Anode for secondary battery and manufacturing method therefor

Abstract

The present disclosure relates to an anode for a secondary battery, comprising: an anode current collector; a first anode mixture layer provided on the anode current collector; and a second anode mixture layer provided on the first anode mixture layer, wherein the first anode mixture layer includes a first anode active material, a first rubber-based binder, and a first cellulose derivative, and the second anode mixture layer includes a second anode active material, a second rubber-based binder, and a second cellulose derivative.

Description

Secondary battery negative electrode and method for manufacturing the same

[0001] The present disclosure relates to a negative electrode of a secondary battery and a method for manufacturing the same.

[0002] Unlike primary batteries, secondary batteries are rechargeable, and demand is gradually increasing due to their potential for miniaturization and high capacity. These secondary batteries are manufactured in the form of single battery cells packaged into a pack or packs of dozens of connected cells, and are widely used as power sources for mobile phones, laptops, and electric vehicle motors.

[0003] Lithium-ion batteries have a higher energy density, larger capacity per unit area, a lower self-discharge rate, and a longer lifespan than nickel-manganese or nickel-cadmium batteries. Additionally, they lack the memory effect, offering convenience of use and long lifespan characteristics.

[0004] A lithium secondary battery utilizes a positive electrode and a negative electrode made of active materials capable of lithium ion intercalation and deintercalation, and electrical energy is produced by oxidation and reduction reactions when lithium ions are intercalated or deintercalated from the positive and negative electrodes while the electrolyte is charged therein.

[0005] Various studies are being conducted to improve the electrical energy of these lithium secondary batteries.

[0006] One embodiment of the present disclosure can provide a secondary battery negative electrode with improved adhesion and ion conductivity and a method for manufacturing the same.

[0007] In addition, one embodiment of the present disclosure can provide a secondary battery negative electrode in the form of a dual layer in which the particle distribution of the upper and lower layers is uniformly controlled using a novel method, and a method for manufacturing the same.

[0008] Meanwhile, the present disclosure can be widely applied in the field of green technology, such as electric vehicles, battery charging stations, energy storage systems (ESS), and other photovoltaic and wind power generation that utilize batteries. In addition, the present disclosure can be used in eco-friendly mobility, including electric vehicles and hybrid vehicles, to prevent climate change by suppressing air pollution and greenhouse fluid emissions.

[0009] One embodiment of the present disclosure includes a negative electrode for a secondary battery and a method for manufacturing the same.

[0010] In one embodiment, the negative electrode for the secondary battery comprises a negative electrode current collector; a first negative electrode composite layer provided on the negative electrode current collector; and a second negative electrode composite layer provided on the first negative electrode composite layer; wherein the first negative electrode composite layer comprises a first negative electrode active material, a first rubber-based binder, and a first cellulose derivative, and the second negative electrode composite layer comprises a second negative electrode active material, a second rubber-based binder, and a second cellulose derivative, and the thermogravimetric analysis (TGA) result may satisfy the following equation 1.

[0011] (Relationship 1) TW2 / TW 1+2 ≤ 0.95

[0012] In the above relationship 1, TW 1+2is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ in the entire area of ​​the first and second cathode composite layers, and TW2 may be the average of the weight loss ratio of the second cathode composite layer in a temperature range of 300 ℃ to 500 ℃ in an area corresponding to 40% of the total depth of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer.

[0013] In one embodiment, in the above relationship 1, TW2 / TW 1+2 It can be 0.9 or less.

[0014] In one embodiment, the thermogravimetric analysis (TGA) result may further satisfy the following relationship 2.

[0015] (Equation 2) 0.85 ≤ TW 1+2

[0016] In the above relationship 2, TW 1+2 is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit may be %.

[0017] In one embodiment, the negative electrode for the secondary battery comprises a negative electrode current collector; a first negative electrode composite layer provided on the negative electrode current collector; and a second negative electrode composite layer provided on the first negative electrode composite layer; wherein the first negative electrode composite layer comprises a first negative electrode active material, a first rubber-based binder, and a first cellulose derivative, and the second negative electrode composite layer comprises a second negative electrode active material, a second rubber-based binder, and a second cellulose derivative, and the pyrolysis-gas chromatography (Py-GC) result may satisfy the following equation 3.

[0018] (Relationship 3) GW2 / GW 1+2 ≤ 0.99

[0019] In the above relationship 3, GW1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 may be a measured value in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers in the direction from the surface of the second cathode composite layer toward the first cathode composite layer, and GW2 and GW 1+2 may be the value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight.

[0020] In one embodiment, in the relationship 3 above, GW2 / GW 1+2 It can be 0.9 or less.

[0021] In one embodiment, the pyrolysis-gas chromatography (Py-GC) result may further satisfy the following relationship 4.

[0022] (Relationship 4) GW 1+2 ≥ 5,000,000

[0023] In the above Equation 4, GW 1+2 may be a measured value in the entire area of ​​the first and second cathode composite layers.

[0024] In one embodiment, the content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first cathode composite layer, and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second cathode composite layer may satisfy the following formulas 1 to 3.

[0025] (Equation 1) RB1 > RB2

[0026] (Equation 2) CD1 < CD2

[0027] (Equation 3) CD1 > RB2

[0028] In the above Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.

[0029] In one embodiment, the difference value (CD2-CD1) between the content of the first cellulose derivative (CD1) included in the first cathode composite layer and the content of the second cellulose derivative (CD2) included in the second cathode composite layer may be 0.2 wt% or more.

[0030] In one embodiment, the average composite density of the first cathode composite layer and the second cathode composite layer is 1.5 g / cc to 1.7 g / cc, and the content of the second rubber-based binder in the second cathode composite layer may be 0.2 wt% or more.

[0031] In one embodiment, the coating weight per unit area (Loading Weight, LW) for the entire first and second cathode composite layer may be 4 mg / cm² to 20 mg / cm².

[0032] In one embodiment, the content of the first rubber-based binder (RB1) included in the first cathode composite layer is 1.0 wt% to 2.4 wt%, the content of the second rubber-based binder (RB2) included in the second cathode composite layer is 0.2 wt% to 0.8 wt%, the content of the first cellulose derivative (CD1) included in the first cathode composite layer is 0.8 wt% to 1.4 wt%, and the content of the second cellulose derivative (CD2) included in the second cathode composite layer is 1.2 wt% to 1.8 wt%.

[0033] In one embodiment, the first and second rubber-based binders may each be one or more selected from the group consisting of a styrene-butadiene-based binder, an acrylated styrene-butadiene-based binder, an acrylonitrile-styrene-butadiene copolymer-based binder, a styrene-acrylate-based binder, and a styrene-butadiene-styrene-based binder.

[0034] In one embodiment, the first and second cellulose derivatives may each be one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethylcellulose (CMC-Li), sodium salt of carboxymethylcellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose.

[0035] In one embodiment, the average coating adhesion of the first and second cathode composite layers to the cathode current collector may be 0.29 N / 18 mm or more.

[0036] In one embodiment, the method for manufacturing a negative electrode for a secondary battery comprises: a slurry preparation step of preparing a first negative electrode slurry comprising a first solvent, a first conductive material, a first rubber-based binder, a first cellulose derivative, and a first negative electrode active material; a second negative electrode slurry comprising a second solvent, a second conductive material, a second rubber-based binder, a second cellulose derivative, and a second negative electrode active material; and a negative electrode composite layer provision step of coating the first negative electrode slurry and the second negative electrode slurry onto a negative electrode current collector, drying and rolling to sequentially provide a first negative electrode composite layer and a second negative electrode composite layer on the negative electrode current collector; and the thermogravimetric analysis (TGA) results may satisfy the following equation 1.

[0037] (Relationship 1) TW2 / TW 1+2 ≤ 0.95

[0038] In the above relationship 1, TW 1+2 is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ in the entire area of ​​the first and second cathode composite layers, and TW2 may be the average of the weight loss ratio of the second cathode composite layer in a temperature range of 300 ℃ to 500 ℃ in an area corresponding to 40% of the total depth of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer.

[0039] In one embodiment, in the above relationship 1, TW2 / TW 1+2 It can be 0.9 or less.

[0040] In one embodiment, the thermogravimetric analysis (TGA) result may further satisfy the following relationship 2.

[0041] (Equation 2) 0.85 ≤ TW 1+2

[0042] In the above relationship 2, TW 1+2 is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit may be %.

[0043] In one embodiment, the method for manufacturing a negative electrode for a secondary battery comprises: a slurry preparation step of preparing a first negative electrode slurry comprising a first solvent, a first conductive material, a first rubber-based binder, a first cellulose derivative, and a first negative electrode active material; a second negative electrode slurry comprising a second solvent, a second conductive material, a second rubber-based binder, a second cellulose derivative, and a second negative electrode active material; and a negative electrode composite layer provision step of coating the first negative electrode slurry and the second negative electrode slurry onto a negative electrode current collector, drying and rolling to sequentially provide a first negative electrode composite layer and a second negative electrode composite layer on the negative electrode current collector, wherein the pyrolysis-gas chromatography (Py-GC) result may satisfy the following equation 3.

[0044] (Relationship 3) GW2 / GW 1+2 ≤ 0.99

[0045] In the above relationship 3, GW 1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 may be a measured value in an area corresponding to 40% of the total depth of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer. Additionally, GW2 and GW 1+2 may be the value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight.

[0046] In one embodiment, in the relationship 3 above, GW2 / GW 1+2 It can be 0.9 or less.

[0047] In one embodiment, the pyrolysis-gas chromatography (Py-GC) result may further satisfy the following relationship 4.

[0048] (Relationship 4) GW 1+2 ≥ 5,000,000

[0049] In the above Equation 4, GW1+2 may be a measured value in the entire area of ​​the first and second cathode composite layers.

[0050] In one embodiment, the content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first cathode composite layer, and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second cathode composite layer may satisfy the following formulas 1 to 3.

[0051] (Equation 1) RB1 > RB2

[0052] (Equation 2) CD1 < CD2

[0053] (Equation 3) CD1 > RB2

[0054] In the above Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.

[0055] In one embodiment, the difference value (CD2-CD1) between the content of the second cellulose derivative (CD1) included in the first cathode composite layer and the content of the second cellulose derivative (CD2) included in the second cathode composite layer may be 0.2 wt% or more.

[0056] In one embodiment, the first and second cathode slurries each have a viscosity of 6,000 cP to 11,000 cP, and the difference in solid content between the first and second cathode slurries may be 4% or less.

[0057] In one embodiment, the first and second rubber-based binders may each be one or more selected from the group consisting of a styrene-butadiene-based binder, an acrylated styrene-butadiene-based binder, an acrylonitrile-styrene-butadiene copolymer-based binder, a styrene-acrylate-based binder, and a styrene-butadiene-styrene-based binder.

[0058] In one embodiment, the first and second cellulose derivatives may each be one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethylcellulose (CMC-Li), sodium salt of carboxymethylcellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose.

[0059] In one embodiment, in the step of providing the cathode composite layer, the first cathode slurry is coated on the cathode current collector, and the second cathode slurry is coated on the first cathode slurry, and then dried simultaneously to be manufactured.

[0060] In one embodiment, in the step of providing the cathode composite layer, the first cathode slurry can be coated on the cathode current collector and dried once, then the second cathode slurry is coated and dried twice.

[0061] In one embodiment, a secondary battery comprising the aforementioned negative electrode for a secondary battery is included.

[0062] According to one embodiment of the present disclosure, a secondary battery negative electrode with improved adhesion and ion conductivity and a method for manufacturing the same may be provided.

[0063] In addition, according to one embodiment of the present disclosure, a secondary battery negative electrode in the form of a dual layer in which the particle distribution of the upper and lower layers is uniformly controlled using a novel method and a method for manufacturing the same may be provided.

[0064] FIG. 1 is a drawing illustrating a negative electrode for a secondary battery according to one embodiment of the present disclosure.

[0065] Figure 2 is a schematic diagram showing the manufacturing process of a conventional negative electrode for a secondary battery.

[0066] FIG. 3 is a schematic diagram showing the manufacturing process of a negative electrode for a secondary battery according to one embodiment of the present disclosure.

[0067] FIG. 4 is a flowchart illustrating a method for manufacturing a negative electrode for a secondary battery according to one embodiment of the present disclosure.

[0068] Figure 5 is a diagram confirming the surface contact angle according to Manufacturing Example 1 and Manufacturing Example 2.

[0069] Figure 6 shows the results of EDS analysis after dyeing with OsO4 on the cross-section of the cathodic composite immediately after rolling in Example 1.

[0070] Figure 7 shows the results of EDS analysis after staining with OsO4 on the cross-section of the cathode composite from which the SEI layer was removed after performing the cycle of Example 1.

[0071] Figure 8 shows the results of EDS analysis after staining the cross-section of the cathodic composite with OsO4 following the performance of the cycle of Example 10.

[0072] Figure 9 shows the results of EDS analysis after staining the cross-section of the cathode mixture with OsO4 following the performance of the cycle of Comparative Example 5.

[0073] Figure 10 shows the results of analyzing the cross-section of the cathodic composite with EDS after staining with OsO4 following the cycle of Example 13.

[0074] Figure 11 shows the results of EDS analysis after staining the cross-section of the cathode mixture with OsO4 following the performance of the cycle of Comparative Example 6.

[0075] Hereinafter, the present disclosure will be described in detail (with reference to the attached drawings). However, this is merely illustrative and the present disclosure is not limited to the specific embodiments described illustratively.

[0076] In the present disclosure, expressions such as “have,” “may have,” “include,” or “may include” indicate the presence of such features (e.g., numerical values, functions, actions, or components such as parts) and do not exclude the presence of additional features.

[0077] Among the physical properties mentioned in this disclosure, if the measurement temperature affects the physical property, unless specifically otherwise specified, said physical property is the property measured at room temperature and atmospheric pressure.

[0078] The term "room temperature" as used herein refers to a natural temperature that is not heated or cooled, and may mean, for example, any temperature within the range of 10°C to 30°C, for example, about 15°C or higher, about 18°C ​​or higher, about 20°C or higher, about 23°C or higher, about 27°C or lower, or 25°C. Unless specifically defined in this disclosure, the unit of temperature is Celsius (°C).

[0079] Among the physical properties mentioned in this specification, if the measured pressure affects the physical property, unless specifically otherwise defined, the physical property is the property measured at atmospheric pressure. The term atmospheric pressure used in this disclosure refers to natural pressure that is not pressurized or depressurized, and typically refers to atmospheric pressure within the range of about 700 mmHg to 800 mmHg.

[0080] FIG. 1 is a drawing illustrating a negative electrode for a secondary battery according to one embodiment of the present disclosure.

[0081] Referring to FIG. 1, a negative electrode (100) for a secondary battery according to one embodiment of the present disclosure may include a negative electrode current collector (10); a first negative electrode composite layer (110) provided on the negative electrode current collector (10); and a second negative electrode composite layer (120) provided on the first negative electrode composite layer (110).

[0082] The first cathode composite layer (110) comprises a first cathode active material, a first rubber-based binder, and a first cellulose derivative, and the second cathode composite layer (120) may comprise a second cathode active material, a second rubber-based binder, and a second cellulose derivative. The content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first cathode composite layer (110), and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second cathode composite layer (120) may satisfy the following formulas 1 to 3.

