Film and battery pouch comprising same

Abstract

The present invention can provide a film having excellent electrolyte solution resistance, which can continuously and non-destructively discharge gas generated inside a battery not only under high-pressure conditions but also under low-pressure conditions, while effectively blocking external moisture and atmosphere (air) from entering the battery. The present invention can provide a pouch for a battery capable of further improving the stability and lifespan of the battery by including the film in at least a portion thereof.

Description

Technical Field

[0001] The present disclosure relates to a film and a battery pouch including the same. Background Art

[0002] Pouch-type batteries have attracted much attention due to their high energy density per unit weight, low price, easy modification, and ability to be stacked in a highly integrated manner.

[0003] Because pouch-type batteries use flexible exterior materials, improving safety is a primary research priority. Lithium secondary batteries, in particular, are susceptible to swelling, a phenomenon in which the battery expands due to abnormal operating conditions such as electrolyte decomposition, internal short circuits, overcharge conditions exceeding the allowable current and voltage, exposure to high temperatures, and deformation caused by drops or external impacts. If gas generation continues to increase (continuous swelling), the pouch's deformation can damage the exterior (forming holes), potentially leading to ignition or explosion.

[0004] Therefore, it is necessary to introduce a device that can discharge the gas generated in the battery to the outside. In one example, Patent Document 1 discloses a battery that forms a vent hole in a bag shell for discharging gas from the inside of the bag, and covers the vent hole with a vent cap that opens when the gas pressure in the shell reaches a threshold value, thereby ensuring quality and stability by maintaining the sealing of the pouch-type battery under normal circumstances and being able to quickly vent gas in the event of an accident. However, the battery of Patent Document 1 has the following defects: it cannot be reused after the vent cap is vented, does not include other alternative elements that can prevent accidents when the vent cap cannot be properly vented due to unexpected reasons in the event of an accident, and does not consider the problem of external moisture or atmosphere entering through the vent cap.

[0005] [Prior art literature]

[0006] [Patent Document]

[0007] (Patent Document 1) Korean Patent Application No. 2015-0034498 Summary of the Invention

[0008] Technical Purpose

[0009] The present disclosure provides a membrane that can continuously and non-destructively discharge gases generated in a secondary battery not only under high-pressure conditions but also under low-pressure conditions, while effectively blocking external moisture and atmosphere (air) from entering the secondary battery and having excellent electrolyte solution tolerance.

[0010] The present disclosure also provides a battery pouch that can further improve the stability and lifespan of a secondary battery by including the above-mentioned film in at least a portion thereof.

[0011] Technical Solution

[0012] One aspect of the present disclosure may relate to a membrane having different gas permeabilities on both sides to discharge the gas generated in the secondary battery to the outside and prevent external air and water vapor from penetrating into the interior of the secondary battery. From the side in contact with the interior of the secondary battery, the membrane comprises a protective layer, an active layer and a support layer. The protective layer comprises an amorphous perfluorinated polymer to have tolerance to the electrolyte solution of the secondary battery. Under the condition of a relative pressure value of 20 pounds force per square inch (psi), the ratio of the forward permeability of the gas generated in the secondary battery to the reverse permeability of the air is more than 20, wherein the forward direction is the direction from the inside of the secondary battery to the outside of the secondary battery, and the reverse direction is the direction from the outside of the secondary battery to the inside of the secondary battery.

[0013] In one embodiment, under the condition of a relative pressure value of 20psi, the forward permeability of the gas generated in the secondary battery of the membrane of the present invention can be 5 gas generation units (GPU) or more, under the condition of a relative pressure value of 40psi, the forward permeability of the gas generated in the secondary battery can be 10GPU or more, or under the condition of a relative pressure value of 50psi, the forward permeability of the gas generated in the secondary battery can be 15GPU or more.

[0014] In one embodiment, the reverse permeability of air of the membrane of the present disclosure may be less than 0.1 GPU at a relative pressure value of 15 psi, less than 0.5 GPU at a relative pressure value of 20 psi, or less than 1 GPU at a relative pressure value of 60 psi.

[0015] In one embodiment, the protective layer may further include at least one of polyimide, Nafion, or polydimethylsiloxane.

[0016] In one embodiment, the contact angle of the protective layer with respect to the electrolyte solution of the secondary battery may be 30° or greater.

[0017] In one embodiment, the active layer may absorb gas generated in the secondary battery and transport the gas to the outside.

[0018] In one embodiment, the active layer may include a cross-linked structure of cellulose and a compound including two or more carboxylic acids.

[0019] In one embodiment, the cross-linked structure of cellulose and the compound including two or more carboxylic acids may be represented by Formula 1 below.

[0020] [Formula 1]

[0021]

[0022] In the above formula 1, R1 to R4 may be the same or different and may each independently be hydrogen, deuterium, hydroxyl, substituted or unsubstituted alkyl, or substituted or unsubstituted alkoxy; Y1 may be a directly linked, substituted or unsubstituted alkylene, a substituted or unsubstituted alkenylene, a substituted or unsubstituted arylene, or a combination of substituents selected from the group consisting of a directly linked, substituted or unsubstituted alkylene, a substituted or unsubstituted alkenylene, and a substituted or unsubstituted arylene; R1 may be an integer from 1 to 10, wherein if R1 is 2 or more, R1 may be the same or different from each other; R2 may be an integer from 1 to 7, wherein if R2 is 2 or more, R2 may be the same or different from each other; R3 may be an integer from 1 to 9, wherein if R3 is 2 or more, R3 may be the same or different from each other; and R4 may be an integer from 1 to 8, wherein if R4 is 2 or more, R4 may be the same or different from each other.

