Electrode assembly including surface-treated separator, secondary battery including same, and method for manufacturing electrode assembly

Abstract

The present invention relates to an electrode assembly, a secondary battery including the same, and a method for manufacturing the electrode assembly, and by performing a corona surface treatment on a portion of a separator surface located inside a unit cell, it is possible to increase the interfacial adhesion between the separator and the electrode without inhibiting electrolyte impregnation.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0166693 dated December 2, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an electrode assembly including a surface-treated separator, a secondary battery including the same, and a method for manufacturing the electrode assembly. [Background technology]

[0003] In recent years, the depletion of fossil fuels has led to rising energy prices and growing concern over environmental pollution, making the demand for environmentally friendly alternative energy sources an essential factor for future life. As a result, research into various power generation technologies, such as atomic, solar, wind, and tidal power, has been ongoing, and there has also been great interest in power storage devices to use the energy produced in this way more efficiently.

[0004] In particular, as technological development and demand for mobile devices increases, the demand for batteries as an energy source is rapidly increasing, and research is being conducted on batteries that can meet various demands.

[0005] Typically, in terms of battery shape, there is a high demand for square-type secondary batteries and pouch-type secondary batteries that are thin and can be applied to products such as mobile phones, and in terms of materials, there is a high demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries that have advantages such as high energy density, discharge voltage, and output stability.

[0006] In general, a secondary battery has an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between them, built into a battery case, and is sealed so that a positive electrode lead and a negative electrode lead extending from the positive electrode tab and the negative electrode tab, respectively, are exposed.

[0007] Meanwhile, the electrode assembly has a structure in which a positive electrode, a separator, and a negative electrode are sequentially stacked. Fig. 1 is a schematic diagram showing a folding phenomenon of a separator of an electrode assembly. Referring to Fig. 1, in the electrode assembly 1, a folding phenomenon of the separator 50 occurs due to various flow processes occurring during the manufacturing process of a secondary battery. In particular, such a folding phenomenon is frequently induced at an edge region A of the separator 50.

[0008] Fig. 2 is a schematic diagram showing the front of a conventional electrode assembly. Referring to Fig. 2, the folded electrode assembly 1 has a structure in which a positive electrode 30, a negative electrode 40, and a plurality of unit cells, each having a separator 50 interposed between the positive electrode 30 and the negative electrode 40, are wound up with a sheet-shaped separator sheet 60. Here, the unit cells include an A-type bicell 10 in which the positive electrode 30 / separator 50 / negative electrode 40 / separator 50 / positive electrode 30 are stacked in this order, and a C-type bicell 20 in which the negative electrode 40 / separator 50 / positive electrode 30 / separator 50 / negative electrode 40 are stacked in this order.

[0009] The conventional electrode assembly 1 has a problem that a separate adhesive layer is not formed on the separator 50, and therefore the adhesive strength between the electrode and the separator 50 is low. In order to solve this problem, excessive dry adhesive strength may be realized by a process such as lamination or heat press for a unit cell in which the electrode and the separator 50 are stacked. However, in this case, although the adhesive strength between the electrode and the separator 50 of the unit cell can be significantly increased, the electrolyte impregnation and gas discharge properties are significantly reduced because the process such as lamination or heat press is performed on the entire surface of the electrode and the separator 50, and this may cause a cause of deterioration in the performance of the secondary battery, such as lithium plating.

[0010] Therefore, there is a need to develop a method for improving the adhesive strength between the separator and the electrode interface, improving electrolyte impregnation, and preventing the separator from breaking. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made to solve the above problems, and aims to provide an electrode assembly capable of preventing a separator from breaking, a secondary battery including the same, and a method for manufacturing the electrode assembly. [Means for solving the problem]

[0012] The present invention provides an electrode assembly applicable to a secondary battery. In one embodiment, the electrode assembly according to the present invention has a structure in which n (n is an integer of 2 or more) unit cells, each including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, are stacked, and a separator sheet is disposed between the unit cells. The n is, for example, an integer in the range of 2 to 20. The separator interposed in the unit cell includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, and the separator sheet is structured not to be corona surface-treated.

[0013] The present invention also provides a secondary battery including the above-mentioned electrode assembly. For example, the secondary battery is a pouch-type secondary battery.

[0014] The present invention also provides a method for manufacturing an electrode assembly for a secondary battery. In one embodiment, the method for manufacturing an electrode assembly according to the present invention includes the steps of performing a corona discharge on one or both sides of a separator to perform a surface treatment, forming a unit cell including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and manufacturing an electrode assembly by positioning n (n is an integer of 2 or more) unit cells on a sheet-like separator sheet and rolling up the separator sheet in one direction. Here, the separator interposed in the unit cell includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated. Also, the separator sheet is structured not to be corona surface-treated. Effect of the Invention

