Electrode current collector, and lithium secondary battery, battery module, and battery pack comprising same

Abstract

The electrode current collector according to the present invention comprises: a polymer resin layer; a first metal layer disposed on one surface of the polymer resin layer; and a second metal layer provided on the other surface of the polymer resin layer, in which the first metal layer and the second metal layer contain a shape memory alloy (SMA), and the shape memory alloy (SMA) is designed such that an external force is applied to the polymer resin layer by shape deformation when a temperature of the shape memory alloy (SMA) is greater than a predetermined temperature.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2023-0110180, filed on August 22, 2023, the disclosure of which is incorporated herein by reference.

[0002] This invention relates to an electrode current collector and a lithium secondary battery, battery module and battery pack containing the same. Background Technology

[0003] With the development and increasing demand for electric vehicles and energy storage systems (ESS), the demand for batteries as energy sources has increased significantly. Therefore, research is being conducted on batteries that can meet various needs.

[0004] In particular, to enable batteries to be used for longer periods after a single charge, it is necessary to increase battery capacity, and the fabrication technology of large-area electrodes is crucial for improving capacity. However, during the fabrication of large-area electrodes, electrode performance may be degraded, and there are concerns about heat propagation to other electrodes due to thermal runaway in the event of a fire.

[0005] In lithium-ion batteries, a rapid temperature rise in the electrodes can occur due to both thermal and physical factors. Thermal factors include overcharging or overloading caused by misuse or charger malfunction. Physical factors include internal short circuits caused by damage to the separator due to external impact, leading to contact issues between the negative and positive electrode materials. If the electrode temperature rises rapidly in this manner, the battery becomes highly unstable due to reactions between the electrolyte and lithium or the generation of hydrogen and oxygen within the battery. The electrolyte solvent decomposes, producing gases that can ignite and cause a battery explosion.

[0006] Conventional lithium-ion batteries contain only a single metal layer as the electrode current collector. Specifically, an aluminum single metal layer is used as the positive electrode current collector, and a copper single metal layer is used as the negative electrode current collector. However, because these single metal layers have very high electrical and thermal conductivity, the time it takes for the battery to reach high temperatures due to abnormal behavior is very short, raising concerns about heat propagation caused by thermal runaway.

[0007] Therefore, by using an electrode current collector that includes a polymer resin layer disposed between two metal layers instead of a conventional electrode current collector, the weight can be reduced compared to an electrode current collector formed of metal, thus significantly improving the energy density per unit weight, and improving safety in the event of a fire by causing a short circuit between the electrodes.

[0008] However, for electrode current collectors that include a polymer resin layer disposed between two metal layers, although mechanical safety against foreign objects (such as spikes) can be improved, there is a need to improve safety against heat propagation in the event of an actual fire. Summary of the Invention

[0009] Technical issues

[0010] One aspect of the present invention provides an electrode current collector and an electrode assembly and a lithium secondary battery comprising the same, wherein the electrode current collector not only has excellent fire safety, heat resistance and heat shielding effect, but also can be lightweight to improve energy density.

[0011] Technical solution

[0012] To address the aforementioned problems, this invention provides an electrode current collector.

[0013] [1] The present invention provides an electrode current collector, the electrode current collector comprising: Polymer resin layer; A first metal layer disposed on one surface of the polymer resin layer; and A second metal layer disposed on another surface of the polymer resin layer. The first and second metal layers contain shape memory alloys (SMAs), and Shape memory alloys (SMAs) are designed to apply external forces to the polymer resin layer through shape deformation when the temperature of the shape memory alloy (SMA) exceeds a predetermined temperature.

[0014] [2] The present invention provides the electrode current collector described in [1] above, wherein the shape memory alloy (SMA) comprises at least one of copper-zinc alloy, copper-tin alloy, magnesium-copper alloy, nickel-titanium alloy and copper-aluminum-nickel alloy.

[0015] [3] The present invention provides an electrode current collector as described in any one or more of [1] or [2] above, wherein the amount of shape memory alloy (SMA) is in the range of 20% to 100% by weight based on the total weight of the metal layers.

