A negative electrode for a secondary battery, a method for manufacturing the same, and a secondary battery containing the same

Abstract

To provide a negative electrode for a secondary battery that can prevent cracks and peeling of a negative electrode active material layer when a negative electrode is cut, a manufacturing method of the negative electrode, and a secondary battery comprising the negative electrode.SOLUTION: The invention provides a negative electrode for a secondary battery in which a negative electrode active material layer is formed on at least one surface of a current collector, where the negative electrode for a secondary battery satisfies the condition 2, namely, the breaking stress is 3.6 N or more, where the breaking stress is a value measured by pressing the negative electrode active material layer with a linear tip having a width of 2.5 mm and a sharp end at a speed of 10 μm / s.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] [Cross-reference of related applications] This application claims priority under Korean Patent Application No. 10-2021-0112407 dated August 25, 2021, and all content disclosed in the said Korean Patent Application is incorporated herein as part of this specification.

[0002] This invention relates to a negative electrode for a secondary battery, a method for manufacturing the same, and a secondary battery containing the same. [Background technology]

[0003] Due to technological advancements and increasing demand for mobile devices, the demand for rechargeable batteries as an energy source has increased rapidly. Among these rechargeable batteries, lithium-ion batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0004] Furthermore, with the growing concern for environmental issues, much research is being conducted on electric vehicles (EVs) and hybrid electric vehicles (HEVs) as alternatives to vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution. As a power source for such electric vehicles (EVs) and hybrid electric vehicles (HEVs), lithium-ion batteries with high energy density, high discharge voltage, and output stability are mainly being researched and used.

[0005] These lithium secondary batteries are generally manufactured by stacking or winding the positive and negative electrodes with a separator membrane in between, and then incorporating them together with the electrolyte into a secondary battery case.

[0006] In this process, the negative electrode is manufactured by applying an active material slurry containing the negative electrode active material to a metal current collector, then drying and rolling it, and cutting it with a unit electrode or the like. However, depending on the physical properties of the negative electrode, there is a problem in that cracks and / or delamination of the negative electrode active material layer occur during the cutting process.

[0007] However, such defects in the negative electrode can drastically reduce battery performance during the later manufacturing of secondary batteries, posing a safety risk.

[0008] Therefore, the development of technology that can solve this problem is necessary. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a negative electrode for a secondary battery that can prevent cracking and detachment of the negative electrode active material layer during negative electrode cutting by manufacturing the negative electrode, a method for manufacturing the same, and a secondary battery containing the same. [Means for solving the problem]

[0010] A negative electrode for a secondary battery according to one embodiment of the present invention is A negative electrode for a secondary battery, wherein a negative electrode active material layer is formed on at least one surface of the current collector, The negative electrode satisfies at least one of the following conditions 1 and 2: [Condition 1] The continuous adhesive force in the thickness direction of the negative electrode for the secondary battery is 30 gf / 20 mm or more. [Condition 2] The fracture stress must be 3.6N or greater. The fracture stress is characterized by being measured by pressing the negative electrode active material layer at a speed of 10 μm / s with a sharp, single-ended tip having a width of 2.5 mm.

[0011] In this case, the continuous adhesive force under condition 1 is the adhesive force between active material layers per 10 μm in the thickness direction of the negative electrode.

[0012] Further, the negative electrode active material layer contains a negative electrode active material, a conductive material, and a binder. In order to satisfy the condition that the continuous adhesive force of the above-mentioned condition 1 is 30 gf / 20 mm or more, the content of the binder contained in each active material layer per 10 μm in the thickness direction of the negative electrode may be 2% by weight or more based on the total weight of each active material layer having a thickness of 10 μm.

[0013] Furthermore, when the negative electrode satisfies the condition 1, the porosity of the negative electrode may be 28% or less, and more specifically, may be 5% to 28%.

[0014] More specifically, the negative electrode may satisfy all of the condition 1 and the condition 2.

