Electrode manufacturing system and electrode manufacturing method for improving adhesive strength

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 priority rights based on Korean Patent Application No. 10-2022-0121746, filed on September 26, 2022.

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

[0003] Due to technological advancements and increasing demand for mobile devices, the demand for rechargeable batteries is also rapidly increasing. Among these, lithium-ion batteries are widely used as an energy source for various electronic products, including mobile devices, due to their high energy density, high operating voltage, and excellent storage and lifespan characteristics.

[0004] The electrode manufacturing process for producing electrodes for lithium secondary batteries (hereinafter referred to as the "electrode process") includes a coating process in which an electrode slurry containing electrode active material is applied to the surface of a metal foil which serves as a current collector; a drying process to remove the solvent from the electrode slurry; a rolling process in which the dried electrode is rolled; and notching and slitting processes in which electrode tabs are formed on the electrode and the electrode is cut according to dimensions.

[0005] In this process, the electrode drying step involves placing the electrode into an electrode drying oven configured to allow the injection of hot air and / or irradiation with radiant heat, and the drying process proceeds while the electrode moves inside the drying oven at a predetermined speed.

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

[0007] On the other hand, electrodes contain a binder to ensure that the electrode active material and conductive material, which constitute the electrode, form a solid mass between them, and to provide interfacial adhesion between the electrode active material layer and the current collector. PVDF (Polyvinylidene fluoride) binders have excellent adhesive properties and are chemically stable in the electrolyte, so they are widely used as electrode binders, especially for positive electrodes.

[0008] Such PVDF-based binders possess diverse crystalline phases such as alpha, beta, and gamma due to thermal / mechanical treatment, and it is known that a higher proportion of the gamma phase is advantageous for electrode adhesion.

[0009] While maintaining excellent electrode production speed, technological development is needed for electrode manufacturing systems and methods that increase the proportion of the gamma phase in the PVDF-based binder. [Overview of the project] [Problems that the invention aims to solve]

[0010] The present invention aims to solve the above-mentioned problems and to provide an electrode manufacturing system that offers excellent electrode production speed while also being able to change the crystalline phase of the PVDF-based binder to improve adhesive strength, as well as a manufacturing method using the same. [Means for solving the problem]

[0011] According to one embodiment of the present invention, an electrode manufacturing system is provided. The electrode manufacturing system may include a transfer section including a transfer roller configured to support and transfer a long sheet-like electrode substrate in one direction; a coating section for applying an electrode slurry containing a polyvinylidene fluoride (PVDF) binder onto an electrode current collector; a drying section for drying the electrode substrate coated with the electrode slurry; and a heat treatment section located downstream of the drying section and configured to apply heat to the electrode substrate discharged from the drying section.

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

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

[0014] In one embodiment of the present invention, the heat source may be a heating roller in which a heating wire is built into the inside of a transfer roller for transporting an 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 an electrode substrate and an infrared heater configured to apply infrared radiation.

[0016] An electrode manufacturing system according to one embodiment of the present invention may further include a control unit for controlling the operation of the heat source.

[0017] In one embodiment of the present invention, the transfer unit may be configured to transfer the electrode substrate at a speed of 50 to 100 m / min.

[0018] In one embodiment of the present invention, the transfer unit may be configured to transfer the electrode substrate at a speed of 70 to 100 m / min.

[0019] In one embodiment of the present invention, the coating part includes a first coating part that applies an electrode slurry containing a PVDF-based binder to one surface of the electrode current collector, and a second coating part that applies an electrode slurry containing a PVDF-based binder to the other surface of the electrode current collector. The drying part includes a first drying part that dries the electrode base material that has passed through the first coating part, and a second drying part that dries the electrode base material that has passed through the second coating part. The heat treatment part includes a first heat treatment part that is disposed downstream of the first drying part and is configured to apply heat to the electrode base material carried out from the first drying part, and a second heat treatment part that is disposed downstream of the second drying part and is configured to apply heat to the electrode base material carried out from the second drying part. The electrode base material transferred by the transfer part may be configured to sequentially pass through the first coating part, the first drying part, the first heat treatment part, the second coating part, the second drying part, and the second heat treatment part.

