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

Abstract

The present invention relates to a negative electrode for a secondary battery and a jelly-roll type electrode assembly comprising the same. The negative electrode satisfies a certain range of a creep rate condition represented by Formula 1 by having a negative electrode current collector, and when applied to a jelly-roll type electrode assembly, even though it contains a silicon-based negative electrode active material, since the stress generated from the outer edge portion is significantly low, it is possible to control the deformation and / or swelling of the electrode assembly, and since the stress accumulated in the negative electrode current collector is greatly reduced, the risk of internal disconnection of the electrode assembly is reduced, and thus excellent safety can be ensured.

Description

Technical Field

[0001] This 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 including the negative electrode.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0135030, filed on October 12, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Recently, secondary batteries have been widely used not only in small devices, such as handheld electronic devices, but also in medium and large devices, such as hybrid vehicles, electric vehicle battery packs, or energy storage devices.

[0004] Based on the shape of the battery casing, such secondary batteries are classified as cylindrical batteries or prismatic batteries that are contained in a cylindrical or square metal can, and pouch batteries that are contained in a pouch-shaped casing made of aluminum laminate.

[0005] Furthermore, the electrode assembly housed in the battery casing is a power generation element capable of charging and discharging, having a stacked structure of positive electrode / separator / negative electrode. It is classified into two types: a folded electrode assembly (jelly roll) obtained by inserting a separator between long, sheet-like positive and negative electrodes coated with active material and then winding them; and a stacked electrode assembly obtained by continuously stacking multiple positive and negative electrodes of predetermined size with separators inserted between them. Of these two types, the jelly roll type has the advantages of ease of manufacturing and high energy density per unit weight.

[0006] Figure 1 This is a schematic perspective view of a conventional jelly roll-type electrode assembly. (See reference) Figure 1 The jelly roll-shaped electrode assembly 100 includes a positive electrode plate 110, a negative electrode plate 120, and a diaphragm 130 inserted between the positive electrode plate 110 and the negative electrode plate 120, and the positive electrode plate 110, the diaphragm 130 and the negative electrode plate 120 are stacked in sequence to have a winding structure.

[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 tab 111 bonded to an uncoated portion of the positive electrode current collector where no positive electrode active material layer is 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 tab 121 bonded to an uncoated portion of the negative electrode current collector where no negative electrode active material layer is formed.

[0008] Additionally, the electrode assembly 100 includes a plurality of circular 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 circular portions 140, 140'.

[0009] Since the jelly roll-type electrode assembly 100 is formed by winding the positive electrode plate 110 and the negative electrode plate 120 using metal-based positive and negative current collectors, it may unfold due to the restoring force of the metal. Furthermore, the lithium secondary battery containing this electrode assembly may deform or expand during charging due to the stress difference between the circular portions 140, 140' and the flat portions 150, 150', especially due to the stress concentrated at the intersection of the circular portions 140, 140' and the flat portions 150, 150'.

[0010] In particular, when silicon-based active materials are used to increase the charge and discharge capacity of secondary batteries, the large volume change of silicon-based active materials during charge and discharge significantly increases the stress accumulated in the negative electrode plate 120, leading to a high risk of internal wire breakage.

[0011] Therefore, although methods have been proposed to introduce “winding and fixing tape” to wrap the outer periphery of the electrode assembly in the same direction as the winding direction of the electrode assembly, or to fix the outermost end with tape after winding, the methods of introducing winding and fixing tape or fixing the end with tape not only fail to adequately suppress the expansion of the electrode assembly that may occur during the charging and discharging of the lithium secondary battery or the deformation that may occur during charging and discharging due to the stress difference between the inner and outer edges, but also fail to prevent internal wire breakage of the negative electrode plate because the stress accumulated in the negative electrode plate is very high.

[0012] Therefore, there is a need to develop an electrode and / or electrode assembly that can suppress deformation and expansion of lithium secondary batteries, especially those containing silicon-based materials as negative active materials, during charge and discharge due to stress differences at the outer edge of the electrode assembly, and can prevent internal wire breakage.

[0013] [Patent Literature]

[0014] Korean Patent Publication No. 10-2016-0034028 Summary of the Invention

[0015] [Technical Issues]

[0016] Therefore, the present invention aims to provide a jelly roll type electrode assembly, wherein the electrode assembly has a large charge-discharge capacity by comprising a silicon-based negative electrode active material, can control the deformation and / or expansion of the electrode assembly by reducing the stress generated by the outer edge during the charge and discharge of the secondary battery, and improves the risk of internal wire breakage in the electrode assembly by significantly reducing the stress accumulated in the negative electrode plate.

