Negative electrode current collector and can-type secondary battery

Abstract

The negative electrode current collector according to the present invention has a thickness of 6 μm to 10 μm, and a work hardening exponent n according to the following formula 1 of 0.10 to 0.25. [Equation 1] σ = K × ε n In the above formula 1, σ is the true stress, K is the strength coefficient, ε is the true strain, and n is the work hardening exponent.

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Applications Nos. 10-2023-0028787, 10-2023-0044730, 10-2023-0052680, 10-2023-0058313, and 10-2024-0028937, filed with the Korean Intellectual Property Office on March 3, 2023, April 5, 2023, April 21, 2023, May 4, 2023, and February 28, 2024, respectively, the contents of which are incorporated herein by reference in their entireties.

[0002] The present invention relates to a negative electrode current collector and a can-type secondary battery manufactured using the same. [Background technology]

[0003] As technological development and demand for electric vehicles and energy storage systems (ESS) increases, the demand for batteries as energy sources is rapidly increasing, and research into batteries that can meet various needs is being conducted. In particular, research into lithium secondary batteries, which have high energy density and excellent life and cycle characteristics as power sources for such devices, is being actively conducted.

[0004] Generally, lithium secondary batteries are classified into can-type batteries, in which an electrode assembly is incorporated into a cylindrical or prismatic metal can, and pouch-type batteries, in which an electrode assembly is incorporated into a pouch-type case made of an aluminum laminate sheet, depending on the material of the battery case. The electrode assembly is a power generating element that can be charged and discharged and includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. Here, the negative electrode may have a structure in which a negative electrode current collector and a negative electrode active material layer are sequentially stacked, and the negative electrode current collector is typically made of copper foil.

[0005] However, due to their structural characteristics, can-type batteries experience stress concentration in the lateral direction. However, if a negative electrode current collector with a specific direction is designed without considering this directionality and used, there is a problem of reduced lifespan due to a short circuit of the negative electrode. Therefore, there is a need to design a negative electrode current collector with mechanical properties such as high elongation and high strength that are suitable for use in can-type batteries. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is intended to solve the above problems, and provides a negative electrode current collector having mechanical properties suitable for application to can-type secondary batteries, and a can-type secondary battery manufactured using the same. [Means for solving the problem]

[0007] In one aspect, the present invention provides a negative electrode current collector having a thickness of 6 μm to 10 μm and a work hardening exponent n according to the following formula 1 of 0.10 to 0.25. [Equation 1] σ = K × ε n In the above formula 1, σ is the true stress, K is the strength coefficient, ε is the true strain, and n is the work hardening exponent.

[0008] The negative electrode current collector has a dislocation density of 4×10 7 / mm 2 It can be more than that.

[0009] The negative electrode current collector has a yield strength of 31 kgf / mm 2 It can be more than that.

[0010] The negative electrode current collector may have an elastic modulus of 130 GPa to 140 GPa.

[0011] The negative electrode current collector may have an elongation of 13% or more.

[0012] The negative electrode current collector may include a copper thin film. The copper thin film may be an electrolytic copper foil, and the electrolytic copper foil may include a drum surface and an air surface facing the drum surface. The average size of the crystal grains included in the drum surface may be 0.50 μm or less. The average size of the crystal grains included in the air surface may be 0.68 μm or less. The average size of the crystal grains included in the drum surface may be smaller than the average size of the crystal grains included in the air surface.

[0013] The negative electrode current collector may have TC(200) and TC(220) defined by the following formula 2 of 2.20 or less.

number

[0014] The TC(111) defined by the formula 2 may be 2.20 or less. The ratio of the TC(111) to the TC(200) (TC(111) / TC(200)) may be 0.8 or more. The TC(311) defined by the formula 2 may be 2.20 or less.

[0015] The ratio of TC(200) to the sum of TC(111), TC(200), TC(220), and TC(311) defined by the formula 2 may be 40% or less, and the ratio of the sum of TC(220) and TC(311) to the sum of TC(111), TC(200), TC(220), and TC(311) may be 50% or more. The ratio of TC(111) to the sum of TC(111), TC(200), TC(220), and TC(311) defined by the formula 2 may be 20% or more.

[0016] In another aspect, the present invention provides a can-type secondary battery including an electrode assembly including a negative electrode, a separator, and a positive electrode stacked in order and wound in one direction, and a can-type case containing the electrode assembly, wherein the negative electrode includes the above-described negative electrode current collector. The can-type case may be cylindrical. The can-type secondary battery may be a cylindrical battery with a diameter of 15 mm or more. [Effects of the Invention]

[0017] The negative electrode current collector according to the present invention has a thickness of 6 μm to 10 μm and a work-hardening exponent n of 0.10 to 0.25, and therefore has a higher work-hardening capacity than negative electrode current collectors that do not satisfy these numerical ranges, thereby providing high processability and excellent mechanical properties suitable for application to can-type secondary batteries. Specifically, the negative electrode current collector according to the present invention can be stretched without short circuits or cracks even when deformed into a jelly-roll shape and inserted into a can-type case, and has high mechanical strength. [Brief explanation of the drawings]

[0018] The drawings attached to the specification illustrate preferred embodiments of the present invention and, together with the above-described content of the invention, serve to further understand the technical concept of the present invention, and the present invention should not be interpreted as being limited solely to the matters depicted in such drawings.