[0020] In one embodiment of the present invention, the heat treatment part may include an opening and closing partition for blocking at least a part of the space where the heat source applies heat from the outside.

[0021] In one embodiment of the present invention, the heat treatment part may be configured to apply heat only to the grounded part where the electrode active material layer is formed on the electrode base material.

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

[0023] In one embodiment of the present invention, the heat treatment step may be to apply heat of 170 °C or higher to the electrode base material.

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

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

[0026] In one embodiment of the present invention, in the drying stage, the drying temperature can be in the range of 80 to 120 °C.

Advantages of the Invention

[0027] According to the present invention, the heat treatment unit additionally heats the dried electrode substrate to induce recrystallization of the PVDF-based binder, increasing the proportion of gamma-phase crystals, thereby improving the adhesion of the electrode.

[0028] According to the present invention, recrystallization through annealing of the heat treatment unit is used without the need to reduce the transfer speed of the electrode substrate, so the production efficiency of the electrode is also excellent.

[0029] According to the present invention, the solvent that may remain on the electrode substrate carried out from the drying oven can be completely removed while passing through the heat treatment unit, so the time required for the vacuum drying process that follows after drying can be reduced.

Brief Description of the Drawings

[0030] [Figure 1] It is a schematic diagram showing an electrode manufacturing system according to an embodiment of the present invention. [Figure 2] It is an enlarged view of the heat treatment unit in FIG. 1. [Figure 3] It is an enlarged view of the heat treatment unit according to an embodiment of the present invention. [Figure 4] It is an enlarged view of the heat treatment unit according to an embodiment of the present invention. [Figure 5] It is a schematic diagram showing an electrode manufacturing system according to an embodiment of the present invention. [Figure 6]This is a schematic diagram showing an electrode manufacturing system in the form of a two-layer structure, as in one example of the present invention. [Figure 7] This is a flowchart showing the procedure for an electrode manufacturing method in one example of the present invention. [Modes for carrying out the invention]

[0031] The present invention can be modified in various ways and may take many forms; therefore, specific embodiments are illustrated in the drawings and described in detail herein. However, this is not intended to limit the present invention to any particular disclosure, but rather to be understood to include all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0032] In this application, terms such as “includes” and “have” are intended to specify the presence of features, numbers, stages, operations, components, parts, or combinations thereof described in the specification, without prejudice to the existence or possibility of adding one or more other features, numbers, stages, operations, components, parts, or combinations thereof. Furthermore, when a part such as a layer, film, region, or plate is said to be “on top” of another part, this includes not only when it is “directly on top” of the other part, but also when there is another part in between. Conversely, when a part such as a layer, film, region, or plate is said to be “below” another part, this includes not only when it is “directly below” the other part, but also when there is another part in between. Also, in this application, being “placed on top” may include being placed not only at the top but also at the bottom.

[0033] In this specification, the term "electrode substrate" includes both an electrode current collector coated with an electrode slurry and an electrode current collector in which the electrode slurry coated on the electrode current collector has been dried, forming an electrode active material layer on the electrode current collector.

[0034] This invention provides an electrode manufacturing system, an electrode manufacturing method using the same, and an electrode manufactured therefrom.

[0035] Polyvinylidene fluoride (PVDF) binders are commonly used as electrode binders. PVDF binders have alpha (α), beta (β), gamma (γ), and delta (δ) crystalline phases, and the type and proportion of these phases affect the adhesive strength of the PVDF binder. Specifically, the gamma (γ) crystalline phase is known to be advantageous for improving adhesive strength compared to other crystalline phases. Therefore, increasing the proportion of the gamma (γ) crystalline phase in a PVDF binder can increase the electrode adhesive strength without increasing the binder content.

[0036] In PVDF-based binders contained within electrodes, one possible method to increase the proportion of the gamma (γ) crystal phase is to recrystallize 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] The electrode drying process involves applying high temperatures to the electrode substrate as it moves through a drying oven. Theoretically, it might be possible to recrystallize the crystalline phase of the PVDF binder into a gamma (γ) crystalline phase by setting the drying temperature to 170°C or higher. However, in practice, recrystallizing the PVDF binder during the electrode drying process in a production environment is practically impossible or difficult.