[0015] The present invention increases the interfacial adhesion between the separator and the electrodes forming the electrode assembly without decreasing the impregnation with the electrolyte. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing a separator folding phenomenon that occurs in a conventional electrode assembly; [Diagram 2] FIG. 1 is a schematic diagram showing a laminated structure of a conventional electrode assembly. [Diagram 3] 2 is a schematic diagram illustrating a layered structure of an electrode assembly according to an embodiment; FIG. [Figure 4] 5A to 5C are schematic diagrams showing a manufacturing process of the electrode assembly. [Diagram 5] FIG. 2 is a schematic diagram showing an electrode stacking structure according to an embodiment. [Figure 6] 1 is a schematic diagram illustrating an adhesive pattern of a separator located inside a unit cell according to an embodiment; [Figure 7] 2 is a schematic diagram illustrating a layered structure of an electrode assembly according to an embodiment; FIG. [Figure 8] FIG. 2 is a schematic diagram showing an adhesive pattern of a separation membrane according to an embodiment. [Figure 9] FIG. 2 is a schematic diagram showing a process of subjecting a separation membrane surface to a corona treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention provides an electrode assembly applicable to a secondary battery. In one embodiment, the electrode assembly according to the present invention has a structure in which n (n is an integer of 2 or more) unit cells, each including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, are stacked, and a separator sheet is disposed between the unit cells. The n is, for example, an integer in the range of 2 to 20. The separator interposed in the unit cell includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, and the separator sheet is structured not to be corona surface-treated.

[0018] In one embodiment, the separator sheet is wound around the stacked unit cells while being inserted between the stacked unit cells, thereby forming a stack-and-fold structure of the electrode assembly according to the present invention.

[0019] In one example, in the electrode assembly according to the present invention, the unit cell includes an A-type bicell and a C-type bicell, the separator of the unit cell includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, and a plurality of A-type bicells and C-type bicells are alternately arranged above and below with a separator sheet between them.

[0020] In one embodiment, the unit cell includes a positive electrode tab extending in one direction of the positive electrode and a negative electrode tab extending in one direction of the negative electrode. Here, the direction in which the positive electrode tab is formed may be the same as or opposite to the direction in which the negative electrode tab is formed. In addition, the separator includes a first adhesive portion that is corona surface-treated in an edge region where the positive electrode tab is located, and a second adhesive portion that is corona surface-treated in an edge region where the negative electrode tab is located.

[0021] In one embodiment, the surface of the separation membrane has a structure in which bonded portions and non-bonded portions are arranged alternately.

[0022] In another embodiment, the adhesive portion is formed on one or both sides of the separation membrane.

[0023] In a specific example, the area where the adhesive parts are formed is in the range of 10% to 70% of the area of ​​the separation membrane.

[0024] In another specific example, the bonds form a pattern, the pattern being one or more of a stripe, a grid, a dot, and a polygon.

[0025] The present invention also provides a secondary battery including the above-mentioned electrode assembly. For example, the secondary battery is a pouch-type secondary battery.

[0026] The present invention also provides a method for manufacturing an electrode assembly for a secondary battery. In one embodiment, the method for manufacturing an electrode assembly according to the present invention includes: performing a surface treatment on one or both sides of the separator by corona discharge; forming a unit cell including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and positioning n (n is an integer of 2 or more) unit cells on a sheet-like separator sheet, and winding the separator sheet in one direction to manufacture an electrode assembly.

[0027] Here, the separator interposed in the unit cell includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, and the separator sheet is not corona surface-treated.

[0028] In one embodiment, the surface treatment step comprises charging the surface of the separation membrane via a plasma generator.

[0029] In a specific example, during corona discharge, the discharge range is in the range of 1.0 to 3.0 kV.

[0030] In another specific example, the discharge rate during corona discharge is 30 to 300 W·min / m 2 is in the range.

[0031] Since the present invention can be modified in various ways and has various embodiments, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to the specific disclosed form, and it can be understood as including all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0032] In this application, the terms "comprise" and "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and may be understood as not precluding the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. In addition, when a layer, film, region, plate, or other part is described as being "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there is another part in between. Conversely, when a layer, film, region, plate, or other part is described as being "under" another part, this includes not only the case where it is "directly under" the other part, but also the case where there is another part in between. In addition, in this application, being "on" may include not only the case where it is located on the top, but also the case where it is located on the bottom.

[0033] In the present invention, the X-axis direction refers to a direction perpendicular to a direction in which an electrode tab (positive electrode tab or negative electrode tab) protrudes in an electrode assembly having a stacked structure, the Y-axis direction refers to a direction in which an electrode tab (positive electrode tab or negative electrode tab) protrudes, and the Z-axis direction refers to a direction perpendicular to the X-axis and Y-axis directions.

[0034] The present invention provides an electrode assembly, a lithium secondary battery including the same, and a method for manufacturing the electrode assembly.

[0035] A typical stack type or stack / fold type electrode assembly includes a separator sheet and a plurality of unit cells stacked with the separator sheet interposed therebetween. The unit cell has a structure in which positive and negative electrodes are alternately stacked with a separator interposed therebetween. If a separate adhesive layer is not formed on the separator located inside the unit cell of the folded electrode assembly, the separator may be broken due to peeling at the interface between the separator and the electrode caused by various flows during the process. Meanwhile, in order to improve the adhesive strength between the separator and the electrode interface, excessive dry adhesive strength may be realized in processes such as lamination or heat press on the entire surface of the separator. In this case, the adhesive strength between the electrode and the separator of the unit cell may be greatly increased, but the electrolyte impregnation and gas discharge may be greatly reduced, which may cause a decrease in the performance of the secondary battery, such as Li plating.

