Pouch film for secondary battery, method for manufacturing pouch film and pouch-type secondary battery

Abstract

A pouch film for a secondary battery according to one embodiment of the present disclosure comprises: an opaque portion disposed on both edges based on the longitudinal direction of the pouch film; and a transparent portion disposed between the opaque portions, wherein the length of the transparent portion may be 20% or more and less than 70% based on the total length of the pouch film.

Description

Technology Field

[0001] The present disclosure relates to a pouch film for a secondary battery, a method for manufacturing a pouch film, and a pouch-type secondary battery. Background Technology

[0002] Recently, research on electric vehicles (EVs) capable of replacing fossil fuel-based vehicles, which are one of the major causes of air pollution, is actively underway, and the demand for secondary batteries with high discharge voltage and output stability as a power source for these EVs is increasing.

[0003] Secondary batteries are classified into pouch, cylindrical, and prismatic types depending on the type of outer casing. Among these, pouch-type secondary batteries, in which the electrode assembly is housed within a pouch case, possess several advantages, including low manufacturing costs and the ease of constructing high-capacity battery packs by connecting multiple unit cells in series and / or parallel; consequently, research and development in this area are actively underway. Accordingly, there is a need for research on pouches that are economical, ensure stability, and offer high utility in the manufacturing and usage processes of secondary batteries. The problem to be solved

[0004] One aspect of the present disclosure is to provide an economical and stable pouch film.

[0005] One aspect of the present disclosure is to provide a pouch film capable of internal inspection of a secondary battery.

[0006] One aspect of the present disclosure is to provide an economical and stable pouch-type secondary battery.

[0007] One aspect of the present disclosure is to provide a pouch-type secondary battery with internal verification capabilities. means of solving the problem

[0008] A pouch film for a secondary battery according to one embodiment of the present disclosure comprises: an opaque portion disposed on both edges based on the longitudinal direction of the pouch film; and a transparent portion disposed between the opaque portions, wherein the length of the transparent portion may be 20% or more and less than 70% based on the total length of the pouch film.

[0009] The above opaque and transparent parts may each include an inner resin layer and an outer resin layer.

[0010] The above internal resin layer may include at least one selected from the group consisting of polypropylene, acid-modified polypropylene, polyethylene, and polycarbonate.

[0011] The above outer resin layer may include at least one selected from the group consisting of polyethylene terephthalate, nylon, polyethylene naphthalate, and polyurethane.

[0012] The above opaque portion may include a metal layer.

[0013] The above opaque portion may further include a metal layer between the inner resin layer and the outer resin layer.

[0014] The metal layer may include at least one selected from the group consisting of aluminum (Al), iron (Fe), chromium (Cr), nickel (Ni), copper (Cu), silver (Ag), platinum (Pt) and alloys thereof.

[0015] The thickness ratio of the outer resin layer and the metal layer included in the opaque part may be 1:2 to 1:1.

[0016] The above transparent part may not include a metal layer.

[0017] The above transparent part may have a light transmittance of 85% or more.

[0018] The thickness ratio of the outer resin layer included in the opaque part and the outer resin layer included in the transparent part may be 3:10 to 4:7.

[0019] A method for manufacturing a pouch film for a secondary battery according to one embodiment of the present disclosure comprises: an opaque portion disposed on both edges based on the longitudinal direction of the pouch film; and a transparent portion disposed between the opaque portions, wherein the length of the transparent portion may be 20% or more and less than 70% based on the total length of the pouch film.

[0020] The above method for manufacturing a pouch film for a secondary battery may include the steps of: forming an outer resin layer; laminating a metal layer on both edges of the outer resin layer with respect to the length direction of the outer resin layer; and laminating an inner resin layer on the outer resin layer and the metal layer.

[0021] In the step of laminating the metal layer, the length of the portion of the outer resin layer where the metal layer is not laminated may be 20% or more and less than 70% based on the total length of the outer resin layer.

[0022] The above lamination can be performed by at least one method selected from the group consisting of dry lamination, extrusion lamination, heat fusion, adhesive lamination, and compression lamination.

[0023] A pouch-type secondary battery according to one embodiment of the present disclosure comprises: an electrode assembly; and a pouch outer material housing the electrode assembly, wherein the pouch outer material comprises: an opaque portion disposed on both edges based on the longitudinal direction of the pouch outer material; and a transparent portion disposed between the opaque portions, and the length of the transparent portion may be 20% or more and less than 70% based on the total length of the pouch outer material.

[0024] The above pouch outer material may include a storage portion in which an electrode assembly is stored and a sealing portion that seals the outer surface of the storage portion.

[0025] The length (a) of the portion where the storage portion and the opaque portion overlap may be greater than or equal to the depth (b) of the storage portion.

[0026] The length (c) of the sealing portion may be at least 1.5 times the depth (b) of the storage portion. Effects of the invention

[0027] According to one embodiment of the present disclosure, the manufacturing cost of a pouch film can be reduced.

[0028] According to one embodiment of the present disclosure, the stability of the pouch film can be ensured.