[0038] Even if the drying oven temperature is set to 170°C or higher, the electrode slurry contains a solvent, and the ambient temperature decreases due to the heat of vaporization when the solvent evaporates. Therefore, the temperature of the electrode substrate moving in the drying oven can only be much lower than 170°C, specifically 80-120°C. Furthermore, in recent electrode manufacturing systems, the transfer speed of the electrode substrate is set to 50-100 m / min, more specifically 70-100 m / min, in order to maximize electrode productivity, so the drying temperature inside the drying oven may be even lower. As the transfer speed of the electrode substrate increases, the time the electrode substrate remains in the drying oven inevitably decreases, so increasing the transfer speed of the electrode substrate makes recrystallization of the PVDF-based binder even more difficult during electrode drying.

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

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

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

[0042] In one example, the electrode manufacturing system according to the present invention includes a transfer section including a transfer roller configured to support a long sheet-like electrode substrate and transport it in one direction; a coating section for applying an electrode slurry containing a polyvinylidene fluoride (PVDF) binder onto an electrode current collector; a drying section for drying the electrode substrate to which the electrode slurry has been applied; and a heat treatment section located downstream of the drying section and configured to apply heat to the electrode substrate that has been transported out of the drying section.

[0043] The transfer unit may include a plurality of transfer 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 can be transferred in one direction by the rotational motion of the transfer rollers. The transfer unit may include an unwinder configured to unwind a wound current collector sheet and a rewinder for winding the electrode substrate into a roll.

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

[0045] The electrode slurry may comprise 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 comprise a PVDF-based binder and may also comprise other types of binders. In specific examples, the PVDF-based binder comprises one or more of the following: a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride, and mixtures thereof. The monomer copolymerizable with vinylidene fluoride may comprise 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 above-mentioned solvent is not particularly limited as long as it is a solvent for the manufacture of electrodes for secondary batteries, and specific examples include NMP (N-Methyl-2-pyrrolidone) and water.

[0047] The drying section dries the electrode slurry by applying heat to the electrode substrate to remove the solvent in the electrode slurry. The drying section includes a drying oven or heating furnace, and any drying oven or heating furnace commonly known in the art may be used. Such a drying oven or heating furnace or heating furnace may employ a hot air method, a radiant heat method, a direct heating method, or an induction heating method, or a combination of these methods may be applied.

[0048] The heat treatment unit described above applies heat to the electrode substrate removed from the drying unit to recrystallize the crystalline phase of the PVDF-based binder in the electrode substrate. Specifically, the PVDF-based binder is a polymer consisting of PVDF monomer-bonds or PVDF monomers and monomers of other substances. PVDF can form various crystalline phases depending on the temperature conditions, and the crystalline phase state can affect not only the binding properties of the polymer but also the electrode properties. More specifically, the crystalline phase of PVDF has alpha (α), beta (β), gamma (γ), and other crystalline phases depending on the arrangement of the chains. In this case, the gamma (γ) crystalline phase has higher binding properties than other crystalline phases, so it is preferable to increase the proportion of the gamma (γ) phase to improve the binding properties of the binder.

[0049] The inventors of the present invention observed the phase change of PVDF in response to heat treatment temperature through various experiments and observations. As a result, they found that when heat of 170°C or higher, which is the crystal 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 the gamma (γ) crystal phase increases significantly. This PVDF-based binder with a high proportion of gamma (γ) phase increases the adhesion strength of the electrode and can effectively reduce the delamination 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, by providing a heat treatment section downstream of the drying section, can manufacture electrodes in which high-temperature heat is applied to the electrode substrate after drying is complete, thereby improving the bonding strength through a crystalline change in the PVDF-based binder in the electrode substrate.

[0051] In some embodiments, the heat treatment unit includes a heat source configured to apply heat of 170°C or higher to the electrode substrate. The heat source may be configured to apply heat of 170°C or higher, specifically 170°C to 300°C, to the electrode substrate for recrystallization of the PVDF binder. It is undesirable if the electrode substrate temperature exceeds 300°C, as this may cause combustion of the PVDF binder.