[0017] [Technical Solution]

[0018] To solve the above problems,

[0019] One embodiment of the present invention provides a negative electrode for a secondary battery, the negative electrode comprising: a negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector; the negative electrode mixture layer comprising silicon material as a negative electrode active material, and when the creep rate of the negative electrode current collector is measured under tension conditions of 22±2°C and 300 MPa, the negative electrode current collector satisfies the following equation: falling between 20 μm / s and 50 μm / s.

[0020] [Formula 1]

[0021] C60-C2 / 58

[0022] In Equation 1,

[0023] C60 represents the change in length of the negative current collector 60 seconds after the tension is applied.

[0024] C2 represents the change in length of the negative current collector 2 seconds after the tension is applied.

[0025] Here, the tensile strength of the negative electrode current collector can be 20–45 kg / mm². 2 And the elongation rate is over 5%.

[0026] In addition, the negative electrode active material may include one or more silicon materials selected from the group consisting of Si, SiC and SiO2 (where 0.5≤z≤2.5).

[0027] Here, the content of the silicon material can be 1 to 40 parts by weight relative to 100 parts by weight of the negative electrode mixture layer.

[0028] In addition, the negative electrode active material may include one or more carbon materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black and carbon fiber.

[0029] In addition, the negative electrode current collector may include one or more 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.

[0030] In addition, one embodiment of the present invention provides a jelly roll-shaped electrode assembly, the electrode assembly comprising: a positive electrode; a negative electrode as described in the present invention; and a diaphragm inserted between the positive electrode and the negative electrode;

[0031] It also has a wound structure in which the positive electrode, the separator, and the negative electrode are stacked in sequence.

[0032] Furthermore, one embodiment of the present invention provides a cylindrical secondary battery comprising the above-described jelly roll-shaped electrode assembly.

[0033] [Beneficial Effects]

[0034] The negative electrode for secondary batteries according to the present invention has a negative electrode current collector that meets a specific range of creep rate conditions represented by Formula 1. Even if it contains silicon-based negative electrode active material, the deformation and / or expansion of the electrode assembly can be controlled due to the significantly low stress generated from the outer edge. Moreover, since the stress accumulated in the negative electrode current collector is significantly reduced, the risk of internal wire breakage of the electrode assembly is reduced, thus exhibiting excellent safety. Attached Figure Description

[0035] Figure 1 It is a perspective view schematically showing a conventional electrode assembly. Detailed Implementation

[0036] The present invention can have various modifications and implementations, therefore specific embodiments are shown in the accompanying drawings and described in detail in the description.

[0037] However, it should be understood that the present invention is not limited to the specific implementation, but includes all modifications, equivalents or substitutions within the spirit and technical scope of the present invention.

[0038] The terms “comprising,” “including,” and “having” as used herein indicate the presence of the features, figures, steps, actions, constituent elements, or components or combinations thereof described in the specification, and should be understood to exclude the possibility of the presence or addition of more than one other feature, figure, step, action, constituent element, component or combination thereof.

[0039] Furthermore, when a portion of a layer, film, region, or plate is disposed "on" other portions, this includes not only the case where a portion is disposed "directly" on other portions, but also the case where a third portion is interposed therebetween. Conversely, when a portion of a layer, film, region, or plate is disposed "below" other portions, this includes not only the case where a portion is disposed "directly" below other portions, but also the case where a third portion is interposed therebetween. Moreover, in this application, "on" can include not only the case where it is disposed on the upper part, but also the case where it is disposed on the lower part.

[0040] In this invention, "brittleness" refers to the phenomenon that a material is destroyed instead of undergoing plastic deformation when subjected to external force.

[0041] Furthermore, in this invention, "main component" refers to a component that comprises 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more relative to the total weight of the material being applied; in some cases, it may refer to 100% by weight of the material. For example, "silicon as the main component" means that it may contain particles of Si, SiO, and / or SiO2 comprising 80% by weight or more, 90% by weight or more, or 98% by weight of the total weight; in some cases, it may contain 100% by weight of the aforementioned component.

[0042] The present invention will now be described in further detail.

