Electrode manufacturing system and method for improving adhesion - Patents.com

Abstract

The present invention relates to an electrode manufacturing system, an electrode manufacturing method, and an electrode manufactured thereby. The electrode manufacturing system includes a heat treatment section that is provided downstream of a drying section and heats an electrode substrate to a high temperature. The heat treatment process has the advantage of changing the crystal phase of the PVDF binder of the electrode substrate, thereby increasing the adhesive strength of the electrode and preventing the detachment of the electrode active material layer.

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2022-0121746, filed on September 26, 2022.

[0002] The present invention relates to a system for manufacturing electrodes for secondary batteries, an electrode manufacturing method, and an electrode manufactured by the method, for improving adhesive strength. [Background technology]

[0003] The demand for secondary batteries is also increasing rapidly due to technological development and increasing demand for mobile devices. Among them, lithium secondary batteries are widely used as an energy source for various electronic products as well as various mobile devices due to their high energy density, operating voltage, and excellent storage and life characteristics.

[0004] The electrode manufacturing process (hereinafter referred to as the "electrode process") for manufacturing electrodes for lithium secondary batteries includes a coating process for applying an electrode slurry containing an electrode active material to the surface of a metal foil as a current collector, a drying process for removing the solvent from the electrode slurry, a rolling process for rolling the dried electrode, and a notching and slitting process for forming an electrode tab on the electrode and cutting the electrode according to size.

[0005] Among these, the electrode drying process is carried out by placing the electrodes in an electrode drying oven capable of injecting hot air and / or radiating radiant heat, and the electrodes are transported within the drying oven at a predetermined speed to perform the drying process.

[0006] Conventional electrode manufacturing systems and methods are configured to pass electrodes through a drying oven at a transport speed of 10 to 40 m / min. In recent years, however, there has been a trend toward increasing the transport speed of the electrodes traveling through the drying oven to 70 to 100 m / min in order to improve the production efficiency of the electrode process.

[0007] On the other hand, electrodes contain binders to ensure that the electrode active material and conductive material, which are the materials that make up the electrode, are well lumped together and to provide interfacial adhesion between the electrode active material layer and the current collector. PVDF (Polyvinylidene fluoride)-based binders have excellent adhesive strength and are chemically stable against electrolytes, so they are widely used as electrode binders, especially as positive electrode binders.

[0008] Such PVDF-based binders have various crystal structure phases such as alpha, beta, and gamma, which are formed by thermal / mechanical treatment, and it is known that a higher proportion of the gamma phase is more advantageous for electrode adhesion.

[0009] There is a need to develop technology for electrode manufacturing systems and methods that can increase the proportion of gamma phase in PVDF-based binders while also achieving superior electrode production speed. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been made to solve the above problems, and aims to provide an electrode manufacturing system that has excellent electrode production speed while being capable of changing the crystal phase of a PVDF-based binder to improve adhesive strength, and a manufacturing method using the same. [Means for solving the problem]

[0011] According to one embodiment of the present invention, there is provided an electrode manufacturing system, which may include a transport unit including a transport roller configured to support and transport a long sheet-like electrode substrate in one direction, a coating unit that applies an electrode slurry including a polyvinylidene fluoride (PVDF)-based binder onto an electrode current collector, a drying unit that dries the electrode substrate coated with the electrode slurry, and a heat treatment unit that is disposed downstream of the drying unit and configured to apply heat to the electrode substrate discharged from the drying unit.

[0012] In one embodiment of the present invention, the heat treatment section may include a heat source configured to apply heat of 170° C. or more to the electrode substrate.

[0013] In one embodiment of the present invention, the heat sources may be arranged in a number n (n is an integer of 2 or more) in the direction in which the electrode substrate is transported (MD; Machine direction), and the n (n is an integer of 2 or more) heat sources may be independently controlled.

[0014] In an embodiment of the present invention, the heat source may be a heating roller having a heating wire built in a transport roller for transporting the electrode substrate.

[0015] In one embodiment of the present invention, the heat source may be selected from a laser module configured to apply a laser to the electrode substrate, and an infrared heater configured to apply infrared rays.

[0016] The electrode manufacturing system according to an embodiment of the present invention may further include a control unit that controls the operation of the heat source.

[0017] In one embodiment of the present invention, the transport section may be configured to transport the electrode base material at a speed of 50 to 100 m / min.

[0018] In one embodiment of the present invention, the transport section may be configured to transport the electrode base material at a speed of 70 to 100 m / min.

[0019] In an embodiment of the present invention, the coating unit includes a first coating unit configured to apply an electrode slurry containing a PVDF-based binder to one surface of an electrode collector, and a second coating unit configured to apply an electrode slurry containing a PVDF-based binder to the other surface of the electrode collector. The drying unit includes a first drying unit configured to dry the electrode base material that has passed through the first coating unit, and a second drying unit configured to dry the electrode base material that has passed through the second coating unit. The heat treatment unit includes a first heat treatment unit disposed downstream of the first drying unit and configured to apply heat to the electrode base material discharged from the first drying unit, and a second heat treatment unit disposed downstream of the second drying unit and configured to apply heat to the electrode base material discharged from the second drying unit. The electrode base material transported by the transport unit may be configured to sequentially pass through the first coating unit, the first drying unit, the first heat treatment unit, the second coating unit, the second dryer, and the second heat treatment unit.