[0052] In some embodiments, n heat sources (where n is an integer of 2 or more) are spaced apart in the MD (Machine direction) direction, which is the direction in which the electrode substrate coated with electrode slurry is transported, and these n heat sources (where 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, electrode substrates 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 current collector, the thickness of the current collector, etc., and the heat treatment conditions that can maximize adhesion differ for each electrode model. Therefore, in order to perform heat treatment according to heat treatment conditions optimized for each electrode model, it is preferable that multiple heat sources be controlled independently.

[0053] In some embodiments, the heat source may be a heating roller in which a heat ray is embedded inside a transfer roller for transporting an electrode substrate. The heat ray is inserted inside the transfer roller, and the heat applied from the heat ray is transferred via the transfer roller to the electrode substrate supported by the transfer roller.

[0054] In some embodiments, the heat source can be selected from a laser module configured to apply a laser to the electrode substrate and an infrared heater configured to apply infrared radiation. The laser module may be configured to directly irradiate the electrode substrate with laser light, and the infrared 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 control unit that controls the operation of the n (where n is an integer of 2 or more) heat sources. Specifically, the control unit controls whether a laser module, an infrared heater, or a heating roller is activated, or the output size of the thermal energy applied by each heat source.

[0056] Furthermore, the present invention provides a method for manufacturing electrodes.

[0057] In this invention, the above-described description of the electrode manufacturing system is also applicable to the electrode manufacturing method, and therefore, redundant specific explanations are omitted.

[0058] Figure 7 is a flowchart illustrating the electrode manufacturing method according to the present invention. Referring to Figure 7, the electrode manufacturing method according to one embodiment of the present invention includes a slurry coating layer formation step (S10) in which an electrode slurry containing a polyvinylidene fluoride (PVDF) binder is applied to an electrode current collector, a drying step (S20) in which the electrode substrate on which the slurry coating layer has been formed is dried, and a heat treatment step (S30) in which heat is applied to the dried electrode substrate to change the crystalline phase of the PVDF binder in the electrode substrate.

[0059] The slurry coating layer formation step (S10) described above is the step of applying an electrode slurry containing a PVDF-based binder onto an electrode current collector that is being transported in one direction.

[0060] The above drying step (S20) can be performed by drying the electrode substrate on which the electrode slurry coating layer has been formed using the above-described drying oven. In some embodiments, in the above drying step (S20), the transfer 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, from the viewpoint 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 above drying temperature refers to the temperature of the electrode substrate being transferred 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 solvent, and the transfer speed of the electrode substrate reaches 50 m / min to 100 m / min, so the temperature of the electrode substrate is lower than 170°C, in the range of 150°C or lower, more specifically 70 to 140°C, more specifically 75 to 130°C, and even more specifically 80 to 120°C.

[0061] The above heat treatment step (S30) may be a step in which high heat is applied to the electrode substrate that has undergone the drying step (S20) to change the crystalline phase of the PVDF-based binder. As a result of the above heat treatment step (S30), the crystalline structures of the alpha and beta phases of the PVDF-based binder are recrystallized into the crystalline structure of the gamma phase, thereby increasing the proportion of the gamma phase in the PVDF-based binder.

[0062] In some embodiments, the heat treatment step (S30) may include a process of applying heat of 170°C or higher 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 electrode manufacturing method according to the present invention may further include a step (S40) of vacuum drying to completely remove moisture from the dried electrode. The vacuum drying step (S40) is a separate step distinct from the heat treatment step (S30), and the drying temperature in the vacuum drying step (S40) can be 80 to 120°C. Since water is also removed in the heat treatment step, the electrode manufacturing method according to the present invention can reduce the time required for the vacuum drying step and ultimately increase the production efficiency of electrode manufacturing.

[0064] Specific examples of the present invention will be described in detail below with reference to the attached drawings.

