Manufacturing method and drying apparatus of electrode for secondary battery

Abstract

According to an embodiment of the present disclosure, a method for manufacturing an electrode for a secondary battery comprises the steps of: applying a slurry containing an active material and a solvent onto a current collector; and, when the degree of drying of the slurry reaches a reference value while the current collector passes through a drying device, drying the slurry using induction heating of an induction heating unit.

Description

Technology Field

[0001] The present disclosure relates to an electrode for a secondary battery, and specifically to a method for manufacturing an electrode for a secondary battery and a drying apparatus. Background Technology

[0002] Recently, with the increasing demand for mobile devices such as smartphones, tablet PCs, and wireless earphones, as well as the full-scale development of electric vehicles, energy storage batteries, robots, and satellites, research on high-performance rechargeable batteries capable of repeated charging and discharging as energy sources is actively underway. Representative rechargeable batteries include lithium-ion batteries, lead-acid batteries, and alkaline batteries.

[0003] A secondary battery may include electrodes and a separator. The separator may be placed between the electrodes. The electrodes may include a cathode and an anode.

[0004] Electrodes can be manufactured through a process of applying a slurry onto a current collector and then drying it. In particular, depending on the drying temperature of the slurry and the amount of solvent in the slurry, cracks may occur on the surface of the electrode or binder migration may occur, which can significantly affect the performance of the electrode due to lithium plating (Li-plating) or increased resistance. Accordingly, methods are being sought to manufacture high-capacity (or low-solids) electrodes and improve productivity while ensuring stable drying capabilities without defects. The problem to be solved

[0005] According to one embodiment, a method for manufacturing an electrode for a secondary battery and a drying apparatus having stable drying capability and improved productivity are provided. means of solving the problem

[0006] According to one embodiment, a method for manufacturing an electrode for a secondary battery may include the step of applying a slurry containing an active material and a solvent onto a current collector, and the step of drying the slurry using induction heating of an induction heating unit when the degree of drying of the slurry reaches a reference value while the current collector passes through a drying device.

[0007] According to one embodiment, a drying device for an electrode for a secondary battery may include a drying chamber comprising a plurality of regions through which a current collector coated with a slurry passes, and an induction heating unit disposed in a reference region among the plurality of regions where the degree of drying of the slurry reaches a reference value, and which heats the slurry by an induction heating method while the current collector passes through the reference region. Effects of the invention

[0008] According to one embodiment, a method for manufacturing an electrode for a secondary battery and a drying apparatus having stable drying ability and improved productivity can be provided. Brief explanation of the drawing

[0009] FIG. 1 is a schematic diagram illustrating a method for manufacturing an electrode for a secondary battery and a drying apparatus according to one embodiment of the present disclosure. FIG. 2 is a drawing for explaining a method for manufacturing an electrode for a secondary battery and a drying apparatus according to one embodiment of the present disclosure. FIG. 3 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to one embodiment of the present disclosure. Specific details for implementing the invention

[0010] The structural or functional descriptions of the embodiments disclosed in this specification or application are merely illustrative for the purpose of explaining embodiments according to the technical concept of the present invention. Embodiments according to the technical concept of the present invention may be implemented in various forms other than those disclosed in this specification or application, and the technical concept of the present invention is not to be interpreted as being limited to the embodiments described in this specification or application.

[0011] FIG. 1 is a schematic diagram illustrating a method for manufacturing an electrode for a secondary battery and a drying apparatus according to one embodiment of the present disclosure.

[0012] Referring to FIG. 1, the current collector (20) may include at least one of copper, aluminum, stainless steel, titanium, and nickel. The current collector (20) may be implemented as a thin film structure such as a foil.

[0013] In one embodiment, the current collector (20) may be moved along the direction of travel. For example, the current collector (20) may be moved by the rotation of a roller. A slurry supplied by a coating die (10) may be applied to the current collector (20) being transported. The slurry may include a solvent, a conductive material, an active material, and a binder. The slurry may be a fluid having fluidity. The coating die (10) may be a device that ejects the slurry through a non-pulsating pump or a piston pump to coat the current collector (20) moving in the direction of travel with a uniform thickness. Here, the current collector (20) coated with the slurry may be referred to as an electrode semi-finished product (200). That is, the electrode semi-finished product (200) may be manufactured by applying the slurry to the current collector (20). The electrode semi-finished product (200) may be an intermediate product used to manufacture an electrode.

[0014] In one embodiment, the electrode semi-finished product (200) may pass through the drying device (100) along the direction of travel. The drying device (100) may dry the electrode semi-finished product (200) to manufacture an electrode. For example, when the electrode semi-finished product (200) is introduced into the interior of the drying device (100), the electrode semi-finished product (200) may be dried to manufacture an electrode. The electrode may be one of a cathode and an anode for a secondary battery. The secondary battery may be a lithium secondary battery, but is not limited thereto and may be various types of secondary batteries.

[0015] In one embodiment, the drying device (100) can dry the electrode semi-finished product (200) through hot air and induction heating. The present disclosure will be described in more detail below.

[0016] FIG. 2 is a drawing for explaining a method for manufacturing an electrode for a secondary battery and a drying apparatus according to one embodiment of the present disclosure.

