Negative electrode for secondary battery and jelly roll type electrode assembly containing the same

Abstract

To provide a negative electrode for a secondary battery in which the risk of a short circuit inside the electrode assembly is improved.SOLUTION: The present invention relates to a negative electrode for a secondary battery and a jelly roll type electrode assembly including the same. The negative electrode satisfies the creep rate condition shown in the equation 1 within a specific range. When applied to the jelly roll type electrode assembly, even when the negative electrode contains a silicon (Si)-based active material, the stress generated at the outer edge is significantly low, such that deformation and / or expansion of the electrode assembly can be suppressed, and the stress accumulated in a negative electrode current collector can be significantly reduced. As a result, there is a low risk of internal short circuit in the electrode assembly, which is advantageous in that it is highly safe.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a secondary battery used in a jelly roll type electrode assembly, and a jelly roll type electrode assembly containing the same.

[0002] This application claims priority under Korean Patent Application No. 10-2021-0135030 dated October 12, 2021, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification. [Background technology]

[0003] Recently, secondary batteries have been widely applied not only to small devices such as portable electronic devices, but also to medium and large-sized devices such as battery packs for hybrid and electric vehicles, or power storage devices.

[0004] These rechargeable batteries are classified into cylindrical or rectangular batteries, in which the jelly roll is housed in a cylindrical or rectangular metal can, and pouch-type batteries, in which the jelly roll is housed in a pouch-type case made of aluminum laminate sheet, depending on the shape of the battery case.

[0005] Furthermore, the electrode assemblies housed in the battery case are power generation elements capable of charging and discharging, consisting of a stacked structure of positive electrode / separating membrane / negative electrode. They are classified into two types: foldable electrode assemblies (jelly rolls), which are wound with a long sheet-like positive electrode coated with active material and a negative electrode interposed with a separating membrane, and stacked electrode assemblies, which are sequentially stacked with a number of positive and negative electrodes of a predetermined size interposed with a separating membrane. Of these, jelly rolls have the advantages of being easy to manufacture and having a high energy density per unit weight.

[0006] Figure 1 is a schematic perspective view of a typical jelly roll type electrode assembly. Referring to Figure 1, the jelly roll type electrode assembly 100 includes a positive electrode plate 110, a negative electrode plate 120, and a separation membrane 130 interposed between the positive electrode plate 110 and the negative electrode plate 120, and has a configuration in which the positive electrode plate 110, the separation membrane 130, and the negative electrode plate 120 are sequentially stacked and wound up.

[0007] Here, the positive electrode plate 110 includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and a positive electrode tap 111 joined to a blank portion of the positive electrode current collector where the positive electrode active material layer is not formed. The negative electrode plate 120 includes a negative electrode current collector, a negative electrode active material layer formed on the negative electrode current collector, and a negative electrode tap 121 joined to a blank portion of the negative electrode current collector where the negative electrode active material layer is not formed.

[0008] Furthermore, the electrode assembly 100 includes a plurality of rounded portions 140, 140' located on both sides of the electrode assembly 100 formed by winding, and a plurality of flat portions 150, 150' separated by the rounded portions 140, 140'.

[0009] The above-mentioned jelly roll type electrode assembly 100 is formed by winding together positive electrode plates 110 and negative electrode plates 120, which use a positive electrode current collector and a negative electrode current collector made of metal as the base material. Therefore, after winding, there is a risk of winding loosening due to the restoring force of the metal. When charging a lithium secondary battery containing this assembly, the stress difference between the rounded portions 140, 140' and the flat portions 150, 150', particularly the stress concentrated at the contact points (the boundary between the inner and outer edges) of the rounded portions 140, 140' and the flat portions 150, 150', can induce deformation of the electrode assembly or cause expansion of the electrode assembly.

[0010] In particular, when using silicon (Si)-based active material in the negative electrode to increase the charge / discharge capacity of a secondary battery, the stress accumulated on the negative electrode plate 120 increases significantly due to the large volume change of the silicon (Si)-based active material during charging and discharging, thus increasing the risk of internal wire breakage.