[0029] According to one embodiment of the present disclosure, a pouch film capable of internal verification of a secondary battery can be provided.

[0030] According to one embodiment of the present disclosure, the manufacturing cost of a pouch-type secondary battery can be reduced.

[0031] According to one embodiment of the present disclosure, the stability of a pouch-type secondary battery can be secured.

[0032] According to one embodiment of the present disclosure, a pouch-type secondary battery capable of internal verification can be provided. Brief explanation of the drawing

[0033] FIG. 1 is a plan view schematically showing the shape of a pouch film according to one embodiment of the present disclosure as viewed from the top surface. FIG. 2 is a cross-sectional view schematically showing a cross-section of a pouch film according to one embodiment of the present disclosure. FIG. 3 is a cross-sectional view schematically illustrating the lamination process of a pouch film according to one embodiment of the present disclosure. FIG. 4 is a plan view schematically showing the shape of a pouch-type secondary battery according to one embodiment of the present disclosure as viewed from the top surface. FIG. 5 is a plan view schematically showing the shape of a pouch-type secondary battery according to one embodiment of the present disclosure as viewed from the side. Specific details for implementing the invention

[0034] Hereinafter, the technology disclosed in this specification and its embodiments are described in detail with reference to the attached drawings. However, the embodiments of the technology may be modified in various different forms, and their scope is not limited to the embodiments described below. Furthermore, the technology disclosed in this specification may not only be applied in a limited manner to the configurations of the embodiments described below, but may also be configured by selectively combining all or part of each embodiment to allow for various modifications.

[0035] Pouch film for secondary batteries

[0036] A pouch film (100) for a secondary battery according to one embodiment of the present disclosure comprises: an opaque portion (11) disposed on both edges based on the length direction of the pouch film; and a transparent portion (21) disposed between the opaque portions, wherein the length of the transparent portion may be 20% or more and less than 70% based on the total length of the pouch film.

[0037] The above pouch film may include opaque portions disposed at both edges and transparent portions disposed between the opaque portions. Accordingly, the condition of the electrodes, electrolyte, etc. inside the battery can be easily observed and evaluated through the transparent portions without disassembling the pouch-type secondary battery. In addition, the manufacturing cost of the pouch film can be reduced by manufacturing the transparent portions at a relatively lower cost compared to the opaque portions. Furthermore, by adjusting the length of the transparent portions to be between 20% and less than 70% of the total length of the pouch film, ease of internal observation can be ensured, while simultaneously ensuring mechanical stability of vulnerable parts of the pouch outer material (e.g., corner portions of the housing portion molded to accommodate the electrode assembly) during the manufacturing of the pouch-type secondary battery.

[0038] Hereinafter, the pouch film is described in detail with reference to FIGS. 1 and FIGS. 2.

[0039] FIG. 1 is a plan view schematically showing the shape of a pouch film according to one embodiment of the present disclosure as viewed from the top surface.

[0040] The above pouch film may include opaque portions disposed at both edges based on the length direction of the pouch film and transparent portions disposed between the opaque portions. The length direction of the pouch film is indicated by the x-axis direction of FIG. 1 and may refer to the direction in which electrode tabs (not shown) are connected during the manufacture of a pouch-type secondary battery. In the following description of the components of the pouch film, length may refer to the length measured based on the length direction of the pouch film. The area between the opaque portions, which is the area where the transparent portion is disposed, may refer to the remaining area of ​​the pouch film excluding the area where the opaque portion is disposed.

[0041] The length of the transparent portion may be 20% or more and less than 70% based on the total length of the pouch film. For example, the length of the transparent portion may be 30% or more and less than 60%, and 35% or more and 56% or less based on the total length of the pouch film.

[0042] If the length of the transparent portion is less than 20% of the total length of the pouch film, the area of ​​the transparent portion disposed on the pouch film is small, making it difficult to observe the interior of the pouch-type secondary battery. Additionally, it may be difficult to reduce the manufacturing cost of the pouch film. If the length of the transparent portion is 70% or more of the total length of the pouch film, it may be difficult to ensure mechanical stability of the vulnerable portion of the pouch outer material when manufacturing the pouch-type secondary battery.

[0043] FIG. 2 is a cross-sectional view schematically showing a cross-section of a pouch film according to one embodiment of the present disclosure.

[0044] The opaque portion (11) and the transparent portion (21) may each include an inner resin layer (31) and an outer resin layer (33). The inner resin layer and the outer resin layer are transparent, and the specific transparency is not limited as long as it is easy to observe the interior by passing through the resin layer. For example, the light transmittance of the inner resin layer and the outer resin layer may be 85% or higher. More specifically, the light transmittance of the inner resin layer and the outer resin layer may be 90% or higher. The method of measuring the light transmittance is not limited. For example, the method of measuring the light transmittance may be measured using a visible light transmittance meter at a wavelength of 550 nm.

[0045] The inner resin layer may be disposed on the inner side of the pouch outer material in which the electrode assembly is housed during the manufacture of a pouch-type secondary battery. The material of the inner resin layer is not particularly limited as long as it has excellent water resistance, electrolyte resistance, heat resistance, etc., and is easy to mold and seal. In one embodiment, the inner resin layer may include at least one selected from the group consisting of polypropylene, acid-modified polypropylene, polyethylene, and polycarbonate.