[0015] On the other hand, according to another embodiment of the present invention, the negative electrode has a porosity. A method for manufacturing the negative electrode for a secondary battery is as follows: (a) Applying a negative electrode active material slurry to at least one surface of a current collector; (b) Drying the negative electrode active material slurry to form a negative electrode active material layer; and (c) Rolling the negative electrode active material layer to manufacture a negative electrode for a secondary battery; including A method for manufacturing a negative electrode for a secondary battery is provided, which satisfies at least one of the following condition 1, condition 3, and condition 4, and the incompatible deformation of the following condition 3 or condition 4 is represented by the following formula 1: [Condition 1] The continuous adhesive force in the thickness direction of the negative electrode for the secondary battery is 30 gf / 20 mm or more. [Condition 3] The incompatible deformation (Misfit Strain) ε mf generated during drying in step (b) is 0.1% or less. [Condition 4] The incompatible deformation (Misfit Strain) ε mf generated during rolling in step (c) is 0.1% or less. [Formula 1]

[0016] [Number]

[0017] Here, the drying stress (σ) can be obtained by the following formula 2. [Formula 2]

[0018]

Number

[0019] In the formula 2 above, t s is the thickness of the current collector, t c is the thickness of the dried negative electrode active material layer, Es is the elastic modulus of the current collector, L is the length of the current collector in the direction parallel to the protruding direction of the tab, ν s is the Poisson's ratio of the current collector, and D is the degree of deflection of the current collector due to the drying.

[0020] The rolling stress (σ) can be the rolling load acting per unit area.

[0021] The electrode elastic modulus (E e ) of the negative electrode can be obtained by the following formula 3. [Formula 3]

[0022]

Number

[0023] In the formula 3 above, E tot is the overall elastic modulus of the current collector and the dried or rolled negative electrode active material layer, E f is the elastic modulus of the current collector, T f is the thickness of the current collector, and T e is the thickness of the dried or rolled negative electrode active material layer.

[0024] According to another embodiment of the present invention, the present invention also provides a secondary battery including a negative electrode for a secondary battery.

Brief Description of the Drawings

[0025] [Figure 1] This is a graph of the continuous adhesive strength of the negative electrode manufactured according to Comparative Example 1. [Figure 2] This is a graph showing the continuous adhesive strength of the negative electrode manufactured according to Example 1. [Figure 3] This is a graph showing the continuous adhesive strength of the negative electrode manufactured according to Example 2. [Figure 4] This is a graph showing the continuous adhesive strength of the negative electrode manufactured according to Example 3. [Figure 5] This is a micrograph of the negative electrode of Comparative Example 1, according to Experimental Example 5. [Figure 6] This is a micrograph of the negative electrode of Example 1 according to Experimental Example 5. [Figure 7] This is a micrograph of the negative electrode of Example 2 according to Experimental Example 5. [Figure 8] This is a micrograph of the negative electrode of Example 3 according to Experimental Example 5. [Modes for carrying out the invention]

[0026] Terms and words used herein and in the claims should not be interpreted in their usual or dictionary sense, but rather in a sense that is appropriate to the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention. Accordingly, the embodiments described herein and the configurations shown in the drawings are merely preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and there are various equivalents and modifications that can be used instead of these at the time of filing, and the scope of the present invention is not limited to the embodiments described below.

[0027] According to one embodiment of the present invention, A negative electrode for a secondary battery, wherein a negative electrode active material layer is formed on at least one surface of the current collector, The negative electrode satisfies at least one of the following conditions 1 and 2: [Condition 1] The continuous adhesive force in the thickness direction of the negative electrode for the secondary battery is 30 gf / 20 mm or more. [Condition 2] The fracture stress must be 3.6N or greater. The fracture stress is a value measured by pressing the negative electrode active material layer at a speed of 10 μm / s with a 2.5 mm wide, sharp-ended tip, and a negative electrode for a secondary battery is provided.

[0028] Specifically, the continuous adhesive strength in condition 1 refers to the adhesive strength between active material layers per 10 μm in the thickness direction of the negative electrode. That is, when measuring the adhesive strength between active material layers per 10 μm, if the adhesive strength is less than 30 gf / 20 mm in any section, it is considered that condition 1 is not met.