[0023] In one embodiment, R1 to R4 may be the same or different, and may each independently be a substituted or unsubstituted methyl group.

[0024] In one embodiment, the tensile strength of the support layer may be 0.1 to 10 kgf / mm². 2 ).

[0025] In one embodiment, the support layer may comprise a porous support.

[0026] In one embodiment, the porous support may have a nonwoven fabric form, a woven form, or a mesh form in which polymer fibers are irregularly entangled together.

[0027] In one embodiment, the support layer may comprise a polymer coating on at least one side of the porous support.

[0028] In one embodiment, the polymer coating may comprise one or more of polysulfone, polyethersulfone, polycarbonate, polyethylene oxide, polyimide, polyetherimide, polyetheretherketone, polypropylene, polymethylpentene, polymethylchloroacrylate, or polyvinylidene fluoride.

[0029] In one embodiment, the support layer may include a gutter layer on at least one side.

[0030] In one embodiment, a guide layer may be included on both sides of the support layer.

[0031] In one embodiment, each guide layer may independently include polydimethylsiloxane.

[0032] In one embodiment, the water contact angle of the outermost layer of the membrane may be 80° to 120°, the outermost layer being in contact with the external air.

[0033] Another aspect of the present disclosure may relate to a battery pouch including the above-described film in at least a portion thereof, wherein gas generated in a secondary battery is non-destructively discharged to the outside through the film.

[0034] Technical Effects

[0035] The present disclosure can provide a membrane that can continuously and non-destructively discharge gases generated in secondary batteries under both high-pressure and low-pressure conditions, while effectively blocking the ingress of external moisture and atmospheric air (air) through the battery, and having excellent electrolyte solution tolerance. The present disclosure can provide a battery pouch that can further improve the stability and life of the battery by including the above-mentioned membrane in at least a portion thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Exemplary structures of films of the present disclosure are shown.

[0037] Figure 2 Another exemplary structure of a film of the present disclosure is shown.

[0038] Figure 3 Yet another exemplary structure of the membrane of the present disclosure is shown.

[0039] Figure 4 An exemplary structure of the support layer of the present disclosure is shown.

[0040] Figure 5 Images showing evaluation results of resistance of protective layer surfaces to electrolyte solutions in Examples and Comparative Examples.

[0041] Figure 6 This is an image of the depth-direction structure of the film of the present disclosure observed using a confocal laser scanning microscope (CLSM).

[0042] Figure 7 These are images showing the evaluation results of the water contact angles of the outermost layers of the films of Examples and Comparative Examples. DETAILED DESCRIPTION

[0043] The terms or words used in the present specification and claims should not be construed as limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts consistent with the technical ideas of the present disclosure based on the principle that the inventor can appropriately define term concepts in order to explain his or her invention in the best manner.

[0044] Therefore, it should be understood that the configuration of the embodiment described in this specification is one of the most preferred embodiments of the present disclosure and does not represent the entire technical concept of the present disclosure. Therefore, there may be various equivalents and modifications that can replace the embodiment at the time of submitting this application.

[0045] In this specification, a singular expression includes a plural expression unless the context clearly indicates otherwise.

[0046] In the specification, if a component “includes” a certain element, it means that the component may further include other elements, rather than excluding other elements, unless otherwise explicitly stated. Therefore, for example, a composition comprising compound A may include compounds other than A. However, in certain embodiments, the term “comprising” also encompasses limited meanings such as “substantially / inherently consisting of” and “consisting of”, and for example, “a composition comprising compound A” may also (substantially / inherently) consist of compound A.

[0047] In this regard, as used in the specification, it should be understood that terms such as "provided with" or "having" are intended to indicate the presence of implemented features, numbers, operations, components or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, operations, components or combinations thereof.

[0048] In the specification, if any member is located "on" another member, it includes not only a case where the member is in contact with another member but also a case where another member or substance exists between the two members.

[0049] If an amount, concentration or other value or parameter is given in this specification as a list of ranges, expected ranges, expected upper limits and expected lower limits, it is understood that it specifically discloses all ranges that can be formed by any pairing of any upper limit or expected value and any lower limit or expected value, regardless of whether the range is disclosed separately. If a numerical range is mentioned in the specification, unless otherwise indicated, for example, unless there are limiting terms such as greater than and less than, the range is intended to include the endpoint values and all integers and fractions within the range. The scope of the present disclosure is not intended to be limited to the specific values mentioned when defining the range.

[0050] In the physical properties mentioned in this specification, when the measurement temperature affects the relevant physical properties, the physical properties are measured at room temperature unless otherwise specified. The term room temperature is a natural temperature without heating or cooling, and may mean, for example, any temperature within the range of about 10 degrees Celsius (° C.) to 30° C., about 23° C., or about 25° C. In addition, unless otherwise specified, the temperature unit in the specification is ° C.

[0051] In addition, among the physical properties mentioned in the specification, when the measurement pressure has an influence on the relevant physical properties, the physical properties are measured under normal pressure, that is, atmospheric pressure (about 1 atm) unless otherwise specified.

[0052] One aspect of the present disclosure relates to a membrane having different gas permeabilities on both sides to discharge gases generated in a secondary battery to the outside and prevent external air and water vapor from penetrating into the interior of the secondary battery. The membrane comprises, from the side in contact with the interior of the secondary battery, a protective layer, an active layer, and a support layer. The protective layer comprises an amorphous perfluorinated polymer, is resistant to the electrolyte solution of the secondary battery, and has a ratio of a forward permeability of gases generated in the secondary battery to a reverse permeability of air of 20 or greater under a relative pressure of 20 pounds-force per square inch (psi), wherein the forward direction is from the interior of the secondary battery to the exterior of the secondary battery, and the reverse direction is from the exterior of the secondary battery to the interior of the secondary battery.

