Pouch-type secondary battery

Abstract

The present specification relates to a pouch-type secondary battery having excellent fire resistance and safety, the pouch-type secondary battery comprising: an electrode assembly comprising a positive electrode and a negative electrode; and a pouch-type case in which the electrode assembly is accommodated, wherein: the pouch-type case comprises a foam body; and the foam body comprises a foaming agent, an inorganic filler, and an organic binder, has an impact absorption energy density of 0.17J / cm2 or more, and an expansion rate (E) of 1.8 or more derived by formula 1.

Description

Pouch-type secondary battery

[0001] Cross-citation with related applications

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0196776 filed on December 26, 2024, Korean Patent Application No. 10-2025-0084739 filed on June 25, 2025, and Korean Patent Application No. 10-2025-0166730 filed on November 6, 2025, and all contents disclosed in said Korean patent application documents are incorporated herein as part of the specification.

[0003] Technology field

[0004] In this specification, technology relating to a pouch-type secondary battery is disclosed.

[0005]

[0006] Secondary batteries are used in a wide range of fields, including small products such as digital cameras, P-DVDs, MP3 players, mobile phones, PDAs, portable game devices, power tools, and E-bikes, as well as large products requiring high output such as electric vehicles and hybrid vehicles, and power storage devices and backup power storage devices that store surplus power or renewable energy.

[0007] As the scope of applications for secondary batteries expands, demands for their safety are increasing. During the charging and discharging process, the temperature of the electrodes can rise rapidly, posing a risk of fire or explosion. For instance, if thermal runaway occurs in a secondary battery equipped in an electric vehicle, it can lead to a major fire or a series of explosions that affect adjacent vehicles, potentially resulting in casualties and property damage.

[0008] Specifically, during the charging and discharging process, secondary batteries may experience thermal runaway, such as ignition or explosion, due to internal factors or external impacts, including electrolyte leakage, excessive gas generation, and internal short circuits. In particular, when multiple secondary batteries are installed in a device, such as an electric vehicle, significant damage can occur due to thermal propagation, where a fire or explosion in only one battery spreads to adjacent batteries.

[0009] Therefore, technology is needed to prevent damage caused by heat propagation and fire.

[0010]

[0011] In this specification, a pouch-type secondary battery with excellent fire resistance and safety is provided by applying a foam to a pouch-type case that can stably and effectively delay or block thermal propagation and thermal runaway even when a thermal event occurs.

[0012]

[0013] [1] In one embodiment, the electrode assembly comprises an anode and a cathode; and a pouch-type case in which the electrode assembly is housed; wherein the pouch-type case comprises a foam, the foam comprises a foaming agent, an inorganic filler, and an organic binder, and the foam has an impact absorption energy density of 0.17 J / cm² 2 The above describes a pouch-type secondary battery having an expansion rate (E) of 1.8 or higher derived by the following formula 1.

[0014] [Equation 1]

[0015] E = (T e - T i ) / T i

[0016] In the above Equation 1,

[0017] T i is the initial thickness (㎛) of the foam, and Te is the full expansion thickness (μm) of the foam above.

[0018] [2] The present invention relates to a pouch-type secondary battery of [1], wherein the foam has an Expansion Toughness Index (ETI) of 3.0 cm derived by the following Equation 2. 2 It can be more than / J.

[0019] [Equation 2]

[0020] ETI = E / F

[0021] In the above Equation 2,

[0022] E is the expansion rate, derived by Equation 1 above, and F is the shock absorption energy density (J / cm²) of the foam. 2 )am.

[0023] [3] The present invention relates to a pouch-type secondary battery of [2], wherein the foam has an expansion strength index (ETI) of 3.0 cm derived by Equation 2. 2 / J to 19.0cm 2 / J could be.

[0024] [4] The present invention relates to at least one pouch-type secondary battery among [1] to [3], wherein the pouch-type case comprises a structure in which a plurality of layers are stacked, and the foam may be disposed on one or more surfaces selected from the group consisting of at least one interface between the layers, the innermost surface and the outermost surface of the pouch-type case.

[0025] [5] The present invention relates to at least one pouch-type secondary battery among [1] to [4], wherein the foam has an impact absorption energy density of 0.17 J / cm² 2 Up to 0.70 J / cm 2 And, the foam may have an expansion rate (E) derived by the above formula 1 of 1.8 to 6.0.

[0026] [6] In the present invention, in at least one pouch-type secondary battery of [1] to [5], the foaming agent may be included in an amount of 20 to 90 parts by weight relative to 100 parts by weight of the foam.

[0027] [7] The present invention relates to at least one pouch-type secondary battery among [1] to [6], wherein the organic binder may include an elastic binder and a reinforcing binder.

[0028] [8] In the pouch-type secondary battery of [7], the present invention can satisfy K of Formula 3 below from 0.4 to 2.2.

[0029] [Equation 3]

[0030] K = B e / B r

[0031] In the above Equation 3,

[0032] B e is the weight percentage of the elastic binder based on the total weight of the foam, and B r is the weight percentage of the reinforcing binder based on the total weight of the foam.

[0033] [9] The present invention, in the pouch-type secondary battery of [7], the elastic binder comprises one or more selected from the group consisting of styrene-butadiene rubber, nitrile rubber, polyester resin, cellulose resin, urethane resin and silicone rubber, and the reinforcing binder may comprise one or more selected from the group consisting of epoxy resin and phenolic resin.

[0034]

[0010] The present invention may have a weight ratio of the inorganic filler and the foaming agent in at least one of [1] to [9] of the pouch-type secondary battery, in which the weight ratio may be 1:1 to 1:36.

[0035]

[0011] The present invention relates to at least one pouch-type secondary battery among [1] to

[0010] , wherein the foaming agent is foamed at a temperature of 130°C or higher, the foamed foaming agent forms a three-dimensional network structure having pores, and the inorganic filler may have a structure disposed within the pores.

[0036]

[0012] The present invention relates to at least one pouch-type secondary battery among [1] to

[0011] , wherein the foaming agent may include one or more selected from the group consisting of lithium silicate, potassium silicate, sodium silicate, zirconium silicate, magnesium silicate, and titanium silicate.

[0037]

[0013] The present invention relates to at least one pouch-type secondary battery among [1] to

[0012] , wherein the foaming agent comprises sodium silicate, and the sodium silicate may satisfy Formula 4 below:

[0038] [Equation 4]

[0039] 2 ≤ M S / M N ≤ 4.5

[0040] In the above Equation 4,

[0041] M S is the molar ratio of SiO2 contained in the above sodium silicate, and M N This is the molar ratio of Na2O contained in the above sodium silicate.

[0042]

[0014] The present invention relates to at least one pouch-type secondary battery among [1] to

[0013] , wherein the inorganic filler may include one or more selected from the group consisting of titanium dioxide, alumina, kaolin, zirconia, silica, zinc oxide and boehmite.

[0043]

[0015] In the present invention, in at least one pouch-type secondary battery among [1] to

[0014] , the thickness of the foam may be 10 μm to 1000 μm.

[0044]

[0045] The pouch-type secondary battery according to the present specification includes a foam, thereby effectively delaying or preventing heat propagation and / or thermal runaway even when a thermal event occurs, and thus can have excellent fire resistance and safety.

[0046] Specifically, the foam has excellent internal moisture retention capabilities even in environments with large temperature fluctuations, thereby ensuring processability during battery box manufacturing and durability for long-term use. Furthermore, while the foam allows for maximum foaming effects through foaming at a specific temperature, it exhibits superior thickness expansion rates and the ability to maintain this state, enabling stable control of heat propagation or thermal runaway.

[0047]

[0048] FIG. 1 is a schematic diagram showing a cross-section of a foamed body before foaming according to the present specification.

[0049] FIG. 2 is a schematic diagram showing a cross-section of a foam after foaming according to the present specification.

[0050]

[0051] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0052] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0053] In this specification, each of the phrases such as “A or B”, “at least one of A and B”, “at least one of A or B”, “A, B or C”, “at least one of A, B and C”, and “at least one of A, B, or C” may include any one of the items listed together in the corresponding phrase, or all possible combinations thereof.