[0043] Secondary batteries use negative terminals

[0044] One embodiment of the present invention provides a negative electrode for a secondary battery, the negative electrode comprising: a negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector; the negative electrode mixture layer comprising silicon material as a negative electrode active material.

[0045] Furthermore, when the creep rate of the negative electrode current collector was measured under tension conditions of 22±2℃ and 300MPa, the negative electrode current collector satisfied the following equation, falling between 20μm / s and 50μm / s:

[0046] [Formula 1]

[0047] C60-C2 / 58

[0048] In Equation 1,

[0049] C60 represents the change in length of the negative current collector 60 seconds after the tension is applied.

[0050] C2 represents the change in length of the negative current collector 2 seconds after the tension is applied.

[0051] The negative electrode for secondary batteries according to the present invention is used in a jelly roll type electrode assembly and comprises a negative electrode mixture layer manufactured by coating, drying and pressing a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector.

[0052] Here, the negative current collector may include a metal sheet that satisfies the creep rate condition represented by Equation 1 within a specific range.

[0053] Equation 1 above represents the ratio between the length change (C2) of the negative electrode current collector 2 seconds after the tension is applied and the length change (C60) of the negative electrode current collector 60 seconds after the tension is applied, when the creep rate of the negative electrode current collector is measured by applying a tension of 300 MPa at room temperature. More specifically, "creep rate" is the degree of deformation of the negative electrode current collector over time, representing the rate of change of the length of the negative electrode current collector with time when a constant force is applied to the metal sheet at a specific temperature. The construction of the negative electrode current collector according to the present invention includes a negative electrode current collector having a creep rate at a specific time interval (60 seconds - 2 seconds = 58 seconds) represented by Equation 1, that is, a negative electrode current collector satisfying a specific deformation rate range at a specific time interval (58 seconds).

[0054] In one example, the negative current collector according to the present invention can satisfy the creep rate condition represented by Equation 1 within the range of 20 μm / s to 50 μm / s, specifically within the range of 20 μm / s to 45 μm / s; 20 μm / s to 40 μm / s; 20 μm / s to 30 μm / s; 25 μm / s to 40 μm / s; 35 μm / s to 45 μm / s; or 25 μm / s to 30 μm / s.

[0055] By controlling the creep rate of the negative electrode current collector within the aforementioned range, this invention prevents excessive volume increase of the electrode assembly due to a significantly low creep rate when using a jelly roll-type electrode assembly, and also prevents an increased risk of negative electrode current collector breakage due to excessive creep rate. On the other hand, since the creep rate can be affected by the measurement temperature, applied tension, composition of the negative electrode current collector, and grain size, even for the same negative electrode current collector, Equation 1 may yield different values ​​due to these factors.

[0056] In addition to the creep rate condition represented by Equation 1, the negative electrode current collector can also satisfy tensile strength and / or elongation within a specific range. Generally, metal fragments generated during the cutting process of electrode manufacturing may partially exist on the negative electrode current collector, which may cause poor OCV (open circuit voltage) in the battery process. To prevent the negative electrode current collector from becoming brittle, the negative electrode current collector of the present invention can control the tensile strength and / or elongation within a specific range.

[0057] In one example, the tensile strength of the negative current collector can be between 20 and 45 kg / mm². 2 Specifically, between 20 and 40 kg / mm 2 25~45kg / mm 2 25~40kg / mm 2 30~40kg / mm 2 Or 32~38kg / mm 2between.

[0058] In another example, the elongation of the negative current collector can be more than 5%, specifically between 5% and 18%, 5% and 15%, 8% and 13%, 9% and 12%, 10% and 15%, 11% and 15%, or 11% and 12%.

[0059] Furthermore, if the negative electrode current collector is used in the industry as an electrode current collector for secondary batteries, it can be used without any particular restrictions. For example, the negative electrode current collector can use copper, aluminum, stainless steel, nickel, titanium, and calcined carbon, which have high conductivity and do not cause chemical changes in the battery. In the case of aluminum or stainless steel, it can include metal sheets that have been surface-treated with carbon, nickel, titanium, silver, etc.

[0060] In addition, the thickness of the negative electrode current collector can be 1μm to 500μm, specifically between 1μm to 300μm, 1μm to 200μm, 1μm to 100μm, 1μm to 90μm, 1μm to 50μm, 10μm to 200μm, 50μm to 300μm, 80μm to 200μm, or 100μm to 180μm.