[0083] (Equation 1) RB1 > RB2

[0084] (Equation 2) CD1 < CD2

[0085] (Equation 3) CD1 > RB2

[0086] (In Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.)

[0087] FIG. 2 is a schematic diagram showing the manufacturing process of a conventional negative electrode for a secondary battery. FIG. 3 is a schematic diagram showing the manufacturing process of a negative electrode for a secondary battery according to one embodiment of the present disclosure.

[0088] Referring to FIGS. 2 and 3, the difference between a conventional negative electrode for a secondary battery and a negative electrode for a secondary battery according to one embodiment of the present disclosure is explained.

[0089] Referring to FIG. 2, a conventional negative electrode for a secondary battery was manufactured by coating a negative electrode slurry onto a current collector such as copper foil (1). At this time, the negative electrode slurry was prepared by mixing an additive containing a negative electrode active material, a binder, etc., in a solvent. After coating the negative electrode slurry onto the current collector and drying it, the negative electrode for a secondary battery was manufactured by rolling the copper foil (1) in the form of a negative electrode composite (2, 3) coated thereon.

[0090] At this time, during the process of drying the cathode slurry, the particles in the cathode slurry move together with the evaporation of the solvent, resulting in an uneven particle size distribution, and in severe cases, problems such as the additive moving only to the upper side within the cathode mixture (2, 3) occurred.

[0091] In particular, when a cathode composite (2, 3) is provided using a cathode slurry having different compositions, divided into a lower layer (2) and an upper layer (3) on a copper foil (1), this problem is further exacerbated. Specifically, during the process of coating and drying the cathode slurry constituting the lower layer (2) and the upper layer (3), the solvent volatilizes, and migration of the binder from the lower layer (2) to the upper layer (3) occurs along with the solvent moving upward.

[0092] Due to the migration of this binder, the lower layer (2) of the cathode composite (2, 3) has reduced adhesion to the copper foil (1), resulting in reduced ion mobility, and problems such as the cathode composite (2, 3) easily detaching during the cycling process and the rapid deterioration of capacitance characteristics occurred.

[0093] On the other hand, referring to FIG. 3, a negative electrode for a secondary battery according to an embodiment of the present disclosure may include a first negative electrode composite layer (110) and a second negative electrode composite layer (120) sequentially provided on a negative electrode current collector (10). A negative electrode for a secondary battery according to an embodiment of the present disclosure may be manufactured by preparing a first negative electrode slurry constituting the first negative electrode composite layer (110) and a second negative electrode slurry constituting the second negative electrode composite layer (120), respectively, coating them on the negative electrode current collector (10), and then drying and rolling.

[0094] At this time, the first cathode composite layer (110) and the second cathode composite layer (120) may each include a first and second cathode active material, a first and second rubber-based binder, and a first and second cellulose derivative, and the first and second rubber-based binder and the first and second cellulose derivative provided in the first and second cathode composite layers (110, 120) may be included in a controlled amount.

[0095] In the negative electrode for a secondary battery according to the present disclosure, by including the first and second rubber-based binders and the first and second cellulose derivatives in controlled amounts, a difference in chemical and physical properties between the first and second negative electrode composite layers (110, 120) coated on the negative electrode current collector can be intentionally formed. Additionally, based on the difference in chemical and physical properties between the first and second negative electrode composite layers (110, 120), a difference in energy levels can occur, and as a result, migration of the first rubber-based binder from the lower layer to the upper layer can be effectively prevented.

[0096] Specifically, after coating the first cathode slurry and the second cathode slurry on the cathode current collector (10), the first rubber-based binder may move due to the solvent that evaporates during the drying process. At this time, the migration of the first rubber-based binder present in the lower layer can be prevented by the energy level difference between the upper and lower layers. As a result, in the cathode for a secondary battery according to the embodiment of the present disclosure, the first cathode composite layer (110) and the second cathode composite layer (120) provided on the cathode current collector (10) can be uniformly distributed with the initially designed composition without being affected by the solvent drying process.

[0097] In addition, the negative electrode for a secondary battery according to the embodiment of the present disclosure can effectively prevent migration from the lower layer to the upper layer of the first rubber-based binder, thereby preventing the non-conductiveness of the second negative electrode composite layer (120) and forming a predetermined pore to effectively improve the electrochemical characteristics of the secondary battery.

[0098] Hereinafter, a negative electrode for a secondary battery according to one embodiment of the present disclosure will be specifically described with reference to FIG. 1.

[0099] Referring to FIG. 1, the negative electrode (100) for a secondary battery of the present disclosure may include a first negative electrode composite layer (110) and a second negative electrode composite layer (120) sequentially provided on a negative electrode current collector (10). The first negative electrode composite layer (110) and the second negative electrode composite layer (120) may be formed by coating the first negative electrode slurry and the second negative electrode slurry, respectively, onto the negative electrode current collector (10), and then drying and / or rolling.

[0100] The content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first cathode composite layer (110), and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second cathode composite layer (120) may satisfy the following formulas 1 to 3.

[0101] (Equation 1) RB1 > RB2

[0102] (Equation 2) CD1 < CD2

[0103] (Equation 3) CD1 > RB2

[0104] The content of the first and second rubber-based binders (RB1, RB2) and the content of the first and second cellulose derivatives (CD1, CD2) respectively provided in the first cathode composite layer (110) and the second cathode composite layer (120) can be provided to satisfy the above-described formulas 1 to 3.

[0105] If the difference in energy levels between the first cathode composite layer (110) and the second cathode composite layer (120) is too small, migration of the first rubber-based binder from the lower layer to the upper layer occurs, and if the difference in energy levels between the first cathode composite layer (110) and the second cathode composite layer (120) is too large, the adhesive strength may be reduced due to the difference in physical properties at the interface between the first cathode composite layer (110) and the second cathode composite layer (120). The difference in energy levels can be confirmed by the contact angle of the surfaces of the first and second cathode composite layers (110, 120).

[0106] A negative electrode (100) for a secondary battery according to one embodiment of the present disclosure is provided in a dual-layer form consisting of a first and second negative electrode composite layer (110, 120) on a negative electrode current collector (10), and is provided to satisfy the ranges of Equations 1 to 3 described above, thereby effectively controlling the energy level to a predetermined range.

[0107] The difference value (CD2-CD1) between the content of the second cellulose derivative (CD2) included in the second cathode composite layer (120) and the content of the first cellulose derivative (CD1) included in the first cathode composite layer (110) may be 0.2 wt% or more.

[0108] By providing a difference value (CD2-CD1) of 0.2 wt% or more between the content (CD2) of the second cellulose derivative included in the second cathode composite layer (120) and the content (CD1) of the first cellulose derivative included in the first cathode composite layer (110), a difference in polarity between the first and second cathode composite layers (110, 120) is created, so that the interface between the first and second cathode composite layers (110, 120) can act as an obstacle to the migration of the first rubber-based binder.

[0109] Specifically, the difference value (CD2-CD1) between the content (CD2) of the second cellulose derivative included in the second cathode composite layer (120) and the content (CD1) of the first cellulose derivative included in the first cathode composite layer (110) may be 0.2 wt% to 2 wt%, or 0.2 wt% to 1.5 wt%, or 0.2 wt% to 1.2 wt%, or 0.2 wt% to 1 wt%, or 0.2 wt% to 0.8 wt%, or 0.2 wt% to 0.6 wt%.

[0110] The average composite density of the first cathode composite layer (110) and the second cathode composite layer (120) is 1.5 g / cc to 1.7 g / cc, and the content of the second rubber-based binder in the second cathode composite layer (120) may be 0.2% or more.

[0111] If the average composite density of the first and second cathode composite layers (110, 120) is less than 1.5 g / cc, the capacity per unit area decreases and becomes problematic, and if it exceeds 1.7 g / cc, the particle density increases and the mobility of ions may decrease.

[0112] In addition, if the content of the second rubber-based binder in the second cathode composite layer (120) is less than 0.2%, micro-cracks may occur during the process of performing the cycle of the secondary battery, and the lifespan characteristics may be degraded.

[0113] The negative electrode (100) for a secondary battery according to an embodiment of the present disclosure can improve the electrochemical characteristics of the secondary battery by controlling the average composite density of the first and second negative electrode composite layers (110, 120) to the aforementioned range, and at the same time controlling the content of the first and second rubber-based binders that can affect the composite density of the second negative electrode composite layer (120).

[0114] The loading weight (LW) per unit area for the entire first and second cathode composite layers (110, 120) may be 4 mg / cm² to 20 mg / cm². If the loading weight per unit area for the entire first and second cathode composite layers (110, 120) is less than 4 mg / cm², the effect according to the present disclosure is insufficient, and if it exceeds 20 mg / cm², cracks may occur during the process of performing the secondary battery cycle, which may cause problems.

[0115] Specifically, the coating weight per unit area for the entire first and second cathode composite layer may be 4 mg / cm² to 19 mg / cm², or 8 mg / cm² to 17 mg / cm², or 10 mg / cm² to 17 mg / cm², or 12 mg / cm² to 17 mg / cm², or 13.5 mg / cm² to 17 mg / cm².

[0116] The negative electrode (100) for a secondary battery of the present disclosure can be manufactured by coating first and second negative electrode slurries on a negative electrode current collector (10), and then drying and rolling. In this process, the first and second negative electrode slurries can be provided as the first negative electrode composite layer (110) and the second negative electrode composite layer (120) with a thickness reduced from the initial coated thickness.

[0117] By providing the first cathode composite layer (110) and the second cathode composite layer (120) within the aforementioned range, migration of the first rubber-based binder that may occur in the first cathode composite layer (110) can be effectively prevented, and the ion migration speed by the first and second cathode composite layers (110, 120) can be improved.

[0118] The content (RB1) of the first rubber-based binder included in the first cathode composite layer (110) may be 1.0 wt% to 2.4 wt%, and the content (RB2) of the second rubber-based binder included in the second cathode composite layer (120) may be 0.2 wt% to 0.8 wt%. Additionally, the content (CD1) of the first cellulose derivative included in the first cathode composite layer (110) may be 0.8 wt% to 1.4 wt%, and the content (CD2) of the second cellulose derivative included in the second cathode composite layer (120) may be 1.2 wt% to 1.8 wt%.

[0119] If the content (RB1) of the first rubber-based binder included in the first cathode composite layer (110) is less than 1.0 wt%, the adhesion to the cathode current collector (10) is reduced and becomes a problem, and if it exceeds 2.4 wt%, the electrochemical properties of the secondary battery may be reduced due to the excessively high adhesion in the first cathode composite layer (110).

[0120] In addition, if the content (RB1) of the second rubber-based binder included in the second cathode composite layer (120) is less than 0.2 wt%, processability may be reduced and micro-cracks may be formed on the surface, which may reduce cycle characteristics, and if it is more than 0.8 wt%, the tortuosity of the second cathode composite layer (120) may increase, which may reduce the mobility of lithium ions.

[0121] If the content (CD1) of the first cellulose derivative included in the first cathode composite layer (110) is less than 0.8 wt%, the dispersion stabilization of the first cathode composite layer (110) is reduced and becomes problematic, and if it exceeds 1.4 wt%, the cathode for the secondary battery in the first cathode composite layer (110) may have brittle characteristics and microcracks may occur.

[0122] Additionally, if the content (CD2) of the second cellulose derivative included in the second cathode composite layer (120) is less than 1.2 wt%, it is difficult to control the difference in energy levels between the first cathode composite layer (110) and the second cathode composite layer (120), and if it exceeds 1.8 wt%, the mobility of lithium ions may be reduced. The cathode may have brittle characteristics, and microcracks may occur.

[0123] Additionally, when the coating weight per unit area for the entire first and second cathode composite layers (110, 120) is 13.5 mg / cm², the minimum value of the content (RB2) of the second rubber-based binder included in the second cathode composite layer (120) is 0.4 wt%, and when the coating weight per unit area for the entire first and second cathode composite layers (110, 120) is 15 mg / cm², the minimum value of the content (RB2) of the second rubber-based binder included in the second cathode composite layer (120) is approximately 0.6 wt%, and when the coating weight per unit area for the entire first and second cathode composite layers (110, 120) is 17 mg / cm², the minimum value of the content (RB2) of the second rubber-based binder included in the second cathode composite layer (120) is approximately It can be 0.8 wt%.

[0124] In a negative electrode (100) for a secondary battery according to an embodiment of the present disclosure, by controlling the coating weight per unit area for the entire first and second negative electrode composite layers (110, 120) and the content (RB2) of the second rubber-based binder included in the second negative electrode composite layer (120) to be within the aforementioned range, migration of the first rubber-based binder in the first negative electrode composite layer (110) can be effectively prevented and at the same time, the electrochemical and cycle characteristics of the secondary battery can be effectively improved.

[0125] In the negative electrode (100) for a secondary battery according to the present disclosure, the average adhesion strength of the first and second negative electrode composite layers (110, 120) to the negative electrode current collector (10) may be 0.29 N / 18 mm or more.

[0126] In addition, in a secondary battery using the negative electrode (100) for the secondary battery, when the secondary battery is discharged at 1C for 10 seconds at an SOC of 50%, the DC-IR may be 1.24 Ω or less. The negative electrode (100) for the secondary battery according to the embodiment of the present disclosure may exhibit an average adhesion strength within the aforementioned range and may exhibit low resistance in the secondary battery.

[0127] The first and second rubber-based binders may be the same or different. Additionally, the first and second cellulose derivatives may be the same or different.

[0128] Specifically, the first and second rubber-based binders may each be one or more selected from the group consisting of a styrene-butadiene-based binder, an acrylated styrene-butadiene-based binder, an acrylonitrile-styrene-butadiene binder, a styrene-acrylate-based binder, and a styrene-butadiene-styrene-based binder.

[0129] In addition, the first and second cellulose derivatives may each be one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethylcellulose (CMC-Li), sodium salt of carboxymethylcellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose.

[0130] In the negative electrode (100) for a secondary battery according to an embodiment of the present disclosure, the FWHM (Full Width at Half Maximum) of the Gaussian curve for the Os atomic ratio distribution analyzed by EDS (Energy Dispersive Spectroscopy) after dyeing the cross-sections of the first and second negative electrode composite layers (110, 120) with OsO4 may be 1 μm to 55 μm. Additionally, the average value according to the Gaussian curve may exist in an area of ​​40% or less in the direction from the surface of the negative current collector toward the surface of the second negative electrode composite layer with respect to 100% of the total thickness of the first and second negative electrode composite layers.

[0131] The above negative electrode (100) for the secondary battery can be assembled into a secondary battery using a positive electrode and an electrolyte, etc. The above EDS can be verified by using the negative electrode (100) for the secondary battery in a discharged state after performing CC-CV charge-discharge cycles of the secondary battery at 0.5C / 4.2V and 0.5C / 2.5V 10 to 20 times. The method of the above CC-CV charge-discharge cycle can be performed at 0.5C / 4.4V and 0.5C / 2.5V and can be varied in various ways depending on the type of positive electrode active material, but is not limited thereto.