[0029] This continuous adhesive strength is similar to the method used to measure the adhesive strength of a manufactured negative electrode. Specifically, double-sided tape is applied to a glass slide, a 30mm x 125mm punched-out negative electrode is placed on top, and then a 20mm wide Scotch Magic Tape (registered trademark) is applied to the top surface of the negative electrode. Then, to ensure uniform adhesion between the negative electrode and the glass slide, and between the negative electrode and the Scotch Magic Tape (registered trademark), the slide is passed through a laminator at room temperature. After that, the force required to peel the Scotch Magic Tape (registered trademark) from the negative electrode is measured by pulling it at 100mm / min using a UTM (TA Corporation) instrument. At this time, the measurement angle between the glass slide and the negative electrode is 90°. Subsequently, after removing the peeled upper active material layer, the Scotch Magic Tape (registered trademark) is applied and the force required to peel it from the negative electrode is measured by pulling it at 100mm / min using a UTM (TA Corporation) instrument. The value measured is obtained by continuing to remove the peeled active material layer in this manner and performing an adhesive strength test.

[0030] If the adhesive strength is less than 30 gf / 20 mm in any of the measured values, it is determined that condition 1 is not met.

[0031] In other words, the inventors of this application confirmed that cracks or detachment of the negative electrode active material layer do not occur during cutting of the negative electrode when the above condition 1 is met.

[0032] There are various methods for satisfying this condition 1, and regardless of the method, if condition 1 is satisfied, cracks and delamination of the negative electrode active material layer will not occur. However, as one example, in order to satisfy condition 1, the negative electrode active material layer includes a negative electrode active material, a conductive material, and a binder, and the binder content in each active material layer per 10 μm in the thickness direction of the negative electrode may be 2% by weight or more based on the total weight of each active material layer with a thickness of 10 μm.

[0033] In other words, the active material layer must contain at least 2% by weight of binder per 10 μm thickness, which is equivalent to the binder being uniformly distributed at a concentration of at least 2% by weight everywhere. When the binder is contained at a concentration of at least 2% by weight in every section, the continuous adhesive strength can satisfy condition 1.

[0034] Furthermore, when the negative electrode satisfies condition 1, the porosity of the negative electrode may be 28% or less, more specifically 5% to 28%, and more specifically 10% to 25%.

[0035] The aforementioned porosity can be determined by measuring the negative electrode surface at 2,500x magnification using a scanning electron microscope (FE-SEM) (Hitachi S-4800 Scanning Electron Microscope), and then calculating the area ratio of surface voids observed in an arbitrarily sampled area (10 μm or more horizontally, 15 μm or more vertically) within the measured image, relative to the total area, and converting this to volume.

[0036] If the void ratio is excessively large, outside the aforementioned range, the adhesive strength of the negative electrode may decrease, which is undesirable.

[0037] On the other hand, even if condition 1 is not met, the inventors of this application have confirmed that, as explained above, if the fracture stress of the negative electrode under condition 2 is 3.6 N or more, cracks or delamination of the negative electrode active material layer will not occur.

[0038] More specifically, the fracture stress may be between 3.6N and 5N.

[0039] The fracture stress, as explained above, may be a value measured by pressing the negative electrode active material layer at a speed of 10 μm / s with a 2.5 mm wide, sharp-ended tip, or more specifically, a value measured by pressing vertically from above at a 90-degree angle to the negative electrode using a DHR (TA Corporation).

[0040] If the fracture stress satisfies the conditions according to the present invention, cracks or delamination of the negative electrode active material layer will not occur.

[0041] If the fracture stress is excessively small and falls outside the scope of the present invention, cracks or delamination of the negative electrode active material layer may occur, and if it is excessively large, the flexibility will be excessively reduced, which is undesirable. The aforementioned fracture stress can be controlled by adjusting the unsuitable deformation during drying and rolling in the manufacturing stage of the negative electrode, as described below.

[0042] Therefore, more specifically, the negative electrode can satisfy both condition 1 and condition 2.

[0043] On the other hand, according to the present invention or another embodiment, a method for manufacturing the negative electrode for a secondary battery, (a) A step of applying a negative electrode active material slurry to at least one surface of the current collector; (b) A step of drying the negative electrode active material slurry to form a negative electrode active material layer; and (c) A step of rolling the negative electrode active material layer to manufacture a negative electrode for a secondary battery; Includes, A method for manufacturing a negative electrode for a secondary battery is provided that satisfies at least one of the following conditions 1, 3, and 4, and the non-conforming deformation of condition 3 or 4 is represented by the following formula 1. [Condition 1] The continuous adhesive force in the thickness direction of the negative electrode for the secondary battery is 30 gf / 20 mm or more. [Condition 3] The misfit strain that occurs during drying in stage (b) must be 0.1% or less. [Condition 4] The misfit strain that occurs during rolling in stage (c) must be 0.1% or less. [Formula 1]

[0044]

number

[0045] As a result of diligent research by the inventors of this application, as explained above, it has been confirmed that in order for the fracture stress of the negative electrode for secondary batteries to have the aforementioned value, the unsuitable deformation that occurs during the manufacturing process must satisfy at least one of the above conditions 3 and 4.