[0019] [Figure 1] 1 is a diagram showing a secondary battery according to an embodiment of the present invention; [Figure 2] 1A and 1B are diagrams illustrating the structure of a cap assembly according to one embodiment of the present invention. [Figure 3] 1 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Example 1, photographed at a magnification of 2000 times. [Figure 4] 1 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Example 2, photographed at a magnification of 2000 times. [Figure 5] 1 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Example 3, photographed at a magnification of 2000 times. [Figure 6] 1 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Comparative Example 3, photographed at a magnification of 2000 times. [Figure 7] 1 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Comparative Example 4, photographed at a magnification of 2000 times. DETAILED DESCRIPTION OF THE INVENTION

[0020] The advantages and features of the present invention, as well as methods for achieving them, will become clearer with reference to the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and can be embodied in various different forms. However, the embodiments are provided to fully disclose the present invention and to fully convey the scope of the invention to those skilled in the art to which the present invention pertains, and the present invention is defined by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

[0021] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense that can be commonly understood by a person having ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries should not be interpreted ideally or excessively unless they are clearly and specifically defined.

[0022] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular includes the plural unless otherwise stated in the text. As used in this specification, the words "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements in addition to the elements mentioned.

[0023] In this specification, when a part is said to include a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified to the contrary.

[0024] In this specification, the phrase "A and / or B" means A, or B, or A and B.

[0025] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0026] In this specification, the "strain hardening exponent n" means the gradient in a logarithmic diagram of true stress (σ)-true strain (ε), and is defined by the following formula 1.

[0027] [Equation 1] σ = K × ε n

[0028] In the above formula 1, σ is the true stress, K is the strength coefficient, ε is the true strain, and n is the work hardening exponent.

[0029] In this specification, the term "crystal grain" refers to a single crystal particle unit having a regular atomic arrangement.

[0030] In this specification, the term "texture index TC(hkl)" refers to the texture index of the (hkl) crystal plane of the negative electrode current collector, determined using an XRD graph obtained by X-ray diffraction analysis of the negative electrode current collector at 25°C, and is defined by the following formula 2:

[0031]

number

[0032] In Equation 2, I(hkl) is the peak intensity of the (hkl) crystal plane in the XRD graph obtained by X-ray diffraction analysis of the negative electrode current collector at 25°C, I0(hkl) is the peak intensity of the (hkl) crystal plane in the XRD graph of the reference sample, and I0(111)=100, I0(200)=46, I0(220)=20, and I0(311)=17.

[0033] <Negative electrode current collector> The negative electrode current collector according to the present invention has a thickness of 6 μm to 10 μm, and a work hardening exponent n according to the following formula 1 of 0.10 to 0.25.

[0034] [Equation 1] σ = K × ε n

[0035] In the above formula 1, σ is the true stress, K is the strength coefficient, ε is the true strain, and n is the work hardening exponent.

[0036] The negative electrode current collector of the present invention will be described in more detail below.

[0037] The thickness of the negative electrode current collector according to the present invention may be 6 μm to 10 μm, specifically 6 μm to 8 μm. When the thickness of the negative electrode current collector is within this range, the size of the crystal grains contained in the current collector is coarse compared to the thickness of the current collector, and dislocations can easily move and accumulate in the crystal grains. As a result, there is a problem that the negative electrode current collector used in a can-type secondary battery may break prematurely before it is sufficiently deformed.

[0038] Therefore, the present inventors have found that when the work hardening exponent n of the negative electrode current collector according to the above formula 1 satisfies 0.10 to 0.25, it is possible to ensure the strength and elongation of the negative electrode current collector suitable for application to can-type secondary batteries, and have completed the present invention.

[0039] The negative electrode current collector according to the present invention may have a work hardening exponent n, as determined by the following formula 1, of 0.10 to 0.25, specifically 0.10 to 0.20, and more specifically 0.12 to 0.16.

[0040] [Equation 1] σ = K × ε n

[0041] In Equation 1, σ is the true stress, K is the strength coefficient, ε is the true strain, and n is the work hardening index. Here, true stress refers to the value obtained by dividing the load applied to a material by the actual area of ​​the cross-sectional area on which the load acts. The true strain of ε refers to the value obtained by dividing the deformation amount of the material by the length after deformation. The work hardening index refers to the slope of a logarithmic true stress-true strain diagram. The work hardening index n can be determined from a stress-strain curve obtained by conducting a tensile test using an extensometer (manufacturer: ZwickRoell, product name: videoXtens biax 2-150 HP). Here, the extensometer can be a measuring device used to measure the elongation of the negative electrode current collector while a load is applied to the negative electrode current collector.

[0042] In the present invention, if the work-hardening exponent n of the negative electrode current collector is less than 0.10, the negative electrode current collector will not be hardened by processing, and sufficient strength will not be ensured. When applied to and used in can-type secondary batteries, the negative electrode current collector will not withstand the processing, resulting in problems such as cracking or short circuits even under the same load. In addition, in the present invention, if the work-hardening exponent n of the negative electrode current collector is greater than 0.25, the crystal grains will become ultrafine, resulting in insufficient elongation, and the negative electrode current collector will break under repeated loads when applied to can-type secondary batteries. The work-hardening exponent of the negative electrode current collector can be controlled by, for example, adjusting the type and content of additive elements, heat treatment conditions, etc.

[0043] The dislocation density of the negative electrode current collector is 4.0 × 10 7 / mm 2 That's it, 4.0 x 10 7 / mm 2~5.5×10 7 / mm 2 , 4.0×10 7 / mm 2 ~5.3×10 7 / mm 2 , or 4.0 × 10 7 / mm 2 ~4.5×10 7 / mm 2 Dislocation density refers to the total dislocation length per unit volume.

[0044] Here, the half width of each peak is measured in an XRD graph obtained by X-ray diffraction analysis of the negative electrode current collector, and the dislocation density can be calculated from the half width.

[0045] Specifically, an X-ray diffraction (XRD) graph of the negative electrode current collector is obtained by performing X-ray diffraction analysis at 25° C. Here, the X-ray diffraction analysis can be performed at 25° C. using an X-ray diffraction analyzer (Bruker AXS D4 Endeavor) under the following conditions:

[0046] -Source:Cu radiation(Kα1:Kα2=8:2) -2θ: 40°~91° - Step size: 0.0015° / s -total scan time: 168 min -Voltage: 40kV -Current: 40mA

[0047] Next, the half-width is determined from the peak of each crystal plane (hkl) from the obtained XRD graph.

