【Title of the Invention】 ELECTRODE SLURRY COATING DEVICE AND METHOD CAPABLE OF MEASURING RESIDUAL OIL LEVEL 5 【Technical Field】 This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0177350, filed on December 17, 2020, and the entire contents of the Korean patent application are incorporated herein by reference. The present invention relates to an electrode slurry coating apparatus and method, and 10 more particularly, to an electrode slurry coating apparatus and method capable of measuring a remaining oil level. 【Background Art】 Recently, secondary batteries capable of charging and discharging have been widely used as energy sources of wireless mobile devices. In addition, the secondary battery has 15 attracted attention as an energy source of an electric vehicle, a hybrid electric vehicle, etc., which are proposed as a solution for air pollution of existing gasoline vehicles and diesel vehicles using fossil fuel. Therefore, the types of applications using the secondary battery are currently much diversified due to the advantages of the secondary battery, and it is expected that the secondary battery will be applied to many fields and products in the future. 20 Such secondary batteries may be classified into lithium ion batteries, lithium ion polymer batteries, lithium polymer batteries, etc., depending on the composition of the 3 electrode and the electrolyte, and among them, the amount of use of lithium-ion polymer batteries that are less likely to leak electrolyte and are easy to manufacture is on the increase. In general, secondary batteries are classified into cylindrical batteries and prismatic batteries in which an electrode assembly is embedded in a cylindrical or rectangular metal can, depending on the shape of a battery case, 5 and pouch-type batteries in which the electrode assembly is embedded in a pouch-type case of an aluminum laminate sheet. The electrode assembly built into the battery case is composed of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and is a power generating element capable of charging and discharging. The electrode assembly is 10 classified into a jelly-roll type in which a positive electrode and a negative electrode which are long sheet-shaped and are coated with active materials are wound with a separator interposed therebetween, and a stack type in which a plurality of positive electrodes and negative electrodes of a predetermined size are sequentially stacked while a separator is interposed therebetween. 15 Further, the electrode included in the secondary battery may be manufactured by coating an electrode slurry including an electrode active material on a current collector, and a metal foil made of aluminum or copper may be used as the current collector. Such a metal foil may go through the rolling process in order to planarize the surface. In this process, rolling oil is used for lubrication. As such, rolling oil elements remain on the 20 metal foil after the rolling process. Likewise, when there is remaining oil on the metal foil, a collapsed or disconnected phenomenon of the electrode slurry may occur during the coating of the electrode slurry. Conventionally, a dyne test was performed to measure the remaining oil level on the 4 metal foil used as the current collector. This is a scheme of a broken degree of a liquid film by coating a reagent like 2-ethoxyethanol on a metal foil. However, in a conventional dyne test scheme, there may be an error in the measured remaining oil level due to the difference in the reagent or contamination of the reagent. Therefore, there 5 is a need for a technology for accurately recognizing the remaining oil level. 【Disclosure】 【Technical Problem】 The present invention is believed to solve at least some of the above problems. For 10 example, an aspect of the present invention provides an electrode slurry coating apparatus and method for accurately recognizing the remaining oil level on the surface of a metal foil used as a current collector. 【Technical Solution】 An apparatus for coating an electrode slurry according to the present invention 15 includes: a coater which coats an electrode slurry on a metal foil; a remaining oil level measuring unit which measures a remaining oil level on a surface of the metal foil before coating the electrode slurry; and a controller which determines whether the remaining oil level is excessive from a measurement value of the remaining oil level, and determines whether to coat the electrode slurry therefrom. 20 In a specific example, the remaining oil level measuring unit may measure at least one of a spread degree and a contact angle of the electrode slurry dropped on the metal foil. 5 More specifically, the remaining oil level measuring unit includes: a syringe which drops an electrode slurry on a metal foil; and a vision camera which photographs shapes of the electrode slurry dropped by the syringe, collects images obtained by photographing the shapes of the electrode slurry, and measures a spread degree or a contact angle of the dropped 5 electrode slurry from the photographed images. At this time, the vision camera senses the metal foil shown on an image and at least one of color, brightness, and chroma of the dropped electrode slurry, and measures a diameter or a contact angle of the electrode slurry dropped by the syringe. In a specific example, the syringe and the vision camera are positioned on the upper 10 side of the coater on the basis of the coating direction, and the syringe is positioned on the upper side of the vision