[0020] In an embodiment of the present invention, the heat treatment section may include an openable partition for isolating at least a portion of a space to which the heat source applies heat from the outside.

[0021] In an embodiment of the present invention, the heat treatment section may be configured to apply heat only to a ground portion where an electrode active material layer is formed on the electrode substrate.

[0022] According to another embodiment of the present invention, there is provided a method for manufacturing an electrode. The method for manufacturing an electrode according to the present invention may include a step of forming a slurry coating layer by applying an electrode slurry containing a polyvinylidene fluoride (PVDF)-based binder onto an electrode current collector, a step of drying the electrode substrate on which the slurry coating layer is formed, and a step of applying heat to the dried electrode substrate to change the crystalline phase of the PVDF-based binder in the electrode substrate.

[0023] In one embodiment of the present invention, the heat treatment step may involve applying heat of 170° C. or more to the electrode substrate.

[0024] In one embodiment of the present invention, the transport speed of the electrode substrate in the drying step may be in the range of 50 to 100 m / min.

[0025] In one embodiment of the present invention, the transport speed of the electrode substrate in the drying step may be in the range of 70 to 100 m / min.

[0026] In one embodiment of the present invention, the drying temperature in the drying step may be in the range of 80 to 120°C. Effect of the Invention

[0027] According to the present invention, the heat treatment section applies additional heat to the dried electrode substrate to induce recrystallization of the PVDF-based binder, increasing the proportion of gamma phase crystals, thereby improving the adhesive strength of the electrode.

[0028] According to the present invention, since recrystallization is performed through annealing of the heat treatment portion without the need to reduce the transport speed of the electrode substrate, the production efficiency of the electrode is excellent.

[0029] According to the present invention, the solvent that may remain in the electrode substrate after being removed from the drying oven can be completely removed by passing through the heat treatment unit, so that the time required for the vacuum drying process that is carried out after drying can be reduced. [Brief description of the drawings]

[0030] [Figure 1] 1 is a schematic diagram showing an electrode manufacturing system according to an embodiment of the present invention; [Diagram 2] 2 is an enlarged view of the heat treatment section in FIG. 1. [Diagram 3] 2 is an enlarged view of a heat treatment unit according to an embodiment of the present invention; [Figure 4] 2 is an enlarged view of a heat treatment unit according to an embodiment of the present invention; [Diagram 5] 1 is a schematic diagram showing an electrode manufacturing system according to an embodiment of the present invention. [Figure 6]FIG. 1 is a schematic diagram showing an electrode manufacturing system in the form of a two-layer structure in one example of the present invention. [Figure 7] 1 is a flowchart showing the steps of an electrode manufacturing method according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Since the present invention can be modified in various ways and can have various forms, specific embodiments are illustrated in the drawings and described in detail in this specification, but it is not intended to limit the present invention to the specific disclosed forms, but to include all modifications, equivalents, or alternatives falling within the spirit and technical scope of the present invention.

[0032] In this application, the terms "comprise" and "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and may be understood as not precluding the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. In addition, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only the case where it is "directly under" the other part, but also the case where there is another part in between. In addition, in this application, being "on" may include not only the case where it is located on the top, but also the case where it is located on the bottom.

[0033] In this specification, the electrode base material is a concept that includes both an electrode current collector to which an electrode slurry is applied, and an electrode current collector to which an electrode active material layer is formed by drying the electrode slurry applied to the electrode current collector.

[0034] The present invention provides an electrode manufacturing system, an electrode manufacturing method using the same, and an electrode manufactured thereby.

[0035] Polyvinylidene fluoride (PVDF)-based binders are commonly used as binders for electrodes. The crystal structure of PVDF-based binders has alpha (α), beta (β), gamma (γ) and delta (δ) crystal phases, and the type and ratio of the crystal phases affect the adhesive strength of the PVDF-based binder. Specifically, it is known that the gamma (γ) crystal phase is more advantageous for improving adhesive strength than other crystal phases. Therefore, by increasing the ratio of the gamma (γ) crystal phase in the PVDF-based binder, the adhesive strength of the electrode can be increased without increasing the binder content.

[0036] In order to increase the proportion of gamma (γ) crystal phase in the PVDF-based binder contained in the electrode, it is possible to consider a method of recrystallizing the alpha (α) and beta (β) crystal phases into the gamma (γ) crystal phase. However, such recrystallization requires heating the PVDF-based binder to a temperature of 170°C or higher, which is the crystal melting temperature (Tm).

[0037] During the electrode drying process, high heat is applied to the electrode substrate as it travels through a drying oven. In theory, it may be possible to set the drying temperature during the drying process to 170°C or higher and recrystallize the crystalline phase of the PVDF-based binder into the gamma (γ) crystalline phase. However, it is practically impossible or difficult to recrystallize the PVDF-based binder during the electrode drying process at the production site.

[0038] Even if the drying temperature of the drying oven is set to 170°C or higher, the electrode slurry contains a solvent, and the surrounding temperature is lowered due to the heat of vaporization when the solvent evaporates, so the temperature of the electrode substrate traveling in the drying oven can only be much lower than 170°C, specifically 80 to 120°C. In addition, in recent electrode manufacturing systems, the transport speed of the electrode substrate is set to 50 to 100 m / min, more specifically 70 to 100 m / min, in order to maximize the productivity of the electrode, so the drying temperature in the drying oven can be lower. As the transport speed of the electrode substrate increases, the time that the electrode substrate remains in the drying oven can only be reduced, and the increase in the transport speed of the electrode substrate makes it more difficult to recrystallize the PVDF-based binder during electrode drying.

