Electrode assembly including a surface-treated separation membrane, secondary battery including the same, and method for manufacturing the 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 priority under Korean Patent Application No. 10-2022-0166693 dated 2 December 2022, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification.

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

[0003] In recent years, rising energy prices due to the depletion of fossil fuels and growing concern about environmental pollution have made environmentally friendly alternative energy sources an essential factor for future life. Therefore, research into diverse power production technologies such as nuclear, solar, wind, and tidal power continues, and there is also significant interest in power storage devices to utilize this produced energy more efficiently.

[0004] In particular, as technological development and demand for mobile devices increase, the demand for batteries as an energy source is rapidly rising, and research is being conducted accordingly on batteries that can meet diverse requirements.

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

[0006] Generally, a rechargeable battery has an electrode assembly inside the battery case that includes a positive electrode, a negative electrode, and a separator membrane placed between them, with the positive and negative electrode tabs sealed so that the extended positive and negative electrode leads are exposed.

[0007] On the other hand, the electrode assembly includes a structure in which a positive electrode, a separator membrane, and a negative electrode are sequentially stacked. Figure 1 is a schematic diagram showing the bending phenomenon of the separator membrane in the electrode assembly. Referring to Figure 1, the electrode assembly 1 experiences bending of the separator membrane 50 due to various flow processes that occur during the manufacturing of the secondary battery. In particular, this bending phenomenon is frequently induced in the edge region A of the separator membrane 50.

[0008] Figure 2 is a schematic diagram showing the front view of a conventional electrode assembly. Referring to Figure 2, the folded electrode assembly 1 has a structure in which a positive electrode 30, a negative electrode 40, and multiple unit cells with a separation membrane 50 interposed between the positive electrode 30 and the negative electrode 40 are wound on a sheet-like separation sheet 60. Here, the unit cells include a type A bicell 10 stacked in the order of positive electrode 30 / separation membrane 50 / negative electrode 40 / separation membrane 50 / positive electrode 30, and a type C bicell 20 stacked in the order of negative electrode 40 / separation membrane 50 / positive electrode 30 / separation membrane 50 / negative electrode 40.

[0009] Conventional electrode assemblies 1 have a problem in that a separate adhesive layer is not formed on the separation membrane 50, resulting in low adhesion between the electrode and the separation membrane 50. To solve this problem, excessive dry adhesion may be achieved on the unit cell in which the electrode and separation membrane 50 are laminated through processes such as lamination or heat pressing. However, while this can greatly increase the adhesion between the electrode and the separation membrane 50 of the unit cell, since the lamination or heat pressing process is performed on the entire surface of the electrode and separation membrane 50, electrolyte impregnation and gas discharge performance are greatly reduced, which may lead to factors that degrade the performance of secondary batteries, such as lithium plating.

[0010] Therefore, there is a need to develop a method that improves the adhesion between the separation membrane and the electrode interface, provides excellent electrolyte impregnation, and prevents the separation membrane from bending. [Overview of the project] [Problems that the invention aims to solve]

[0011] The present invention is intended to solve the above problems, and provides an electrode assembly capable of preventing the folding phenomenon of a separation membrane, a secondary battery including the same, and a method for manufacturing the above electrode assembly.

Means for Solving the Problems

[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 unit cells (n is an integer of 2 or more) including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode are stacked, and a separation sheet is disposed between the unit cells. The above n is, for example, an integer in the range of 2 to 20. The separation membrane interposed in the unit cell includes an adhered portion surface-treated by corona and a non-adhered portion not surface-treated by corona, and the above separation sheet has a structure not surface-treated by corona.

[0013] In addition, the present invention provides a secondary battery including the above-described electrode assembly. For example, the above secondary battery is a pouch-type secondary battery.

[0014] In addition, the present invention 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 a step of performing corona discharge on one or both surfaces of a separation membrane for surface treatment, a step of forming a unit cell including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, and a step of positioning n unit cells (n is an integer of 2 or more) on a sheet-like separation sheet and winding the separation sheet in one direction to manufacture an electrode assembly. Here, the separation membrane interposed in the unit cell includes an adhered portion surface-treated by corona and a non-adhered portion not surface-treated by corona. In addition, the above separation sheet has a structure not surface-treated by corona.

Effects of the Invention

[0015] The present invention will increase the interfacial adhesive force between the electrode and the separation membrane that forms the electrode assembly without reducing the impregnation property with respect to the electrolytic solution.