[0132] Specifically, the negative electrode (100) for a secondary battery in the discharged state can be cut to a predetermined size and prepared as a sample for analyzing the EDS through pretreatment, OsO4 (osmium tetraoxide) impregnation, and drying.

[0133] The above pretreatment can be performed by immersing a negative electrode (100) for a secondary battery, cut to a predetermined size, in a pretreatment solvent and then drying it in a vacuum oven for 6 to 30 hours to remove the electrolyte, lithium salt, SEI film, etc. remaining on the negative electrode (100) for the secondary battery. In addition, after the above pretreatment is completed, the removal of the electrolyte, lithium salt, SEI film, etc. can be confirmed by extracting the above pretreatment solvent and performing NMR analysis. For example, this can be confirmed by the presence or absence of the LiPF6 peak in the above NMR analysis. In addition, the completion of the above pretreatment can be verified by confirming the Li-F and PO peaks through XPS analysis of the pretreated electrode.

[0134] Conditions such as the pretreatment solvent, temperature, and time for removing the above electrolyte, lithium salt, SEI film, etc., can be controlled in various ways. The above pretreatment solvent may be one or more selected from the group consisting of DMC, acetone, ethanol, and deionized water.

[0135] Next, the negative electrode (100) for a secondary battery with the above-mentioned pretreatment completed is OsO4 Impregnation can be performed. The negative electrode for the secondary battery is OsO4 The first and second rubber-based binders contained in the lower layer, the first cathode active material layer (110), and the upper layer, the second cathode active material layer (120), respectively, can be dyed by impregnation.

[0136] The above OsO4 Impregnation can be performed for 12 to 36 hours and then dried. The OsO4 The negative electrode (100) for a secondary battery dyed by impregnation can be manufactured into a sample that is a cross-section of the dyed negative electrode using argon ion milling, etc.

[0137] The above sample can be analyzed using an energy dispersive X-ray spectroscopy (EDS, Flatquad) detector of a scanning electron microscope (SEM) instrument, and the constituent components included in each of the one side and the other side of the sample can be identified by EDS mapping.

[0138] From the results of the above EDS mapping, a line profile can be extracted in the thickness direction of the negative electrode (100) for the secondary battery, which is in the direction from the upper layer, the second negative electrode composite layer (120), to the lower layer, the first negative electrode composite layer (110).

[0139] The above-mentioned negative electrode (100) for a secondary battery is manufactured as a sample, and the Os intensity, which is the Os-Mαβ value according to the thickness of the double-sided negative electrode (100) obtained using the sample, is plotted. Then, by fitting based on the surface of the central negative electrode current collector (10), a Gaussian curve for the distribution of Os atoms is obtained for the cross-section of the negative electrode (100) for a secondary battery, and the FWHM can be calculated using this. The FWHM may be the average of values ​​obtained by repeating the process five or more times.

[0140] The above sample may have a first cathode composite layer (110) and a second cathode composite layer (120) respectively provided on one side and the other side centered on the cathode current collector (10), and the Gaussian curve may be a FWHM formed by the first cathode composite layer (110) and the second cathode composite layer (120) provided on one side of the cathode current collector (10) or the first cathode composite layer (110) and the second cathode composite layer (120) provided on the other side of the cathode current collector (10). That is, the Gaussian curve may be the FWHM of the first cathode composite layer (110) and the second cathode composite layer (120) provided on one side of the cathode current collector (10) of the sample, which are randomly selected, rather than the average of the first cathode composite layer (110) and the second cathode composite layer (120) provided on one side of the cathode current collector (10), or the FWHM of the first cathode composite layer (110) and the second cathode composite layer (120) provided on the other side of the cathode current collector (10).

[0141] In addition, the error in the data can be reduced by preparing and measuring samples by dividing the region according to the location of the negative electrode (100) for the secondary battery. For example, it may be considered that the coating profile, which is the thickness of the negative electrode composite layer, is formed differently based on the non-negative region (the region where the negative electrode composite layer is not formed) of the negative electrode (100) for the secondary battery. In the negative electrode (100) for the secondary battery, each region can be divided into a top region, a mid region, and a bottom region based on the non-negative region, and five samples can be randomly sampled and measured from each region.

[0142] The FWHM of the Gaussian curve for the above Os atomic ratio distribution may be 1 μm to 55 μm. Specifically, the FWHM of the Gaussian curve for the above Os atomic ratio distribution may be 1 μm to 53 μm, or 5 μm to 52 μm, or 10 μm to 52 μm, or 10 μm to 50 μm, or 15 μm to 50 μm.

[0143] Additionally, the average value obtained from the Gaussian curve may be located within a position that is 40% of the total thickness of the first and second cathode composite layers (110, 120), which is 100%. The position that is 40% of the position may be a direction toward the surface of the second cathode composite layer (120) with the surface of the cathode current collector as a reference point (0%), and the average value of the Gaussian curve may exist within the 40% of the position.

[0144] The mean value obtained from the above Gaussian curve represents the position corresponding to the highest point (peak) of the Gaussian curve, and may be μ (mu), which indicates the central position of the distribution in the above Gaussian curve. The probability density function of the Gaussian distribution in the above Gaussian curve can be expressed as follows.

[0145]

[0146] In the above probability density function, μ can represent the mean value and the median of the Gaussian curve, representing the position of the central axis of the curve. Additionally, σ (sigma) can represent the standard deviation, representing the width or spread of the Gaussian curve.

[0147] That is, by ensuring that the average value obtained from the above FWHM and Gaussian curve is within the aforementioned range, the content of the first and second rubber-based binders between the first negative electrode composite layer (110) and the second negative electrode composite layer (120) included in the negative electrode (100) for the secondary battery is controlled, and the distribution of the first and second rubber-based binders between the first and second negative electrode composite layers (110, 120) is controlled, thereby effectively improving the electrochemical performance of the negative electrode (100) for the secondary battery.

[0148] In a negative electrode (100) for a secondary battery according to one embodiment of the present disclosure, even after performing a cycle, migration of the first rubber-based binder from the first negative electrode composite layer (110) to the second negative electrode composite layer (120) does not occur, and the respective contents of the first and second rubber-based binders in the first negative electrode composite layer (110) and the second negative electrode composite layer (120) can be maintained. In addition, the first and second rubber-based binders in the first and second negative electrode composite layers (110, 120) are uniformly distributed even after performing a cycle, so that the contents of the first and second rubber-based binders in the first and second negative electrode composite layers (110, 120), analyzed by dyeing with OsO4, can be maintained within the aforementioned range.

[0149] If the coating weight decreases, the FWHM of the Gaussian curve may decrease. For example, as the coating weight decreases, the FWHM of the Gaussian curve may decrease within the aforementioned range.

[0150] A negative electrode (100) for a secondary battery according to one embodiment of the present disclosure may be manufactured into a secondary battery using a positive electrode, an electrolyte, etc., and the negative electrode (100) for a secondary battery obtained from the secondary battery may be shown as follows by thermogravimetric analysis (TGA) or pyrolysis-gas chromatography (Py-GC). The secondary battery may be verified by performing CC-CV charge-discharge cycles 10 to 20 times at 0.5C / 4.2V (or 0.5C / 4.4V) and 0.5C / 2.5V, and then using the negative electrode (100) for a secondary battery in a discharged state. On the other hand, the method of the CC-CV charge-discharge cycle is one example and is not limited thereto.

[0151] In a negative electrode (100) for a secondary battery according to one embodiment of the present disclosure, the thermogravimetric analysis (TGA) result may satisfy the following equation 1.

[0152] (Relationship 1) TW2 / TW 1+2 ≤ 0.95

[0153] In the above relationship 1, TW 1+2 is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and TW2 may be the average value of the weight loss ratio of the second cathode composite layer in a temperature range of 300 ℃ to 500 ℃ over an area corresponding to a depth of 70% to 90% of the total thickness of the second cathode composite layer, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer. Additionally, TW2 and TW 1+2 Each unit of may be %. The thermogravimetric analysis (TGA) may be performed under conditions of a temperature range of 300 ℃ to 500 ℃, a heating rate of 5 ℃ / min, and a nitrogen atmosphere (nitrogen gas flow rate 100 mL / min).

[0154] Specifically, the above TW2 may refer to an area up to 80% of the thickness of the surface of the second cathode composite layer (120) with respect to the thickness of the second cathode composite layer (120).

[0155] More specifically, the above TW2 / TW 1+2 It can be 0.9 or less.

[0156] The above-mentioned negative electrode (100) for a secondary battery can improve the cycle characteristics of the secondary battery by ensuring that the thermogravimetric analysis obtained for the above-mentioned first and second negative electrode composite layers (110, 120) satisfies the aforementioned relationship 1, thereby maintaining stability without a change in the composition of the first and second negative electrode composite layers (110, 120) even after performing a cycle on the above-mentioned negative electrode (100).

[0157] In addition, the thermogravimetric analysis (TGA) results above can further satisfy the following relationship 2 along with the above relationship 1.

[0158] (Equation 2) 0.85 % ≤ TW 1+2

[0159] In the above relationship 2, TW 1+2 is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit may be %.

[0160] In a negative electrode (100) for a secondary battery according to one embodiment of the present disclosure, the pyrolysis-gas chromatography (Py-GC) result may satisfy the following relationship 3.

[0161] (Relationship 3) GW2 / GW 1+2 ≤ 0.99

[0162] In the above relationship 3, GW 1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 may be a measured value in an area corresponding to 70% to 90% of the total depth of the second cathode composite layer, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer. Here, GW2 and GW 1+2 may be a value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight. In addition, the pyrolysis-gas chromatography (Py-GC) may be performed under conditions of a pyrolysis temperature in the range of 300 ℃ to 500 ℃, a pyrolysis time of 5 2 to 15 2 seconds, and a heating rate of 5 ℃ / min of the gas chromatography oven.

[0163] Specifically, the above GW2 may refer to an area up to 80% of the thickness of the surface of the second cathode composite layer (120) with respect to the thickness of the second cathode composite layer (120).

[0164] More specifically, the above GW2 / GW 1+2 It can be 0.9 or less.

[0165] The above-mentioned negative electrode (100) for the secondary battery satisfies the aforementioned relationship 3 for the pyrolysis-gas chromatography obtained for the above-mentioned first and second negative electrode composite layers (110, 120), so that even after performing a cycle on the above-mentioned negative electrode (100) for the secondary battery, no movement or migration of the first and second rubber-based binders occurs in the first and second negative electrode composite layers (110, 120), thereby improving the electrochemical characteristics of the secondary battery.

[0166] The above pyrolysis-gas chromatography (Py-GC) results may further satisfy the following relationship 4.

[0167] (Relationship 4) GW 1+2 ≥ 5,000,000

[0168] In the above Equation 4, GW 1+2 may be a measured value in the entire area of ​​the first and second cathode composite layers.

[0169] FIG. 4 is a flowchart illustrating a method for manufacturing a negative electrode for a secondary battery according to one embodiment of the present disclosure.

[0170] Referring to FIG. 4, a method for manufacturing a negative electrode for a secondary battery according to an embodiment of the present disclosure may include: a slurry preparation step of preparing a first negative electrode slurry comprising a first solvent, a first conductive material, a first rubber-based binder, a first cellulose derivative, and a first negative electrode active material; a second negative electrode slurry comprising a second solvent, a second conductive material, a second rubber-based binder, a second cellulose derivative, and a second negative electrode active material; and a negative electrode composite layer provision step of coating the first negative electrode slurry and the second negative electrode slurry onto a current collector, drying and rolling to sequentially provide a first negative electrode composite layer and a second negative electrode composite layer on the negative electrode current collector.

[0171] The first rubber-based binder included in the first cathode slurry and the second rubber-based binder included in the second cathode slurry may be the same or different. Additionally, the rubber-based binder included in the first cathode slurry and the rubber-based binder included in the second cathode slurry may be the same or different.

[0172] In the negative electrode for a secondary battery manufactured by the above method for manufacturing a negative electrode for a secondary battery, the FWHM (Full Width at Half Maximum) of the Gaussian curve for the Os atomic ratio distribution analyzed by EDS (Energy Dispersive Spectroscopy) after dyeing the cross-section of the first and second negative electrode composite layers with OsO4 may be 1 μm to 55 μm.

[0173] In addition, the average value of the Gaussian curve for the Os atomic ratio distribution analyzed by EDS (Energy Dispersive Spectroscopy) after dyeing the cross-sections of the first and second cathode composite layers with OsO4 may exist in an area of ​​40% or less in the direction from the surface of the cathode current collector toward the surface of the second cathode composite layer, with respect to the total thickness of 100% of the first and second cathode composite layers.

[0174] In the method for manufacturing a negative electrode for a secondary battery according to an embodiment of the present disclosure, the manufactured negative electrode for a secondary battery can be manufactured into a secondary battery together with a positive electrode, etc. After performing a cycle, the secondary battery may appear as follows by thermogravimetric analysis (TGA) or pyrolysis-gas chromatography (Py-GC).

[0175] In the above method for manufacturing a negative electrode for a secondary battery, the thermogravimetric analysis (TGA) result may satisfy the following equation 1.

[0176] (Relationship 1) TW2 / TW 1+2 ≤ 0.95

[0177] In the above relationship 1, TW 1+2 is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and TW2 may be the average value of the weight loss ratio of the second cathode composite layer in a temperature range of 300 ℃ to 500 ℃ over an area corresponding to 40% of the total depth of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer. Additionally, TW2 and TW 1+2 Each unit of may be %. The thermogravimetric analysis (TGA) may be performed under conditions of a temperature range of 300 ℃ to 500 ℃, a heating rate of 5 ℃ / min, and a nitrogen atmosphere (nitrogen gas flow rate 100 mL / min).

[0178] Specifically, the above TW2 may refer to an area up to 80% of the thickness from the surface of the second cathode composite layer with respect to 100% of the thickness of the second cathode composite layer.

[0179] More specifically, the above TW2 / TW 1+2 It can be 0.9 or less.

[0180] In addition, the thermogravimetric analysis (TGA) results above can further satisfy the following relationship 2 along with the above relationship 1.

[0181] (Equation 2) 0.85 % ≤ TW 1+2

[0182] In the above relationship 2, TW 1+2 is the average value of the weight loss ratio in a temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit may be %.

[0183] In a method for manufacturing a negative electrode for a secondary battery according to one embodiment of the present disclosure, a value obtained by dividing the area of ​​the styrene peak (104 m / z) obtained through pyrolysis-gas chromatography (Py-GC) by the amount of the sample can be obtained, and as a result, the following relationship 3 can be satisfied.

[0184] (Relationship 3) GW2 / GW 1+2 ≤ 0.99

[0185] In the above relationship 3, GW 1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 may be a measured value in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer. Here, GW2 and GW 1+2 ≠ a value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight. In addition, in the pyrolysis-gas chromatography (Py-GC), the column is DB-5 (length: 60 m, inner diameter: 0.25 mm, film thickness: 0.25 μm), and the temperature condition can be maintained at 50 ℃ for 5 minutes, then increased by 10 ℃ per minute to maintain at 300 ℃ for 20 minutes.

[0186] Specifically, the above GW2 may refer to an area up to 80% of the thickness from the surface of the second cathode composite layer with respect to 100% of the thickness of the second cathode composite layer.