[0017] Referring to FIG. 2, the electrode semi-finished product (200) may include a current collector (210) and a slurry (220).

[0018] The current collector (210) can receive electrons from the outside to cause an electrochemical reaction to occur in the active material and transfer the electrons to the active material, or receive electrons from the active material and transfer electrons to the outside. For example, the current collector (210) can be implemented as a thin film structure, such as a foil, having a thickness of 5, 6, 8, 10 micrometers, etc. For example, the current collector (210) may include at least one of copper, aluminum, stainless steel, titanium, and nickel. In addition, the current collector (210) may include various materials such as metals with high conductivity.

[0019] The slurry (220) may be applied to the current collector (210). In one embodiment, the slurry (220) may be applied to at least one surface of the current collector (210). For example, the slurry (220) may be applied to one or both surfaces of the current collector (210).

[0020] The slurry (220) may include a solvent, an active material, a conductive material, and a binder. The slurry (220) may be prepared by mixing the active material, the conductive material, and the binder in a solvent.

[0021] The solvent can disperse the active material, conductive material, and binder. In one embodiment, the solvent may be a substance in a liquid state. For example, the solvent may be distilled water or pure water (Deionized water). Pure water refers to liquid water from which all ions have been removed. The type of solvent may vary depending on the types of the active material, conductive material, and binder.

[0022] Active materials can be classified into positive electrode active materials and negative electrode active materials depending on the type.

[0023] In one embodiment, the positive active material of the positive type may include a material capable of inserting and extracting lithium (Li) ions. The positive active material may be a lithium metal oxide. For example, the positive active material may include at least one of a lithium manganese-based oxide, a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium nickel manganese-based oxide, a lithium nickel cobalt manganese-based oxide, a lithium nickel cobalt aluminum-based oxide, a lithium iron phosphate-based compound, a lithium manganese phosphate-based compound, a lithium cobalt phosphate-based compound, and a lithium vanadium phosphate-based compound, but is not limited to specific examples. An electrode semi-finished product (200) containing the positive active material of the positive type may be used to manufacture a positive type electrode (300).

[0024] In one embodiment, the negative electrode active material, which is of the negative electrode type, may be a material capable of absorbing and extracting lithium ions. For example, the negative electrode active material may include at least one of carbon-based materials such as natural graphite, artificial graphite, crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, lithium alloys, silicon (Si), and tin (Sn). According to one embodiment, the negative electrode active material may be a material obtained by mixing natural graphite and artificial graphite in a certain ratio, but is not limited to specific examples. An electrode semi-finished product (200) containing the negative electrode active material may be used to manufacture a negative electrode (300).

[0025] The conductive material may be a material having electrical conductivity. The conductive material may be used without special restrictions as long as it is a material having electrical conductivity without causing chemical changes. For example, the conductive material may include at least one of the following materials: carbon-based materials such as natural graphite, artificial graphite, carbon nanotubes (CNT), and graphene; metal powders such as copper, nickel, aluminum, and silver; metal fibers; or conductive polymers such as polyphenylene derivatives.

[0026] The binder can attach the active material and the conductive material onto the current collector (210). For example, the binder may be styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The type of material included in the binder may vary depending on the type of material included in the active material or the conductive material.

[0027] The electrode semi-finished product (200) may have different types of materials included in the current collector (210) and the slurry (220), respectively, depending on the type of electrode (300) to be manufactured. The type of electrode (300) may be either a positive electrode or a negative electrode.

[0028] A current collector (210) coated with a slurry (220) can pass through a drying device (100). For example, an electrode semi-finished product (200) can be introduced into the drying device (100). The electrode semi-finished product (200) can be dried while passing through the drying device (100). Once the drying of the electrode semi-finished product (200) is complete, an electrode (300) can be manufactured.

[0029] The drying device (100) can dry the slurry (220). For example, the drying device (100) can gradually dry the slurry (220) to solidify it. The degree of drying can be expressed as a solid content (%).

[0030] The drying device (100) may include a hot air supply unit (110) and an induction heating unit (120).

[0031] The hot air supply unit (110) can supply hot air to the slurry (220) of the electrode semi-finished product (200) while the electrode semi-finished product (200) passes through the interior. That is, the hot air can gradually vaporize the solvent of the slurry (220). The vaporized solvent can be removed from the electrode (200). The vaporized solvent can be discharged to the outside of the drying device (100).

[0032] In one embodiment, the hot air supply unit (110) may include a boiler and a circulation fan. The boiler may be a heating device using a heat transfer fluid. The heat transfer fluid may be a fluid other than steam or water, and may be a substance having a high heat transfer coefficient at high temperatures. The boiler may generate high-temperature hot air by heating air using the heat transfer fluid. The circulation fan may generate airflow. For example, the circulation fan may include a motor and a rotating blade. When the rotational force of the motor is transmitted to the rotating blade, the rotating blade rotates to generate airflow. In one embodiment, the circulation fan may supply hot air to the slurry (220) and discharge the solvent vaporized from the slurry (220) to the outside of the drying chamber. The circulation fan may be connected to a nozzle placed in at least one of the upper and lower parts of the drying chamber. For example, the nozzle may be configured in the form of a perforated nozzle, a slit nozzle, etc. That is, the hot air supply unit (110) can dry the electrode semi-finished product (200) through convective heat transfer.

