Title of Invention: Method for manufacturing a secondary battery with improved resistance technical field [One] This application was filed on 2020.05.06. Claims the benefit of priority based on Korean Patent Application No. 10-2020-0054039, and all contents disclosed in the document of the Korean patent application are incorporated as a part of this specification. [2] The present invention relates to a method for manufacturing a secondary battery having improved resistance by using an electrode slurry containing succinonitrile when manufacturing a lithium secondary battery. background [3] With the increase in technology development and demand for mobile devices, the demand for secondary batteries is also rapidly increasing. Among them, a lithium secondary battery is widely used as an energy source for various electronic products as well as various mobile devices in that it has high energy density and operating voltage and excellent preservation and lifespan characteristics. [4] The secondary battery is classified into a coin-type battery, a cylindrical battery, a prismatic battery, and a pouch-type battery according to the shape of the battery case. In a secondary battery, an electrode assembly mounted inside a battery case is a charging/discharging power generating element having a stacked structure of an electrode and a separator. [5] The electrode assembly is a sheet-type electrode assembly coated with an active material, with a separator interposed between a positive electrode and a negative electrode, and is of a jelly roll type, in which a plurality of positive and negative electrodes are sequentially stacked with a separator interposed therebetween, a stack type, and a stack type. The unit cells can be roughly classified into a stack/folding type in which the unit cells are wound with a long-length separation film. [6] Among these, in the case of a battery having a stacked or stacked/folding structure, a lamination process for bonding an electrode and a separator is essential when manufacturing the battery. The lamination process is a process of attaching an electrode and a separator, and when the electrode and the separator are separated, the yield and processability are very poor during battery assembly. In addition, it is impossible to assemble a stacked or stacked/folded battery without a lamination process. [7] Conventionally, a binder layer is formed on the surface of the separator for a lamination process, and then the electrode and the separator are adhered under conditions of high temperature and high pressure. However, in this process, the separator is damaged, and the binder used as an adhesive remains molten and acts as a resistance in the battery, thereby deteriorating the battery performance. [8] In particular, in the case of the negative electrode, since the component of the binder used in the electrode is different from that of the separator binder, it does not adhere well even if the lamination process is fixed, so a greater pressure is required during lamination. At this time, the positive electrode has a problem in that the resistance increases due to a stronger pressure than necessary. [9] Specifically, in the lamination process, the same temperature and pressure are applied to the anode and the cathode since the electrodes are stacked in the order of anode/separator/cathode and then temperature and pressure are applied to the stacked electrode (lamination cell). In the case of the positive electrode, the binder material in the electrode is PVDF, which is the same as the binder used for the separator, so adhesion is sufficiently secured even at low temperature/pressure. there is. Therefore, it is essential to apply high temperature and high pressure to secure the adhesive force of the negative electrode. Due to this, as the lamination process proceeds excessively on the positive electrode, a lot of the binder at the interface between the positive electrode and the separator is melted and acts as a resistance on the interface. In addition, the resistance increases as the pores of the separator positioned between the anode and the cathode decrease due to excessive pressure. [10] Therefore, there is a need to develop a secondary battery electrode manufacturing method capable of preventing damage to the separator and increase in resistance of the positive electrode due to excessive high temperature and high pressure during lamination. DETAILED DESCRIPTION OF THE INVENTION technical challenge [11] The present invention has been devised to solve the above problems, and improves the adhesion between the negative electrode and the separator during the lamination process, minimizes damage to the separator and the positive electrode due to high pressure, and provides a method for manufacturing a secondary battery with improved resistance in the battery. it's about means of solving the problem [12] The method of manufacturing a secondary battery with improved resistance according to the present invention, [13] Preparing an electrode slurry containing succinonitrile (S1), applying and drying the electrode slurry on a current collector to prepare an electrode having an electrode mixture layer (S2), alternately stacking the electrode and a separator Manufacturing the electrode assembly (S3), a lamination step of heating and pressurizing the electrode assembly (S4), and accommodating the laminated electrode assembly in a battery case and injecting an electrolyte solution (S5). [14] In one example, the succinonitrile is included in an amount