[0061] In addition, the negative electrode mixture layer includes a silicon material as the negative electrode active material. As a metallic component, the silicon material may include one or more silicon materials selected from the group consisting of Si, SiC, and SiO2 (where 0.5 ≤ z ≤ 2.5). Specifically, the silicon material may include pure silicon particles and / or silicon oxide particles.

[0062] In addition, the content of silicon material relative to 100 parts by weight of the negative electrode mixture layer can be 1 to 40 parts by weight. Specifically, the content of silicon material relative to 100 parts by weight of the negative electrode mixture layer can be 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.

[0063] Pure silicon (Si) exhibits a high theoretical capacity of 4020 mAh / g, and since silicon atoms can react with up to 4.4 lithium atoms, high charge-discharge capacity can be achieved in secondary batteries made from silicon-based materials. However, due to the large volume change of silicon materials during charge-discharge, considerable stress is applied to the outer edge of the jelly roll-type electrode assembly, leading to deformation and / or expansion of the electrode assembly. Furthermore, in cases with high silicon content, internal wire breakage due to damage to the negative electrode current collector may occur. However, the negative electrode for secondary batteries of the present invention has a negative electrode current collector that satisfies the creep rate condition represented by Formula 1 within a specific range. When applied to the negative electrode of a jelly roll-type electrode assembly, as the negative electrode active material of the secondary battery, even if it contains a considerable amount of silicon material, it can prevent electrode assembly deformation and / or expansion due to stress generated at the outer edge of the electrode assembly and prevent internal wire breakage.

[0064] In addition to silicon materials, the negative electrode mixture layer may further contain carbon materials as negative electrode active materials. Specifically, the negative electrode active material may further contain carbon materials whose main component is carbon atoms, such carbon materials may be selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black and carbon fibers.

[0065] In this case, the carbon material content relative to 100 parts by weight of the negative electrode mixture layer can be 60 to 99 parts by weight. Specifically, the carbon material content relative to 100 parts by weight of the negative electrode mixture layer can be 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 80 parts by weight; 65 to 75 parts by weight; 91 to 97 parts by weight; or 81 to 89 parts by weight.

[0066] The negative electrode according to the present invention, by having the above-described composition, not only achieves high charge and discharge capacity, but also, if used in a jelly roll-type electrode assembly, reduces the stress generated from the outer edge of the electrode assembly. This reduces the stress accumulated at the outer edge and effectively improves the safety of the secondary battery.

[0067] Jelly roll type electrode assembly

[0068] In addition, one embodiment of the present invention provides a jelly roll-shaped electrode assembly, the electrode assembly comprising: a positive electrode; a negative electrode according to the present invention; and a diaphragm inserted between the positive electrode and the negative electrode;

[0069] And has a wound structure in which the positive electrode, the separator, and the negative electrode are laminated in sequence. The jelly roll type electrode assembly according to the present invention includes a positive electrode, a negative electrode, and a separator, and is manufactured by winding them in a circular shape in a state where the positive electrode and the negative electrode are laminated on both sides of the separator. Here, including the negative electrode of the present invention as the negative electrode of the electrode assembly can greatly reduce the stress accumulated in the outer edge portion of the electrode assembly, particularly in the circular portion of the outer edge portion formed by winding.

[0070] Here, since the negative electrode contains components having the same functions and effects as the negative electrode for a secondary battery described above, detailed description thereof will be omitted.

[0071] On the other hand, the positive electrode provided in the jelly roll type electrode assembly according to the present invention is for the jelly roll type electrode assembly, and includes a positive electrode mixture layer manufactured by coating, drying, and pressing a positive electrode active material on a positive electrode current collector, and may selectively include a conductive material, a binder, and other additives as needed.

[0072] Although the positive electrode active material may include materials commonly applied to lithium secondary batteries, it may preferably include a composite lithium metal oxide containing three or more elements selected from the group consisting of nickel, cobalt, manganese, and aluminum; and in some cases, the composite lithium metal oxide may take the form of being doped with other transition metals (M 1 ). For example, the positive electrode active material may be a composite lithium metal oxide represented by the following Chemical Formula 1 that can be reversibly inserted and extracted:

[0073] [Chemical Formula 1]

[0074] Li x [Ni y Co z Mn w M 1 v O u

[0075] In Chemical Formula 1,

[0076] 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, and

[0077] x, y, z, w, v, and u are 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, respectively.

