Battery case and secondary battery comprising same

Abstract

The present invention relates to a battery case having excellent durability and a secondary battery including same. The battery case according to the present invention includes a first polymer layer, a second polymer layer, and a gas barrier layer interposed between the first polymer layer and the second polymer layer, and includes one or more cup parts curved in one direction, and has a K value of 63.0 or greater as defined by the following Equation (1). Equation (1): K = P / C +50D. In Equation (1), P is a thickness value of the battery case measured in ㎛, C is a depth value of the cup part measured in mm, and D is a ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer.

Description

Battery case and secondary battery including the same

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0065145, filed May 20, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a battery case having excellent durability and a secondary battery including the same.

[0003] Secondary batteries are generally manufactured by applying electrode active material slurry to a positive electrode current collector and a negative electrode current collector to manufacture a positive electrode and a negative electrode, laminating them on both sides of a separator to form an electrode assembly of a predetermined shape, then housing the electrode assembly in a battery case and injecting an electrolyte.

[0004] As the electrode assembly increases in thickness, i.e., as more electrodes are stacked, more active material can be contained, thereby increasing battery capacity. However, if the thickness and configuration of the battery case are not appropriately adjusted, problems such as cracks and corrosion at the corners are likely to occur.

[0005] Therefore, there is a need to develop a battery case that can accommodate a high-capacity, thick electrode assembly while also being durable.

[0006] The present invention provides a battery case designed so that the thickness of each layer and the depth of the cup portion satisfy a specific formula, and a secondary battery including the same having improved durability.

[0007] [1] The present invention comprises a first polymer layer, a second polymer layer, and a gas barrier layer interposed between the first polymer layer and the second polymer layer,

[0008] comprising one or more cup portions curved in one direction;

[0009] A battery case is provided, wherein the K value according to the following equation (1) is 63.0 or more.

[0010] Equation (1): K = P / C + 50D

[0011] In the above equation (1),

[0012] P is the thickness value of the battery case measured in μm,

[0013] C is the depth value of the cup part measured in mm,

[0014] D is the ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer.

[0015] [2] The present invention provides a battery case having a thickness of 100 µm to 1,000 µm in the above [1].

[0016] [3] The present invention provides a battery case in which the depth of the cup portion is 1 mm or more and 70 mm or less in the above [1] or [2].

[0017] [4] The present invention provides a battery case in which, in at least one of the above [1] to [3], the P / C of the above formula (1) is 19.5 or more.

[0018] [5] The present invention provides a battery case in which the thickness of the first polymer layer is 10 µm to 300 µm in at least one of the above [1] to [4].

[0019] [6] The present invention provides a battery case in which the thickness of the second polymer layer is 10 µm to 300 µm in at least one of the above [1] to [5].

[0020] [7] The present invention provides a battery case in which the thickness of the gas barrier layer is 50 µm or more and 900 µm or less, in at least one of the above [1] to [6].

[0021] [8] The present invention provides a battery case in which, in at least one of the above [1] to [7], the gas barrier layer comprises at least one metal selected from among SUS, Ni, Fe, Co, Cr, Mo, Ta, W, Ti, and Re; or an alloy of the metal and Al.

[0022] [9] The present invention provides a battery case in which D of the formula (1) is 0.80 or more in at least one of the above [1] to [8].

[0023]

[0010] The present invention provides a secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case according to at least one of [1] to [9], wherein the electrode assembly and the electrolyte are accommodated in a cup portion of the battery case.

[0024]

[0011] The present invention provides a secondary battery having an S value of 37.0 or more according to the following formula (2) in the above

[0010] .

[0025] Equation (2): S = P / T Х N + 20D

[0026] In the above equation (2),

[0027] P is the thickness value of the battery case measured in μm,

[0028] T is the thickness value of the electrode assembly measured in mm, and if it includes two or more electrode assemblies, it is the sum of these thickness values,

[0029] N is the number of cups in the battery case,

[0030] D is the ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer.

[0031]

[0012] The present invention provides a secondary battery in which the electrode assembly has a thickness of 1 mm to 150 mm in the above

[0010] or

[0011] .