[0046] Therefore, if the negative electrode is manufactured in such a way that conditions 3 and 4 are met, the effects of this application can be achieved.

[0047] If the above conditions are met, negative electrode cracking or detachment will not occur as an effect intended by the present invention.

[0048] Condition 1 is as explained above.

[0049] The deformations that do not conform to conditions 3 and 4 are determined by formula 1, and the method for determining the drying or rolling stress and the elastic modulus of the negative electrode is described below.

[0050] Specifically, the drying stress (σ) can be a value obtained by the following equation 2. [Formula 2]

[0051]

number

[0052] In the above equation 2, t s t is the thickness of the current collector. c The thickness of the dried negative electrode active material layer is E sν is the elastic modulus of the current collector, L is the length of the current collector in the direction parallel to the protruding direction of the tab, and s is the Poisson's ratio of the current collector, and D is the degree of deformation of the current collector due to drying.

[0053] Here, the thickness of the current collector and the negative electrode active material layer, and the length of the current collector can be determined by eye, and the elastic modulus and Poisson's ratio of the current collector represent the values ​​possessed by the metal making up the current collector, which are predetermined values. For example, the elastic modulus of Al is 7.19 × 10⁻⁶. 2 Therefore, Poisson's ratio can be 0.34, and the elastic modulus of Cu is 1.25 × 10⁻⁶. 3 The Poisson's ratio can be 0.34. Furthermore, the degree of deformation of the current collector can be measured using a laser and a position sensor to determine the degree of bending of the negative electrode. The degree of bending is measured at the height of the Z-axis when the negative electrode is bent downwards or upwards, with the dried negative electrode fitted into a flat holder and viewed from the side.

[0054] Furthermore, the rolling stress (σ) mentioned above differs from the drying stress and refers to the rolling load acting per unit area.

[0055] The rolling load is the rolling force applied to the negative electrode during rolling and can be selected by the operator.

[0056] Furthermore, the negative electrode elastic modulus (E e ) can be the value obtained by the following equation 3. [Formula 3]

[0057]

number

[0058] In the above formula 3, E tot The elastic modulus of the current collector and the dry negative electrode active material layer or the rolled negative electrode active material layer is E. f The elastic modulus of the current collector is T. f The thickness of the current collector and Te This is the thickness of the negative electrode active material layer after drying or after rolling.

[0059] The aforementioned E f The elastic modulus of the current collector, the thickness of the current collector, and the thickness of the negative electrode active material layer are as described above, E tot The overall elastic modulus was measured using DMA equipment (viscoelasticity measurement equipment).

[0060] Substituting the drying or rolling stress and the negative electrode modulus obtained in this way into Equation 1, if the condition that at least one of the non-conforming deformations is 0.1% or less is met, the fracture stress of the negative electrode becomes 3.6 N or more, and the effect intended by the present invention can be achieved.

[0061] Therefore, it is possible to determine whether the conditions of the present invention are met from the manufacturing stage, to quickly detect defects, and to prevent cracking and / or detachment of the negative electrode active material layer, thereby preventing a decrease in the performance and safety of the secondary battery, including the defect.

[0062] On the other hand, according to yet another embodiment of the present invention, the present invention also provides a secondary battery including the negative electrode for the secondary battery.

[0063] Since other manufacturing methods and components of the aforementioned secondary battery are known in the industry, further explanation is omitted in this specification and they are included within the scope of the present invention.

[0064] The present invention will be described in detail below based on preferred embodiments of the present invention with reference to examples, comparative examples, and the accompanying drawings.

[0065] <Comparative Example 1> (When the negative electrode continuous adhesive strength is 30 gf or less, and the drying / rolling misfit strain is 0.1% or more) A slurry for the active material layer was prepared by mixing a mixture of synthetic graphite as the active material, a binder (SBR and CMC mixed in a 2:1 weight ratio), and carbon black as a conductive material in a weight ratio of 96:2.5:1.5, with water as the dispersion medium, in a weight ratio of 1:2.