[0036] Therefore, the present invention provides an electrode assembly having a structure in which a positive electrode, a negative electrode, and a plurality of unit cells each having a separator interposed between the positive electrode and the negative electrode are wound up in a sheet-shaped separator sheet, and the separator of the unit cell includes an adhesive portion that is surface-treated with a corona, and the adhesive portion is formed in an edge region where an electrode tab is located to improve the adhesive strength of the edge region of the separator and ensure wetting by allowing an electrolyte to be impregnated between unadhesive portions where no adhesive portion is formed.

[0037] Hereinafter, an electrode assembly according to the present invention, a lithium secondary battery including the same, and a method for manufacturing the electrode assembly will be described in detail.

[0038] Fig. 3 is a schematic diagram showing the front of an electrode assembly according to an embodiment of the present invention, and Fig. 4 is a schematic diagram showing a state in which unit cells sequentially arranged on a separator sheet are wound to manufacture an electrode assembly. Referring to Figs. 3 and 4, the electrode assembly 100 of the present invention is an electrode assembly having a structure in which a positive electrode 130, a negative electrode 140, and a plurality of unit cells, each having a separator 150 interposed between the positive electrode 130 and the negative electrode 140, are wound up on a sheet-shaped separator sheet 160, and the unit cells include A-type bicells 110 and C-type bicells 120, and the separator 150 of the unit cells includes an adhesive portion 151 that is corona surface-treated and an unadhesive portion 152 that is not corona surface-treated, and the A-type bicells 110 and C-type bicells 120 are alternately arranged up and down with the separator sheet 160 between them, and the separator sheet 160 is not corona surface-treated.

[0039] Specifically, the electrode assembly 100 has a structure in which a plurality of unit cells are stacked, and the unit cells include an A-type bicell 110 and a C-type bicell 120. The A-type bicell 110 has a structure in which a positive electrode 130, a separator 150, a negative electrode 140, a separator 150, and a positive electrode 130 are stacked in sequence, and the C-type bicell 120 has a structure in which a negative electrode 140, a separator 150, a positive electrode 130, a separator 150, and a negative electrode 140 are stacked in sequence. In the unit cell having such a stacked structure, the A-type bicell 110 and the C-type bicell 120 are stacked up and down facing each other with a separator sheet 160 interposed therebetween, resulting in a structure as shown in FIG.

[0040] The electrode assembly 100 of the present invention may be applied to any structure in which unit cells are stacked, and may be, for example, a stack type structure, a stack / folding type structure, or a lamination / stack type structure.

[0041] The separator 150 of the unit cell of the present invention includes an adhesive portion 151 that is corona surface-treated, which can improve the adhesive strength between the separator 150 and the electrodes. In addition, the separator 150 of the unit cell of the present invention includes an unadhesive portion 152 that is not corona surface-treated, and an electrolyte can be impregnated between the unadhesive portion 152 that is not corona surface-treated and the electrodes facing above and below, so that the adhesive portion 151 and the unadhesive portion 152 form a pattern, which can prevent the electrolyte or air bubbles from being trapped.

[0042] Meanwhile, the separator sheet 160 is not corona surface treated. The electrode assembly of the present invention has a structure in which the separator sheet 160 and unit cells are laminated. When the separator sheet 160 facing the positive electrode 130 or the negative electrode 140 of the unit cell is folded due to a decrease in adhesive strength, the folding of the separator sheet 160 is less likely than when the separator membrane 150 inside the unit cell is folded. Meanwhile, the electrolyte impregnation between the separator sheet 160 and the electrodes may become an issue. Therefore, rather than corona surface treating the separator sheet 160 to improve the adhesive strength with the electrodes of the unit cells, the separator sheet 160 is not corona surface treated to improve the electrolyte impregnation.

[0043] FIG. 5 is a schematic diagram showing a side view of an electrode assembly according to an embodiment of the present invention, and FIG. 6 is a schematic diagram showing an adhesive pattern of a separator located inside a unit cell according to an embodiment of the present invention. Referring to FIG. 5 and FIG. 6, the unit cell of the present invention includes a positive electrode tab 131 extending in one direction of the positive electrode 130 and a negative electrode tab 141 extending in one direction of the negative electrode 140. The separator 150 of the present invention includes a first adhesive portion 151a formed by performing a corona surface treatment on an edge region where the positive electrode tab 131 is located, and a second adhesive portion 151b formed by performing a corona surface treatment on an edge region where the negative electrode tab 141 is located. In the electrode assembly 100 having a stacked form as in the present invention, an area where the interfacial adhesive force between the separator 150 of the unit cell and the electrode is weak is an edge region of the separator 150 located in a direction in which the electrode tab protrudes. During the electrode assembly process, the electrode tab may be bent to form a gap between the separator 150 and the electrode, and the separator 150 may be broken due to the occurrence of such a gap. Therefore, the present invention is characterized in that the separator 150 of the unit cell includes an adhesive portion 151 that is corona surface-treated, and that the edge region where the electrode tab is located is corona surface-treated.