[0054]

[0055] The pouch-type secondary battery described in this specification comprises at least one of the technical configurations described below, and may comprise any combination of technically feasible configurations among the technical configurations below.

[0056] The above pouch-type secondary battery is described in detail below.

[0057]

[0058] Pouch-type secondary battery

[0059] In one embodiment, the apparatus comprises: an electrode assembly including an anode and a cathode; and a pouch-type case in which the electrode assembly is housed; wherein the pouch-type case comprises a foam, the foam comprises a foaming agent, an inorganic filler, and an organic binder, and the foam has an impact absorption energy density of 0.17 J / cm² 2 The above foam is provided as a pouch-type secondary battery having an expansion rate (E) of 1.8 or higher derived by the following formula 1.

[0060] [Equation 1]

[0061] E = (Te - T i ) / T i

[0062] In the above Equation 1,

[0063] T i is the initial thickness (㎛) of the foam above, and

[0064] T e is the full expansion thickness (μm) of the foam above.

[0065] By including the foam in the pouch-type case of the above pouch-type secondary battery, when a thermal event occurs in the pouch-type secondary battery, the distance from adjacent secondary batteries can be increased through sufficient expansion and maintenance of the expanded state, thereby delaying or preventing thermal runaway and thermal propagation, and thereby improving safety.

[0066] In one embodiment, the pouch-type secondary battery may further include an electrolyte. Examples of the electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0067] Specifically, the electrolyte may include an organic solvent and a lithium salt. Additionally, the electrolyte may further include an additive.

[0068]

[0069] (1) Electrode assembly

[0070] The electrode assembly according to the present invention may include an anode and a cathode.

[0071] anode

[0072] The above anode may include an anode active material.

[0073] ​The above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation, and is not particularly limited as long as it is a positive electrode active material used in the field. Specifically, the above-mentioned positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the above-mentioned lithium metal oxide may be a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2Examples include )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, such that 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc., and any one or more of these compounds may be included.

[0074] The above positive electrode may include a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector.

[0075] The above positive current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above positive current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy, preferably aluminum.

[0076] The thickness of the above positive current collector can typically be 3 to 500 μm.

[0077] The above positive current collector may form fine irregularities on its surface to strengthen the bonding force of the positive active material. For example, the above positive current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0078] The positive active material layer may be disposed on at least one surface of the positive current collector. Specifically, the positive active material layer may be disposed on one or both surfaces of the positive current collector.

[0079] The above-described positive active material layer may include the positive active material described above.

[0080] The above positive active material may be included in the above positive active material layer in an amount of 80% to 99% by weight, specifically 85% to 98% by weight.

[0081] The above-described positive active material layer may optionally further include a binder and / or a conductive material together with the positive active material described above.

[0082] The above binder is a component that assists in the binding of active materials and conductive materials, and in binding to current collectors, and specifically may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0083] The above binder may be included in the positive active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to sufficiently secure binding strength between components such as the positive active material.

[0084] The above conductive material can be used to assist and enhance conductivity in a secondary battery, and is not particularly limited as long as it is conductive without causing chemical changes. Specifically, the above cathode conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably may include carbon nanotubes for the purpose of enhancing conductivity.

[0085] The above conductive material may be included in the above positive active material layer in an amount of 1% to 20% by weight, preferably 1.2% to 10% by weight, in order to sufficiently ensure electrical conductivity.

[0086] The thickness of the above positive active material layer may be 5㎛ to 500㎛, preferably 20㎛ to 200㎛.

[0087] The anode may be manufactured by applying and drying an anode slurry composition prepared by dissolving or dispersing an anode active material, and optionally a binder and a conductive material, in an anode slurry solvent on an anode current collector, or by casting the anode slurry composition onto a separate support and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0088] The above anode slurry solvent may include organic solvents such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone, and may be used in an amount that results in a desirable viscosity when including the anode active material, binder, and conductive material. For example, the concentration of the solid component including the anode active material, and optionally the binder and conductive material, may be 50 to 95 weight%, preferably 70 to 95 weight%, and more preferably 70 to 90 weight%.

[0089]

[0090] cathode

[0091] The above cathode can be opposite to the above anode.

[0092] The above cathode may include a cathode active material.

[0093] The above-mentioned negative electrode active material is a material capable of reversibly inserting / extracting lithium ions and may include at least one selected from the group consisting of carbon-based active materials, (meta)metal-based active materials, and lithium metal, and specifically may include at least one selected from carbon-based active materials and (meta)metal-based active materials. In this specification, the term (meta)metal-based active material may be a comprehensive expression encompassing both metal-based active materials and metal-based active materials.

[0094] The above carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and specifically may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0095] The above (quasi)metallic active material may include at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium with at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (quasi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; etc.

[0096] More specifically, the above (quasi)metallic active material may include a silicon-based active material.

[0097] The above silicon-based active material is silicon (Si) and silicon oxide (SiOx(O2)). <x<2)로 표시될 수 있음. 바람직하게는 SiO일 수 있음) 및 실리콘-탄소 복합체(Si / C Composite)로 이루어진 군에서 선택된 적어도 1종을 포함할 수 있다.

[0098] Specifically, the negative electrode active material may include at least one of a carbon-based active material and a silicon-based active material, and specifically, may include a carbon-based active material and a silicon-based active material. When the negative electrode active material includes a carbon-based active material and a silicon-based active material, the weight ratio of the carbon-based active material and the silicon-based active material may be 50:50 to 99:1, specifically 70:30 to 99:1, more specifically 85:15 to 99:1, and even more specifically 90:10 to 99:1.

[0099]

[0100] The above cathode may include a cathode current collector; and a cathode active material layer disposed on at least one surface of the cathode current collector. In this case, the cathode active material may be included in the cathode active material layer.

[0101] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the above-mentioned negative current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy.

[0102] The above-mentioned cathode current collector can typically have a thickness of 3 to 500 μm.

[0103] The above-mentioned negative current collector may form fine irregularities on its surface to strengthen the bonding force of the negative active material. For example, the above-mentioned negative current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0104]

[0105] The above negative electrode active material layer may be disposed on at least one surface of the negative electrode current collector, specifically on one or both surfaces of the negative electrode current collector. The negative electrode active material may be included in the negative electrode active material layer in an amount of 60% to 99% by weight, preferably 75% to 95% by weight.

[0106] The above-described cathode active material layer may optionally further include a binder and / or a conductive material together with the cathode active material described above.

[0107] The binder is used to improve the performance of the battery by enhancing the adhesion between the negative electrode active material layer and the negative electrode current collector, and may include, for example, at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and materials in which hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also include various copolymers thereof. there is.

[0108] The above binder may be included in the cathode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0109] The above conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0110] The above conductive material may be included in the above negative electrode active material layer in an amount of 0.5% to 10% by weight, preferably 1% to 5% by weight.

[0111] The thickness of the above negative electrode active material layer may be 10㎛ to 200㎛, preferably 20㎛ to 150㎛.

[0112] The above cathode can be manufactured by applying a cathode slurry composition, prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a cathode slurry solvent, onto a cathode current collector and drying it, or by casting the cathode slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0113] The above cathode slurry solvent may include, for example, at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate the dispersion of the cathode active material, binder, and / or conductive material. The solid content of the above cathode slurry composition may be 30% to 80% by weight, specifically 40% to 70% by weight.

[0114]

[0115] The electrode assembly may further include a separator interposed between the anode and the cathode.

[0116] As the above separator, a conventional porous polymer film used as a separator, such as a polyolefin-based polymer film made of ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, may be used alone or in a laminate thereof, or a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., may be used, but is not limited thereto. In addition, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0117]

[0118] (2) Pouch-type case

[0119] The pouch-type case according to the present invention accommodates the electrode assembly and includes a foam.

[0120] In one embodiment, the pouch-type case may include a structure in which a plurality of layers are laminated. Specifically, the pouch-type case may include a substrate layer that protects the electrode assembly from external impact and performs electrical insulation, a barrier layer that blocks the penetration of external gas or moisture and reinforces the mechanical strength of the case, and a sealant layer that stably seals the electrode assembly within the storage space and ensures insulation and corrosion resistance as a surface in contact with the electrode assembly.