[0032] The battery case according to the present invention is configured such that the thickness of each layer constituting the battery case satisfies a specific formula by reflecting the depth of the cup portion, so that even if a thick electrode assembly is accommodated, there is a low possibility of cracks occurring at the corners, and thus corrosion problems caused by this are prevented, which has the advantage of preventing the problem.

[0033] Figure 1 is a diagram showing a cross-sectional structure of a pouch film laminate according to one embodiment.

[0034] Figures 2 and 3 are diagrams showing the structure of a battery case according to one implementation example, respectively.

[0035] Fig. 4 is a diagram showing the structure of an electrode assembly according to one embodiment.

[0036] Hereinafter, the present invention will be described in more detail.

[0037]

[0038] With the recent rise in demand for high-capacity batteries, such as those for electric vehicles, the rated capacity of secondary batteries is increasing. Consequently, the size and thickness of electrode assemblies are also increasing, and the thickness of battery cases must also increase to match this trend.

[0039] For example, in pouch-type secondary batteries, if the pouch is formed deeper to match the increased thickness of the electrode assembly, greater stretching occurs, thinning the pouch. If charging and discharging are repeated in this state, the expansion and contraction of the electrode assembly exerts force on the thinned pouch, causing cracks. This can lead to electrolyte leakage and battery corrosion.

[0040] Therefore, this problem can be prevented by increasing the thickness of the battery case, but if the thickness of the battery case is increased indiscriminately, there is a concern that the energy density and durability of the case may decrease. Therefore, it is necessary to establish a standard so that the thickness of each layer forming the battery case can be appropriately selected by reflecting the thickness of the electrode assembly.

[0041] Accordingly, the present invention has been completed by finding out that durability can be implemented excellently when the depth of the cup portion in which the electrode assembly is to be accommodated and the thickness of each layer forming the battery case satisfy specific conditions.

[0042]

[0043] A battery case according to the present invention comprises a first polymer layer, a second polymer layer, and a gas barrier layer interposed between the first polymer layer and the second polymer layer, and comprises at least one cup portion curved in one direction, and is characterized in that the K value according to the following formula (1) is 63.0 or more.

[0044] Equation (1): K = P / C + 50D

[0045] In the above equation (1),

[0046] P is the thickness value of the battery case measured in μm,

[0047] C is the depth value of the cup part measured in mm,

[0048] D is the ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer.

[0049] Meanwhile, the K value according to the above formula (1) may be 63.0 or more, preferably 70.0 or more, and more preferably 75.0 or more. However, considering the energy density of the cell and the insulation of the case, it is preferably 500.0 or less, 300.0 or less, or 120.0 or less. If the K value is 63.0 or more, the gas barrier layer is implemented with a sufficient thickness considering the depth of the cup portion and the total thickness of the battery case, so that cracks in the battery case can be prevented from occurring due to external force.

[0050] Specifically, when the P / C value of the above equation (1) decreases, i.e., when the depth of the cup portion increases relative to the thickness of the battery case, it is necessary to increase the D value, i.e., the thickness of the gas barrier layer relative to the polymer layer, to enhance the durability of the battery case. Since the gas barrier layer contains a metal component, an increase in the thickness of the gas barrier layer relative to the polymer layer is advantageous for improving the durability of the battery case.

[0051] On the other hand, if the thickness ratio of the gas barrier layer to the polymer layer is made too large to increase durability, problems such as reduced sealing strength or insulation breakdown due to damage to the outer polymer layer may occur, which may limit the depth of the cup portion.

[0052] Accordingly, the present invention is significant in that it provides a standard for determining how much the thickness of each layer forming the battery case must be adjusted according to the depth of the cup portion through the K value according to the above formula (1) to achieve excellent performance.

[0053] Below, each component of the present invention is described in more detail.

[0054]

[0055] Battery Case

[0056] A battery case according to the present invention will be described with reference to FIGS. 1 to 3.

[0057] A battery case according to the present invention comprises a first polymer layer (10), a second polymer layer (30), and a gas barrier layer (20) interposed between the first polymer layer (10) and the second polymer layer (30). Specifically, the battery case is manufactured by molding a pouch film laminate in which the first polymer layer (10), the gas barrier layer (20), and the second polymer layer (30) are sequentially provided, and includes at least one cup portion (110a, 110b). Fig. 1 illustrates a cross-sectional structure of the pouch film laminate.

