Electrode manufacturing apparatus and electrode manufacturing method using the same

Abstract

The present invention relates to an electrode manufacturing apparatus and a manufacturing method using the same, and the manufacturing apparatus and method have a configuration in which a first electrode slurry is applied to a first surface of an electrode sheet when the electrode sheet is transported in a horizontal direction relative to the direction in which gravity acts, a second electrode slurry is applied to a second surface of the electrode sheet transported in a vertical direction relative to the direction in which gravity acts, and then the electrode is dried in two stages, thereby improving both processability and productivity during electrode manufacturing. In addition, the manufactured electrode has excellent adhesive strength between the electrode sheet and the active material layer, and the active material layers formed on both sides of the electrode sheet have an advantage that the porosity of the active material layers formed on both sides of the electrode sheet can be easily controlled in a single manufacturing process, so that electrodes having various porosity patterns can be manufactured.

Description

[Technical Field]

[0001] The present invention relates to an electrode manufacturing apparatus and an electrode manufacturing method using the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0064000, filed May 25, 2022, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference. [Background technology]

[0003] In recent years, secondary batteries have been widely applied not only to small devices such as portable electronic devices but also to medium- to large-sized devices such as battery packs for hybrid and electric vehicles and power storage devices. Among these secondary batteries, much research has been conducted on lithium secondary batteries, which have high energy density and discharge voltage, and they have also been commercialized and widely used.

[0004] A secondary battery includes an electrode assembly including a positive electrode, a negative electrode, and a separator, an electrolyte, and a multilayer exterior material that protects them as a main body. Such a secondary battery can be used in the form of a battery module equipped with multiple cells.

[0005] Here, the electrode assemblies are roughly classified into cylindrical and plate types depending on the form (external structure) in which they are housed in a case, and into jelly roll and stack types depending on the stacking form (internal structure) of the electrode assemblies.

[0006] Among these, jelly-roll electrode assemblies are formed by stacking long sheet-shaped positive and negative electrodes with a separator interposed therebetween and then winding them into a cylindrical structure so that the cross section is circular, or by winding the cylindrical structure and then compressing it in one direction to form a roughly plate-like cross section. While jelly-roll electrode assemblies are suitable for cylindrical batteries, they suffer from drawbacks such as peeling of the electrode active material and low space utilization when applied to prismatic or pouch-shaped batteries. Another limitation is that it is difficult for the electrolyte to completely penetrate the center of the wound electrode assembly during battery assembly.

[0007] Meanwhile, the stacked electrode assembly may be formed into a plate-like structure by cutting out positive and negative electrodes into a predetermined size and then stacking them sequentially with a separator interposed therebetween. Therefore, the stacked electrode assembly has the advantage of easily obtaining a rectangular shape, but has the disadvantage of being complicated to manufacture and having the electrodes be easily pressed when subjected to an impact, which may cause a short circuit.

[0008] To solve these problems, a stack-folding type electrode assembly has been developed, which is an electrode assembly with an advanced structure that is a combination of the jelly roll type and the stack type. The stack-folding type electrode assembly has a structure in which a full cell with a positive electrode / separator / negative electrode structure of a certain unit size or a bicell with a positive electrode (negative electrode) / separator / negative electrode (positive electrode) / separator / positive electrode (negative electrode) using a long, continuous separator film.

[0009] However, in general, stack-folded electrode assemblies have their outer surfaces wrapped in separator films, and some full-cell or bi-cell sides have multiple separator films, which reduces wettability during electrolyte impregnation during battery manufacturing. Because electrolyte is an essential component for battery operation, poor wettability of the electrolyte can lead to reduced battery performance and shortened lifespan.

[0010] To address these issues, conventional techniques have been developed to either introduce through-holes into separators provided in electrodes or to control the porosity of active material layers formed on both sides of electrode sheets according to the position of each electrode stacked in a stack-folding electrode assembly. However, introducing through-holes into separators can lead to the risk of short circuits. Furthermore, techniques for controlling the porosity of active material layers formed on electrode surfaces have limitations in that it is difficult to individually adjust the porosity according to the position of the active material layer relative to the electrode sheet during the electrode manufacturing process. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2007-0114412 [Patent Document 2] Korean Patent Publication No. 10-2013-0144120 Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, an object of the present invention is to provide an electrode having improved wettability to an electrolyte when applied to a jelly roll type and / or stack folding type electrode assembly, and a technique for manufacturing the same. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, in one embodiment, the present invention provides an electrode manufacturing apparatus including: a coating unit that applies electrode slurry to a surface of an electrode sheet that is transported horizontally and vertically relative to the direction in which gravity acts; and a drying unit that dries the applied electrode slurry, wherein the coating unit includes a first coating unit that applies a first electrode slurry to a first surface of the electrode sheet that is transported horizontally relative to the direction in which gravity acts; and a second coating unit that applies a second electrode slurry to a second surface of the electrode sheet that has been coated with the first electrode slurry and is transported vertically relative to the direction in which gravity acts.