[0078] In one example, the positive electrode active material may comprise materials selected from 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 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 One or more compounds in the group consisting of O2.

[0079] Additionally, the positive electrode can be a material with high conductivity that does not cause chemical changes in the relevant battery as the positive electrode current collector. For example, copper, aluminum, stainless steel, nickel, titanium, and calcined carbon can be used, and in the case of aluminum or stainless steel, it can include metal sheets that have been surface-treated with carbon, nickel, titanium, silver, etc.

[0080] Furthermore, the positive electrode current collector has micro-uneven surfaces to increase the adhesion strength of the positive electrode active material, and it can take various forms, including films, sheets, foils, meshes, porous materials, foams, and non-woven fabrics. In addition, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the current collector can be appropriately applied in the range of 3–500 μm.

[0081] Furthermore, the diaphragm disposed in the jelly roll-type electrode assembly according to the present invention is an insulating membrane with high ion permeability and mechanical strength. Although there are no particular limitations as long as it is a material commonly used in the industry, it may specifically comprise one or more polymers selected from the group consisting of chemically resistant / hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymers. The diaphragm may take the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the aforementioned polymers, and in some cases, it may take the form of a composite membrane obtained by coating organic or inorganic substances onto a porous polymer substrate with an organic adhesive. Moreover, the average pore size of the diaphragm may be 0.01–10 μm, and the average thickness may be 5–300 μm.

[0082] Cylindrical secondary battery

[0083] Furthermore, one embodiment of the present invention provides a cylindrical secondary battery comprising the jelly roll-shaped electrode assembly of the present invention.

[0084] 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 is inserted into a cylindrical metal can serving as a battery casing and an electrolyte is injected. The cylindrical secondary battery according to the present invention is equipped with the jelly-roll-type electrode assembly of the present invention, which has significantly low stress at the outer edge of the electrode assembly and significantly low internal accumulated stress, thereby allowing for high battery capacity. Furthermore, even if it contains silicon-based negative electrode active material with a large rate of volume change during charge and discharge, internal wire breakage does not occur, providing an advantage of excellent safety.

[0085] Since the jelly roll-shaped electrode assembly has the same function and role as the jelly roll-shaped electrode assembly described above, detailed descriptions related to it will be omitted here.

[0086] Furthermore, the electrolyte is commonly used in the industry and can be used without any particular restrictions. Specifically, the electrolyte, as a lithium salt-containing electrolyte, can be composed of an electrolyte and a lithium salt, and can use non-aqueous organic solvents, organic solid electrolytes, and inorganic solid electrolytes as the electrolyte.

[0087] For example, the non-aqueous organic solvent may be an aprotic organic solvent, such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triethyl phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, ethyl propionate, etc.

[0088] The organic solid electrolyte may be, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate polymer, polylysine, a polyester sulfide, polyvinylidene fluoride, or a polymeric material containing ionically dissociable groups.

[0089] The inorganic solid electrolyte may be, for example, lithium nitrides, halides and sulfates, such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc.

[0090] The lithium salt, being a highly soluble substance in non-aqueous electrolytes, can be, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, or LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, lithium imino, etc.

[0091] In addition, to improve charge / discharge properties and non-flammability, electrolytes can be supplemented with substances such as pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds. Alzolidinediones, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, and aluminum trichloride. In some cases, halogenated solvents such as carbon tetrachloride and trifluoroethylene can be added to impart non-flammability. Furthermore, carbon dioxide gas, FEC (fluoroethylene carbonate), and PRS (propenesulfonyl lactone) can be added to improve high-temperature storage properties.

[0092] [Modes for Implementing the Invention]

[0093] Examples 1 and 2 and Comparative Examples 1 and 2. Manufacturing of negative electrodes for jelly roll-type electrode assemblies

[0094] The negative electrode slurry for lithium secondary batteries is manufactured as follows: The following materials are weighed and added, and mixed at 2,000 rpm for 60 minutes: 86 parts by weight of artificial graphite and 10 parts by weight of silicon particles as negative electrode active materials; 2 parts by weight of carbon black as conductive materials; and 2 parts by weight of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders. Furthermore, the negative electrode used in the jelly roll electrode assembly is manufactured as follows: A copper sheet having the properties shown in Table 1 is prepared, and the negative electrode slurry (average thickness: 10 μm) is coated on both sides of the prepared copper sheet, and the sheet is dried and calendered.