[0121] The above substrate layer may be formed of an insulating material. Specifically, the substrate layer may comprise one or more selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazole, polyarylate, Teflon, and glass fiber. The substrate layer may be formed as a single layer or a multilayer structure. Additionally, an adhesive layer may be included as needed.

[0122] The above barrier layer is laminated between the above substrate layer and the above sealant layer to secure the mechanical strength of the pouch, block the entry of gases or moisture from outside the secondary battery, and prevent electrolyte leakage from inside the pouch-type battery case.

[0123] The barrier layer may include a metal, specifically, and may be formed as an aluminum alloy thin film. The aluminum alloy thin film may include one or more metal elements other than aluminum (Al), for example, selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si), and zinc (Zn).

[0124] The sealant layer may be formed from a material having insulating, corrosion-resistant, and sealing properties. Specifically, since the sealant layer comes into direct contact with the electrode assembly and / or electrolyte inside the pouch-type battery case, it may be formed from a material having insulating and corrosion-resistant properties. In addition, since the sealant layer must completely seal the inside of the pouch-type battery case to block material movement between the inside and outside, it may be formed from a material having high sealing properties (e.g., excellent thermal sealing strength). To ensure such insulating, corrosion-resistant, and sealing properties, the sealant layer may be formed from a polymer material.

[0125] The sealant layer may be composed of one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylenebenzobisoxazole, polyarylate, Teflon, and glass fiber, and preferably may be composed of a polyolefin resin such as polypropylene (PP) and / or polyethylene (PE). Specifically, the polypropylene may include one or more selected from the group consisting of cast polypropylene (CPP), acid modified polypropylene (PPA), polypropylene-ethylene copolymer, and polypropylene-butylene-ethylene terpolymer.

[0126] In one embodiment, the pouch-type case includes a structure in which a plurality of layers are laminated, and the foam may be disposed on one or more surfaces selected from the group consisting of at least one interface between the layers, the innermost surface, and the outermost surface of the pouch-type case. For example, the foam may be disposed at one or more locations selected from between the substrate layer and the barrier layer, between the barrier layer and the sealant layer, the outermost surface of the substrate layer, or the innermost surface of the sealant layer.

[0127] In one embodiment, the area of ​​the foam may be smaller than the area of ​​other layers included in the pouch-type case. Specifically, the area of ​​the foam may be limited to an area less than or equal to the total area of ​​the sealant layer, excluding the edge region that is heat-fused to contact each other to seal the electrode assembly from the outside.

[0128] In this way, by limiting the area of ​​the foam to within the area excluding the contact area of ​​the sealant layer, the foam can effectively expand when a thermal event occurs without impairing the sealing performance of the pouch case, thereby stably securing the gap between the electrode assembly and the adjacent battery.

[0129]

[0130] foam

[0131] The foam according to the present invention comprises a foaming agent, an inorganic filler, and an organic binder, and has an impact absorption energy density of 0.17 J / cm² 2 The above is the case, and the expansion rate (E) derived by the following Equation 1 is 1.8 or higher.

[0132] [Equation 1]

[0133] E = (T e - T i ) / T i

[0134] In the above Equation 1,

[0135] T i is the initial thickness (㎛) of the foam above, and

[0136] T e is the full expansion thickness (μm) of the foam above.

[0137] The above shock absorption energy density is the shock energy (J) required for fracture or breakage of the specimen, measured through the Izod impact test (modified ASTM D256 method), divided by the cross-sectional area (cm²) of the specimen. 2 Value divided by ) (J / cm 2 It means ) and is an indicator representing the impact resistance per unit area of ​​the above foam.

[0138] The above expansion rate represents the degree of thickness increase after foaming the foam as a ratio to the initial thickness. Specifically, a foam cut to a width and length of 5 cm and a thickness of 100 µm is placed on an insulation board, and then a heating plate heated to 750°C is brought into contact with the side opposite to the surface in contact with the insulation board for 30 seconds to induce foaming. After foaming is complete, the thickness of the foam (fully expanded thickness, T e Measure the initial thickness (T) before foaming. i Calculated according to the above Equation 1 by comparing with ).

[0139] When the temperature of a secondary battery rises above a certain temperature due to the occurrence of a specific event, the above foam expands in volume, and as a result, the distance between adjacent secondary batteries increases, which can prevent the transfer of heat or fire.

[0140] Furthermore, the foam described above possesses excellent fire resistance and heat resistance by comprising a foaming agent, an organic binder, and an inorganic filler. The foaming agent can play a role in delaying the temperature rise through latent heat as moisture vaporizes at high temperatures, and suppressing heat transfer by increasing the distance between cells through expansion. Additionally, the function of this foaming agent can be optimally realized when the organic binder and the inorganic filler work together. Specifically, the organic binder maintains the moisture contained in the foaming agent at a level above a certain threshold despite changes in the external environment, thereby ensuring the foaming phenomenon manifests stably. Moreover, the inorganic filler improves the durability of the foam, ensuring stability during long-term use, while contributing to the realization of a foam with flexibility and high strength.

[0141] Meanwhile, FIG. 1 is a schematic diagram showing a cross-section of a foamed body before foaming. Referring to FIG. 1, before the foamed body (10) is foamed, the organic binder (13) acts as a matrix, and the foaming agent (11) and inorganic filler (12) may have a structure filled within the organic binder matrix.

[0142] FIG. 2 is a schematic diagram showing a cross-section of a foam after foaming. Referring to FIG. 2, when the foam (10) is foamed at a temperature above a certain level, the organic binder (13) still maintains the matrix, and the foaming agent (11) forms a three-dimensional network structure having pores (14). Additionally, the inorganic filler (12) can be dispersed within the pores (14) formed by the foaming agent (11) to more firmly support the three-dimensional network structure.

[0143] In one embodiment, the thickness of the foam may be 10㎛ to 1000㎛. Specifically, the thickness of the foam may be 10㎛ or more, 20㎛ or more, 30㎛ or more, 50㎛ or more, 60㎛ or more, 70㎛ or more, or 80㎛ or more. Additionally, the thickness of the foam may be 1000㎛ or less, 900㎛ or less, 700㎛ or less, 500㎛ or less, 300㎛ or less, 200㎛ or less, 180㎛ or less, 150㎛ or less, or 120㎛ or less. The above numerical ranges may be combined with one another without limitation. When the thickness of the foam satisfies the above range, it is possible to prevent the energy density of the secondary battery from decreasing due to an excessive increase in the thickness of the pouch-type case. At the same time, when a thermal event occurs, the foam expands to effectively secure the spacing between secondary batteries and block heat transfer, thereby suppressing the spread of thermal runaway and improving the safety of the secondary batteries.

[0144]

[0145] Below, the above foam is described in more detail.

[0146]

[0147] Shock absorption energy density and expansion rate

[0148] Typically, when a secondary battery ignites, a large amount of gas is rapidly generated internally, placing the interior of the battery under high temperature and / or high pressure conditions. If heat is transferred to adjacent secondary batteries under these circumstances, a chain reaction of thermal runaway may occur, potentially severely compromising the safety of the battery system.

[0149] To solve the above problem, the present invention provides a pouch-type case comprising a foam. Specifically, the foam is placed within the pouch-type case to physically separate adjacent secondary batteries, and the foam stably maintains the separated state through expansion and cushioning action even in high temperature and high pressure environments.

[0150] Accordingly, the foam according to the present invention can block or delay the direct conduction of heat to adjacent cells, and consequently, effectively prevent heat transfer between cells and the occurrence of sequential thermal runaway. Therefore, the present invention can improve the structural stability of secondary batteries and significantly improve the safety of high-energy density battery systems.

[0151] Specifically, the foam of the present invention satisfies an impact absorption energy density of 0.17 J / cm² or more and an expansion rate of 1.8 or more calculated by the following formula (1).