[0014] At this time, the first coating unit and the second coating unit may each be implemented using at least one of a slot die coater and a slot nozzle coater.

[0015] In addition, the first coating unit and the second coating unit may be disposed at positions spaced apart such that the time it takes for the second electrode slurry to be applied by the second coating unit to any point included in the electrode sheet immediately after the first electrode slurry is applied by the first coating unit is 2 seconds or less.

[0016] The drying unit may include a first drying unit that irradiates light or wavelengths onto the electrode slurry applied to both sides of the electrode sheet to perform primary drying, and a second drying unit that applies heat to the primarily dried electrode slurry to perform secondary drying.

[0017] For example, the first drying unit may include an ultraviolet dryer, a near-infrared dryer, or a far-infrared dryer, and the second drying unit may include at least one of a hot air dryer and a vacuum oven.

[0018] In one embodiment, the present invention provides an electrode manufacturing method carried out by the electrode manufacturing apparatus according to the present invention.

[0019] Specifically, the electrode manufacturing method includes the steps of applying a first electrode slurry to a first surface of an electrode sheet transported horizontally relative to the direction in which gravity acts, applying a second electrode slurry to a second surface of the electrode sheet transported vertically relative to the direction in which gravity acts and having the first electrode slurry applied thereto, and drying the electrode sheet having the first electrode slurry and the second electrode slurry applied thereto on both surfaces.

[0020] The first electrode slurry and the second electrode slurry each have a viscosity of 1,000 cps to 20,000 cps at 25°C, and the ratio (B1 / B2) of the viscosity of the first electrode slurry (B1) to the viscosity of the second electrode slurry (B2) may be 1.5 to 10.

[0021] The first electrode slurry and the second electrode slurry may have a solid content of 60% by weight or more.

[0022] The electrode sheet can be transported at a speed of 30 to 100 m / min.

[0023] In addition, the step of drying the electrode sheet may include a primary drying step of pre-drying the electrode slurry applied to both surfaces of the electrode sheet using light or wavelengths, and a secondary drying step of completely drying the pre-dried electrode slurry using heat.

[0024] Furthermore, in one embodiment, the present invention provides an electrode sheet manufactured by the electrode manufacturing apparatus according to the present invention described above.

[0025] The electrode sheet includes a first active material layer and a second active material layer formed on both sides, respectively, and the first active material layer and the second active material layer may have a difference in porosity. [Effects of the Invention]

[0026] The electrode manufacturing apparatus and manufacturing method according to the present invention are configured to apply a first electrode slurry to a first surface of an electrode sheet when the electrode sheet is transported horizontally relative to the direction in which gravity acts, apply a second electrode slurry to a second surface of the electrode sheet when the electrode sheet is transported perpendicularly relative to the direction in which gravity acts, and then dry the electrode in two stages, thereby improving both the process efficiency and productivity during electrode manufacturing.

[0027] Furthermore, the electrode manufactured by the electrode manufacturing apparatus and manufacturing method according to the present invention has excellent adhesive strength between the electrode sheet and the active material layer, and the porosity of both sides of the active material layer can be easily controlled. Furthermore, active material layers with different porosities can be formed in a single manufacturing process, which has the advantage of enabling the manufacturing of electrodes with a variety of porosity patterns. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic diagram showing the structure of an electrode manufacturing apparatus according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] Because the present invention is susceptible to various modifications and can have various embodiments, specific embodiments are described in detail in the detailed description.

[0030] However, this is not intended to limit the invention to any particular embodiment, but is to be understood as including all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0031] In the present invention, the terms "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and are understood as not precluding the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0032] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0033] In the present invention, the term "electrode sheet" may refer to the electrode current collector itself, or may refer to the electrode current collector in a state where an active material layer is formed on the surface thereof.

[0034] The present invention will now be described in more detail.

[0035] <Electrode manufacturing equipment> In one embodiment, the present invention comprises: a coating unit that applies electrode slurry to the surface of the electrode sheet that is transported in horizontal and vertical directions relative to the direction in which gravity acts; a drying unit that dries the applied electrode slurry, The coating portion is a first coating unit that applies a first electrode slurry to a first surface of the electrode sheet that is transported in a horizontal direction relative to the direction in which gravity acts; and a second coating unit that applies a second electrode slurry to a second surface of the electrode sheet that has been coated with the first electrode slurry and is transported in a direction perpendicular to the direction in which gravity acts.