[0039] The present invention is characterized in that, in the electrode manufacturing system and electrode manufacturing method, a heat treatment section is provided downstream of a drying section so that high-temperature heat can be applied to the electrode substrate after the electrode substrate is dried in order to recrystallize the crystalline phase of the PVDF-based binder in the electrode into the gamma phase without reducing the production speed of the electrode.

[0040] Specifically, the electrode manufacturing system according to the present invention has a separate heat treatment section disposed downstream of the drying section for supplying high-temperature heat to the dried electrode substrate, and the heat treatment section supplies sufficient heat to the electrode substrate to recrystallize the alpha (α) and beta (β) crystal phases of the PVDF-based binder into the gamma (γ) crystal phase, thereby increasing the proportion of the gamma phase in the PVDF-based binder and improving the adhesive strength of the electrode.

[0041] The electrode manufacturing system according to the present invention will be described in detail below.

[0042] In one example, an electrode manufacturing system according to the present invention includes a transport unit including a transport roller configured to support and transport a long sheet-like electrode substrate in one direction, a coating unit that applies an electrode slurry including a polyvinylidene fluoride (PVDF)-based binder onto an electrode current collector, a drying unit that dries the electrode substrate coated with the electrode slurry, and a heat treatment unit that is disposed downstream of the drying unit and configured to apply heat to the electrode substrate discharged from the drying unit.

[0043] The transport unit may include a plurality of transport rollers located below the electrode substrate, each of which is configured to rotate by a driving force applied from a motor, and the electrode substrate may be transported in one direction by the rotational motion of the transport rollers. The transport unit may include an unwinder configured to unwind the wound current collector sheet, and a rewinder for winding the electrode substrate onto a roll.

[0044] The coating unit includes a slot die coater for applying an electrode slurry, and a coating roller disposed opposite the slot die. The electrode slurry discharged from the slot die coater is applied onto the electrode substrate supported and transported by the coating roller, thereby forming an electrode slurry coating layer.

[0045] The electrode slurry may include an electrode active material, a binder, a conductive material, and a solvent. The electrode active material may be a positive electrode active material or a negative electrode active material. The binder may include a PVDF-based binder, and may additionally include other types of binders. In a specific example, the PVDF-based binder includes one or more of a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and a monomer copolymerizable therewith, and a mixture thereof. The monomer copolymerizable with vinylidene fluoride may include one or more selected from vinyl fluoride, trifluoroethylene (TrFE), chlorofluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro(alkyl vinyl) ether, perfluoro(1,3-dioxole), and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD).

[0046] The solvent is not particularly limited as long as it is a solvent for producing a slurry for a secondary battery electrode, and specific examples thereof include NMP (N-Methyl-2-pyrrolidone) and water.

[0047] The drying unit dries the electrode slurry by applying heat to the electrode substrate to remove the solvent in the applied electrode slurry. The drying unit includes a drying furnace or a drying oven, and the drying furnace or the drying oven may be one commonly known in the art. The drying furnace or the drying oven may be a hot air type, a radiant heat type, a direct heating type, an induction heating type, or the like, or a mixture of these may be used.

[0048] The heat treatment section applies heat to the electrode substrate discharged from the drying section to recrystallize the crystalline phase of the PVDF-based binder in the electrode substrate. Specifically, the PVDF-based binder is a polymer formed by bonding between PVDF monomers or between PVDF monomers and monomers of other substances, and PVDF can have various crystalline phases depending on the temperature conditions. Depending on the crystalline phase state, the binding property of the polymer as well as the electrode characteristics can be affected. More specifically, the crystalline phase of PVDF has alpha (α), beta (β), gamma (γ), and other crystalline phases depending on the arrangement form of the chain. At this time, since the gamma (γ) crystalline phase has a higher binding property than other crystalline phases, it is preferable to increase the proportion of the gamma (γ) phase in order to increase the binding property of the binder.

[0049] The inventors of the present invention have observed the phase change of PVDF according to the heat treatment temperature through various experiments and observations. As a result, when heat of 170°C or more, which is the crystalline melting temperature (Tm) of PVDF, is supplied to a dried electrode substrate, recrystallization of alpha (α) and beta (β) crystals is induced, and the proportion of gamma (γ) crystal phase is significantly increased. As a result, it has been found that a PVDF-based binder having a high proportion of gamma (γ) phase increases the adhesive strength of an electrode and can effectively reduce detachment of the electrode active material layer during the rolling and slitting processes after the drying process.

[0050] Therefore, the present invention provides an annealing system that can manufacture an electrode having improved binding strength by applying high temperature heat to the electrode substrate after drying by providing a heat treatment section downstream of the drying section and changing the crystallinity of the PVDF-based binder in the electrode substrate.

[0051] In some embodiments, the heat treatment section includes a heat source configured to apply heat of 170° C. or more to the electrode base material. The heat source may be configured to apply heat of 170° C. or more, specifically, 170° C. to 300° C., to the electrode base material for recrystallization of the PVDF-based binder. If the electrode base material is heated to a temperature of more than 300° C., the PVDF-based binder may burn, which is not preferable.