[0066] Using a slot die, the slurry for the active material layer was coated onto one surface of a copper (Cu) thin film, which was a negative electrode current collector with a thickness of 10 μm, and dried under vacuum at 130°C for 1 hour to form an active material layer. The active material layer thus formed was rolled using a roll pressing method to produce a negative electrode with an active material layer with a thickness of 80 μm.

[0067] The porosity of the manufactured negative electrode was 30%. The porosity was determined by measuring the negative electrode surface at 2,500x magnification using a scanning electron microscope (FE-SEM) (Hitachi S-4800 Scanning Electron Microscope), and then calculating the area ratio of surface voids observed in an arbitrarily sampled area (10 μm or more horizontally, 15 μm or more vertically) within the measured image, relative to the total area, and converting it to volume.

[0068] <Example 1> (When the negative electrode continuous adhesive strength is 30 gf or more, and the drying / rolling misfit strain is 0.1% or more) In Comparative Example 1, the anode was manufactured in the same manner as in Comparative Example 1, except that the weight ratio of active material:binder:conductive material was mixed at 96:2.8:1.2 and the rolling process was performed so that the active material layer had a thickness of 75 μm. The porosity of the manufactured anode was 25%.

[0069] <Example 2> (When the negative electrode continuous adhesion strength is 30 gf or less, the misfit strain is 0.1% or less, and the misfit strain is 0.1% or more) In Comparative Example 1, the anode was manufactured in the same manner as in Comparative Example 1, except that the slurry for the active material layer was dried under vacuum at 100°C for 30 minutes, then dried under vacuum at 110°C for 30 minutes, and then dried again under vacuum at 130°C for 30 minutes to form the active material layer. The porosity of the manufactured anode was 30%.

[0070] <Example 3> (When the negative electrode continuous adhesive strength is 30 gf or less, and the misfit strain during drying is 0.1% or more / the misfit strain during rolling is 0.1% or less) In Comparative Example 1, the anode was manufactured in the same manner as in Comparative Example 1, except that the active material layer was primary-rolled to a thickness of 90 μm, and then secondary-rolled again to a thickness of 80 μm. The porosity of the manufactured anode was 30%.

[0071] <Experimental Example 1> The continuous adhesive strength of the negative electrodes manufactured in Comparative Example 1 and Examples 1-3 was measured and is shown in Figures 1-4 below.

[0072] The continuous adhesive strength of the negative electrode is measured by applying double-sided tape to a glass slide, placing a 30mm x 125mm punched-out negative electrode on top, and then attaching a 20mm wide Scotch Magic Tape (registered trademark) to the top surface of the negative electrode. To ensure uniform adhesion between the negative electrode and the glass slide, and between the negative electrode and the Scotch Magic Tape (registered trademark), the slide is passed through a laminator (Supernex-synC325, 9 speed settings) at room temperature. The force required to peel the Scotch Magic Tape (registered trademark) from the negative electrode is then measured by pulling it at 100mm / min using a UTM (TA Corporation) instrument. At this time, the measurement angle between the glass slide and the negative electrode is 90°. Subsequently, after removing the peeled upper active material layer, the Scotch Magic Tape (registered trademark) is attached, and the force required to peel it from the negative electrode is measured again by pulling it at 100mm / min using a UTM (TA Corporation) instrument. The adhesive strength test is then performed by continuing to remove the peeled active material layer in this manner, and the measured value refers to the value obtained.

[0073] By examining Figures 1 to 4 below, it can be confirmed that the continuous negative electrode adhesive strength of Comparative Example 1, Examples 2 and 3 is 30 gf / 20 mm or less in some sections, while the continuous negative electrode adhesive strength of Example 1 is 30 gf / 20 mm or more in all sections.

[0074] <Experimental Example 2> The misfit strains of the negative electrodes produced in Comparative Example 1 and Examples 1-3 during the drying and rolling processes were calculated and are shown in Table 1 below.

[0075] [Table 1]

[0076] Referring to Table 1 above, it can be confirmed that Comparative Example 1 and Example 1 both had drying and rolling misfit strain of 0.1% or more, while Examples 2 and 3 had at least one of them at 0.1% or less.