[0058] Meanwhile, examples of battery cases according to the present invention are illustrated in FIGS. 2 and 3. The cup portion (110a, 110b) is a space (112) for accommodating an electrode assembly (not shown) and an electrolyte (not shown), and is manufactured by drawing and forming a pouch film laminate (1) using a punch or the like. At this time, the drawing and forming can be performed by pressing the punch toward the second polymer layer (30) of the pouch film laminate (1).

[0059] The above battery case (100) may include one cup portion (110a) as shown in FIG. 2, or may include two cup portions (110a, 110b) as shown in FIG. 3.

[0060] Meanwhile, the battery case (100) according to the present invention includes a lower case (110) and an upper case (120), and the cup portions (110a, 110b) may be formed in only one of the lower case (110) and the upper case (120), or may be formed in both. When the pouch film laminate (1) is formed with a 1-cup forming device, a battery case having a 1-cup portion can be manufactured, as shown in FIG. 2, and when it is formed with a 2-cup forming device, a battery case having cup portions formed in both the lower case (110) and the upper case (120) can be manufactured, as shown in FIG. 3.

[0061]

[0062] According to one embodiment of the present invention, the thickness of the battery case refers to the thickness of the pouch film laminate, and may be 100 µm to 1,000 µm, specifically 110 µm to 900 µm, and more specifically 120 µm to 700 µm.

[0063] Additionally, the depth of the cup portion may be changed according to the thickness of the electrode assembly to be accommodated, but may be, for example, 1 mm or more, specifically 3 mm or more, more specifically 7 mm or more, and may be 70 mm or less, specifically 60 mm or less, more specifically 50 mm or less.

[0064] Meanwhile, the P / C of the above formula (1) may be 19.5 or more, preferably 23.0 or more. When the P / C value is 19.5 or more, the thickness of the battery case is sufficiently secured when the depth of the cup part is taken into account, so there is an advantage in that the proportion occupied by the gas barrier layer in the pouch film laminate can be reduced. However, when the energy density of the cell is taken into account, the P / C is preferably 250.0 or less, specifically 100.0 or less.

[0065]

[0066] Below, each layer of the battery case is described in detail.

[0067]

[0068] first polymer layer

[0069] The above first polymer layer (10) is arranged on the outermost layer of the battery case to protect the electrode assembly from external impact and electrically insulate it, and may be made of one or more polymer materials selected from the group consisting of, for example, polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon.

[0070] The above first polymer layer (10) may have a single-layer structure, or may have a multi-layer structure in which different polymer films (12, 14) are laminated as illustrated in Fig. 1. When the first polymer layer (10) has a multi-layer structure, an adhesive layer (16a) may be interposed between the polymer films.

[0071] Meanwhile, the thickness of the first polymer layer (10) may be 10 µm to 300 µm, preferably 20 µm to 250 µm, and more preferably 30 µm to 200 µm. It is advantageous in terms of durability for the first polymer layer to have a thickness of 10 µm or more. However, if the thickness of the first polymer layer is excessively thick, the formability may deteriorate, so it is preferably 300 µm or less. The above thickness is the thickness including the adhesive layer (16a) when the first polymer layer (10) has a multilayer structure.

[0072] In a preferred embodiment, the first polymer layer (10) may be a laminate of a polyethylene terephthalate (PET) film and a nylon film. In this case, it is preferred that the nylon film be disposed on the gas barrier layer (20) side, i.e., on the inside, and the PET film be disposed on the surface side of the battery case.

[0073] Polyethylene terephthalate (PET) has excellent durability and electrical insulation properties, and when a PET film is placed on the surface side, it exhibits excellent durability and insulation properties. However, in the case of the PET film, the adhesion with the aluminum alloy thin film constituting the gas barrier layer (20) is weak, and the stretching behavior is also different. Therefore, when the PET film is placed on the gas barrier layer side, the substrate layer and the gas barrier layer may be peeled off during the forming process, and the gas barrier layer may not be stretched uniformly, which may cause a problem of reduced formability. In contrast, since the stretching behavior of a nylon film is similar to that of an aluminum alloy thin film constituting the gas barrier layer (20), when a nylon film is placed between the polyethylene terephthalate and the gas barrier layer, an effect of improving formability can be obtained.

