Title of the invention: Battery cell including a magnetic material-formed separator and method for evaluating battery cell safety according to internal short circuit using the same technical field [One] This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0116176 on September 20, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification. [2] The present invention relates to a battery cell including a separator in which a magnetic material is formed, and a method for evaluating the safety of the battery cell according to an internal short circuit using the same. background [3] As the price of energy sources increases due to the depletion of fossil fuels and interest in environmental pollution is increasing, the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life. In particular, as technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is rapidly increasing. [4] In general, in a secondary battery, an electrode assembly is assembled with a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The assembled electrode assembly is mounted in a battery case, and an electrolyte is injected to prepare a battery cell. [5] Among secondary batteries, lithium secondary batteries are being used in various fields due to their excellent electrical properties. However, the lithium secondary battery has a problem in that safety is low. For example, a lithium secondary battery may ignite or explode in an abnormal operating state such as overcharge, overdischarge, exposure to high temperature, or electrical short circuit. Specifically, heat and gas are generated as an active material or electrolyte, which is a component of a battery cell, undergoes a decomposition reaction. The generated heat and gas increase the temperature and pressure inside the battery cell. The elevated temperature and pressure further accelerate the decomposition reaction, and eventually cause ignition or explosion. [6] Therefore, it is very important to secure the safety of the battery cell, and one of the methods is to evaluate the safety of the battery cell when an internal short circuit occurs. However, in the prior art, in order to induce an internal short circuit, a method in which a heating element is put inside the battery cell to induce internal heat, a method in which a separator is pre-drilled and a chemical treatment is applied to the portion to melt at a constant temperature, or a method of forming a certain type of metal There are methods such as inserting a material and applying an external force to tear the separator and induce an internal short circuit. However, these methods have limitations in that the separator is deformed or is different from the actual use environment of the battery cell. DETAILED DESCRIPTION OF THE INVENTION technical challenge [7] The present invention was devised to solve the above problems, a battery cell capable of testing safety due to an internal short circuit without physically deforming the structure of the battery cell, and a battery cell safety evaluation method according to an internal short circuit using the same aims to provide means of solving the problem [8] In order to achieve the above object, the battery cell according to the present invention has a structure in which an electrode assembly including a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode is accommodated in a battery case, [9] The separation membrane may include a perforated line formed in all or part of the separation membrane; and a magnetic material formed in an area adjacent to the perforation line but not overlapping, and continuously or discontinuously arranged at positions spaced apart from each other by a predetermined interval along the perforation line. [10] In one example, the perforated line forms a two-dimensional closed shape on the surface of the separator. In another example, the perforation line has a structure in which a plurality of through-type slits or bead-type non-through grooves are discontinuously arranged. [11] In one example, the magnetic material is in a powder form, and is fully or partially impregnated in the separation membrane. In another example, the magnetic material is in the form of a bar, and a separator is attached to one or both surfaces. [12] In a specific example, the magnetic material has a structure including a magnetic core and an insulating polymer shell surrounding the core. For example, the core is one or more alloys selected from the group consisting of iron (Fe), nickel (Ni), cobalt (Co), gadolinium (Gd), terbium (Tb), and dysprosium (Dy). In addition, the insulating polymer shell is formed of a polymer film. [13] In one example, the battery cell according to the present invention is a lithium secondary battery. [14] The present invention also provides a method for evaluating the safety of a battery cell according to an internal short circuit using the battery cell described above. [15] In one example, the evaluation method includes inducing a short circuit inside the battery cell. In a specific example, the battery cell has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is accommodated in a battery case. The separation membrane may include a perforated line formed in all or part of the separation membrane; and a magnetic material formed in an area adjacent to the perforation line but not overlapping, and continuously or discontinuously arranged at positions spaced apart from each other by a predetermined interval along the perforation line. In addition, in the step of inducing the internal short circuit of the battery cell, in a state in which the magnet is adjacent to or in contact with the outer peripheral surface of the battery cell, the magnet is rotated and the perforated line of the separator is partially or completely broken in response to the rotational movement of the magnet. is carried out [16] In one example, the perforated line forms a two-dimensional closed shape on the surface of the separator. [17] In a specific example, the step of inducing the internal short circuit of the battery cell is performed during a charge/discharge cycle for the battery cell. Effects of the Invention [18] The battery cell according to the present invention can induce an internal short circuit without physically deforming the structure of the battery cell, and can be effectively applied to a method for evaluating the safety of a battery cell according to an internal short circuit. Brief description of the drawing [19] 1 is an exploded view schematically showing the structure of a battery cell according to an embodiment of the present invention. [20] 2 to 5 are front views schematically showing a separation membrane provided with a perforated line and a magnetic material according to an embodiment of the present invention, respectively. [21] 6 is a schematic diagram illustrating a process of inducing an internal short circuit using a magnet in a battery cell according to an embodiment of the present invention. Best mode for carrying out the invention [22] As used throughout the specification of the present invention, terms such as "comprises" or "have" are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, but one It should be understood that it does not preclude the possibility of the presence or addition of or more other features or numbers, steps, operations, components, parts, or combinations thereof. [23] Also, when a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where it is "on" another part, but also the case where there is another part in between. Conversely, when a part of a layer, film, region, plate, etc. is said to be “under” another part, it includes not only cases where it is “directly under” another part, but also cases where another part is in between. In addition, in the specification of the present invention, "on" may include the case of being disposed not only on the upper part but also on the lower part. [24] [25] Hereinafter, the present invention will be described in detail. [26] The present invention relates to a battery cell in which a perforated line and a magnetic body are formed in a separator. Specifically, the battery cell according to the present invention has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is