of 5 to 40% by weight based on the total weight of the electrode mixture layer. [15] In another example, preparing the electrode slurry (S1) includes uniformly dispersing succinonitrile in the electrode slurry. [16] In one example, the manufacturing of the electrode (S2) includes applying the electrode slurry to one or both sides of the current collector and drying the electrode to which the electrode slurry is applied. [17] In a specific example, in the step of drying the electrode slurry, the distribution of succinonitrile in the slurry is rearranged so that the content of succinonitrile in the surface layer of the electrode far from the current collector is greater than the content of succinonitrile in the inner layer of the electrode close to the current collector characterized in that [18] In addition, in the step of drying the electrode slurry, the succinonitrile is characterized in that it is located on the upper end or surface of the electrode. The 'top end of the electrode' refers to an end region of the electrode located in a direction far from the current collector, and the 'surface' refers to one surface that will come into contact with the separator, not the current collector. [19] In another example, manufacturing the electrode (S2) further includes cooling the electrode coated with the electrode slurry to room temperature to solidify the liquid succinonitrile. [20] In one example, the lamination step (S4) of heating and pressing the electrode assembly is a step of heating and pressing the electrode assembly to a temperature equal to or higher than the melting point of succinonitrile. [21] Specifically, the heating temperature of the electrode assembly is 57° C. or higher, and the pressurization of the electrode assembly is performed at a pressure of 30 kgf/cm or less. [22] At this time, the succinonitrile is characterized in that it acts as a binder to adhere between the electrode and the separator. [23] In another example, it is characterized in that the succinonitrile in the electrode is eluted into the electrolyte in the step (S5) of accommodating the laminated electrode assembly in a battery case and injecting the electrolyte. Effects of the Invention [24] Since the secondary battery manufacturing method according to the present invention does not require a high-pressure process as in the prior art during the lamination process, damage to the separator and the electrode can be minimized and process costs can be reduced. [25] In addition, since succinonitrile located on the surface of the electrode acts as an adhesive between the electrode and the separator, there is an effect of improving the adhesion between the electrode and the separator. [26] In addition, since succinonitrile in the electrode is dissolved by the electrolyte, there is no resistor present at the electrode and the interface between the electrode and the separator, so that as a result, the resistance of the battery can be lowered. Brief description of the drawing [27] 1 is a schematic diagram showing a conventional secondary battery manufacturing method. [28] 2 is a flowchart illustrating a method of manufacturing a secondary battery according to the present invention. [29] 3 is a schematic diagram showing a method of manufacturing a secondary battery according to an embodiment of the present invention. Best mode for carrying out the invention [30] Hereinafter, the present invention will be described in detail. Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention based on the principle that it can be defined as [31] [32] 1 is a schematic diagram showing a conventional secondary battery manufacturing method. [33] Referring to FIG. 1 , in the conventional battery constituting the secondary battery, the binder coating layer 20 was provided on both surfaces of the separator 100 in the battery. The first electrode 200 and the second electrode 300 were alternately disposed on each surface of the binder coating layer 20 to prepare an electrode assembly. Thereafter, a lamination process was performed under conditions of high temperature/high pressure on both sides of the stacked electrode assembly as shown in FIG. 1A. Thereafter, as shown in FIG. 1B , the electrode assembly was housed in a battery case, and electrolyte was injected to prepare a secondary battery 1 . [34] In the conventional method as described above, the binder coating layer 20 was used to increase the adhesive force between the separator 100 and the electrodes 200 and 300, but in the manufacture of the secondary battery 1, the binder coating layer 20 is still configured. Because it remains as an internal resistance, there is a problem that the performance of the battery is inferior. [35] On the other hand, as the negative electrode binder, Styrene-Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) are mixed and used, and as the binder of the binder layer on the positive electrode binder and the separator, polyvinylidene fluoride is used. Polyvinylidene fluoride (PVDF) is being used. [36] In a typical negative electrode, the binder in the negative electrode has a different composition from the binder of the binder coating layer 20 on the separator 100, and thus a stronger pressure is required as the adhesive strength is somewhat decreased during the lamination process. [37] Due to the high-pressure lamination process for improving adhesion between the negative electrode and the separator, a phenomenon in which the resistance continued to increase occurred in the case of the positive electrode