[0033] The induction heating unit (120) can heat the slurry (220) through induction heating. Induction heating may be a heating method utilizing the Faraday-Lenz electromagnetic induction phenomenon. For example, the induction heating unit (120) may include an induction coil. In this case, the induction coil may be installed in a spiral shape. When a high-frequency current is applied to the induction coil, magnetic flux is formed, and an induced current may be generated by the magnetic flux. The induced current generates Joule heat, and the interior of the slurry (220) may be heated according to the Joule heat. For example, the frequency of the high-frequency current may be 20 kHz to 35 kHz. However, this is merely one example, and the frequency of the high-frequency current may be varied to various values. Here, induction heating has the technical effect of enabling efficient rapid heating by concentrating energy on the parts requiring heating, and enabling rapid and uniform control.

[0034] The induction heating unit (120) can heat the slurry (220) without contact. In one embodiment, the induction heating unit (120) may be positioned to face one side of the current collector (210) coated with the slurry (220). For example, the induction heating unit (120) may be positioned so that the slurry (220) is positioned between the current collector (210) and the induction heating unit (120). In another embodiment, the induction heating unit (120) may be positioned to face one side of the current collector (210) coated with the slurry (220) and the other side. For example, the induction heating unit (120) may be positioned so that the current collector (210) is positioned between the slurry (220) and the induction heating unit (120).

[0035] In one embodiment, the drying device (100) may include a drying chamber. The drying chamber may include a plurality of zones (zone 1 to zone 10). For example, the length of each of the plurality of zones (zone 1 to zone 10) may be 5m.

[0036] Each of the multiple zones (zone 1 to zone 10) may be a zone through which the electrode semi-product (200) passes. The electrode semi-product (200) may be dried while passing through each zone (zone 1 to zone 10). That is, each of the multiple zones (zone 1 to zone 10) may represent a drying section where the slurry (220) is dried. While the electrode semi-product (200) passes through each of the multiple zones (zone 1 to zone 10), the slurry (220) of the electrode semi-product (200) may be dried through hot air. That is, while the electrode semi-product (200) passes through each of the multiple zones (zone 1 to zone 10) in sequence according to the direction of travel, the degree of drying of the slurry (220) may gradually increase.

[0037] Hot air may be supplied to the slurry (220) by the hot air supply unit (110) in at least one of the plurality of zones (zone 1 to zone 10). Each of the plurality of zones (zone 1 to zone 10) may correspond to the degree to which the electrode semi-finished product (200) or the slurry (220) is dried. For example, the first zone (zone 1) may be a zone where the slurry (220) is dried from 0% to 10% while passing through the slurry (220), the second zone (zone 2) may be a zone where the slurry (220) is dried from 10% to 20%, and the third zone (zone 3) may be a zone where the slurry (220) is dried from 20% to 30%. In a similar manner, zone 8 may be a zone where the slurry (220) is dried from 70% to 80%, zone 8 may be a zone where the slurry (220) is dried from 80% to 90%, and zone 10 may be a zone where the slurry (220) is dried from 90% to 100%. Here, the degree of drying in each zone (zone 1 to zone 10) may vary depending on the temperature of the hot air provided in each zone (zone 1 to zone 10), the size of each zone (zone 1 to zone 10), etc. That is, the temperature and wind speed of the hot air in each zone (zone 1 to zone 10) can be set independently.

[0038] The induction heating unit (120) may be placed in a reference area among a plurality of areas (zone 1 to zone 10) of the drying chamber. The induction heating unit (120) may heat the slurry (220) by an induction heating method while the slurry (220) passes through the reference area. For example, the reference area may be the eighth area (zone 8).

[0039] In one embodiment, the induction heating unit (120) may be located in the center portion within the reference area. The center portion may be a location for induction heating the center portion among the side portion and the center portion of the electrode semi-finished product (200). The induction heating unit (120) is positioned in the center portion within the reference area to induction heat the center portion of the electrode semi-finished product (200) passing through the reference area. Accordingly, the drying deviation between the side portion and the center portion of the electrode semi-finished product (200) can be reduced.

[0040] In one embodiment, the reference zone may be a zone among a plurality of zones (zone 1 to zone 10) where the degree of drying of the solvent of the slurry (220) by hot air reaches a reference value. Meanwhile, although FIG. 2 shows 10 zones (zone 1 to zone 10), this is merely one embodiment and can be implemented with varying numbers. In addition, the degree of drying corresponding to each zone (zone 1 to zone 10) can be implemented with various variations.

[0041] In one embodiment, the drying device (100) may further include a control unit. The control unit can control the overall operation of the drying device (100). For example, the control unit can control the temperature of the hot air and the rotational speed (rpm) of the circulation fan. The control unit can control the output (kW) of the induction heating unit (120).

[0042] The electrode (300) can be manufactured by drying the electrode semi-finished product (200). The electrode (300) may be an electrode used in a secondary battery. In one embodiment, the secondary battery may be a lithium secondary battery, etc.