[0187] More specifically, the above GW2 / GW 1+2 It can be 0.9 or less.

[0188] The above pyrolysis-gas chromatography (Py-GC) results may further satisfy the following relationship 4.

[0189] (Relationship 4) GW 1+2 ≥ 5,000,000

[0190] In the above Equation 4, GW 1+2 may be a measured value in the entire area of ​​the first and second cathode composite layers.

[0191] The content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first cathode composite layer, and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second cathode composite layer may satisfy the following formulas 1 to 3.

[0192] (Equation 1) RB1 > RB2

[0193] (Equation 2) CD1 < CD2

[0194] (Equation 3) CD1 > RB2

[0195] (In Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.)

[0196] In addition, the difference value (CD2-CD1) between the content of the second cellulose derivative (CD2) included in the second cathode composite layer and the content of the first cellulose derivative (CD1) included in the first cathode composite layer may be 0.2 wt% or more.

[0197] In the above slurry preparation step, the first and second cathode slurries each have a viscosity of 6,000 cP to 11,000 cP, and the second cathode slurry may have a viscosity of 6,000 cP to 11,000 cP. In addition, the difference in solid content between the first and second cathode slurries may be 4% or less.

[0198] If the viscosity of the first cathode slurry is less than 6,000 cP, migration of the rubber-based binder may occur, and the adhesion between the first cathode composite layer formed by the first cathode slurry and the cathode current collector is low, which is problematic. In addition, if the viscosity of the first cathode slurry exceeds 11,000, it is not uniformly coated on the cathode current collector, which is problematic.

[0199] If the viscosity of the second cathode slurry is less than 6,000 cP, processability is reduced during the production of an electrode with high loading, which is problematic, and if it exceeds 11,000 cP, the surface becomes passivated, which may reduce the mobility of lithium ions.

[0200] If the difference in solid content between the first and second cathode slurries exceeds 4%, micronization of the first rubber-based binder included in the first cathode slurry may occur, and accordingly, the electrochemical characteristics and cycle characteristics of the secondary battery may be degraded.

[0201] In the step of providing the cathode composite layer above, the first cathode slurry is coated onto the cathode current collector, the second cathode slurry is coated onto the first cathode slurry, and then dried simultaneously to be manufactured.

[0202] In this manner, when the first cathode slurry is coated and the second cathode slurry is coated almost simultaneously, and then the first and second cathode slurries are dried together, the interfacial adhesion between the first and second cathode slurries can be improved. Additionally, by reducing heterogeneity between the interfaces of the first and second cathode slurries, the mobility of lithium ions can be improved.

[0203] Alternatively, in the step of providing the cathode composite layer, the first cathode slurry can be coated onto the cathode current collector and dried once, then the second cathode slurry is coated and dried twice.

[0204] As described above, when the first cathode slurry is coated and then dried once to coat the second cathode slurry, the coating of the second cathode slurry is easy, thereby improving processability. In addition, by drying once and then drying twice, separate drying processes can be applied, allowing for effective control of the physical properties of the first and second cathode composite layers formed by the first and second cathode slurries.

[0205] In the following, the aforementioned negative electrode for a secondary battery, the positive electrode used together with the negative electrode, the separator, the electrolyte, etc. are described.

[0206] The negative electrode for the secondary battery described above may include a negative electrode current collector and first and second negative electrode composite layers provided on one or more of one side and the other side of the negative electrode current collector.

[0207] The first and second cathode composite layers can be provided by coating the first and second cathode slurries, respectively, onto the cathode current collector, and then drying and rolling.

[0208] Non-limiting examples of the above-mentioned cathode current collector include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and a polymer substrate coated with a conductive metal. The above-mentioned cathode current collector is not limited thereto, but, for example, may be 10 μm to 50 μm.

[0209] The first and second cathode slurries may each be prepared by adding and mixing the first and second cathode active materials, the first and second rubber-based binders, and the first and second cellulose derivatives to the first and second solvents, respectively. Additionally, the first and second cathode slurries may further include a cathode additive.

[0210] The first and second negative electrode active materials may be the same or different from each other. The first and second negative electrode active materials may be materials capable of adsorbing and desorbing lithium ions. For example, the first and second negative electrode active materials may be carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials; or tin (Sn)-containing materials.

[0211] Specifically, the first negative electrode active material may include a carbon-based material, and the second negative electrode active material may include a silicon-containing material. Alternatively, the first negative electrode active material may include a silicon-containing material, and the second negative electrode active material may include a carbon-based material.

[0212] Examples of the above-mentioned amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF).

[0213] Examples of the above-mentioned crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0214] The above lithium metal may be pure lithium metal or lithium metal with a protective layer formed thereon for inhibiting dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector may be used as a negative electrode active material layer. In one embodiment, a lithium thin film layer may be used as a negative electrode active material layer.

[0215] Examples of elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0216] The above silicon-containing material can provide increased capacity characteristics. The above silicon-containing material is Si, SiOx (0 <x<2), 금속 도핑된 SiOx (0<x<2), 실리콘-탄소 복합체 등을 포함할 수 있다. 상기 금속은 리튬 및 / 또는 마그네슘을 포함할 수 있으며, 금속 도핑된 SiOx (0<x<2)는 금속 실리케이트를 포함할 수 있다.

[0217] The first and second rubber-based binders may each include nano-sized particles having a hydrophilic surface. The first and second rubber-based binders can improve the binding force between particles contained within the first and second cathode slurries and improve the adhesion force between the first and second cathode composites and the cathode current collector. Additionally, the first and second rubber-based binders can prevent the first and second cathode composites from developing cracks or the like due to external forces by providing elasticity and flexibility to the first and second cathode composites.

[0218] The above rubber-based binder may be one or more selected from the group consisting of styrene-butadiene-based binders, acrylated styrene-butadiene-based binders, acrylonitrile-styrene-butadiene binders, styrene-acrylate-based binders, and styrene-butadiene-styrene-based binders.

[0219] The first and second cellulose derivatives can each control the viscosity of the first and second cathode slurries. In addition, the first and second cellulose derivatives can maintain a uniform distribution of particles within the first and second cathode slurries, thereby ensuring that the physical properties of the first and second cathode composites are uniformly provided.

[0220] A method for manufacturing a negative electrode for a secondary battery, wherein the first and second cellulose derivatives are one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethyl cellulose (CMC-Li), sodium salt of carboxymethyl cellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose.

[0221] The above-mentioned cathode additive may include a conductive agent. The conductive agent may be added to enhance the conductivity and / or the mobility of lithium ions or electrons of the first and second cathode composite layers. For example, the conductive agent may include, but is not limited to, carbon-based conductive agents such as graphite, carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, etc., and metal-based conductive agents such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0222] The first and second solvents may be the same or different from each other. The first and second solvents may be selected in various ways depending on the types of the first and second cathode active materials. The first and second solvents may be used to uniformly mix the particles constituting the first and second cathode slurries.

[0223] Non-limiting examples of the first and second solvents mentioned above include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc.

[0224] The first and second cathode slurries can be prepared by mixing the first and second cathode active materials in the first and second solvents. The first and second cathode composite layers can be prepared by coating / depositing the first and second cathode slurries onto a cathode current collector, followed by drying and rolling.

[0225] The above coating process may be carried out using methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, but is not limited thereto.

[0226] The positive electrode for the secondary battery described above may include a positive current collector and a positive composite layer provided on one or more of one side and the other side of the positive current collector. The positive composite layer may be provided as a dual layer consisting of an upper layer and a lower layer, or as a single layer consisting of one layer.

[0227] The above anode composite layer can be provided by coating the anode slurry onto the anode current collector, followed by drying and rolling.

[0228] The anode current collector may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The anode current collector may also include carbon, nickel, titanium, aluminum or stainless steel surface-treated with silver. The anode current collector may be, for example, 10 μm to 50 μm, although not limited thereto.

[0229] The above anode slurry can be prepared by mixing a particulate anode active material, a conductive material, and an anode binder in an anode solvent.

[0230] The above-mentioned cathode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0231] According to exemplary embodiments, the cathode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0232] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may comprise a layered structure or a crystalline structure represented by the following chemical formula 1.

[0233] [Chemical Formula 1]

[0234] Li x Ni a M b O 2+z

[0235] In Chemical Formula 1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.4, and -0.5≤z≤0.1 may be used. As described above, M may include Co, Mn, and / or Al.

[0236] The chemical structure represented by Chemical Formula 1 represents the bonding relationships contained within the layered or crystal structure of the cathode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn may be provided as the main active element of the cathode active material together with Ni. Chemical Formula 1 is provided to express the bonding relationships of the main active elements and should be understood as encompassing the introduction and substitution of additional elements.

[0237] In one embodiment, auxiliary elements may be further included to enhance the chemical stability of the cathode active material or the layered structure / crystal structure by adding to the main active element. The auxiliary elements may be incorporated together within the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the range of the chemical structure represented by Chemical Formula 1.

[0238] The above auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The above auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the cathode active material together with Co or Mn, such as Al.

[0239] For example, the above-mentioned positive active material or the above-mentioned lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following chemical formula 1-1.

[0240] [Chemical Formula 1-1]

[0241] Li x Ni a M1 b1 M2 b2 O 2+z

[0242] In Chemical Formula 1, M1 may include Co, Mn and / or Al. M2 may include the auxiliary element described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0243] The above-described cathode active material may further include a coating element or a doping element. For example, elements substantially identical or similar to the auxiliary elements described above may be used as coating elements or doping elements. For example, any of the elements described above may be used alone or in combination of two or more as coating elements or doping elements.

[0244] The coating element or doping element may be present on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal composite oxide particles and be included within the bonding structure represented by Formula 1 or Formula 1-1.

[0245] The above-mentioned cathode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0246] The content of Ni in the above NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.5 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0247] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0248] In some embodiments, the positive electrode active material may include, for example, a Mn-rich active material having a chemical structure or crystal structure represented by Formula 2, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) active material, or a Co-less active material.

[0249] [Chemical Formula 2]

[0250] p[Li2MnO3]·(1-p)[Li q JO2]

[0251] Of chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0252] The above-mentioned cathode conductive material may be added to enhance the conductivity of the cathode composite layer and / or the mobility of lithium ions or electrons. For example, the above-mentioned cathode conductive material may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, ketjenblack, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, etc., and metal-based conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0253] The anode binder may include polyvinylidenefluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (Poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as the anode binder.

[0254] Non-limiting examples of the above anode solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0255] If necessary, the anode slurry may further include a thickener and / or a dispersant, etc. In one embodiment, the anode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0256] The above anode slurry can be prepared by mixing the above anode active material in a solvent. After coating the above anode slurry onto an anode current collector, an anode composite layer can be prepared by drying and rolling.

[0257] The above coating process may be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting, but is not limited thereto. The above anode composite layer may further include a binder and optionally may further include a conductive material, a thickener, etc.

[0258] The negative electrode for the secondary battery described above may be laminated with the positive electrode, and may include a separator and a liquid electrolyte to allow only ions to move without direct contact between them. Alternatively, when using a solid electrolyte, a solid electrolyte may be interposed between the negative electrode and the positive electrode for the secondary battery, and the separator and the liquid electrolyte may be optionally included or omitted.

[0259] A separator may be interposed between the anode and the cathode. The separator may be configured to prevent an electrical short circuit between the anode and the cathode and to allow for the flow of ions. According to an embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0260] For example, the separator may comprise a porous polymer film or a porous nonwoven fabric. The porous polymer film may comprise polyolefin-based polymers such as ethylene polymer, propylene polymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer. The porous nonwoven fabric may comprise high-melting-point glass fibers, polyethylene terephthalate fibers, etc. The separator may also comprise ceramic-based materials. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0261] The above-described separator may have a single-layer or multi-layer structure comprising the polymer film and / or nonwoven fabric described above.

[0262] The negative and positive electrodes for the secondary battery described above may be assembled facing each other with a separator interposed between them to form an electrode assembly.

[0263] According to exemplary embodiments, the electrode assembly may be formed by repeating an anode, a cathode, and a separator. In some embodiments, the electrode assembly may be of a winding type, a stacking type, a zigzag folding type, or a stack-folding type.

[0264] A lithium secondary battery can be defined by housing the above electrode assembly together with an electrolyte within a case. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0265] The non-aqueous electrolyte comprises a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - It is expressed as and the anion (X) of the above lithium salt - As F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N- Examples of the back can be given.

[0266] The above organic solvent may include an organic compound that has sufficient solubility for the lithium salt and additive and does not have reactivity in the battery. For example, the above organic solvent may include at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

[0267] As the above organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC), vinylene carbonate (VC), methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethyl ethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), Fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran,THF, 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide (DMSO), acetonitrile, dimethoxyethane (DME), diethoxyethane (DEE), sulfolane, gamma-butyrolactone, and propylene sulfite, etc., may be used. These may be used alone or in combination of two or more.

[0268] The above additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sulfone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds.

[0269] The above cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0270] The above fluorine-substituted cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc.

[0271] The above sulfone-based compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0272] The above cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0273] The above-mentioned cyclic sulfite compounds may include ethylene sulfite, butylene sulfite, etc.

[0274] The above phosphate-based compounds may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0275] The above borate-based compounds may include lithium bis(oxalate) borate, etc.

[0276] When an electrode assembly using a solid electrolyte as the above-mentioned separator is housed in a case, it can be housed without a liquid electrolyte. The solid electrolyte may include a sulfide-based electrolyte. In one embodiment, the solid electrolyte may include an oxide-based amorphous solid electrolyte.

[0277] As a non-limiting example, the sulfide-based electrolyte is Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n(m, n are positive numbers, Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , (p, q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li7 - x PS6 - x Cl x (0≤x≤2), Li7 - x PS6 - x Br x (0≤x≤2), Li7 - x PS6 - x I x It may include (0≤x≤2), etc. These can be used individually or in combination of two or more.

[0278] In one embodiment, the solid electrolyte may include, for example, an oxide-based amorphous solid electrolyte such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0279] In the assembly step above, the anode, separator, and cathode are stacked to form an electrode assembly, and the electrode assembly can be housed in a case. An anode tab and a cathode tab may protrude from the anode current collector and the cathode current collector, respectively, and extend to one side of the case. Each of the anode tab and the cathode tab may be fused together with at least a part of the case and connected to an anode lead and a cathode lead that extend or are exposed to the outside of the case.

[0280] For example, the above case may be a pouch-type case, a rectangular case, a cylindrical case, a coin-type case, etc.

[0281] The above formation step can perform charging and discharging on the case housing the electrode assembly after the above assembly step is completed. In the above formation step, the lithium secondary battery can be activated. Specifically, the lithium secondary battery can be charged with a low current.

[0282] In addition, the present disclosure may include a secondary battery comprising the aforementioned negative electrode for a secondary battery. By effectively preventing the migration of a rubber-based binder that may occur at the negative electrode for the secondary battery, the electrochemical properties and cycle properties of the secondary battery can be improved.

[0283] Examples and comparative examples of the present disclosure are described below. However, the following examples are merely preferred embodiments of the present disclosure and the scope of the rights of the present disclosure is not limited by the following examples.