[0016] [4] The present invention provides an electrode current collector described in any one or more of [1] to [3] above, wherein the polymer resin layer comprises at least one selected from polyester resin, epoxy resin, phenolic resin, melamine resin, polyurethane resin, silicone resin, EVA resin, rubber resin, acrylic resin and polyether urethane resin.

[0017] [5] The present invention provides an electrode current collector according to any one or more of [1] to [4] above, wherein the thickness ratio of the polymer resin layer to the first metal layer or the second metal layer is in the range of 1:1 to 1:10.

[0018] [6] The present invention provides an electrode current collector according to any one or more of [1] to [5] above, wherein the thickness of the polymer resin layer is 3 μm to 18 μm.

[0019] [7] The present invention provides an electrode current collector described in any one or more of [1] to [6] above, wherein the thickness of the first metal layer and the second metal layer is independently 10 μm to 30 μm.

[0020] The present invention also provides a lithium secondary battery comprising the above-described electrode current collector.

[0021] [8] The present invention provides a lithium secondary battery, the lithium secondary battery comprising: An electrode assembly having a structure in which multiple electrodes and multiple diaphragms are alternately stacked. Each electrode includes an electrode current collector and an electrode active material layer disposed on the electrode current collector, and At least one of the plurality of electrode current collectors is one or more of the electrode current collectors described in [1] to [7] above.

[0022] The present invention also provides a battery module and a battery pack comprising the above-mentioned lithium secondary battery.

[0023] [9] The present invention provides a battery module comprising a plurality of lithium secondary batteries as described above [8].

[0024]

[10] The present invention provides a battery pack comprising a plurality of battery modules described above [9].

[0025] Beneficial effects

[0026] The electrode current collector according to the invention comprises a polymer resin layer between two metal layers, wherein the metal layers comprise a shape memory alloy (SMA). Since the shape memory alloy (SMA) is designed such that when its temperature exceeds a predetermined temperature, external force is applied to the polymer resin layer through shape deformation, and as the shape memory alloy (SMA) shrinks, an electrical disconnection state between the electrodes is induced by additional pressure on the polymer resin layer, thereby improving safety.

[0027] Furthermore, the lithium secondary battery according to the present invention can not only improve mechanical safety against foreign objects (such as nails), but also improve safety against heat propagation in the event of a fire.

[0028] Furthermore, in cases where the battery module and battery pack according to the invention include multiple of the aforementioned electrode current collectors, high-capacity and large-area batteries can be achieved by maximizing safety against heat propagation in the event of a fire. Attached Figure Description

[0029] Figure 1 This is a schematic cross-sectional view of the electrode current collector according to the present invention.

[0030] Figure 2 and Figure 3 Each is a cross-sectional view showing a lithium secondary battery including an electrode current collector according to the present invention. Detailed Implementation

[0031] The advantages, features, and implementation methods of the present invention will be illustrated by the following description of embodiments in conjunction with the accompanying drawings. However, the present invention can be embodied in different forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to make this disclosure comprehensive and complete, and to fully convey the scope of the invention to those skilled in the art. Furthermore, the invention is defined only by the scope of the claims. The same reference numerals throughout the drawings denote the same constituent elements.

[0032] Unless otherwise defined, all terms used herein (including technical and scientific terms) are intended to have the meaning understood by one of those skilled in the art. Furthermore, unless explicitly and specifically defined, terms as defined in general dictionaries should not be interpreted in an unusual or exaggerated manner.

[0033] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the invention. In this specification, singular terms may include plural forms unless otherwise indicated. It should also be understood that, when used in this specification, the terms “comprising” and / or “containing” designate the presence of the stated constituent elements, but do not exclude the presence or addition of more than one other constituent element.

[0034] In this specification, unless otherwise specifically stated to the contrary, when it is said that a part contains a certain component, it means that it may also contain other components, rather than excluding other components.

[0035] In this specification, the description of "A and / or B" means A, or B, or A and B.