[0152] As described above, by simultaneously satisfying the shock absorption energy density and expansion rate, the foam not only exhibits excellent durability and processability but also significantly improved fire resistance and thermal safety. Conversely, if the shock absorption energy density of the foam is 0.17 J / cm² 2 If the thickness expansion rate is less than 1.8, cracks or damage may occur due to impact applied during the manufacturing process of the pouch-type secondary battery or during the transfer process. In addition, if the thickness expansion rate due to foaming is low, the heat propagation blocking effect may be insufficient, or if the expansion rate is not maintained stably, the heat blocking effect may be easily weakened, resulting in reduced thermal safety.

[0153] In particular, the foam according to the present invention is applied to a pouch-type case, and unlike foams applied to battery modules or battery packs, it must be able to secure a sufficient separation distance in the event of a thermal event even under thin thickness conditions. Therefore, the foam must secure a certain level of expandability while simultaneously possessing a certain level of strength and flexibility.

[0154] Therefore, the foam of the present invention simultaneously satisfies two numerical requirements—shock absorption energy density and expansion rate—thereby ensuring excellent durability and flexibility even under thin thickness conditions, thereby securing stability during the manufacturing process. Furthermore, through a sufficient thickness expansion rate, it effectively blocks heat propagation between adjacent secondary batteries and stably maintains its thickness after foaming even in high-temperature and high-pressure environments that occur during ignition, thereby significantly improving the thermal safety of the secondary battery.

[0155] The expansion rate and shock absorption energy density of the above foam can be influenced by various factors. As the foam expands in the thickness direction during the foaming process, it forms a number of pore structures; however, a foam having such pore structures can easily undergo deformation in which its thickness decreases again due to external pressure. Therefore, in order to prevent the phenomenon of the thickness decreasing again after foaming, a configuration capable of supporting the pore structure so that it does not collapse is required.

[0156] For example, when inorganic fillers are included, the type, content, and shape of the inorganic fillers can affect the mechanical stability of the foam. When inorganic fillers are properly dispersed, they are placed inside the pores of the three-dimensional network structure formed during the foaming process, and can support the pores so that they do not easily collapse under external pressure. In this case, the content of the inorganic fillers can also affect the final expansion thickness of the foam. For instance, if the inorganic filler content is too low, the support strength of the pore structure is insufficient, which may reduce the thickness retention after foaming; conversely, if the inorganic filler content is excessively high, foaming may not occur sufficiently, which may reduce the expansion rate.

[0157] As another example, the type and content of the blowing agent can also affect the expansion rate and shock absorption energy density. Blowing agents generate gas as they decompose under specific temperature conditions, and the final expansion rate reached by the foam can vary depending on the decomposition temperature characteristics of the blowing agent. Furthermore, the size and distribution of pores formed vary depending on the type and content of the blowing agent, which in turn affects the thickness and rigidity of the framework forming the three-dimensional network structure.

[0158] As another example, the type and content of the organic binder can also affect the expansion rate and shock absorption energy density. The organic binder contributes to the mechanical strength of the foam prior to foaming. By forming a structure that supports inorganic particles and the blowing agent within the foam, the organic binder can reduce the failure rate caused by breakage during processes such as drops or impacts. Furthermore, the organic binder contributes to maintaining a matrix structure that allows for stable processing during foaming. Specifically, if the organic binder content is too low, the foamed structure becomes weak, increasing the risk of breakage due to impact; conversely, if the organic binder content is excessively high, the thickness expansion rate may not be sufficiently secured.

[0159] The expansion rate (E) of the foam defined by Equation 1 above may be affected by the factors mentioned above. When all the effects of these factors are taken into account, the expansion rate (E) of the foam defined by Equation 1 above may be 1.8 to 6.0. Specifically, the expansion rate (E) defined by Equation 1 above may be 1.8 or higher, 2.0 or higher, 2.1 or higher, 2.2 or higher, 2.5 or higher, 3.0 or higher, or 3.7 or higher. Additionally, the expansion rate (E) defined by Equation 1 above may be 6.0 or lower, 5.8 or lower, 5.5 or lower, 5.0 or lower, or 4.9 or lower. The above numerical ranges may be combined without limitation. For example, the expansion rate (E) defined by Equation 1 above may be 1.8 to 6.0, 1.8 to 5.8, or 2.0 to 5.8.

[0160] The above expansion rate performs the function of suppressing heat transfer by securing the distance between the secondary battery where ignition has occurred and other adjacent secondary batteries, and a larger value is desirable. However, it is difficult to ensure sufficient safety if the expansion rate is simply large. For example, even if the expansion rate is excessively large, if the shock-absorbing energy density is low, the foam may crack or break due to mechanical impact, and consequently, there is a risk that the separation function and heat insulation effect will be weakened.

[0161] Therefore, it is desirable for the foam to be designed to simultaneously satisfy the aforementioned range of shock absorption energy density. By satisfying these two physical properties—expansion rate and shock absorption energy density—in a balanced manner, the foam possesses sufficient mechanical stability even at a thin thickness, while effectively maintaining the distance between adjacent cells upon ignition to prevent thermal runaway diffusion.

[0162] In one embodiment, the shock absorption energy density of the arc body is 0.17 J / cm² 2 Up to 0.70 J / cm 2It may be. The above shock absorption energy density refers to the impact resistance per unit area of ​​the foam and may be an indicator representing the degree to which damage or cracking caused by external impact can be suppressed. Specifically, the above shock absorption energy density is 0.17 J / cm² 2 Above, 0.18 J / cm² 2 Above, 0.20 J / cm² 2 Above, 0.22 J / cm² 2 Above, 0.24 J / cm 2 Above, 0.30 J / cm² 2 Above, 0.35 J / cm² 2 Above, or 0.40 J / cm² 2 It may be more than that. In addition, the shock absorption energy density is 0.70 J / cm². 2 Below, 0.68 J / cm² 2 Below, 0.66 J / cm² 2 Below, 0.65 J / cm 2 Below, 0.60 / cm 2 Less than, or 0.55 J / cm² 2 It may be less than or equal to. The above numerical ranges may be combined without limitation. For example, the shock absorption energy density is 0.17 J / cm². 2 Up to 0.70 J / cm 2 , 0.18J / cm 2 Up to 0.70 J / cm 2 , or 0.20 J / cm 2 Up to 0.70 J / cm 2 It may be possible. When the shock-absorbing energy density satisfies the above range, it is possible to prevent the foam from being damaged by impact or shaking that occurs during the handling and assembly process of the pouch-type case manufacturing process. In addition, when the shock-absorbing energy density of the foam satisfies the above range, damage caused by the molding process of the pouch-type case and external impact can be prevented, and at the same time, the foamed thickness can be stably maintained even in a thermal runaway situation.

[0163]

[0164] Expansion strength index

[0165] In one embodiment, the foam has an Expansion Toughness Index (ETI) of 3.0 cm derived by the following Formula 2. 2 It can be more than / J.

[0166] [Equation 2]

[0167] ETI = E / F

[0168] In the above Equation 2,

[0169] E is the expansion rate, derived by Equation 1 above, and F is the shock absorption energy density (J / cm²) of the foam. 2 )am.

[0170] The aforementioned Expansion Toughness Index (ETI) is the ratio of the expansion rate to the shock absorption energy density, and is a comprehensive indicator of thermal and mechanical stability that indicates whether the foam can maintain impact resistance while securing a thickness expansion of a certain amount or more during foaming.

[0171] When the composition and process conditions of the foam appropriately balance the shock absorption energy density and the expansion rate, the Expansion Strength Index (ETI), defined by Equation 2 below, can be secured above a specific threshold value. In particular, when the ETI is 3.0 cm 2 In the case of / J or higher, the foam can maintain its thickness stably after foaming in a high-temperature and high-pressure environment while securing sufficient impact resistance, so it can be said to have optimal conditions for preventing heat propagation and runaway between secondary batteries.

[0172] Specifically, the foam applied to pouch-type secondary batteries must not easily crack or break due to impacts or vibrations that may occur during movement or handling in the manufacturing process; therefore, it is necessary to possess sufficient durability to ensure stable use in the batch and molding processes. However, merely ensuring mechanical durability is not sufficient; it must exhibit an excellent thickness expansion rate during the foaming process in the event of a thermal event to secure the distance between internal components of the electrode assembly or between adjacent cells. Furthermore, this secured separation must be stably maintained even in high-temperature and high-pressure environments to effectively prevent heat propagation to adjacent cells and thermal runaway.