[0046] The specific form of the internal resin layer is not limited. For example, the internal resin layer may be an acid-modified polypropylene (PPA) layer that facilitates metal adhesion laminated on a sealant layer that facilitates sealing.

[0047] The above-mentioned outer resin layer may be disposed on the outer surface of the pouch outer material in which the electrode assembly is housed during the manufacture of a pouch-type secondary battery. The material of the above-mentioned outer resin layer is not particularly limited as long as it has excellent water resistance, insulation, heat resistance, surface rigidity, etc., and is easy to mold. In one embodiment, the above-mentioned outer resin layer may include at least one selected from the group consisting of polyethylene terephthalate, nylon, polyethylene naphthalate, and polyurethane.

[0048] The specific form of the above-mentioned outer resin layer is not limited. For example, the outer resin layer may be a first outer resin layer having excellent heat resistance and easy molding, and a second outer resin layer having excellent surface rigidity, bonded together by an adhesive layer.

[0049] In one embodiment, the opaque portion (11) may include a metal layer (32). By including the metal layer, the opaque portion can secure mechanical strength. Accordingly, the mechanical strength of the pouch film can be improved, thereby ensuring mechanical stability of the vulnerable portion of the pouch outer material when manufacturing a pouch-type secondary battery.

[0050] In one embodiment, the opaque portion (11) may further include a metal layer (32) between the inner resin layer (31) and the outer resin layer (33). By placing the metal layer between the inner resin layer and the outer resin layer, corrosion and mechanical damage to the metal layer can be prevented, thereby ensuring the stability of the pouch film. The material of the metal layer is not particularly limited as long as it has excellent mechanical strength, water resistance, etc., and is easy to mold. In one embodiment, the metal layer may include at least one selected from the group consisting of aluminum (Al), iron (Fe), chromium (Cr), nickel (Ni), copper (Cu), silver (Ag), platinum (Pt), and alloys thereof.

[0051] In one embodiment, the ratio of the thickness of the outer resin layer and the metal layer included in the opaque part may be 1:2 to 1:1. If the ratio of the thickness of the outer resin layer to the thickness of the metal layer included in the opaque part is less than 0.5, the thickness of the outer resin layer may not be sufficiently secured, so insulation may not be secured or it may be difficult to prevent damage to the metal layer. If the ratio of the thickness of the outer resin layer to the thickness of the metal layer included in the opaque part exceeds 1, the thickness of the metal layer may not be sufficiently secured, so it may be difficult to secure mechanical stability of the vulnerable part of the pouch outer material when manufacturing a pouch-type secondary battery.

[0052] In one embodiment, the transparent portion may not include a metal layer. By including only the outer resin layer and the inner resin layer and not the opaque metal layer, the transparent portion can ensure ease of internal observation. Additionally, by using less of the metal layer, which has a relatively high manufacturing cost during pouch film manufacturing, the manufacturing cost of the pouch film can be reduced.

[0053] The transparency of the transparent portion is not specifically limited as long as it is easy to observe the interior by passing through the transparent portion. For example, the light transmittance of the transparent portion may be 85% or higher. More specifically, the light transmittance of the transparent portion may be 90% or higher. The method of measuring the light transmittance is not limited. For example, the method of measuring the light transmittance may be measured using a visible light transmittance meter at a wavelength of 550 nm.

[0054] The thickness of the outer resin layer included in the opaque portion may be thinner than the thickness of the outer resin layer included in the transparent portion. Therefore, even if the opaque portion further includes a metal layer between the outer resin layer and the inner resin layer and the transparent portion does not include a metal layer, the total thickness of the pouch film may be constant.

[0055] In one embodiment, the ratio of the thickness of the outer resin layer included in the opaque part to the thickness of the outer resin layer included in the transparent part may be 3:10 to 4:7. If the ratio of the thickness of the outer resin layer included in the opaque part to the thickness of the outer resin layer included in the transparent part is less than 0.3, the thickness of the outer resin layer included in the opaque part is not sufficiently secured, so insulation may not be secured or it may be difficult to prevent damage to the metal layer. If the ratio of the thickness of the outer resin layer included in the opaque part to the thickness of the outer resin layer included in the transparent part exceeds 0.57, the thickness of the metal layer laminated on the outer resin layer of the opaque part cannot be sufficiently secured, so it may be difficult to secure mechanical stability of the vulnerable part of the pouch outer material when manufacturing a pouch-type secondary battery.

[0056] Method for manufacturing pouch film

[0057] A method for manufacturing a pouch film for a secondary battery according to one embodiment of the present disclosure comprises: opaque portions disposed on both edges based on the longitudinal direction of the pouch film; and transparent portions disposed between the opaque portions, wherein the length of the transparent portions may be 20% or more and less than 70% based on the total length of the pouch film.

[0058] FIG. 3 is a cross-sectional view schematically illustrating the lamination process of a pouch film according to one embodiment of the present disclosure.