[0036] In this specification, unless otherwise expressly stated, "%" indicates weight.

[0037] Electrode current collector

[0038] The electrode current collector according to the present invention will be described below.

[0039] Figure 1 This is a schematic cross-sectional view of the electrode current collector according to the present invention.

[0040] Reference Figure 1 The electrode current collector 10 according to the present invention includes a polymer resin layer 11, a first metal layer 13A disposed on one surface of the polymer resin layer, and a second metal layer 13B disposed on the other surface of the polymer resin layer, wherein the first metal layer 13A and the second metal layer 13B comprise a shape memory alloy (SMA). The shape memory alloy (SMA) is designed such that when the temperature of the shape memory alloy (SMA) is higher than a predetermined temperature, an external force is applied to the polymer resin layer through shape deformation.

[0041] Conventional lithium-ion batteries contain only a single metal layer as the electrode current collector. Specifically, an aluminum single metal layer is used as the positive electrode current collector, and a copper single metal layer is used as the negative electrode current collector. However, because these single metal layers have very high electrical and thermal conductivity, the time it takes for the battery to reach high temperatures due to abnormal behavior is very short, raising concerns about heat propagation caused by thermal runaway.

[0042] Therefore, by using an electrode current collector that includes a polymer resin layer disposed between two metal layers instead of a conventional electrode current collector, the weight can be reduced compared to an electrode current collector formed of metal, thus significantly improving the energy density per unit weight, and improving safety in the event of a fire by causing a short circuit between the electrodes.

[0043] However, for electrode current collectors that include a polymer resin layer disposed between two metal layers, although mechanical safety against foreign objects (such as spikes) can be improved, there is a need to improve safety against heat propagation in the event of an actual fire.

[0044] Therefore, by utilizing the property of shape memory alloy (SMA) to recover its original shape at high temperature, the inventors designed an electrode current collector comprising a polymer resin layer and a first metal layer and a second metal layer, wherein the first metal layer and the second metal layer comprise shape memory alloy (SMA) and are disposed on two surfaces of the polymer resin layer.

[0045] The electrode has a structure in which an electrode active material layer is disposed on an electrode current collector, wherein an electrode tab is formed and protrudes from one side of the electrode, and an electrode lead can be connected to the electrode tab to transmit the power generated in the electrode to the outside.

[0046] According to the invention, the first and second metal layers comprise a shape memory alloy (SMA), which allows the electrode current collector to contract along with the SMA at high temperatures. Therefore, the electrode tabs in contact with the electrode current collector contract, but the electrode leads do not, as they are fixed by welding to the busbar or the like. Thus, the contracted tabs, as described above, induce an electrical disconnection from the electrode leads and have a time-delay effect on heat propagation in the event of a battery fire.

[0047] Furthermore, the electrode current collector according to the present invention can improve fire safety, heat resistance and heat shielding effect.

[0048] (1) Polymer resin layer

[0049] The polymer resin layer is the base resin, which prevents abnormal heat transfer between the electrode current collector and the electrode active material layer, and also reduces the weight of the electrode current collector and mitigates external impacts.

[0050] The polymer resin layer may include, for example, at least one selected from polyester resins, epoxy resins, phenolic resins, melamine resins, polyurethane resins, silicone resins, EVA resins, rubber resins, acrylic resins, and polyether urethane resins.

[0051] Specifically, the polymer resin layer may comprise at least one substance selected from the following: polyimide (PI), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyacrylonitrile (PAN), polyethylene (PE), polyamide (PA), and polypropylene (PP). Furthermore, the polymer resin layer may be a thermosetting resin or a photocurable resin, and preferably comprises an ultraviolet-curable resin.

[0052] Depending on the requirements, the polymer resin layer may contain photoinitiators, such as benzoin compounds, acetophenone compounds, acylphosphine oxide compounds, titanoceramic compounds, thioxanone compounds, or peroxide compounds, or photoinitiators such as amines or quinones. It may also contain curing accelerators, such as amines, imidazoles, phosphorus compounds, boron compounds, and phosphoboron curing accelerators. Furthermore, the polymer resin layer may contain thermal initiators, such as peroxides like azodicarbonamide, benzoyl peroxide, or acetyl peroxide.