Brief Description of the Drawings

[0016] [Figure 1] It is a schematic diagram showing the folding phenomenon of the separator that occurred in the conventional electrode assembly. [Figure 2] It is a schematic diagram showing the laminated structure of the conventional electrode assembly. [Figure 3] It is a schematic diagram showing the laminated structure of the electrode assembly according to one embodiment. [Figure 4] It is a schematic diagram showing the manufacturing process of the electrode assembly. [Figure 5] It is a schematic diagram showing the electrode laminated structure according to one embodiment. [Figure 6] It is a schematic diagram showing the adhesion pattern of the separator located inside the unit cell according to one embodiment. [Figure 7] It is a schematic diagram showing the laminated structure of the electrode assembly according to one embodiment. [Figure 8] It is a schematic diagram showing the adhesion pattern of the separator according to one embodiment. [Figure 9] It is a schematic diagram showing the process of corona treatment on the surface of the separator.

MODE FOR CARRYING OUT THE INVENTION

[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 unit cells (n is an integer of 2 or more) including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are laminated, and a separation 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 adhered portion subjected to corona surface treatment and a non-adhered portion not subjected to corona surface treatment, and the separation sheet has a structure not subjected to corona surface treatment.

[0018] In one embodiment, the separation sheet has a structure that is wound while wrapping the unit cells via between the laminated unit cells. Thereby, the electrode assembly according to the present invention forms a stack-and-folding structure.

[0019] In one example, in the electrode assembly according to the present invention, the unit cell includes a type A bicell and a type C bicell, the separation membrane of the unit cell includes an adhesive portion that has been corona surface-treated and an unadhesive portion that has not been corona surface-treated, and a plurality of type A bicells and type C bicells are arranged alternately in the upper and lower halves with a separation sheet in between.

[0020] In one embodiment, the unit cell includes a positive electrode tab formed extending in one direction from the positive electrode and a negative electrode tab formed extending in one direction from the negative electrode. Here, the direction in which the positive electrode tab is formed and the direction in which the negative electrode tab is formed may be the same or opposite to each other. The separation film also includes a first adhesive portion corona-treated on the edge region where the positive electrode tab is located and a second adhesive portion corona-treated on the edge region where the negative electrode tab is located.

[0021] In one embodiment, the surface of the separation membrane has a structure in which adhered portions and unadhered portions are arranged alternately with each other.

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

[0023] In specific examples, the area where the adhesive zone is formed is in the range of 10% to 70% of the area of ​​the separation membrane.

[0024] In another specific example, the adhesive portion forms a pattern. This pattern is one or more of the following: stripe, grid, dot, and polygon.

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

[0026] Furthermore, the present invention 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 is: The steps include surface treatment of one or both sides of the separation membrane by performing corona discharge, The steps include forming a unit cell comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, The method includes the steps of: positioning n unit cells (where n is an integer of 2 or more) on a sheet-like separation sheet, and winding the separation sheet in one direction to manufacture an electrode assembly.

[0027] Here, the separation membrane interposed within the unit cell includes an adhesive portion that has undergone corona surface treatment and an unadhesive portion that has not undergone corona surface treatment. Furthermore, the separation sheet described above has a structure that does not undergo corona surface treatment.

[0028] In one embodiment, the surface treatment step involves charging the surface of the separation film 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, during corona discharge, the discharge rate is 30-300 W·min / m 2 It is within the range.

[0031] The present invention is subject to various modifications and may have a variety of embodiments; therefore, 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 any particular form of disclosure, but rather should be understood to include all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0032] In this application, terms such as “includes” and “have” are intended to specify the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, without prejudice to the existence or possibility of adding one or more other features, numbers, steps, actions, components, parts, or combinations thereof. Furthermore, when a part such as a layer, film, region, or plate is said to be “on top” of another part, this includes not only when it is “directly on top” of the other part, but also when there is another part in between. Conversely, when a part such as a layer, film, region, or plate is said to be “below” another part, this includes not only when it is “directly below” the other part, but also when there is another part in between. Furthermore, in this application, being “on top” may include being located not only at the top but also at the bottom.

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

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

[0035] Conventional stacked or stacked / folded electrode assemblies include a separation sheet and multiple unit cells stacked via the separation sheet. Each unit cell has a structure in which positive and negative electrodes are alternately stacked with a separation membrane in between. If a separate adhesive layer is not formed on the separation membrane located inside the unit cells of a folded electrode assembly, various flow conditions during the process can cause the separation membrane to peel off from the electrode interface and fold. On the other hand, in order to improve the adhesion between the separation membrane and the electrode interface, excessive dry adhesion may be applied to the entire surface of the separation membrane through processes such as lamination or heat pressing. In this case, the adhesion between the electrode of the unit cell and the separation membrane can be greatly increased, but electrolyte impregnation and gas discharge performance are greatly reduced, which can lead to performance degradation factors in secondary batteries such as lithium plating.