[0284] Preparation of the example of preparation

[0285] Preparation Example 1

[0286] Earth-like synthetic graphite (ES2, Shinzoom) with an average particle size (D50) of 14 μm was used as the cathode active material, and a cathode slurry was prepared by adding styrene-butadiene rubber (SBR) as a rubber-based binder and sodium carboxymethyl cellulose (Na-CMC) as a cellulose derivative at 1.2 wt% and 1.2 wt%, respectively. The prepared cathode slurry was uniformly coated on both sides of a copper foil (8 μm thick), followed by drying and rolling to produce a cathode with a cathode composite layer formed on the copper foil. At this time, the average loading level, which is the coating weight per unit area, was 10.5 mg / cm². 2 It was made so that it would become.

[0287] Preparation Example 2

[0288] A cathode was prepared in the same manner as in Preparation Example 1, except that SBR and CMC were used at 1.2 wt% and 1.6 wt%, respectively.

[0289] Preparation of Examples and Comparative Examples

[0290] Example 1 (Cathode loading level 10.5 mg / cm² 2 )

[0291] As a negative electrode active material, clay-like artificial graphite (ES2, Shinzoom) with an average particle size (D50) of 14 μm was used. Additionally, styrene-butadiene rubber (SBR) as a rubber-based binder and sodium carboxymethyl cellulose (Na-CMC) as a cellulose derivative were prepared in the weight ratios shown in Table 1 below, added to distilled water, and mixed to prepare the first and second negative electrode slurries, respectively. The prepared first and second negative electrode slurries were uniformly coated on both sides of a copper foil (8 μm thick), and then dried and rolled to produce a negative electrode. At this time, a coater was used to directly coat the first negative electrode slurry onto the copper foil so that it was placed on the lower layer, and the second negative electrode slurry was coated on top of the first negative electrode slurry so that it was placed on the upper layer. After coating the first and second negative electrode slurries together, they were dried simultaneously to produce a negative electrode for a secondary battery consisting of a dual layer of an upper negative electrode composite and a lower negative electrode composite on the copper foil. At this time, the average loading level (coating weight per unit area) of the upper and lower cathode mixtures is 10.5 mg / cm² 2 It was designed to be as follows. In Table 1 below, the content of SBR and CMC contained in the upper and lower cathode composites, respectively, is expressed in weight percent based on the solid content. At this time, the first and second cathode slurries each had a solid content in the range of 53% to 55% and a viscosity of 7,000 ± 1,000 cP. In addition, the total composite density of the prepared upper and lower cathode composites was 1.62 g / cc. The coater residence time was set to 1.1 min. Here, the coater residence time is the time during which coating is performed inside the coater, and a shorter time indicates a faster coating speed. (Coater residence time = Length of drying oven (m) / Coating speed (m / min))

[0292] At room temperature, NCM613 (ME-6SC4, BE), MWCNT as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were prepared in a weight ratio of 97.5:1:1.5 and mixed with NMP to prepare an anode slurry. The anode slurry was uniformly coated and rolled on both sides of an aluminum foil (15 μm thick) to produce an anode for a secondary battery.

[0293] The cathode and anode were made so that the N / P ratio was 1.1, and the other coating, drying, and rolling processes were manufactured similarly.

[0294] An electrode assembly was formed by interposing a polyethylene separator (thickness 13 μm) between the manufactured anode and cathode. The electrode assembly was housed inside a pouch (case), and three sides were sealed, excluding the surface for electrolyte injection. At this time, electrode leads were connected to the uninsulated parts of the anode and cathode, respectively, and the electrode leads were drawn out to the outside of the pouch.

[0295] A lithium secondary battery was manufactured by injecting an electrolyte into a pouch, sealing the surface of the electrolyte injection area, and then impregnating it for 12 hours.

[0296] The electrolyte was prepared by first preparing a 1M LiPF6 solution (a mixed solvent of EC / EMC / DEC in a volume ratio of 25:30:45) and then adding 1 wt% of FEC (fluoroethylene carbonate), 0.3 wt% of VC (vinylethylene carbonate), 1.0 wt% of LiPO2F2 (lithium difluorophosphate), 0.5 wt% of PS (1,3-propane sultone), and 0.5 wt% of PRS (prop-1-ene-1,3-sultone) based on the total weight of the electrolyte.

[0297] The manufactured lithium secondary battery was charged (CC-CV 1 / 3C 4.4 V 0.05C CUT-OFF) using a charge / discharger in a 25 ℃ chamber, and then discharged (CC 1 / 3C 2.5 V CUT-OFF) to perform a formation process (CC: Constant Current, CV: Constant Voltage).

[0298] Examples 2 to 11 (Cathode loading level 10.5 mg / cm² 2 )

[0299] A lithium secondary battery was manufactured by varying only the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries and the coater residence time when manufacturing the cathode, while keeping the rest the same as in Example 1. The content of the rubber-based binder and cellulose derivative and the coater residence time are shown in Table 1.

[0300] Comparative Examples 1 to 5 (Cathode loading level 10.5 mg / cm² 2 )

[0301] A lithium secondary battery was manufactured by varying only the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries and the coater residence time when manufacturing the cathode, while keeping the rest the same as in Example 1. The content of the rubber-based binder and cellulose derivative and the coater residence time are shown in Table 1.

[0302] Classification Upper layer cathode slurry (wt%) Lower layer cathode slurry (wt%) Compound density (g / cc) Coater residence time (min) CMCSBR CMCSBR Example 1 1.40.2 1.2 2.41.621.1 Example 2 1.50.2 1.2 2.41.621.1 Example 3 1.60.2 1.2 2.41.621.1 Example 4 1.80.2 1.2 2.41.621.1 Example 5 1.40.2 1.41.621.1 Example 6 1.80.2 1.42.41.621.1 Example 7 1.60.2 1.2 1.81.621.1 Example 8 1.60.2 1.2 1.4 1.621.1 Example 9 1.60.21.2 11.621.1 Example 10 1.60.21.2 1.4 1.620.8 Example 1 1.60.21.2 0.61.621.1 Comparative Example 1 1.20.21.22 4 1.621.1 Comparative Example 2 10.212 4 1.621.1 Comparative Example 3 1.20.21.62 4 1.621.1 Comparative Example 4 1.60.21.62 4 1.621.1 Comparative Example 5 1.20.21.22 4 1.620.8

[0303] Examples 12 to 15 (Cathode loading level 13.5 mg / cm² 2 )

[0304] A lithium secondary battery was manufactured in the same manner as in Example 1, differing only in the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries and the cathode loading level when manufacturing the cathode. The content of the rubber-based binder and cellulose derivative is shown in Table 2. In the dual-layer cathode for the secondary battery, the average loading level of the upper and lower cathode composites was 13.5 mg / cm². 2 It was made so that it would become.

[0305] Comparative Example 6 (Cathode loading level 13.5 mg / cm² 2 )

[0306] A lithium secondary battery was manufactured in the same manner as in Example 1, differing only in the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries and the cathode loading level when manufacturing the cathode. The content of the rubber-based binder and cellulose derivative is shown in Table 2. In the dual-layer cathode for the secondary battery, the average loading level of the upper and lower cathode composites was 13.5 mg / cm². 2 It was made so that it would become.

[0307] Classification Upper layer cathode slurry (wt%) Lower layer cathode slurry (wt%) Compound density (g / cc) Coater residence time (min) CMCSBR CMCSBR Example 1 2 1.6 0.4 1.2 2.4 1.6 2 1.1 Example 1 3 1.6 0.4 1.2 1.8 1.6 2 1.1 Example 1 4 1.7 0.4 1.2 1.8 1.6 2 1.1 Example 1 5 1.8 0.4 1.2 1.8 1.6 2 1.1 Comparative Example 6 1.2 0.4 1.2 2.4 1.6 2 1.1

[0308] Examples 16 to 19 (Cathode loading level 15.0 mg / cm² 2 )

[0309] A lithium secondary battery was manufactured by varying only the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries, the cathode loading level, the composite density, and the coater residence time when manufacturing the cathode, while keeping all other conditions the same as in Example 1. The content of the rubber-based binder and cellulose derivative is shown in Table 3. In the dual-layer cathode for the secondary battery, the average loading level of the upper and lower cathode composites was 15.0 mg / cm². 2 It was made so that it would become.

[0310] Comparative Example 7 (Cathode loading level 15.0 mg / cm² 2 )

[0311] A lithium secondary battery was manufactured by varying only the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries, the cathode loading level, the composite density, and the coater residence time when manufacturing the cathode, while keeping all other conditions the same as in Example 1. The content of the rubber-based binder and cellulose derivative is shown in Table 3. In the dual-layer cathode for the secondary battery, the average loading level of the upper and lower cathode composites was 15.0 mg / cm². 2 It was made so that it would become.

[0312] Classification Upper layer cathode slurry (wt%) Lower layer cathode slurry (wt%) Compound density (g / cc) Coater residence time (min) CMCSBR CMCSBR Example 16 1.6 0.4 1.2 2.4 1.5 2.1.25 Example 17 1.6 0.4 1.2 1.8 1.5 2.1.25 Example 18 1.7 0.4 1.2 1.8 1.5 2.1.25 Example 19 1.8 0.4 1.2 1.8 1.5 2.1.25 Comparative Example 7 1.2 0.4 1.2 2.4 1.5 2.1.25

[0313] Examples 20 to 23 (Cathode loading level 17.0 mg / cm² 2 )

[0314] A lithium secondary battery was manufactured by varying only the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries, the cathode loading level, the composite density, and the coater residence time when manufacturing the cathode, while keeping all other conditions the same as in Example 1. The content of the rubber-based binder and cellulose derivative is shown in Table 4. In the dual-layer cathode for the secondary battery, the average loading level of the upper and lower cathode composites was 17.0 mg / cm². 2 It was made so that it would become.

[0315] Comparative Example 8 (Cathode loading level 17.0 mg / cm² 2 )

[0316] A lithium secondary battery was manufactured by varying only the content of the rubber-based binder and cellulose derivative included in the first and second cathode slurries, the cathode loading level, the composite density, and the coater residence time when manufacturing the cathode, while keeping all other conditions the same as in Example 1. The content of the rubber-based binder and cellulose derivative is shown in Table 4. In the dual-layer cathode for the secondary battery, the average loading level of the upper and lower cathode composites was 17.0 mg / cm². 2 It was made so that it would become.

[0317] Classification Upper layer cathode slurry (wt%) Lower layer cathode slurry (wt%) Compound density (g / cc) Coater residence time (min) CMCSBRCMCSBR Example 20 1.6 0.4 1.2 2.4 1.5 2.1.25 Example 21 1.6 0.4 1.2 1.8 1.5 2.1.25 Example 22 1.7 0.4 1.2 1.8 1.5 2.1.25 Example 23 1.8 0.4 1.2 1.8 1.5 2.1.25 Comparative Example 8 1.2 0.4 1.2 2.4 1.5 2.1.25

[0318] Example 24 (Cathode loading level 10.5 mg / cm² 2 )

[0319] A lithium secondary battery was manufactured in the same manner as in Example 1, with only the type and content of the rubber-based binder included in the first and second cathode slurries, the content of the cellulose derivative included in the first and second cathode slurries, and the coater residence time being different when manufacturing the cathode. Styrene-acrylate (SA) was used as the rubber-based binder instead of styrene-butadiene rubber (SBR), and this is shown in Table 5.

[0320] Comparative Example 9 (Cathode loading level 10.5 mg / cm² 2 )

[0321] A lithium secondary battery was manufactured in the same manner as in Example 1, with only the type and content of the rubber-based binder included in the first and second cathode slurries, the content of the cellulose derivative included in the first and second cathode slurries, and the coater residence time being different when manufacturing the cathode. Styrene-acrylate (SA) was used as the rubber-based binder instead of styrene-butadiene rubber (SBR), and this is shown in Table 5.

[0322] Classification Upper layer cathode slurry (wt%) Lower layer cathode slurry (wt%) Compound density (g / cc) Coater residence time (min) CMCSACMCSA Example 2 4 1.6 0.2 1.2 1.4 1.6 2 1.1 Comparative Example 9 1.2 0.2 1.2 2.4 1.6 2 1.1

[0323] Evaluation of Manufacturing Examples, Examples, and Comparative Examples

[0324] Figure 5 is a diagram confirming the surface contact angle according to Manufacturing Example 1 and Manufacturing Example 2.

[0325] In order to confirm surface characteristics according to the content of CMC, the surface contact angle of the negative electrode for a secondary battery prepared in Preparation Example 1 and Preparation Example 2 was confirmed.

[0326] The contact angle was measured at room temperature by dropping a standard solvent (water, diiodomethane) onto the surface of the cathode of each of Preparation Example 1 and Preparation Example 2. The surface energy of the solid was measured using the Owens-Wendt-Rabel-Kaelble method (OWRK method), and the polarity of Preparation Examples 1 and 2 was calculated using the following Young's equation.

[0327] (Young's equation)

[0328] σ s = σ sl +σ l · cosθ

[0329] σ sl = σ s +σ l - 2 · {(σ s D · σ l D ) ½ +(σ s p · σ l p ) ½}

[0330] Here, θ is the contact angle, and σ s is the solid-gas interface energy, and σ sl is the solid-liquid interface energy, and σ l represents the surface tension (liquid-gas) as the interfacial energy between the liquid and gas.

[0331] Also, σ s D , σ l D , σ s p , and σ l p Each reflects the standard values ​​of the measured standard solvents, where P is 51.0 mN / m and D is 21.8 mN / m for water, and P is 1.3 mN / m and D is 49.5 mN / m for diiodomethane.

[0332] Table 6 below shows the results of measuring surface energy and contact angle according to Preparation Example 1 and Preparation Example 2.

[0333] Classification CMC Content (wt%) Electrode Surface Contact Angle Measurement Surface Energy (Polarity) [mN / m] Contact Angle [°] σ s pWater Diiodomethane Preparation Example 11.26.369.011.6 Preparation Example 21.631.525.49.8

[0334] Referring to Figure 5 and Table 6, it was confirmed that the surface energy and contact angle varied significantly depending on the CMC content, and that the polarity varied.

[0335] While the surface energy of Preparation Example 1 was 6.3 mN / m, Preparation Example 2, which contained more CMC, increased to 31.5 mN / m, approximately five times. In addition, it was confirmed that there was a significant difference in the contact angle with respect to water, with Preparation Example 1 having an angle of 69° and Preparation Example 2 having an angle of 25.4°.

[0336] In other words, it was confirmed that by controlling the content of CMC contained within the cathode, the polarity can be varied, thereby generating a difference in energy levels. Using this principle, experiments were conducted in the examples and comparative examples with varying CMC content in the upper and lower cathode composites, and the content range capable of effectively blocking SBR migration caused by the difference in energy levels was identified.

[0337] Below, for each negative electrode for a secondary battery, the cross-section of the negative electrode composite was analyzed using EDS (Energy Dispersive Spectroscopy) to evaluate the staining with OsO4, thermogravimetric analysis (TGA), pyrolysis-gas chromatography (Py-GC), coating adhesion (electrode adhesion) to the current collector, resistance, cycle characteristics at 45°C, and rapid charging characteristics at 25°C.