[0059] In one embodiment, the method for manufacturing the pouch film may include the steps of: forming an outer resin layer; laminating a metal layer on both edges of the outer resin layer with respect to the longitudinal direction of the outer resin layer; and laminating an inner resin layer on the outer resin layer and the metal layer. By laminating a metal layer only on both edges of the outer resin layer after forming the outer resin layer, an opaque portion including a metal layer and a transparent portion not including a metal layer can be formed. Accordingly, mechanical stability of the opaque portion including the metal layer can be secured, and ease of internal observation of the transparent portion not including the metal layer can be secured.

[0060] In one embodiment, in the step of laminating the metal layer, the length of the portion of the outer resin layer where the metal layer is not laminated may be 20% or more and less than 70% based on the total length of the outer resin layer. By adjusting the length of the portion where the metal layer is not laminated to within the above range, both mechanical strength and ease of internal observation of the pouch film can be secured. If the length of the portion where the metal layer is not laminated is less than 20% based on the total length of the outer resin layer, the area of ​​the transparent portion is not sufficiently secured, making it difficult to easily observe the interior of the pouch-type secondary battery and making it difficult to reduce manufacturing costs. If the length of the portion where the metal layer is not laminated is 70% or more based on the total length of the outer resin layer, the area of ​​the opaque portion containing the metal layer is not sufficiently secured, making it difficult to secure mechanical stability of the vulnerable portion of the pouch outer material.

[0061] The method of laminating the metal layer or the method of laminating the internal resin layer is not particularly limited. In one embodiment, the lamination may be performed by at least one method selected from the group consisting of dry lamination, extrusion lamination, thermal fusion, adhesive lamination, and compression lamination.

[0062] In the method for manufacturing the above pouch film, the components included in the transparent and opaque parts (e.g., the outer resin layer, inner resin layer, metal layer, and their specific material, shape, thickness, physical properties, etc.) can be applied in the same way as the pouch film described above, so a detailed description is omitted.

[0063] Pouch-type secondary battery

[0064] A pouch-type secondary battery (200) according to one embodiment of the present disclosure is a pouch-type secondary battery comprising an electrode assembly; and a pouch outer material that accommodates the electrode assembly, wherein the pouch outer material comprises an opaque portion (12) disposed on both edges based on the length direction of the pouch outer material; and a transparent portion (22) disposed between the opaque portions, and the length of the transparent portion may be 20% or more and less than 70% based on the total length of the pouch outer material.

[0065] The above pouch-type secondary battery may include opaque portions positioned at both edges along the longitudinal direction of the pouch outer material and transparent portions positioned between the opaque portions. Accordingly, the condition of the electrodes, electrolyte, etc. inside the battery can be easily observed and evaluated through the transparent portions without disassembling the pouch-type secondary battery. In addition, the manufacturing cost of the pouch-type secondary battery can be reduced by manufacturing the transparent portions at a relatively lower cost compared to the opaque portions. Furthermore, by adjusting the length of the transparent portions to be between 20% and less than 70% of the total length of the pouch outer material, ease of internal observation can be ensured, while simultaneously ensuring mechanical stability of vulnerable parts of the pouch outer material (e.g., corner portions of the housing portion molded to accommodate the electrode assembly).

[0066] FIG. 4 is a plan view schematically showing the shape of a pouch-type secondary battery according to one embodiment of the present disclosure as viewed from the top surface.

[0067] The above pouch outer material may include opaque portions positioned at both edges based on the length direction of the pouch outer material and transparent portions positioned between the opaque portions. The length direction of the above pouch outer material is indicated by the x-axis direction of FIG. 4 and may refer to the direction in which the electrode tab (60) is connected in the pouch-type secondary battery. In the following description of the components of the pouch outer material, length may refer to the length measured based on the length direction of the above pouch outer material. The area between the opaque portions, which is the area where the transparent portion is positioned, may refer to the remaining area of ​​the above pouch outer material excluding the area where the opaque portion is positioned.

[0068] The length of the transparent portion (22) may be 20% or more and less than 70% based on the total length of the pouch outer material. For example, the length of the transparent portion may be 25% or more and less than 60%, and 30% or more and less than 50% based on the total length of the pouch outer material.

[0069] If the length of the transparent portion is less than 20% of the total length of the pouch outer material, the area of ​​the transparent portion placed on the pouch outer material is small, making it difficult to observe the interior of the pouch-type secondary battery. In addition, it may be difficult to reduce the manufacturing cost of the pouch-type secondary battery. If the length of the transparent portion is 70% or more, it may be difficult to ensure mechanical stability of the vulnerable portion of the pouch outer material when manufacturing the pouch-type secondary battery.

[0070] In the above pouch-type secondary battery (200), the components included in the transparent portion (22) and the opaque portion (12) (e.g., the outer resin layer, inner resin layer, metal layer, and the specific material, shape, thickness, physical properties, etc.) can be applied in the same way as the pouch film (100) described above, so a detailed description is omitted.

[0071] In one embodiment, the pouch outer material may include a storage portion (40) in which an electrode assembly is stored and a sealing portion (50) that seals the outer surface of the storage portion.