[0043] The electrode (300) may include a current collector (310) and a coating layer (320). The electrode (300) may be classified into either a cathode or an anode depending on the type. Depending on the type of the electrode (300), the type of material included in each of the current collector (310) and the coating layer (320) may vary.

[0044] The current collector (310) may be a dried current collector (210). In one embodiment, the current collector (310) may have the same material and structure as the current collector (210). The description of the current collector (210) described above may be applied in the same way to the current collector (310).

[0045] The coating layer (320) may include an active material, a conductive material, and a binder. The coating layer (320) may be a dried slurry (220). For example, the coating layer (320) may be a slurry (220) from which the solvent has been removed from the solvent, active material, conductive material, and binder contained in the slurry (220).

[0046] In one embodiment, the reference value may be determined based on experimentally obtained data.

[0047] In one embodiment, the reference value may be included in a range greater than 65% and less than 100%. For example, the reference region may be one of the regions existing between the region corresponding to 65% and the region corresponding to 100% where the degree of drying of the solvent of the slurry (220) by hot air is 65%.

[0048] In one embodiment, the reference value may be included in a range greater than 72.5% and less than 95%. For example, the reference region may be one of the regions existing between the region corresponding to 72.5% and the region corresponding to 95% where the degree of drying of the solvent of the slurry (220) by hot air is 72.5%.

[0049] In one embodiment, the reference value may be included in a range of 80% or more and 90% or less. For example, the reference area may be one of the areas where the degree of drying of the solvent of the slurry (220) by hot air corresponds to 80%, the area corresponding to 90%, and the areas in between.

[0050] In one embodiment, the output value of the induction heating unit (120) can be determined based on experimentally obtained data.

[0051] In one embodiment, the control unit can control the output of the induction heating unit (120) to a value within the range of 2.4 kW to 3.2 kW. Specifically, the control unit can control the output of the induction heating unit (120) to a value included in the range greater than 2.4 kW and less than 3.2 kW.

[0052] In one embodiment, the control unit can control the output of the induction heating unit (120) to a value within the range of 2.6 kW to 3.0 kW. Specifically, the control unit can control the output of the induction heating unit (120) to a value included in the range greater than 2.6 kW and less than 3.0 kW.

[0053] Meanwhile, when drying the slurry (220) with only hot air, it is difficult to dry the inside of the slurry (220) because the hot air transfers heat from the surface of the slurry (220). In particular, when the loading amount of active material is increased to improve energy density, the thickness of the slurry (220) becomes relatively thicker and the unit amount of solvent that needs to be dried increases, and due to this structure, it may become difficult to dry the inside of the slurry (220). At this time, if the drying temperature is increased, thermal wrinkles or curls may occur due to the thermal expansion of the current collector (210).

[0054] Additionally, the slurry (220) applied to the current collector (210) may have a difference in loading amount depending on the area, such as the center area and the side area. In this case, the center area of ​​the slurry (220) may be dried to an appropriate level, but cracks may occur on the surface of the side area of ​​the slurry (220) due to over-drying, or the side area of ​​the slurry (220) may be dried to an appropriate level, but the center area of ​​the slurry (220) may not be dried to an appropriate level. In this case, there is a method to proceed with drying at a low drying speed, but there is a problem of reduced productivity.

[0055] According to one embodiment of the present disclosure, the drying device (100) can improve the manufacturing speed and productivity of the electrode stably without defects by drying the slurry (220) through induction heating of the induction heating unit (120) placed in the reference area as well as hot air. In particular, the slurry (220) can be efficiently dried to the inside through induction heating, thereby preventing defects caused by the difference in the amount of heat transferred to the surface and the inside.

[0056] In addition, according to one embodiment of the present disclosure, the variation in drying speed between the center region and the side region can be reduced even when the drying speed increases with increasing the coating speed. By preventing binder migration due to rapid drying, the deterioration of electrode quality, such as adhesion, can be prevented.

[0057] Below, we will explain the result data obtained under various design conditions.

[0058] Table 1 below shows the design conditions of each embodiment, and Table 2 below shows the result data of each embodiment. Examples 1A to 1C are embodiments of drying an electrode semi-finished product (200) through hot air and induction heating. Each of Examples 1B and 1C represents drying conditions (coating speed, solid content, loading amount, output, hot air temperature, etc.) that are more difficult to dry normally compared to Example 1A. Examples 2A to 2C are embodiments of drying an electrode semi-finished product (200) through hot air. Each of Examples 2B and 2C represents drying conditions (coating speed, solid content, loading amount, hot air temperature, etc.) that are more difficult to dry normally compared to Example 2A.

[0059] Examples Coating speed (m / min) Solids (%) Loading amount (mg / cm2) Output (kW) Hot air temperature (°C) 1A 10 50 10 4.0 80 1B 10 40 13 8.5 120 1C 15 40 10 7.0 110 2A 10 50 10 0 100 2B 10 40 13 0 150 2C 15 40 10 0 140

[0060] In Table 1, the coating speed indicates the distance traveled by the electrode semi-finished product (200) per unit time. That is, the higher the coating speed, the shorter the residence time inside the drying device (100). The solid content may indicate the degree of drying of the slurry (220) or the amount of solvent contained in the slurry (220). For example, a higher percentage of solid content may indicate a greater degree of drying or a smaller amount of solvent contained in the slurry (220). The loading amount may indicate the mass per unit area where the slurry (220) or active material is applied. The output indicates the output of the induction heating unit (120), and the hot air temperature may indicate the temperature of the hot air provided by the hot air supply unit (110).