[0011] In contrast, methods have been proposed such as introducing a winding fixing tape that wraps around the outer periphery of the electrode assembly in the same direction as the winding direction of the electrode assembly, or fixing the terminal end of the outermost edge with a tape after winding. However, the methods of introducing the winding fixing tape or fixing the terminal end with a tape cannot sufficiently suppress the swelling of the electrode assembly and the twist during charge and discharge due to the stress difference between the inner and outer edges that may occur during charge and discharge of the lithium secondary battery. Moreover, since the stress accumulated in the negative electrode plate is very high, there is a limit to preventing internal disconnection of the negative electrode plate.

[0012] Therefore, there is a need to develop an electrode and / or electrode assembly that suppresses deformation and swelling due to stress differences at the outer edges of the electrode assembly that may occur during charge and discharge of a lithium secondary battery, particularly a secondary battery containing a silicon (Si)-based material as the negative electrode active material, and does not cause internal disconnection.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0014] Therefore, an object of the present invention is to provide a jelly roll type electrode assembly that contains a silicon (Si)-based material as the negative electrode active material, has excellent charge and discharge capacity, reduces the stress generated at the outer edge during charge and discharge of the secondary battery, suppresses deformation and / or swelling of the electrode assembly, while significantly reducing the stress accumulated in the negative electrode plate and improving the risk of short circuit inside the electrode assembly.

Means for Solving the Problems

[0015] In order to solve the problems as described above, In one embodiment of the present invention, It includes a negative electrode current collector and a negative electrode composite material layer provided on the negative electrode current collector, The above negative electrode composite layer contains silicon material as the negative electrode active material. The above negative electrode current collector provides a negative electrode for a secondary battery that satisfies the following equation 1 to be 20 μm / sec to 50 μm / sec when measuring the creep rate under tensile conditions of 22 ± 2°C and 300 MPa:

[0016] [Formula 1] C60-C2 / 58

[0017] In formula 1, C60 indicates the change in length of the negative electrode current collector after 60 seconds have elapsed since the application of tensile force. C2 represents the change in length of the negative electrode current collector after 2 seconds have elapsed since the application of tensile force.

[0018] Here, the negative electrode current collector has a current capacity of 20-45 kg / mm². 2 It may have a tensile strength and an elongation of 5% or more.

[0019] Furthermore, the above negative electrode active material is Si, SiC, and SiO z (However, it may contain one or more silicon-based substances within the range of 0.5 ≤ z ≤ 2.5.)

[0020] In this case, the silicon material may be included in an amount of 1 to 40 parts by weight per 100 parts by weight of the negative electrode composite layer.

[0021] Furthermore, the above-mentioned negative electrode active material may further contain one or more carbon materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, and carbon fibers.

[0022] Furthermore, the negative electrode current collector may include one or more thin metal sheets selected from the group consisting of copper, aluminum, stainless steel, nickel, titanium, and calcined carbon, and the average thickness of the negative electrode current collector may be 1 μm to 500 μm.

[0023] Furthermore, in one embodiment, the present invention is The invention includes a positive electrode, a negative electrode as described above, and a separation membrane interposed between the positive electrode and the negative electrode. The present invention provides a jelly roll type electrode assembly having a structure in which a positive electrode, a separation membrane, and a negative electrode are sequentially stacked and wound together.

[0024] Furthermore, in one embodiment, the present invention is The present invention provides a cylindrical secondary battery including the jelly roll type electrode assembly described above. [Effects of the Invention]

[0025] The negative electrode for a secondary battery according to the present invention has the advantage of being highly safe because, by providing a negative electrode current collector that satisfies the creep rate conditions shown in Equation 1 within a specific range, even when containing a silicon (Si)-based negative electrode active material, the stress generated at the outer edge is significantly low, which not only suppresses deformation and / or expansion of the electrode assembly but also significantly reduces the stress accumulated in the negative electrode current collector, thus reducing the risk of internal short circuits in the electrode assembly. [Brief explanation of the drawing]

[0026] [Figure 1] This is a schematic perspective view of a conventional electrode assembly. [Modes for carrying out the invention]

[0027] While the present invention may be subject to various modifications and may have various embodiments, we will now describe a specific embodiment in detail.