[0072] FIG. 5 is a plan view schematically showing the shape of a pouch-type secondary battery according to one embodiment of the present disclosure as viewed from the side.

[0073] If the above-mentioned storage portion is molded to accommodate an electrode assembly, its shape is not limited. For example, in FIG. 5, the storage portion is shown as having the same depth in the vertical direction relative to the sealing portion, but it may have a shape with different depths in the vertical direction relative to the sealing portion, or it may have a cover portion shape in which no depth is formed in one direction.

[0074] In one embodiment, the length (a) of the portion where the storage portion and the opaque portion overlap may be greater than or equal to the depth (b) of the storage portion. The length (a) of the portion where the storage portion and the opaque portion overlap may refer to the sum of the lengths of the portions where the opaque portions on both sides overlap with the storage portion, based on the length direction of the pouch outer material (x-axis direction in FIG. 4). The depth (b) of the storage portion may refer to the total depth of the storage portion formed in the thickness direction of the pouch outer material (z-axis direction in FIG. 4) so ​​that the electrode assembly can be stored. If the length (a) of the portion where the storage portion and the opaque portion overlap is less than the depth (b) of the storage portion, the pouch metal layer may be excessively stretched during the pouch molding process, making it difficult to ensure mechanical stability of the vulnerable portion of the pouch outer material.

[0075] In one embodiment, the length (c) of the sealing portion may be 1.5 times or more the depth (b) of the storage portion. The length (c) of the sealing portion may refer to the length of either of the sealing portions located on both sides based on the longitudinal direction of the pouch outer material. If the length (c) of the sealing portion is less than 1.5 times the depth (b) of the storage portion, the pouch metal layer may be excessively stretched during the pouch molding process, making it difficult to secure mechanical stability of the vulnerable portion of the pouch outer material.

[0076] The structure of the electrode assembly above is not particularly limited. For example, the electrode assembly may have a structure comprising one or more unit cells, and the unit cells may include a positive electrode and a negative electrode.

[0077] The anode and cathode may each include a current collector; and a composite layer formed on at least one surface of the current collector. The type, thickness, etc., of the anode current collector and the cathode current collector are not particularly limited. For example, aluminum foil (Al-Foil) may be used as the anode current collector, and copper foil (Cu-Foil) may be used as the cathode current collector. Additionally, the thickness of the anode current collector and the cathode current collector may each be, for example, 10 to 50 μm.

[0078] The above positive electrode composite layer and negative electrode composite layer are active layers comprising an active material that substantially participates in the electrochemical reaction of a secondary battery, wherein the positive electrode composite layer comprises a positive active material and the negative electrode composite layer may comprise a negative active material.

[0079] The above-mentioned cathode active material is not particularly limited and may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0080] According to exemplary embodiments, the cathode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0081] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may comprise a layered structure or a crystalline structure represented by the following chemical formula 1.

[0082] [Chemical Formula 1]

[0083] Li x Ni a M b O 2+z

[0084] In the above chemical formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1 may be used. As described above, M may include Co, Mn, and / or Al.

[0085] The chemical structure represented by Chemical Formula 1 above represents the bonding relationships included within the layered or crystal structure of the cathode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn may be provided as the main active element of the cathode active material together with Ni. Chemical Formula 1 above is provided to express the bonding relationships of the main active elements and should be understood as encompassing the introduction and substitution of additional elements.

[0086] In one embodiment, auxiliary elements may be further included to enhance the chemical stability of the cathode active material or the layered structure / crystal structure by adding to the main active element. The auxiliary elements may be incorporated together within the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the range of the chemical structure represented by Chemical Formula 1.

[0087] The above auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The above auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the cathode active material together with Co or Mn, such as Al.

[0088] For example, the above-mentioned positive electrode active material or the above-mentioned lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0089] [Chemical Formula 1-1]

[0090] Li x Ni a M1 b1 M2 b2 O 2+z

[0091] In Chemical Formula 1-1, M1 may include Co, Mn and / or Al. M2 may include the auxiliary element described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0092] The above-described cathode active material may further include a coating element or a doping element. For example, elements substantially identical or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, any of the elements described above may be used alone or in combination of two or more as coating elements or doping elements.

[0093] The coating element or doping element may be present on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal composite oxide particles and be included within the bonding structure represented by Formula 1 or Formula 1-1.

[0094] The above-mentioned cathode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0095] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by adopting a high-Ni composition in the cathode active material as described above, a high-capacity cathode and a high-capacity lithium secondary battery can be provided.

[0096] However, as the Ni content increases, the long-term storage stability and lifespan stability of the anode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, lifespan stability and capacity retention characteristics can be improved through Mn while maintaining electrical conductivity by including Co.

[0097] The content of Ni in the above NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0098] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0099] In some embodiments, the positive electrode active material may include, for example, a Mn-rich active material having a chemical structure or crystal structure represented by Formula 2, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) active material, or a Co-less active material.