[0061] Examples Drying complete Electrode adhesion error Center area Side 1A O O 0.21 X 1B O O 0.19 X 1C O O 0.20 X 2A O O 0.20 X 2B X O 0.12 O (Center area: undried)(Side area: cracked) 2C X O 0.14 O (Center area: undried)(Side area: cracked)

[0062] In Table 2, O for "Drying Complete" indicates that the slurry (220) of the corresponding embodiment is completely dried (i.e., the solvent is completely vaporized), and X for "Drying Complete" indicates that the slurry (220) is not completely dried (i.e., the solvent is not completely vaporized). In particular, the status of drying completion may vary by region. For example, if the center region of the electrode semi-product (200) is not sufficiently dried, an incomplete drying defect may occur, or if the side region of the electrode semi-product (200) is over-dried, a crack defect may occur. This is because the drying speed of the side region is faster than the drying speed of the center region. Electrode adhesion can serve as an indicator of the electrode quality or whether binder migration has occurred. Binder migration refers to the phenomenon where the binder moves according to the movement of the solvent as the solvent dries on the surface. O for "Defect" indicates that a phenomenon adversely affecting the quality of the electrode has occurred, and X for "Defect" indicates that the quality of the electrode is normal.

[0063] In the case of Example 1A, a slurry (220) with a solid content of 50% was prepared by adding 5 parts by weight of a graphite-based conductive agent, 1.2 parts by weight of carboxymethylcellulose, 1.5 parts by weight of styrene-butadiene rubber, and pure water to an active material in which natural graphite and artificial graphite were mixed in a certain ratio. The slurry (220) was uniformly applied to a current collector (210) of 6 μm copper thin film with a loading amount of 10 mg / cm². The current collector (210) coated with the slurry (220) was passed into the interior of a drying device (100) at a coating speed of 10 m / min. Inside the drying device (100), the current collector (210) coated with the slurry (220) was heated by an induction heating unit (120) with an output of 4.0 kW, and then hot air at 80 degrees was supplied to manufacture an electrode (300). The final electrode was manufactured by rolling the electrode (300) using a roll press rolling facility. In the case of Example 1A, the center region and the side region were dried normally as shown in Table 2, and a result was obtained in which the electrode adhesion strength was similar even though the hot air temperature was lower compared to Example 2A.

[0064] In the case of Example 1B, 5 parts by weight of a graphite-based conductive agent, 1.2 parts by weight of carboxymethylcellulose, 1.5 parts by weight of styrene-butadiene rubber, and pure water were added to an active material in which natural graphite and artificial graphite were mixed in a certain ratio to prepare a slurry (220) with a solid content of 40%. The slurry (220) was uniformly applied to a current collector (210) of 6 μm copper thin film with a loading amount of 13 mg / cm². The current collector (210) coated with the slurry (220) was passed into the interior of a drying device (100) at a coating speed of 10 m / min. Inside the drying device (100), an electrode (300) was manufactured by heating with an induction heating unit (120) with an output of 8.5 kW and then supplying hot air at 120 degrees. The final electrode was manufactured by sufficiently rolling the electrode (300) using a roll press rolling facility. In the case of Example 1B, the center region and side region were dried normally as shown in Table 2, and although the electrode adhesion strength decreased slightly compared to Example 1A, the result was similar to Example 1A with a value within the error range.

[0065] In the case of Example 1C, a slurry (220) with a solid content of 40% was prepared by adding 5 parts by weight of a graphite-based conductive agent, 1.2 parts by weight of carboxymethylcellulose, 1.5 parts by weight of styrene-butadiene rubber, and pure water to an active material in which natural graphite and artificial graphite were mixed in a certain ratio. The slurry (220) was uniformly applied to a current collector (210) of 6 μm copper thin film with a loading amount of 10 mg / cm². The current collector (210) coated with the slurry (220) was passed into the interior of a drying device (100) at a coating speed of 15 / min. Inside the drying device (100), an electrode (300) was manufactured by heating with an induction heating unit (120) with an output of 7.0 kW and then supplying hot air at 110 degrees. The electrode (300) was sufficiently rolled using a roll press rolling facility to manufacture the final electrode. In the case of Example 1C, as shown in Table 2, the center area and side area were dried normally, and although the electrode adhesion strength decreased slightly compared to Example 1A, the result was similar to Example 1A with a value within the margin of error.