[0053] In this specification, "the interior of the secondary battery" may refer to the space where the electrode assembly and the electrolyte solution are located, which is connected to the case that contains the electrode assembly and the electrolyte solution, and "the exterior of the secondary battery" refers to the space connected to the case and may refer to the space other than the interior. The case may be a cylindrical can, a prismatic can, or a bag, specifically, a bag.

[0054] The amorphous perfluorinated polymer may be, for example, one or more selected from poly(tetrafluoroethylene-co-2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole) and polytetrafluoroethylene.

[0055] The amorphous perfluorinated polymer may have a molar weight of, for example, 100 to 1000 grams per mole (g / mol). In another exemplary embodiment, the molar weight of the amorphous perfluorinated polymer may be 150 g / mol or more, 200 g / mol or more, 250 g / mol or more, or 300 g / mol or more, or 900 g / mol or less, 800 g / mol or less, 700 g / mol or less, 600 g / mol or less, 500 g / mol or less, or 400 g / mol or less.

[0056] The membrane of the present disclosure may include, for example, a protective layer, an active layer, and / or a supporting layer from the side in contact with the interior of the secondary battery. Each layer may be formed to be in direct contact with an adjacent layer or in indirect contact via another layer therebetween.

[0057] The membrane of the present disclosure may be resistant to the electrolyte solution of a secondary battery because the protective layer includes, for example, an amorphous perfluorinated polymer.

[0058] In the specification, “the membrane has resistance to the electrolyte solution of the secondary battery” means that the side of the membrane in contact with the interior of the secondary battery will not dissolve, or will not absorb or permeate the electrolyte solution and / or vapor from the electrolyte solution even if initially exposed to the electrolyte solution and / or vapor from the electrolyte solution, or exposed for a considerable period of time.

[0059] For example, under the condition of a relative pressure value of 20 psi, the ratio of the forward permeability of the gas generated in the secondary battery of the membrane of the present disclosure to the reverse permeability of the air is greater than 20. In another exemplary embodiment, under the condition of a relative pressure value of 20 psi, the ratio of the forward permeability of the gas generated in the secondary battery of the membrane of the present disclosure to the reverse permeability of the air may be greater than 25, greater than 30, or greater than 35, or less than 100, less than 90, or less than 80.

[0060] Under the condition of a relative pressure value of 20psi, the forward permeability of the gas produced in the secondary battery of the membrane of the present disclosure can be more than 5 gas generation units (GPU). In this specification, gas permeability properties can be measured by the method according to the evaluation example described later. In this specification, the relative pressure value can represent the pressure value based on the atmospheric pressure of 0psi. In another exemplary embodiment, under the condition of a relative pressure value of 20psi, the forward permeability of the gas produced in the secondary battery of the membrane of the present disclosure can be more than 6GPU or more than 7GPU, or less than 15GPU, less than 10GPU, less than 9GPU or less than 8GPU.

[0061] Under conditions of a relative pressure value of, for example, 40 psi, the forward permeability of the gas generated in the secondary battery of the membrane of the present disclosure may be 10 GPU or more. In another exemplary embodiment, under conditions of a relative pressure value of 40 psi, the forward permeability of the gas generated in the secondary battery of the membrane of the present disclosure may be 11 GPU or more, 12 GPU or more, 13 GPU or more, 14 GPU or more, or 15 GPU or less, or 20 GPU or less, or 19 GPU or less, or 18 GPU or less, or 17 GPU or less, or 16 GPU or less.

[0062] For example, under a relative pressure of 50 psi, the forward permeability of the gas generated in the secondary battery of the membrane of the present disclosure may be 15 GPU or more. In another exemplary embodiment, under a relative pressure of 50 psi, the forward permeability of the gas generated in the secondary battery of the membrane of the present disclosure may be 16 GPU or more, 17 GPU or more, or 18 GPU or more, or 25 GPU or less, 24 GPU or less, 23 GPU or less, 22 GPU or less, 21 GPU or less, or 20 GPU or less.

[0063] Under the condition of a relative pressure value of 15 psi, the reverse permeability of air of the membrane of the present disclosure may be, for example, 0.1 GPU or less.

[0064] Under the condition of a relative pressure value of 20 psi, the reverse permeability of air of the membrane of the present disclosure may be 0.5 GPU or less. In another exemplary embodiment, under the condition of 20 psi, the reverse permeability of air of the membrane of the present disclosure may be 0.4 GPU or less, 0.3 GPU or less, or 0.2 GPU or less.

[0065] Under the condition of a relative pressure value of 60 psi, the reverse permeability of air of the membrane of the present disclosure may be, for example, 1 GPU or less. In another exemplary embodiment, under the condition of a relative pressure value of 60 psi, the reverse permeability of air of the membrane of the present disclosure may be 0.9 GPU or less, 0.8 GPU or less, or 0.7 GPU or less.