[0074]

[0075] gas barrier layer

[0076] The gas barrier layer (20) is intended to secure the mechanical strength of the battery case, block the ingress of gas or moisture from outside the secondary battery, and prevent leakage of electrolyte.

[0077] As the thickness of the gas barrier layer increases, the formability improves, the critical forming depth increases, and the resistance to external stress after forming improves. Therefore, the thickness of the gas barrier layer may be 50 ㎛ or more, preferably 70 ㎛ or more, and more preferably 100 ㎛ or more. However, as the energy density of the cell may decrease as the thickness of the gas barrier layer increases, the thickness may be 900 ㎛ or less, preferably 700 ㎛ or less, and more preferably 500 ㎛ or less.

[0078] Meanwhile, the gas barrier layer may include one or more metals selected from SUS, Ni, Fe, Co, Cr, Mo, Ta, W, Ti, and Re; or an alloy of the metal and Al, and specifically may be formed of an aluminum alloy thin film.

[0079] Preferably, the aluminum alloy thin film may have an iron (Fe) content of 1.2 wt% to 1.7 wt%, preferably 1.3 wt% to 1.7 wt%, and more preferably 1.3 wt% to 1.45 wt%. When the iron (Fe) content in the aluminum alloy thin film is 1.2 wt% or more, the strength of the aluminum alloy thin film can be increased, thereby preventing cracks and pinholes from occurring during forming. However, considering flexibility, formability, and bendability, it is preferable that the iron (Fe) content is 1.7 wt% or less.

[0080]

[0081] second polymer layer

[0082] The second polymer layer (30) is bonded through heat compression to seal the battery case and is located on the innermost layer of the battery case.

[0083] The second polymer layer (30) must have insulating and corrosion resistance properties because it is the surface that comes into contact with the electrolyte and electrode assembly after cell assembly, and must completely seal the inside to block material movement between the inside and the outside, so it must have high sealing properties.

[0084] The second polymer layer (30) may be formed of, for example, one or more selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, and Teflon, and among these, it is particularly preferable to include polypropylene (PP) which has excellent mechanical properties such as tensile strength, rigidity, surface hardness, wear resistance, and heat resistance, and chemical properties such as corrosion resistance.

[0085] More specifically, the second polymer layer (30) may include polypropylene, cast polypropylene (CPP), acid modified polypropylene, polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0086] The above second polymer layer (30) may have a single-layer structure or may have a multi-layer structure including two or more layers made of different polymer materials.

[0087] Meanwhile, the thickness of the second polymer layer (30) may be 10 µm to 300 µm, preferably 20 µm to 250 µm, and more preferably 30 µm to 200 µm. A thickness of 30 µm or more of the second polymer layer is advantageous in terms of sealing durability and insulation. However, if the thickness of the second polymer layer is excessively thick, flexibility may be reduced, so it is preferably 300 µm or less.

[0088] Meanwhile, D of the above formula (1), that is, the ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer, may be 0.80 or more, preferably 1.00 or more, and more preferably 1.20 or more. This means that the gas barrier layer, that is, the metal layer, accounts for a large proportion in the battery case, so that when the D value is designed as described above, excellent durability can be secured even if a relatively thicker electrode assembly is accommodated. That is, even if the P / C value of the above formula (1) decreases, it becomes easy to control the K value to 63.0 or more. However, when the insulation of the case is taken into consideration, the D is preferably 9.00 or less, specifically 5.00 or less, and more specifically 2.50 or less.

[0089]

[0090] Secondary battery

[0091] Below, a secondary battery including the above battery case is described.

[0092]

[0093] A secondary battery according to one embodiment of the present invention comprises an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and the battery case, wherein the electrode assembly and the electrolyte are accommodated in a cup portion of the battery case.