[0036] 1 is a structural diagram that schematically shows the structure of an electrode manufacturing apparatus 10 according to the present invention. The electrode manufacturing apparatus 10 according to the present invention will be described below with reference to FIG.

[0037] The electrode manufacturing apparatus 10 according to the present invention includes a coating unit that applies electrode slurry to the surface of the electrode sheet E in accordance with the direction in which the sheet E is transported horizontally and vertically relative to the direction in which gravity acts, and a drying unit that dries the applied electrode slurry.

[0038] Here, the electrode sheet E may be transported by a roll-to-roll transport unit to improve the efficiency of the electrode manufacturing process. The transport unit may have a structure in which transport rollers 310 and 320 are arranged on the upper and / or lower surfaces of the electrode sheet E supplied from a winding roll (not shown) on which the electrode sheet E is wound. Specifically, at least one of the transport rollers 310 and 320 may be arranged on the upper and / or lower surfaces of the electrode sheet E. When the transport rollers 310 and 320 are arranged on the upper and / or lower surfaces, respectively, they may transport the electrode sheet E by rotating in opposite directions (e.g., R: counterclockwise, R': clockwise) while facing the electrode sheet at positions spaced apart from each other. In addition, the transport rollers 310 and 320 may be located upstream of a position where a coating unit is arranged and / or downstream of a position where a drying unit is arranged, based on the running direction D of the electrode sheet E, to avoid interference with the electrode slurry coated on the electrode sheet E.

[0039] The take-up roll (not shown) and transfer rollers 310 and 320 may be positioned so that the electrode sheet E is transferred horizontally relative to the direction of gravity but can change direction midway to be transferred vertically. Specifically, the first transfer roller 310, which primarily contacts the electrode sheet E supplied from the take-up roll, may be located below the take-up roll so that the electrode sheet E can be transferred in the direction of gravity before contact. The electrode sheet E that comes into contact with the first transfer roller 310 has its transfer direction changed by the first transfer roller 310. The second transfer roller 320, which secondarily contacts the electrode sheet E whose transfer direction has been changed, may be positioned at a height corresponding to that of the first transfer roller 310 so that the electrode sheet E can be transferred in a direction perpendicular to the direction of gravity after contacting the first transfer roller 310. As a result, the electrode sheet supplied from the take-up roll (not shown) may travel horizontally to the direction in which gravity acts until it reaches the first transfer roller 310, and may travel vertically to the direction in which gravity acts after passing through the first transfer roller 310.

[0040] In addition, the electrode sheet E may have a surface coated with electrode slurry by a coating unit while traveling in each direction. Specifically, the coating unit applies a first electrode slurry S to a first surface of the electrode sheet E that is transported in a horizontal direction relative to the direction in which gravity acts. 1st and a first coating unit 110 that applies second electrode slurry S to the second surface of the electrode sheet that is transported in a direction perpendicular to the direction in which gravity acts. 2nd and a second coating unit 120 that applies a coating agent to the electrode sheet E. Here, the first surface of the electrode sheet E refers to the surface (i.e., the lower surface) that is located below the electrode sheet E when the electrode sheet E is transported in a direction perpendicular to the direction in which gravity acts, and the second surface may refer to the surface (i.e., the upper surface) that is the other side of the first surface and that is located above the electrode sheet E when the electrode sheet E is transported in a direction perpendicular to the direction in which gravity acts.

[0041] The first coating unit 110 and the second coating unit 120 may be any type commonly used in the industry without any particular limitations, and specifically, may be one or more of a slot die coater and a slot nozzle coater, respectively.

[0042] In addition, the first coating unit 110 and the second coating unit 120 may be spaced apart from each other by a predetermined distance to coat the electrode slurry on the surface of the electrode sheet E when the electrode sheet E is continuously transported in a horizontal direction and a vertical direction relative to the direction in which gravity acts. Specifically, the first electrode slurry S coated by the first coating unit 110 1st When the electrode sheet is transported in a direction perpendicular to the direction of gravity, the first electrode slurry S is located below the electrode sheet E. 1st Since gravity is applied to the electrode sheet E, the adhesive force between the electrode sheet E and the first electrode slurry S may not be sufficient. Therefore, the first coating unit 110 and the second coating unit 120 are configured to apply the first electrode slurry S to the electrode sheet E when the electrode sheet E is transported in a direction perpendicular to the direction in which gravity acts. 1st In order to prevent the detachment and / or loss of the first electrode slurry S, any point included in the electrode sheet E is coated with the first electrode slurry S by the first coating unit 110. 1st Immediately after the second electrode slurry S is applied, the second coating unit 120 applies the second electrode slurry S 2nd The adhesive may be spaced apart so that it takes 2 seconds or less for the adhesive to be applied.