having the same or similar binder component as the separator. [38] [39] The present invention relates to a method of manufacturing a secondary battery having improved resistance in order to solve the above problems. [40] 2, the secondary battery manufacturing method according to the present invention, [41] Preparing an electrode slurry containing succinonitrile (S1); preparing an electrode having an electrode mixture layer formed thereon by applying and drying the electrode slurry on a current collector (S2); manufacturing an electrode assembly by alternately stacking the electrodes and the separator (S3); [42] a lamination step of heating and pressing the electrode assembly (S4); and accommodating the laminated electrode assembly in a battery case and injecting an electrolyte (S5). [43] [44] First, succinonitrile (Succinonitrile, SN) will be described. Succinonitrile is a material mainly used as an electrolyte additive for lithium secondary batteries. It does not interfere with the formation of the SEI (Solid Electrolyte Interface) film of the negative electrode, and does not change the cycle life and capacity of the battery. [45] In addition, succinonitrile exists in the form of a very viscous wax at room temperature, and has a melting point of 57° C. Therefore, when succinonitrile is cooled to room temperature after liquefaction, it is converted into a wax form and can serve as an adhesive between the electrode and the separator. [46] And, since succinonitrile has high solubility in water, succinonitrile, which is solid at room temperature, may be dissolved in water and exist in a liquid state. [47] And, since the succinonitrile is soluble in a non-aqueous solvent that can be used as an electrolyte, for example, a solvent of carbonates, etc., the succinonitrile present in the form of an adhesive is dissolved during injection of the electrolyte and dispersed into the electrolyte, and an additive to the electrolyte will act as [48] [49] Hereinafter, the secondary battery manufacturing method of the present invention will be described in detail for each step. [50] First, in the step (S1) of preparing the electrode slurry, a step of uniformly dispersing succinonitrile in the electrode slurry is performed. [51] Accordingly, the electrode slurry exhibits a structure in which an electrode active material, a binder, a conductive material, and succinonitrile are uniformly dispersed in a solvent. Specifically, in the electrode slurry according to the present invention, the solvent may be an aqueous solvent containing water or a non-aqueous solvent such as NMP or carbonates. The electrode slurry according to the present invention may be prepared by mixing succinonitrile, a binder, and a conductive material in a solvent to prepare a pre-dispersed slurry, and adding an electrode active material to the pre-dispersed slurry. At this time, the succinonitrile is dissolved in water and uniformly dispersed in the liquid phase in the slurry. The manufacturing sequence or method of the pre-dispersion slurry is not limited thereto. [52] [53] Second, the electrode slurry in which the succinonitrile prepared in the step (S1) of preparing the electrode slurry is uniformly dispersed is applied to the current collector and dried to prepare an electrode having an electrode mixture layer (S2). [54] Specifically, the step (S2) of manufacturing the electrode may include applying the electrode slurry to one or both sides of the current collector and drying the electrode to which the electrode slurry is applied. The step of drying the electrode may be sequentially performed after the coating step, and the electrode drying may be performed simultaneously with the application. [55] In the electrode drying process, the solvent is removed from the electrode slurry coated on the current collector to form an electrode mixture layer. At this time, the content of succinonitrile may be 0.1 to 5% by weight, preferably 1.5 to 2% by weight based on the total weight of the electrode mixture. In this case, the weight of the electrode mixture means the weight of the remaining portion from which the solvent is removed through drying in the electrode slurry. When the content of succinonitrile is within the above range, the electrode may be stably adhered to the separator, and the resistance of the battery may be maintained low. When the content of succinonitrile is less than 0.1 wt%, the adhesion between the electrode and the separator may decrease, and if the content of succinonitrile exceeds 5 wt%, the resistance of the battery may increase. [56] Meanwhile, in the step of applying and drying the electrode slurry on the current collector, the content and arrangement of succinonitrile uniformly dispersed in the slurry before and after drying are changed. The drying temperature is different for each section, but it is preferable that the maximum is 110°C. [57] In a state before the slurry is applied to the electrode current collector and dried, an electrode slurry layer is formed on the current collector. In this case, since succinonitrile is dissolved in a solvent such as water in the electrode slurry layer, it is evenly dispersed in the entire area of ​​the slurry layer. [58] However, in the subsequent drying process, as the solvent in the electrode slurry is vaporized, the distribution of succinonitrile in the electrode mixture layer is somewhat different from the distribution in the electrode slurry. [59] In general, the density of succinonitrile is 0.985 g/cc, and as the solvent in the electrode