[0066] The present invention can provide a membrane that can continuously and non-destructively discharge the gas generated inside the secondary battery not only under a high-pressure condition greater than 20psi, but also under a low-pressure condition below 20psi, while effectively blocking external moisture and atmosphere (air) from entering the battery, and having excellent tolerance to electrolyte solution. In the present disclosure, high-pressure conditions refer to pressure conditions under which at least a portion of the secondary battery shell is ruptured and causes a considerable risk of ignition or explosion, and can refer to, for example, a pressure greater than 20psi, greater than 50psi, or greater than 100psi. Low-pressure conditions can refer to a range of less than 20psi of atmospheric pressure while discharging the gas generated inside the secondary battery to the outside, and can have a relatively low risk of shell damage.

[0067] The protective layer may further include at least one of polyimide, Nafion, or polydimethylsiloxane. If the protective layer further includes at least one of polyimide, Nafion, or polydimethylsiloxane, the weight ratio of at least one of polyimide, Nafion, or polydimethylsiloxane to the amorphous perfluorinated polymer may be, for example, in the range of 0.1 to 20. In another embodiment, it may be greater than 0.1, greater than 0.2, greater than 0.3, greater than 0.4, greater than 0.5, greater than 0.6, greater than 0.7, greater than 0.8, greater than 0.9, greater than 1, greater than 2, greater than 3, greater than 4, or greater than 5, or less than 18, less than 16, less than 14, less than 12, less than 10, or less than 6. Since the protective layer of the present disclosure further includes at least one of polyimide, Nafion, or polydimethylsiloxane, gas permeability can be further improved, or defects such as pinholes can be further controlled.

[0068] The contact angle of the protective layer relative to the electrolyte solution of the secondary battery may be, for example, 30° or more. In this specification, “the contact angle relative to the electrolyte solution of the secondary battery” may refer to the initial contact angle and / or the contact angle after being exposed to the electrolyte solution for a certain period of time. The contact angle of the electrolyte solution can be measured according to the evaluation example described later. In another exemplary embodiment, the contact angle of the protective layer relative to the electrolyte solution of the secondary battery may be 35° or more, 40° or more, or 45° or less, or 80° or less, 75° or less, 70° or less, 65° or less, 60° or less, or 55° or less.

[0069] The thickness of the protective layer may be, for example, less than 10 micrometers (μm). In another embodiment, the thickness of the protective layer may be less than 9 μm, less than 8 μm, less than 7 μm, less than 6 μm, less than 5 μm, less than 4 μm, less than 3 μm, less than 2 μm or less than 1 μm, or more than 0.01 μm, more than 0.05 μm or more than 0.1 μm, but is not limited thereto. In this specification, the “thickness of layer A” may refer to the thickness of layer A itself, or may refer to the thickness measured, for example, when layer A overlaps with other layers, including the portion where layer A overlaps with other layers. In this specification, “thickness” may be the average thickness, maximum thickness and / or minimum thickness of the thickness measured at any position.

[0070] Since the membrane of the present disclosure includes the above protective layer in the innermost layer of the membrane, the membrane's resistance to the electrolyte solution can be further improved. In this specification, "the innermost layer of the membrane" may refer to a side of each layer of the membrane that contacts the interior of the secondary battery.

[0071] The membrane of the present disclosure may include, for example, an active layer. For example, the active layer may be formed on the side opposite to the side of the protective layer that contacts the interior of the secondary battery.

[0072] The active layer can, for example, absorb gases generated in the secondary battery and transport them toward the outside. The gases may include, for example, gases generated when a solid electrolyte interface (SEI) film is formed during the formation process of the secondary battery and / or gases abnormally generated due to decomposition of the electrolyte solution, excessive moisture content in the secondary battery, short circuits, overcharging, and / or overdischarging. The specific composition of the gas may vary depending on the combination of the electrolyte used in the secondary battery, the solvent in the electrolyte solution, the positive electrode active material, the negative electrode active material, and the binder, but generally exhibits similar properties with CO2 as the main component. The gas may include: H2; O2; CO; CO2; and / or hydrocarbon gases such as CH4, C2H2, C2H4, C2H6, C3H6, and C3H8; and combinations thereof, and the ratio of CO2 gas to the total gas generated may be 50% or more. Since the membrane of the present disclosure includes an active layer having the properties described later, the gas generated in the secondary battery can permeate in the forward direction (from the inside to the outside of the membrane) via a solution-diffusion mechanism.

[0073] The active layer may include, for example, a cross-linked structure of cellulose and a compound containing two or more carboxylic acids. In the present disclosure, the spaces between the cellulose polymer chains of the active layer can be kept constant, and the packing density and arrangement of the polymers can be improved, thereby more effectively performing the above functions.

[0074] The cross-linked structure of cellulose and a compound containing two or more carboxylic acids can be represented by, for example, the following Formula 1.

[0075] [Formula 1]

[0076]

[0077] In Formula 1, R1 to R4 may be the same or different and may each independently be hydrogen, deuterium, hydroxyl, substituted or unsubstituted alkyl, or substituted or unsubstituted alkoxy; Y1 may be a directly attached, substituted or unsubstituted alkylene, a substituted or unsubstituted alkenylene, a substituted or unsubstituted arylene, or a combination of substituents selected from the group consisting of a directly attached, substituted or unsubstituted alkylene, a substituted or unsubstituted alkenylene, and a substituted or unsubstituted arylene; R1 may be an integer from 1 to 10, wherein if R1 is 2 or more, R1 may be the same or different from each other; R2 may be an integer from 1 to 7, wherein if R2 is 2 or more, R2 may be the same or different from each other; R3 may be an integer from 1 to 9, wherein if R3 is 2 or more, R3 may be the same or different from each other; and R4 may be an integer from 1 to 8, wherein if R4 is 2 or more, R4 may be the same or different from each other. From the viewpoint of achieving the purpose of discharging gas generated inside the secondary battery to the outside while preventing external air and / or water vapor from penetrating into the secondary battery, it is preferred that R1 to R4 are each independently a substituted or unsubstituted methyl group.