[0043] For example, the first coating unit 110 and the second coating unit 120 are configured such that a given point of the electrode sheet E is coated with the first electrode slurry S by the first coating unit 110. 1st After the second electrode slurry S is applied, the second coating unit 120 applies the second electrode slurry S 2nd The distance can be such that the time it takes for the adhesive to be applied is 0.1 to 1.5 seconds.

[0044] The electrode slurry applied by the first coating unit 110 and the second coating unit 120 may be dried by a drying unit. The drying unit may include first drying units 210a and 210b that temporarily dry the electrode slurry applied to both sides of the electrode sheet E, and a second drying unit 220 that completely dries the temporarily dried electrode slurry.

[0045] Specifically, the first drying sections 210a and 210b dry the first electrode slurry S of the electrode sheet E under gravity. 1st The device is a device for pre-drying an electrode slurry to prevent the detachment and / or loss of the active material and maintain its shape, and can irradiate the electrode slurry with light or wavelengths. Generally, electrode slurries are dried by applying high-temperature hot air, but this method has the problem of taking a long time to dry the electrode slurry. Furthermore, if the temperature of the hot air is increased to solve this problem, the tendency for the slurry surface to dry increases, which can lead to migration of the binder to the slurry surface due to the volatilized solvent, thereby reducing the adhesive strength between the active material layer and the electrode sheet. The present invention provides a device for pre-drying an electrode slurry S that is applied to an electrode sheet without these problems and is subjected to gravity acting in the opposite direction to the direction of adhesion to the electrode sheet. 1st For faster drying, energy can be applied in the form of light or wavelengths to pre-dry the electrode slurry.

[0046] The first drying units 210a and 210b may include, for example, an ultraviolet dryer, a near-infrared dryer, a far-infrared dryer, etc. Specifically, they may include a far-infrared dryer that emits energy with a wavelength of 1 μm or more, more specifically, 5 μm or more, 10 μm or more, or 20 μm or more, to achieve a uniform drying rate of the electrode slurry. Unlike near-infrared dryers and infrared dryers commonly used in the industry, the far-infrared dryer has a long light or wavelength, is energy efficient, and can apply energy uniformly not only to the surface but also to the interior of the slurry, thereby advantageously increasing the adhesive strength between the slurry and the electrode sheet in a short period of time.

[0047] At this time, the first drying sections 210a and 210b were operated at 50 kW / m 2 ~1,000kW / m 2 and specifically 50 kW / m 2 ~500kW / m 2 , 50kW / m 2 ~250kW / m 2 , or 50kW / m 2 and 200 kW / m 2 In the present invention, by controlling the power density of the first drying sections 210a and 210b within the above range, the first electrode slurry S applied to the first surface of the electrode sheet E during horizontal transport can be released at a power density of 1000 W / m. 1st This allows the active material layer to dry quickly before it is desorbed and / or lost, and can prevent uneven drying of the active material layer caused by excessive power density.

[0048] The second drying unit 220 is a device for uniformly and completely drying the pre-dried electrode slurry using light or wavelength, and can apply heat to the pre-dried electrode slurry.

[0049] In addition, the second drying unit 220 may include a separate wall that blocks off the periphery except for an entrance / exit for introducing and discharging the electrode sheet E. When the electrode sheet E is introduced into the wall, the second drying unit 220 applies energy in the form of heat to the surface of the electrode sheet E to dry the electrode slurry on the electrode sheet E. Here, the wall may function to minimize loss of the applied heat, and therefore is preferably made of a heat insulating material.

[0050] The second drying unit 220 may include any device commonly used in the art for applying energy in the form of heat, without any particular limitation. Specifically, the second drying unit 220 may include a hot air dryer, a vacuum oven, etc., used alone or in combination.

[0051] Furthermore, the second drying unit 220 may further include a filtering device that generates an additional air flow inside the wall so that the air flows along the surface of the electrode slurry and re-collects and filters the air to filter out solvent components that have evaporated to the surface as the electrode slurry dries, and a heat exchanger that recovers heat energy from the collected air flow. By further including a filtering device and a heat exchanger in the second drying unit 220 according to the present invention, it is possible to improve both the drying efficiency of the electrode slurry and the energy efficiency during the process.