[0044] Specifically, the separator 150 includes a first adhesive portion 151a that is corona surface-treated in an edge region where the positive electrode tab 131 is located, and a second adhesive portion 151b that is corona surface-treated in an edge region where the negative electrode tab 141 is located, thereby increasing the adhesive strength of the edge region where the electrode tabs are located and solving the problem of the separator 150 of the unit cell folding. In addition, since an unbonded portion 152 that is not corona pattern-treated is located in the region between the first adhesive portion 151a and the second adhesive portion 151b, the electrolyte can smoothly flow to the unbonded portion 152, thereby improving electrolyte impregnation.

[0045] In a specific example, the adhesive part 151 of the present invention may be formed on one or both sides of the separation membrane 150. Although Figs. 3 to 5 show that the adhesive part 151 is formed on both sides of the separation membrane 150, it goes without saying that the adhesive part 151 may be formed on only one side of the separation membrane 150. However, when the adhesive part 151 is formed on only one side of the separation membrane 150, the electrolyte impregnation may increase, but the adhesive strength between the other side of the separation membrane 150 where the adhesive part 151 is not formed and the electrode tab may decrease, so it is preferable to form the adhesive part 151 on both sides of the separation membrane 150.

[0046] In addition, the separators 150 of the unit cells of the present invention may have the same shape of the coating portion. In this case, since the separators 150 used in one unit cell are the same, the process time for manufacturing the electrode assembly 100 may be relatively shortened and the productivity may be improved.

[0047] Meanwhile, the adhesion portion 151 may be in the range of 10% to 70% of the total area of ​​the separation membrane 150, preferably in the range of 20% to 60%, and more preferably in the range of 30% to 50%. If the adhesion portion 151 is less than 10% of the total area of ​​the separation membrane 150, the area required for adhesion to the electrode may be insufficient, and sufficient adhesion may not be ensured. Also, if the adhesion portion 151 is more than 70% of the total area, the area of ​​the unbonded portion 152 becomes small, and the flow of the electrolyte is reduced, so that traps may occur more frequently.

[0048] Also, the adhesive portion 151 forms a regular pattern on the separator 150, and the pattern may be one or more of a stripe, a grid, a dot, and a polygon. It is preferable to form the adhesive portion 151 in a stripe pattern in order to improve the productivity of the electrode assembly and the internal flow of the electrolyte.

[0049] Furthermore, the number of repetitions of the pattern in the separator 150 is preferably 1 to 4. If the number of repetitions of the pattern exceeds 4, the pattern of the coating portion in the separator 150 becomes excessively fine, and the productivity of the electrode assembly 100 decreases.

[0050] Meanwhile, the separator 150 of the present invention can be used without any particular limitation as long as it is generally used as the separator 150 in a lithium secondary battery, and in particular, it is preferable that the separator 150 has low resistance to ion migration of the electrolyte and has excellent electrolyte humidification ability. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric such as a high melting point glass fiber or a polyethylene terephthalate fiber, can be used. In addition to the above-mentioned materials, the separator 150 can be manufactured using a polymer having high heat resistance. In addition, the separator 150 of the present invention can be an organic / inorganic composite porous SRS (Safety-Reinforcing Separators) separator. In a specific example, the SRS separator may be manufactured by using inorganic particles and a binder polymer as active layer components on a polyolefin-based or polyester-based separator substrate, and the separator 150 may be a porous thin film having a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm.

[0051] Meanwhile, the separator sheet 160 of the present invention may also be made of a mixture of one or more of the materials mentioned above.

[0052] Also, the corona surface treatment source may be air, oxygen (O2) or nitrogen (N2). Corona surface treatment can achieve a significant improvement in wettability due to the synergistic effect of the physical surface modification by the discharge itself and the chemical surface modification by the generation of functional groups. In such chemical surface modification, high-energy electrons or ions collide with the separation membrane 150 substrate to generate radicals and ions, which react with the surrounding air, oxygen, nitrogen, ozone, moisture, etc., introducing polar functional groups such as carbonyl groups, carboxyl groups, hydroxyl groups, and cyano groups, resulting in chemical surface modification.

[0053] The corona surface treatment source may also perform corona treatment using plasma using a polymer. That is, when highly energetic particles in a plasma state collide with the surface of the substrate of the separation membrane 150, the energy is transferred to the collided surface of the separation membrane 150, and the separation membrane 150 may be chemically or physically activated to improve adhesion between the polymer mixture layers.

[0054] Meanwhile, the binder polymer mixture may include a porous inorganic filler and a binder polymer. The inorganic filler may be added to the binder polymer mixture to increase the mechanical strength of the separator 150, thereby ensuring the safety of the battery against external forces. In the separator 150, the inorganic fillers are connected and fixed by the binder polymer, and a heat-resistant pore structure is formed by the interstitial volume between the inorganic fillers, thereby improving the electrochemical safety and performance of the battery at the same time.