[0028] However, this should be understood not as an attempt to limit the present invention to any particular embodiment, but rather as including all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0029] In the present invention, terms such as "includes" or "having" are intended to specify the presence of features, numbers, stages, operations, components, parts, or combinations thereof as described in the specification, and should be understood not to preemptively exclude the presence or possibility of adding one or more other features, numbers, stages, operations, components, parts, or combinations thereof.

[0030] Furthermore, in this invention, when a part such as a layer, film, region, or plate is described as being "on top" of another part, this includes not only the case where it is "directly on top" of the other part, but also the case where another part is located in between. Conversely, when a part such as a layer, film, region, or plate is described as being "below" another part, this includes not only the case where it is "directly below" the other part, but also the case where another part is located in between. Also, in this application, "located on top" may include not only the upper part, but also the case where it is located at the bottom.

[0031] In this invention, "brittleness" refers to the phenomenon in which a material breaks with little or no plastic deformation when subjected to an external force.

[0032] Furthermore, in the present invention, "main component" means a component that accounts for 80% or more, 90% or more, 95% or more, or 97.5% or more by weight of the total weight of the target substance, and in some cases, it may also mean a component that accounts for 100% by weight. For example, "main component is silicon" may mean particles that contain silicon (Si), silicon monoxide (SiO) and / or silicon dioxide (SiO2) in amounts of 80% or more, 90% or more, or 98% or more by weight, and in some cases, it may contain 100%.

[0033] The present invention will be described in more detail below.

[0034] <Negative electrode for secondary batteries> In one embodiment, the present invention is It includes a negative electrode current collector and a negative electrode composite material layer provided on the negative electrode current collector, The above negative electrode composite layer contains silicon material as the negative electrode active material. The above negative electrode current collector provides a negative electrode for a secondary battery that satisfies the following equation 1 to be 20 μm / sec to 50 μm / sec when measuring the creep rate under conditions of 22 ± 2°C and a tensile force of 300 MPa:

[0035] [Formula 1] C60-C2 / 58

[0036] In formula 1, C60 indicates the change in length of the negative electrode current collector after 60 seconds have elapsed since the application of tensile force. C2 represents the change in length of the negative electrode current collector after 2 seconds have elapsed since the application of tensile force.

[0037] The negative electrode for a secondary battery according to the present invention is used in a jelly roll type electrode assembly and includes a negative electrode composite layer manufactured by coating, drying, and pressing a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector.

[0038] Here, the negative electrode current collector may include a thin metal plate that satisfies the creep rate conditions shown in Equation 1 within a specific range.

[0039] Equation 1 above represents the ratio over time between the change in length of the negative electrode current collector after 2 seconds (C2) and the change in length of the negative electrode current collector after 60 seconds (C60), when measuring the creep rate of the negative electrode current collector by applying a tensile force of 300 MPa at room temperature. More specifically, "creep rate" refers to the degree of deformation of the negative electrode current collector over time, and indicates the rate of change in the length of the negative electrode current collector over time when a constant force is applied to a thin metal plate at a specific temperature. The negative electrode current collector according to the present invention has a configuration that includes a negative electrode current collector that satisfies the creep rate at a specific time interval (60 seconds - 2 seconds = 58 seconds) shown in Equation 1, that is, the deformation rate at a specific time interval (58 seconds), within a specific range.