[0052] Meanwhile, the electrode manufacturing apparatus 10 according to the present invention may further include inspection units 330a and 330b for measuring the loading amount and / or thickness of each electrode slurry coated on both sides of the electrode sheet E after the electrode slurry has been coated on both sides of the electrode sheet E and before the electrode slurry is dried in the drying unit. Specifically, the inspection units 330a and 330b may include an optical system, a spectroscopy, etc., and may measure or determine the thickness and / or loading amount of the electrode slurry coated on the surface of the electrode sheet E. The electrode manufacturing apparatus 10 may control the drying conditions of the first drying units 210a and 210b and the second drying unit 220 before drying the electrode slurry according to the results measured and / or determined by the inspection units 330a and 330b, thereby reducing the defective rate of electrodes.

[0053] The electrode manufacturing apparatus 10 according to the present invention, having the above-described configuration, can improve the space utilization of production facilities and the productivity during electrode manufacturing. Furthermore, the electrode manufacturing apparatus 10 can manufacture electrodes with different porosities on both sides when forming active material layers of the same composition on the electrode sheet by selectively applying gravity to the first side of the electrode sheet during electrode manufacturing. Therefore, the electrodes manufactured thereby can be useful for electrode assemblies with low electrolyte wettability, such as jelly roll and / or stack folding electrode assemblies.

[0054] <Electrode manufacturing method> In one embodiment, the present invention provides an electrode manufacturing method carried out using the electrode manufacturing apparatus according to the present invention.

[0055] An electrode manufacturing method according to the present invention has a configuration in which electrode slurries are applied to both surfaces of a transported electrode sheet and then dried twice. Specifically, the electrode manufacturing method includes the steps of applying a first electrode slurry to a first surface of an electrode sheet transported horizontally with respect to the direction of gravity, applying a second electrode slurry to a second surface of the electrode sheet transported vertically with respect to the direction of gravity and having the first electrode slurry applied thereto, and drying the electrode sheet having the first and second electrode slurries applied thereto.

[0056] The step of applying the first electrode slurry is a step of applying the electrode slurry to the first surface of the electrode sheet, that is, the surface on which gravity acts in the direction opposite to the direction of adhesion between the electrode sheet and the electrode slurry, when the electrode sheet is transported in a direction perpendicular to the direction of gravity. When the first electrode slurry applied in this process is dried, it can form an active material layer having a porosity greater than the average porosity of the active material layers formed on both surfaces of the electrode sheet.

[0057] In addition, the step of applying the second electrode slurry is a step of applying the electrode slurry to the surface of the electrode sheet on which gravity acts in the direction in which the adhesive force between the electrode sheet and the electrode slurry acts, i.e., the second surface, when the electrode sheet is transported in a direction perpendicular to the direction in which gravity acts. When the second electrode slurry applied in this process is dried, it can form an active material layer having a porosity smaller than the average porosity of the active material layers formed on both surfaces of the electrode sheet.

[0058] Here, the first electrode slurry and the second electrode slurry applied to both sides of the electrode sheet may have a high solid content in terms of uniformity of the electrode composition and battery capacity. Specifically, the first electrode slurry and the second electrode slurry may each contain a solid content of 60 wt % or more based on the weight of the total slurry, more specifically, 60 to 95 wt %, 60 to 90 wt %, 65 to 85 wt %, or 65 to 80 wt %.

[0059] The first electrode slurry and the second electrode slurry may have a viscosity within a specific range. Specifically, the first electrode slurry and the second electrode slurry may each have a viscosity of 1,000 cps to 20,000 cps at 25° C., more specifically, 1,000 cps to 10,000 cps, 1,000 cps to 8,000 cps, 2,000 cps to 6,000 cps, 5,000 cps to 15,000 cps, 8,000 cps to 15,000 cps, 3,000 cps to 5,000 cps, or 10,000 cps to 12,000 cps.

[0060] The first electrode slurry and the second electrode slurry may have a certain viscosity ratio. For example, the viscosity (B1) of the first electrode slurry and the viscosity (B2) of the second electrode slurry may have a ratio (B1 / B2) of 1.5 to 10, specifically 1.5 to 8, 2 to 6, 2 to 4, or 2.5 to 3.5. The viscosity of the first electrode slurry and the second electrode slurry may be adjusted by controlling the solid content and / or the binder content in the slurries, but is not limited thereto.

[0061] By controlling the viscosity and viscosity ratio of the first electrode slurry and the second electrode slurry to satisfy the above ranges, the present invention not only realizes high adhesion between the first surface of the electrode sheet and the first electrode slurry, prevents detachment and loss of the first active material layer, and improves drying efficiency during drying of the electrode, but also enables active material layers with uniform porosity to be formed on both surfaces of the electrode sheet.

[0062] Furthermore, the step of drying the electrode sheet may include a step of drying the electrode slurry applied to both sides of the electrode sheet, and the step may include a primary drying step of pre-drying the electrode slurry applied to both sides of the electrode sheet using light or wavelength, and a secondary drying step of completely drying the pre-dried electrode slurry using heat.