[0077] The stress and elastic modulus are determined by equation 2, the rolling load, and equation 3, and the misfit strain is determined from equation 1 based on these values.

[0078] <Experimental Example 3> The fracture stresses of the negative electrodes manufactured in Comparative Example 1 and Examples 1-3 were measured and are shown in Table 2 below.

[0079] The fracture stress is measured using a DHR (TA Corporation) instrument, by pressing the negative electrode active material layer vertically from above at a 90-degree angle at a speed of 10 μm / s with a 2.5 mm wide, sharp-ended tip.

[0080] [Table 2]

[0081] When examining Table 2, and comparing it with Experimental Example 2, it can be confirmed that if at least one of the misfit strains in the drying or rolling process is 0.1% or less, the fracture stress will be 3.6 N or more.

[0082] <Experimental Example 4> The negative electrodes manufactured in Comparative Example 1 and Examples 1-3 were notched in half to examine for the presence or absence of cracks.

[0083] The presence or absence of cracks was checked by taking a microscopic photograph of the upper part of the negative electrode in a vertical direction and visually inspecting it, and the results are shown in Figures 5 to 8 below.

[0084] By examining Figures 5 to 8, we can confirm that cracks occurred only in Comparative Example 1, which did not satisfy either Condition 1 and Condition 2, or Condition 1, Condition 3, and Condition 4.

[0085] Therefore, it can be seen that the intended effect of the present invention can be obtained if any one of the above conditions 1 to 4 is met.

[0086] Anyone with ordinary skill in the art to which this invention belongs can make various applications and modifications within the scope of this invention based on the above. [Industrial applicability]

[0087] The negative electrode for secondary batteries according to the present invention satisfies specific conditions, so problems of cracking and detachment of the negative electrode active material layer do not occur during negative electrode cutting. Therefore, it has the effect of resolving problems of performance degradation or reduced safety in secondary batteries containing such negative electrodes.

Claims

1. A negative electrode for a secondary battery, wherein a negative electrode active material layer is formed on at least one surface of the current collector, The negative electrode for the secondary battery satisfies the following condition 2: [Condition 2] The fracture stress must be 3.6 N or more and 5 N or less. The fracture stress is measured by pressing the negative electrode active material layer at a speed of 10 μm / s with a 2.5 mm wide, single-ended tip. (Negative electrode for secondary battery)

2. A method for manufacturing a negative electrode for a secondary battery as described in claim 1, (a) A step of applying a negative electrode active material slurry to at least one surface of the current collector, (b) A step of drying the negative electrode active material slurry to form a negative electrode active material layer, and (c) A step of rolling the negative electrode active material layer to manufacture a negative electrode for a secondary battery, Includes, At least one of the following conditions 3 and 4 is satisfied, and the non-conforming deformation of either condition 3 or condition 4 is expressed by the following formula 1. [Condition 3] In the above step (b), the unsuitable deformation (ε) occurs during drying. ｍｆ ) is 0.1% or less. [Condition 4] In step (c) above, the unsuitable deformation (ε) that occurs during rolling ｍｆ ) is 0.1% or less. [Formula 1] [Math 1] And, The drying stress (σ) is calculated using the following equation 2: [Formula 2] [Math 2] In the above formula 2, t ｓ The thickness of the current collector is t. ｃ The thickness of the dried negative electrode active material layer is E ｓ ν is the elastic modulus of the current collector, L is the length of the current collector in the direction parallel to the protruding direction of the tab, and ｓ is the Poisson's ratio of the current collector, and D is the degree of deformation of the current collector due to drying. Rolling stress (σ) is the rolling load acting per unit area. Electrode elastic modulus (E ｅ ) can be calculated using the following formula 3: [Formula 3] [Math 3] In the formula 3, E ｔｏｔ is the elastic modulus of the entire current collector and the dried negative electrode active material layer or the rolled negative electrode active material layer, Ef is the elastic modulus of the current collector, T ｆ is the thickness of the current collector, and T ｅ is the thickness of the dried negative electrode active material layer or the rolled negative electrode active material layer, a method for manufacturing a negative electrode for a secondary battery.

3. A secondary battery comprising a negative electrode for a secondary battery as described in claim 1.

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