[0100] [Chemical Formula 2]

[0101] p[Li2MnO3]·(1-p)[Li q JO2]

[0102] Of chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0103] The above-mentioned negative electrode active material is not particularly limited and may include a material capable of adsorbing and desorbing lithium ions. For example, the above-mentioned negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber; lithium metal; lithium alloy; silicon (Si)-containing material or tin (Sn)-containing material.

[0104] Examples of the above-mentioned amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0105] Examples of the above-mentioned crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0106] The above lithium metal may be pure lithium metal or lithium metal with a protective layer formed thereon for inhibiting dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector may be used as a negative electrode active material layer. In one embodiment, a lithium thin film layer may be used as a negative electrode active material layer.

[0107] Examples of elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0108] The above silicon-containing material can provide increased capacity characteristics. The above silicon-containing material is Si, SiOx(0 <x<2), 탄소 코팅된 SiOx(0<x<2), 금속 도핑된 SiOx(0<x<2), 실리콘-탄소 복합체 등을 포함할 수 있다. 상기 금속은 리튬 및 / 또는 마그네슘을 포함할 수 있으며, 금속 도핑된 SiOx(0<x<2)는 금속 실리케이트를 포함할 수 있다.

[0109] The anode composite layer and the cathode composite layer may each further include a conductive material. The conductive material is not particularly limited and, for example, may be at least one selected from graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube (CNT); metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. If the anode composite layer further includes a conductive material, its content may, for example, be 0.1 to 5 weight% based on the total weight of the anode composite layer. Additionally, if the cathode composite layer further includes a conductive material, its content may, for example, be 0.1 to 5 weight% based on the total weight of the cathode composite layer.

[0110] The anode composite layer and the cathode composite layer may each further include a binder. The binder is not particularly limited. The binder included in the anode composite layer may, for example, be at least one selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), carboxymethylcellulose (CMC), ethylcellulose, acrylic resin, styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). Additionally, the binder included in the cathode composite layer may, for example, be a rubber-based binder such as styrene-butadiene rubber (SBR), fluororubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, silane rubber; and at least one selected from cellulose-based binders such as carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, and methylcellulose, or alkali metal salts thereof (Na, K, or Li). If the anode composite layer further includes a binder, the content thereof may be, for example, 0.1 to 5 weight% based on the total weight of the anode composite layer. Additionally, if the cathode composite layer further includes a binder, the content thereof may be, for example, 0.1 to 5 weight% based on the total weight of the cathode composite layer.

[0111] The unit cell according to the embodiments described above may not include a separator between the anode and the cathode, or it may further include a separator. If the unit cell further includes a separator, the separator may be a polyolefin-based polymer separator such as polyethylene or polypropylene, glass fiber, polyester, polytetrafluoroethylene, or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. Additionally, the separator may be coated with a composition containing ceramic components, etc., to ensure heat resistance or mechanical strength, and may optionally be composed of a single layer or a multilayer structure. A separator having the compounds, structures, etc. described above may be applied as the separator, but is not limited thereto.

[0112] The unit cell included in the pouch-type secondary battery according to the embodiments described above may further include a solid electrolyte. That is, the unit cell included in the pouch-type secondary battery may include a solid electrolyte without including a separator between the positive electrode and the negative electrode. The solid electrolyte is not particularly limited and, for example, may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a polymer-based solid electrolyte.

[0113] In the case where the pouch-type secondary battery according to the above-described embodiments does not further include a solid electrolyte, the secondary battery can be manufactured by housing a unit cell including the above-described positive and negative electrodes in a pouch, which is a battery case, and then injecting an electrolyte.

[0114] The above electrolyte may include an organic solvent and a lithium salt. The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used individually or in a mixture of two or more types. When two or more types are mixed, the mixing ratio can be appropriately adjusted according to the desired battery performance. The lithium salt is a substance that dissolves in the organic solvent and acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. As the lithium salt, known substances may be used at a concentration suitable for the purpose. If necessary, the above electrolyte may further include known solvents and known additives to improve charge / discharge characteristics, flame retardancy characteristics, etc.

[0115] Examples

[0116] In the following, embodiments of the present invention are further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present invention and are not intended to limit the appended claims. It is obvious to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and spirit of the present invention, and that such variations and modifications fall within the scope of the appended claims.

[0117] 1. Pouch film manufacturing

[0118] (1) Example 1

[0119] Transparent polyethylene terephthalate (PET) resin and nylon resin were passed through a roller and laminated to form an outer resin layer of a PET / nylon pouch film, wherein the thickness of the edges on both sides is 30 μm and the thickness of the central portion located between the edges is 70 μm. At this time, the length of the portion with a thickness of 70 μm in the outer resin layer was formed to be 35% of the total length of the outer resin layer.

[0120] Subsequently, the aluminum foil coated with the outer resin layer and adhesive was passed together through a roller to laminate an aluminum metal layer. At this time, the metal layer was laminated with a thickness of 40 μm only on both edges of the outer resin layer, which had a thickness of 30 μm.