[0055] The concentration of the inorganic filler may be 60 to 90 wt %, and preferably 70 to 80 wt %, based on the weight of the polymer mixture layer. If the concentration of the inorganic filler is too low, the desired level of mechanical strength cannot be maintained, and conversely, if the concentration of the inorganic filler is too high, the porosity of the separation membrane 150 cannot be ensured due to an excessive amount of inorganic components, and the ion conductivity may decrease, resulting in a problem of increased internal resistance.

[0056] Fig. 7 is a schematic diagram showing a side view of an electrode assembly according to another embodiment of the present invention, and Fig. 8 is a schematic diagram showing an adhesive pattern of a separator located inside a unit cell according to another embodiment of the present invention. Referring to Figs. 7 and 8, the electrode assembly 200 of the present invention has a structure in which unit cells are stacked with a separator sheet 260 interposed therebetween. Here, the unit cell includes an A-type bicell 210 in which a positive electrode 230 / separator 250 / negative electrode 240 / separator 250 / positive electrode 230 are stacked in this order, and a C-type bicell 220 in which a negative electrode 240 / separator 250 / positive electrode 230 / separator 250 / negative electrode 240 are stacked in this order.

[0057] The separator 250 of the present invention has a structure in which the bonded parts 251 and the unbonded parts 252 are alternately arranged, and includes a third bonded part located between the first bonded part 251a and the second bonded part 251b, and the number of the third bonded parts may be n (n is an integer of 1 or more). That is, the separator 250 may include a third bonded part 251c between the first bonded part 251a formed by performing a corona surface treatment on the edge region where the tab (positive electrode tab 231) of the positive electrode 230 is located, and the second bonded part 251b formed by performing a corona surface treatment on the edge region where the negative electrode tab 241 is located, and here, the number of the third bonded parts 251c may be one or more. FIG. 7 shows the electrode assembly 200 in which one third bonded part 251c is formed between the first bonded part 251a and the second bonded part 251b, but is not limited thereto. In this manner, by additionally forming the third adhesive part 251c on the surface of the separator 250, it is possible to increase the interfacial adhesive strength between the separator 250 and the electrode in the central region as well as the edge region of the separator 250. However, if the area of ​​the third adhesive part 251c is too large or if there are too many third adhesive parts 251c, the electrolyte impregnation property may decrease, so it is preferable to appropriately form the third adhesive part 251c according to the purpose.

[0058] 9 is a schematic diagram showing a plasma generating apparatus for performing a corona treatment on a surface of a separator according to an embodiment of the present invention. Referring to Fig. 9, the separator 150 to be corona-treated by the plasma generating apparatus 170 is the separator 150 inserted into a unit cell, and Fig. 9 shows the corona treatment on one side of the separator 150, but is not limited thereto, and the corona surface treatment may be performed on both sides of the separator 150.

[0059] In a specific example of the present invention, the corona surface treatment is performed by charging the surface of the separation membrane 150 using a plasma generator 170. In one example, the device for corona treating the surface of the separation membrane 150 may include a roller unit 171 including a metal member 172, and a plasma generator 173 disposed at a distance from the roller unit 171 to generate plasma through an interaction with the metal member 172 and irradiate the plasma onto the surface of the separation membrane 150. The plasma generator 173 is spaced apart from the separation membrane 150 to generate plasma through an interaction with the metal member 172 and irradiate the plasma onto the surface of the separation membrane 150. One type of plasma generated at this time may be plasma due to corona discharge. Specifically, the plasma generating unit 173 may include a main body 174 disposed at a distance from the roller unit 171, an electrode member 175 coupled to the main body 174 and configured to generate plasma on the surface of the separation membrane 150 located opposite the metal member 172 to form an adhesive layer on the surface of the separation membrane 150, and a guide member 176 for fixing the electrode member 175 and the main body 174 or for moving the position of the electrode member 175 in a direction perpendicular to the transport direction of the separation membrane 150 (TD direction).

[0060] The body 174 is elongated in a direction (TD) perpendicular to the transport direction of the separation membrane 150, and may have a length equal to or greater than the width of the separation membrane 150. The body 174 may be made of a non-metallic material.

[0061] The electrode member 175 may be disposed on the outer surface of the body 174 corresponding to the moving direction (MD direction) of the separation membrane 150, and may be configured in a plurality of pieces and arranged side by side in a direction (TD direction) perpendicular to the moving direction of the separation membrane 150. The electrode member 175 must include at least a pair of electrode members 175 to perform corona surface treatment on edges located on both sides in the moving direction (MD direction) of the separation membrane 150, and additional electrode members 175 may be provided to perform corona surface treatment on areas other than the edges located on both sides as necessary. By providing a plurality of electrode members in this manner, an adhesive layer is formed only on the surface of the separation membrane 150 located between the electrode members 175 and the metal member 172, and no plasma is generated on the surface of the separation membrane 150 where the electrode members 175 are not present, so that a non-adhesive layer is formed and a stripe-patterned adhesive layer may be formed.

[0062] The electrode member 175 may be, for example, a corona discharge electrode. Plasma may be stably generated by interaction with the metal member 172 through the corona discharge electrode, and the surface of the separator 150 may be corona-treated.