[0048] Here, the full width at half maximum (FWHM) or FWHM refers to the difference between the two 2θ values ​​at half the maximum of each peak. Specifically, the FWHM is measured from the peak of the (111) crystal plane of the negative electrode current collector, which is observed in the measurement range of 2θ from 42° to 45°. The FWHM is measured from the peak of the (200) crystal plane of the negative electrode current collector, which is observed in the measurement range of 2θ from 49° to 52°. The FWHM is measured from the peak of the (220) crystal plane of the negative electrode current collector, which is observed in the measurement range of 2θ from 73° to 76°. The FWHM is measured from the peak of the (311) crystal plane of the negative electrode current collector, which is observed in the measurement range of 2θ from 89° to 91°.

[0049] Next, the dislocation density of the negative electrode current collector can be calculated from the half-width measured by the above-mentioned method.

[0050] Here, the dislocation density can be determined by known methods. For example, in the present invention, the dislocation density can be calculated by at least one of the following methods: the Scherrer method, the uniform deformation model (UDM), the uniform stress deformation model (USDM), the uniform deformation energy density model (UDEDM), Williamson-Hall analysis, or a model using the modified Warren-Abelbach equation and the modified Williamson-Hall equation, but is not limited to these. When the dislocation density of the negative electrode current collector satisfies the above numerical range, the negative electrode current collector has fine crystal grains, which facilitates dislocation movement and prevents dislocations from easily accumulating in the crystal grains, resulting in improved elongation and smooth deformation behavior.

[0051] In the present invention, the yield strength of the negative electrode current collector is 31 kgf / mm 2 Specifically, 31kgf / mm 2 ~32kgf / mm 2 , more specifically 31 kgf / mm 2 ~31.5kgf / mm 2Here, yield strength refers to the maximum stress that can be applied to a material without causing plastic deformation. The yield strength of the negative electrode current collector can be measured using an extensometer (manufacturer: ZwickRoell, product name: videoXtens biax 2-150 HP). If the yield strength of the negative electrode current collector satisfies the above numerical range, problems such as cracking or breakage of the negative electrode current collector can be prevented when the negative electrode current collector is applied to a can-type secondary battery where lateral stress is concentrated.

[0052] In the present invention, the elastic modulus of the negative electrode current collector may be 130 GPa to 140 GPa, specifically 130 GPa to 135 GPa, and more specifically 130 GPa to 133 GPa. Here, the elastic modulus refers to the gradient of the elastic section of a stress-strain curve obtained by conducting a tensile test. The elastic modulus of the negative electrode current collector may be measured using an extensometer (manufacturer: ZwickRoell, product name: videoXtens biax 2-150 HP). When the elastic modulus of the negative electrode current collector satisfies the above numerical range, sufficient work hardening ability is ensured, allowing the negative electrode current collector to withstand loads generated during processing, thereby providing the advantage of excellent durability.

[0053] In the present invention, the elongation of the negative electrode current collector may be 13% or more, specifically 13% to 18%, and more specifically 13% to 16%. Here, the elongation refers to the true strain of the negative electrode current collector. The elongation of the negative electrode current collector may be measured using an extensometer (manufacturer: ZwickRoell, product name: videoXtens biax 2-150 HP). When the elongation of the negative electrode current collector satisfies the above numerical range, the deformation behavior of the negative electrode current collector is smooth, and therefore, even when the negative electrode current collector is used in a can-type secondary battery, problems such as short circuits and cracks can be prevented.

[0054] Meanwhile, the texture index of a specific crystal plane of the negative electrode current collector in the present invention can further confirm the physical properties of the negative electrode current collector.

[0055] The texture index TC(hkl) of the negative electrode current collector according to the present invention means the texture index of the (hkl) crystal plane of the negative electrode current collector, determined using an XRD graph obtained by X-ray diffraction analysis of the negative electrode current collector at 25°C, and is defined by the following Equation 2:

[0056]

number

[0057] In the above formula 2, I(hkl) is the peak intensity of the (hkl) crystal plane in an XRD graph obtained by X-ray diffraction analysis of the negative electrode current collector at 25°C, I0(hkl) is the peak intensity of the (hkl) crystal plane in the XRD graph of the reference sample, I0(111) = 100, I0(200) = 46, I0(220) = 20, and I0(311) = 17.

[0058] Specifically, the texture index TC(hkl) of the negative electrode current collector is determined as follows.

[0059] First, X-ray diffraction (XRD) is performed at 25°C to obtain an XRD graph of the negative electrode current collector, and the texture indices for the (111) crystal plane, (200) crystal plane, (220) crystal plane, and (311) crystal plane of the negative electrode current collector can be calculated using Equation 2. Here, the X-ray diffraction analysis can be performed at 25°C using an X-ray diffraction analyzer (Bruker AXS D4 Endeavor) under the following conditions.

[0060] -Source:Cu radiation(Kα1:Kα2=8:2) -2θ: 40°~91° - Step size: 0.0015° / s -total scan time: 168 min -Voltage: 40kV -Current: 40mA

[0061] Next, the peak intensity I(hkl) of each crystal plane (hkl) is determined from the obtained XRD graph. Specifically, the peak intensity of the (111) crystal plane of the negative electrode current collector can be measured in the measurement range where 2θ is 42° to 45°. The peak intensity of the (200) crystal plane of the negative electrode current collector can be measured in the measurement range where 2θ is 49° to 52°. The peak intensity of the (220) crystal plane of the negative electrode current collector can be measured in the measurement range where 2θ is 73° to 76°. The peak intensity of the (311) crystal plane of the negative electrode current collector can be measured in the measurement range where 2θ is 89° to 91°.