accommodated in a battery case. In addition, the separation membrane may include a perforated line formed in all or part of the separation membrane; and a magnetic material formed in an area adjacent to the perforation line but not overlapping, and continuously or discontinuously arranged at positions spaced apart from each other by a predetermined interval along the perforation line. [27] The battery cell according to the present invention can be effectively applied to the internal short circuit test. The magnetic material is bonded to the separation membrane, and when the magnet is moved from the outside, the magnetic material also moves in response to the movement of the magnet. Stress is also applied to the separation membrane according to the movement direction of the magnetic material. For example, when the magnet is moved or rotated in a state in which the magnet is in contact with or adjacent to the outside of the battery cell, the magnetic material formed on the separator moves in response to the movement of the magnet. When the magnetic material moves, the perforated line adjacent to the magnetic material is broken, thereby inducing an internal short circuit of the battery cell. [28] In addition, the magnetic body according to the present invention is formed in a region adjacent to the perforation line but does not overlap, and is continuously or discontinuously arranged at positions spaced apart from each other by a predetermined interval along the perforation line. For example, when a perforation line including a linear section is formed in the separator, a first point of the perforation line and a second point spaced apart from the first point by a predetermined interval are set. A magnetic body is respectively formed in a region adjacent to the first and second points of the perforated line. In this case, the magnetic material may be linearly connected or may have a structure formed separately near the first and second points. In the present invention, when the magnet rotates outside the battery cell, the magnetic material located near the first point of the perforation line and the magnetic material located near the second point of the perforation line move in different directions. Through this, when the magnetic material formed spaced apart at two points moves in different directions, stress is also applied to the perforated lines formed in the separator in different directions. Stresses applied in different directions partially break the perforation line and induce an internal short circuit of the battery cell. [29] In one example, the perforation line forms a two-dimensional closed shape on the surface of the separator. The present invention induces more clearly the internal short circuit of the battery cell according to the rotation of the external magnet by forming a perforated line of a closed shape. In a specific example, the two-dimensional closed shape formed by the perforation line may be a shape in which a diameter in one direction and a diameter in a direction perpendicular to the one direction are different from each other. This is to make it easier to break the perforated line when the magnet is rotated outside the battery cell. For example, the two-dimensional closed shape formed by the perforation line is an ellipse, a rectangle, or a triangular shape in which either side has different lengths. [30] In another example, the perforation line has a structure in which a plurality of through-type slits or bead-type non-through grooves are discontinuously arranged. Specifically, the perforated line has a structure in which a plurality of through-type slits or bead-type non-penetrating grooves are spaced apart at regular intervals and arranged. Discontinuously arranging the perforated line prevents the perforated portion of the separator from being broken even by a small impact. [31] In the present invention, the magnetic material has a structure coupled to the separation membrane in various forms. For example, the magnetic material is in a powder form, and is fully or partially impregnated in the separation membrane. For another example, the magnetic material is in the form of a bar, and a separator is attached to one or both surfaces. When the magnetic material is in the form of a powder, the magnetic material may be applied to one surface of the separator in a state of being mixed with a binder near the perforation line. In addition, when the magnetic material is in the form of a bar, the magnetic material may be bonded to the separator with a binder interposed therebetween. [32] In one example, the magnetic material has a structure including a magnetic core and an insulating polymer shell surrounding the core. For example, the core is one or more alloys selected from the group consisting of iron (Fe), nickel (Ni), cobalt (Co), gadolinium (Gd), terbium (Tb), and dysprosium (Dy). In addition, the insulating polymer shell has a structure formed of a polymer film. By forming the insulating polymer shell on the magnetic core, there is an effect of providing electrical insulation without reducing the magnetism of the magnetic material. [33] [34] In addition, the present invention provides a method for evaluating the safety of a battery cell according to an internal short circuit using the battery cell described above. [35] In one example, the evaluation method includes inducing a short circuit inside the battery cell. The battery cell has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is accommodated in a battery case, and the separator includes a perforated line formed in all or part of the separator; and a magnetic material formed in an area adjacent to the perforation line but not overlapping, and continuously or discontinuously arranged at positions spaced apart from each other by a predetermined interval along the perforation line. Specifically, the step of inducing the internal short circuit of the battery cell includes rotating the magnet in a state in which the magnet is adjacent to or in contact with the outer peripheral surface of the battery cell, and the perforation line of the separator is partially or completely broken in response to the rotational movement of the magnet. and is carried out [36] In one example, the perforated line forms a two-dimensional closed shape on the surface of the separator. The shape formed by the perforation line is the same as described above. [37] In a specific example, the step of inducing the internal short circuit of the battery cell is performed during a charge/discharge cycle for the battery cell. For example, the charging/discharging cycle test may be performed on the battery cell, but the internal short circuit test of the battery cell may be performed assuming that the battery cell internal short circuit occurs during the charging/discharging cycle. [38] In the present invention, the 'internal short circuit test' is a test for evaluating the resistance to internal short circuits among the safety tests of a battery cell, and is a test that simulates a case in which a positive electrode and a negative electrode are short-circuited inside a battery cell. In the internal short circuit test, an internal short circuit is generated for a fully charged battery cell and the behavior of the battery cell is evaluated. In general, when an internal short circuit occurs in a cell, the voltage decreases as the battery cell is discharged, and when the voltage decreases below a certain value, the presence or absence of rupture of the battery cell, a change in voltage or temperature, etc. are evaluated. [39] In one example, the battery cell according to the present invention includes 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 electrolyte. [40] The positive electrode has a structure in which a positive electrode active material layer is laminated on one or both surfaces of a positive electrode current collector. In one example, the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder polymer, and if necessary, may further include a positive electrode additive commonly used in the art. [41] 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. [42] For example, the lithium-containing transition metal oxide is Li x CoO 2 (0.5