[0052] In some embodiments, the heat sources are arranged in a machine direction (MD) in which the electrode substrate coated with the electrode slurry is transported, and the n heat sources (n is an integer of 2 or more) are spaced apart from one another, and the n heat sources (n is an integer of 2 or more) can be controlled independently. This allows the electrode substrate to be heat-treated according to conditions optimized for each electrode model. That is, the electrode substrate can be classified into various models according to the type of electrode active material, the composition of the electrode active material layer, the thickness of the electrode active material layer, the type of collector, the thickness of the collector, etc., and the heat treatment conditions that can maximize the adhesive strength differ depending on the electrode model. Therefore, in order to perform heat treatment according to the heat treatment conditions optimized for each electrode model, it is preferable to independently control a plurality of heat sources.

[0053] In some embodiments, the heat source may be a heating roller having a heat ray built in a transport roller for transporting the electrode substrate. The heat ray is inserted in the transport roller, and the heat applied from the heat ray is transferred through the transport roller to the electrode substrate supported by the transport roller.

[0054] In some embodiments, the heat source may be selected from a laser module configured to apply a laser to the electrode substrate and an infrared heater configured to apply infrared light. The laser module may be configured to directly irradiate the electrode substrate with laser light, and the IR heater may be configured to irradiate the electrode substrate with radiant heat using an infrared lamp or the like.

[0055] In some embodiments, the electrode manufacturing system of the present invention further includes a controller that controls the operation of the n heat sources (n is an integer of 2 or more). Specifically, the controller controls whether or not the laser module, the infrared heater, or the heating roller is operated, or the output size of the thermal energy applied by each heat source.

[0056] The present invention also provides a method for manufacturing an electrode.

[0057] In the present invention, the above-mentioned description of the electrode manufacturing system is also applicable to the electrode manufacturing method, and a detailed description thereof will be omitted.

[0058] 7 is a flow chart for explaining a method for manufacturing an electrode according to the present invention. Referring to FIG. 7, the method for manufacturing an electrode according to the present invention includes a step of forming a slurry coating layer (S10) by applying an electrode slurry containing a polyvinylidene fluoride (PVDF)-based binder onto an electrode current collector, a step of drying (S20) by drying the electrode substrate on which the slurry coating layer is formed, and a step of heat treatment (S30) by applying heat to the dried electrode substrate to change the crystal phase of the PVDF-based binder in the electrode substrate.

[0059] The slurry coating layer forming step (S10) is a step of coating an electrode slurry including a PVDF-based binder on an electrode collector being transported in one direction.

[0060] In the drying step (S20), the electrode substrate on which the electrode slurry coating layer is formed may be dried using the drying oven described above. In some embodiments, in the drying step (S20), the transport speed of the electrode substrate may be 50 to 100 m / min, preferably 70 to 100 m / min, and more preferably 80 to 100 m / min, in terms of electrode production efficiency. In the drying step (S20) according to some embodiments, the drying temperature of the drying oven may be in the range of 80 to 120° C. Here, the drying temperature refers to the temperature of the electrode substrate transported in the drying oven. Even if the temperature of the drying oven is set to 170° C. or higher, the electrode slurry during drying contains a solvent, and the transport speed of the electrode substrate reaches 50 m / min to 100 m / min, so that the temperature of the electrode substrate is in the range of 150° C. or lower, which is lower than 170° C., specifically 70 to 140° C., more specifically 75 to 130° C., and even more specifically 80 to 120° C.

[0061] The heat treatment step (S30) may be a step of changing the crystal phase of the PVDF-based binder by applying high temperature heat to the electrode substrate that has been subjected to the drying step (S20). The heat treatment step (S30) recrystallizes the alpha and beta phase crystal structures of the PVDF-based binder into a gamma phase crystal structure, thereby increasing the proportion of the gamma phase in the PVDF-based binder.

[0062] In some embodiments, the heat treatment step (S30) may include applying heat of 170° C. or more to the electrode substrate. In some embodiments, the time for applying heat in the above temperature range may be 10 seconds to 1 hour, more specifically 30 seconds to 30 minutes, and even more specifically 1 minute to 10 minutes.

[0063] In some embodiments, the method for manufacturing an electrode according to the present invention may further include a step of vacuum drying (S40) to completely remove moisture from the dried electrode. The vacuum drying step (S40) is an independent step distinct from the heat treatment step (S30), and the drying temperature in the vacuum drying step (S40) may be 80 to 120° C. In the method for manufacturing an electrode according to the present invention, since water is also removed in the heat treatment step, the time required for the vacuum drying step can be reduced, ultimately improving the production efficiency of the electrode manufacturing.

[0064] Hereinafter, specific examples of the present invention will be described in detail with reference to the accompanying drawings.

[0065] (First embodiment) Fig. 1 is a schematic diagram showing an electrode manufacturing system according to a first embodiment of the present invention, and Fig. 2 is an enlarged view of a heat treatment section of Fig. 1. Referring to Fig. 1, an electrode manufacturing system 100 according to the present invention includes a transfer section 120, a coating section 130, a drying section 140, and a heat treatment section 150.