[0053] The thickness of the polymer resin layer can be from 3 μm to 18 μm, preferably from 3 μm to 15 μm, and more preferably from 4 μm to 8 μm. When the thickness of the polymer resin layer is less than 3 μm, it may hinder abnormal heat transfer due to its thinness, and the effect of reducing the weight of the electrode current collector and mitigating external shocks may be insignificant. Conversely, when the thickness is greater than 18 μm, the battery thickness increases significantly, thereby increasing resistance, which may adversely affect the energy density. When the thickness of the polymer resin layer meets the above-mentioned numerical range, the energy density of the battery can be improved while inducing an electrically disconnected state from other electrodes or maintaining physical electrical insulation.

[0054] (2) Metal layer

[0055] The first and / or second metal layers comprise a shape memory alloy (SMA). A shape memory alloy (SMA) is an alloy with strong resilience, meaning it possesses the property of returning to its original shape at high temperatures even after being deformed into a different shape. Shape memory alloys (SMAs) can be prepared using materials capable of shape memory through a shape memory process, and thus possess the property of deforming the remembered shape at high temperatures.

[0056] Shape memory alloys (SMAs) are designed to apply external forces to the polymer resin layer through shape deformation when the temperature exceeds a predetermined temperature. Specifically, because the electrode current collector according to the invention can shrink with the shape memory alloy (SMA) at high temperatures by utilizing the properties of the SMA, the electrode current collector according to the invention has a time delay effect on heat propagation in the event of a battery fire by inducing an electrically disconnected state from other electrodes.

[0057] Shape memory alloys (SMAs) may contain at least one of copper-zinc alloys, copper-tin alloys, magnesium-copper alloys, nickel-titanium alloys, and copper-aluminum-nickel alloys.

[0058] Based on the total weight of the metal layers, the amount of shape memory alloy (SMA) can range from 20% to 100% by weight, preferably 30% to 100% by weight, and more preferably 50% to 100% by weight. When the amount of shape memory alloy (SMA) meets the above-mentioned numerical range, the shape memory alloy (SMA) can be easily applied, and during abnormal battery behavior, the electrode current collector can contract with the shape memory alloy (SMA) at high temperatures. This can induce an electrical disconnection state between the battery electrodes, thereby improving battery safety.

[0059] In addition to shape memory alloy (SMA), the first and / or second metal layers may, if desired, additionally comprise: stainless steel, aluminum, copper, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys, which may specifically comprise aluminum when the electrode current collector is positive and copper when the electrode current collector is negative.

[0060] Furthermore, fine irregularities can be formed on the surface of the first metal layer and / or the second metal layer to enhance the adhesion to the electrode material mixture layer. The first metal layer and / or the second metal layer can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0061] The thickness of the first metal layer and / or the second metal layer can be from 10 μm to 30 μm, preferably from 18 μm to 28 μm, and more preferably from 18 μm to 25 μm. When the thickness of the first metal layer and / or the second metal layer is less than 10 μm, it becomes difficult to maintain its shape as an electrode because the first metal layer and / or the second metal layer are too thin, making it difficult to function as a support and control the physical properties of the electrode. Conversely, when the thickness is greater than 30 μm, the energy density may decrease due to the excessive increase in battery weight and thickness.

[0062] The thickness ratio of the polymer resin layer to the first metal layer and / or the second metal layer can be in the range of 1:1 to 1:10, preferably 1:1.5 to 1:5, and more preferably 1:1.5 to 1:3. When the thickness ratio of the polymer resin layer to the first metal layer and / or the second metal layer meets the above-mentioned numerical range, there is an effect of improving battery safety and increasing battery energy density through electrical short circuit.