camera on the basis of the coating direction. In a specific example, the controller compares the measured spread degree or contact angle of the electrode slurry with a reference value, and when the spread degree is less than the reference value or the contact angle exceeds the reference value, it may be determined that 15 the remaining oil level is excessive. At this time, when the remaining oil level on the surface of the metal foil is within a predetermined range, the controller may control the coater to discharge the electrode slurry. Further, the electrode slurry coating apparatus according to the present invention may further include a cleaning unit which cleans the metal foil. 20 The controller may transfer the metal foil, which has been determined to have an excessive remaining oil level on the surface, to the cleaning unit to allow the metal foil to be cleaned. As such, the remaining oil level measuring unit may remeasure the remaining oil 6 level for the cleaned metal foil, and the controller may redetermine whether to coat an electrode slurry on the cleaned metal foil. Further, the present invention provides a method of coating an electrode slurry. The method of coating an electrode slurry according to the present invention includes: preparing a metal foil for an e 5 lectrode current collector; measuring a remaining oil level on the metal foil; and determining whether the remaining oil level is excessive from a measurement value of the remaining oil level, and determining whether to coat the electrode slurry therefrom. In a specific example, during the measuring of remaining oil level on the metal foil, 10 the measuring unit measures at least one of a spread degree and a contact angle of the electrode slurry dropped on the metal foil. At this time, the measuring of the remaining oil level on the metal foil may be performed right before coating the electrode slurry. In a specific example, the measuring of the remaining oil level on the metal foil may 15 be performed by dropping an electrode slurry on the metal foil by a syringe, photographing shapes of the electrode slurry dropped by the syringe using a vision camera, collecting images obtained by photographing the shapes of the electrode slurry, and then measuring at least one of a spread degree and a contact angle of the electrode slurry from the images. The vision camera may sense the metal foil and at least one of color, brightness, and 20 chroma of the dropped electrode slurry, and measure a diameter or a contact angle of the electrode slurry dropped by the syringe. Further, when the spread degree is less than the reference value or the contact angle exceeds the reference value, it may be determined that the remaining oil level is excessive. 7 When it is determined that the remaining oil level on the surface of the metal foil is excessive, the method may further include cleaning the metal foil. Further, the electrode slurry coating method according to the present invention may further include remeasuring the remaining oil level for the cleaned metal foil, and redetermining whe 5 ther to coat an electrode slurry on the cleaned metal foil. 【Advantageous Effects】 According to the present invention, it is possible to more accurately recognize the remaining oil level on the metal foil by dropping an electrode slurry on a metal foil before coating the electrode slurry and measuring the spread degree and a contact angle of the 10 dropped electrode slurry. 【Brief Description of the Drawings】 FIG. 1 is a block diagram showing a configuration of an electrode slurry coating apparatus according to the present invention. FIG. 2 shows the shape of an electrode slurry dropped on a metal foil. 15 FIG. 3 is a schematic diagram showing an electrode slurry coating apparatus according to an embodiment of the present invention. FIGS. 4 and 5 each are a schematic diagram showing an electrode slurry coating apparatus according to another embodiment of the present invention. FIG. 6 is a block diagram showing the configuration of an electrode slurry coating 20 apparatus according to further another embodiment of the present invention. FIG. 7 is a flowchart illustrating an order of an electrode slurry coating method according to the present invention. 8 【Detailed Description of the Preferred Embodiments】 Hereinafter, the present invention will be described in detail with reference to the drawings. The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may properly define the 5 concept of the terms in order to best describe its invention. The terms and words should be construed as meaning and concept consistent with the technical idea of the present invention. In this application, it should be understood that terms such as "include" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or a combination thereof described on the specification, and they do not exclude in advance the 10 possibility of the presence or addition of one or more other features or numbers, steps, operations, components, parts or combinations thereof. Also, when a portion such as a layer, a film, an area, a plate, etc. is referred to as being "on" another portion, this includes not only the case where the portion is "directly on" the another portion but also the case where further another portion is interposed therebetween. On the other hand, when a portion such as a 15 layer, a film, an area, a plate, etc. is referred to as being "under" another portion, this includes not only the case where the portion is "directly under" the another portion but also the case where further another portion is interposed therebetween. In addition, to be disposed "on" in the present application may include the case disposed at the bottom as well as the top. Hereinafter, the present invention will be described in detail with reference to the 20 drawings. FIG. 1 is a block diagram showing a configuration of an electrode slurry coating apparatus according to the present invention. 