[0065] (First Embodiment) Figure 1 is a schematic diagram showing an electrode manufacturing system according to a first embodiment of the present invention, and Figure 2 is an enlarged view of the heat treatment section of Figure 1. Referring to Figure 1, the 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 transfer unit 120 may include a plurality of transfer rollers 121, which rotate by power transmitted from a motor (not shown) to transfer the electrode substrate 110 in one direction. The transfer unit 120 may include an unwinder 122 configured to unwind a wound current collector sheet and a rewinder (not shown) for winding the electrode substrate on a roll.

[0067] In some embodiments, the transfer unit 120 may be configured to transfer the electrode substrate 110 at a speed of 50 to 100 m / min, preferably 70 to 100 m / min, and more preferably 80 to 100 m / min. As a result, the electrode manufacturing system 100 according to the present invention is extremely efficient in producing electrodes.

[0068] The coating section 130 may include a slot die coater 132 for discharging electrode slurry 111 and a coating roller 131 positioned opposite the slot die coater 132. The electrode slurry 111 discharged from the slot die coater 132 is applied onto an electrode substrate 110, which is supported and transported by the coating roller 131, forming an electrode slurry coating layer.

[0069] The drying section 140 may include one or more drying ovens configured to dry the electrode substrate 110, which is 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. The set drying temperature of each of the plurality of drying zones may be controlled independently. Specifically, a temperature-boosting drying zone in which the drying rate of the electrodes increases may be located at the front end, and a constant-rate drying zone in which the drying rate increased in the temperature-boosting drying zone is kept constant may be located downstream of the temperature-boosting drying zone. A rate-decreasing drying zone may be located downstream of the constant-rate drying zone in which drying is almost complete and the drying rate of the electrodes decreases.

[0071] In one embodiment, the drying oven may include drying means for drying the electrode slurry applied to the electrode. The drying means is not limited to any means that can supply thermal energy to the electrode slurry and remove 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 described above may be configured to spray hot air toward an electrode substrate 110 being transported in a 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 injection nozzle installed in the drying oven and configured to spray hot air toward an electrode substrate, a fan for supplying the outside air heated by the heat exchanger to the hot air injection nozzle via a duct connected to the internal space of the drying oven, and a damper installed in the duct for adjusting the amount of hot air supplied.

[0074] The heater may be configured to irradiate radiant heat onto the electrode substrate 110 being transported in a drying oven. It may further include a shielding film as needed. The shielding film may be coupled below the heater to adjust the position and / or area of ​​the region irradiated by the radiant heat emitted from the heater.

[0075] The drying section 140 plays a role in drying the solvent of the slurry coating layer, and the number or arrangement of drying ovens can be suitably changed depending on the composition of the electrode slurry 111 and the coating thickness of the electrode slurry.

[0076] Figure 2 is a schematic diagram showing an enlarged view of the heat treatment section 150 of the electrode manufacturing system 100 in Figure 1. Referring to Figures 1 and 2, the heat treatment section 150 is located downstream of the drying section 140. In some embodiments, the heat treatment section 150 is located near the outlet of the drying section 140, and by applying high-temperature heat to the electrode substrate 110 before its temperature drops after being discharged from the drying section 140, the recrystallization efficiency of the PVDF binder can be improved.

[0077] The heat treatment unit 150 includes a heat source 151, which is configured to apply additional heat to the electrode substrate 110 after drying is complete. The heat source 151 may be configured to apply heat of 170°C or higher to the electrode substrate 110, thereby recrystallizing the alpha (α) and beta (β) crystalline phases of the PVDF-based binder contained in the electrode active material layer into a gamma (γ) crystalline phase, which can improve the electrode adhesion strength.

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

[0079] In some embodiments, the heat source 151 can be selected from a laser module configured to apply a laser to the electrode substrate and an infrared heater configured to apply infrared radiation. The laser module may be configured to directly irradiate the electrode substrate with laser light, and the infrared 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 control unit to independently control the plurality of heat sources 151 and to control the on-off control of the heat sources 151 and / or 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 areas of the electrode substrate 110 where the electrode active material layer is formed. If high heat is applied to the areas where the electrode active material layer is not formed and the current collector is exposed, heat wrinkles may occur near the boundary between the areas due to the difference in elongation rates between the areas. By applying heat only to the areas with heat, the risk of defects caused by heat wrinkles can be reduced.