[0036] Therefore, the present invention relates to an electrode assembly having a structure in which a plurality of unit cells, each having a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, are wound together in a sheet-like separation sheet, wherein the separation membrane of the unit cell includes an adhesive portion that has been corona surface treated, and the adhesive portion is formed in the edge region where the electrode tab is located to improve the adhesive strength of the edge region of the separation membrane, and wettability is ensured so that an electrolyte can be impregnated between the unadhesive portions where no adhesive portion is formed.

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

[0038] Figure 3 is a schematic diagram showing the front view of an electrode assembly according to one embodiment of the present invention, and Figure 4 is a schematic diagram showing how an electrode assembly is manufactured by winding up unit cells that are sequentially arranged on a separation sheet. Referring to Figures 3 and 4, the electrode assembly 100 of the present invention is an electrode assembly 100 having a structure in which a positive electrode 130, a negative electrode 140, and a plurality of unit cells in which a separation membrane 150 is interposed between the positive electrode 130 and the negative electrode 140 are wound up on a sheet-like separation sheet 160, the unit cells include A-type bicells 110 and C-type bicells 120, the separation membrane 150 of the unit cell includes an adhesive portion 151 that has been corona surface-treated and an unadhesive portion 152 that has not been corona surface-treated, the plurality of A-type bicells 110 and C-type bicells 120 are arranged alternately above and below with the separation sheet 160 in between, and the separation sheet 160 is not corona surface-treated.

[0039] Specifically, the electrode assembly 100 has a structure in which multiple unit cells are stacked, and the unit cells include type A bicells 110 and type C bicells 120. The type A bicell 110 has a structure in which a positive electrode 130, a separation membrane 150, a negative electrode 140, a separation membrane 150, and a positive electrode 130 are stacked sequentially, and the type C bicell 120 has a structure in which a negative electrode 140, a separation membrane 150, a positive electrode 130, a separation membrane 150, and a negative electrode 140 are stacked sequentially. In a unit cell having such a stacked structure, the type A bicell 110 and the type C bicell 120 are stacked facing each other vertically with a separation sheet 160 in between, resulting in the structure shown in Figure 3.

[0040] The electrode assembly 100 of the present invention can be applied to any structure in which unit cells are stacked, but examples of such structures include a stacked structure, a stack / folding structure, or a lamination / stack structure.

[0041] The separation membrane 150 of the unit cell of the present invention includes a corona-treated adhesive portion 151, which can improve the adhesion between the separation membrane 150 and the electrode. Furthermore, the separation membrane 150 of the unit cell of the present invention includes an unadhesive portion 152 that is not corona-treated, and an electrolyte can be impregnated between the unadhesive portion 152 and the electrodes facing each other vertically. The adhesive portion 151 and the unadhesive portion 152 form a pattern, which can prevent the electrolyte or bubbles from being trapped.

[0042] On the other hand, the separation sheet 160 is not subjected to corona surface treatment. The electrode assembly of the present invention has a structure in which the separation sheet 160 and the unit cell are stacked. The separation sheet 160, which faces the positive electrode 130 or negative electrode 140 of the unit cell from above and below, is less likely to break due to a decrease in adhesive strength than the separation membrane 150 inside the unit cell breaks. On the other hand, the electrolyte impregnation between the separation sheet 160 and the electrode can be a problem. Therefore, rather than performing corona surface treatment on the separation sheet 160 to improve the adhesive strength with the electrode of the unit cell, the separation sheet 160 is not subjected to corona surface treatment in order to improve electrolyte impregnation.

[0043] Figure 5 is a schematic diagram showing a side view of an electrode assembly according to one embodiment of the present invention, and Figure 6 is a schematic diagram showing the adhesion pattern of a separation membrane located inside a unit cell according to one embodiment of the present invention. Referring to Figures 5 and 6, the unit cell of the present invention includes a positive electrode tab 131 extending in one direction from the positive electrode 130 and a negative electrode tab 141 extending in one direction from the negative electrode 140. The separation membrane 150 of the present invention includes a first adhesive portion 151a formed by corona surface treatment on the edge region where the positive electrode tab 131 is located, and a second adhesive portion 151b formed by corona surface treatment on the edge region where the negative electrode tab 141 is located. In an electrode assembly 100 in a stacked configuration as in the present invention, the region where the interfacial adhesion between the separation membrane 150 of the unit cell and the electrode is weak is the edge region of the separation membrane 150 located in the direction in which the electrode tab protrudes. During the electrode assembly process, the electrode tab may bend, forming a gap between the separation membrane 150 and the electrode, and there is a problem that such a gap can cause the separation membrane 150 to bend. Therefore, the present invention includes an adhesive portion 151 that performs corona surface treatment on the separation membrane 150 of the unit cell, and is characterized in that corona surface treatment is performed on the edge region where the electrode tab is located.