[0078] The thickness of the active layer may be, for example, 10 μm or less. In another exemplary embodiment, the thickness of the active layer may be 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less, or 0.01 μm or more, 0.05 μm or more, or 0.1 μm or more, but is not limited thereto.

[0079] The membranes of the present disclosure may include, for example, a support layer.

[0080] The tensile strength of the support layer can be, for example, 0.1 to 10 kgf / mm². 2 If the support layer has the above-mentioned tensile strength, the film of the present disclosure may have excellent mechanical strength.

[0081] The support layer may include, for example, a porous support. The porous support may have, for example, a nonwoven fabric form in which polymer fibers are irregularly entangled, a woven form, or a mesh form. The polymer may be, for example, polypropylene (PP), poly(methyl methacrylate) (PMMA), polyethylene (PE), polyethylene terephthalate (PET), and polyethersulfone (PES), but is not limited thereto.

[0082] The thickness of the porous support layer may be, for example, 50 μm to 150 μm, but is not limited thereto. In another exemplary embodiment, the thickness of the porous support may be 60 μm or more, 70 μm or more, 80 μm or more, or 90 μm or less, or 140 μm or less, 130 μm or less, 120 μm or less, 110 μm or less, or 100 μm or less.

[0083] The porosity of the porous support may be 10% to 90%, but is not limited thereto. Porosity can be measured by Archimedes' principle. In another exemplary embodiment, the porosity of the porous support may be 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, or 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, or 20% or less.

[0084] The support layer may include, for example, a polymer coating on at least one side of the porous support. The polymer coating may be formed on one or both sides of the porous support.

[0085] The polymer coating may include, for example, one or more selected from polysulfone, polyethersulfone, polycarbonate, polyethylene oxide, polyimide, polyetherimide, polyetheretherketone, polypropylene, polymethylpentene, polymethylchloroacrylate, polyvinylidene fluoride, and combinations thereof.

[0086] The thickness of the support layer may be, for example, 1 μm to 1000 μm.

[0087] Since the present disclosure includes the support layer as described above, the shape of the membrane may be maintained, the target mechanical strength may be obtained, and the overall gas permeability of the membrane may not be impaired.

[0088] The membrane of the present disclosure may include, for example, a guide layer on at least one side of the support layer. From the perspective of maintaining the shape of the membrane, it is desirable to include a guide layer between the active layer and the support layer, and from the perspective of maintaining the shape of the membrane and blocking external air or water vapor, it is more desirable to include a guide layer on both sides of the support layer.

[0089] Each guide layer may independently include, for example, polydimethylsiloxane. Based on the dry weight of the guide layer, the content of polydimethylsiloxane may be 90 wt % or more, 95 wt % or more, 99 wt % or more, or 100 wt %.

[0090] The thickness of the guide layer may be, for example, 10 micrometers (μm) or less. If the guide layer is formed on both sides of the support layer, the thickness of the guide layer may refer to the thickness of each guide layer or the sum of the thicknesses of the guide layers.

[0091] The outermost layer of the film in contact with the external air may have a water contact angle of, for example, 80° to 120°. The water contact angle of the outermost layer of the film can be measured according to the evaluation examples described later. In another exemplary embodiment, the water contact angle of the outermost layer of the film may be 85° or more, 90° or more, or 95° or less, 115° or less, 110° or less, or 105° or less. In the present disclosure, by controlling the water contact angle of the outermost layer of the film as described above, external moisture and / or air can be more effectively blocked without hindering the discharge of internally generated gases.

[0092] In the present disclosure, each of the aforementioned layers, such as the protective layer, active layer, support layer, and / or guide layer, may or may not overlap with adjacent layers. In an exemplary embodiment, at least a portion of the protective layer may or may not overlap with the active layer. In another exemplary embodiment, at least a portion of the guide layer may or may not overlap with the support layer or the active layer.

[0093] Another aspect of the present disclosure relates to a battery pouch in which the above-mentioned film is contained in at least a portion thereof, wherein gas generated inside a secondary battery is discharged to the outside non-destructively through the film.

[0094] Unless otherwise specifically stated, the contents regarding the above-mentioned film are also applicable to the disclosure regarding the battery pouch of the present disclosure.

[0095] Generally, in order to solve the defect that the generation of gas increases due to abnormal operation of the battery, thereby causing ignition or explosion, an exhaust system is introduced. The exhaust system is, for example, a device that allows the internal gas to be discharged to the outside when the internal pressure of the secondary battery reaches a certain level. However, it is difficult to reuse the secondary battery after exhaust, and there is a lack of a stability enhancement system that can be considered as an alternative when the exhaust system does not work properly due to unforeseen reasons. However, according to the present disclosure, by including the above-mentioned film in at least a part of the battery bag, the gas generated inside the battery can be continuously and non-destructively discharged not only under high pressure conditions but also under low pressure conditions, thereby further improving the life, tolerance and stability of the battery. In addition, by combining the film with the existing exhaust system and applying it to the battery, the above-mentioned effect can be further improved.

[0096] Another aspect of the present disclosure relates to a secondary battery including a battery pouch, and an electrode assembly and an electrolyte solution in the battery pouch.

[0097] The contents related to the film and / or the battery pouch can be similarly applied to the contents related to the secondary battery of the present disclosure unless otherwise specifically stated.