[0062] Next, the peak intensity of the (hkl) crystal plane is determined in the XRD graph of the standard sample. For example, the XRD diffraction peak intensity I0(hkl) for each crystal plane of the standard powder defined by the ICDD (International Center for Diffraction Data) is determined.

[0063] Finally, the arithmetic mean value of I(hkl) / I0(hkl) for all crystal planes is calculated, and then the texture index TC(hkl) for a specific (hkl) plane can be calculated by dividing I(hkl) / I0(hkl) for that specific (hkl) plane by the arithmetic mean value.

[0064] The negative electrode current collector according to the present invention may have TC(200) and TC(220), as defined by Equation 2, of 2.20 or less. Specifically, the TC(200) and TC(220) may be 0.40 to 2.20, 0.50 to 1.80, or 0.80 to 1.80. By selecting a negative electrode current collector having TC(200) and TC(220) satisfying the above numerical ranges and manufacturing the negative electrode, stress concentration in a specific direction of the negative electrode current collector can be prevented. This can be applied when designing a can-type secondary battery to prevent negative electrode short circuits that may occur due to stress concentration in the lateral direction. A negative electrode current collector having TC(200) and / or TC(220) exceeding 2.20 may be unable to withstand processing and may cause short circuits when applied to can-type secondary batteries, which have a clear specific direction and experience stress concentration in the lateral direction.

[0065] The TC(111) and / or TC(311) of the negative electrode current collector, as well as the TC(200) and TC(220), may be 2.20 or less. Specifically, the TC(111) may be 0.80 to 1.80, and the TC(311) may be 0.40 to 2.20 or 0.50 to 1.80. When the texture indexes of all crystal planes of the negative electrode current collector are 2.20 or less, it can be confirmed that the negative electrode current collector does not experience stress concentration in a specific direction. In particular, when the TC(111) is less than 0.80, the negative electrode current collector may have high strength but not be suitable for use in can-type secondary batteries due to insufficient deformation.

[0066] The ratio of TC(111) to TC(200) of the negative electrode current collector (TC(111) / TC(200)) may be 0.8 or more, 0.9 or more, 1.0 or more, or 1.0 to 2.0. When the TC(111) / TC(200) ratio satisfies the above range, excellent mechanical properties suitable for application to can-type secondary batteries can be ensured.

[0067] Meanwhile, in the negative electrode current collector of the present invention, the ratio of TC(200) to the sum of TC(111), TC(200), TC(220), and TC(311) may be 40% or less, specifically less than 35%, more specifically less than 30%, or 25% to 30%. When the ratio of TC(200) to the sum of TC(111), TC(200), TC(220), and TC(311) satisfies this range, the negative electrode current collector can achieve mechanical properties that are durable when used in a can-type secondary battery where the specific direction of the negative electrode current collector is not clear and lateral stress is concentrated.

[0068] In the negative electrode current collector of the present invention, the ratio of the sum of TC(220) and TC(311) to the sum of TC(111), TC(200), TC(220), and TC(311) can be 50% or more, specifically 50% to 65%, more specifically 50% to 60%, or 53% to 60%. If the ratio of the sum of the texture indices of the (200) and (311) crystal planes to the sum of the texture indices of the (111), (200), (220), and (311) crystal planes is less than 50%, the Schmid factor decreases, resulting in an inconsistent mechanical deformation behavior of the negative electrode current collector and inability to optimize tensile strength and elongation. As a result, when the negative electrode current collector is applied to a can-type secondary battery where lateral stress is concentrated, it may not withstand the process, resulting in cracks or fracture of the negative electrode current collector.

[0069] In the negative electrode current collector of the present invention, the ratio of TC(111) to the sum of TC(111), TC(200), TC(220) and TC(311) can be 20% or more, specifically 20% to 30%, more specifically 22% to 30%.

[0070] Meanwhile, the negative electrode current collector of the present invention may be conductive and not cause chemical changes in the battery. For example, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy. Preferably, the negative electrode current collector of the present invention may include a copper thin film. In this case, the copper thin film may be an electrolytic copper foil. Specifically, the copper thin film may be an electrolytic copper foil manufactured by an electrolytic plating process. By manufacturing the copper thin film by an electrolytic plating process, the thickness of the negative electrode current collector can be reduced, thereby improving the energy density of the battery.

[0071] The negative electrode current collector can be a commercially available negative electrode current collector, or can be manufactured by a method known in the art, such as a method for manufacturing an electrolytic copper foil. Specifically, the method for manufacturing an electrolytic copper foil can be performed as follows: First, a reaction vessel is prepared, which includes a negative electrode rotating drum and a positive electrode plate facing the negative electrode rotating drum. The reaction vessel is filled with an electrolyte containing a mixture of copper sulfate and water. Next, the negative electrode rotating drum is rotated while applying electricity to the negative electrode rotating drum and the positive electrode plate, and copper is electrodeposited on the surface of the negative electrode rotating drum. The electrodeposited copper is then continuously extracted from the reaction vessel to obtain a copper thin film. The obtained copper thin film is rolled using a roll press process, and the rolled copper thin film is then slit and sheeted to produce a copper current collector.

[0072] On the other hand, in the electrolytic copper foil produced by the above-mentioned method, one side of the electrolytic copper foil that contacts the negative electrode rotating drum is called the drum side, and the other side facing the drum side is called the air side.