[0044] Specifically, the separation membrane 150 includes a first adhesive portion 151a, which is corona surface treated at the edge region where the positive electrode tab 131 is located, and a second adhesive portion 151b, which is formed by corona surface treatment at the edge region where the negative electrode tab 141 is located. This enhances the adhesive strength at the edge regions where the electrode tabs are located, thus solving the problem of the separation membrane 150 of a unit cell breaking. Furthermore, since there is an unadhesive portion 152 that is not corona pattern treated in the region between the first adhesive portion 151a and the second adhesive portion 151b, the electrolyte can flow smoothly into the unadhesive portion 152, improving electrolyte impregnation.

[0045] In specific examples, the adhesive portion 151 of the present invention may be formed on one or both sides of the separation membrane 150. Figures 3 to 5 show that the adhesive portion 151 is formed on both sides of the separation membrane 150, but of course, the adhesive portion 151 may be formed on only one side of the separation membrane 150. However, while the electrolyte impregnation may increase when the adhesive portion 151 is formed on only one side of the separation membrane 150, the adhesive strength between the other side of the separation membrane 150 where the adhesive portion 151 is not formed and the electrode tab may decrease, so it is preferable to form the adhesive portion 151 on both sides of the separation membrane 150.

[0046] Furthermore, the separation membranes 150 of the unit cells of the present invention may have the same shape for their coating portions. When assembled in this manner, since the separation membranes 150 used within a single unit cell are identical, the process time when manufacturing the electrode assembly 100 can be relatively shortened, potentially improving productivity.

[0047] On the other hand, the adhesive 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 adhesive portion 151 is less than 10% of the total area of ​​the separation membrane 150, the area necessary for adhesion to the electrode may be insufficient, and sufficient adhesion may not be ensured. Also, if the adhesive portion 151 exceeds 70% of the total area, the area of ​​the unadhered portion 152 becomes smaller, and the flow of the electrolyte decreases, so traps may occur more frequently.

[0048] Furthermore, the adhesive portion 151 forms a regular pattern with the separation membrane 150, and the pattern may consist of one or more of the following: stripe, grid, dot, and polygon. Preferably, it is formed with a stripe pattern to improve the productivity of the electrode assembly and to facilitate internal flow of the electrolyte.

[0049] Furthermore, the number of repetitions of the pattern within the separation membrane 150 is preferably 1 to 4 times. If the number of repetitions of the pattern exceeds 4 times, the pattern of the coating portion within the separation membrane 150 becomes excessively dense, reducing the productivity of the electrode assembly 100.

[0050] On the other hand, the separation membrane 150 of the present invention can be used without particular limitations as long as it is a material that is normally used as a separation membrane 150 in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte while having excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, for example, porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. In addition, ordinary porous nonwoven fabrics, for example, nonwoven fabrics made from high melting point glass fibers, polyethylene terephthalate fibers, etc., can also be used. Of course, in addition to the materials described above, the separation membrane 150 can also be manufactured using polymers with high heat resistance. Furthermore, the separation membrane 150 of the present invention may be a porous SRS (Safety-Reinforcing Separators) membrane with a composite porous structure of inorganic materials. In a specific example, the SRS separation membrane can be manufactured using inorganic particles and a binder polymer as active layer components on a separation membrane substrate of the polyolefin series or polyester series. Furthermore, the separation membrane 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] On the other hand, the separation sheet 160 of the present invention may also be composed of any one or more mixtures selected from the materials described above.

[0052] Furthermore, the corona surface treatment source can be air, oxygen (O2), or nitrogen (N2). Corona surface treatment can achieve a significant improvement in wettability through the synergistic effect of physical surface modification by the discharge itself and chemical surface modification by functional group formation. Such chemical surface modification occurs when high-energy electrons and ions collide with the separation membrane 150 substrate, generating radicals and ions. These then react with the surrounding air, oxygen, nitrogen, ozone, and moisture, introducing polar functional groups such as carbonyl groups, carboxyl groups, hydroxyl groups, and cyano groups, thus causing chemical surface modification.

[0053] Furthermore, the corona surface treatment source can also perform corona treatment using a plasma containing polymers. That is, when high-energy particles placed in a plasma state collide with the surface of the separation membrane 150 substrate, the energy is transferred to the surface of the collisioned separation membrane 150, and the separation membrane 150 can be chemically or physically activated to improve the adhesion between the polymer mixture layers.