[0173] To evaluate this, the present invention introduces an expansion strength index that indicates the correlation between shock absorption energy density and expansion rate. A higher value of the expansion strength index signifies greater expansion of the foam at the same shock absorption energy density, while a lower value signifies a relatively higher shock absorption energy density at the same expansion rate. In particular, when the expansion strength index is sufficiently large, it can effectively suppress heat propagation to adjacent cells and thermal runaway even if an abnormal high-temperature and high-pressure environment is created inside the pouch-type secondary battery, thereby serving as a key indicator for ensuring the safety of the battery system.

[0174] However, the expansion strength index does not necessarily exhibit an excellent value simply by increasing the expansion rate; if the impact resistance is low, making it difficult to handle during the manufacturing process or easily damaged by external impact, it is difficult to secure performance as a foam. Therefore, in the present invention, it was confirmed that when the expansion strength index calculated according to [Equation 2] satisfies a specific threshold value or higher, the foam can simultaneously secure mechanical durability and thermal safety. That is, the foam of the present invention is optimally applicable to pouch-type secondary batteries and can guarantee process stability and long-term reliability even in thin case structures.

[0175] In one embodiment, the expansion strength index (ETI) derived by Equation 2 is 3.0 cm 2 It may be greater than / J. This means that the foam can exhibit sufficient thickness expansion without being easily damaged by impact or external force, resulting in excellent heat propagation blocking effects between secondary batteries and the ability to stably maintain thickness after foaming in high-temperature and high-pressure environments. Specifically, the expansion strength index is 3.0cm 2 / J or more, 3.2cm 2 / J or more, 3.3cm 2 / J or more, 3.5cm 2 / J or more, 4.0cm 2 / J, 4.5cm 2 / J or more or 5.0cm 2 It can be more than / J.

[0176] Furthermore, while it can be understood that a higher expansion strength index ensures thermal safety, exceeding a certain value may result in reduced mechanical strength, potentially causing cracks in the foam prior to expansion or reduced long-term durability. Therefore, the expansion strength index is 19.0 cm 2 / J Below, 19.5cm 2 / J or less, 18.0cm 2 / J Below, 18.5cm2 / J Below, 17.5cm 2 / J or less, 17.0cm 2 / J or less, 16.5cm 2 / J or less, 16.0cm 2 / J Below, 15.8cm 2 / J or less, 14.0cm 2 / J or less, 13.0cm 2 / J or less, 12.0cm 2 / J or less, 11.0cm 2 / J or less, or 10.8cm 2 It may be less than / J.

[0177] The above numerical ranges can be combined without limitation. For example, the expansion strength index (ETI) derived by Equation 2 above is 3.0 cm 2 / J to 19.0cm 2 / J, 3.0m 2 / J to 17.0cm 2 / J, 3.2cm 2 / J to 16.0cm 2 / J, or 3.2cm 2 / J to 15.8cm 2 / J could be.

[0178] Therefore, satisfying the above range of the expansion strength index serves as an important technical indicator that the foam possesses both durability and expansion characteristics sufficient to ensure the safety of the pouch-type secondary battery.

[0179]

[0180] The foam may include a foaming agent, an inorganic filler, and an organic binder. By including these components, excellent fire resistance and heat resistance can be expected. The foaming agent has excellent ability to delay the temperature rise by latent heat as moisture vaporizes at high temperatures, increase the thickness of the foam through expansion, and maintain the increased thickness, thereby effectively suppressing heat transfer. This function can be optimally achieved by including the organic binder and the inorganic filler together. For example, by ensuring that the moisture contained in the foaming agent is maintained above a certain level even in the operating environment of a secondary battery, a foaming effect can be implemented in a timely manner when a thermal event occurs while the battery box is operating in an electrical device. This enables the realization of a flexible and high-strength foam with excellent durability and stability for long-term use.

[0181]

[0182] Below, foaming agents, inorganic fillers, and organic binders capable of implementing the above-mentioned effects are described in detail.

[0183]

[0184] blowing agent

[0185] The blowing agent may be included in an amount of 20 to 90 parts by weight relative to 100 parts by weight of the foam. Preferably, the blowing agent may be included in an amount of 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, or 40 parts by weight or more, and may also be included in an amount of 90 parts by weight or less, 85 parts by weight or less, 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less. When the blowing agent is applied to the foam with such content, a sufficient foam expansion rate can be achieved, and excellent durability of the three-dimensional network formed after foaming can be expected. As a result, the blowing agent can effectively prevent heat propagation and thermal runaway by separating the distance between the point where a thermal event occurs and other adjacent members, and maintaining this separated distance for a certain period of time. In addition, since the content of the foaming agent can contribute to better withstanding potential damage to the foam during the process of placing and processing the foam in a secondary battery or battery box, it may be desirable to apply the above content.

[0186] The above foaming agent may include one or more selected from the group consisting of lithium silicate, potassium silicate, sodium silicate, zirconium silicate, magnesium silicate, and titanium silicate.

[0187] The aforementioned silicates, namely water glass, may be materials that undergo dehydration along with a polycondensation reaction caused by heat. The moisture generated in this way vaporizes and moves outward, which can cause foaming. That is, if the temperature of the foam rises abnormally, the foaming agent can expand the volume of the foam, thereby preventing heat propagation and improving safety.

[0188] The foaming agent may preferably include sodium silicate. The sodium silicate may satisfy Formula 4 below:

[0189] [Equation 4]

[0190] 2.0 ≤ M S / M N ≤ 4.5

[0191] In the above Equation 4, M S is the molar ratio of SiO2 contained in the above sodium silicate, and M N This is the molar ratio of Na2O contained in the above sodium silicate.

[0192] In the above Equation 1, M S / M N The value of may be 2.0 or greater, 2.5 or greater, or 3.0 or greater, and may also be 4.5 or less, 4.0 or less, or 3.5 or less. The above M S / M N If the value satisfies the above range, a foamed composition with excellent mechanical strength and foaming properties can be realized. In addition, when a sodium silicate satisfying the above range is applied, the foaming agent may have a specific strength to maintain the expanded thickness and may be desirable for achieving a sufficient foamed expansion thickness.

[0193] In one embodiment, the foaming agent is foamed at a temperature of 130°C or higher, the foamed foaming agent forms a three-dimensional network structure having pores, and the inorganic filler may have a structure disposed within the pores.

[0194]

[0195] Weapon filler

[0196] The above-mentioned inorganic filler may have a plate-like structure. While the thickness resulting from foam expansion and the ability to maintain this thickness may play an important role in the foam, such a rate of thickness change may lose its significance if the foam itself burns easily or has poor durability. Accordingly, by including the above-mentioned inorganic filler, the heat resistance or fire resistance of the foam can be significantly improved, and excellent mechanical strength can be secured. When the above-mentioned inorganic filler has a plate-like structure, there is an advantage in that it can optimally perform the function of supporting the pores of the three-dimensional network so that they are not compressed by external pressure after the foam is foamed.

[0197] The above inorganic filler may include one or more selected from the group consisting of titanium dioxide, alumina, kaolin, zirconia, silica, zinc oxide, and boehmite.

[0198] The above inorganic filler may be included in an amount of 50 parts by weight or less per 100 parts by weight of the foam. Preferably, the above inorganic filler may be included in the foam in an amount of 40 parts by weight or less, 30 parts by weight or less, or 20 parts by weight or less, and may also be included in an amount of 5 parts by weight or more, 10 parts by weight or more, or 15 parts by weight or more.