[0095] Here, the creep rate of the copper sheet is measured as follows: The copper sheet is cut into test pieces 150 mm long and 12.7 mm wide, fixed on a UTM measuring instrument, and a constant tension of 300 MPa is applied at 22°C to measure the change in length of the copper sheet over time. Then, the creep rate (μm / s) is calculated from the measurement results using Equation 1 below.

[0096] [Formula 1]

[0097] C60-C2 / 58

[0098] In Equation 1,

[0099] C60 represents the change in length of the negative current collector 60 seconds after the tension is applied.

[0100] C2 represents the change in length of the negative current collector 2 seconds after the tension is applied.

[0101] [Table 1]

[0102] <![CDATA[Tensile strength [kg / mm 2 > Elongation [%) Creep rate [μm / second] Example 1 34.2 11.8 27.1 Example 2 33.6 12.1 40.1 Comparative Example 1 36.3 11.3 6.53 Comparative Example 2 32.8 12.6 65.1

[0103] Examples 3 to 4 and Comparative Examples 3 to 4. Manufacturing of jelly roll type electrode assemblies

[0104] The positive electrode slurry for lithium secondary batteries is manufactured as follows: First, N-methylpyrrolidone is injected into a homogenizer, and the following materials (relative to 100 parts by weight of solid positive electrode slurry) are weighed and added, and mixed at 2,000 rpm for 60 minutes: 97.8 parts by weight of LiNi as the positive electrode active material. 0.6 Co 0.2 Mn 0.2 O2; 0.7 parts by weight of carbon black as a conductive material; and 1.5 parts by weight of PVdF as a binder. The prepared positive electrode slurry is coated on both sides of an aluminum sheet, and then the sheet is dried and rolled to manufacture the positive electrode.

[0105] The jelly roll-type electrode assembly is manufactured as follows: a porous polyethylene (PE) film (average thickness: 20 μm) is inserted between the manufactured positive electrode and the negative electrode manufactured in Examples 1 to 2 and Comparative Examples 1 to 2, and then wound up. Here, the negative electrodes used in the electrode assemblies manufactured in each example and comparative example are shown in Table 2 below.

[0106] [Table 2]

[0107] Type of negative electrode used Example 3 Negative electrode in Example 1 Example 4 Negative electrode in Example 2 Comparative Example 3 Negative electrode in Comparative Example 1 Comparative Example 4 Negative electrode in Comparative Example 2

[0108] Experimental Example

[0109] The following experiments were conducted to evaluate the performance of the negative electrode for a secondary battery according to the present invention, and the performance of a jelly roll-type electrode assembly including the negative electrode.

[0110] a) Evaluation of internal wire breakage

[0111] The evaluation focused on cylindrical secondary batteries manufactured by inserting the electrode assemblies produced in Examples 3 to 4 and Comparative Examples 3 to 4 into cylindrical containers and injecting electrolytes, and evaluated whether internal breaks occurred in the cylindrical secondary batteries.

[0112] Specifically, after each cylindrical secondary battery was charged and discharged 10 times in CC / CV mode, the secondary batteries were disassembled to check for internal breaks in the negative terminal. Here, charging was performed at 1C until 4.25V, and discharging was performed at a constant current of 1C until 2.5V. The results are shown in Table 3 below.

[0113] b) Evaluation of charge / discharge battery life

[0114] The charge-discharge battery life was evaluated using cylindrical secondary batteries manufactured by inserting the electrode assemblies produced in Examples 3 to 4 and Comparative Examples 3 to 4 into cylindrical containers and injecting electrolyte.

[0115] The battery was charged at a constant temperature of 45°C in 0.33C constant current (CC) mode until the voltage reached 4.2V. Then, it was discharged in 0.33C CC (CC) mode until the voltage reached 2.5V, and then discharged in CV (CV) mode until the current value reached 0.05% of the initial current value to check the discharge capacity of the first round.

[0116] Then, the same charge-discharge procedure was performed 200 times. The discharge capacity measured in the last round was divided by the discharge capacity measured in the first round to calculate the 0.33C charge-discharge capacity retention rate. The calculation results are shown in Table 3.