[0054] On the other hand, the above-mentioned binder polymer mixture may contain porous inorganic fillers and binder polymers. By adding inorganic fillers to the binder polymer mixture to increase the mechanical strength of the separation membrane 150, the safety of the battery against external forces can be ensured. In such a separation membrane 150, the inorganic fillers are connected and fixed by the binder polymer, and the interstitial volume between the inorganic fillers forms a heat-resistant porous structure, thereby simultaneously improving the electrochemical safety and performance of the battery.

[0055] The concentration of the inorganic filler can be 60-90% by weight, preferably 70-80% by weight, based on the weight of the polymer mixture layer. If the concentration of the inorganic filler is too low, the desired degree 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 the excess inorganic components, which can lead to a decrease in ionic conductivity and an increase in internal resistance.

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

[0057] The separation membrane 250 of the present invention has a structure in which bonded portions 251 and unbonded portions 252 are arranged alternately, and includes a third bonded portion located between a first bonded portion 251a and a second bonded portion 251b, where there may be n third bonded portions (n ​​is an integer of 1 or more). That is, the separation membrane 250 may include a third bonded portion 251c between a first bonded portion 251a formed by corona surface treatment on the edge region where the tab of the positive electrode 230 (positive electrode tab 231) is located, and a second bonded portion 251b formed by corona surface treatment on the edge region where the negative electrode tab 241 is located, where there may be one or more third bonded portions 251c. Figure 7 shows, but is not limited to, an electrode assembly 200 in which one third bonded portion 251c is formed between the first bonded portion 251a and the second bonded portion 251b. By forming a third adhesive portion 251c on the surface of the separation membrane 250 in this manner, the interfacial adhesion between the separation membrane 250 and the electrode can be increased not only in the edge region of the separation membrane 250 but also in the central region. However, if the area of ​​the third adhesive portion 251c is too large or the number of third adhesive portions 251c is too large, the electrolyte impregnation may decrease, so it is preferable to form the third adhesive portion 251c appropriately according to the purpose.

[0058] Figure 9 is a schematic diagram showing a plasma generator for corona treatment of the surface of a separation membrane according to one embodiment of the present invention. Referring to Figure 9, the separation membrane 150 that is corona surface treated by the plasma generator 170 is a separation membrane 150 inserted inside a unit cell. Figure 9 shows the corona treatment being performed on one side of the separation membrane 150, but it is not limited to this, and both sides of the separation membrane 150 can be corona surface treated.

[0059] In a specific example of the present invention, the corona surface treatment is performed by charging the surface of the separation film 150 using a plasma generator 170. In one example, the apparatus for corona treating the surface of the separation film 150 may include a roller section 171 including a metal member 172, and a plasma generating section 173 positioned away from the roller section 171, which generates plasma through interaction with the metal member 172 and irradiates the surface of the separation film 150. The plasma generating section 173 generates plasma through interaction with the metal member 172 at a distance from the separation film 150 and irradiates the surface of the separation film 150. One form 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 positioned at a distance from the roller unit 171, an electrode member 175 coupled to the main body 174 and generating 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 that fixes the electrode member 175 to the main body 174 or moves the position of the electrode member 175 in a direction perpendicular to the transport direction of the separation membrane 150 (TD direction).

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

[0061] The electrode members 175 are arranged on the outer surface of the main body 174 corresponding to the transport direction (MD direction) of the separation membrane 150, and may consist of multiple members arranged in a direction perpendicular to the transport direction (TD direction) of the separation membrane 150. At least one pair of electrode members 175 must be provided to perform corona surface treatment on the edges located on both sides of the transport direction (MD direction) of the separation membrane 150, and additional electrode members 175 may be provided as needed to perform corona surface treatment on areas other than the edges located on both sides. By providing multiple electrode members in this way, 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 since plasma is not generated on the surface of the separation membrane 150 where there are no electrode members 175, an unadhesive layer is formed, which can form a stripe-like patterned adhesive layer.

[0062] The electrode member 175 may, in specific examples, be a corona discharge electrode. By interacting with the metal member 172 via the corona discharge electrode, plasma can be stably generated, and corona surface treatment can be performed on the surface of the separation film 150.