[0040] As an example, the negative electrode current collector according to the present invention can satisfy the creep rate conditions shown in Equation 1, which are 20 μm / sec to 50 μm / sec, specifically 20 μm / sec to 45 μm / sec, 20 μm / sec to 40 μm / sec, 20 μm / sec to 30 μm / sec, 25 μm / sec to 40 μm / sec, 35 μm / sec to 45 μm / sec, or 25 μm / sec to 30 μm / sec.

[0041] The present invention, by controlling the creep rate of the negative electrode current collector within the above range, prevents excessive volume increase of the electrode assembly due to a significantly low creep rate when used as a negative electrode current collector in a jelly roll type electrode assembly, while also preventing an increased risk of fracture of the negative electrode current collector due to an excessive creep rate. On the other hand, the above creep rate can be affected by the measurement temperature, the applied tensile force, the components constituting the negative electrode current collector, the size of the crystal grains, etc., so even for the same negative electrode current collector, the value of Equation 1 will differ depending on the above-mentioned factors.

[0042] Furthermore, the negative electrode current collector can satisfy the tensile strength and / or elongation within a specific range, in addition to the creep rate condition shown in Equation 1. Generally, during the manufacturing of the electrodes, fragments of thin metal sheets may be generated in the cutting process and remain on the negative electrode current collector, which can cause OCV (open circuit voltage) failures in the battery process. To prevent such a decrease in the brittleness of the negative electrode current collector, the negative electrode current collector of the present invention can adjust the tensile strength and / or elongation within a specific range.

[0043] As an example, the negative electrode current collector described above has a current capacity of 20-45 kg / mm². 2 It can exhibit a tensile strength of 20-40 kg / mm². 2 , 25~45 kg / mm 2 , 25-40 kg / mm 2 , 30-40 kg / mm 2 , or 32-38 kg / mm 2 It can demonstrate the tensile strength.

[0044] As another example, the above-mentioned negative electrode current collector can exhibit an elongation rate of 5% or more, specifically, an elongation rate of 5% to 18%, 5% to 15%, 8% to 13%, 9% to 12%, 10% to 15%, 11% to 15%, or 11% to 12%.

[0045] Furthermore, the above-mentioned negative electrode current collector can be applied without particular limitations, as long as it is used in the industry as an electrode current collector for secondary batteries. For example, the above-mentioned negative electrode current collector can be made of copper, aluminum, stainless steel, nickel, titanium, calcined carbon, etc., which have high conductivity without inducing chemical changes in the battery. In the case of aluminum or stainless steel, it may also include thin metal sheets surface-treated with carbon, nickel, titanium, silver, etc.

[0046] Furthermore, the thickness of the negative electrode current collector may be between 1 μm and 500 μm, specifically between 1 μm and 300 μm, 1 μm and 200 μm, 1 μm and 100 μm, 1 μm and 90 μm, 1 μm and 50 μm, 10 μm and 200 μm, 50 μm and 300 μm, 80 μm and 200 μm, or 100 μm and 180 μm.

[0047] Furthermore, the above-mentioned negative electrode composite layer contains a silicon material as a negative electrode active material. The above-mentioned silicon material is a substance that mainly contains silicon (Si) as a metallic component, and may contain one or more of Si, SiC, and SiOz (where 0.5 ≤ z ≤ 2.5). Specifically, the above-mentioned silicon material may contain pure silicon particles and / or silicon oxide particles.

[0048] Furthermore, the silicon material may be included in an amount of 1 to 40 parts by weight per 100 parts by weight of the negative electrode composite layer, specifically in amounts of 1 to 30 parts by weight, 1 to 20 parts by weight, 1 to 10 parts by weight, 4 to 22 parts by weight, 15 to 30 parts by weight, 20 to 40 parts by weight, 25 to 35 parts by weight, 3 to 8 parts by weight, or 11 to 19 parts by weight per 100 parts by weight of the negative electrode composite layer.