9 Referring to FIG. 1, an electrode slurry coating apparatus 100 according to the present invention includes: a coater 110 which coats an electrode slurry on a metal foil; a remaining oil level measuring unit 120 which measures a remaining oil level on a surface of the metal foil before coating the electrode slurry; and a controller 130 which determines whether the remaining oil level i 5 s excessive from a measurement value of the remaining oil level, and determines whether to coat the electrode slurry therefrom. According to the present invention, it is possible to more accurately recognize the remaining oil level on the metal foil by dropping an electrode slurry on a metal foil before coating the electrode slurry and measuring the spread degree and a contact angle of the 10 dropped electrode slurry. FIG. 3 is a schematic diagram showing an electrode slurry coating apparatus according to an embodiment of the present invention. Referring to FIG. 3 together with FIG. 1, the electrode slurry coating apparatus 100 according to the present invention includes a coater 110 which coats an electrode slurry 20 on 15 a metal foil 10. The coater 110 may be positioned to be spaced apart from the metal foil 10 by a predetermined distance. Various types of coater 110 may be used. Specifically, a slot die type, in which a discharge port, through which an electrode slurry is discharged, is formed in a slit shape along the coating width, may be used. In this case, the coater may include a main body and a tip formed on the lower surface of the main body. A discharge path, on which the 20 supplied electrode slurry may be moved, is formed at the main body, and a discharge port, through which the electrode slurry is discharged, may be formed at the end of the tip. The discharge port may have a slit shape extended in the width direction along the end of the tip, and the thickness may be adjusted according to the thickness of the electrode slurry coated on 10 the metal foil. Further, the electrode slurry 10 is stored in a separate slurry supply tank (not shown), and the electrode slurry 10 may be supplied to the coater 110 through a supply pipe connected to the coater 110. Other details about the coater 110 are known to those of ordinary skill in the art, and thus detailed description thereof will be omitted. Further, th 5 e metal foil 10 may be in a state that has been wound on a separate roll or has gone through a rolling process, and when the coating is started, the metal foil 10 is unwound and is supplied to the coater. The metal foil 10 may be what is used as a positive electrode current collector or a negative electrode current collector. 10 In the present invention, the positive electrode collector generally has a thickness of 3 to 500 micrometers. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel of which the surface has been treated with 15 carbon, nickel, titanium, silver, or the like. The current collector may have fine irregularities on the surface thereof to increase the adhesion of the positive electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible. The negative electrode collector generally has a thickness of 3 to 500 micrometers. 20 The negative electrode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel of which the surface has been treated with carbon, nickel, titanium, silver or the like, aluminum11 cadmium alloy, or the like. In addition, like the positive electrode current collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric. Further, the electrode slurry 20 include 5 s an electrode active material and a solvent and may further include a conductive material and a binder in addition to an electrode active material. In the present invention, the positive electrode active material is a material capable of causing an electrochemical reaction and a lithium transition metal oxide, and contains two or 10 more transition metals. Examples thereof include: layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2) substituted with one or more transition metals; lithium manganese oxide substituted with one or more transition metals; lithium nickel oxide represented by the formula LiNi1-yMyO2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga and contains at least one of the above elements, 0.01 ≦ y ≦ 0.7); lithium 15 nickel cobalt manganese composite oxide represented by the formula Li1+zNibMncCo1- (b+c+d)MdO(2-e)Ae such as Li1+zNi1/3Co1/3Mn1/3O2, Li1+zNi0.4Mn0.4Co0.2O2 etc. (wherein - 0.5≤z≤0.5, 0.1≤b≤0.8, 0.1≤c≤0.8, 0≤d≤0.2, 0≤e≤0.2, b+c+d<1, M = Al, Mg, Cr, Ti, Si or Y, and A = F, P or Cl); olivine-based lithium metal phosphate represented by the formula Li1+xM1-yM'yPO4-zXz (wherein M = transition metal, preferably Fe, Mn, Co or Ni, M'= Al, Mg 20 or Ti, X = F, S or N, and -0.5≤x≤0.5, 0≤y≤0.5, 0≤z≤0.1). Examples of the negative electrode active material include carbon such as nongraphitized carbon and graphite carbon; metal complex oxide such as LixFe2O3(0≤x≤1), 12 LixWO2(0≤x≤1), SnxMe1-xMe’yOz (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, groups 1, 2, and 3 of the periodic table, halogen; 0