[0073] The average size of the crystal grains on the drum surface may be 0.50 μm or less, specifically 0.40 μm to 0.50 μm, and more specifically 0.45 μm to 0.50 μm. The average size of the crystal grains on the air surface may be 0.68 μm or less, specifically 0.60 μm to 0.68 μm, and more specifically 0.63 μm to 0.68 μm. The average size of the crystal grains refers to the average size of crystal grains clearly separated by high-angle grain boundaries, and can be measured by calculating the misorientation angle using EBSD. When the average size of the crystal grains contained on the drum surface or the air surface satisfies the above range, the number of crystal grains in the thickness direction of the electrodeposited copper foil is ensured, and the electrodeposited copper foil has a bimodal structure in microstructure. Therefore, accumulation of dislocations occurs only in coarse crystal grains, and dislocation movement is suppressed in fine crystal grains. As a result, high tensile strength and improved elongation are simultaneously ensured, and mechanical properties suitable for can-type secondary batteries can be obtained.

[0074] In the present invention, the average size of the crystal grains contained on the drum side may be smaller than the average size of the crystal grains contained on the air side, in which case the fine crystal grains contained on the drum side hinder dislocation movement and the coarse crystal grains contained on the air side accumulate dislocations, thereby facilitating plastic deformation of the electrodeposited copper foil and improving the elongation and strength of the electrodeposited copper foil.

[0075] The negative electrode current collector may have fine irregularities on its surface to enhance bonding strength with the negative electrode active material. For example, the negative electrode current collector may have various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, or a nonwoven fabric.

[0076] <Can-type secondary battery> Next, the can-type secondary battery according to the present invention will be described.

[0077] The can-type secondary battery of the present invention includes an electrode assembly and a can-type case containing the electrode assembly. The electrode assembly includes a negative electrode, a separator, and a positive electrode stacked in this order, and is wound in one direction. Here, the negative electrode includes the above-mentioned negative electrode current collector.

[0078] According to one embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. In this case, the negative electrode current collector is the negative electrode current collector according to the present invention.

[0079] According to another embodiment of the present invention, the negative electrode may not have a negative electrode active material layer formed on the negative electrode current collector. Specifically, the negative electrode may be the negative electrode current collector itself manufactured according to the present invention, or a specific metal may be physically bonded, rolled, or deposited on the negative electrode current collector. The specific metal may be deposited by electrochemical deposition or chemical vapor deposition (CVD). In this case, the specific metal bonded / rolled / deposited on the negative electrode current collector may include one metal or an alloy of two metals selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In).

[0080] The negative electrode active material layer may contain a negative electrode active material, and may further contain a conductive material, a binder, and the like, as needed.

[0081] The negative electrode active material may include at least one selected from the group consisting of lithium metal, a carbon material capable of reversibly intercalating / deintercalating lithium ions, a metal or an alloy of such a metal and lithium, a metal composite oxide, a material capable of doping and dedoping lithium, and a transition metal oxide.

[0082] As the carbon material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in a lithium ion secondary battery can be used without particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or both of these can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature fired carbon) or hard carbon, mesophase pitch carbide, fired coke, and the like.

[0083] As the metal or an alloy of these metals and lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn or an alloy of these metals and lithium can be used.

[0084] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1) and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) can be used.

[0085] As the substance capable of doping and undoping lithium, Si, SiO x(0 < x ≤ 2), Si - Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO₂, Sn - Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc. can be mentioned, and also, at least one of these can be mixed with SiO₂ and used. As the element Y, it can be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0086] Examples of the transition metal oxide include lithium - containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0087] The negative electrode active material can be contained in an amount of 60 wt% to 99 wt%, preferably 70 wt% to 99 wt%, more preferably 80 wt% to 98 wt% based on the total weight of the negative electrode active material layer.

[0088] The negative electrode conductive material is a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. Examples of such a conductive material include carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with highly developed crystal structures; conductive fibers such as carbon fibers and metal fibers; carbon fluoride powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0089] The negative electrode conductive material can be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0090] The negative electrode binder is a component that helps bind the negative electrode conductive material, negative electrode active material, and negative electrode current collector together. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0091] Typically, the negative electrode binder can be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0092] Meanwhile, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0093] The positive electrode current collector only needs to be conductive without causing chemical changes to the battery, and is not particularly limited. For example, as the current collector, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used.

[0094] The positive electrode current collector can have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesive force to the positive electrode active material layer. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0095] The positive electrode active material layer can contain a positive electrode active material, and can further contain a conductive material, a binder, etc. as necessary.

[0096] The positive electrode active material can be a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it can include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1O4 (where 0 < Z1 < 2), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r2, and s2 are the atomic fractions of the respective independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is one or more selected from Al, Mg, and Ti, X is one or more selected from F, S, and N, -0.5 ≦ a ≦ 0.5, 0 ≦ x ≦ 0.5, 0 ≦ b ≦ 0.1), etc., and any one or two or more of these compounds can be included.

[0097] Among them, in terms of being able to enhance the capacity characteristics and stability of the battery, the lithium metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 1 / 3 Mn 1 / 3 Co 1 / 3 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15)O2, and Li(Ni 0.8 Mn 0.1 Co 0.1 )O2), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2), or lithium nickel manganese cobalt aluminum oxide (e.g., Li(NI 0.86 Co 0.05 Mn 0.07 Al 0.02 )O2), lithium iron phosphate (e.g., LiFePO4), etc., and any one or a mixture of two or more of these may be used.

[0098] The positive electrode active material may be contained in an amount of 60% to 99% by weight, preferably 70% to 99% by weight, and more preferably 80% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0099] The positive electrode conductive material is a component for further improving the conductivity of the positive electrode active material. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, carbon powders such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powders such as natural graphite, artificial graphite, and graphite with highly developed crystal structures; conductive fibers such as carbon fiber and metal fiber; carbon fluoride powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0100] Typically, the positive electrode conductive material can be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0101] The positive electrode binder is a component that serves to bind the active material and conductive material together and to bind them to the current collector.