slurry layer is vaporized due to the low density, the succinonitrile moves according to the vaporization direction of the solvent. That is, succinonitrile, which was evenly dispersed in the electrode slurry layer applied on the current collector, moves to the electrode slurry layer region far from the current collector through vaporization of the solvent during the drying process. [60] Accordingly, in the step of drying the electrode slurry applied on the current collector, the succinonitrile content in the electrode surface layer far from the current collector is greater than the succinonitrile content in the electrode inner layer close to the current collector. The distribution of is rearranged. Specifically, the content of succinonitrile in the electrode mixture layer may be in a form in which a concentration gradient is formed from the electrode inner layer near the current collector toward the electrode surface layer. [61] In addition, the succinonitrile is located in a region far from the current collector, that is, at the upper end or on the surface. Here, the 'top end of the electrode' means an end region of the electrode located in a direction far from the current collector, and the 'surface' means a surface that will come into contact with the separator, not the current collector. In addition, when the succinonitrile is located on the upper end or the surface of the current collector, it means that 90% or more of the succinonitrile included in the electrode mixture layer is located on the upper end or the surface of the electrode mixture layer. [62] Meanwhile, the manufacturing of the electrode of the present invention (S2) may further include the step of solidifying the liquid succinonitrile by cooling the electrode coated with the electrode slurry to room temperature. Specifically, succinonitrile present in the electrode mixture layer on the current collector after the drying process is in a liquid state due to heat applied to the electrode mixture layer during the drying process. After drying, the liquid succinonitrile inside the electrode mixture layer is finally solidified through a process of cooling the electrode to room temperature. As mentioned in the description of the succinonitrile, succinonitrile is converted into a wax form when cooled to room temperature after liquefaction, and may serve as a binder when heat is applied during a subsequent lamination process. [63] After the electrode manufacturing step (S2) is performed, the electrode assembly is manufactured by alternately stacking the electrode and the separator (S3). In the present invention, the electrode may be an anode and/or a cathode. The manufacturing of the electrode assembly may be performed by a conventional and well-known method, and in the present invention, it may be said that it is preferable to manufacture a stack-folding type or a stack type electrode assembly. As will be described later, succinonitrile acts as a binder between the electrode and the separator. [64] After the step (S3) of manufacturing the electrode assembly, a lamination step (S4) of heating and pressing the previously prepared electrode assembly is performed. [65] Specifically, the lamination step of the present invention is a step of heating and pressurizing the electrode assembly to a temperature equal to or higher than the melting point of succinonitrile, specifically, the heating temperature is 57 ° C. or higher, preferably 60 to 70 ° C., and the pressure range is It is characterized in that it is 30 kgf/cm or less. [66] In the conventional lamination process, a pressure of 10 to 50 kgf/cm is applied at a temperature of 70 to 100°C. Through this, the electrode and the separator are strongly attached, and in general, the thickness of the separator fabric is reduced by about 10% through the lamination process as described above. [67] However, in the lamination step of the present invention, the electrode assembly is performed at a temperature of 57°C or higher, preferably 60 to 70°C. As the electrode assembly is laminated at the above temperature, the succinonitrile present in the solid state is phase-converted to the liquid phase after the step (S2) of manufacturing the electrode. Accordingly, the succinonitrile converted to the liquid phase is uniformly spread between the interface between the electrode and the separator according to the pressure applied to the electrode assembly in the lamination step. In addition, since lamination is performed at a relatively low temperature unlike the conventional lamination process through the above temperature conditions, it is possible to not only reduce the process cost, but also prevent damage such as shrinkage of the separator due to high temperature. [68] In addition, succinonitrile in the electrode is characterized in that it acts as a binder between the electrode and the separator. Specifically, the succinonitrile is uniformly spread between the interface between the electrode and the separator due to heating and pressure in the lamination step. Since the liquid succinonitrile exhibits a sticky property, the adhesion between the electrode and the separator can be improved. there is. Subsequently, after the lamination process, succinonitrile is solidified in the form of wax at room temperature and acts as a binder for bonding the electrode and the separator. [69] In addition, the lamination step is performed by pressing the electrode assembly at a pressure of 30 kgf/cm or less, preferably 1 to 10 kgf/cm, more preferably 1 to 5 kgf/cm. According