[0066] The transport unit 120 may include a plurality of transport rollers 121, and the transport rollers 121 may be rotated by power of a motor (not shown) to transport the electrode substrate 110 in one direction. The transport unit 120 may include an unwinder 122 configured to unwind the wound current collector sheet, and a rewinder (not shown) for winding the electrode substrate on a roll.

[0067] In some embodiments, the transport unit 120 may be configured to transport the electrode base material 110 at a speed of 50 to 100 m / min, preferably 70 to 100 m / min, and more preferably 80 to 100 m / min. This allows the electrode manufacturing system 100 according to the present invention to have extremely excellent electrode production efficiency.

[0068] The coating unit 130 may include a slot die coater 132 that discharges the electrode slurry 111, and a coating roller 131 disposed facing the slot die coater 132. The electrode slurry 111 discharged from the slot die coater 132 is applied onto the electrode substrate 110 supported and transported by the coating roller 131, to form an electrode slurry coating layer.

[0069] The drying section 140 may include one or more drying ovens configured to dry the electrode substrate 110 transported by the transport roller 121 at a high temperature.

[0070] In one embodiment, the drying oven may be divided into a plurality of drying zones, and the set drying temperature of each of the plurality of drying zones may be controlled independently. Specifically, a temperature increasing drying zone in which the drying rate of the electrode increases may be disposed at the front end, and a constant rate drying zone in which the drying rate increased in the temperature increasing drying zone is kept constant may be disposed downstream of the temperature increasing drying zone. A falling rate drying zone in which the drying rate of the electrode decreases as the drying is almost completed may be disposed downstream of the constant rate drying zone.

[0071] In one embodiment, the drying oven may include a drying means for drying the electrode slurry applied to the electrode. The drying means is not limited as long as it is a means capable of supplying thermal energy to the electrode slurry and removing the solvent in the electrode slurry to dry the electrode slurry.

[0072] According to one embodiment, the drying means may be one or two selected from a hot air supply unit and a heater.

[0073] The hot air supply unit may be configured to spray hot air toward the electrode substrate 110 transported in the drying oven. In one embodiment, the hot air supply unit may include a heat exchanger (not shown) for heating supplied outside air, a hot air spray nozzle installed in the drying oven and configured to spray hot air toward the electrode substrate, a blower fan for supplying the outside air heated by the heat exchanger to the hot air spray nozzle through a duct connected to the inner space of the drying oven, and a damper installed in the duct for adjusting the supply amount of hot air.

[0074] The heater may be configured to irradiate radiant heat to the electrode substrate 110 transported in the drying oven. If necessary, the heater may further include a shielding film. The shielding film may be bonded below the heater in order to adjust the position and / or area of ​​the region irradiated with the radiant heat emitted from the heater.

[0075] The drying unit 140 serves to dry the solvent in the slurry coating layer, and the number or arrangement of the drying ovens may be suitably changed depending on the composition of the electrode slurry 111 and the coating thickness of the electrode slurry.

[0076] Fig. 2 is a schematic diagram showing an enlarged heat treatment section 150 of the electrode manufacturing system 100 of Fig. 1. Referring to Fig. 1 and Fig. 2, the heat treatment section 150 is disposed downstream of the drying section 140. In some embodiments, the heat treatment section 150 is disposed near the outlet of the drying section 140, and applies high-temperature heat to the electrode substrate 110 before the temperature of the electrode substrate 110 discharged from the drying section 140 drops, thereby improving the recrystallization efficiency of the PVDF-based binder.

[0077] The heat treatment unit 150 includes a heat source 151, which is configured to apply additional heat to the dried electrode substrate 110. The heat source 151 may be configured to apply heat of 170° C. or more to the electrode substrate 110, which may cause the alpha (α) and beta (β) crystal phases of the PVDF-based binder contained in the electrode active material layer to be recrystallized into a gamma (γ) crystal phase, thereby improving the electrode adhesion.

[0078] The heat sources 151 are arranged in a number n (n is an integer greater than or equal to 2) in the direction in which the electrode substrate 110 is transported (MD; Machine direction), and the n (n is an integer greater than or equal to 2) heat sources 151 can be controlled independently.

[0079] In some embodiments, the heat source 151 may be selected from a laser module configured to apply a laser to the electrode substrate and an infrared heater configured to apply infrared light. The laser module may be configured to directly irradiate the electrode substrate with laser light, and the IR heater may be configured to irradiate the electrode substrate with radiant heat using an infrared lamp or the like.

[0080] In some embodiments, the electrode manufacturing system 100 may further include a controller for independently controlling the plurality of heat sources 151 and for controlling on-off control of the heat sources 151 and / or control of the output of the heat sources 151 .

[0081] In some embodiments, the heat treatment unit 150 may be configured to apply heat only to the grounded portion where an electrode active material layer is formed on the electrode substrate 110. If high-temperature heat is applied to an uncoated portion where no electrode active material layer is formed and the current collector is exposed, heat wrinkles may occur near the boundary between the uncoated portion and the grounded portion due to the difference in elongation rate between the uncoated portion and the grounded portion, so by applying heat only to the grounded portion, the risk of defects caused by heat wrinkles may be reduced.

[0082] In some embodiments, the heat treatment unit 150 may further include an openable partition for isolating at least a portion of the space to which the heat source applies heat from the outside. The partition serves to protect workers from high temperature heat.