[0102] Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

[0103] Typically, the positive electrode binder can be contained in an amount of 1 to 20% by weight, preferably 1 to 15% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0104] On the other hand, the separator may be any separator that is normally used as a separator in a secondary battery, and is particularly preferably one that has low resistance to ion migration of the electrolyte and has excellent ability to retain moisture in the electrolyte solution.

[0105] For example, the separator may be a porous polymer film containing a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used as the separator.

[0106] The secondary battery according to an embodiment of the present invention may include an electrolyte. In this case, the electrolyte may be a non-aqueous electrolyte. The non-aqueous electrolyte may include an organic solvent and a lithium salt commonly used in the art, but is not particularly limited thereto.

[0107] The organic solvent may be any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent that can be used include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC).

[0108] Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0109] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be 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 is preferably contained in the electrolyte at a concentration of approximately 0.6 mol% to 2 mol%.

[0110] Meanwhile, the non-aqueous electrolyte according to the present invention may further contain an additive, although this is not essential, to further improve the physical properties of the secondary battery.

[0111] Examples of such additives include at least one selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, nitrile compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0112] The cyclic carbonate compound may be, for example, vinylene carbonate (VC) or vinyl ethylene carbonate (VEC).

[0113] The halogen-substituted carbonate compound may be, for example, fluoroethylene carbonate (FEC).

[0114] The nitrile compound may be, for example, succinonitrile, adiponitrile, hexanetricyanide, 1,4-dicyano-2-butene, or the like.

[0115] The sultone compound may be, for example, 1,3-propane sultone, 1,3-propene sultone, or the like.

[0116] The sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0117] The phosphate-based compound may be, for example, one or more compounds selected from the group consisting of lithium difluoro(bisoxalate)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0118] The borate-based compound may be, for example, tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), or the like.

[0119] The benzene-based compound may be, for example, fluorobenzene, the amine-based compound may be, for example, triethanolamine or ethylenediamine, and the silane-based compound may be, for example, tetravinylsilane.

[0120] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte solution, and may be one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bis(oxalatoborate) (LiB(C2O4)2)), and LiBF4.

[0121] Meanwhile, the additives may be used alone or in combination of two or more.

[0122] The total amount of the additives may be 1 wt % to 20 wt %, preferably 1 wt % to 15 wt %, based on the total weight of the electrolyte. When the additives are contained within this range, a stable coating is formed on the electrode, ignition during overcharge can be suppressed, and side reactions or residual or precipitated additives can be prevented during the initial activation process of the secondary battery.

[0123] The can-type secondary battery of the present invention can be fabricated by placing an electrode assembly formed by disposing a separator between a positive electrode and a negative electrode in a can-type case, injecting an electrolyte, and sealing the can-type case. Alternatively, the electrode assemblies can be stacked, impregnated with an electrolyte, and then placed in a can-type case and sealed.

[0124] The can-shaped case may be cylindrical or prismatic. The above-described electrode assembly may be incorporated into the can-shaped case. According to an embodiment of the present invention, the can-shaped secondary battery may be a cylindrical secondary battery. Cylindrical batteries have the advantages of high energy density per volume and ease of mass production.

[0125] Meanwhile, the can-type secondary battery according to the present invention may be a cylindrical battery having a form factor ratio (defined as the value obtained by dividing the diameter of a cylindrical battery by its height, i.e., the ratio of the diameter T to the height H) of 0.2 or more, 0.4, or 0.4 to 0.6. Here, the form factor refers to values ​​indicating the diameter and height of a cylindrical battery.

[0126] The can-type secondary battery according to the present invention can be a cylindrical battery with a diameter of 15 mm or more, 40 mm or more, or 45 mm or more. For example, the following can-type secondary batteries can be used: 1865 cells (diameter 18 mm, height 65 mm, form factor ratio 0.277), 2170 cells (diameter 21 mm, height 70 mm, form factor ratio 0.3), 46110 cells (diameter 46 mm, height 110 mm, form factor ratio 0.418), 48110 cells (diameter 48 mm, height 110 mm, form factor ratio 0.436), 4880 cells (diameter 48 mm, height 80 mm, form factor ratio 0.600), and 4680 cells (diameter 46 mm, height 80 mm, form factor ratio 0.575). In the form factor numbers, the first two digits indicate the cell diameter, and the following two or three digits indicate the cell height.

[0127] FIG. 1 is a diagram showing a secondary battery according to an embodiment of the present invention, and FIG. 2 is a diagram showing the structure of a cap assembly according to an embodiment of the present invention.

[0128] The can-shaped case 130 is a container for accommodating the electrode assembly 120 and the electrolyte, has an opening at the top, and may be made of a conductive metal material such as aluminum or steel. The can-shaped case 130 can accommodate the electrode assembly 120 and the electrolyte in its inner space through the opening at the top.

[0129] If necessary, the can-shaped case 130 may include a beading portion 60 and a crimping portion 70. The beading portion 60 may be formed by pressing the periphery of the outer periphery of the can-shaped case 130. The beading portion 60 prevents the electrode assembly 120 housed inside the can-shaped case 130 from being removed through the top opening of the can-shaped case 130 and may function as a support portion on which the cap assembly 140 is placed. The crimping portion 70 may be formed on the top of the beading portion 60 and may have an extended and bent shape to enclose a portion of the outer periphery and the top surface of the cap assembly 140 disposed on the beading portion 60.

[0130] Next, the cap assembly 140 is for sealing the top opening of the can-shaped case 130, and can include a top cap 10, a safety vent 20, and a CID filter 30, as shown in FIG.