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

[0083] (Second Embodiment) Figures 3 and 4 are enlarged views of the heat treatment unit according to the second embodiment of the present invention. The following explanation will focus on the differences from the heat treatment unit according to the first embodiment.

[0084] Referring to Figure 3, the heat source 251 of the heat processing unit 250 according to the second embodiment may be a heating roller with a heat ray built in. The heat ray is inserted inside the transfer roller, and the heat applied from the heat ray is transferred to the electrode substrate 210 via the transfer roller.

[0085] The heating element described above is not particularly limited as long as it is capable of heating the temperature of the heating roller, and specifically, an induction heating coil can be exemplified. An alternating current voltage may be applied to the induction heating coil in order to generate thermal energy in a short time. The alternating current voltage applied to the induction heating coil may have a frequency in the range of approximately 100 kHz to 500 kHz. An alternating current power supply may be connected to the induction heating coil. When an alternating current voltage is applied to the induction heating coil, an electromotive force is induced by electromagnetic induction, and the electrodes can be heated by the induced current generated by the electromotive force.

[0086] In some embodiments, the induction heating coil may have an additional magnetic material installed in its core to focus the magnetic flux generated by the induction heating coil. The magnetic core can adjust the amount of thermal energy by adjusting the path of the magnetic field induced by the induction heating coil.

[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 output of the heating wire built into the heating roller.

[0088] Referring to Figure 4, the heat treatment unit 250 may include an openable partition wall 252 to isolate at least a portion of the space in which the heat source 251 applies heat from the outside. The openable partition wall 252 is located outside the heat treatment unit 250 to prevent thermal energy from escaping to the outside, thereby ensuring the safety of workers from high temperatures, while simultaneously reducing heat loss in the heat treatment unit 250, allowing the heat treatment unit 250 to maintain a high temperature. The partition wall 252 may be an openable structure located on both sides of the heat treatment unit 250 in the direction MD in which the electrode substrate 210 moves, positioned at a predetermined distance from the heat treatment unit 250, and including an entrance / exit 253 that allows workers to easily enter and exit the heat treatment unit 250 as needed.

[0089] (Third embodiment) Figure 5 is a schematic diagram showing an electrode manufacturing system according to a third embodiment of the present invention. Referring to Figure 5, the electrode manufacturing system 300 includes a heat processing unit 350 provided downstream of the drying unit and consisting of n (n is an integer of 2 or more) heat sources 351 that apply additional heat to the electrode substrate 310 after drying is complete, and may further include a control unit 360 that controls the operation of the n (n is an integer of 2 or more) heat sources 351.

[0090] Furthermore, 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 processing unit 350 and sends the collected information to the control unit 360. Specifically, the measuring unit 370 means that it collects temperature information of the electrode slurry 311 formed on the electrode substrate 310. The measuring unit 370 may include a temperature measuring sensor capable of measuring the surface temperature of the electrode substrate 310, and the temperature measuring sensor may be located adjacent to the point where the heat processing unit 350 ends. The measuring unit 370 may include a function to transmit the temperature information measured from the electrode substrate 310 that has passed through the heat processing unit 350 to the control unit 360. On the other hand, 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 to receive temperature information transmitted by the measurement unit 370. The control unit 360 compares the temperature information received from the measurement unit 370 with a set range to determine the temperature level of the electrode substrate 310, and if the surface temperature received from the measurement unit 370 does not reach the set range, it can control whether or not n (n is an integer of 2 or more) heat sources 351 are operating and the intensity of the thermal energy supplied by the operating heat sources 351.

[0092] Furthermore, the control unit 360 may include a data processing function that allows the operator to input a set range and compare it with the temperature set range received from the measurement unit 370 to determine whether the set range has been reached. If the surface temperature received from the measurement unit 370 does not reach the set range, the control unit 360 can control the operation of the heat source 351 by ordering it to start operating the heat source 351 that has been stopped, or by ordering it to increase the output intensity of the operating heat source 351, so that the surface temperature reaches the set range. Conversely, if the surface temperature received from the measurement unit 370 reaches the set range, the control unit 360 can order it to maintain the output intensity of the operating heat source 351 so that the surface temperature remains within the set range. In this case, the control unit 360 can independently control the n (where n is an integer of 2 or more) heat sources 351.