[0338] Evaluation method of OsO4 staining by EDS (Energy Dispersive Spectroscopy) analysis of the cross-section of the cathodic composite

[0339] For the EDS analysis of the cross-section of the cathode composite, the cathode prepared according to the examples and comparative examples was manufactured into a secondary battery, and then 15 CC-CV charge-discharge cycles were performed at 0.5C / 4.4V and 0.5C / 2.5V, and the cathode prepared after discharge was used.

[0340] The cathode was cut to a size of 1 cm x 1 cm, and after pretreatment, samples were prepared by OsO4 (osmium tetraoxide) staining and argon ion milling. The samples were prepared in the following manner. The manufactured cathode was divided into top, mid, and bottom sections based on its position, and a total of 5 samples of 1 cm x 1 cm were prepared and measured in each of the top, mid, and bottom sections. That is, the average values ​​measured for a total of 15 samples—5 from the top section, 5 from the mid section, and 5 from the bottom section—are shown in the table. Here, the top, mid, and bottom sections were defined considering the thickness profile of the cathode composite layer on the cathode; starting from the uncoated area (where the current collector is exposed) on the cathode, the areas were divided into the top, mid, and bottom sections, respectively, and 1 cm x 1 cm samples were randomly prepared.

[0341] For pretreatment, the cathode was sequentially immersed in DMC, acetone, ethanol, and deionized water, and then dried in a vacuum oven for 24 hours to remove the electrolyte, lithium salt, and SEI film. After the pretreatment was completed, the solvents used for pretreatment were extracted, and the removal of the electrolyte and lithium salt was confirmed by identifying the LiPF6 peak in NMR analysis and the Li-F peak in XPS analysis of the pretreated electrode.

[0342] After pretreatment was completed, OsO4 staining was performed. The cathode was placed in a container containing OsO4 and sealed; after 48 hours, the cathode was removed and placed in a vacuum oven to be dried for 48 hours. As a result, the SBR contained in the upper and lower cathode composite layers was stained by OsO4.

[0343] Subsequently, a cross-section of the stained cathode was fabricated using argon ion milling. Using an energy dispersive X-ray spectroscopy (EDS, Flatquad) detector of a scanning electron microscope (SEM), the components within the upper and lower cathode composite layers formed on one side and the other side of the fabricated cathode were EDS mapped to obtain an EDS mapping image for Os. From the obtained EDS mapping image, a line profile was performed at the 1 / 5 point from the left in the horizontal direction, and the EDS mapping image was quantified to extract line profiles in the thickness direction of the upper and lower cathode composite layers. The x-axis of the extracted line profile represents the position in the depth direction of the cathode (μm), and the y-axis represents Os intensity in Os mass%. In addition, to improve the accuracy of the data, values ​​with an FWHM of 300 μm or more were excluded from the data as they were determined to be measurement errors.

[0344] From the extracted line profile results, the Os intensity (Os-Mαβ value) according to the thickness of one side and the other side of the cathode was plotted. Then, by fitting based on the central cathode current collector, a Gaussian curve of the Os distribution across the cathode cross-section was obtained, and the position (%) of the mean value and the FWHM value were calculated. At this time, the mean value and FWHM value of the Gaussian curve were obtained for a randomly selected side of either one side or the other side of the cathode.

[0345] The Gaussian curve was generated using graphing software called OriginLab. Specifically, the raw data of the line profile was graphed in OriginLab and used. After selecting the graph obtained by OriginLab, the Gaussian curve was obtained using Gadgets-Quick fit-Peak (Gauss) from the menu, and the FWHM and mean values ​​were calculated.

[0346] The FWHM value using the Gaussian curve was calculated in the following way. The Gaussian curve was represented using the function below.

[0347]

[0348] Here, is the maximum height of the peak, μ is the position of the center of the peak, and σ (sigma) represents the standard deviation.

[0349] In addition, the FWHM value in the Gaussian curve was calculated using the following formula.

[0350]

[0351] That is, for the Gaussian curve obtained using OriginLab, using the aforementioned function and formula, each The FWHM value was obtained using , μ, and σ (sigma).

[0352] Here, the position of the average value (%) refers to the part where the average value of the Gaussian curve appears, meaning the region where the average value according to the Gaussian curve appears relative to the cathode current collector located at the center of the cathode (i.e., the height in the direction from the surface of the cathode current collector toward the surface of the cathode composite layer).

[0353] Thermogravimetric analysis (TGA)

[0354] Thermogravimetric analysis of the cross-section of the cathode composite was performed using the cathode prepared according to the examples and comparative examples, which was then manufactured into a secondary battery, followed by 15 CC-CV charge-discharge cycles at 0.5C / 4.4V and 0.5C / 2.5V, and the cathode prepared after discharge.

[0355] For thermogravimetric analysis, the sample was scraped from the cathode using a knife, and the entire cathode mixture contained both the upper and lower cathode mixtures. The upper cathode mixture was scraped up to a depth of 40% from the surface. By scraping the upper cathode mixture up to 40% of the area, the inclusion of the lower cathode mixture was prevented.

[0356] Thermogravimetric analysis was performed using the average value of five weight loss ratio measurements in a temperature range of 300 ℃ to 500 ℃, under conditions of a temperature range of 300 ℃ to 500 ℃, a heating rate of 5 ℃ / min, and a nitrogen atmosphere (nitrogen gas flow rate 100 mL / min).

[0357] Pyrolysis-gas chromatography (Py-GC)

[0358] Pyrolysis-gas chromatography of the cross-section of the cathode composite was performed using the cathode prepared according to the examples and comparative examples, which was then manufactured into a secondary battery, followed by 15 CC-CV charge-discharge cycles at 0.5C / 4.4V and 0.5C / 2.5V, and the cathode prepared after discharge.

[0359] For the sample for pyrolysis-gas chromatography, the cathodic composite was scraped from the cathode using a knife. The entire cathodic composite included both the upper and lower layers, and the upper layer was scraped from the surface to a depth of 40% of the total 100% of the cathodic composite. By limiting the scraping area of ​​the upper layer in this manner, the inclusion of the lower layer was prevented.

[0360] In pyrolysis-gas chromatography (Py-GC), a DB-5 column (length: 60 m, inner diameter: 0.25 mm, film thickness: 0.25 μm) was used, and the temperature conditions were maintained at 50 ℃ for 5 minutes, then increased by 10 ℃ per minute to 300 ℃ for 20 minutes.

[0361] Evaluation method for adhesion strength (electrode coating adhesion strength) across the entire house

[0362] Each manufactured cathode was cut to a size of 18 mm x 150 mm, and a tape with a width of 18 mm was attached to the cathode current collector side. Then, a roller with a load of 2 kgf was used to ensure sufficient adhesion. Afterward, the upper cathode composite layer was adhered to one side of a tensile tester (IMADA, DS2-50N) using double-sided tape, and the current collector was attached to the opposite side of the tensile tester to measure the adhesion strength.

[0363] Resistance evaluation method

[0364] In the secondary battery using each manufactured negative electrode, DC-IR was measured when discharging at 1C for 10 seconds at an SOC of 50%.

[0365] Method for evaluating cycle characteristics of a secondary battery at 45°C

[0366] For each lithium secondary battery according to the examples and comparative examples, the cycle characteristics of SOC2-96 were evaluated using 0.5C / 4.4V and 0.5C / 2.5V CC-CV charge / discharge capacities at a temperature of 45°C as reference capacities.

[0367] Method for evaluating the rapid charging characteristics of a secondary battery at 25°C

[0368] For each lithium secondary battery according to the example and comparative example, the three-electrode cell was CC charged to 4.4V at a C-rate in the range of 1.25 to 3.0C at a temperature condition of 25℃, and the SOC point at which the CCV value of the negative electrode for each C-rate became constant at 0V or lower was found and designated as the charging limit, and a step-charging protocol was configured such that the charging time was 20 minutes by giving an SOC margin to each of the comparative example and the example.

[0369] Rapid charge / discharge characteristics were evaluated at SOC 10-80, 20 minutes charge, and 0.5C / 2.5V.

[0370] Figure 6 shows the results of SEM / EDS analysis of the cross-section of the cathode composite immediately after rolling of Example 1, stained with OsO4. Figure 7 shows the results of EDS analysis of the cross-section of the cathode composite from which the SEI layer was removed after performing the cycle of Example 1, stained with OsO4.

[0371] Referring to Fig. 6, regarding the negative electrode of the secondary battery before performing the cycle in Example 1, it was confirmed that SBR was uniformly distributed in the upper negative electrode composite layer and the lower negative electrode composite layer, respectively. That is, in Example 1, it was confirmed that no migration of SBR occurred during drying while manufacturing the upper negative electrode composite layer and the lower negative electrode composite layer.

[0372] Here, Figure 7 was measured in the same manner as Figure 6, but surface treatment was performed before measurement to prevent dyeing resistance caused by the SEI layer. Specifically, the prepared sample was immersed in a mixed solvent of ethanol and distilled water (90:10 vol%) at room temperature for 6 hours, and then dried to confirm.

[0373] Referring to Fig. 7, it was confirmed that SBR was uniformly distributed in the upper cathode composite layer and the lower cathode composite layer, respectively. In addition, it was confirmed that the distinction between the upper cathode composite layer and the lower cathode composite layer was clearly visible.

[0374] Table 7 shows the cathode loading level of 10.5 mg / cm² for Examples 1 to 11 and Comparative Examples 1 to 5. 2 This is the result of verifying the electrode adhesion, resistance, cycle characteristics, rapid charging characteristics, and EDS analysis results in the case.

[0375] Figure 8 shows the results of EDS analysis after staining the cross-section of the cathode composite with OsO4 following the cycle of Example 10. Figure 9 shows the results of EDS analysis after staining the cross-section of the cathode composite with OsO4 following the cycle of Comparative Example 5.

[0376] Classification Upper Cathode Slurry (wt%) Lower Cathode Slurry (wt%) Coater Residence Time (min) Coating Adhesion (N / 18mm) Battery Resistance (mOhm) Cycle Characteristics (%, ~800 cycles, 45℃) Fast Charge (%, ~400 cycles, 25℃, 20 min) EDS Analysis 1 (Average Value Location %) EDS Analysis 2 (FWHM μm)CMCSBRCMCSBR Example 1 1.40.21.22.41.10.381.06686.473.94054.7 Example 2 1.50.21.22.41.10.431.05986.588.439.238.4 Example 3 1.60.21.22.41.10.51.05586.593.535.619.4 Example 4 1.80.21.22.41.10.531.0578691.329.216.0 Example 5 1.40.212.41 .10.47 1.05285.190.537.523.7 Example 6 1.80.21.42.41.10.531.0685.389.436.919.9 Example 7 1.60.21.21.81.10.411.04686.39437.133.7 Example 8 1.60.21.21.41.10.321.03386.894.136.239.5 Example 9 1.60.21.211.10.291.01486.993.836.652.9 Example 101.60.21.21.40.80.301.05286.592.037.641.4 Example 1 1 1 1 60.21.20.61.10.231.05479.270.239.855.0 Comparative Example 1 1 20.21.22.41.10.311.10286.659.941.768 .6 Comparative Example 2 10.2 12.4 1.10.2 11.1 73.6 55.3 42.9 91.2 Comparative Example 3 1.20.2 1.6 2.4 1.10.1 61.1 22 72.8 50.7 47.3 11 3.3 Comparative Example 4 1.6 0.2 1.6 2.4 1.10.2 31.1 34 65 47.9 42.2 61.3 Comparative Example 5 1.20.2 1.22 40.8 0.1 91.1 47 72.1 53.3 45.4 11 5.9

[0377] In Table 7, the cycle characteristics are the result of performing 800 cycles at 45°C, and the rapid charging is the result of performing 400 cycles at 25°C for 20 minutes. In the following, the upper cathode slurry and the lower cathode slurry are each coated onto a cathode current collector and dried, and are provided as an upper cathode composite layer and a lower cathode composite layer, respectively.

[0378] Referring to Table 7, it was confirmed that Examples 1 to 11 exhibited superior electrode coating adhesion and resistance compared to Comparative Examples 1 to 5. Additionally, it was confirmed that Examples 1 to 11 showed higher cycle characteristics and rapid charging characteristics compared to Comparative Examples 1 to 5.

[0379] Comparing Examples 1 to 4, similarly excellent adhesion, resistance, cycle characteristics, and rapid charging characteristics were exhibited even when the CMC content of the upper cathode slurry was varied from 1.4 to 1.8 wt%. Furthermore, among these, Examples 3 and 4 exhibited the best cycle characteristics and rapid charging characteristics.

[0380] When comparing Example 1 and Example 5, when the CMC content of the lower cathode slurry was varied, the cycle characteristics were similar, but the rapid charging characteristics of Example 5 were superior to those of Example 1.

[0381] When comparing Example 4 and Example 6, when the CMC content of the lower cathode slurry was varied, the cycle characteristics were similar, but the rapid charging characteristics of Example 4 were slightly better than those of Example 6.

[0382] In addition, when comparing Example 3 with Examples 7, 8, and 9, when the CMC and SBR contents included in the upper cathode slurry were the same, excellent adhesion and resistance characteristics were exhibited when the CMC included in the lower cathode slurry was 1.2 wt%, and when the SBR included in the lower cathode slurry was 1.8 wt%, 1.4 wt%, and 1 wt%. In other words, it was confirmed that reducing the SBR content of the lower cathode slurry was particularly advantageous for rapid charging characteristics.

[0383] Examples 8 and 10 represent cases where the content of CMC and SBR included in the upper and lower cathode slurries, respectively, was kept the same, while only the coating speed was varied. Example 10 had a coating residence time of 0.8 min, which is faster than Example 8. When comparing Example 8 and Example 10, it was confirmed that the coating adhesion, resistance, cycle characteristics, and rapid charging characteristics were all similar. In other words, the cathode for a secondary battery according to this example maintained excellent performance even when coated within a short time, as in Example 10, thus providing the advantage of being able to increase the process speed.

[0384] Examples 9 and 11 are the results of varying only the SBR content included in the lower anode slurry, while varying the CMC and SBR content of the upper and lower layers, respectively. When comparing Example 9 and Example 11, the coating adhesion, battery resistance, cycle characteristics, and rapid charging characteristics were all relatively superior in Example 9 compared to Example 11. That is, according to the embodiments of the present disclosure, it was confirmed that SBR migration hardly occurs even when the SBR content in the lower anode slurry is high, and that the effect of SBR is fully manifested, and that the performance of the secondary battery is maximized when a certain level of SBR content is satisfied. In other words, according to the embodiments of the present disclosure, SBR within a predetermined range is included in the upper and lower anode slurries, and by simultaneously controlling the content and physical properties of each material included in the upper and lower anode slurries, migration caused by these SBRs can be prevented, thereby further improving the performance of the secondary battery.

[0385] As in Comparative Example 1, when the CMC content of the upper cathode slurry is low and the SBR content of the lower cathode slurry is high, it was confirmed that the adhesion is at a decent level, but the resistance is high and the cycle characteristics and rapid charging characteristics are low.

[0386] Compared to Comparative Example 2 and Example 5, it was confirmed that when the CMC content included in the upper cathode slurry was low, the adhesion, resistance, cycle characteristics, and rapid charging characteristics were all low.