[0063] The guide member 176 can fix a plurality of electrode members 175 to the main body 174, and each of the plurality of electrode members 175 can be moved in a direction perpendicular to the transport direction of the separation membrane 150 (TD direction). In a specific example, the guide member 176 may include a guide groove (not shown) formed to be long in a direction perpendicular to the transport direction of the separation membrane 150 (TD direction), and a fixing member (not shown) for fastening and fixing the electrode members 175 to the guide groove. The electrode members 175 are detachable from the guide groove and have a structure that allows them to slide along the guide groove and change their position. Since the electrode members 175 can be detached from the guide groove, the number of electrode members 175 can be adjusted, and since the electrode members 175 can slide along the guide groove, the position of the electrode members 175 can be adjusted according to the application to adjust the position and pattern width of the adhesive layer formed on the surface of the separation membrane 150.

[0064] On the other hand, the guide member 176 may include a display member (not shown) on its surface with a scale marked in a direction perpendicular to the transport direction of the separation film 150 (TD direction). The position of the electrode member 175 can be accurately confirmed via 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, 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 uniform corona surface treatment on the surface of the separation film, and if it exceeds 3.0 kV, it may be difficult to operate the corona generator when performing corona treatment in a fine pattern, so it is preferable that the discharge be within the above range.

[0066] Furthermore, the discharge rate during corona surface treatment is 30-300 W·min / m 2 It can be in the range of 100-200 W·min / m², preferably 100-200 W·min / m². 2 It can be within this range. The discharge rate is 30 W·min / m 2 If the value is less than 300 W·min / m², it may be difficult to achieve the desired effect due to the difficulty in performing a fine surface treatment on the separation membrane surface. 2 If the discharge exceeds this range, it may alter the physical properties of the separation membrane; therefore, it is preferable that the discharge be within the above range.

[0067] Furthermore, the present invention 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 is an electrode assembly having a structure in which a positive electrode, a negative electrode, and a plurality of unit cells with a separation membrane interposed between the positive electrode and the negative electrode are wound on a sheet-like separation sheet, wherein the unit cells include A-type bicells and C-type bicells, the separation membrane of the unit cell includes an adhesive portion that has been corona surface-treated and an unadhesive portion that has not been corona surface-treated, the plurality of A-type bicells and C-type bicells are arranged alternately in the upper and lower halves with a separation sheet in between, and the separation sheet is not corona surface-treated.

[0068] The lithium secondary battery of the present invention has a structure in which the electrode assembly is sealed inside the battery case together with the electrolyte. The type of secondary battery is not particularly limited, but specific examples include 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-forming slurry containing an electrode active material is applied to an electrode current collector to form an electrode active material layer. 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, and the electrode active material may be a positive electrode active material or a negative electrode active material. Furthermore, the electrode slurry may further contain a conductive material and a binder in addition to the electrode active material.

[0071] In this invention, the positive electrode current collector is generally made with 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, calcined carbon, or aluminum or stainless steel with surface treatment of carbon, nickel, titanium, silver, etc. can be used. The current collector can also have fine irregularities formed on its surface to increase the adhesion strength of the positive electrode active material, and can take various forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0072] In the case of the negative electrode current collector sheet, it is generally made with a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, similar to the positive electrode current collector, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0073] In the present invention, the positive electrode active material is a substance capable of undergoing an electrochemical reaction, and contains two or more transition metals as a lithium transition metal oxide. For example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), etc. which are layered compounds substituted with one or more transition metals; lithium manganese oxide substituted with one or more transition metals; chemical formula LiNi 1-y M y O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn or Ga, contains one or more of the above elements, and 0.01 ≦ y ≦ 0.7) represented by lithium nickel-based oxide; Li 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., such as Li 1+z Ni b Mn c Co 1-(b+c+d) M d O (2-e) A e (where -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, A = F, P or Cl) represented by lithium nickel cobalt manganese composite oxide; chemical formula Li 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 such, but are not limited thereto.

[0074] The negative electrode active material is, for example, carbon such as graphitized 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 at 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 chemical changes 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 above-mentioned binder is a component that helps to bond the active material to conductive materials and to the current collector, and is usually added at a concentration of 1 to 30% by weight based on the total weight of the mixture containing the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0077] On the other hand, such electrode slurries can be manufactured by dissolving electrode active materials, conductive materials, binders, etc., in a solvent. The solvent is not particularly limited in type as long as it can disperse the electrode active materials, etc., and either aqueous or non-aqueous solvents 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 of these alone or a mixture of two or more can be used. The amount of solvent used is not particularly limited, as long as it can be adjusted so that the slurry has a suitable viscosity, taking into consideration the slurry coating thickness, production yield, workability, etc.

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

[0079] As an organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move is not particularly limited and can be used. Specifically, the above organic solvents may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; and carbonate 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 more preferably are mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate).