[0199] In one embodiment, the weight ratio of the inorganic filler to the foaming agent may be 1:1 or more, 1:2 or more, or 1:3 or more, or the weight ratio of the inorganic filler to the foaming agent may be 1:36 or less, 1:30 or less, 1:20 or less, 1:10 or less, 1:7 or less, 1:5 or less, or 1:4 or less. The above numerical ranges may be combined with one another without limitation. For example, the weight ratio of the inorganic filler to the foaming agent may be 1:1 to 1:36, specifically 1:2 to 1:36, and more specifically 1:3 to 1:36. When the weight ratio of the inorganic filler to the foaming agent satisfies the above range, a foam with excellent thermal safety and processability can be realized, as both the expansion rate and shock absorption energy density are excellent.

[0200] When the above-mentioned type and content of the inorganic filler are satisfied, more desirable results can be obtained in optimally realizing the aforementioned expected effects intended to be obtained by introducing the inorganic filler.

[0201]

[0202] organic binder

[0203] The above organic binder can form a matrix that supports the entire foam inside the foam and can impart adhesive strength and flexibility to the foam. Although a self-standing foam can be manufactured using only a gel-state foaming agent and a sufficient foaming effect can be achieved, there is a problem that the durability and flexibility are poor, and the foam can be easily damaged during the process of processing the finished product after attaching it in place.

[0204] In order to improve the flexibility of the foam and eliminate its brittle nature, one may consider adding a moisturizer capable of holding moisture, such as glycerin. However, this type of moisturizer, such as glycerin, is prone to deformation not only at high temperatures of 50°C or higher but also at low temperatures of 0°C or lower, and does not exhibit a moisturizing effect, which limits the environments in which it can be utilized.

[0205] To solve these problems, the foam may include an organic binder. By applying this, a foam with excellent adhesion and durability can be realized, and as a result, there is an advantage that the foam can be utilized even in high-temperature environments of 130°C or higher. In addition, the organic binder can improve adhesion between materials and between the foam and the member to which it is attached through hydrogen bonding with the inorganic filler and the foaming agent, and can improve the flexibility and elasticity of the foam.

[0206] The above organic binder may be included in an amount of 50 parts by weight or less per 100 parts by weight of the foam. Preferably, the above organic binder may be included in the foam in an amount of 40 parts by weight or less, 30 parts by weight or less, or 20 parts by weight or less, and may also be included in the foam in an amount of 5 parts by weight or more, 10 parts by weight or more, or 15 parts by weight or more.

[0207] The above organic binder is a styrene-butadiene-based rubber such as styrene-butadiene rubber (SBR), styrene-butadiene-styrene rubber (SBS), or modified rubbers thereof; a silicone rubber such as polydimethylsiloxane (PDMS), polymethylvinylsiloxane (PMVS), or phenyl-silicone rubber; a nitrile-based rubber such as nitrile-butadiene rubber (NBR), hydrogenated nitrile-butadiene rubber (HNBR), carboxylated nitrile-butadiene rubber, nitrile-butadiene rubber latex (NBR latex), or modified rubbers thereof; a polyester-based resin such as polyethylene terephthalate, polybutylene terephthalate, etc.; a cellulose-based resin such as cellulose acetate (CA), cellulose butyrate (CB), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), or hydroxypropylmethyl cellulose (HPMC); It may include one or more selected from the group consisting of epoxy-putty, epoxy resins such as bisphenol A diglycidyl ether (DGEBA), bisphenol F diglycidyl ether (DEGBF), and novolac epoxy; phenol resins; and urethane resins.

[0208] By including an organic binder satisfying the above content and type in the foam, the flexibility of the foam and the adhesive strength can be improved.

[0209]

[0210] Preferably, two or more types of the above organic binder may be applied, and the above organic binder may include an elastic binder and a reinforcing binder. The above elastic binder may include one or more selected from the group consisting of styrene-butadiene rubber, nitrile rubber, polyester resin, cellulose resin, urethane resin, and silicone rubber, and the above reinforcing binder may include one or more selected from the group consisting of epoxy resin and phenolic resin.

[0211] When a reinforcing binder is used in the above organic binder, a three-dimensional network structure can be formed upon drying, and this structure combines with the three-dimensional network structure formed as the foaming agent expands. In this case, the reinforcing binder and the foaming agent chemically form hydrogen bonds and structurally intertwine to form a more robust network structure, thereby preventing cracks from occurring in the foam.

[0212] In addition, elastic binders can compensate for the increased brittleness and reduced flexibility that may result from using reinforcing binders. That is, when two types of binders are used as described above, they can function more optimally for securing adhesion and flexibility, and can also have the effect of increasing durability.

[0213] Preferably, the reinforcing binder may be processed to include one or more additives such as a curing agent, silica, metal powder, or plasticizer, and in this case, it may be preferable to use epoxy putty. In addition, it may be preferable to use styrene-butadiene-based rubber as the elastic binder.

[0214] When two or more types of the above organic binders are included, each organic binder may be independently selected and applied appropriately within the aforementioned content range, but the content of the mixed organic binder may be applied so as not to exceed the above range.

[0215] In one embodiment, the elastic binder and the reinforcing binder may each be included in an amount of 5% by weight or more based on the total weight of the foam. When the content of the elastic binder and the reinforcing binder satisfies the above range, the flexibility and durability of the foam can be effectively improved simultaneously. As a result, the shock absorption energy density of the foam can be improved.

[0216] In one embodiment, the foam may satisfy K of Formula 3 below in a range of 0.4 to 2.2:

[0217] [Equation 3]

[0218] K = B e / B r

[0219] In the above Equation 3,

[0220] B e is the weight percentage of the elastic binder based on the total weight of the foam, and B r K is the weight percentage of the reinforcing binder based on the total weight of the foam. The K value is an indicator representing the mixing ratio of the elastic binder and the reinforcing binder within the foam, and the two binders work complementarily to optimize the mechanical properties and flexibility of the foam.

[0221] The value of K in Equation 3 above may be 0.40 or higher, 0.45 or higher, 0.5 or higher, or 0.8 or higher, and may be 2.2 or lower, 2.1 or lower, 2.0 or lower, or 1.5 or lower. The above numerical ranges may be combined with one another without limitation. For example, the above K may be 0.4 to 2.2, specifically 0.5 to 2.1, and more specifically 0.8 to 2.0. When the above K value satisfies the above range, the balance of the two binders is optimized so that the foam simultaneously secures impact resistance and flexibility, and can stably withstand external shocks and heat generated during the cell manufacturing process.

[0222] In one embodiment, the foam may further include additives to improve volume expansion rate and thermal insulation, and may further include one or more selected from vermiculite and perlite.

[0223]

[0224] The above foam is not subject to any particular restrictions on its shape. The foam may be in the form of a sheet, such as a foam pad; in this case, the sheet may refer to a self-supporting, independent sheet or a sheet coated on a specific substrate and attached to the substrate. Additionally, the shape of the sheet may be identical to the shape of various components within a secondary battery or battery box, or it may be formed to be smaller or larger than such components.

[0225] In addition, the foam can be molded to fit the shape of the space where it is to be applied. For example, if the foam is to be applied to the empty space remaining after the electrode assembly is accommodated inside a battery case, it can be molded to fit the shape of that space and applied; similarly, it can be molded to fit the shape of the space within the housing of a battery box. In this way, when the foam is not in the form of a sheet, the expansion rate and compression rate can be measured and derived by substituting them with the change in average diameter as the average of the major and minor axes.

[0226]

[0227] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are merely examples to aid in understanding the invention and do not limit the scope of the invention. It is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of this description, and it is natural that such variations and modifications fall within the scope of the appended claims.

[0228]

[0229] Example 1

[0230] (Preparation of foamed composition)

[0231] A foamed composition was prepared by adding sodium silicate with a molar ratio of SiO2:Na2O of 3.2:1 as a foaming agent, kaolin as an inorganic filler, styrene-butadiene rubber (SBR) as an elastic binder among organic binders, and epoxy putty (3M, Scotch-Weld Epoxy Adhesive 2214, 100% solid content) as a reinforcing binder to water and mixing them so that the weight ratio based on solid content was 20:20:30:30.

[0232] (Manufacture of pouch-type cases containing foam)

[0233] The foamed composition prepared above was spray-coated onto a polyethylene terephthalate (PET) film and dried at 90°C for 10 minutes to produce a foam with a thickness of 100 μm. At this time, the thickness refers to the thickness of the foam itself excluding the film.

