is not required, there is no need to operate a solvent recovery device, which has the advantage of reducing battery manufacturing costs and preventing environmental problems such as carbon dioxide and organic solvent emissions. Brief explanation of the drawing

[0095] Figure 1 illustrates the basic structure of a secondary battery. Figure 2 illustrates a drying device for a secondary battery. Figure 3 illustrates the process of making an active material film and attaching a current collector to the film to form an electrode plate. Figure 4 illustrates an electrode structure for a secondary battery. Figure 5 is a figure illustrating the process of forming voids between active materials in a wet electrode process. Figure 6 illustrates a typical twin-screw mixer configuration. Figure 7 illustrates the process of making a mixture for a dry electrode by applying a screw mixer. Specific details for implementing the invention

[0096] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In this process, the thickness of lines or the size of components shown in the drawings may be exaggerated for clarity and convenience of explanation.

[0097] Furthermore, the terms described below are defined in consideration of their functions in the present invention, and these may vary depending on the intent or practice of the user or operator. Therefore, the definitions of these terms should be based on the content throughout this specification.

[0098] In addition, the following embodiments are not intended to limit the scope of the present invention but are merely exemplary details of the components presented in the claims of the present invention, and embodiments including components that are included in the technical concept throughout the specification of the present invention and are substitutable as equivalents for the components of the claims may be included in the scope of the present invention.

[0099] The dry electrode manufacturing process currently under review forms a film by fiberizing PTFE (Polytetrafluoroethylene), which does not adhere to the active material, to form pores, but it has the disadvantage that mass production is difficult due to the high temperature characteristics of PTFE.

[0100] As a way to overcome this, films can be continuously produced even with a standard twin-screw extruder by heating and stirring the thermoplastic resin and active material.

[0101] However, in this case, a problem arises where the electrolyte cannot be injected because there are no gaps between the active materials.

[0102] In this case, a method can be applied to forcibly create pores using organic or inorganic foaming agents. That is, when mixing the active material powder and binder using a twin-screw extruder, a foaming agent is also added and mixed together.

[0103] During stirring, the binder melts and mixes evenly with the active material and foaming agent, after which it passes through a section set above the temperature at which the foaming agent decomposes.

[0104] In this section, the foaming agent decomposes due to heat, releasing gases such as carbon dioxide, nitrogen, and water vapor. These gases then dissolve into the molten binder, and as they pass through the nozzle and are extruded in a film shape, the pressure decreases, causing the gases to expand and form voids in the spaces between the active materials.

[0105] Since all organic and inorganic foaming agents emit even small amounts of carbon dioxide or water, this method conflicts with the goal of helping to reduce carbon dioxide by consuming less electricity through the elimination of dryers during the electrode manufacturing process; therefore, while it can be used for dry electrodes for secondary batteries, it is not desirable.

[0106] If pores are formed using organic or inorganic foaming agents, one may consider capturing the emitted carbon dioxide using a capture facility.

[0107] Another foaming method involves using gases or supercritical fluids such as carbon dioxide, nitrogen, helium, butane, pentane, and hydrocarbons.

[0108] The active material and binder are fed into a screw extruder, heated to melt the binder, and stirred. Then, carbon dioxide, nitrogen, helium, butane, pentane, hydrocarbon gases, etc., which are brought to a supercritical state using a gas or supercritical pump, are impregnated into the molten and stirred liquid, and the mixture of this supercritical fluid, active material, and binder is further stirred.

[0109] When this material is extruded through the nozzle, the gas evenly distributed between the binders, or one or more gases in a supercritical state such as nitrogen, helium, butane, pentane, carbon dioxide, hydrocarbons, and carbon dioxide, expand to form microbubbles.

[0110] Figure 4 illustrates an electrode structure for a secondary battery.

[0111] Looking at Figure 4, round active materials with a particle size of about 10 µm are attached by a binder having pores connected between them.