[0063] The drying step of the present invention includes a primary drying step in which the first electrode slurry is temporarily dried in a short time by applying high energy to the first surface of the electrode sheet, to prevent the first electrode slurry from being detached and / or lost on the first surface of the electrode sheet, to which gravity acts in the direction opposite to the direction in which the adhesive force between the electrode sheet and the electrode slurry acts.

[0064] For this purpose, the primary drying stage involves applying high energy to the first electrode slurry using heat or wavelengths and applying 50 kW / m 2 ~1,000kW / m 2 It is possible to add energy at a power density of 50 kW / m 2 ~500kW / m 2 , 50kW / m 2 ~250kW / m 2 , or 50kW / m 2 and 200 kW / m 2 By controlling the power density applied in the primary drying step within the above range, the present invention can significantly increase the molecular momentum of the solvent contained in the first electrode slurry and the second electrode slurry before the first electrode slurry is detached and / or lost, thereby enabling rapid drying without a rapid increase in the surface temperature of each electrode slurry and preventing uneven drying of the active material layer due to excessive power density.

[0065] The secondary drying step is a step of applying heat to both sides of the electrode sheet to dry the pre-dried electrode slurry uniformly and completely. The secondary drying step may completely remove the solvent remaining in the slurry by applying heat using at least one of a hot air dryer and a vacuum oven.

[0066] At this time, the temperature of heat applied to the electrode slurry during the secondary drying step may be 150°C or higher, specifically 150 to 200°C.

[0067] Meanwhile, in the present invention, the electrode sheet transport speed can be controlled to a predetermined range to adjust the loading amount and drying rate of the electrode slurry applied to the surface of the electrode sheet. Specifically, the electrode sheet can be transported at a speed of 30 to 100 m / min, more specifically, 30 to 80 m / min or 30 to 60 m / min. If the electrode sheet transport speed exceeds this range, not only will the energy density of the manufactured electrode decrease, but the time during which gravity acts on the first electrode slurry applied to the first surface will be significantly reduced, resulting in insufficient porosity difference between the active material layers formed on both surfaces of the electrode sheet. Furthermore, if the electrode sheet transport speed is lower than this range, it will take a considerable amount of time for the first electrode slurry applied to the first surface of the electrode sheet to dry, resulting in detachment and / or loss of the first active material layer formed on the first surface.

[0068] <Manufactured secondary battery electrodes> Furthermore, in one embodiment, the present invention provides an electrode for a secondary battery manufactured by the above-described electrode manufacturing method.

[0069] The electrode for a secondary battery according to the present invention is a positive electrode or a negative electrode for use in a lithium secondary battery, and is manufactured by the electrode manufacturing apparatus and / or electrode manufacturing method according to the present invention. The electrode is manufactured by applying a first electrode slurry to a first side of the electrode sheet while the electrode sheet is continuously traveling horizontally and vertically relative to the direction in which gravity acts, and applying a second electrode slurry to a second side of the electrode sheet being transported horizontally, and then drying the electrode in two stages, and is technically characterized in that the porosity on both sides of the active material layer is different by i) controlling the viscosity conditions of the first electrode slurry and the second electrode slurry, and ii) allowing gravity to act on the first side, on which the first electrode slurry is applied before drying, in a direction opposite to the direction in which the adhesive force between the electrode sheet and the first electrode slurry acts.

[0070] The secondary battery electrode according to the present invention has different porosities between the active material layers on both sides, thereby exhibiting excellent electrolyte wettability while maintaining a high energy density of the electrode. This advantageously allows for easily overcoming electrolyte wettability issues associated with electrode assembly structures such as jelly-roll and stack-folding electrode assemblies. Furthermore, the electrode has excellent thickness uniformity, thereby enabling high performance, such as battery energy density. Furthermore, the electrode has improved electrolyte wettability, allowing for uniform formation of an electrode film on the surface during a battery activation process, thereby further improving electrode performance.

[0071] In this case, the active material layers formed on both sides of the secondary battery electrode may have an average porosity of 20 to 40%, or 20 to 30%, and the difference in average porosity between the active material layers formed on both sides of the secondary battery electrode may be 1 to 10%, or 1 to 5%.

[0072] By ensuring that the porosity and average porosity difference of the active material layers provided on both surfaces of the electrode satisfy the above ranges, the present invention can prevent a decrease in the energy density of the electrode due to a porosity and porosity difference exceeding the above ranges, and can prevent a failure to improve the electrolyte wettability of the electrode due to a porosity and porosity difference not satisfying the above ranges.