[0098] The electrode assembly may include, for example, a positive electrode, a negative electrode, and / or a separator. As the electrode assembly, all known electrode assemblies may be applied. The electrode assembly may be, for example, a jelly roll type, a stack type, and / or a stack-fold type, but is not limited thereto.

[0099] The positive electrode may include, for example, a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector may, for example, be a thin plate of aluminum, stainless steel, or nickel. Alternatively, the positive electrode current collector may be a porous material in the form of a mesh or lattice, and to prevent oxidation, a coating material coated with an anti-oxidation metal or alloy film may be used. The positive electrode active material layer may include a known positive electrode active material, a binder, and / or a conductive material. The positive electrode active material may be, for example, a compound capable of reversibly intercalating and deintercalating lithium, and may be a lithium-transition metal composite oxide containing lithium and at least one transition metal selected from nickel, cobalt, manganese, and aluminum, but is not limited thereto. The binder may be, for example, at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, and fluororubber, but is not limited thereto. The conductive material may be, for example, one or more selected from the group consisting of graphite, carbon black, carbon nanotubes, metal powder, and conductive oxides, but is not limited thereto.

[0100] The negative electrode may include, for example, a negative electrode current collector and a negative electrode active material layer. Examples of the negative electrode current collector include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, and the like, and aluminum-cadmium alloys. Furthermore, as with the positive electrode current collector, fine concave-convex structures may be formed on the surface to enhance the binding force with the negative electrode active material. Various forms such as films, sheets, foils, meshes, porous materials, foams, and non-woven materials may also be used. The negative electrode active material layer may include a known negative electrode active material, a binder, and / or a conductive material. The negative electrode active material may be, for example, a silicon-based or carbon-based negative electrode active material. For example, the silicon-based negative electrode active material may be at least one selected from SiOx (0≤x≤2) particles, Si-C composites, and Si-Y alloys (where Y is an element selected from alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, and combinations thereof). The carbon-based negative electrode active material may be, for example, one or more selected from artificial graphite, natural graphite, and graphitized mesophase carbon microbeads, but is not limited thereto. The binder contained in the negative electrode active material layer may be, for example, an aqueous binder or a rubber-based binder. The aqueous binder may be at least one selected from the group consisting of polyvinyl alcohol, polyacrylic acid, polyethylene glycol, polyacrylonitrile, polyacrylamide, carboxymethyl cellulose, and combinations thereof, but is not limited thereto. The rubber-based binder may be, for example, at least one selected from the group consisting of styrene-butadiene rubber, hydrogenated nitrile rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof, which does not dissolve well in aqueous solvents such as water but disperses smoothly in aqueous solvents, but is not limited thereto. The conductive material contained in the negative electrode active material layer may be, for example, one or more selected from the group consisting of graphite, carbon black, carbon nanotubes, metal powder, conductive oxide, and combinations thereof, but is not limited thereto.

[0101] The diaphragm has the function of physically separating the electrodes, and a commonly used diaphragm can be used without particular limitation. In particular, it is desirable to have a diaphragm with low resistance to ion movement in the electrolyte solution and excellent electrolyte absorption capacity. The diaphragm can be formed using a porous, non-conductive or insulating material, and can be an independent component, or can be a coating added to the positive electrode and / or the negative electrode. The diaphragm can be, for example, a film formed using polyethylene such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, a polyolefin polymer such as polypropylene, polybutene, polypentene, or a mixture thereof.

[0102] The electrolyte solution may include an organic solvent and a lithium salt. Any organic solvent may be used without particular limitation, as long as it is a medium through which ions associated with the electrochemical reaction of the battery can move. The organic solvent may particularly include: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; ether solvents such as dibutyl ether, tetrahydrofuran, etc.; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene, fluorobenzene, etc.; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC), etc.; alcohol solvents such as ethanol, isopropanol, etc.; nitriles such as R-CN (R is C2-C 20 Straight chain, branched or cyclic structure hydrocarbon group, which may contain a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. As the lithium salt, any compound that can provide lithium ions used in the battery can be used without particular limitation. The lithium salt can specifically include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2. The concentration of the lithium salt can be in the range of 0.1 to 2.0 moles (M). If the concentration of the lithium salt is within the above range, the electrolyte solution can have appropriate conductivity and viscosity, and thus can exhibit excellent electrolyte performance, and lithium ions can move efficiently.

[0103] The secondary battery of the present disclosure may further include, for example, an exhaust system. The exhaust system is a system that irreversibly exhausts gas abnormally generated inside the battery, and a well-known exhaust system can be applied without particular limitation.

[0104] Hereinafter, in order to specifically illustrate the above-mentioned disclosure of the present disclosure and the expected action and effect of the present disclosure, the present disclosure will be described in detail with reference to the embodiments. However, the embodiments can be modified into various other forms, and the scope of this specification should not be interpreted as being limited to the embodiments. It should be emphasized that the embodiments represent the present disclosure and are provided to explain the present disclosure in more detail to those skilled in the art.

[0105] Example 1

[0106] Formed as Figure 3 The membrane shown has a structure in which a protective layer 20, an active layer 10, a first guide layer 401, a support layer 30 and a second guide layer 402 are stacked in sequence.

[0107] Support layer 30 is formed by casting a 50 μm thick polymer coating solution onto a 95 μm to 100 μm thick polyester nonwoven fabric (porous support, 301) to form a polymer coating layer 302, and then immersing the cast nonwoven fabric in water. In this case, a polysulfone solid was added to an N,N-dimethylformamide (DMF) solution and dissolved at 80°C to 85°C for at least 12 hours to obtain a polymer coating solution. The polysulfone solid content in this solution was 18% by weight.