[0081] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the lithium salt can 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, etc. 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 components of the electrolyte described above, the electrolyte may also contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be present in an amount of 0.1 to 5% by weight relative to the total weight of the electrolyte.

[0083] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly by placing a separation membrane between the positive electrode and the negative electrode, and then injecting an electrolyte after placing the electrode assembly in a cylindrical or rectangular battery case. Alternatively, the electrode assembly can be manufactured by stacking the electrode assemblies, impregnating them with an electrolyte, and then sealing the resulting product in a battery case.

[0084] When manufacturing the lithium secondary battery of the present invention, the electrode assembly may be dried to remove one or more organic solvents selected from the group consisting of N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate, which were used during the production of the positive electrode. If an electrolyte with the same components as the organic solvent used during the production of the positive electrode is used, the step of drying the electrode assembly may be omitted.

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

[0086] The battery case can be one of those commonly used in this field, and there are no restrictions on its external shape depending on the battery's application; for example, it can be cylindrical, rectangular, pouch-type, or coin-type, using a can.

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

[0088] Furthermore, the present invention provides a method for manufacturing an electrode assembly. Descriptions that overlap with the above-mentioned detailed description of the electrode assembly may be omitted, and all specific details are referenced.

[0089] In one example, the 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 having a separation membrane interposed between the positive electrode and the negative electrode are wound on a sheet-like separation sheet, and includes the steps of: surface treatment by performing corona discharge on one or both sides of a separation membrane substrate; stacking a positive electrode sheet and a negative electrode sheet with a corona discharge-treated separation membrane interposed between them, cutting them to a predetermined size to manufacture unit cells including A-type bicells and C-type bicells; and positioning a plurality of unit cells on a sheet-like separation sheet, 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 arranged alternately above and below with the separation sheet in between, wherein the separation membrane of the unit cell includes an adhesive portion that has been corona surface-treated and an unadhesive portion that has not been corona surface-treated, and the separation sheet is not corona surface-treated.

[0090] The step of surface treating one or both sides of the separation membrane substrate by performing corona discharge involves transporting the separation membrane substrate by a roller section including a metal member, and generating plasma on the surface of the separation membrane substrate through interaction with the metal member from a plasma generation section positioned separately from the roller section to form an adhesive layer. In a specific example, the plasma generator includes an electrode member, and generates plasma through interaction between the electrode member and the metal member. In this case, the electrode member may consist of a corona discharge electrode. An adhesive layer is formed only on the separation membrane surface located between the electrode member and the metal member, and since no plasma is generated on the separation membrane surface where there is no electrode member, an unadhesive layer is formed, which can form a stripe-like patterned adhesive layer.

[0091] The step of manufacturing a unit cell including the above-mentioned Type A bicell and Type C bicell involves stacking each positive electrode substrate, negative electrode substrate, and corona-surface-treated separation membrane substrate, which are transported by rollers, to match a Type A bicell structure (a structure in which positive electrode, separation membrane, negative electrode, separation membrane, and positive electrode are stacked sequentially) or a Type C bicell structure (a structure in which negative electrode, separation membrane, positive electrode, separation membrane, and negative electrode are stacked sequentially), cutting them to a predetermined size, and heat-sealing them using a laminator or heat press to manufacture a unit cell such as a Type A bicell or a Type C bicell.

[0092] The step of manufacturing the above electrode assembly involves positioning multiple 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 arranged alternately above and below each other with the separation sheet in between. An electrode assembly can be manufactured in which an A-type bicell is located in the center, after being wound up by positioning an A-type bicell at the starting point of winding and arranging them sequentially in a repeating pattern such as C-type bicell, C-type bicell, A-type bicell, C-type bicell, C-type bicell, and so on. Alternatively, an electrode assembly can be manufactured in which a C-type bicell is located in the center, after being wound up by positioning a C-type bicell at the starting point of winding and arranging them sequentially in a repeating pattern such as A-type bicell, A-type bicell, C-type bicell, C-type bicell, and so on.

[0093] On the other hand, the separation sheet is not subjected to corona surface treatment. Since the probability of the separation sheet bending due to flow when stacked with the unit cell is lower than the probability of the separation membrane inside the unit cell bending, the separation sheet is not subjected to corona surface treatment in order to improve electrolyte impregnation rather than to increase the interfacial adhesion between the separation sheet and the electrodes of the unit cell.

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

[0095] In the step of surface-treating one or both sides of the separation membrane substrate by performing corona discharge, the edges on both sides in the direction in which the separation membrane is transported (MD direction) correspond to positions that face the electrode tabs inside the unit cell that are subsequently manufactured, both above and below. Therefore, by performing corona surface treatment on the edges on both sides in the direction in which the separation membrane is transported (MD direction) during the corona surface treatment of the separation membrane substrate, the adhesion between the electrode edge where the electrode tab of the unit cell is subsequently located and the edge region of the separation membrane facing it can be improved.