[0073] The present invention will be described in more detail below with reference to examples and experimental examples.

[0074] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0075] <Examples and Comparative Examples> A positive electrode for a secondary battery was manufactured using an electrode manufacturing device equipped with a first coating unit and a second coating unit that apply electrode slurry to both sides of an electrode sheet, and a first drying unit and a second drying unit that continuously dry the applied electrode slurry.

[0076] Specifically, first, LiNi with a particle size of 5 μm was used as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2 was prepared and mixed with N-methylpyrrolidone (NMP) as a carbon-based conductive material and polyvinylidene fluoride as a binder to produce a first electrode slurry (solid content: 75%) and a second electrode slurry (solid content: 70%). Each slurry was then poured into the first and second coating sections, coated on both sides of an aluminum sheet, and dried to produce a positive electrode for a secondary battery.

[0077] At this time, the distance between the first and second coating units was set so that immediately after the first electrode slurry was applied to any point on the electrode sheet by the first coating unit, the time it took for the second electrode slurry to be applied by the second coating unit was within 1 second (1 second ± 0.3 seconds), and the running speed of the aluminum sheet was adjusted to 50 m / min.

[0078] In addition, (1) the running direction of the electrode sheet when the first coating unit and the second coating unit are operating (based on the direction in which gravity acts), (2) the viscosity of the first electrode slurry and the second electrode slurry at 25°C, and (3) the drying method of the first drying unit and the second drying unit are as shown in Table 1 below.

[0079] [Table 1]

[0080] <Experimental Example> In order to evaluate the physical properties of the secondary battery electrode manufactured according to the present invention, the following experiments were carried out.

[0081] a) Evaluation of adhesive strength between the electrode sheet and the first active material layer The positive electrodes for secondary batteries fabricated in the Examples and Comparative Examples were cut into rectangles measuring 2.5 cm wide x 10 cm long, and cellophane tape was attached to the surface of the first active material layer formed using the first electrode slurry. The plain portion of the electrode sheet, where no active material layer was formed, was then fixed, and the cellophane tape attached to the active material layer was peeled off in a 180° direction at a rate of 50 mm / min, and the stress was measured. The average value was calculated by performing 10 measurements and determining the average adhesive strength between the electrode sheet and the first active material layer. The results are shown in Table 2 below.

[0082] b) Evaluation of the solid content loss rate of the first active material layer The first active material layer formed using the first electrode slurry was separated from each of the positive electrodes for secondary batteries fabricated in the Examples and Comparative Examples and weighed. The weight change relative to the solid content of each slurry was then calculated. A negative weight change was determined to indicate a loss of electrode active material. The results are shown in Table 2.

[0083] c) Evaluation of thickness uniformity of the active material layer The cross-sectional structures of the positive electrodes for secondary batteries fabricated in the Examples and Comparative Examples were analyzed using a scanning electron microscope (FE-SEM, JEOL JSM-7200F) to obtain cross-sectional images. The thicknesses of five or more random active material layers were measured from the obtained images, and the standard deviation was calculated to evaluate the uniformity of each active material layer formed on both sides of the electrode sheet. A standard deviation of 10% or less of the average thickness of the active material layers was evaluated as "pass," and a standard deviation of more than 10% was evaluated as "fail." The results are shown in Table 2.

[0084] d) Evaluation of the porosity of the active material layer The thickness and weight per unit area of the positive electrodes for secondary batteries fabricated in the Examples and Comparative Examples were measured, and the measured density of the active material layer, including voids, was determined by dividing the measured weight per unit area by the volume obtained by multiplying the measured thickness and unit area. Separately, the theoretical density was determined by multiplying the distribution amount per unit area of the components constituting the electrode (electrode active material, conductive material, binder, etc.) by their known true density values. The porosity of the active material layer was calculated from the measured density and theoretical density of the active material layer using the following formula, and the results are shown in Table 2 below.

[0085] Porosity (%) = [(theoretical density of active material layer) / (measured density of active material layer) - 1] × 100

[0086] [Table 2]

[0087] As shown in Table 2 above, it can be seen that the electrode manufacturing apparatus and electrode manufacturing method according to the present invention are excellent not only in processability and productivity of secondary batteries, but also in the physical properties of the manufactured electrodes.

[0088] Specifically, it was confirmed that the positive electrode of the example according to the present invention had high adhesive strength of the first active material layer, which was subjected to gravity in the direction opposite to the direction of adhesive strength between the electrode sheet and the active material layer during manufacturing, and had little loss of solid content. It was also confirmed that each active material layer formed on the electrode sheet had excellent thickness uniformity and exhibited a porosity of 20 to 30%.