[0094] Specifically, referring to FIGS. 2 and 3, the electrode assembly is housed in the cup portion (110a, 110b), an electrolyte is injected, and then the upper case (120) is folded so that it is on top of the lower case (110) so that the electrode assembly and the electrolyte can be sealed from the outside. Then, the secondary battery can be manufactured by performing a sealing process by thermally compressing the corner portions of the upper case (120) and the lower case (110).

[0095] Meanwhile, a secondary battery according to an embodiment of the present invention may have an S value of 37.0 or more, 40.0 or more, or 45.0 or more according to the following formula (2), and in this case, it is preferable in that the durability of the battery case is appropriately secured when the thickness of the electrode assembly is taken into consideration. However, when the energy density and insulation are taken into consideration, it may be 400.0 or less, 300.0 or less, or 85.0 or less.

[0096] Equation (2): S = P / T × N + 20D

[0097] In the above equation (2),

[0098] P is the thickness value of the battery case measured in μm,

[0099] T is the thickness value of the electrode assembly measured in mm, and if it includes two or more electrode assemblies, it is the sum of these thickness values,

[0100] N is the number of cups in the battery case,

[0101] D is the ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer.

[0102]

[0103] Since the battery case has been described in detail above, the electrode assembly and electrolyte will be described in more detail below.

[0104]

[0105] electrode assembly

[0106] In the present invention, it is preferable that the electrode assembly be a stacked electrode assembly having a structure in which a positive electrode and a negative electrode are sequentially stacked with a separator between them. The present invention utilizes the capacity improvement effect obtained by stacking electrodes in parallel while resolving the problem of battery case damage that occurs due to the thickening of the electrode assembly, and is therefore suitable for application to a stacked electrode assembly.

[0107] Meanwhile, the thickness of the electrode assembly may be 1 mm to 150 mm, specifically 3 mm to 120 mm, and more specifically 7 mm to 100 mm.

[0108] As depicted in FIG. 4, the electrode assembly (200) may be provided with a plurality of electrode tabs (230) welded to each other. The plurality of electrode tabs (230) may be connected to a plurality of electrodes (210) and may protrude outwardly from the electrode assembly (200) to act as a passage through which electrons may move between the inside and the outside of the electrode assembly (200).

[0109] The electrode tab (230) connected to the positive electrode and the electrode tab (230) connected to the negative electrode may protrude in different directions with respect to the electrode assembly (200). However, this is not limited to the present invention, and the electrode tab (230) connected to the positive electrode and the electrode tab (230) connected to the negative electrode may also protrude in the same direction while being parallel to each other.

[0110] Meanwhile, the positive electrode, negative electrode, separator, and electrolyte may be used in the present invention without limitation if they are commonly used in secondary batteries, but the following description may be referred to as a preferred example.

[0111] The positive electrode is a sheet-shaped positive electrode, and may include a positive electrode current collector made of a metal thin plate with excellent conductivity, such as aluminum foil, and a positive electrode active material layer coated on one or both surfaces thereof. The negative electrode is a sheet-shaped negative electrode, and may include a negative electrode current collector made of a metal thin plate with excellent conductivity, such as copper (Cu) or nickel (Ni) foil, and a negative electrode active material layer coated on one or both surfaces thereof.

[0112] The above-described positive electrode active material layer may include a lithium metal oxide containing lithium and a transition metal such as cobalt, manganese, and / or nickel as a positive electrode active material, and may further include a conductive material and / or a binder as needed. The positive electrode active material, conductive material, and binder may be any of a variety of materials commonly used in the manufacture of secondary batteries without limitation.

[0113] Specifically, the positive electrode may include at least one selected from the group consisting of a lithium nickel-based composite oxide, a lithium manganese-based composite oxide, and a lithium iron phosphate-based composite oxide as a positive electrode active material, and preferably may include a lithium nickel-based composite oxide, and the lithium nickel-based composite oxide may be represented by the following chemical formula 1.

[0114] [Chemical Formula 1]

[0115] Li 1+x (Ni a Co b Mn c M d )O2

[0116] In the above chemical formula 1,

[0117] M is at least one selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0118] -0.4≤x≤0.4, 0.30≤a≤1, 0≤b≤0.70, 0≤c≤0.70, 0≤d≤0.10, a+b+c+d=1.