[0131] The top cap 10 has a protruding positive terminal and an exhaust port (not shown) perforated therein. A safety vent 20 may be located at the bottom of the top cap 10. A portion of the upper surface of the CID filter 30 is connected to the safety vent 20, and a portion of the lower surface of the CID filter 30 may be connected to an electrode of the electrode assembly 120. When gas is generated from the electrode assembly 120 due to overcharging, high temperature, or other causes, increasing the withstand pressure, the safety vent 20 reverses its shape and protrudes upward to allow the gas to be exhausted. The CID filter 30 also moves upward, causing the area of ​​the notch T to break and interrupt the flow of current. This prevents further overcharging and battery explosion.

[0132] The cap assembly 140 may also include an insulating gasket 32 ​​that provides airtightness between the top cap 10 and the can-shaped case 130. The top cap 10 may be crimped onto a beading portion 60 formed on the can-shaped case 130 and fixed by a crimping portion 70. The top cap 10 is a component made of a conductive metal material and may cover an upper opening of the can-shaped case 130. The top cap 10 may be electrically connected to the positive electrode of the electrode assembly 120 and may be electrically insulated from the can-shaped case 130 via the gasket 32. Therefore, the top cap 10 may function as a positive terminal of the secondary battery. The top cap 10 may have a protrusion formed at its center that protrudes upward, and the protrusion may be in contact with an external power source to apply current from the external power source.

[0133] The secondary battery according to an embodiment of the present invention can be used not only as a battery cell used as a power source for a small device, but also as a unit battery in a medium- to large-sized battery module including a plurality of battery cells. Preferred examples of the medium- to large-sized device include an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and an energy storage system (ESS).

[0134] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for facilitating understanding of the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present description, and it goes without saying that such changes and modifications are within the scope of the appended claims.

[0135] [Experimental Example 1: Measurement of mechanical properties of negative electrode current collector] Commercially available electrolytic copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 with thicknesses of 4.5 μm, 6 μm, 8 μm, 10 μm, and 12 μm were prepared as negative electrode current collectors. The work hardening index, yield strength, elastic modulus, ultimate tensile strength, and elongation of the electrolytic copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 were measured. Here, the work hardening index, yield strength, elastic modulus, ultimate tensile strength, and elongation were measured using an extensometer (manufacturer: ZwickRoell, product name: videoXtens biax 2-150 HP) under the measurement conditions of ASTM D 882. The measurement results are shown in Table 1 below.

[0136] [Experimental Example 2: Calculation of dislocation density of negative electrode current collector] (1) XRD analysis of negative electrode current collector X-ray diffraction analysis (XRD) was performed on each of the electrodeposited copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 prepared in Experimental Example 1. Here, the X-ray diffraction analysis was performed at 25°C using an X-ray diffraction analyzer (Bruker AXS D4 Endeavor) under the following conditions.

[0137] -Source:Cu radiation(Kα1:Kα2=8:2) -2θ: 40°~91° - Step size: 0.0015° / s -total scan time: 168 min -Voltage: 40kV -Current: 40mA

[0138] (2) Calculation of dislocation density in the negative electrode current collector The electrodeposited copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 were subjected to X-ray diffraction analysis by the above-mentioned method, and the half-width of each peak was measured from the obtained XRD graph. The dislocation density of the negative electrode current collector was calculated by averaging the values ​​calculated by the UDM (Uniform Deformation Model), USDM (Uniform Stress Deformation Model), and UDEDM (Uniform Deformation Energy Density Model). The calculation results are shown in Table 1 below.

[0139] [Experimental Example 3: Observation of the microstructure of the negative electrode current collector] The microstructures of the electrodeposited copper foils of Examples 1 to 3 and Comparative Examples 3 and 4 prepared in Experimental Example 1 were observed and are illustrated in FIGS.

[0140] FIG. 3 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Example 1, photographed at a magnification of 2000 times.

[0141] FIG. 4 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Example 2, photographed at a magnification of 2000 times.

[0142] FIG. 5 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Example 3, photographed at a magnification of 2000 times.

[0143] FIG. 6 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Comparative Example 3, photographed at a magnification of 2000 times.

[0144] FIG. 7 is an EBSD Inverse Pole Figure (IPF) map of the air side of the electrodeposited copper foil of Comparative Example 4, photographed at a magnification of 2000 times.

[0145] Furthermore, the average grain size (unit: μm) on the air side and drum side of each of the electrodeposited copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 was measured from the IPF maps and is shown in the following Table 1. Here, the average grain size means the average size of crystal grains clearly separated by high-angle grain boundaries, and can be measured by a method of calculating the misorientation angle using EBSD.

[0146] [Experimental Example 4: Observation of the occurrence of cracks / short circuits in the negative electrode current collector in a can-type secondary battery] (1) Manufacturing of can-type secondary batteries LiCoO2, polyvinylidene fluoride (PVdF), carbon nanotubes (CNTs), and carbon black were added to N-methylpyrrolidone (NMP) solvent in a weight ratio of 97.59:1.18:0.24:0.09 and stirred to prepare a cathode slurry. The cathode slurry was applied to one side of a 10 μm-thick aluminum thin film at a concentration of 18.60 mg / cm. 2 The dried cathode slurry was rolled and dried in a vacuum oven at 130°C for 6 hours, and then punched to prepare a cathode.

[0147] Negative electrode slurry was applied to one side of each of the electrodeposited copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 prepared in Experimental Example 1, and then vacuum dried to prepare negative electrodes. Specifically, spherical artificial graphite, carbon black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were added to distilled water in a weight ratio of 97.35:0.5:1.15:1, and the mixture was stirred to prepare negative electrode slurry. The negative electrode slurry was applied to one side of the electrodeposited copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 in an amount of 10.48 mg / cm. 2 The dried negative electrode slurry was rolled and subjected to a primary heat treatment at 160°C for 3 hours in a vacuum oven, a secondary heat treatment at 50°C for 50 minutes, and a third heat treatment at 25°C for 15 minutes to prepare a negative electrode.