[0083] Second embodiment 3 and 4 are enlarged views of the heat treatment section according to the second embodiment of the present invention. The following description will focus on the differences from the heat treatment section according to the first embodiment.

[0084] 3, the heat source 251 of the heat treatment unit 250 according to the second embodiment may be a heating roller having a heat ray built in. The heat ray is inserted inside the transport roller, and heat applied from the heat ray is transferred to the electrode substrate 210 through the transport roller.

[0085] The heat wire is not particularly limited as long as it can heat the temperature of the heating roller, and specifically, an induction heating coil can be exemplified. An AC voltage can be applied to the induction heating coil to generate heat energy in a short time. The AC voltage applied to the induction heating coil can have a frequency in the range of about 100 kHz to 500 kHz. An AC power source can be connected to the induction heating coil. When an AC voltage is applied to the induction heating coil, an electromotive force is induced by the electromagnetic induction phenomenon, and the electrodes can be heated by the induced current generated by the electromotive force.

[0086] In some embodiments, the induction heating coil may further include a magnetic core to focus the magnetic flux generated by the induction heating coil. The magnetic core may adjust the path of the magnetic field induced by the induction heating coil to adjust the amount of heat energy.

[0087] The control unit can suitably control the amount of thermal energy applied to the electrode substrate by controlling the on-off operation and / or the output of the heat rays contained in the heating roller.

[0088] 4, the thermal processing unit 250 may include an openable partition 252 for isolating at least a part of the space to which the heat source 251 applies heat from the outside. The openable partition 252 is located outside the thermal processing unit 250 to prevent thermal energy from escaping to the outside, thereby ensuring the safety of the operator from high temperature heat, and at the same time, reduces the loss of heat generated in the thermal processing unit 250, thereby allowing the thermal processing unit 250 to maintain a high temperature. The partitions 252 are located on both sides of the thermal processing unit 250 in the direction MD in which the electrode substrate 210 advances, and may have an openable structure including an entrance 253 that is spaced a predetermined distance from the thermal processing unit 250 and allows the operator to easily enter and exit the thermal processing unit 250 as needed.

[0089] Third embodiment Fig. 5 is a schematic diagram showing an electrode manufacturing system according to a third embodiment of the present invention. Referring to Fig. 5, an electrode manufacturing system 300 includes a heat processing unit 350 provided downstream of a drying unit and configured with n heat sources 351 (n is an integer of 2 or more) for applying additional heat to an electrode substrate 310 for which drying has been completed, and may further include a control unit 360 for controlling the operation of the n heat sources 351 (n is an integer of 2 or more).

[0090] Also, the electrode manufacturing system 300 may further include a measuring unit 370 that collects surface temperature information of the electrode substrate 310 that has passed through the heat treatment unit 350 and transmits the collected information to the control unit 360. Specifically, the measuring unit 370 refers to a unit that collects temperature information of the electrode slurry 311 formed on the electrode substrate 310. The measuring unit 370 may include a temperature measuring sensor that may measure the surface temperature of the electrode substrate 310, and the temperature measuring sensor may be located adjacent to a point where the heat treatment unit 350 ends. The measuring unit 370 may include a function of transmitting temperature information measured from the electrode substrate 310 that has passed through the heat treatment unit 350 to the control unit 360. Meanwhile, the control unit may receive temperature information from the measuring unit and may be equipped with a display that displays the received temperature information.

[0091] The control unit 360 may include a function of receiving temperature information transmitted by the measurement unit 370. The control unit 360 may compare the temperature information received from the measurement unit 370 with a set range to determine the temperature level of the electrode base material 310, and may control whether or not n (n is an integer of 2 or more) heat sources 351 are operated and the intensity of the thermal energy supplied by the operating heat sources 351 when the surface temperature received from the measurement unit 370 does not reach the set range.

[0092] In addition, the control unit 360 may include a data processing function for an operator to input a set range, compare the set temperature range received from the measurement unit 370, and determine whether the set range has been reached. When the surface temperature received from the measurement unit 370 does not reach the set range, the control unit 360 may control the operation of the heat source 351 by, for example, commanding the operation of the stopped heat source 351 to be started so that the surface temperature reaches the set range, or commanding the output intensity of the operating heat source 351 to be increased. Conversely, when the surface temperature received from the measurement unit 370 reaches the set range, the control unit 360 may command the output intensity of the operating heat source 351 to be maintained so that the surface temperature maintains the set range. In this case, the control unit 360 may independently control the n heat sources 351 (n is an integer of 2 or more).

[0093] (Fourth embodiment) Fig. 6 is a schematic diagram showing an electrode manufacturing system according to a fourth embodiment of the present invention. Referring to Fig. 6, an electrode manufacturing system 400 is an embodiment for manufacturing an electrode having electrode active material layers formed on both sides of an electrode current collector.

[0094] Referring to FIG. 6, an electrode manufacturing system 400 according to the present invention includes a transfer unit 420, a first coating unit 430a, a second coating unit 430b, a first drying unit 440a, a second drying unit 440b, a first heat treatment unit 450a, and a second heat treatment unit 450b, and the electrode substrate transferred by the transfer unit is configured to sequentially pass through the first coating unit 430a, the first drying unit 440a, the first heat treatment unit 450a, the second coating unit 430b, the second drying unit 440b, and the second heat treatment unit 450b.