[0049] Pure silicon (Si) exhibits a high theoretical capacity of 4020 mAh / g, and since silicon atoms (Si) can react with up to 4.4 lithium atoms, a high charge-discharge capacity can be achieved when manufacturing a secondary battery using silicon (Si) material as the main component. However, silicon material undergoes a large volume change during the charge-discharge process, and considerable stress acts on the outer edge of the jelly-roll type electrode assembly, causing deformation and / or expansion of the electrode assembly. If the silicon content is high, internal short circuits may occur due to damage to the negative electrode current collector. However, the negative electrode for secondary batteries of the present invention is equipped with a negative electrode current collector that satisfies the creep rate conditions shown in Equation 1 within a specific range. When applied to the negative electrode of a jelly-roll type electrode assembly, even if a considerable amount of silicon material is included as the negative electrode active material of the secondary battery, deformation and / or expansion of the electrode assembly and internal short circuits due to stress generated at the outer edge of the electrode assembly can be prevented.

[0050] Furthermore, the above-mentioned negative electrode composite layer may further contain carbon materials in addition to silicon materials as negative electrode active materials. Specifically, the above-mentioned negative electrode active materials may further contain carbon materials mainly composed of carbon atoms, and such carbon materials include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers.

[0051] In this case, the carbon material may be included in an amount of 60 to 99 parts by weight per 100 parts by weight of the negative electrode composite layer, specifically in amounts of 70 to 99 parts by weight, 80 to 99 parts by weight, 90 to 99 parts by weight, 78 to 96 parts by weight, 70 to 85 parts by weight, 60 to 20 parts by weight, 65 to 75 parts by weight, 91 to 97 parts by weight, or 81 to 89 parts by weight per 100 parts by weight of the negative electrode composite layer.

[0052] The negative electrode according to the present invention, having the above-described configuration, not only realizes a high charge / discharge capacity for secondary batteries, but when used in a jelly roll type electrode assembly, it can reduce the stress generated at the outer edge of the electrode assembly and reduce the stress accumulated at the outer edge, thereby effectively improving the safety of secondary batteries.

[0053] <Jelly Roll Type Electrode Assembly> Furthermore, in one embodiment, the present invention is The invention includes a positive electrode, the negative electrode described above, and a separation membrane interposed between the positive electrode and the negative electrode. The present invention provides a jelly roll type electrode assembly having a structure in which a positive electrode, a separation membrane, and a negative electrode are sequentially stacked and wound together.

[0054] The jelly roll type electrode assembly according to the present invention includes a positive electrode, a negative electrode, and a separation membrane, and is manufactured by winding the positive electrode and negative electrode into a round shape with the positive electrode and negative electrode laminated on both sides of the separation membrane, respectively. In this case, the negative electrode of the present invention is included as the negative electrode of the electrode assembly, which can further reduce the stress on the outer edge of the electrode assembly, especially the rounded portion of the outer edge formed by winding, and can significantly reduce the amount of stress accumulated in the electrode assembly.

[0055] Here, the negative electrode mentioned above includes a configuration that has the same function and role as the negative electrode for secondary batteries described above, so a detailed explanation of this will be omitted.

[0056] On the other hand, the positive electrode provided in the jelly roll type electrode assembly according to the present invention comprises a positive electrode composite layer manufactured by coating, drying, and pressing a positive electrode active material onto a positive electrode current collector, and may further selectively contain conductive materials, binders, and other additives as needed.

[0057] The above positive electrode active material may include those commonly applied to lithium secondary batteries, but preferably includes a lithium metal composite oxide containing three or more elements selected from the group consisting of nickel, cobalt, manganese, and aluminum. The above lithium metal composite oxide may, in some cases, have a form doped with other transition metals (M 1 ). For example, the above positive electrode active material may be a lithium metal composite oxide represented by the following Chemical Formula 1 capable of reversible intercalation and deintercalation:

[0058] [Chemical Formula 1] Li x [Ni y Co z Mn w M 1 v O u

[0059] In the above Chemical Formula 1, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, x, y, z, w, v, and u are respectively 1.0 ≦ x ≦ 1.30, 0.1 ≦ y < 0.95, 0.01 < z ≦ 0.5, 0 ≦ w ≦ 0.5, 0 ≦ v ≦ 0.2, and 1.5 ≦ u ≦ 4.5.