[0112] That is, Figure 4 is a three-dimensional visualization of the cross-section of a battery electrode, where a) is an SEM image magnified 500 times with a hole drilled in a part of the electrode, b) is an SEM image magnified 4000 times with the yellow square area of ​​the hole in the above a) photo, c) is an enlarged image of the green area of ​​the above b) photo, and d) is an image with the void area of ​​the above c) clearly processed.

[0113] In the above wet process, after coating the slurry, the solvent is blown away to form voids (shown in black in Fig. 4d).

[0114] Figure 5 shows the process of forming voids between active materials in a wet electrode process.

[0115] Figure 5 illustrates the current production method of a LIB (lithium-ion battery) electrode, where a) shows a wet film with a uniform distribution, b) shows a state where the interior is filled as the solvent evaporates and shrinks, c) shows a state where the solvent continues to evaporate but partially fills the capillaries to form a network and the shrinkage is terminated, d) shows the residual liquid (solvent) remaining in the pores, and e) shows a dried film in which all the liquid (solvent) has evaporated.

[0116] However, unlike the wet process described above, dry electrodes cannot use a solvent, and since the binder must be melted with heat and stirred, voids cannot be formed through the drying process.

[0117] Therefore, the present invention aims to realize pores inside the electrode using a foaming method, and intends to apply methods using organic or inorganic foaming agents and methods using gas or supercritical fluid.

[0118] This process is explained in detail through Figures 6 and 7 as follows.

[0119] Screw mixers are used as single or twin units and consist of a configuration in which interchangeable blades of various shapes are connected in series on a single long shaft.

[0120] In particular, for example, regarding blade pitch, if a blade having a pitch of 2 turns relative to the blade diameter is placed after a blade having a pitch of 1 turn relative to the blade diameter for the same length, high pressure is applied in the 2-pitch blade area compared to the previous shear.

[0121] Conversely, if a 1-pitch blade is placed after a 2-pitch blade, low pressure is applied in the 1-pitch blade section. Therefore, in order to remove gas attached to the surface of the material being stirred in the mixer, a hole is made in the barrel in this low-pressure section to discharge the gas.

[0122] As shown in Figure 6, in a typical twin screw mixer configuration example, the 'Y' section is a low-pressure section compared to the 'X' section (i.e., the blade pitch of the Y section is larger than the blade pitch of the X section), so if a hole is formed here, gas can be discharged through this.

[0123] When preparing a mixture for dry electrodes using the said method, voids are formed inside the binder in the following manner.

[0124] To explain Figure 7, 1 is the powder mixture, 2 is heating and melting, 3 is conveying and stirring, 4 is additional heating and stirring, 5 is conveying, and 6 is the joining section.

[0125] In order to form pores using a foaming agent in the structure of Fig. 7, first, the foaming agent powder is added together with the powder mixture of No. 1 (active material + binder + conductive material) and supplied.

[0126] This mixture passes through section 2, is heated and melted, and in section 3, this melted mixture is evenly stirred.

[0127] The foaming agent of the stirred molten mixture passes through section 4, which is heated above the foaming temperature of the foaming agent, becomes a gas, and mixes with the molten mixture. After passing through section 6 and being compressed, it exits through the nozzle, and the gas mixed in the molten liquid expands in volume to form bubbles.

[0128] At this time, placing an additional stirring blade in section 6 is advantageous for evenly mixing the gas.

[0129] Here, depending on the amount of foaming agent added or temperature conditions, it becomes a closed pore or an open pore.

[0130] Another example describes a case where a gas or supercritical fluid is used as the foaming agent.

[0131] Powder mixture No. 1 is supplied with only active material + binder + conductive material without foaming agent, then similarly passes through section No. 2 and is heated to melt the binder, and then passes through sections No. 3 and 4 and is mixed.

[0132] Next, it is desirable to impregnate the last part of the 5th transfer step by applying carbon dioxide, nitrogen, helium, butane, pentane, hydrocarbon gas, etc., in a gaseous or supercritical fluid state.