[0121] Subsequently, transparent polypropylene (PP) and acid-treated polypropylene (PPa) resins were extruded and passed through a roller together with a laminate in which the outer resin layer and the metal layer were laminated to laminate an inner resin layer with a thickness of 80 μm. Accordingly, a pouch film was manufactured in which an opaque portion comprising an outer resin layer, a metal layer, and an inner resin layer is disposed at both edges, and a transparent portion comprising an outer resin layer and an inner resin layer is disposed between the opaque portions.

[0122] (2) Example 2

[0123] A pouch film was manufactured in the same manner as in Example 1, except that the length of the portion with a thickness of 70 μm in the outer resin layer was formed to be 56% of the total length of the outer resin layer.

[0124] (3) Comparative Example 1

[0125] A pouch film was manufactured in the same manner as in Example 1, except that the length of the portion with a thickness of 70 μm in the outer resin layer was formed to be 12% of the total length of the outer resin layer.

[0126] (4) Comparative Example 2

[0127] A pouch film was manufactured in the same manner as in Example 1, except that the length of the portion with a thickness of 70 μm in the outer resin layer was formed to be 74% of the total length of the outer resin layer.

[0128] (5) Comparative Example 3

[0129] A pouch film was manufactured in the same manner as in Example 1, except that the length of the portion with a thickness of 70 μm in the outer resin layer was formed to be 92% of the total length of the outer resin layer.

[0130] 2. Manufacturing of pouch-type secondary batteries

[0131] A pouch outer material was manufactured by forming a pouch film prepared according to the above examples and comparative examples using a pouch forming device. At this time, a first storage portion and a second storage portion were formed in the pouch outer material, each capable of covering and storing an electrode assembly from the upper and lower directions, and the sum of the total depths of the storage portions was 7.5 mm.

[0132] A cathode slurry containing 95 wt% of artificial graphite as a cathode active material was prepared, the cathode slurry was coated onto a copper foil (Cu-foil) with a thickness of 20 μm, dried at a temperature of 120°C, and then rolled to produce a cathode with a thickness of 150 μm. An anode slurry containing 94 wt% of LiCoO2 as an anode active material was prepared, the anode slurry was coated onto an aluminum foil (Al-foil) with a thickness of 20 μm, dried at a temperature of 120°C, and then rolled to produce an anode with a thickness of 150 μm. An electrode assembly was prepared by interposing a polyolefin separator between the anode and the cathode prepared according to the above.

[0133] Subsequently, the electrode assembly was housed in the pouch outer material, and an electrolyte solution in which 1M LiPF6 was dissolved in a solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) was injected. Subsequently, the outer surface of the housing portion was sealed to manufacture a pouch-type secondary battery. At this time, the length of the area in which the transparent portion is formed relative to the total length of the pouch outer material in the pouch-type secondary battery is shown in Table 1 below.

[0134] 3. Internal Observation and Stability Evaluation of Secondary Batteries

[0135] (1) Internal observation evaluation of secondary battery

[0136] The condition of the electrodes and electrolyte inside the battery was observed through a transparent portion formed in the outer casing of the pouch without disassembling the pouch-type secondary battery manufactured according to the above examples and comparative examples. At this time, the internal observation of the battery was performed by placing a 1,000-lumen (lm) LED light vertically with respect to the pouch-type secondary battery and fixing the distance between the light source and the sample at 30 centimeters (cm). As a result of the internal observation, ○ was indicated if the internal condition, such as the electrode surface and the remaining amount of electrolyte, was easy to check, and Х was indicated if it was difficult to check the condition.

[0137] (2) Tensile strength evaluation

[0138] The tensile strength of the pouch films prepared according to the above examples and comparative examples was measured using Universal Testing Machines (UTM) from Instron and is shown in Table 1 below.

[0139] (3) Stability evaluation during high-temperature storage

[0140] The pouch-type secondary battery prepared according to the above examples and comparative examples was charged at room temperature at a 1C rate with CC CV (4.2V, 0.05C cut-off) and then stored at a high temperature in a 60℃ oven for 4 weeks. At this time, if no crack was found in the corner portion of the electrode assembly housing of the pouch outer material, it was marked with ○, and if a crack was found, it was marked with ×, as shown in Table 1 below.

[0141] Transparent section length / Pouch film length (%) Transparent section length / Pouch exterior material length (%) Internal observation results of the secondary battery Tensile strength (N / mm²) 2 ) Stability during high-temperature storage Example 1 35 30 ○ 79.5 ○ Example 2 56 50 ○ 78.8 ○ Comparative Example 1 12 10 × 80.2 ○ Comparative Example 2 74 70 ○ 76.4 × Comparative Example 3 92 90 ○ 75.6 ×

[0142] Referring to Table 1, Examples 1 and 2, in which the length of the transparent portion formed on the pouch film satisfies a condition of being 20% ​​or more and less than 70% of the total length of the pouch film, and the length of the transparent portion formed on the formed pouch outer material also satisfies a condition of being 20% ​​or more and less than 70% of the total length of the pouch outer material, can be confirmed to have excellent tensile strength and stability during high-temperature storage, while also allowing for easy internal observation without disassembling the secondary battery. On the other hand, in Comparative Example 1, in which the length of the transparent portion formed on the pouch film is less than 20% of the total length of the pouch film and the length of the transparent portion formed on the formed pouch outer material is less than 20% of the total length of the pouch outer material, it can be confirmed that internal observation of the secondary battery is not easy. This indicates that it is difficult to observe the interior of the secondary battery without disassembling it because the area of ​​the transparent portion is not sufficiently secured.