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

[0094] Referring to Figure 6, the 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 is configured such that the electrode substrate transferred by the transfer unit passes 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 in sequence.

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

[0096] The second coating section 430b is configured to apply electrode slurry to the second surface of the electrode substrate discharged from the first heat treatment section 450a where no electrode active material layer is formed, the second drying section 440b is configured to dry the electrode slurry applied to the second surface, and the second heat treatment section 450b is configured to apply heat to the electrode substrate discharged from the second drying section 440b.

[0097] By heating the electrode substrate with the second heat treatment unit 450b, 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 can increase. Such an electrode manufacturing system 400, by adopting a two-layer structure, can 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 and improving the adhesion strength of the electrode substrate 410.

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

[0099] The present invention can be more clearly understood by the following embodiments, which are merely illustrative examples and not intended to limit the present invention.

[0100] <Example 1> LiNi 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 an N-methylpyrrolidone solvent in a weight ratio of 97:1.5:1.5. The solid content of the positive electrode slurry was 70% by weight.

[0101] Using a slot die coater, the positive electrode slurry was applied onto a 12 μm thick aluminum foil, and the electrode substrate coated with the positive electrode slurry was passed through a drying oven to complete the drying process. Subsequently, the electrode substrate, after being removed from the drying oven, was heated to 170°C using a heating roller to produce the positive electrode. During the application, drying, and heat treatment of the positive electrode slurry, the transfer speed of the electrode substrate was 80 m / min, and the maximum temperature of the electrode substrate moving within the drying oven was 120°C.

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

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

[0104] <Comparative Example 1> The positive electrode was manufactured in the same manner as in Example 1, except that the step of heating the electrode substrate, which had been dried in Example 1, to a temperature of 170°C was omitted.

[0105] <Comparative Example 2> The positive electrode was manufactured in the same manner as in Example 1, except that the electrode substrate, which had been dried 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 proportion of gamma-type crystals> In each cathode of Examples 1 to 3 and Comparative Examples 1 to 2, the crystallization ratio of the gamma (γ) phase of PVDF was measured using a Bruker BioSpin DSX400 under the following conditions. 19 F-NMR measurements were performed.

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

[0108] In the obtained spectrum, the peak height (H α ) of the signal of the α-type crystal appearing at the position of -79.6 ppm, and the peak height (H α+β ) of the signal of the combined α-type crystal and β-type crystal appearing at the position of -93.7 ppm, and the peak heights (H γ ) of the signals of the γ-type crystal appearing at the positions of -101.3 ppm and -84.2 ppm were used to calculate the ratio of the γ-type structure crystal using the following formula. And the results are shown in Table 1.

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

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

[0111] The positive electrodes manufactured in Examples 1 to 3 and Comparative Examples 1 to 2 above were cut into a length of 150 mm and a width of 20 mm, and the positive electrode surface was attached to a slide glass with 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 a region corresponding to half of the longitudinal direction of the positive electrode. Then, a roller was rotated 10 times so that the double-sided tape was uniformly attached to produce an evaluation sample.

[0112] Next, the slide glass part of the evaluation sample was fixed to the sample stage of a universal testing machine (Universal Testing Machine, UTM) (product name: LS5, manufacturer: LLOYD), and the half of the positive electrode to which the slide glass was not attached was connected to the load cell of the UTM equipment. A force of 90° was applied to the load cell at a speed of 100 mm / min, and the load applied to the load cell was measured while moving it to 50 mm. At this time, after obtaining the average value of the load measured in the 20 mm to 40 mm section of the traveling section, it was repeated a total of 5 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 electrode manufactured according to the present invention had a higher proportion of the gamma-type crystalline phase of PVDF compared to the positive electrode manufactured by the comparative example. This indicates that the positive electrodes according to Examples 1 to 3 also exhibit superior adhesive strength compared to the positive electrode of the comparative example.