[0148] A separator was interposed between the negative electrode and the positive electrode to fabricate an electrode assembly, which was then placed inside a battery can and an electrolyte was injected into the can to fabricate a battery cell. The electrolyte was prepared by dissolving 1M LiPF6 in a mixed organic solvent of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) in a volume ratio of 1:1:1, and adding 5 wt% vinylene carbonate (VC).

[0149] (2) Observation of cracks / short circuits Next, the can-type secondary batteries manufactured using the electrolytic copper foils of Examples 1 to 3 and Comparative Examples 1 to 6 as negative electrode current collectors were subjected to 500 cycles of charging and discharging at 3.0 V to 4.25 V under conditions of 0.5 C / 1.0 C at 45° C., and the presence or absence of cracks / short circuits in the negative electrode was observed. The observation results are shown in Table 1 below.

[0150] -〇: Crack / short circuit occurs -×: No cracks / short circuits occur

[0151] [Table 1]

[0152] As shown in Table 1, in Examples 1 to 3, the negative electrode current collector has a thickness of 6 μm to 10 μm and a work hardening exponent n of 0.10 to 0.25. Therefore, it can be confirmed that the negative electrode current collector can be stretched without cracking / short circuiting even when it is deformed into a jelly roll shape and inserted into a can-shaped case due to its high work hardening ability.

[0153] [Experimental Example 5: Texture Index (TC) Analysis of Negative Electrode Current Collector] For each of the electrodeposited copper foils of Examples 1 to 3 and Comparative Examples 1 to 6, TC(111), TC(200), TC(220) and TC(311) defined by the following formula 2 were calculated from the XRD graph obtained by X-ray diffraction analysis according to Experimental Example 2. The results are shown in Table 2 below.

[0154]

number

[0155] In Equation 2, I(hkl) is the peak intensity of the (hkl) crystal plane in the XRD graph of the negative electrode current collector at 25°C, I0(hkl) is the peak intensity of the (hkl) crystal plane in the XRD graph of the reference sample, and I0(111) = 100, I0(200) = 46, I0(220) = 20, and I0(311) = 17.

[0156] [Table 2]

[0157] From the calculation results, the ratio (Relative Texture Coefficient) of TC(hkl) on each crystal plane to the sum of TC(111), TC(200), TC(220) and TC(311) was calculated and shown in Table 3 below.

[0158] [Table 3]

Claims

1. The thickness is 6 μm to 10 μm, A negative electrode current collector having a work hardening exponent n according to the following formula 1 of 0.10 to 0.25: [Expression 1] σ=K×ε ｎ In the above formula 1, σ is the true stress, K is the strength coefficient, ε is the true strain, and n is the work hardening exponent.

2. Dislocation density is 4×10 ７ / mm ２ The negative electrode current collector according to claim 1 .

3. Yield strength is 31 kgf / mm ２ The negative electrode current collector according to claim 1 .

4. 2. The negative electrode current collector according to claim 1, having an elastic modulus of 130 GPa to 140 GPa.

5. The negative electrode current collector according to claim 1 , which has an elongation of 13% or more.

6. The negative electrode current collector of claim 1 , wherein the negative electrode current collector comprises a copper thin film.

7. the copper thin film is an electrolytic copper foil, The negative electrode current collector according to claim 6 , wherein the electrolytic copper foil includes a drum surface and an air surface facing the drum surface.

8. The negative electrode current collector according to claim 7 , wherein the average size of the crystal grains contained in the drum surface is 0.50 μm or less.

9. The negative electrode current collector of claim 7 , wherein the average size of the crystal grains contained in the air surface is 0.68 μm or less.

10. The negative electrode current collector of claim 7 , wherein an average size of crystal grains contained in the drum surface is smaller than an average size of crystal grains contained in the air surface.

11. The negative electrode current collector according to claim 1, wherein TC(200) and TC(220) defined by the following formula 2 are 2.20 or less: [Equation 1] In the formula 2, I(hkl) represents the peak intensity of the (hkl) crystal plane in an XRD graph obtained by X-ray diffraction analysis of the negative electrode current collector at 25°C, I ０ (hkl) is the peak intensity of the (hkl) crystal plane in the XRD graph of the reference sample, I ０ (111)=100,I ０ (200)=46,I ０ (220)=20,I ０ (311) = 17.

12. The negative electrode current collector according to claim 11, wherein the negative electrode current collector has a TC(111) defined by the formula 2 of 2.20 or less.

13. 13. The negative electrode current collector according to claim 12, wherein the ratio of the TC(111) to the TC(200) (TC(111) / TC(200)) is 0.8 or more.

14. The negative electrode current collector according to claim 11, wherein the negative electrode current collector has a TC(311) defined by the formula 2 of 2.20 or less.

15. 12. The negative electrode current collector according to claim 11, wherein the ratio of TC(200) to the sum of TC(111), TC(200), TC(220), and TC(311) defined by Equation 2 is 40% or less, and the ratio of the sum of TC(220) and TC(311) to the sum of TC(111), TC(200), TC(220), and TC(311) is 50% or more.

16. 12. The negative electrode current collector according to claim 11, wherein the ratio of TC(111) to the sum of TC(111), TC(200), TC(220), and TC(311) defined by the formula 2 is 20% or more.

17. an electrode assembly including a negative electrode, a separator, and a positive electrode stacked in order and wound in one direction; a can-shaped case in which the electrode assembly is housed, A can-type secondary battery, wherein the negative electrode comprises the negative electrode current collector according to claim 1 .

18. 18. The can-type secondary battery according to claim 17, wherein the can-type case is cylindrical.

19. 18. The can-type secondary battery according to claim 17, wherein the can-type secondary battery is a cylindrical battery having a diameter of 15 mm or more.

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