[0063] The guide member 176 may fix the electrode members 175 to the body 174 and move each of the electrode members 175 in a direction (TD direction) perpendicular to the transport direction of the separation membrane 150. In a specific example, the guide member 176 may include a guide groove (not shown) formed long in the direction (TD direction) perpendicular to the transport direction of the separation membrane 150, and a fixing member (not shown) that fastens and fixes the electrode member 175 in the guide groove. The electrode member 175 is detachable from the guide groove and has a structure that allows the electrode member 175 to slide along the guide groove and change its position. Since the electrode member 175 can be detached from the guide groove, the number of the electrode members 175 can be adjusted, and since the electrode member 175 can slide along the guide groove, the position of the electrode member 175 can be adjusted according to the purpose to adjust the position of the adhesive layer formed on the surface of the separation membrane 150 and the pattern width.

[0064] Meanwhile, the guide member 176 may include a display member (not shown) having a scale marked on its surface in a direction (TD direction) perpendicular to the transport direction of the separation membrane 150. The position of the electrode member 175 can be accurately confirmed through the display member, thereby improving the precision of the corona surface treatment.

[0065] In a specific example of the present invention, the discharge range during corona surface treatment may be in the range of 1.0 to 3.0 kV, and preferably in the range of 1.5 to 2.5 kV. If the discharge range is less than 1.0 kV, it is difficult to perform a uniform corona surface treatment on the surface of the separation membrane, and if it exceeds 3.0 kV, it may be difficult to operate the corona generating device when performing corona treatment in a fine pattern, so it is preferable to discharge within the above range.

[0066] In addition, the discharge rate during corona surface treatment is 30 to 300 W·min / m 2 and preferably in the range of 100 to 200 W·min / m 2 The discharge rate can be in the range of 30 W min / m 2 If it is less than 300W·min / m, it may be difficult to perform detailed surface treatment on the separation membrane surface and it may be difficult to achieve the desired effect. 2 If the discharge current exceeds this range, the physical properties of the separation membrane may change. Therefore, it is preferable to discharge the battery within the above range.

[0067] The present invention also provides a lithium secondary battery including the electrode assembly described above. In a specific example, the electrode assembly included in the lithium secondary battery of the present invention may be an electrode assembly having a structure in which a positive electrode, a negative electrode, and a plurality of unit cells, each having a separator interposed between the positive electrode and the negative electrode, are wound up in a sheet-like separator sheet, the unit cells include A-type bicells and C-type bicells, the separator of the unit cells includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, the plurality of A-type bicells and C-type bicells are alternately arranged above and below with the separator sheet interposed therebetween, and the separator sheet is not corona surface-treated.

[0068] The lithium secondary battery of the present invention has a structure in which an electrode assembly is sealed inside a battery case together with an electrolyte. The type of the secondary battery is not particularly limited, but specific examples thereof may be lithium secondary batteries such as lithium ion (Li-ion) secondary batteries, lithium polymer (Li-polymer) secondary batteries, or lithium ion polymer (Li-ion polymer) secondary batteries, which have advantages such as high energy density, discharge voltage, and output stability.

[0069] In the lithium secondary battery of the present invention, the electrode may have a structure in which an electrode active material layer is formed by applying an electrode forming slurry containing an electrode active material onto an electrode current collector. The electrode slurry may be applied to at least one surface of the current collector.

[0070] In this case, the electrode current collector may be a positive electrode current collector or a negative electrode current collector, the electrode active material may be a positive electrode active material or a negative electrode active material, and the electrode slurry may further include a conductive material and a binder in addition to the electrode active material.

[0071] In the present invention, the positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may have fine irregularities on its surface to increase the adhesive force of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0072] In the case of a sheet for a negative electrode current collector, it is generally made to a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, like the positive electrode current collector, the surface can be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0073] In the present invention, the positive electrode active material is a material capable of undergoing an electrochemical reaction, and contains two or more transition metals as a lithium transition metal oxide, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2) substituted with one or more transition metals; a lithium manganese oxide substituted with one or more transition metals; a compound represented by the chemical formula LiNi 1-y M y Lithium nickel oxide represented by LiO2 (wherein M=Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, containing one or more of the above elements, and 0.01≦y≦0.7); 1+z Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O2, etc., Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (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); 1+x M1-y M' y PO 4-z X z (Here, M = transition metal, preferably Fe, Mn, Co or Ni, M' = Al, Mg or Ti, X = F, S or N, -0.5 ≦ x ≦ +0.5, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.1), and examples include olivine-type lithium metal phosphates represented by the formula, but are not limited thereto.

[0074] The negative electrode active material is, for example, carbon such as graphitizable carbon and graphite-based carbon; Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. can be used.

[0075] The above conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0076] The binder is a component that aids in binding the active material and conductive material and binding to the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers.

[0077] Meanwhile, such an electrode slurry may be prepared by dissolving an electrode active material, a conductive material, a binder, and the like in a solvent. The type of the solvent is not particularly limited as long as it can disperse the electrode active material, and either an aqueous solvent or a non-aqueous solvent can be used. For example, the solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or a mixture of two or more of these may be used. The amount of the solvent used is not particularly limited as long as it can be adjusted to a level that allows the slurry to have a suitable viscosity in consideration of the coating thickness of the slurry, production yield, workability, and the like.