[0095] The electrode manufacturing system 400 may be divided into two layers based on the second coating unit 430b, which is a point where the upper and lower surfaces of the electrode substrate 410 transported by the transport unit 420 are inverted. Specifically, the first coating unit 430a, the first drying unit 440a, and the first heat treatment unit 450a may be arranged in the lower layer, and the second coating unit 430b, the second drying unit 440b, and the second heat treatment unit 450b may be arranged in the higher layer.

[0096] The second coating unit 430b is configured to apply electrode slurry to a second surface of the electrode base material transported from the first heat treatment unit 450a on which an electrode active material layer is not formed, the second drying unit 440b is configured to dry the electrode slurry applied to the second surface, and the second heat treatment unit 450b is configured to apply heat to the electrode base material transported from the second drying unit 440b.

[0097] The second heat treatment unit 450b heats the electrode substrate, thereby increasing the proportion of the gamma crystal phase in the PVDF-based binder of the electrode active material layer formed on the second surface of the electrode substrate. The electrode manufacturing system 400 employs a two-layer structure to heat-treat both sides of the electrode substrate 410 at high temperatures, thereby changing the crystal phase of the PVDF-based binder of the electrode active material layer formed on both sides of the electrode substrate 410, thereby improving the adhesive strength of the electrode substrate 410.

[0098] The second coating unit 430b, the second drying unit 440b and the second heat treatment unit 450b differ only in that they are for coating, drying and heat treatment of the other side of the electrode substrate, and their specific contents are the same as those of the first coating unit 430a, the first drying unit 440a and the first heat treatment unit 450a, so duplicated explanations will be omitted.

[0099] The present invention may be more clearly understood from the following examples, which are merely for the purpose of illustrating the present invention and are not intended to limit the present invention.

[0100] <Example 1> LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 A positive electrode slurry was prepared by mixing and stirring O2, carbon black as a conductive material, and PVDF as a binder in a weight ratio of 97:1.5:1.5 in N-methylpyrrolidone solvent. The solid content of the positive electrode slurry was 70 wt%.

[0101] The positive electrode slurry was applied onto an aluminum foil having a thickness of 12 μm using a slot die coater, and the electrode substrate coated with the positive electrode slurry was passed through a drying oven to complete drying. The electrode substrate was then conveyed out of the drying oven and heated to a temperature of 170° C. using a heating roller to manufacture a positive electrode. The conveying speed of the electrode substrate during application, drying and heat treatment of the positive electrode slurry was 80 m / min, and the maximum temperature of the electrode substrate traveling in the drying oven was 120° C.

[0102] <Example 2> A positive electrode was prepared in the same manner as in Example 1, except that heat was applied to the electrode substrate removed from the drying oven using IR instead of a heating roller.

[0103] <Example 3> A positive electrode was prepared in the same manner as in Example 1, except that the electrode substrate removed from the drying oven was heated to a temperature of 180°C.

[0104] <Comparative Example 1> A positive electrode was prepared in the same manner as in Example 1, except that the process of heating the electrode substrate after drying in Example 1 to a temperature of 170° C. was omitted.

[0105] <Comparative Example 2> A positive electrode was manufactured in the same manner as in Example 1, except that the electrode substrate after drying in Example 1 was heated to a temperature of 120° C. after being removed from the drying oven.

[0106] <Experimental Example 1: Calculation of the ratio of gamma type crystals> In order to measure the crystallization ratio of the gamma (γ) phase of PVDF in each of the positive electrodes of Examples 1 to 3 and Comparative Examples 1 and 2, a solid-state measurement was performed under the following conditions using a DSX400 manufactured by Bruker Biospin Corporation. 19 F-NMR measurements were carried out.

[0107] Probe: 2.5mm MAS probe Measurement mode: Single pulse (pulse mode: zg0) 19F90°Pulse width: 5.0μsec Repeat wait time: 4sec MAS rotation speed: 32000Hz Measurement temperature: room temperature (25℃) Internal standard: C6F6 (-163.6ppm)

[0108] In the spectrum obtained, the peak height (H α ) and the peak height (H α+β ), the peak heights of the signals of γ-type crystals appearing at -101.3 ppm and -84.2 ppm (H γ The ratio of γ-type crystals was calculated from the above data using the following formula. The results are shown in Table 1.

[0109] Percentage of γ-type crystals (%) = {(H γ / (H α+β +H α +H γ )}×100

[0110] <Experimental Example 2: Measurement of adhesive strength> The adhesive strength of each of the positive electrodes of Examples 1 to 3 and Comparative Examples 1 and 2 was measured as follows, and the results are shown in Table 1.

[0111] The positive electrodes produced in Examples 1 to 3 and Comparative Examples 1 to 2 were cut to 150 mm and 20 mm wide, and the positive electrode surface was attached to a slide glass having a length of 75 mm and a width of 25 mm in the longitudinal direction using double-sided tape. That is, the slide glass was attached to an area corresponding to half of the positive electrode in the longitudinal direction. Then, a roller was rotated 10 times to uniformly attach the double-sided tape to produce an evaluation sample.

[0112] Next, the glass slide portion of the evaluation sample was fixed to the sample stage of a Universal Testing Machine (UTM) (product name: LS5, manufacturer: LLOYD), and the positive electrode half to which the glass slide was not attached was connected to the load cell of the UTM equipment. The load cell was subjected to a 90° force at a speed of 100 mm / min, and the load applied to the load cell was measured as it was moved up to 50 mm. The average load measured in the 20 mm to 40 mm section of the travel section was calculated, and this was repeated a total of five times, and the average value was evaluated as the positive electrode adhesive strength (gf / 20 mm) of each sample.