[0119] The above 1+x represents the molar ratio of lithium in the lithium nickel-based composite oxide, and may be -0.1≤x≤0.2, or 0≤x≤0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based composite oxide can be stably formed.

[0120] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based composite oxide, and may be 0.70≤a<1, 0.80≤a<1, or 0.90≤a<1. When the molar ratio of nickel satisfies the above range, a high energy density is exhibited, enabling high capacity implementation.

[0121] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel composite oxide, and is 0. <b≤0.25, 0<b≤0.15, 또는 0<b≤0.05일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0122] The above c represents the molar ratio of manganese among all metals excluding lithium in the lithium nickel composite oxide, and is 0. <c≤0.25, 0<c≤0.15, 또는 0<c≤0.05일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타난다.

[0123] The above d represents the molar ratio of the M element among the total metal excluding lithium of the lithium nickel-based composite oxide, and the above d may be 0≤d≤0.08, 0≤d≤0.05, or 0≤d≤0.03.

[0124] Specifically, a, b, c and d of the above chemical formula 1 are 0.80≤a<1, 0, respectively. <b≤0.15, 0<c≤0.15, 0≤d≤0.05를 만족할 수 있다.

[0125] When the lithium nickel composite oxide is an NCM oxide containing all of nickel, cobalt, and manganese, the resistivity of the positive electrode is formed low, so the phenomenon of insulation deterioration due to an increase in the thickness of the electrode assembly described above becomes more evident, and thus the effect of configuring it to satisfy the above formula (1) can be maximized.

[0126] Meanwhile, the lithium manganese composite oxide is Li p Mn 1-q M a q A2, Li p Mn2O 4-r X r , Li p Mn 2-q M a q M b r A4, Li p Co 1-q M a q A2, Li p Co 1-q M a q O 2-r X r , Li p Ni 1-q M a q O 2-r X r , Li p Ni 1-q Co q O 2-r X r , Li p Ni 1-q-r Co qM a r A w , Li p Ni 1-q-r Co q M a r O 2-w X w , Li p Ni 1-q-r Mn q M a r A w and Li p Ni 1-q-r Mn q M a r O 2-w X w It may be one or more selected from the group consisting of, wherein p, q, r and w are 0.9≤p≤1.6, 0≤q≤1, 0≤r≤1, 0≤w≤2, respectively, and M a Wow M b are the same or different and are at least one element selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth elements, A is at least one element selected from the group consisting of O, F, S and P, and X is at least one element selected from the group consisting of F, S and P.

[0127] In addition, the lithium iron phosphate composite oxide can be represented by the following chemical formula 2.

[0128] [Chemical Formula 2]

[0129] LiFe 1-k M c k PO4

[0130] In the above chemical formula 2,

[0131] M c is at least one selected from Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir and V,

[0132] 0≤k<1.

[0133] The above-described negative electrode active material layer may include a negative electrode active material such as a carbonaceous material such as graphite; a metal or an alloy composed of the metal; an oxide of the metal; and a composite of the metal and carbon, and may further include a conductive material and / or a binder as needed. The negative electrode active material, conductive material, and binder may be various materials commonly used in the manufacture of secondary batteries without limitation.

[0134] The above separator may be a conventional porous polymer film used as a separator in the past, for example, a polyolefin-based porous polymer film such as an ethylene homopolymer, a propylene homopolymer, a copolymer of ethylene and butene, a copolymer of ethylene and hexene, and a copolymer of ethylene and methacrylate, etc., used alone or in a laminated manner. In addition, a polyolefin-based porous polymer film coated with inorganic particles (e.g., Al2O3) or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used, but is not limited thereto.

[0135]

[0136] electrolyte

[0137] In one embodiment of the present invention, the electrolyte may be used without limitation as long as lithium ions generated by an electrochemical reaction at the electrode during charge and discharge can move, and for example, a lithium salt dissolved in a non-aqueous organic solvent may be used.

[0138] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt may be appropriately changed within a generally usable range, but is preferably used within a range of 0.1 M to 5.0 M, and preferably 0.1 M to 3.0 M.

[0139] The above non-aqueous organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, cyclic carbonate-based solvents such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate; linear carbonate-based organic solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and ethyl methyl carbonate (EMC); or mixed organic solvents thereof may be used.