[0078] Meanwhile, in the lithium secondary battery, the electrolyte may include an organic solvent and a lithium salt that are commonly used in electrolytes, and is not particularly limited.

[0079] The organic solvent may be used without any particular limitation, so long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent that can be used include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0080] Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant, which can improve the charge / discharge performance of the battery, and low-viscosity linear carbonate-based compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are more preferred.

[0081] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

[0082] In addition to the above electrolyte components, the electrolyte may further contain one or more additives such as pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the battery life characteristics, suppressing the decrease in battery capacity, improving the battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 5% by weight based on the total weight of the electrolyte.

[0083] The lithium secondary battery of the present invention may be manufactured by forming an electrode assembly by disposing a separator between a positive electrode and a negative electrode, and then inserting the electrode assembly into a cylindrical or prismatic battery case and then injecting an electrolyte into the battery case. Alternatively, the electrode assemblies may be stacked, impregnated with an electrolyte, and then inserted into a battery case and sealed.

[0084] When manufacturing the lithium secondary battery of the present invention, the electrode assembly may be dried to remove at least one organic solvent used in manufacturing the positive electrode, selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate. If an electrolyte having the same composition as the organic solvent used in manufacturing the positive electrode is used as the electrolyte, the process of drying the electrode assembly may be omitted.

[0085] Unlike the above-described lithium secondary batteries, the lithium secondary battery according to another embodiment of the present invention may be an all-solid-state battery.

[0086] The battery case may be one commonly used in the art, and the shape of the battery case is not limited depending on the application of the battery. For example, the battery case may be a cylindrical type using a can, a square type, a pouch type, a coin type, or the like.

[0087] The lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, energy storage systems (ESS), and electric vehicles such as hybrid electric vehicles (HEV), etc.

[0088] The present invention also provides a method for manufacturing an electrode assembly. Any overlapping description with the above detailed description of the electrode assembly may be omitted, and all detailed descriptions are quoted from the above detailed description.

[0089] In one embodiment, a method for manufacturing an electrode assembly according to the present invention is a method for manufacturing an electrode assembly having a structure in which a positive electrode, a negative electrode, and a plurality of unit cells, each having a separator interposed between the positive and negative electrodes, are wound up in a sheet-like separator sheet, the method comprising the steps of: performing a surface treatment on one or both sides of a separator substrate by performing a corona discharge; stacking the positive electrode sheet and the negative electrode sheet with the corona discharge-treated separator interposed therebetween, and cutting the stacked sheets to a predetermined size to manufacture unit cells including A-type bicells and C-type bicells; and positioning the unit cells on the sheet-like separator sheet, and winding the separator sheet in one direction to manufacture an electrode assembly having a structure in which the A-type bicells and the C-type bicells are alternately arranged above and below with the separator sheet interposed therebetween, the separator membrane of the unit cells includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, and the separator sheet is not corona surface-treated.

[0090] In the step of performing surface treatment on one or both sides of the separator substrate by corona discharge, the separator substrate is transported by a roller unit including a metal member, and a plasma generator disposed apart from the roller unit generates plasma on the surface of the separator substrate by interaction with the metal member to form an adhesive layer. In a specific example, the plasma generator includes an electrode member and generates plasma by interaction between the electrode member and the metal member. In this case, the electrode member may be a corona discharge electrode. An adhesive layer is formed only on the separator substrate surface located between the electrode member and the metal member, and no plasma is generated on the separator substrate surface without the electrode member, so that a non-adhesive layer is formed and a stripe-patterned adhesive layer may be formed.

[0091] In the step of manufacturing a unit cell including the A-type bicell and the C-type bicell, each positive electrode substrate, negative electrode substrate, and corona surface-treated separator substrate are transported by rollers, stacked to match an A-type bicell structure (a structure in which a positive electrode, separator, negative electrode, separator, and positive electrode are stacked in sequence) or a C-type bicell structure (a structure in which a negative electrode, separator, positive electrode, separator, and negative electrode are stacked in sequence), cut into a predetermined size, and heat-sealed using a laminator or a heat press to manufacture a unit cell such as an A-type bicell or a C-type bicell.

[0092] The step of manufacturing the electrode assembly includes placing a plurality of unit cells on a sheet-like separation sheet, and winding the separation sheet in one direction to manufacture an electrode assembly having a structure in which A-type bicells and C-type bicells are alternately arranged above and below with the separation sheet in between. The A-type bicell may be placed at the start point of winding, and then sequentially arranged to have a repeating pattern such as C-type bicells, C-type bicells, A-type bicells, A-type bicells, C-type bicells, and C-type bicells, and then wound to manufacture an electrode assembly in which the A-type bicell is located at the center. Alternatively, the C-type bicell may be placed at the start point of winding, and then sequentially arranged to have a repeating pattern such as A-type bicells, A-type bicells, C-type bicells, C-type bicells, A-type bicells, and A-type bicells, and then wound to manufacture an electrode assembly in which the C-type bicell is located at the center.