[0066] In the case of Example 2A, 5 parts by weight of a graphite-based conductive agent, 1.2 parts by weight of carboxymethylcellulose, 1.5 parts by weight of styrene-butadiene rubber, and pure water were added to an active material in which natural graphite and artificial graphite were mixed in a certain ratio to prepare a slurry (220) with a solid content of 50%. The slurry (220) was uniformly applied to a current collector (210) of 6 μm copper thin film with a loading amount of 10 mg / cm². The current collector (210) coated with the slurry (220) was passed into the interior of a drying device (100) at a coating speed of 10 m / min. Inside the drying device (100), an electrode (300) was manufactured by supplying hot air at 100 degrees without using an induction heating unit (120). The electrode (300) was sufficiently rolled using a roll press rolling facility to manufacture the final electrode. In the case of Example 2A, the center area and side area were dried normally as shown in Table 2.

[0067] In the case of Example 2B, a slurry (220) with a solid content of 40% was prepared by adding 5 parts by weight of a graphite-based conductive agent, 1.2 parts by weight of carboxymethylcellulose, 1.5 parts by weight of styrene-butadiene rubber, and pure water to an active material in which natural graphite and artificial graphite were mixed in a certain ratio. The slurry (220) was uniformly applied to a current collector (210) of 6 μm copper thin film with a loading amount of 13 mg / cm². The current collector (210) coated with the slurry (220) was passed into the interior of a drying device (100) at a coating speed of 10 m / min. Inside the drying device (100), an electrode (300) was manufactured by supplying hot air at 150 degrees without using an induction heating unit (120). The electrode (300) was sufficiently rolled using a roll press rolling facility to manufacture the final electrode. In the case of Example 2B, as shown in Table 2, an undried defect occurred in the center area and a crack defect occurred in the side area. In addition, in the case of Example 2B, a problem occurred in which the electrode adhesion strength decreased compared to Example 2A.

[0068] In the case of Example 2C, a slurry (220) with a solid content of 40% was prepared by adding 5 parts by weight of a graphite-based conductive agent, 1.2 parts by weight of carboxymethylcellulose, 1.5 parts by weight of styrene-butadiene rubber, and pure water to an active material in which natural graphite and artificial graphite were mixed in a certain ratio. The slurry (220) was uniformly applied to a current collector (210) of 6 μm copper thin film with a loading amount of 10 mg / cm². The current collector (210) coated with the slurry (220) was passed into the interior of a drying device (100) at a coating speed of 15 m / min. Inside the drying device (100), an electrode (300) was manufactured by supplying hot air at 140 degrees without using an induction heating unit (120). The electrode (300) was sufficiently rolled using a roll press rolling facility to manufacture the final electrode. In the case of Example 2C, as shown in Table 2, an undried defect occurred in the center area and a crack defect occurred in the side area. In addition, in the case of Example 2C, a problem occurred in which the electrode adhesion strength decreased compared to Example 2A.

[0069] As in Example 1A, even with a relatively low coating speed, high solid content, and low loading amount, the slurry (220) could be completely dried using hot air and induction heating at a significantly lower temperature. As in Example 1B, even with a relatively low solid content and high loading amount, the slurry (220) could be completely dried using hot air and induction heating at a low temperature. As in Example 1C, even with a relatively low solid content and high coating speed, the slurry (220) could be completely dried using hot air and induction heating at a low temperature. Compared to Examples 2A to 2C, where one of the coating speed, solid content, or loading amount is relatively high, Examples 1A to 1C were able to complete drying quickly while maintaining electrode adhesion without defects even at a low hot air temperature.

[0070] In addition, no defects occurred in Example 2A, but defects occurred in Examples 2B and 2C. That is, even if drying is performed under drying conditions like those in Example 2A, there is a possibility that defects may occur if the drying conditions are temporarily changed due to various causes. On the other hand, since no defects occur in the case of Example 1A even when the drying conditions are changed as in Examples 1B and 1C, it has the advantage of being less likely to cause defects than Example 2A.

[0071] Meanwhile, in the case of hot air drying, drying can be achieved through the transfer of convective heat. For example, convective heat can be transferred from the surface of the slurry (220) to the interior to facilitate drying. Additionally, drying can proceed from the side area to the center area of ​​the electrode semi-finished product (200) through the transfer of convective heat. In one embodiment, if the electrode semi-finished product (200) is dried at a low drying speed using hot air, specific issues such as defects may not occur. In another embodiment, if the amount of solvent to be dried per unit time increases, such as due to an increase in solid content or an increase in coating speed, drying imbalance may occur in which the degree of drying varies depending on the area. For example, cracks may occur on the surface due to over-drying in the side area, and incomplete drying may occur in the interior of the center area. According to one embodiment of the present disclosure, the drying capacity can be improved by using an induction heating unit (120) so that drying can proceed not only on the surface of the slurry (220) but also inside. According to one embodiment of the present disclosure, the drying deviation between the side area and the center area can be eliminated by using an induction heating unit (120).

[0072] Table 3 below shows the design conditions of each embodiment, and Table 4 below shows the result data of each embodiment.