[0060] As an example, the above positive electrode active material is LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 [[ID=​​​Co 0.2 Mn 0.15 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may contain one or more compounds selected from the group consisting of O2.

[0061] Furthermore, the positive electrode can be made of a material that has high conductivity without inducing chemical changes in the battery, and can also be used as the positive electrode current collector. For example, stainless steel, aluminum, nickel, titanium, and calcined carbon can be used, and in the case of aluminum or stainless steel, materials that have been surface-treated with carbon, nickel, titanium, silver, etc. can also be used.

[0062] Furthermore, the positive electrode current collector can have fine irregularities formed on its surface to enhance the adhesion of the positive electrode active material, and can take on a variety of forms such as film, sheet, foil, net, porous material, foam, and nonwoven fabric. The average thickness of the current collector can be appropriately applied between 3 and 500 μm, taking into account the conductivity and total thickness of the manufactured positive electrode.

[0063] Furthermore, the separation membrane provided in the jelly roll type electrode assembly according to the present invention is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the industry, but specifically, it can contain one or more polymers from among chemically resistant and hydrophobic polypropylene, polyethylene, or polyethylene-propylene copolymer. The above separation membrane can take the form of a porous polymer substrate such as a sheet or nonwoven fabric containing the above polymer, and in some cases it can take the form of a composite separation membrane in which organic or inorganic particles are coated on the above porous polymer substrate with an organic binder. In addition, the above separation membrane may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0064] <Cylindrical rechargeable battery> Furthermore, in one embodiment, the present invention is The present invention provides a cylindrical secondary battery including a jelly roll type electrode assembly.

[0065] The cylindrical secondary battery according to the present invention has a structure in which the jelly roll type electrode assembly according to the present invention described above is inserted into a cylindrical metal can which is a battery case, and an electrolyte is injected. The cylindrical secondary battery according to the present invention is equipped with a jelly roll type electrode assembly of the present invention in which the stress on the outer edge of the electrode assembly and the stress accumulated in the electrode assembly are significantly low, and exhibits high capacity, and has the advantage of excellent safety as internal short circuits do not occur even when it contains a silicon-based negative electrode active material that has a large volume change rate during charging and discharging.

[0066] Here, the jelly roll type electrode assembly described above includes components that have the same function and role as the jelly roll type electrode assembly described above, so a detailed explanation of this will be omitted.

[0067] Furthermore, the electrolyte mentioned above may be used without particular restriction, as long as it is commonly applied in this industry. Specifically, the electrolyte may be a lithium salt-containing electrolyte, which may consist of an electrolyte and a lithium salt, and the electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0068] As the above non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0069] As the above-mentioned organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymerization agents containing ionic dissociation groups may be used.

[0070] As the inorganic solid electrolyte mentioned above, for example, lithium nitrides, halides, sulfates such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2 may be used.

[0071] The lithium salts mentioned above are readily soluble in non-aqueous electrolytes, such as LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylboronate, imide, etc. may be used.

[0072] Furthermore, the electrolyte may contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, in order to improve charge-discharge characteristics and flame retardancy. In some cases, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further included to impart nonflammability, carbon dioxide gas may be further included to improve high-temperature storage characteristics, and fluoroethylene carbonate (FEC) and propene sultone (PRS) may be further included.

[0073] The present invention will be described in more detail below based on examples and experimental examples. However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0074] (Examples 1-2 and Comparative Examples 1-2. Manufacturing of negative electrodes for jelly roll type electrode assemblies) 86 parts by weight of artificial graphite and 10 parts by weight of silicon (Si) particles as negative electrode active materials, 2 parts by weight of carbon black as a conductive material, and 2 parts by weight of styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) as binders were weighed and added, and mixed at 2,000 rpm for 60 minutes to produce a negative electrode slurry for lithium secondary batteries. Separately, copper sheets with the physical properties shown in Table 1 below were prepared, and the negative electrode slurry was applied to both sides of the prepared copper sheets (average thickness: 10 μm), dried, and rolled to produce a negative electrode used in a jelly roll type electrode assembly.