[0093] Meanwhile, the separator sheet is not subjected to a corona surface treatment because the probability of the separator sheet breaking due to flow when stacked with the unit cells is lower than the probability of the separator membrane inside the unit cells breaking, and therefore the separator sheet is not subjected to a corona surface treatment in order to improve electrolyte impregnation rather than to increase the interfacial adhesive strength between the separator sheet and the electrodes of the unit cells.

[0094] In another example, in a method for manufacturing an electrode assembly according to the present invention, a unit cell includes a positive electrode tab extending in one direction of a positive electrode and a negative electrode tab extending in one direction of a negative electrode, and a separator includes a first adhesive portion formed by subjecting an edge region where the positive electrode tab is located to a corona surface treatment, and a second adhesive portion formed by subjecting an edge region where the negative electrode tab is located to a corona surface treatment.

[0095] In the step of performing surface treatment by performing corona discharge on one or both sides of the separator substrate, the edges of both sides in the direction in which the separator is moved (MD direction) correspond to positions that face the electrode tabs inside the unit cells to be manufactured later. Therefore, by performing corona surface treatment on the edges of both sides in the direction in which the separator is moved (MD direction) during corona surface treatment of the separator substrate, it is possible to improve the adhesive strength between the edge of the electrode where the electrode tab of the unit cell is located and the edge region of the separator facing it.

[0096] In another example, in the method for manufacturing an electrode assembly according to the present invention, the separator may have a structure in which bonded portions and non-bonded portions are alternately arranged, and may include a third adhesive portion located between a first adhesive portion and a second adhesive portion, and the third adhesive portion may be n in number (n is an integer of 1 or more). In order to improve the adhesive strength between the separator and the electrode, one or more third adhesive portions may be formed between the first adhesive portion and the second adhesive portion. The number of third adhesive portions is not particularly limited, and may be set according to the purpose in consideration of the impregnation of the electrolyte. [Explanation of symbols]

[0097] 1, 100, 200: Electrode assembly 10, 110, 210: A-type bicelles 20, 120, 220: C-type bicelles 30, 130, 230: Positive electrode 40, 140, 240: negative electrode 50, 150, 250: Separation membrane 60, 160, 260: Separation sheet 131, 231: Positive electrode tab 141, 241: Negative electrode tab 151, 251: Adhesive part 151a, 251a: 1st adhesive part 151b, 251b: 2nd adhesive part 152, 252: Unbonded part 170: Plasma generator 171: Roller section 172: Metallic parts 173: Plasma generating unit 174: Main body 175: Electrode parts 176: Guide member 251c: 3rd adhesive part

Claims

1. A unit cell including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is stacked in n units (n is an integer of 2 or more), and a separator sheet is disposed between the unit cells; The separator interposed in the unit cell includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, The electrode assembly, wherein the separator sheet is a structure that is not subjected to the corona surface treatment.

2. The electrode assembly according to claim 1 , wherein the separator sheet is wound around the stacked unit cells while being inserted between the stacked unit cells.

3. The unit cell comprises: a positive electrode tab formed by extending in one direction of the positive electrode; a negative electrode tab extending in one direction of the negative electrode, The separation membrane is a first adhesive portion having a corona surface treatment applied to an edge region where the positive electrode tab is located; 2. The electrode assembly of claim 1, further comprising: a second adhesive portion having a corona surface treatment on an edge area where the negative electrode tab is located.

4. The electrode assembly of claim 1 , wherein the surface of the separator has a structure in which the bonded portions and the unbonded portions are alternately arranged.

5. The electrode assembly of claim 1 , wherein the adhesive portion is formed on one or both sides of the separator.

6. The electrode assembly of claim 1, wherein an area where the adhesive is formed is in a range of 10% to 70% of an area of ​​the separator.

7. The adhesive forms a pattern; The electrode assembly of claim 1 , wherein the pattern is at least one of a stripe pattern, a grid pattern, a dot pattern, and a polygon pattern.

8. A secondary battery comprising the electrode assembly according to claim 1.

9. The secondary battery according to claim 8 , wherein the secondary battery is a pouch-type secondary battery.

10. A method for manufacturing an electrode assembly for a secondary battery, comprising: A step of surface treating one or both sides of the separation membrane by corona discharge; forming a unit cell including a positive electrode, a negative electrode, and the separator interposed between the positive electrode and the negative electrode; and placing n (n is an integer of 2 or more) of the unit cells on a sheet-like separator sheet, and winding the separator sheet in one direction to manufacture an electrode assembly, The separator interposed in the unit cell includes an adhesive portion that is corona surface-treated and an unadhesive portion that is not corona surface-treated, The method for manufacturing an electrode assembly, wherein the separation sheet is not subjected to a corona surface treatment.

11. The surface treatment step includes: The method of claim 10, further comprising: charging the surface of the separator via a plasma generator.

12. The method for manufacturing an electrode assembly according to claim 10, wherein the discharge voltage range during corona discharge is in the range of 1.0 to 3.0 kV.

13. During corona discharge, the discharge rate is 30 to 300 W / min / m ２ The method for manufacturing an electrode assembly according to claim 10, wherein the thickness of the electrode assembly is in the range of

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