[0234] Subsequently, a pouch-type case was manufactured by sequentially laminating a polyethylene terephthalate (PET) film with a thickness of 12 μm, on which a foam is positioned on the surface, and a nylon (Ny) film with a thickness of 25 μm as a substrate layer, an aluminum alloy thin film with a thickness of 60 μm as a barrier layer, and a polypropylene film with a thickness of 80 μm as a sealant layer.

[0235]

[0236] Example 2

[0237] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that sodium silicate, kaolin, styrene-butadiene rubber, and epoxy-putty were added to water and mixed when preparing the foamed composition, and the weight ratio based on solid content was adjusted to 40:20:20:20.

[0238]

[0239] Example 3

[0240] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that sodium silicate, kaolin, styrene-butadiene rubber, and epoxy-putty were added to water and mixed when preparing the foamed composition, and the weight ratio based on solid content was adjusted to 60:20:10:10.

[0241]

[0242] Example 4

[0243] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that sodium silicate, kaolin, styrene-butadiene rubber, and epoxy-putty were added to water and mixed when preparing the foamed composition, and the weight ratio based on solid content was adjusted to 60:20:13.5:6.5.

[0244]

[0245] Example 5

[0246] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that sodium silicate, kaolin, styrene-butadiene rubber, and epoxy-putty were added to water and mixed when preparing the foamed composition, and the weight ratio based on solid content was adjusted to 60:20:6.5:13.5.

[0247]

[0248] Example 6

[0249] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that sodium silicate, kaolin, styrene-butadiene rubber, and epoxy-putty were added to water and mixed when preparing the foamed composition, and the weight ratio based on solid content was adjusted to 90:2.5:3.75:3.75.

[0250]

[0251] Comparative Example 1

[0252] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that when preparing the foamed composition, epoxy putty was not added, and sodium silicate, kaolin, and styrene-butadiene rubber were added to water and mixed, with the weight ratio based on solid content adjusted to 60:20:20.

[0253]

[0254] Comparative Example 2

[0255] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that styrene-butadiene was not added when preparing the foamed composition, and sodium silicate, kaolin, and epoxy-putty were added to water and mixed, with the weight ratio based on solid content adjusted to 60:20:20.

[0256]

[0257] Comparative Example 3

[0258] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that sodium silicate, kaolin, styrene-butadiene rubber, and epoxy-putty were added to water and mixed when preparing the foamed composition, and the weight ratio based on solid content was adjusted to 10:20:35:35.

[0259]

[0260] Comparative Example 4

[0261] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that sodium silicate, kaolin, styrene-butadiene rubber, and epoxy-putty were added to water and mixed when preparing the foamed composition, with a weight ratio of 95:2.5:1.25:1.25 based on solid content.

[0262]

[0263] Comparative Example 5

[0264] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that acrylic resin was added instead of epoxy putty when preparing the foamed composition, and sodium silicate, kaolin, styrene-butadiene, and acrylic resin were added to water and mixed, with the weight ratio based on solid content adjusted to 40:20:20:20.

[0265]

[0266] Comparative Example 6

[0267] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that acrylic resin was added instead of epoxy putty when preparing the foamed composition, and sodium silicate, kaolin, styrene-butadiene, and acrylic resin were added to water and mixed, with the weight ratio based on solid content adjusted to 60:20:10:10.

[0268]

[0269] Comparative Example 7

[0270] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that carboxymethylcellulose was added instead of styrene-butadiene when preparing the foaming composition, and sodium silicate, kaolin, epoxy-putty, and carboxymethylcellulose were added to water and mixed, with the weight ratio based on solid content adjusted to 40:20:20:20.

[0271]

[0272] Comparative Example 8

[0273] A pouch-type case containing a foam was produced in the same manner as in Example 1, except that carboxymethylcellulose was added instead of styrene-butadiene when preparing the foaming composition, and sodium silicate, kaolin, epoxy-putty, and carboxymethylcellulose were added to water and mixed, with the weight ratio based on solid content adjusted to 60:20:10:10 dl.

[0274]

[0275] Foaming agent, inorganic filler, binder, sodium silicate, kaolin, SBR, epoxy-putty, acrylic resin, CMC Example 1 20203030--Example 2 40202020--Example 3 60201010--Example 4 602013.56.5--Example 5 60206.513.5--Example 6 902.53.753.75--Comparative Example 1 602020---Comparative Example 2 6020-20--Comparative Example 3 10203535--Comparative Example 4 952.51.251.25--Comparative Example 5 402020-20-Comparative Example 6 602010-10-Comparative Example 7 4020-20-20 Comparative Example 86020-10-10

[0276]

[0277] Experimental Example 1: Measurement of Shock Absorption Energy Density

[0278] This experiment was conducted using a modified Izod impact test according to ASTM D256 standards to evaluate the relative impact resistance of polymer materials.

[0279] Specifically, five plate-shaped specimens were prepared for each example, containing the foams manufactured in Examples 1-6 and Comparative Examples 1-8, with dimensions of 5 cm × 5 cm × 100 µm (based on the thickness of the foam excluding the substrate). No notches were applied to the specimens. While the specimens were fixed to vertical supports, the center was struck using an Izod-type pendulum hammer moving horizontally, with a constant energy of 22 J applied to the hammer. At this time, whether the specimen fractured (or broke) and the energy (J) required upon fracture (or breakage) were recorded, and the average impact absorption energy (J) of the five specimens was calculated for each example and comparative example. This average value was calculated based on the cross-sectional area of ​​the specimen: 0.05 cm² 2 Value calculated by dividing by (= 5cm × 0.01cm) (J / cm 2 ) was used as an indicator of shock absorption energy density.

[0280] The measurement results are shown in Table 2 below.

[0281] Shock Absorption Energy Density (J / cm²) Example 10.653 Example 20.549 Example 30.436 Example 40.465 Example 50.417 Example 60.248 Comparative Example 10.157 Comparative Example 20.146 Comparative Example 30.743 Comparative Example 40.069 Comparative Example 50.125 Comparative Example 60.109 Comparative Example 70.119 Comparative Example 80.109

[0282]

[0283] Experimental Example 2: Measurement of Thickness Expansion Rate

[0284] A pouch-type case containing the foam prepared in Experimental Examples 1-6 and Comparative Examples 1-8 was cut to a width and depth of 5 cm and a thickness of 100 μm (based on the thickness of the foam excluding the pouch-type case). After placing the cut foam on an insulating board, a heating plate heated to 750°C was placed on the opposite side and contact was maintained for 30 seconds to apply heat to the foam. Through this process, the foam was expanded, and the full expansion thickness (T) of the expanded foam e ) was measured. At this time, the measured thickness was based on the thickness of the foam layer itself, excluding the pouch-type case.

[0285] The above measured thickness (T e ) and initial thickness (T i The expansion rate (E) was calculated using ), and the result was substituted into Equation 1 to calculate the expansion strength index (ETI). The calculation results for each experimental example are shown in Table 3 below.

[0286] Initial thickness, T i (㎛) Thickness after foaming, T e (㎛) Expansion rate (E)(T e -T i) / Ti Expansion Strength Index (ETI) (cm² / J) Example 1 103 302.20 3.37 Example 2 101 475 3.70 6.74 Example 3 103 543 4.27 9.79 Example 4 102 59 74.85 10.43 Example 5 102 558 4.47 10.72 Example 6 104 51 13.9 11 15.80 Comparative Example 1 102 276 1.71 10.89 Comparative Example 2 101 247 1.45 9.93 Comparative Example 3 100 107 0.07 0.094 Comparative Example 4 101 325 2.22 32.17 Comparative Example 5 103 247 1.40 11.20 Comparative Example 61023732.6624.40 Comparative Example 71012961.9316.22 Comparative Example 81004073.0728.17

[0287]

[0288] Experimental Example 3: Evaluation of Fairness and Heat Propagation Delay Effects

[0289] (1) Fairness evaluation

[0290] The pouch-type case containing the foam prepared in Examples 1-6 and Comparative Examples 1-8 was cut into a sheet with dimensions of 260 mm × 100 mm × 2 mm (based on the total thickness of the pouch-type case containing the foam). Subsequently, a process evaluation was performed by lifting the sheet horizontally using a suction device and dropping it from a height of 1 m. If the foam was damaged or its shape was deformed after the sheet fell, it was judged as NG, and if the shape was maintained, it was judged as OK. The results are shown in Table 4 below.