[0108] Subsequently, a second guide layer 402 was formed on one side of the support layer 30. The second guide layer 402 was formed by applying a guide layer-forming composition prepared by mixing Isopar G solvent and polydimethylsiloxane (PDMS, Dow Corning Co., Sylgard 184) to the porous support 301 of the support layer 30, and then drying the composition in an oven at 90°C for 5 minutes. In this case, the content of PDMS was 3% by weight based on the guide layer-forming composition.

[0109] Then, a first guide layer 401 was formed on the other side of the support layer 30. The first guide layer 401 was formed by applying a guide layer-forming composition prepared by mixing Isopar G solvent and PDMS (Dow Corning Co., Sylgard 184) on the polymer coating layer 302 of the support layer 30 and drying it in an oven at 90° C. for 5 minutes.

[0110] The active layer 10 was formed by applying a mixture of distilled water, methylcellulose, and maleic acid to the first guide layer 401, followed by drying in a 90°C oven for 5 minutes. In this case, the active layer composition contained 1.5% by weight of methylcellulose and 0.5% by weight of maleic acid. The resulting active layer 10 had a thickness of 1 μm or less.

[0111] The protective layer 20 was formed by applying a protective layer-forming composition prepared by mixing Isopar G solvent, poly(tetrafluoroethylene-co-2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole) (SIGMA-ALDRICH Co., hyflon, 340.12 g / mol), and PDMS (Dow Corning Co., Sylgard 184) on the side of the active layer 10 where the first guide layer 401 was not formed, and then drying in an oven at 90° C. for 5 minutes. In this case, the content of poly(tetrafluoroethylene-co-2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole) was 0.5% by weight, and the content of PDMS was 3% by weight relative to the protective layer-forming composition.

[0112] Example 2

[0113] A film was formed in the same manner as in Example 1, except that an Isopar G solvent was mixed with poly(tetrafluoroethylene-co-2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole) (SIGMA-ALDRICH Co., hyflon, 340.12 g / mol) to prepare a composition for forming a protective layer, and the content of poly(tetrafluoroethylene-co-2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole) was 0.5 wt % relative to the composition for forming a protective layer.

[0114] Comparative Example 1

[0115] A film was formed in the same manner as in Example 1, except that a protective layer-forming composition was prepared by mixing Isopar G solvent and PDMS (Dow Corning Co., Sylgard 184), and the content of PDMS was 3 wt % relative to the protective layer-forming composition.

[0116] Comparative Example 2

[0117] A membrane was formed in the same manner as in Comparative Example 1, except that the second guide layer 402 was not formed on the porous support 301 of the support layer 30 .

[0118] Evaluation Example 1. Gas Permeability

[0119] The gas permeability of the membrane is measured using the constant pressure variable volume method. After the permeability stabilizes (for more than 2 hours), the permeability is quantified using a gas flow meter. More specifically, the membrane is secured to a pressure chamber (filter holder type), gas is applied at a constant pressure, and the flow rate of the gas flowing through the membrane is measured. In this case, the temperature is set to room temperature, and the forward CO2 gas permeability and reverse air permeability are measured while varying the pressure.

[0120] [Table 1]

[0121]

[0122] Evaluation Example 2. Tolerance to Electrolyte Solution

[0123] The resistance of the protective layer surface to electrolyte solutions was measured according to ASTM D5946. Specifically, 5 to 8 microliters (μL) of electrolyte solution (EMC) was added dropwise to the protective layer of the films of Example 2 and Comparative Example 1. The contact angle was then measured using an OCA series optical contact angle measurement and profiling system. Ten measurements were taken for each sample, with one measurement taken every 25 mm.

[0124] As a result, it was confirmed that the contact angle of the protective layer of the film of Example 2 measured 10 times showed a value of 47.5° to 53.3°, and the contact angle of the protective layer of the film of Comparative Example 1 measured 10 times showed a value of 20.1° to 21.8°. That is, it can be seen that in the case of the film of Example 2 having a protective layer formed of poly(tetrafluoroethylene-co-2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole) (SIGMA-ALDRICH Co., hyflon), a large contact angle was shown, and no impregnation of the electrolyte solution was observed even after 2 hours or more, while in the case of the film of Comparative Example 1 having a protective layer formed of PDMS, the contact angle was small, and impregnation of the electrolyte solution occurred ( Figure 5 ).

[0125] Evaluation Example 3. Membrane Structure

[0126] The depth-direction (Z-axis) structure of the film was observed using a confocal laser scanning microscope (CLSM). The CLSM measurement conditions were as follows.

[0127] - Equipment: Olympus, OLS5100,

[0128] -Light source: Laser 405 nm, ~0.95 mW

[0129] -Magnification: 50x

[0130] - Scanning speed: 0.1 to 1 micrometer per second (μ / s)

[0131] As a result, the protective layer, active layer, and first guide layer were confirmed in this order, but at least a portion of each of the protective layer and the first guide layer was impregnated into the active layer ( Figure 6 ).

[0132] Evaluation Example 4: Water contact angle of the outermost layer of the membrane

[0133] The water contact angle of the outermost layer of the membrane was measured according to ASTM D5946. Specifically, 5 to 8 μL of water was dropped onto the outermost layer of each membrane of Example 1 and Comparative Example 2 (the porous support layer in Example 1 and the second guide layer in Comparative Example 2). The contact angle was then measured using an OCA series optical contact angle measurement and profiling system. Ten measurements were performed for each sample, with one measurement taken every 25 mm.