[0115] As described above, the electrodes manufactured according to the present invention have a high gamma-type crystalline phase ratio of 30% or more in the PVDF-based binder and possess excellent adhesive strength.

[0116] Preferred embodiments of the present invention have been described above with reference to the drawings, but a person skilled in the art or a person with ordinary knowledge of the art will understand that the present invention can be modified and altered in various ways without departing from the gist of the invention and the art as described in the claims.

[0117] Therefore, the technical scope of the present invention is not limited to what is described in the summary of the invention in 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: Transfer rollers 122, 422: Unwinder 130: Coating part 131, 431: Coating roller 132, 432: Slot dies 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 unit 450b: Second heat treatment section

Claims

1. A transfer section including a transfer roller configured to support a long sheet-like electrode substrate and to transfer it in one direction, A coating section is formed on the electrode current collector by applying an electrode slurry containing a polyvinylidene fluoride (PVDF)-based binder, A drying section for drying the electrode substrate to which the electrode slurry has been applied, The device includes a heat treatment section, which is positioned downstream of the drying section and includes a heat source configured to apply heat of 170°C to 300°C to the electrode substrate removed from the drying section, and is configured to increase the proportion of the gamma-type crystalline phase of the PVDF-based binder in the electrode substrate to 30% or more. An electrode manufacturing system in which the transfer unit is configured to transfer the electrode substrate at a speed of 50 to 100 m / min.

2. The heat sources are arranged in a number of n (where n is an integer of 2 or more) in the direction in which the electrode substrate is transported. The electrode manufacturing system according to claim 1, wherein the n heat sources (where n is an integer of 2 or more) are controlled independently.

3. The electrode manufacturing system according to claim 1, wherein the heat source is a heating roller in which a heating wire is built inside the transfer roller for transferring the electrode substrate.

4. The electrode manufacturing system according to claim 1, 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 rays.

5. The electrode manufacturing system according to claim 1, further comprising a control unit for controlling the operation of the heat source.

6. The electrode manufacturing system according to claim 1, wherein the transfer unit is configured to transfer the electrode substrate at a speed of 70 to 100 m / min.

7. The coating portion includes a first coating portion which applies an electrode slurry containing the polyvinylidene fluoride (PVDF) binder to one surface of the electrode current collector, and a second coating portion which applies an electrode slurry containing the polyvinylidene fluoride (PVDF) binder to the other surface of the electrode current collector. The drying section includes a first drying section for drying the electrode substrate after passing through the first coating section, and a second drying section for drying the electrode substrate after passing through the second coating section. The heat treatment unit includes a first heat treatment unit located downstream of the first drying unit and configured to apply heat to the electrode substrate discharged from the first drying unit, and a second heat treatment unit located downstream of the second drying unit and configured to apply heat to the electrode substrate discharged from the second drying unit. The electrode manufacturing system according to 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.

8. The electrode manufacturing system according to claim 1, wherein the heat treatment section includes an openable partition wall for isolating at least a portion of the space to which the heat source applies heat from the outside.

9. The electrode manufacturing system according to claim 1, wherein the heat treatment unit is configured to apply heat only to the surface area of ​​the electrode substrate on which the electrode active material layer is formed.

10. A slurry coating layer formation step in which an electrode slurry containing a polyvinylidene fluoride (PVDF) binder is applied to an electrode current collector while the electrode current collector is being transported, A drying step in which the electrode substrate on which the slurry coating layer has been formed is dried while being transported, The process includes a heat treatment step in which, while transferring the dried electrode substrate, heat is applied at a temperature between 170°C and 300°C to change the proportion of the gamma-type crystalline phase of the polyvinylidene fluoride (PVDF) binder in the electrode substrate to 30% or more. An electrode manufacturing method wherein, in the drying stage, the transfer speed of the electrode substrate is in the range of 50 to 100 m / min.

11. The electrode manufacturing method according to claim 10, wherein in the drying step, the transfer speed of the electrode substrate is in the range of 70 to 100 m / min.

12. The electrode manufacturing method according to claim 10, wherein the drying temperature in the drying step is in the range of 80 to 120°C.

Images