[0063] Lithium secondary batteries, battery modules and battery packs

[0064] The lithium secondary battery according to the present invention comprises the electrode current collector of the present invention described above. The lithium secondary battery according to the present invention comprises: An electrode assembly having a structure in which multiple electrodes and multiple diaphragms are alternately stacked. Each electrode includes an electrode current collector and an electrode active material layer disposed on the electrode current collector, and At least one of the plurality of electrode current collectors is the electrode current collector of the present invention described above.

[0065] Figure 2 and Figure 3 Each is a cross-sectional view showing a lithium secondary battery including an electrode current collector according to the present invention.

[0066] Reference Figure 2 and3 Specifically, the lithium secondary battery 100 according to the present invention includes an electrode assembly 50, wherein a positive electrode 15, a separator 19 and a negative electrode 17 are stacked sequentially, wherein the separator 19 is disposed between the positive electrode 15 and the negative electrode 17, the positive electrode 15 includes a positive electrode current collector 15a and a positive electrode active material layer 15b stacked on the positive electrode current collector, and the negative electrode 17 includes a negative electrode current collector 17a and a negative electrode active material layer 17b stacked on the negative electrode current collector, wherein at least one of the positive electrode current collector and the negative electrode current collector is the aforementioned electrode current collector 10 containing a shape memory alloy (SMA).

[0067] The lithium secondary battery 100 according to the present invention may include at least one electrode current collector 10 containing the aforementioned shape memory alloy (SMA), and preferably may include two or more electrode current collectors 10. Specifically, in an electrode assembly 50 having a structure in which multiple electrodes and multiple separators are alternately stacked, an electrode 30 containing the aforementioned electrode current collector 10 containing the shape memory alloy (SMA) may be provided on the outermost side of the electrode assembly 50. The outermost electrode of the lithium secondary battery 100 according to the present invention may be composed of a positive or negative electrode having a structure in which a polymer resin layer is disposed between two metal layers containing the shape memory alloy (SMA); or the electrode located in the central part of the battery may be composed of a positive or negative electrode having a structure in which a polymer resin layer is disposed between two metal layers containing the shape memory alloy (SMA). In the case where the aforementioned electrode 30 is provided on the outermost side of the electrode assembly 50, during abnormal battery behavior, the electrode current collector may shrink at high temperatures as the shape memory alloy (SMA) shrinks. Therefore, the electrode tabs in contact with the electrode current collector will shrink, but the electrode leads will not shrink because they are fixed by welding to the busbar or the like. Therefore, as described above, the contracted tabs induce an electrical disconnection state with the electrode leads and have a time delay effect on heat propagation in the event of a battery fire.

[0068] Since the electrode current collector has already been described above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0069] (positive electrode)

[0070] The positive electrode current collector can contain a highly conductive metal without particular limitations, as long as it is non-reactive within the battery's voltage range and the positive electrode active material layer can easily adhere to it. Examples of materials that can be used as the positive electrode current collector include: stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. Furthermore, the thickness of the positive electrode current collector is typically from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0071] In addition to the positive electrode active material, the positive electrode active material layer may optionally contain conductive materials and adhesives, if desired.

[0072] In this case, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 80% to 99% by weight, more specifically 90% to 98% by weight.

[0073] Conductive materials are used to provide conductivity to the electrodes. Any conductive material can be used without particular limitation, as long as it has suitable electronic conductivity and does not cause chemical changes in the battery. Specific examples of conductive materials can be: graphite, such as natural or artificial graphite; carbonaceous materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be from 0.01% by weight to 10% by weight, preferably from 0.1% by weight to 9% by weight, more preferably from 0.1% by weight to 5% by weight.

[0074] The adhesive improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the adhesive can be: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogen is replaced by lithium (Li), sodium (Na), or calcium (Ca), or various copolymers thereof, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 1% to 10% by weight.

[0075] In addition to using the aforementioned positive electrode active materials, positive electrodes can be prepared according to typical methods for preparing positive electrodes. Specifically, a positive electrode slurry composition prepared by dissolving or dispersing the positive electrode active material, along with optional binders, conductive materials, and dispersants in a solvent, is coated onto a positive electrode current collector, and then the positive electrode can be prepared by drying and calendering the coated positive electrode current collector.