[0134] As a result, it was confirmed that the contact angle of the outermost layer of the film of Example 1 measured 10 times showed a value of 97.0° to 101.5°, and the contact angle of the outermost layer of the film of Comparative Example 2 measured 10 times showed a value of 75.0° to 76.9°. That is, it was found that the film of Example 1 had superior water resistance ( Figure 7 ).

[0135] Evaluation Example 5. Support Layer Tensile Strength

[0136] The tensile strength of the support layers used in the Examples and Comparative Examples was measured using a universal testing machine (UTM) at a speed of 100 millimeters per minute (mm / min) for a support layer having a size of 100 mm*10 mm. The measurement was performed on a total of five support layers. The results confirmed that the tensile strength of each support layer was 1.5 to 2.5 kgf / mm. 2 .

[0137] [Explanation of Reference Numerals]

[0138] 10: Active layer

[0139] 20: Protective layer

[0140] 30: Support layer

[0141] 301: porous support

[0142] 302: Polymer coating

[0143] 40: Diversion layer

[0144] 401: First guide layer

[0145] 402: Second guide layer

Claims

1. A film having different gas permeabilities on both sides to discharge gas generated in a secondary battery to the outside and prevent external air and water vapor from penetrating into the interior of the secondary battery, in, The film includes, from the side in contact with the interior of the secondary battery, a protective layer, an active layer, and a support layer, The protective layer comprises an amorphous perfluorinated polymer to provide resistance to the electrolyte solution of the secondary battery, and Under the condition of a relative pressure value of 20 pounds force per square inch (psi), the ratio of the forward permeability of the gas generated in the secondary battery to the reverse permeability of the air is greater than 20, wherein the forward direction is the direction from the inside of the secondary battery to the outside of the secondary battery, and the reverse direction is the direction from the outside of the secondary battery to the inside of the secondary battery.

2. The film according to claim 1, wherein Under the condition of a relative pressure value of 20psi, the forward permeability of the gas generated in the secondary battery is more than 5 gas generation units (GPU); under the condition of a relative pressure value of 40psi, the forward permeability of the gas generated in the secondary battery is more than 10GPU; or under the condition of a relative pressure value of 50psi, the forward permeability of the gas generated in the secondary battery is more than 15GPU.

3. The film according to claim 1, wherein Under the condition of a relative pressure value of 15psi, the reverse permeability of the air is less than 0.1GPU, under the condition of a relative pressure value of 20psi, the reverse permeability of the air is less than 0.5GPU, or under the condition of a relative pressure value of 60psi, the reverse permeability of the air is less than 1GPU.

4. The film according to claim 1, wherein The protective layer further comprises at least one of polyimide, Nafion or polydimethylsiloxane.

5. The film according to claim 1, wherein The protective layer has a contact angle of 30° or greater with respect to the electrolyte solution of the secondary battery.

6. The film according to claim 1, wherein The active layer absorbs gas generated in the secondary battery and transports the gas to the outside.

7. The film according to claim 1, wherein The active layer includes a cross-linked structure of cellulose and a compound containing two or more carboxylic acids.

8. The film according to claim 7, wherein The cross-linked structure of cellulose and a compound containing two or more carboxylic acids is represented by the following formula 1: [Formula 1] In Formula 1, R1 to R4 are the same or different and are each independently hydrogen, deuterium, hydroxyl, substituted or unsubstituted alkyl, or substituted or unsubstituted alkoxy; Y1 is a directly attached, substituted or unsubstituted alkylene, a substituted or unsubstituted alkenylene, or a substituted or unsubstituted arylene, or a combination of substituents selected from the group consisting of a directly attached, substituted or unsubstituted alkylene, a substituted or unsubstituted alkenylene, and a substituted or unsubstituted arylene; R1 is an integer from 1 to 10, wherein if R1 is 2 or more, R1 are the same or different from each other; R2 is an integer from 1 to 7, wherein if R2 is 2 or more, R2 are the same or different from each other; R3 is an integer from 1 to 9, wherein if R3 is 2 or more, R3 are the same or different from each other; and R4 is an integer from 1 to 8, wherein if R4 is 2 or more, R4 are the same or different from each other.

9. The film according to claim 8, wherein R1 to R4 are the same or different and are each independently a substituted or unsubstituted methyl group.

10. The film according to claim 1, wherein The tensile strength of the support layer is 0.1 to 10 kgf / mm². 2 ).

11. The film according to claim 1, wherein The support layer comprises a porous support.

12. The film according to claim 11, wherein The porous support has a nonwoven fabric form in which polymer fibers are irregularly entangled together, a woven form, or a mesh form.

13. The film according to claim 11, wherein The support layer comprises a polymer coating on at least one side of the porous support.

14. The film according to claim 13, wherein The polymer coating comprises one or more of polysulfone, polyethersulfone, polycarbonate, polyethylene oxide, polyimide, polyetherimide, polyetheretherketone, polypropylene, polymethylpentene, polymethylchloroacrylate or polyvinylidene fluoride.

15. The membrane of claim 1 comprising a flow guide layer on at least one side of the support layer.

16. The membrane of claim 1 comprising a flow guide layer on both sides of the support layer.

17. The membrane according to claim 15 or 16, wherein The guide layers each independently comprise polydimethylsiloxane.

18. The film of claim 1, wherein The water contact angle of the outermost layer of the film, which is in contact with external air, is 80° to 120°.

19. A battery bag comprising the film according to claim 1 in at least a portion thereof, wherein Gas generated in the secondary battery is discharged to the outside through the film in a non-destructive manner.

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