[0089] On the other hand, the comparative electrode showed low adhesive strength between the electrode sheet and the active material layer and high solid content loss. Also, most of the first active material layer, where gravity acts in the direction opposite to the adhesive strength between the electrode sheet and the active material layer, was found to have non-uniform thickness or, even if uniform, to have large differences in porosity.

[0090] From these results, the electrode manufacturing apparatus and electrode manufacturing method according to the present invention not only have excellent space utilization during electrode manufacturing, and excellent processability and productivity, but also have the advantage that the manufactured electrodes have excellent adhesion between the electrode sheet and the active material layer, and the active material layers formed on both sides of the electrode sheet allow for easy porosity control in a single manufacturing process, making it possible to manufacture electrodes with a variety of porosity patterns.

[0091] Although the present invention has been described above with reference to preferred embodiments, it will be understood that those skilled in the art or those having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0092] Therefore, the technical scope of the present invention is not limited to the content described in the Summary of the Invention of the specification, but is defined by the claims. [Explanation of symbols]

[0093] 10: Electrode manufacturing equipment 110: First coating section 120: Second coating section 210a, 210b: 1st drying section 211: Light or wavelength 220:Second drying section 310, 320: Transfer rollers 330a, 330b: Inspection Department E: Electrode sheet D: Running direction of electrode sheet R, R': Rotation direction of the transport roller S 1st : First electrode slurry S 2nd : Second electrode slurry

Claims

1. a coating unit that applies electrode slurry to the surface of the electrode sheet that is transported in horizontal and vertical directions relative to the direction in which gravity acts; a drying unit that dries the applied electrode slurry, The coating portion is a first coating unit that applies a first electrode slurry to a first surface of the electrode sheet that is transported in a horizontal direction relative to the direction in which gravity acts; a second coating unit that applies a second electrode slurry to a second surface of the electrode sheet, which has the first electrode slurry applied thereto and is transported in a direction perpendicular to a direction in which gravity acts, the first electrode slurry applied to the first surface is located under the electrode sheet when the electrode sheet is transported in a direction perpendicular to a direction in which gravity acts; the first active material layer and the second active material layer located on both sides of the electrode sheet have different porosities; The drying section a first drying unit that irradiates the electrode slurry applied to both surfaces of the electrode sheet with light or wavelength to perform primary drying; a second drying section that applies heat to the primarily dried electrode slurry to perform secondary drying, the ratio (B 1 / B 2 ) of the viscosity (B 1 ) of the first electrode slurry to the viscosity (B 2 ) of the second electrode slurry is 1.5 to 10;

2. The electrode manufacturing apparatus of claim 1 , wherein the first coating unit and the second coating unit are applied by at least one of a slot die coater and a slot nozzle coater.

3. 2. The electrode manufacturing apparatus of claim 1, wherein the first coating unit and the second coating unit are disposed at positions spaced apart from each other such that a time required for the second electrode slurry to be applied by the second coating unit immediately after the first electrode slurry is applied by the first coating unit to any point included in the electrode sheet is 2 seconds or less.

4. the first drying unit includes an ultraviolet dryer, a near-infrared dryer, or a far-infrared dryer, The electrode manufacturing apparatus of claim 1 , wherein the second drying unit includes at least one of a hot air dryer and a vacuum oven.

5. An electrode manufacturing method performed by the electrode manufacturing apparatus according to claim 1, applying a first electrode slurry to a first surface of an electrode sheet that is transported in a horizontal direction relative to a direction in which gravity acts; applying a second electrode slurry to a second surface of the electrode sheet, the second surface being conveyed in a direction perpendicular to the direction of gravity and having the first electrode slurry applied thereto; and drying the electrode sheet having the first electrode slurry and the second electrode slurry applied to both sides thereof, the first electrode slurry applied to the first surface is located under the electrode sheet when the electrode sheet is transported in a direction perpendicular to a direction in which gravity acts; The method for manufacturing an electrode, wherein the first active material layer and the second active material layer located on each side of the electrode sheet have different porosities.

6. 6. The method of claim 5, wherein the first electrode slurry and the second electrode slurry each have a viscosity of 1,000 cps to 20,000 cps at 25°C.

7. The electrode manufacturing method according to claim 6 , wherein the first electrode slurry and the second electrode slurry have a solids content of 60% by weight or more.

8. The electrode manufacturing method according to claim 5, wherein the electrode sheet is transported at a speed of 30 to 100 m / min.

9. The step of drying the electrode sheet includes: A primary drying step in which the electrode slurry applied to both sides of the electrode sheet is temporarily dried using light or wavelength; The method for manufacturing an electrode according to claim 5, further comprising a secondary drying step of completely drying the pre-dried electrode slurry using heat.

Images