[0140]

[0141] The above secondary battery can be applied to various devices. For example, it can be applied to electric vehicles such as electric bicycles, electric cars, and hybrid electric vehicles (HEVs).

[0142] Accordingly, according to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided.

[0143] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0144]

[0145] Hereinafter, the present invention will be described in more detail through specific examples.

[0146] [Examples and Comparative Examples: Manufacturing of Battery Cases]

[0147] Example 1

[0148] A polyethylene terephthalate (PET) film with a width of 266 mm, a length of 50 m, and a thickness of 50 μm and a nylon film with a width of 266 mm, a length of 50 m, and a thickness of 100 μm were sequentially bonded to one side of an aluminum alloy film with a width of 266 mm, a length of 50 m, and a thickness of 250 μm using a urethane adhesive by dry lamination, thereby forming a first polymer layer with a thickness of 150 μm.

[0149] Next, a pouch film laminate was manufactured by melting non-stretched polypropylene (CPP) at high temperature and co-extruding it on the opposite side of the aluminum alloy thin film on which the first polymer layer was formed to form a sealant layer (second polymer layer) having a thickness of 100 μm. The total thickness of the pouch film laminate was 500 μm.

[0150] After cutting the above pouch film laminate to a size of 130 mm Х 266 mm, drawing molding was performed in a molding device having a molding section of 100 mm Х 216 mm to manufacture a 1-cup type battery case including a cup section with a depth of 2 mm. The punch and molding section of the molding device have filleted corners and edges, and the corners of the punch have a curvature of 2 mm and the edges have a curvature of 1 mm, and the corners of the molding section have a curvature of 2.3 mm and the edges have a curvature of 1 mm. In addition, the clearance between the punch and the molding section was 0.3 mm.

[0151]

[0152] Examples 2 to 34 and Comparative Examples 1 to 18

[0153] A battery case was manufactured using the same process as Example 1, except that the depth of the cup part, the thickness of the polymer layer, the thickness of the gas barrier layer, etc. were changed as shown in Table 1 below.

[0154]

[0155] [Experimental Example]

[0156] Experimental Example 1: Corrosion Evaluation

[0157] Li[Ni as a cathode active material 0.8 Co 0.1 Mn 0.1 ]The anode containing O2 and A stacked electrode assembly having a total length of 210 mm and a total width of 95 mm was manufactured by alternately stacking negative electrodes containing graphite as a negative active material with a safety reinforced separator (SRS) in between. The electrode assemblies were manufactured in seven thicknesses of 1.9 mm, 3.9 mm, 5.9 mm, 7.9 mm, 9.9 mm, 11.9 mm, and 13.9 mm, and different thicknesses were used depending on the depth of the cup portion of the battery case, as shown in Table 1 below.

[0158] After the electrode assembly was placed in the cup portion of each battery case manufactured in Examples 1 to 34 and Comparative Examples 1 to 18, an electrolyte solution prepared by dissolving 1.0 M LiPF6 in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70 was injected, followed by sealing and performing an activation process to manufacture a pouch-type secondary battery.

[0159] Ten secondary batteries corresponding to each example and comparative example were manufactured, and then the manufactured secondary batteries were charged to 4.2 V at a 0.33 C-rate constant current in a room temperature chamber at 25°C and then discharged to 2.5 V at a 0.33 C constant current. Then, the charging and discharging were repeated 1,000 times under the same conditions as above, and the cell appearance was inspected to determine the number of corroded cells among the ten cells, which are listed in Table 1 below.

[0160]

[0161]

[0162]

[0163]

[0164] Through the results of Table 1 above, it can be confirmed that in the battery cases of Examples 1 to 34, in which the thickness of the battery case, the depth of the cup part, the thickness of the gas barrier layer, and the thickness of the polymer layer were adjusted to satisfy K ≥ 63.0, no corrosion occurred at all in the secondary batteries having an S value of 37.0 or more, but in the battery cases of Comparative Examples 1 to 18, in which K < 63.0, the secondary batteries having an S value of less than 37.0 experienced corrosion in one or more cells.