[0096] In another example, in the method for manufacturing an electrode assembly according to the present invention, the separation membrane has a structure in which bonded portions and unbonded portions are arranged alternately, and includes a third bonded portion located between a first bonded portion and a second bonded portion, and the electrode assembly may consist of n third bonded portions (where n is an integer of 1 or more). To improve the adhesive strength between the separation membrane and the electrode, one or more third bonded portions may be formed between the first bonded portion and the second bonded portion. The number of third bonded portions is not particularly limited, but can be set according to the purpose considering the impregnation properties of the electrolyte. [Explanation of symbols]

[0097] 1, 100, 200: Electrode assembly 10, 110, 210: Type A Buycell 20, 120, 220: Type C Buycell 30, 130, 230: Positive electrode 40, 140, 240: negative electrode 50, 150, 250: Separation membrane 60, 160, 260: Separation sheet 131, 231: Positive 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: Metal components 173: Plasma generation unit 174: Main unit 175: Electrode material 176: Guide member 251c: 3rd adhesive part

Claims

1. A unit cell comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode is stacked in a number of n units (where n is an integer of 2 or more), and a separation sheet is placed between the unit cells. The separation membrane interposed within the unit cell includes a corona-surface-treated adhesive portion that adheres to the positive electrode or the negative electrode and an unadhered portion that is not corona-surface-treated. The separation sheet has a structure that is not subjected to corona surface treatment. The aforementioned unit cell is, A positive electrode tab formed extending in one direction of the positive electrode, The negative electrode tab is formed extending in one direction from the negative electrode, The separation membrane is The edge region where the positive electrode tab is located is a first adhesive portion that has been corona surface treated, An electrode assembly comprising a second adhesive portion, the edge region in which the negative electrode tab is located, which is corona surface treated.

2. The electrode assembly according to claim 1, wherein the separation sheet has a structure in which it is wound up while enclosing the unit cells, passing through the stacked unit cells.

3. The electrode assembly according to claim 1, wherein the surface of the separation membrane has a structure in which the bonded portion and the unbonded portion are arranged alternately with respect to each other.

4. The electrode assembly according to claim 1, wherein the adhesive portion is formed on one or both sides of the separation membrane.

5. The electrode assembly according to claim 1, wherein the area on which the adhesive portion is formed is in the range of 10% to 70% of the area of ​​the separation membrane.

6. The adhesive portion forms a pattern, The electrode assembly according to claim 1, wherein the pattern is one or more of the following: strip-shaped, grid-shaped, dot-shaped, and polygonal.

7. A secondary battery comprising an electrode assembly according to any one of claims 1 to 6.

8. The secondary battery according to claim 7, wherein the secondary battery is a pouch-type secondary battery.

9. A method for manufacturing an electrode assembly for a secondary battery, A step of surface treatment by performing corona discharge on one or both sides of the separation membrane, The steps of forming a unit cell including a positive electrode, a negative electrode, and the separation membrane interposed between the positive electrode and the negative electrode, The process includes the steps of: positioning n units (where n is an integer of 2 or more) on a sheet-like separation sheet, and winding the separation sheet in one direction to manufacture an electrode assembly; The separation membrane interposed within the unit cell includes a corona-surface-treated adhesive portion that adheres to the positive electrode or the negative electrode and an unadhered portion that does not undergo corona surface treatment. The aforementioned separation sheet has a structure that does not undergo corona surface treatment. The aforementioned unit cell is, A positive electrode tab formed extending in one direction of the positive electrode, The negative electrode tab is formed extending in one direction from the negative electrode, The separation membrane is The edge region where the positive electrode tab is located is a first adhesive portion that has been corona surface treated, A method for manufacturing an electrode assembly, comprising: a second adhesive portion, the edge region in which the negative electrode tab is located, which is corona surface treated; and a method for manufacturing an electrode assembly.

10. The aforementioned surface treatment step is, A method for manufacturing an electrode assembly according to claim 9, wherein the surface of the separation membrane is charged via a plasma generator.

11. A method for manufacturing an electrode assembly according to claim 9, wherein the discharge range during corona discharge is in the range of 1.0 to 3.0 kV.

12. During corona discharge, the discharge rate is 30-300 W-min / m ２ A method for manufacturing an electrode assembly according to any one of claims 10 to 11, which falls within the range of claims 10 to 11.

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