[0291] Since shape retention and mechanical stability are important factors during the lamination or transport of the foam in the manufacturing process of pouch-type cases, this experiment allows for the quantitative evaluation of the process durability of the foam.

[0292]

[0293] (2) Evaluation of heat propagation delay effect

[0294] Subsequently, the thermal propagation delay effect was evaluated for Examples 1-6 and Comparative Example 3, which were judged to be OK as a result of the processability evaluation experiment. Specifically, two secondary batteries were manufactured by housing an electrode assembly in a pouch-type case containing each of the foams. At this time, for convenience, one secondary battery was named Cell A and the other secondary battery was named Cell B.

[0295] Subsequently, a heater (120 mm × 60 mm) was placed on top of cell A, a thermocouple was attached between the heater and cell A, and the heater was secured with polyimide tape. Additionally, a thermocouple was attached between cell A and cell B, and also to the center of cell B on the side that does not come into contact with cell A. Then, Superwool insulation (10T, 300 mm × 100 mm) was attached to the outer surface opposite to the side in contact with cell A and cell B, and an aluminum plate (10T, 300 mm × 100 mm) was attached to the outer surface, and the structure was fastened into a laminate by applying pressure of 30 kPa.

[0296] The completed laminate was placed in a SUS box (internal dimensions: length 420 mm × width 125 mm × height 105 mm, thickness 10T) and sealed. Then, thermal runaway of the cell was induced using a heater, and the results were measured. Specifically, the heater was operated at a heating rate of 10℃ / s at room temperature (25℃) to heat the cell until it reached 625℃, and once it reached 625℃, the temperature was maintained. In addition, the elapsed time from when the heater reached 625℃ until the temperatures of Cell A and Cell B reached 250℃ was measured, and the results are shown in Table 4 below.

[0297] Processability Time to reach 250°C for Cell A (s) Time to reach 250°C for Cell B (s) Time required for heat propagation (s) Example 1 OK316231 Example 2 OK329159 Example 3 OK3311885 Example 4 OK3513499 Example 5 OK3312491 Example 6 OK3611579 Comparative Example 1 NG--- Comparative Example 2 NG--- Comparative Example 3 OK314211 Comparative Example 4 NG--- Comparative Example 5 NG--- Comparative Example 6 NG--- Comparative Example 7 NG--- Comparative Example 8 NG---

[0298]

[0299] Referring to Table 4 above, it can be seen that Examples 1 to 6, in which the shock absorption energy density is 0.17 J / cm² or higher and the expansion rate (E) derived by Equation 1 is 2.0 or higher, all received an “OK” judgment in the processability evaluation. In other words, it can be confirmed that no deformation or breakage occurred in Examples 1 to 6 during the molding process.

[0300] In addition, Examples 1 to 6 also demonstrated excellent performance in the thermal propagation delay effect evaluation test. Specifically, in Examples 1 to 6, the time required for heat to propagate to adjacent cells was measured to be 31 seconds or more, up to a maximum of 163 seconds, which means that the effect of delaying thermal runaway was significantly exhibited. This is the result of the foam stably expanding in a high-temperature environment to maintain separation between secondary batteries and effectively block heat conduction.

[0301] On the other hand, among Comparative Examples 1 to 8, only Comparative Example 3 showed an impact absorption energy density of 0.17 J / cm² or higher, receiving an “OK” rating without damage in the processability evaluation. However, in the heat propagation suppression test of Comparative Example 3, Cell B reached 250°C in just 42 seconds, and the time required for heat propagation was only 11 seconds. This indicates that the expansion rate fell short of the standard, resulting in insufficient heat propagation blocking effect.

[0302]

[0303] [Explanation of the symbol]

[0304] 10: Foam

[0305] 11: Foaming agent

[0306] 12: Weapon Filler

[0307] 13: Organic binder

[0308] 14: Qi Gong

Claims

1. An electrode assembly comprising an anode and a cathode; and A pouch-type case in which the above electrode assembly is housed; comprising The above pouch-type case includes a foam, and The above foam comprises a foaming agent, an inorganic filler, and an organic binder, and The above foam has a shock absorption energy density of 0.17 J / cm² 2 That is all, The above foam is a pouch-type secondary battery having an expansion rate (E) of 1.8 or higher derived by the following formula 1: [Equation 1] E = (T e - T i ) / T i In the above Equation 1, T i is the initial thickness (㎛) of the foam above, and T e is the full expansion thickness (μm) of the foam above.

2. In Claim 1, The above foam has an Expansion Toughness Index (ETI) of 3.0 cm, derived by the following Equation 2. 2 / J Lee Sang-in, Pouch-type secondary battery: [Equation 2] ETI = E / F In the above Equation 2, E is the expansion rate derived by Equation 1 above, and F is the shock absorption energy density (J / cm²) of the foam. 2 )am.

3. In Claim 2, The above foam has an expansion strength index (ETI) of 3.0 cm derived by Equation 2. 2 / J to 19.0cm 2 / J, pouch-type secondary battery.

4. In Claim 1, The above pouch-type case includes a structure in which a plurality of layers are stacked, and A pouch-type secondary battery, wherein the foam is disposed on one or more surfaces selected from the group consisting of at least one interface between the layers, the innermost surface and the outermost surface of the pouch-type case.

5. In Claim 1, The above foam has a shock absorption energy density of 0.17 J / cm² 2 Up to 0.70 J / cm 2 And, The above foam is a pouch-type secondary battery having an expansion rate (E) derived by the above formula 1 of 1.8 to 6.

0.

6. In Claim 1, A pouch-type secondary battery comprising the foaming agent in an amount of 20 to 90 parts by weight per 100 parts by weight of the foam.

7. In Claim 1, The above organic binder comprises an elastic binder and a reinforcing binder, forming a pouch-type secondary battery.

8. In Claim 7, The above foam is a pouch-type secondary battery satisfying K of Formula 3 below from 0.4 to 2.2: [Equation 3] K = B e / B r In the above Equation 3, B e is the weight percentage of the elastic binder based on the total weight of the foam, and B r is the weight percentage of the reinforcing binder based on the total weight of the foam.

9. In Claim 7, The above elastic binder comprises one or more selected from the group consisting of styrene-butadiene rubber, nitrile rubber, polyester resin, cellulose resin, urethane resin, and silicone rubber, and A pouch-type secondary battery comprising one or more selected from the group consisting of epoxy resins and phenolic resins, wherein the reinforcing binder above comprises the above reinforcing binder.

10. In Claim 1, A pouch-type secondary battery having a weight ratio of the inorganic filler and foaming agent of 1:1 to 1:

36.

11. In Claim 1, The above foaming agent foams at a temperature of 130°C or higher, and A pouch-type secondary battery having a structure in which the foamed foaming agent forms a three-dimensional network structure having pores, and the inorganic filler is disposed within the pores.

12. In Claim 1, The above foaming agent is, A pouch-type secondary battery comprising one or more selected from the group consisting of lithium silicate, potassium silicate, sodium silicate, zirconium silicate, magnesium silicate, and titanium silicate.

13. In Claim 1, The above foaming agent includes sodium silicate, and A pouch-type secondary battery in which the above sodium silicate satisfies the following Equation 4: [Equation 4] 2 ≤ M S / M N ≤ 4.5 In the above Equation 4, M S is the molar ratio of SiO2 contained in the above sodium silicate, and M N This is the molar ratio of Na2O contained in the above sodium silicate.

14. In Claim 1, The above-mentioned weapon filler is, A pouch-type secondary battery comprising one or more materials selected from the group consisting of titanium dioxide, alumina, kaolin, zirconia, silica, zinc oxide, and boehmite.

15. In Claim 1, A pouch-type secondary battery having a thickness of 10㎛ to 1000㎛ of the foam.

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