[0076] The solvent can be one commonly used in the art, including dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and any one or a mixture of two or more thereof can be used. If the amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that provides excellent thickness uniformity during subsequent coating for positive electrode preparation, then the amount of solvent used may be adequate.

[0077] Alternatively, as another method, the positive electrode can be prepared by casting the positive electrode slurry composition onto a separate support and then stacking the membrane separated from the support onto the positive electrode current collector.

[0078] (Diaphragm)

[0079] The separator separates the negative and positive electrodes and provides a pathway for lithium ions to move. Any separator can be used without particular limitation, as long as it is typically used in lithium-ion secondary batteries. Specifically, separators with high electrolyte retention capacity and low resistance to electrolyte ion migration can be used. In particular, porous polymer membranes can be used, such as porous polymer membranes prepared from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminated structures having two or more layers. Additionally, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0080] (electrolytes)

[0081] Furthermore, the electrolyte used in this invention may include: organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, or molten inorganic electrolytes that can be used in the preparation of lithium secondary batteries, but this invention is not limited thereto.

[0082] Specifically, the electrolyte may contain organic solvents and lithium salts.

[0083] Any organic solvent can be used without particular limitation, as long as it serves as a medium through which ions participating in the battery electrochemical reaction can move. Specifically, the following substances can be used as organic solvents: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic hydrocarbon solvents, such as benzene and fluorobenzene; or carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain double bonds, aromatic rings, or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, which can improve the charge and discharge performance of the battery, with low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate).

[0084] The use of lithium salts is not particularly restricted, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, the anion of the lithium salt can be selected from F... - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - At least one of the following can be used as a lithium salt: LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt can be used in a concentration range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and more preferably 1.0 M to 2.0 M. If the concentration of the lithium salt is within the above range, excellent electrolyte performance can be obtained because the electrolyte can have suitable conductivity and viscosity, and lithium ions can move efficiently.

[0085] To improve battery life characteristics, suppress battery capacity decline, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also contain at least one additive, such as: alkylene carbonate halide compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted sulfadiazine ketones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive content may be from 0.1% by weight to 10.0% by weight, based on the total weight of the electrolyte.

[0086] (negative electrode)

[0087] The negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0088] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and aluminum-cadmium alloys can be used. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0089] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a binder and a conductive material.

[0090] Compounds capable of reversibly inserting and de-intercalating lithium can be used as anode active materials. Specific examples of anode active materials can be: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; (semi-)metallic materials that can be alloyed with lithium, such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloys, Sn alloys, or Al alloys; and (semi-)metal oxides that can be doped and de-doped with lithium, such as SiO2. β (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising (semi-)metallic materials and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more thereof may be used. Furthermore, lithium metal films can be used as anode active materials. Additionally, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical examples of low-crystallinity carbon can be soft carbon and hard carbon, while typical examples of high-crystallinity carbon can be irregular, planar, sheet-like, spherical, or fibrous natural or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature sintered carbon (e.g., coke derived from petroleum or coal tar pitch).

[0091] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80% to 99% by weight, 82% to 99% by weight, or 84% to 99% by weight.

[0092] Adhesives are components that facilitate the bonding between conductive materials, active materials, and current collectors. The amount of adhesive added is typically from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of adhesives include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0093] Conductive materials are components used to further improve the conductivity of the negative electrode active material. Based on the total weight of the negative electrode active material layer, the content of the conductive material can be from 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight. There are no particular restrictions on the conductive material, as long as it is conductive and does not cause adverse chemical changes in the battery. Examples of conductive materials that can be used include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum and nickel powders; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; or polyphenylene derivatives.

[0094] The negative electrode active material layer can be prepared by coating a negative electrode slurry composition onto a negative electrode current collector and drying the coated negative electrode current collector, wherein the negative electrode slurry composition is prepared by dissolving or dispersing an optional binder and conductive material, as well as the negative electrode active material, in a solvent; or by casting the negative electrode slurry composition onto a separate support and then stacking the film layer separated from the support onto the negative electrode current collector.