[0075] In this study, the creep rate of the copper sheet was determined by cutting the copper sheet into test pieces measuring 150 mm in length and 12.7 mm in width, fixing them to a UTM measuring machine, and applying a constant tensile force of 300 MPa at 22°C while measuring the change in the length of the copper sheet over time. Subsequently, the creep rate (unit: μm / sec) was calculated from the measured results using Equation 1 below.

[0076] [Formula 1] C60-C2 / 58

[0077] In formula 1, C60 indicates the change in length of the negative electrode current collector after 60 seconds have elapsed since the application of tensile force. C2 represents the change in length of the negative electrode current collector after 2 seconds have elapsed since the application of tensile force.

[0078] [Table 1]

[0079] (Examples 3-4 and Comparative Examples 3-4. Manufacturing of Jelly Roll Type Electrode Assemblies) N-methylpyrrolidone is injected into a homo mixer, and LiNi is used as the positive electrode active material for 100 parts by weight of the solid content of the positive electrode slurry. 0.6 Co 0.2 Mn 0.2 7.8 parts by weight of O29, 0.7 parts by weight of carbon black as a conductive material, and 1.5 parts by weight of PVDF as a binder were weighed and added, and mixed at 2,000 rpm for 60 minutes to produce a positive electrode slurry for lithium secondary batteries. The produced positive electrode slurry was applied to both sides of an aluminum sheet, dried, and then rolled to produce a positive electrode.

[0080] A porous polyethylene (PE) film (average thickness: 20 μm) was interposed between the manufactured positive electrode and the negative electrodes manufactured in Examples 1-2 and Comparative Examples 1-2, and the assembly was wound up to produce a jelly roll type electrode assembly. The negative electrodes used in the electrode assemblies manufactured in each example and comparative example are shown in Table 2 below.

[0081] [Table 2]

[0082] (Example of experiment) To evaluate the performance of the negative electrode for a secondary battery and the jelly roll type electrode assembly containing the same according to the present invention, the following experiment was conducted.

[0083] i) Evaluation of internal wire breakage The electrode assemblies manufactured in Examples 3-4 and Comparative Examples 3-4 were inserted into cylindrical cans, and electrolyte was injected to produce cylindrical secondary batteries. The presence or absence of internal wire breakage was then evaluated for each of the manufactured cylindrical secondary batteries.

[0084] Specifically, each cylindrical secondary battery that was fabricated was charged and discharged 10 times in CC / CV mode. After that, each secondary battery was disassembled to check for any internal breaks in the negative electrode. During this process, charging was performed at 1C until the voltage reached 4.25V, and discharging was performed at a constant current of 1C until the voltage reached 2.5V. The results are shown in Table 3 below.

[0085] (b) Evaluation of charge / discharge life The electrode assemblies manufactured in Examples 3-4 and Comparative Examples 3-4 were inserted into cylindrical cans, and electrolyte was injected to produce cylindrical secondary batteries. Each of the manufactured cylindrical secondary batteries was then charged in 0.33C CC (Constant Current) mode until the voltage reached 4.2V while maintaining a temperature of 45°C. Subsequently, the batteries were discharged in 0.33C CC (Constant Current) mode until the voltage reached 2.5V, and then further discharged in CV (Constant Voltage) mode until the current value decreased to 0.05% of the initial current value, and the initial discharge capacity was confirmed.

[0086] Subsequently, the same charge-discharge cycle was performed a total of 200 times. The discharge capacity measured in the final cycle was divided by the discharge capacity of the first cycle to calculate the 0.33C charge-discharge capacity retention rate. The results obtained are shown in Table 3.