[0113] [Table 1]

[0114] Referring to Table 1, it was shown that the positive electrodes produced according to the present invention had a higher proportion of gamma type PVDF crystal phase than the positive electrodes produced according to the comparative examples, which showed that the positive electrodes according to Examples 1 to 3 also had a superior effect in adhesive strength compared to the positive electrodes of the comparative examples.

[0115] As described above, the electrode produced according to the present invention has a high gamma crystal phase ratio of 30% or more in the PVDF-based binder, and has excellent adhesive strength.

[0116] Although the preferred embodiments of the present invention have been described above with reference to the drawings, it will be understood that a person skilled in the art or a person having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as described in the claims.

[0117] Therefore, the technical scope of the present invention is not limited to the contents described in the Summary of the Invention of the specification, but is defined by the claims. [Explanation of symbols]

[0118] 100, 200, 300, 400: Electrode manufacturing system 110, 210, 310, 410: Electrode base material 111, 211, 311, 411: Electrode slurry 120, 420:Transfer section 121, 421: Transport roller 122, 422: Unwinder 130: Coating section 131, 431: Coating roller 132, 432: Slot die 140:Drying section 150, 250, 350: Heat treatment section 151, 251, 351: Heat source 252: Bulkhead 253: Entry to exit 360: Control unit 370:Measurement part 423: Rewinder 430a: First coating section 430b: Second coating section 440a: 1st drying section 440b: 2nd drying section 450a: First heat treatment section 450b: Second heat treatment section

Claims

1. A transfer unit including a transfer roller configured to support and transfer a long sheet-like electrode base material in one direction; a coating unit that applies an electrode slurry containing a polyvinylidene fluoride (PVDF)-based binder onto an electrode current collector; a drying section for drying the electrode base material to which the electrode slurry is applied; a heat treatment section disposed downstream of the drying section and configured to apply heat to the electrode base material discharged from the drying section.

2. The electrode manufacturing system according to claim 1 , wherein the heat treatment section includes a heat source configured to apply heat of 170° C. or more to the electrode substrate.

3. The heat sources are arranged in a number n (n is an integer of 2 or more) in a direction in which the electrode base material is transported, The electrode manufacturing system according to claim 2 , wherein the n heat sources (n is an integer equal to or greater than 2) are independently controlled.

4. The electrode manufacturing system according to claim 2 , wherein the heat source is a heating roller having a heat ray built inside a transport roller for transporting the electrode base material.

5. The electrode manufacturing system of claim 2 , wherein the heat source is selected from a laser module configured to apply a laser to the electrode substrate and an infrared heater configured to apply infrared radiation.

6. The electrode manufacturing system according to claim 2 , further comprising a control unit that controls operation of the heat source.

7. The electrode manufacturing system according to claim 1 , wherein the transport unit is configured to transport the electrode base material at a speed of 50 to 100 m / min.

8. The electrode manufacturing system according to claim 7 , wherein the transport unit is configured to transport the electrode base material at a speed of 70 to 100 m / min.

9. the coating unit includes a first coating unit that coats one surface of the electrode collector with an electrode slurry containing a polyvinylidene fluoride (PVDF)-based binder, and a second coating unit that coats the other surface of the electrode collector with an electrode slurry containing a polyvinylidene fluoride (PVDF)-based binder, the drying section includes a first drying section that dries the electrode base material that has passed through the first coating section, and a second drying section that dries the electrode base material that has passed through the second coating section; the heat treatment section includes a first heat treatment section disposed downstream of the first drying section and configured to apply heat to the electrode base material discharged from the first drying section, and a second heat treatment section disposed downstream of the second drying section and configured to apply heat to the electrode base material discharged from the second drying section, 2. The electrode manufacturing system of claim 1, wherein the electrode substrate transported by the transport unit is configured to pass through the first coating unit, the first drying unit, the first heat treatment unit, the second coating unit, the second drying unit and the second heat treatment unit in sequence.

10. The electrode manufacturing system according to claim 2 , wherein the heat treatment section includes an openable partition for isolating from the outside at least a part of the space to which the heat source applies heat.

11. The electrode manufacturing system according to claim 1 , wherein the heat treatment section is configured to apply heat only to a ground portion where an electrode active material layer is formed on the electrode base material.

12. A slurry coating layer forming step of coating an electrode current collector with an electrode slurry containing a polyvinylidene fluoride (PVDF)-based binder; drying the electrode substrate on which the slurry coating layer is formed; and a heat treatment step of applying heat to the dried electrode substrate to change the crystal phase of the polyvinylidene fluoride (PVDF)-based binder in the electrode substrate.

13. The method of claim 12, wherein the heat treatment step applies heat of 170° C. or more to the electrode substrate.

14. The method of claim 12, wherein the electrode substrate is transported at a speed of 50 to 100 m / min during the drying step.

15. The method of claim 12, wherein the electrode substrate is transported at a speed of 70 to 100 m / min during the drying step.

16. The method for manufacturing an electrode according to claim 12, wherein in the drying step, the drying temperature is in the range of 80 to 120°C.

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