[0095] (Battery casing)

[0096] In addition, the lithium secondary battery may optionally include: a battery container housing an electrode assembly containing a positive electrode, a separator, and a negative electrode; and a seal for sealing the battery container.

[0097] Furthermore, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics and capacity retention, it is suitable for portable devices (e.g., mobile phones, laptops and digital cameras) and electric vehicles (e.g., hybrid electric vehicles (HEVs)).

[0098] In particular, to enable batteries to be used for longer periods after a single charge, it is necessary to increase battery capacity, and the fabrication technology of large-area electrodes is crucial for improving capacity. However, during the fabrication of large-area electrodes, electrode performance may be degraded, and there are concerns about heat propagation to other electrodes due to thermal runaway in the event of a fire.

[0099] Therefore, according to another embodiment of the present invention, a battery module comprising a plurality of lithium secondary batteries and a battery pack comprising a plurality of battery modules are provided.

[0100] A battery module refers to a battery assembly in which a certain number of lithium secondary batteries are bundled together and placed in a frame to protect them from external impacts, heat, vibration, etc. A battery pack refers to the final form of a battery system installed in equipment such as electric vehicles.

[0101] Battery modules or battery packs can be used as a power source for at least one medium to large-sized device, including: power tools; electric vehicles (including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs)); or power storage systems.

[0102] In cases where the battery module and battery pack according to the invention include multiple of the above-described electrode current collectors, high-capacity and large-area batteries can be achieved by maximizing safety against heat propagation in the event of a fire.

[0103] In the following description, embodiments of the invention will be presented in a manner readily practiced by those skilled in the art. However, the invention can be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0104] Examples and Comparative Examples

[0105] Example 1

[0106] On both surfaces of polyethylene terephthalate (PET) with a thickness of 6 μm, Ni 50 Ti 50 Alloy physical vapor deposition (PVD) is performed to a thickness of 18 μm to form a first metal layer and a second metal layer, thereby fabricating an electrode current collector.

[0107] <Preparation of Lithium Secondary Batteries>

[0108] The positive electrode active material (NCM65 1520), conductive material (Li-435), and PVDF binder (KF9700, AD-c01) were mixed in N-methylpyrrolidone at a weight ratio of 96.5:1.5:2.0 to prepare the positive electrode slurry.

[0109] A positive electrode slurry is coated on one surface of the electrode current collector prepared above, dried at 140°C, and then rolled to prepare the positive electrode.

[0110] Graphite is used as the negative electrode.

[0111] An electrode assembly is prepared by placing a separator between the positive and negative electrodes prepared by the above method, placing the electrode assembly in a battery case, and then injecting electrolyte into the case to prepare a single battery cell. The electrolyte is prepared by dissolving 0.7M LiPF6 in a mixed organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 2:1:7.

[0112] Example 2

[0113] The battery cell was prepared in the same manner as in Example 1, except that it included multiple electrode assemblies prepared by the above method.

[0114] Comparative Example 1

[0115] The battery cells were prepared in the same manner as in Example 1, except that the battery cells consisted only of electrode current collectors, which were formed of 12 μm thick aluminum metal (a typical metal current collector).

[0116] Comparative Example 2

[0117] The battery cell was prepared in the same manner as in Example 1, except that an electrode current collector was used in which a first metal layer and a second metal layer were formed on two surfaces of polyethylene terephthalate (PET) with a thickness of 6 μm by physical vapor deposition (PVD) of aluminum to a thickness of 1 μm.

[0118] Experimental Example 1

[0119] For the lithium secondary battery cells prepared in Examples 1 and 2 and Comparative Examples 1 and 2, experiments were conducted on 1) the time delay effect of heat propagation, 2) safety against physical impact, and 3) safety against nail penetration. The experimental results are presented in Table 1 below. In Table 1, “◎” indicates very good, “○” indicates good, “Δ” indicates fair, and “X” indicates poor.