[0133] The above-mentioned impregnated gas or supercritical fluid is mixed with the binder and passes through the 6th high-pressure section. As additional stirring is performed under high pressure, the molten mixture and the impregnated gas or supercritical fluid are evenly mixed. As the pressure is released at the moment of exiting through the nozzle, the compressed gas mixed between the binders expands to form bubbles.

[0134] Through this process, depending on the amount of impregnated gas or temperature conditions, it becomes closed pores or connected pores.

[0135] As explained above, conventionally, to manufacture porous electrodes for secondary batteries, a binder solution is prepared by dissolving a binder in a solvent, coated onto a current collector, and then pores are created through a drying process.

[0136] In this process, an expensive dryer is required and high electricity costs are incurred for its operation, but the present invention proposes a manufacturing method in which a binder is melted by heat using a twin-screw mixer and stirred with an active material, and then an organic or inorganic chemical foaming agent or a gas such as carbon dioxide, nitrogen, helium, butane, pentane, hydrocarbon gas, or a supercritical fluid of these gases is stirred, and then foaming occurs while forming pores when the mixture is formed into a film shape through a nozzle.

[0137] This pore formation method eliminates the need for a dryer, which is currently about 100m long according to secondary battery standards, and since the solvent does not evaporate, a solvent recovery device is not required. It can also reduce electricity costs associated with operating the dryer and significantly reduce the factory site area by omitting the dryer.

[0138] Although the present invention has been described in detail through specific embodiments, this is for the purpose of specifically explaining the invention, and the invention is not limited thereto. It is evident that modifications or improvements can be made by those skilled in the art within the technical scope of the invention.

[0139] All simple variations or modifications of the present invention fall within the scope of the present invention, and the specific scope of protection of the present invention will be clarified by the appended claims. Explanation of the symbols

[0140] 1 is the powder mixture, 2 is heating and melting, 3 is conveying and stirring, 4 is additional heating and stirring, 5 is conveying, and 6 is the joining section.

Claims

Claim 1 delete Claim 2 delete Claim 3 delete Claim 4 A method for manufacturing a dry electrode for a secondary battery comprises: a. mixing an active material and a binder and feeding them into a screw mixer; b. heating and melting the mixture while moving it forward by rotating the screw; c. feeding a supercritical fluid into the screw mixer; d. stirring the heated and melted mixture while moving it forward by rotating the screw; e. pushing the stirred mixture forward by applying pressure while rotating the screw to the nozzle end; f. a film manufacturing step in which the mixture discharged in a film shape through the nozzle is compressed through upper and lower rollers; g. attaching the manufactured film to a metal foil to manufacture an electrode; wherein the screw mixer is divided into six sections from feeding to discharging, and the mixture of the active material and binder is fed into section 1, and then the fed mixture is heated as it passes through section 2 to melt the binder, and then mixed as it passes through sections 3 and 4. A method for manufacturing a dry electrode for a secondary battery, characterized in that a supercritical fluid is impregnated in section 5, and the impregnated supercritical fluid passes through a high-pressure section, which is section 6, wherein the blades are arranged such that the pitch of section 6 is smaller than the pitch of section 5, where the distance the center of the blade moves when the shaft of the screw mixer rotates once is called the pitch, thereby forming a higher pressure in section 6 compared to section 5, and accordingly, the supercritical fluid is injected from the low-pressure section 5 and passes through the high-pressure section 6 while undergoing additional stirring, so that the molten mixture and the impregnated supercritical fluid are uniformly mixed to manufacture an electrode for a secondary battery. Claim 5 A method for manufacturing a dry electrode for a secondary battery, characterized by adding a conductive material to the mixture and mixing it according to claim 4. Claim 6 A method for manufacturing a dry electrode for a secondary battery, characterized in that, in claim 4, the supercritical fluid is one or more of carbon dioxide, butane, pentane, and hydrocarbon gas, and when the mixture is discharged through the nozzle in step f, the gas or supercritical fluid mixed in the binder solution expands to form bubbles, and the voids created by the bubbles are filled with an electrolyte. Claim 7 delete

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