[0073] Examples Output (kW) Solids (%) Loading amount (mg / cm²) 2 ) Width (mm) Length (mm) 3A 1.5 50 10 100 100 3B 1.5 65 10 100 100 3C 1.5 80 10 100 100 4A 2.0 50 10 100 100 4B 2.0 65 10 100 100 4C 2.0 80 10 100 100 5A 2.4 50 10 100 100 5B 2.4 65 10 100 100 5C 2.4 80 10 100 100 6A 2.8 50 10 100 100 6B 2.8 65 10 100 100 6C 2.8 80 10 100 100 6D 2.8 90 10 100 100 7A 3.2 50 10 100 100 7B 3.2 65 10 100 100 7C 3.2 80 10 100 100 7D 3.2 90 10 100 100

[0074] The width and length in Table 3 represent the width and length of the electrode semi-finished product (200). Here, the solid content may indicate the degree to which the slurry (220) is dried by hot air. The output and loading amount are omitted in detail as they overlap with the previously described specifications. Examples 3A to 7D are electrode semi-finished products (200) manufactured with the same loading amount, width, and length, dried by induction heating of the induction heating unit (120) under standard conditions (room temperature, standard atmospheric pressure) without hot air. Depending on the design conditions in which the output of the induction heating unit (120) and the % value of the solid content were different, result data as shown in Table 4 below could be obtained.

[0075] Examples error Solvent amount (mg / 100cm³) 2 ) Evaporation solvent volume (mg / 100cm³) 2 ) Drying amount (%) Solid content after drying (%) 3A X 500 33 7 68.17 3B X 350 17 5 75.02 3C X 200 19 9 84.67 4A X 500 58 12 69.35 4B O(boiling) 350 39 11 76.28 4C X 200 37 19 85.98 5A O(boiling) 500 174 35 75.41 5B O(boiling) 350 154 44 83.61 5C X 200 89 45 90.01 6A O(boiling) 500 299 60 83.26 6B O(boiling) 350 188 54 86.06 6C X 200 134 67 93.81 6D X 100 65 65 96.62 7A O(boiling) 500 400 80 90.91 7B O(boiling) 350 264 75 92.08 7C O(crack) 200 172 86 97.28 7D O(crack) 100 89 89 98.91

[0076] The solvent amount represents the mass of solvent per unit area before drying. The evaporated solvent amount represents the mass of solvent vaporized due to drying per unit area. The drying amount may represent a percentage of the ratio between the evaporated solvent amount and the residual solvent amount. The residual solvent amount represents the mass of the solvent remaining after drying (i.e., the solvent amount minus the evaporated solvent amount). The solid content after drying may represent the degree to which the slurry (220) is dried or the amount of solvent contained in the slurry (220) after drying.

[0077] As shown in Table 4, in the case of Examples 3A to 4C, the drying amount was found to be relatively low. In the case of Examples 5A, 5B, 6A, 6B, and 7A to 7D, defects such as boiling or cracking occurred, respectively. In the case of Examples 6C and 6D, the drying amount was found to be relatively high, and no defects occurred.

[0078] Based on the experimental data above, the position and output of the induction heating unit (120) can be determined.

[0079] In one embodiment, the slurry (220) can be dried by induction heating in a range where the solid content of the slurry (220) is greater than 65% and less than 100%. That is, an induction heating unit (120) can be placed in an area between the region corresponding to 65% and the region corresponding to 100% where the degree of solvent drying of the slurry (220) by hot air in the drying device (100).

[0080] In one embodiment, the slurry (220) can be dried by induction heating in a range where the solid content of the slurry (220) is greater than 72.5% and less than 95%. That is, an induction heating unit (120) can be placed in an area between the region corresponding to 72.5% and the region corresponding to 95% where the degree of solvent drying of the slurry (220) by hot air in the drying device (100) can be placed.

[0081] In one embodiment, the slurry (220) can be dried by induction heating in a range where the solid content of the slurry (220) is 80% or more and 90% or less. That is, an induction heating unit (120) can be placed in one of the regions where the degree of drying of the solvent of the slurry (220) by hot air in the drying device (100) corresponds to 80%, the region corresponding to 90%, and the regions existing in between.

[0082] In one embodiment, the output of the induction heating unit (120) can be controlled to a value included in the range greater than 2.4 kW and less than 3.2 kW. In one embodiment, the output of the induction heating unit (120) can be controlled to a value included in the range greater than 2.6 kW and less than 3.0 kW.

[0083] According to an embodiment of the present disclosure, when the solid content is below a certain level (e.g., 65, 70%, etc.), if the output of the induction heating unit (120) is increased above a reference value (e.g., 1.8, 2.0 kW, etc.), defects such as the boiling of the solvent may occur. That is, when the solid content is below a certain level, the output of the induction heating unit (120) cannot be increased above a reference value to prevent the boiling of the solvent. On the other hand, when the solid content is above a certain level, even if the output of the induction heating unit (120) is increased above a reference value, the problem of the solvent boiling can be prevented.

[0084] FIG. 3 is a flowchart illustrating a method for manufacturing an electrode for a secondary battery according to one embodiment of the present disclosure.

[0085] Referring to FIG. 3, a method for manufacturing an electrode (300) for a secondary battery may include a step (S31) of applying a slurry (220) containing an active material and a solvent onto a current collector (210), and a step (S33) of drying the slurry (220) using induction heating of an induction heating unit (120) when the degree of drying of the slurry (220) reaches a reference value while the current collector (210) passes through a drying device (100).