to the present invention, since the electrode and the separator are adhered using succinonitrile located on the upper end or the surface of the electrode mixture layer, a strong level of pressure is not required as in the prior art. Through this, not only can the process cost be reduced, but also physical damage to the separation membrane due to high pressure can be prevented. [70] In the lamination process, the transferred electrode assembly is passed between a pair of rollers and pressed to adhere to each other. Specifically, in the lamination process, a heater is connected to a pair of pressure rollers, and heat is applied to the electrode assembly and pressurized to adhere to each other. [71] In the present invention, lamination by a pressure roller is performed, but it is also possible to apply press lamination. In this case, it is preferable to use a pressure of 1/10 to 1/5 of the pressure conditions of general press lamination. [72] As such, the succinonitrile positioned on the electrode surface may improve the adhesion between the electrode and the separator. This can solve the problem of damage to the separator that may be caused by the conventional lamination process of high temperature and high pressure and the problem of increasing the anode resistance of the battery. And, it is possible to reduce the binder content in the binder layer present on the surface of the separator used in the electrode assembly. In addition, since the lamination process of high temperature and high pressure is not required, the effect of reducing process cost can be expected. [73] [74] Finally, a step (S5) of accommodating the laminated electrode assembly in a battery case and injecting an electrolyte is performed. [75] Specifically, in the step (S5) of accommodating the electrode assembly in the battery case and injecting the electrolyte, succinonitrile in the electrode is eluted into the electrolyte as the electrolyte is injected, and is removed from the interface between the electrode and the separator. Since the succinonitrile eluted into the electrolyte thereafter acts as an additive of the electrolyte, it is possible to prevent the succinonitrile from acting as a resistance component in the electrode mixture layer as a resistance. [76] [77] [78] 3 is a schematic diagram showing a method of manufacturing a secondary battery according to an embodiment of the present invention. 3 shows only the negative electrode and the separator portion in the electrode assembly, and the positive electrode portion is omitted. In addition, it goes without saying that the manufacturing method according to the present invention can be applied to the positive electrode. [79] Referring to FIG. 3 , (a) shows that the negative electrode slurry layer 220 in which succinonitrile 10 is uniformly dispersed is applied on the negative electrode current collector 210 . Then, in (b), as it is dried at a high temperature, the solvent vaporizes in the slurry layer to become a negative electrode mixture layer, and at the same time, the succinonitrile 10 is disposed on the upper end or surface of the negative electrode mixture layer. In (c), the separator 100 is laminated on the dried anode 200, and in (d), succinonitrile acts as a binder for adhering the anode and the separator through a lamination process. Then, in (e), the electrode assembly including the negative electrode and the separator is accommodated in the battery case and the electrolyte is injected, so that succinonitrile is dissolved in the electrolyte solvent and does not exist in the electrode assembly. [80] [81] In summary, since the succinonitrile of the present invention acts as an adhesion means between the electrode and the separator, there is an advantage that adhesion is easy even in the lamination process of lower temperature and pressure compared to the prior art. In addition, since succinonitrile is dissolved in the electrolyte injection process, which is the rear end of the battery manufacturing process, and no longer remains in the interface, the resistance of the battery can be minimized, thereby exhibiting the effect of preventing inferior performance of the battery. [82] [83] Hereinafter, the secondary battery used in the present invention will be described. [84] The electrode used in the present invention is an electrode for a lithium secondary battery. The lithium secondary battery may include, for example, an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; a non-aqueous electrolyte for impregnating the electrode assembly; and a battery case containing the electrode assembly and the non-aqueous electrolyte. [85] The positive electrode has a structure in which a positive electrode mixture layer is laminated on one or both surfaces of a positive electrode current collector. The positive active material may be each independently a lithium-containing oxide, and may be the same or different. As the lithium-containing oxide, a lithium-containing transition metal oxide may be used. In one example, the positive electrode mixture layer includes a conductive material and a binder polymer in addition to the positive electrode active material, and, if necessary, may further include a positive electrode additive commonly used in the art. [86] The positive active material may be a lithium-containing oxide, and may be the same or different. As the lithium-containing oxide, a lithium-containing transition metal oxide may be used. [87] For example, the lithium-containing transition metal oxide is Li x CoO 2 (0.5