[0143] In addition, in Comparative Examples 2 and 3, where the length of the transparent portion formed on the pouch film is 70% or more of the total length of the pouch film and the length of the transparent portion formed on the formed pouch outer material is 70% or more of the total length of the pouch outer material, it can be confirmed that the tensile strength and stability during high-temperature storage are not excellent. This indicates that the mechanical stability of the pouch outer material is not sufficiently secured because the area of ​​the transparent portion, which does not contain aluminum metal with high mechanical strength, is excessively large. Explanation of the symbols

[0144] 11, 12: Opaque parts 21, 22: Transparent part 31: Internal resin layer 32: Metal layer 33: External resin layer 40: Storage compartment 50: Sealing part 60: Electrode tab 100: Pouch film 200: Pouch-type secondary battery

Claims

Claim 1 A pouch film for a secondary battery comprising: opaque portions disposed on both edges based on the longitudinal direction of the pouch film; and transparent portions disposed between the opaque portions, wherein the length of the transparent portions is 20% or more and less than 70% based on the total length of the pouch film. Claim 2 A pouch film for a secondary battery according to claim 1, wherein the opaque portion and the transparent portion each comprise an inner resin layer and an outer resin layer. Claim 3 A pouch film for a secondary battery according to claim 2, wherein the inner resin layer comprises at least one selected from the group consisting of polypropylene, acid-modified polypropylene, polyethylene, and polycarbonate. Claim 4 A pouch film for a secondary battery according to claim 2, wherein the outer resin layer comprises at least one selected from the group consisting of polyethylene terephthalate, nylon, polyethylene naphthalate, and polyurethane. Claim 5 A pouch film for a secondary battery according to claim 1, wherein the opaque portion comprises a metal layer. Claim 6 A pouch film for a secondary battery according to paragraph 2, wherein the opaque portion further comprises a metal layer between the inner resin layer and the outer resin layer. Claim 7 A pouch film for a secondary battery according to claim 5 or 6, wherein the metal layer comprises at least one selected from the group consisting of aluminum (Al), iron (Fe), chromium (Cr), nickel (Ni), copper (Cu), silver (Ag), platinum (Pt), and alloys thereof. Claim 8 A pouch film for a secondary battery according to claim 6, wherein the thickness ratio of the outer resin layer and the metal layer included in the opaque portion is 1:2 to 1:

1. Claim 9 A pouch film for a secondary battery according to claim 1, wherein the transparent portion does not include a metal layer. Claim 10 A pouch film for a secondary battery according to claim 1, wherein the transparent portion has a light transmittance of 85% or more. Claim 11 A pouch film for a secondary battery according to claim 2, wherein the thickness ratio of the outer resin layer included in the opaque portion and the outer resin layer included in the transparent portion is 3:10 to 4:

7. Claim 12 A method for manufacturing a pouch film for a secondary battery, comprising: opaque portions disposed on both edges based on the longitudinal direction of the pouch film; and transparent portions disposed between the opaque portions, wherein the length of the transparent portions is 20% or more and less than 70% based on the total length of the pouch film. Claim 13 In claim 12, the method for manufacturing a pouch film for a secondary battery comprises: a step of forming an outer resin layer; a step of laminating a metal layer on both edges of the outer resin layer with respect to the length direction of the outer resin layer; and a step of laminating an inner resin layer on the outer resin layer and the metal layer. Claim 14 A method for manufacturing a pouch film for a secondary battery according to claim 13, wherein, in the step of laminating the metal layer, the length of the portion of the outer resin layer where the metal layer is not laminated is 20% or more and less than 70% based on the total length of the outer resin layer. Claim 15 A method for manufacturing a pouch film for a secondary battery according to claim 13, wherein the lamination is performed by at least one method selected from the group consisting of dry lamination, extrusion lamination, heat fusion, adhesive lamination, and compression lamination. Claim 16 A pouch-type secondary battery comprising: an electrode assembly; and a pouch outer material housing the electrode assembly, wherein the pouch outer material comprises: an opaque portion disposed on both edges based on the longitudinal direction of the pouch outer material; and a transparent portion disposed between the opaque portions, wherein the length of the transparent portion is 20% or more and less than 70% based on the total length of the pouch outer material. Claim 17 In claim 16, the pouch-type secondary battery comprises a storage portion in which an electrode assembly is housed and a sealing portion that seals the outer surface of the storage portion. Claim 18 A pouch-type secondary battery according to claim 17, wherein the length (a) of the portion where the storage portion and the opaque portion overlap is greater than or equal to the depth (b) of the storage portion. Claim 19 A pouch-type secondary battery according to claim 17, wherein the length (c) of the sealing portion is at least 1.5 times the depth (b) of the storage portion.

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