[0387] In Comparative Example 3 and Example 3, the SBR content of the upper and lower cathode slurries was kept the same, but the CMC content was reversed for verification. It was confirmed that Example 3 showed improved adhesion, resistance, cycle characteristics, and rapid charging characteristics compared to Comparative Example 3.

[0388] When comparing Comparative Example 4 and Example 3, the CMC and SBR content in the upper cathode slurry are the same, and only the CMC content in the lower cathode slurry is different.

[0389] When comparing Example 3 and Comparative Example 4, even when the CMC and SBR contents in the upper cathode slurry are the same, when the CMC content in the lower cathode slurry is higher at 1.6 wt%, the adhesion strength is lower and the resistance is higher.

[0390] Comparative Example 5 is a case in which coating was performed with a shorter coater residence time of 0.8 min compared to Comparative Examples 1 to 4. Comparative Example 1 and Comparative Example 5 have the same CMC and SBR content in the upper and lower cathode slurries, but differ only in the coater residence time; it was confirmed that the coating adhesion, resistance, cycle characteristics, and rapid charging performance were degraded. That is, in Comparative Example 5, the coating adhesion was reduced as the coater residence time was relatively reduced, and as a result, the resistance increased and the electrochemical characteristics of the secondary battery deteriorated.

[0391] In an embodiment according to the present disclosure, by maintaining the coater residence time within a predetermined range, the upper and lower cathode slurries are stably coated onto the current collector, and improved electrochemical properties are exhibited.

[0392] In Table 7, it was confirmed that when adhesion and resistance characteristics were excellent, cycle characteristics and rapid charging characteristics also exhibited similarly excellent characteristics.

[0393] As mentioned above, it was confirmed that adhesion, resistance, cycle characteristics, and rapid charging characteristics are excellent when the content of SBR in the lower cathode slurry is greater than the content of SBR in the upper cathode slurry, the content of CMC in the lower cathode slurry is smaller than the content of CMC in the upper cathode slurry, and the content of CMC in the lower cathode slurry is higher than the content of SBR in the upper cathode slurry.

[0394] In addition, when the content of CMC in the upper cathode slurry was 0.2 wt% or more higher than the content of CMC in the lower cathode slurry, excellent electrochemical characteristics were exhibited. In terms of electrochemical characteristics, it was confirmed that there was a significant difference, particularly in rapid charging characteristics, compared to cycle characteristics.

[0395] That is, in the negative electrode for a secondary battery according to the present embodiment, SBR migration does not occur between the upper negative electrode composite layer and the lower negative electrode composite layer, so the SBR content in the upper negative electrode slurry and the lower negative electrode slurry is maintained, and as a result, excellent adhesion and resistance characteristics were exhibited.

[0396] In contrast, in the comparative example, even when the SBR content in the lower cathode slurry was high, SBR migration occurred during the manufacturing process, and as a result, it was confirmed that the adhesion and resistance characteristics deteriorated. Furthermore, in the comparative example, SBR migrated from the bottom to the top, making the upper cathode composite layer an insulator and significantly degrading the metal filling characteristics.

[0397] Figures 8 and 9 show the results of EDS mapping of the constituent components on both sides of the sample cathodes for Example 10 and Comparative Example 5 using an energy dispersive X-ray spectroscopy (EDS, Flatquad) detector. Line profiles were determined from the surface to the thickness direction for the upper and lower cathode composite layers of Example 10 and Comparative Example 5. After plotting the Os intensity, which is the Os-Mαβ value, the profiles were fitted based on the central cathode current collector. Gaussian curves of the Os distribution of the cathode cross-sections of Example 10 and Comparative Example 5 were obtained, and FWHM values ​​were calculated. The average of the values ​​obtained from at least five repetitions is presented as the EDS analysis result in Table 7. Although Figures 8 and 9 illustrate Example 10 and Comparative Example 5, values ​​were obtained for other examples and comparative examples using the same method.

[0398] In the case of Example 10, it was confirmed that no SBR migration occurred from the lower cathode composite layer to the upper cathode composite layer. On the other hand, in Comparative Example 5, SBR migration occurred from the lower cathode composite layer to the upper cathode composite layer, and as a result, the FWHM value obtained from the Gaussian curve was significantly high at 115.9 μm.

[0399] When comparing Comparative Example 5 and Example 10 (FWHM value 41.4 μm), it was confirmed that Comparative Example 5 had lower coating adhesion, higher resistance, and all performance characteristics such as cycle characteristics and rapid charging were degraded compared to Example 10.

[0400] Looking at the location where the average value appears on the Gaussian curve in Examples 1 to 11 and Comparative Examples 1 to 5, it was confirmed that in Examples 1 to 11, it appeared at 40% or less, whereas in Comparative Examples 1 to 5, it appeared in an area exceeding 40%.

[0401] In addition, the FWHM values ​​of Examples 1 to 11 were shown to be 16 μm to 55 μm, while the FWHM values ​​of Comparative Examples 1 to 5 were shown to be high, ranging from 61.3 μm to 115.9 μm.

[0402] That is, as in Examples 1 to 11, it was confirmed that SBR migration hardly occurs with a Gaussian mean value of 40% or less and a low FWHM value.

[0403] Table 8 shows the results of the thermogravimetric analysis (TGA) of Examples 1 to 11 and Comparative Examples 1 to 5.

[0404] Classification Upper layer cathode slurry (wt%) Lower layer cathode slurry (wt%) Coater residence time (min) △CMC content (Upper layer - Lower layer) (wt%) Weight loss ratio of the entire layer (TW 1+2 %) Weight loss ratio of upper layer (TW2%) Weight loss ratio of upper layer / total layer (TW2 / TW 1+2)CMCSBRCMCSBR Example 1 1.40.2 1.22.41.10.2 1.65 1.57 0.95 Example 2 1.50.2 1.22.41.10.3 1.68 1.29 0.77 Example 3 1.60.2 1.22.41.10.41.61 0.98 0.61 Example 4 1.80.2 1.22.41.10.61.64 0.91 0.55 Example 5 1.40.2 12.41.10.41.671.040.62 Example 61.80.21.42.41.10.41.661.010.61 Example 71.60.21.21.81.10.41.590.950.60 Example 81.60.21.21.41.10.41.581.420.90 Example 91.60.21.211.10.41.220.880.72 Example 101.60.21.21.40.80.41.551.360.88 Example 111.60.21.20.61.10.40.850.750.88 Comparative Example 11.20.21.22.41.101.661.791.08 Comparative Example 210.212.41.101.681.811.08 Comparative Example 31.20.21.62.41.1-0.41.641.921.17 Comparative Example 41.60.21.62.41.101.651.71.03 Comparative Example 51.20.21.22.40.801.671.941.16

[0405] In Table 8, the weight loss ratio of SBR was determined using TGA in the range of 300°C to 500°C for Examples 1 to 11 and Comparative Examples 1 to 5.

[0406] As in Examples 1 to 11, it was confirmed that when the difference in CMC between the upper cathode composite layer and the lower cathode composite layer was 0.2 wt% or more, the weight loss ratio in the upper layer decreased. On the other hand, in Comparative Examples 1 to 5, when the difference in CMC between the upper cathode composite layer and the lower cathode composite layer was 0 wt% or less, the weight loss ratio of the upper layer and the entire layer increased compared to Examples 1 to 11.

[0407] That is, in the case of Examples 1 to 11, the weight loss ratio of the upper layer relative to the entire layer (TW2 / TW) in the thermogravimetric analysis results 1+2) It was confirmed that SBR migration from the lower cathode composite layer to the upper cathode composite layer can be effectively prevented when this is 0.95 or less.

[0408] Table 9 shows the results of confirming the pyrolysis-gas chromatography (Py-GC) analysis of Examples 1 to 11 and Comparative Examples 1 to 5.

[0409] Classification Upper layer cathodic slurry (wt%) Lower layer cathodic slurry (wt%) Coater residence time (min) Ratio of styrene peak area to sample weight of the entire layer (GW 1+2 )Ratio of styrene peak area to sample weight in the upper layer (GW2) Ratio of styrene peak area to sample weight in the upper layer / total layer (GW2 / GW 1+2)CMCSBRCMCSBR Example 1 1.40.21.22.41.114,954,77614,745,1260.99 Example 2 1.50.21.22.41.115,158,11212,858,4320.85 Example 3 1.60.21.22.41.115,058,05211,002,9420.73 Example 4 1.80.21.22.41.115,397,541 10,552,6420.69 Example 5 1.40.2 1.41.1 14,995,479 11,825,4320.79 Example 6 1.80.2 1.42.41.1 15,051,466 11,075,246 0.74 Example 7 1.60.2 1.2 1.81.1 10,833,4828,089,465 0.75 Example 8 1.60.2 1.2 1.41.1 18,126,9077,29 2,3810.90 Example 9 1.60.21.21 1.17,227,1535,508,547 0.76 Example 10 1.60.21.21 1.40.88,462,857 7,165,752 0.85 Example 11 1.60.21.20.61.15,015,2134,490,948 0.90 Comparative Example 11.20.21.22 1.41.115,354,776 18,922,270 1.23 Comparative Example 2 10.2 12.4 1.1 15,342,556 17,952,574 1.17 Comparative Example 3 1.2 0.2 1.6 2.4 1.1 14,897,823 18,995,248 1.28 Comparative Example 4 1.6 0.2 1.6 2.4 1.1 15,286,722 16,963,812 1.11 Comparative Example 5 1.2 0.2 1.2 2.4 0.8 14,998,537 20,486,775 1.37

[0410] In Table 9, SBR present in the upper and lower cathode composite layers of Examples 1 to 11 and Comparative Examples 1 to 5 was confirmed using pyrolysis-gas chromatography. Specifically, styrene (retention time around 7 min, 104 m / z) was detected by the pyrolysis-gas chromatography, and the content of the styrene-based SBR binder was evaluated through the peak area of ​​each product. In Table 8, the styrene peak area of ​​the entire layer (GW 1+2The styrene peak area (GW2) of the upper layer and the value obtained by integrating the graphs are each divided by the weight of the sample being analyzed, and correspond to the area per weight value.

[0411] Samples were prepared, and the SBR content of the entire layer obtained by pyrolysis-gas chromatography was verified for the entire layer (upper and lower cathodic composite layers) and the upper cathodic composite layer respectively, and expressed as a ratio.

[0412] In the case of Examples 1 to 11, the SBR content of the upper layer relative to the entire layer was found to be 1 or less, whereas in Comparative Examples 1 to 5, it was found to be relatively high. That is, in Comparative Examples 1 to 5, a phenomenon occurred in which the SBR contained in the lower cathode composite layer migrated to the upper layer, and as a result, it was confirmed that the ratio in the upper layer was high.

[0413] That is, in the case of Examples 1 to 11, the ratio of the normalized styrene peak area of ​​the upper layer to the entire layer in the pyrolysis-gas chromatography analysis results (GW2 / GW 1+ 2) It was confirmed that SBR migration from the lower cathode composite layer to the upper cathode composite layer can be effectively prevented when this is 0.99 or less.

[0414] Table 10 shows the cathode loading level of 13.5 mg / cm² for Examples 12 to 15 and Comparative Example 6. 2 This is the result of verifying the electrode adhesion, resistance, cycle characteristics, and rapid charging characteristics in that case.

[0415] Figure 10 shows the results of EDS analysis after staining the cross-section of the cathode composite with OsO4 following the cycle of Example 13. Figure 11 shows the results of EDS analysis after staining the cross-section of the cathode composite with OsO4 following the cycle of Comparative Example 6.

[0416] Classification Upper Cathode Slurry (wt%) Lower Cathode Slurry (wt%) Coater Residence Time (min) Coating Adhesion (N / 18mm) Battery Resistance (mOhm) Cycle Characteristics (%, ~800 cycles, 45℃) Fast Charging (%, ~400 cycles, 25℃, 22.5 min) EDS Analysis 1 (Average Value Location %) EDS Analysis 2 (FWHM μm)CMCSBRCMCSBR Example 1 2 1.60.41.22.41.10.521.17285.486.737.741.6 Example 1 3 1.60.41.21.81.10.411.13986.788.337.545.2 Example 1 4 1.70.41.21.81.10.431.14386.690.936.941.5 Example 1 5 1.80.41.21.81.10.421.14585.990.636.838.9 Comparative Example 6 1.20.41.22.41.10.291.22186.261.241.4103.3

[0417] As in Examples 12 to 15, the cathode loading level is 13.5 mg / cm² 2 It was confirmed that even when the amount was increased, the adhesion, resistance, and rapid charging characteristics could be excellently controlled depending on the CMC and SBR content included in the upper and lower cathode composite layers.

[0418] When comparing Examples 12 to 15, there were slight differences in metal filling characteristics depending on the SBR content of the upper cathode composite layer, but all showed excellent values.

[0419] In addition, when comparing Example 13 and Comparative Example 6, it was confirmed that when the CMC content of the upper cathode composite layer was lowered and the SBR content of the lower cathode composite layer was increased, the adhesion strength was low despite the high SBR content of the lower cathode composite layer. This is believed to be because SBR migration occurred in Comparative Example 6 during the manufacturing process.

[0420] Referring to FIGS. 10 and FIGS. 11, the location of the Gaussian average value (B, the length of the portion where the average value obtained by the Gaussian curve appears from the surface of the cathode current collector) with respect to the total thickness of the cross-section of the cathode (A, the total length from the surface of the cathode current collector to the surface of the upper cathode composite layer) could be confirmed. Looking at the location of the Gaussian average value, it was confirmed that in the case of Example 13, it appeared in the approximately 37.5% region, whereas in Comparative Example 6, it appeared in the 41.4% region.

[0421] In addition, in Table 10, it was confirmed that Examples 12 to 15 appeared in the region where the Gaussian mean value was approximately 40% or less, whereas Comparative Example 6 appeared in the region where it was greater than 40%.

[0422] In addition, it was confirmed that the FWHM values ​​of Examples 12 to 15 ranged from 38.9 μm to 45.2 μm, while the FWHM value of Comparative Example 6 was 103.3 μm, which is a high value.

[0423] That is, Examples 12 to 15 showed a Gaussian mean value of 40% or less and a low FWHM value, and almost no SBR migration occurred, and as a result, both cycle characteristics and rapid charging characteristics were superior to Comparative Example 6.

[0424] Table 11 shows the cathode loading level of 15.0 mg / cm² for Examples 16 to 19 and Comparative Example 7. 2 This is the result of verifying the electrode adhesion, resistance, cycle characteristics, and rapid charging characteristics in that case.

[0425] Classification Upper Cathode Slurry (wt%) Lower Cathode Slurry (wt%) Coater Residence Time (min) Coating Adhesion (N / 18mm) Battery Resistance (mOhm) Cycle Characteristics (%, ~800 cycles, 45℃) Fast Charging (%, ~400 cycles, 25℃, 25 min) EDS Analysis 1 (Average Value Location %) EDS Analysis 2 (FWHM μm)CMCSBRCMCSBR Example 16 1.60.41.22.41.250.491.22484.386.638.844.3 Example 17 1.60.41.21.81.250.411.17786.288.938.548.3 Example 18 1.70.41.21.81.250.431.18486.49137.147.0 Example 19 1.80.41.21.81.250.421.18886.290.53743.2 Comparative Example 7 1.20.41.22.41.250.261.28685.959.648.4163.8

[0426] When comparing Examples 12 to 15 of Table 10 with Examples 16 to 19 of Table 11, it was confirmed that in the case of Examples 16 to 19, the adhesion strength, resistance, and rapid charging characteristics were similarly excellent even when the cathode loading level was increased.