[0087] [Table 3]

[0088] As shown in Table 3 above, the cylindrical secondary battery equipped with the negative electrode of the embodiment satisfies the creep rate condition of 20 to 50 μm / sec in Equation 1, exhibits an excellent charge / discharge capacity retention rate of 97% or more, and it was confirmed that deformation and / or expansion of the electrode assembly is prevented, and the occurrence of internal wire breakage is suppressed.

[0089] On the other hand, the secondary battery of Comparative Example 3, which has a negative electrode with a creep rate condition of less than 20 μm / sec in Equation 1, had a high capacity retention rate, but it was confirmed that deformation and / or expansion of the electrode assembly was induced, leading to internal wire breakage.

[0090] Furthermore, in Comparative Example 4, a secondary battery equipped with a negative electrode where the creep rate condition in Equation 1 exceeds 50 μm / sec, internal wire breakage did not occur, but wrinkles formed between the composite layer and the plain portion of the rolled negative electrode. As charging and discharging occurred, damage to the negative electrode occurred, and it was confirmed that this significantly reduced the battery's capacity retention rate.

[0091] These results show that, when applied to a jelly roll type electrode assembly, the negative electrode for secondary batteries according to the present invention, by satisfying the creep rate conditions shown in Equation 1 within a specific range, can significantly reduce the stress generated at the outer edge and significantly reduce the stress accumulated in the negative electrode current collector, even when it contains silicon (Si)-based active material.

[0092] Although preferred embodiments of the present invention have been described above with reference to the present invention, a person skilled in the art or a person with ordinary knowledge in the art will understand that the present invention can be modified and altered in various ways without departing from the spirit and technical domain of the invention as described in the claims.

[0093] Therefore, the technical scope of the present invention is not limited to what is described in the detailed description of the specification, but should be defined by the claims. [Explanation of Symbols]

[0094] 100 electrode assembly 110 Positive plate 111 Positive Tap 120 Negative plate 121 Negative Tap 130 Separation membrane 140 and 140' round section 150 and 150' flat sections

Claims

1. When measuring the creep rate under the conditions of 22±2℃ and a tensile force of 300 MPa, the following equation 1 satisfies 20 μm / sec to 50 μm / sec. [Formula 1] (C60-C2) / 58 In formula 1, C60 indicates the change in length of the negative electrode current collector after 60 seconds have elapsed since the application of tensile force. C2 represents the change in length of the negative electrode current collector after 2 seconds have elapsed since the application of tensile force, and is a negative electrode current collector for a secondary battery.

2. The negative electrode current collector for a secondary battery according to claim 1, comprising a negative electrode composite layer containing a silicon material as the negative electrode active material.

3. A negative electrode current collector for a secondary battery according to claim 1 or 2, used in a jelly roll type electrode assembly.

4. 20~45kg / mm ２ A negative electrode current collector for a secondary battery according to claim 1 or 2, having the tensile strength of the specified value.

5. A negative electrode current collector for a secondary battery according to claim 1 or 2, having an elongation rate of 5% or more.

6. The negative electrode active material is Si, SiC and SiO ｚ The negative electrode current collector for a secondary battery according to claim 2, comprising one or more silicon materials (where 0.5 ≤ z ≤ 2.5).

7. The negative electrode current collector for a secondary battery according to claim 2, wherein the silicon material is contained in an amount of 1 to 40 parts by weight per 100 parts by weight of the negative electrode composite layer.

8. The negative electrode current collector for a secondary battery according to claim 2, wherein the negative electrode active material further comprises one or more carbon materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fibers.

9. A negative electrode current collector for a secondary battery according to claim 1 or 2, comprising one or more thin metal sheets selected from the group consisting of copper, aluminum, stainless steel, nickel, titanium, and calcined carbon.

10. The negative electrode current collector for a secondary battery according to claim 1 or 2, wherein the average thickness is 1 μm to 500 μm.

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