[0165] That is, it can be confirmed that there is an effect of improving the corrosion resistance of a pouch-type secondary battery by adjusting the K value of the above formula (1) to 63.0 or more.

[0166]

[0167] Experimental Example 2: Cell Performance Evaluation

[0168] Among the secondary batteries manufactured in the above Experimental Example 1, the secondary batteries having an electrode assembly thickness of 7 mm or more (Examples 4 to 7, 11 to 14, 18, 19, 23 to 26, 30, 31 and Comparative Examples 1 to 18) were charged to 4.2 V at a 0.33 C-rate constant current in a room temperature chamber at 25°C and then discharged to 2.5 V at a 0.33 C constant current to confirm the initial capacity and energy density. The energy density was calculated by multiplying the discharge capacity of the cell by the average voltage and dividing it by the unit volume, and the average voltage is the value obtained by dividing the curve integral of the capacity-voltage profile by the capacity. Table 2 below lists the average values ​​of the initial capacity and energy density confirmed in 10 cells.

[0169] Next, the charging and discharging were repeated 1,000 times under the same conditions as above, and the capacity retention rate after 1,000 charging and discharging cycles compared to the initial capacity was checked for each of the 10 cells, and the average value was calculated and recorded in Table 2 below.

[0170]

[0171]

[0172] Through the results of Table 2 above, it can be confirmed that the secondary batteries applying the battery cases of the examples satisfying K ≥ 63.0 satisfy S ≥ 37.0, and as the depth of the cup portion increases, that is, as the electrode assembly becomes thicker, the initial capacity tends to increase and the lifespan tends to improve.

[0173] On the other hand, it can be confirmed that the secondary battery using the battery case of the comparative examples with K < 63.0 has S < 37.0 and that the initial capacity increases as the thickness of the electrode assembly increases, but the life characteristics decrease.

[0174] As the thickness of the electrode assembly increases, the force generated by expansion / contraction of the electrode assembly during battery operation also increases, and thus the level of durability required for the battery case also increases. However, the battery cases manufactured in the comparative examples do not satisfy this level, unlike the battery cases manufactured in the examples.

[0175] That is, it can be confirmed that there is an effect of improving the life characteristics of a pouch-type secondary battery by adjusting the K value of the above equation (1) to 63.0 or more.

Claims

Comprising a first polymer layer, a second polymer layer, and a gas barrier layer interposed between the first polymer layer and the second polymer layer, comprising one or more cup portions curved in one direction; A battery case having a K value of 63.0 or more according to the following equation (1): Equation (1): K = P / C + 50D In the above equation (1), P is the thickness value of the battery case measured in μm, C is the depth value of the cup part measured in mm, D is the ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer. In claim 1, A battery case having a thickness of 100㎛ to 1,000㎛. In claim 1, A battery case, wherein the depth of the cup portion is 1 mm or more and 70 mm or less. In claim 1, A battery case in which the P / C of the above formula (1) is 19.5 or more. In claim 1, A battery case, wherein the thickness of the first polymer layer is 10 ㎛ to 300 ㎛. In claim 1, A battery case wherein the thickness of the second polymer layer is 10 ㎛ to 300 ㎛. In claim 1, A battery case wherein the thickness of the gas barrier layer is 50㎛ or more and 900㎛ or less. In claim 1, A battery case, wherein the gas barrier layer comprises at least one metal selected from SUS, Ni, Fe, Co, Cr, Mo, Ta, W, Ti, and Re; or an alloy of the metal and Al. In claim 1, A battery case in which D in the above formula (1) is 0.80 or more. An electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case according to claim 1, A secondary battery, wherein the electrode assembly and electrolyte are accommodated in the cup portion of the battery case. In claim 10, The secondary battery above has an S value of 37.0 or more according to the following formula (2): Equation (2): S = P / T Х N + 20D In the above equation (2), P is the thickness value of the battery case measured in μm, T is the thickness value of the electrode assembly measured in mm, and if it includes two or more electrode assemblies, it is the sum of these thickness values, N is the number of cups in the battery case, D is the ratio of the thickness of the gas barrier layer to the total thickness of the first polymer layer and the second polymer layer. In claim 10, A secondary battery, wherein the thickness of the electrode assembly is 1 mm to 150 mm.

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