[0086] A slurry (220) can be applied to the current collector (210) (S31). For example, the current collector (210) can be moved by the rotation of a roller. When the current collector (210) is moved to the lower part of the die coater (10), the slurry ejected from the die coater (10) can be applied to the current collector (210).

[0087] In one embodiment, the slurry (220) may include a solvent, an active material, a conductive material, and a binder. The active material, the conductive material, and the binder may be dispersed in the solvent.

[0088] And, when the degree of drying of the slurry (220) reaches a reference value while the current collector (210) passes through the drying device (100), the slurry (220) can be dried using induction heating of the induction heating unit (120) (S33).

[0089] In one embodiment, the step of drying the slurry (220) may include the step of moving the collector (210) to pass through the interior of the drying device (100) and the step of supplying hot air to the slurry (220) while it passes through the interior of the drying device (100). For example, the hot air may be supplied by a hot air supply unit (110).

[0090] In one embodiment, the step of drying the slurry (220) can be performed by using induction heating and hot air from an induction heating unit (120) placed in a region while the current collector passes through a region where the degree of drying of the slurry (220) reaches a reference value.

[0091] In one embodiment, the induction heating unit (120) may be placed in a region among a plurality of regions included in the drying device (100) where the degree of drying of the slurry (220) reaches a reference value. Each of the plurality of regions may correspond to the degree of drying of the slurry (220). The region where the degree of drying of the slurry (220) reaches a reference value may be a reference region.

[0092] In one embodiment, the reference value may be included in a range greater than 65% and less than 100%.

[0093] In one embodiment, the reference value may be included in a range greater than 72.5% and less than 95%.

[0094] In one embodiment, the reference value may be included in a range of 80% or more and 90% or less.

[0095] In one embodiment, the output of the induction heating unit (120) may be greater than 2.4 kW and less than 3.2 kW.

[0096] In one embodiment, the output of the induction heating unit (120) may be greater than 2.6 kW and less than 3.0 kW. Explanation of the symbols

[0097] 100: Drying device 110: Hot air supply unit 120: Induction heating unit 200: Electrode semi-finished product 210: Current collector 220: Slurry 300: Electrode 310: Current collector 320: Coating layer

Claims

Claim 1 A method for manufacturing an electrode for a secondary battery, comprising: a step of applying a slurry containing an active material and a solvent onto a current collector; and a step of drying the slurry using induction heating of an induction heating unit when the degree of drying of the slurry reaches a reference value while the current collector passes through a drying device; wherein the reference value is included in a range greater than 65% and less than 100%. Claim 2 A method for manufacturing an electrode for a secondary battery according to claim 1, wherein the induction heating unit is disposed in a reference area among a plurality of areas included in the drying device where the degree of drying of the slurry reaches the reference value. Claim 3 delete Claim 4 A method for manufacturing an electrode for a secondary battery according to claim 1, wherein the reference value is included in a range greater than 72.5% and less than 95%. Claim 5 A method for manufacturing an electrode for a secondary battery, wherein, in paragraph 4, the above reference value is included in the range of 80% or more and 90% or less. Claim 6 A method for manufacturing an electrode for a secondary battery according to claim 1, wherein the output of the induction heating unit is greater than 2.4 kW and less than 3.2 kW. Claim 7 A method for manufacturing an electrode for a secondary battery according to claim 6, wherein the output of the induction heating unit is greater than 2.6 kW and less than 3.0 kW. Claim 8 A method for manufacturing an electrode for a secondary battery according to claim 1, wherein the step of drying the slurry comprises: a step of moving the current collector to pass through the interior of the drying device; and a step of supplying hot air to the slurry while it passes through the interior of the drying device. Claim 9 A method for manufacturing an electrode for a secondary battery according to claim 8, wherein the step of drying the slurry involves drying the slurry using induction heating of the induction heating unit disposed in the region and hot air while the current collector passes through the region where the degree of drying of the slurry reaches the reference value. Claim 10 A method for manufacturing an electrode for a secondary battery according to claim 1, wherein the slurry comprises the active material, conductive material, and binder dispersed in the solvent. Claim 11 A drying device for an electrode of a secondary battery, comprising: a drying chamber including a plurality of regions through which a current collector coated with a slurry passes; and an induction heating unit disposed in a reference region among the plurality of regions where the degree of drying of the slurry reaches a reference value, and heating the slurry by an induction heating method while the current collector passes through the reference region; wherein the reference value is included in a range greater than 65% and less than 100%. Claim 12 A drying apparatus for an electrode for a secondary battery, further comprising: a hot air supply unit that supplies hot air to the slurry while the current collector passes through at least one of the plurality of regions in claim 11. Claim 13 delete Claim 14 In claim 11, the above reference value is a drying device for a secondary battery electrode included in the range greater than 72.5% and less than 95%. Claim 15 In claim 14, the above standard value is a drying device for a secondary battery electrode included in the range of 80% or more and 90% or less. Claim 16 A drying apparatus for a secondary battery electrode according to claim 11, further comprising a control unit that controls the output of the induction heating unit to a value included in a range greater than 2.4kW and less than 3.2kW. Claim 17 In claim 11, the above slurry is a drying apparatus for a secondary battery electrode comprising a solvent and an active material, a conductive material, and a binder dispersed in said solvent.

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