[0120] Specifically, the experimental methods for 1) the time delay effect of heat propagation, 2) safety against physical impact, and 3) safety against nail punctures are as follows.

[0121] 1) Five of the prepared battery cells were formed into a module, and heat was applied to one battery cell at a rate of 0.5°C / second using a heating pad. Thermocouples were used to measure the heat between adjacent cells to evaluate whether there was a time delay in heat transfer.

[0122] 2) The mechanical safety of each battery cell was evaluated by measuring whether it caught fire when the battery cell was charged to 4.4 V at 0.2 C in constant current / constant voltage (CC / CV) mode. A 15.8 mm diameter rod was dropped freely from a height of 610 mm onto the center of the battery cell.

[0123] 3) The mechanical safety of each battery cell is evaluated by conducting a nail penetration test, in which a sharp nail is used to penetrate the prepared battery cell at a speed of 0.1 mm / s. The mechanical safety of each battery cell is evaluated based on whether the battery cell catches fire, the amount of smoke produced, and the size of the flame when it catches fire.

[0124] [Table 1]

[0125] As can be confirmed from [Table 1], for the battery cells prepared by Examples 1 and 2, 1) the time delay effect of heat propagation, 2) the safety against physical impact, and 3) the safety against nail penetration are superior to those prepared by Comparative Examples 1 and 2.

[0126] [Explanation of reference numerals in the attached figures]

[0127] 10: Electrode current collector

[0128] 11: Polymer resin layer

[0129] 13A, 13B: First metal layer, second metal layer

[0130] 15: Positive electrode

[0131] 15a: Positive current collector

[0132] 15b: Positive electrode active material layer

[0133] 17: Negative electrode

[0134] 17a: Negative current collector

[0135] 17b: Negative electrode active material layer

[0136] 19: Diaphragm

[0137] 30: Electrode including electrode current collector 10

[0138] 50: Electrode assembly

[0139] 100: Lithium secondary battery

Claims

1. An electrode current collector, the electrode current collector comprising: Polymer resin layer, A first metal layer disposed on one surface of the polymer resin layer, and A second metal layer is disposed on another surface of the polymer resin layer. The first and second metal layers comprise shape memory alloys (SMAs), and The shape memory alloy (SMA) is designed such that when the temperature of the shape memory alloy (SMA) is higher than a predetermined temperature, external force is applied to the polymer resin layer through shape deformation.

2. The electrode current collector according to claim 1, wherein the shape memory alloy (SMA) comprises at least one of copper-zinc alloy, copper-tin alloy, magnesium-copper alloy, nickel-titanium alloy, and copper-aluminum-nickel alloy.

3. The electrode current collector according to claim 1, wherein the amount of shape memory alloy (SMA) is in the range of 20% to 100% by weight, based on the total weight of the metal layer.

4. The electrode current collector according to claim 1, wherein the polymer resin layer comprises at least one selected from polyester resin, epoxy resin, phenolic resin, melamine resin, polyurethane resin, silicone resin, EVA resin, rubber resin, acrylic resin and polyetherurethane resin.

5. The electrode current collector according to claim 1, wherein the thickness ratio of the polymer resin layer to the first metal layer or the second metal layer is in the range of 1:1 to 1:

10.

6. The electrode current collector according to claim 1, wherein the thickness of the polymer resin layer is from 3 μm to 18 μm.

7. The electrode current collector according to claim 1, wherein the thickness of the first metal layer and the second metal layer is each from 10 μm to 30 μm.

8. A lithium secondary battery, the lithium secondary battery comprising: An electrode assembly having a structure in which multiple electrodes and multiple diaphragms are alternately stacked. Each of the electrodes comprises an electrode current collector and an electrode active material layer disposed on the electrode current collector, and At least one of the plurality of electrode current collectors is the electrode current collector according to any one of claims 1 to 7.

9. A battery module comprising a plurality of lithium secondary batteries as described in claim 8.

10. A battery pack comprising a plurality of battery modules as claimed in claim 9.

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