[0117] [Table 3]

[0118]

[0119] As shown in Table 3, the cylindrical secondary battery with the negative electrode of the embodiment satisfies the creep rate condition of Formula 1 within 20 to 50 μm / s, has an excellent charge and discharge capacity retention rate of over 97%, prevents deformation and / or expansion of the electrode assembly, and suppresses the occurrence of internal wire breaks.

[0120] On the other hand, the secondary battery of Comparative Example 3 has a negative electrode with a creep rate condition of less than 20 μm / s as specified in Formula 1. It has a high capacity retention rate, but it appears to cause deformation and / or expansion of the electrode assembly and internal wire breakage.

[0121] In addition, the secondary battery of Comparative Example 4 has a negative electrode with a creep rate condition greater than 50 μm / s according to Formula 1. Although no internal breakage occurred, wrinkles appeared between the mixture layer of the rolled negative electrode and the uncoated area, and the negative electrode was damaged during charging and discharging, which significantly reduced the capacity retention rate of the battery.

[0122] These results show that, by satisfying the creep rate condition expressed by Equation 1 within a specific range, the negative electrode for secondary batteries according to the present invention, when applied to a jelly roll-type electrode assembly, can significantly reduce the stress generated at the outer edge, even when containing silicon-based negative electrode active materials, and can also significantly reduce the stress accumulated in the negative electrode current collector.

[0123] As described above, the present invention has been described with reference to exemplary embodiments. However, those skilled in the art or those of ordinary skill in the art should understand that various changes and modifications can be made to the present invention without departing from the spirit and scope of the invention as described in the appended claims.

[0124] Therefore, the scope of the present invention is not limited to the contents described in the detailed description of the specification, but should be defined by the claims.

[0125] [Symbol Explanation]

[0126] 100: Electrode assembly

[0127] 110: Positive plate

[0128] 111: Positive electrode tab

[0129] 120: Negative electrode plate

[0130] 121: Negative electrode tab

[0131] 130: Diaphragm

[0132] 140 and 140': Circular part

[0133] 150 and 150': Flat section

Claims

1. A negative electrode for a secondary battery, the negative electrode comprising: A negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector; The negative electrode mixture layer comprises silicon material and one or more carbon materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber as the negative electrode active material, and When the creep rate of the negative electrode current collector was measured under tension conditions of 22±2℃ and 300 MPa, the negative electrode current collector satisfied the following equation, falling between 20 µm / s and 50 µm / s: [Formula 1] (C60-C2) / 58 In Equation 1, C60 represents the change in length of the negative current collector 60 seconds after the tension is applied. C2 represents the change in length of the negative electrode current collector 2 seconds after the tension is applied. The tensile strength of the negative electrode current collector is 20~40 kg / mm². 2 , The silicon material content is 1 to 40 parts by weight relative to 100 parts by weight of the negative electrode mixture layer. The creep rate of the negative electrode current collector was measured as follows: The negative electrode current collector was cut into test pieces 150 mm long and 12.7 mm wide. These test pieces were fixed on a UTM measuring instrument, and a constant tension of 300 MPa was applied at 22°C to measure the change in length of the negative electrode current collector over time. The creep rate, expressed in µm / s, was then calculated from this measurement result using Equation 1 above. The elongation of the negative current collector is 5% or more.

2. The negative electrode for a secondary battery according to claim 1, wherein the tensile strength of the negative electrode current collector is 20~38 kg / mm². 2 .

3. The negative electrode for a secondary battery according to claim 1, wherein the negative electrode active material comprises one or more silicon materials selected from the group consisting of Si, SiC and SiO2, wherein 0.5 ≤ z ≤ 2.

5.

4. The negative electrode for a secondary battery according to claim 1, wherein the negative electrode current collector comprises one or more metal sheets selected from the group consisting of copper, aluminum, stainless steel, nickel, titanium and calcined carbon.

5. The negative electrode for a secondary battery according to claim 1, wherein the average thickness of the negative electrode current collector is 1. m ~500 m.

6. A jelly roll-shaped electrode assembly, the electrode assembly comprising: Positive electrode; negative electrode according to claim 1; and a diaphragm inserted between the positive electrode and the negative electrode; and The positive electrode, the separator, and the negative electrode are stacked in sequence to form a wound structure.

7. A cylindrical secondary battery, the cylindrical secondary battery comprising the jelly roll-shaped electrode assembly according to claim 6.

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