[0427] In addition, when comparing Example 17 with Comparative Example 7, the adhesion strength was low even when the SBR content of the lower cathode composite layer was high, as in Comparative Example 7. This is believed to be because some of the SBR in the lower cathode composite layer migrated during the manufacturing process.

[0428] Looking at the location where the average value appears on the Gaussian curve in Examples 16 to 19 and Comparative Example 7, it was confirmed that in Examples 16 to 19, it appeared at 40% or less, whereas in Comparative Example 7, it appeared in the 48.4% range.

[0429] In addition, it was confirmed that the FWHM values ​​of Examples 16 to 19 were 43.2 μm to 48.3 μm, and the FWHM value of Comparative Example 7 was lower than 163.9 μm.

[0430] That is, as in Examples 16 to 19, when the Gaussian average value is 40% or less and the FWHM value is low, SBR migration hardly occurs, and both cycle characteristics and rapid charging characteristics were superior to Comparative Example 7.

[0431] Table 12 shows the cathode loading level of 17.0 mg / cm² for Examples 20 to 23 and Comparative Example 8. 2 This is the result of verifying the electrode adhesion, resistance, cycle characteristics, and rapid charging characteristics in that case.

[0432] Classification Upper Cathode Slurry (wt%) Lower Cathode Slurry (wt%) Coater Residence Time (min) Coating Adhesion (N / 18mm) Battery Resistance (mOhm) Cycle Characteristics (%, ~800 cycles, 45℃) Fast Charging (%, ~400 cycles, 25℃, 30 min) EDS Analysis 1 (Average Value Location %) EDS Analysis 2 (FWHM μm)CMCSBRCMCSBR Example 201.60.41.22.41.250.461.34180.78338.650.8 Example 211.60.41.21.81.250.371.24482.685.138.255.0 Example 221.70.41.21.81.250.41.24783.286.737.449.5 Example 231.80.41.21.81.250.421.24983.589.936.846.2 Comparative Example 81.20.41.22.41.250.231.40282.153.754.4238.1

[0433] When comparing Examples 16 to 19 of Table 11 with Examples 20 to 23 of Table 12, in the case of Examples 20 to 23, even when the cathode loading level was increased, the resistance increased slightly, but the adhesion strength and rapid charging characteristics showed similarly excellent characteristics.

[0434] In addition, when comparing Comparative Example 7 and Comparative Example 8, it was confirmed that Comparative Example 8 showed lower adhesion, resistance, and rapid charging at a relatively high loading level.

[0435] In other words, it was confirmed that the performance degradation of the secondary battery due to SBR migration became more significant as the loading level increased. On the other hand, in the embodiments of the present disclosure, similar characteristics of the secondary battery were exhibited even at high loading levels, which is judged to be because SBR migration did not occur.

[0436] The FWHM values ​​and Gaussian mean values ​​of Examples 20 to 23 were all lower than those of Comparative Example 8. As a result, in Examples 20 to 23, almost no SBR migration occurred, and both the cycle characteristics and rapid charging characteristics were superior to those of Comparative Example 8.

[0437] That is, when the SBR content of the lower cathode slurry was increased as in Example 20, and when the CMC content of the upper cathode slurry was increased as in Examples 22 and 23, no migration of SBR occurred, and the performance of the secondary battery was similarly excellent.

[0438] Table 13 shows the results of the thermogravimetric analysis (TGA) of Example 8, Example 24, Comparative Example 1, and Comparative Example 9.

[0439] Classification Upper layer cathode slurry (wt%) Lower layer cathode slurry (wt%) Coater residence time (min) △CMC content (Upper layer - Lower layer) (wt%) Weight loss ratio of the entire layer (TW 1+2 ) Upper layer weight loss ratio (TW2) Upper layer / Total layer weight loss ratio (TW2 / TW 1+2 )CMCSBR or SACMCSBR or SA Example 8 1.60.21.21.41.10.41.58 1.42 0.90 Example 2 4 1.60.21.21.41.10.41.56 1.33 0.85 Comparative Example 1 1.20.21.22.41.10 1.66 1.79 1.08 Comparative Example 9 1.20.21.22.41.10 1.67 1.74 1.04

[0440] Referring to Table 13, when other conditions were kept the same and only the type of rubber-based binder in the upper and lower cathode slurries was changed from SBR to SA, Examples 8 and 24 exhibited similar characteristics. In addition, Comparative Examples 1 and 9 showed similar results, and it was confirmed that the weight loss ratio of the upper layer was higher compared to Examples 8 and 24. In other words, even when SA, a type other than SBR, was used as the rubber-based binder, a similar trend to that described above was observed.

[0441] Table 14 shows the results of the pyrolysis-gas chromatography (Py-GC) analysis of Example 8, Example 24, Comparative Example 1, and Comparative Example 9.

[0442] Classification Upper layer cathodic slurry (wt%) Lower layer cathodic slurry (wt%) Coater residence time (min) Ratio of styrene peak area to sample weight of the entire layer (GW 1+2 )Ratio of styrene peak area to sample weight in the upper layer (GW2) Ratio of styrene peak area to sample weight in the upper layer / total layer (GW2 / GW 1+2 )CMCSBR or SACMCSBR or SA Example 8 1.60.21.21.41.18,126,9077,292,3810.90 Example 2 4 1.60.21.21.41.18,382,5527,685,8210.92 Comparative Example 1 1.20.21.22.41.115,354,77618,922,2701.23 Comparative Example 9 1.20.21.22.41.115,153,84617,954,2851.18

[0443] In Table 14, SBR present in the upper and lower cathode composite layers of Examples 8, 24, Comparative Example 1, and Comparative Example 9 was identified using pyrolysis-gas chromatography. Specifically, in Examples 8 and 24, SA was used instead of SBR as the rubber-based binder, respectively, and in Comparative Examples 1 and 9, measurements were taken by similarly changing only the type of rubber-based binder to SA.

[0444] Referring to Table 14, similar results were obtained in Examples 8 and 24 of pyrolysis-gas chromatography, and similar results were obtained in Comparative Examples 1 and 9.

[0445] In other words, it was confirmed that similar characteristics to those described above were exhibited even when the type of rubber binder was changed.

[0446] Those skilled in the art of the present disclosure will understand that the various embodiments described above specifically illustrate the following various aspects.

[0447] Aspect 1. In a negative electrode for a secondary battery according to one aspect of the present disclosure, the negative electrode for the secondary battery comprises: a negative current collector; a first negative composite layer provided on the negative current collector; and a second negative composite layer provided on the first negative composite layer; wherein the first negative composite layer comprises a first negative active material, a first rubber-based binder, and a first cellulose derivative, and the second negative composite layer comprises a second negative active material, a second rubber-based binder, and a second cellulose derivative, and the thermogravimetric analysis (TGA) result may satisfy the following equation 1.

[0448] (Relationship 1) TW2 / TW 1+2 ≤ 0.95

[0449] (In Equation 1, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and TW2 is the average of the weight loss ratio of the second cathode composite layer in the temperature range of 300 ℃ to 500 ℃ over an area corresponding to 40% of the total depth of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer.)

[0450] Aspect 2. In a negative electrode for a secondary battery according to Aspect 1 of the present disclosure, in the above relationship 1, TW2 / TW 1+2It can be 0.9 or less.

[0451] Aspect 3. In a negative electrode for a secondary battery according to aspect 1 or 2 of the present disclosure, the thermogravimetric analysis (TGA) result may further satisfy the following relationship 2.

[0452] (Equation 2) 0.85 ≤ TW 1+2

[0453] (In Equation 2, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit is %)

[0454] Aspect 4. In a negative electrode for a secondary battery according to one aspect of the present disclosure, the negative electrode for the secondary battery comprises: a negative current collector; a first negative composite layer provided on the negative current collector; and a second negative composite layer provided on the first negative composite layer; wherein the first negative composite layer comprises a first negative active material, a first rubber-based binder, and a first cellulose derivative, and the second negative composite layer comprises a second negative active material, a second rubber-based binder, and a second cellulose derivative, and the pyrolysis-gas chromatography (Py-GC) result may satisfy the following equation 3.

[0455] (Relationship 3) GW2 / GW 1+2 ≤ 0.99

[0456] (In Equation 3, GW 1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 is a measured value in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers in the direction from the surface of the second cathode composite layer toward the first cathode composite layer, and GW2 and GW 1+2 is the value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight.)

[0457] Aspect 5. In the negative electrode for a secondary battery according to Aspect 4 of the present disclosure, in the relationship 3, GW2 / GW 1+2 It can be 0.9 or less.

[0458] Aspect 6. In a negative electrode for a secondary battery according to aspect 4 or 5 of the present disclosure, the pyrolysis-gas chromatography (Py-GC) result may further satisfy the following relationship 4.

[0459] (Relationship 4) GW 1+2 ≥ 5,000,000

[0460] (In Equation 4, GW 1+2 is a measured value across the entire area of ​​the first and second cathode composite layers.)

[0461] Aspect 7. In a negative electrode for a secondary battery according to any one of the preceding aspects, the content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first negative electrode composite layer, and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer may satisfy the following formulas 1 to 3.

[0462] (Equation 1) RB1 > RB2

[0463] (Equation 2) CD1 < CD2

[0464] (Equation 3) CD1 > RB2

[0465] (In Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.)

[0466] Aspect 8. In a negative electrode for a secondary battery according to any one of the preceding aspects, the difference value (CD2-CD1) between the content of the first cellulose derivative (CD1) included in the first negative electrode composite layer and the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer may be 0.2 wt% or more.

[0467] Aspect 9. In a negative electrode for a secondary battery according to any one of the preceding aspects, the average composite density of the first negative electrode composite layer and the second negative electrode composite layer is 1.5 g / cc to 1.7 g / cc, and the content of the second rubber-based binder in the second negative electrode composite layer may be 0.2 wt% or more.

[0468] Aspect 10. In a negative electrode for a secondary battery according to any one of the preceding aspects, the coating weight per unit area (Loading Weight, LW) for the entire first and second negative electrode composite layer may be 4 mg / cm² to 20 mg / cm².

[0469] Aspect 11. In a negative electrode for a secondary battery according to any one of the preceding aspects, the content of the first rubber-based binder (RB1) included in the first negative electrode composite layer is 1.0 wt% to 2.4 wt%, the content of the second rubber-based binder (RB2) included in the second negative electrode composite layer is 0.2 wt% to 0.8 wt%, the content of the first cellulose derivative (CD1) included in the first negative electrode composite layer is 0.8 wt% to 1.4 wt%, and the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer is 1.2 wt% to 1.8 wt%.

[0470] Aspect 12. In a negative electrode for a secondary battery according to any one of the preceding aspects, the first and second rubber-based binders may each be one or more selected from the group consisting of a styrene-butadiene-based binder, an acrylated styrene-butadiene-based binder, an acrylonitrile-styrene-butadiene copolymer-based binder, a styrene-acrylate-based binder, and a styrene-butadiene-styrene-based binder.

[0471] Aspect 13. In a negative electrode for a secondary battery according to any one of the preceding aspects, the first and second cellulose derivatives may each be one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethylcellulose (CMC-Li), sodium salt of carboxymethylcellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose.

[0472] Side 14. In a negative electrode for a secondary battery according to any one of the preceding sides, the average coating adhesion of the first and second negative electrode composite layers to the negative electrode current collector may be 0.29 N / 18 mm or more.

[0473] Aspect 15. In a method for manufacturing a negative electrode for a secondary battery according to another aspect of the present disclosure, the method for manufacturing a negative electrode for a secondary battery comprises: a first negative electrode slurry comprising a first solvent, a first conductive material, a first rubber-based binder, a first cellulose derivative, and a first negative electrode active material; a slurry preparation step comprising preparing a second negative electrode slurry comprising a second solvent, a second conductive material, a second rubber-based binder, a second cellulose derivative, and a second negative electrode active material; and a negative electrode composite layer provision step comprising coating the first negative electrode slurry and the second negative electrode slurry onto a negative electrode current collector, drying and rolling to sequentially provide a first negative electrode composite layer and a second negative electrode composite layer on the negative electrode current collector; wherein the thermogravimetric analysis (TGA) results may satisfy the following equation 1.

[0474] (Relationship 1) TW2 / TW 1+2 ≤ 0.95

[0475] (In Equation 1, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and TW2 is the average of the weight loss ratio of the second cathode composite layer in the temperature range of 300 ℃ to 500 ℃ over an area corresponding to 40% of the total depth of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer.)

[0476] Aspect 16. In the method for manufacturing a negative electrode for a secondary battery according to the aforementioned Aspect 15, in the above-mentioned relationship Equation 1, TW2 / TW 1+2 It can be 0.9 or less.

[0477] Aspect 17. In the method for manufacturing a negative electrode for a secondary battery according to the aforementioned Aspect 15 or 16, the thermogravimetric analysis (TGA) result may further satisfy the following relationship 2.

[0478] (Equation 2) 0.85 ≤ TW 1+2

[0479] (In Equation 2, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit is %)

[0480] Aspect 18. In a method for manufacturing a negative electrode for a secondary battery according to another aspect of the present disclosure, the method for manufacturing a negative electrode for a secondary battery comprises: a first negative electrode slurry comprising a first solvent, a first conductive material, a first rubber-based binder, a first cellulose derivative, and a first negative electrode active material; a slurry preparation step comprising preparing a second negative electrode slurry comprising a second solvent, a second conductive material, a second rubber-based binder, a second cellulose derivative, and a second negative electrode active material; and a negative electrode composite layer provision step comprising coating the first negative electrode slurry and the second negative electrode slurry onto a negative electrode current collector, drying and rolling to sequentially provide a first negative electrode composite layer and a second negative electrode composite layer on the negative electrode current collector; and the pyrolysis-gas chromatography (Py-GC) result may satisfy the following equation 3.

[0481] (Relationship 3) GW2 / GW 1+2 ≤ 0.99

[0482] (In Equation 3, GW 1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 is a measured value in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers in the direction from the surface of the second cathode composite layer toward the first cathode composite layer, and GW2 and GW 1+2 is the value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight.)

[0483] Aspect 19. In the method for manufacturing a negative electrode for a secondary battery according to Aspect 18, in the above relationship Equation 3, GW2 / GW 1+2It can be 0.9 or less.

[0484] Side 20. In the method for manufacturing a negative electrode for a secondary battery according to Side 18 or 19, the pyrolysis-gas chromatography (Py-GC) result may further satisfy the following relationship 4.

[0485] (Relationship 4) GW 1+2 ≥ 5,000,000

[0486] (In Equation 4, GW 1+2 is a measured value across the entire area of ​​the first and second cathode composite layers.)

[0487] Aspect 21. In a method for manufacturing a negative electrode for a secondary battery according to any one of the aforementioned aspects, the content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first negative electrode composite layer, and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer may satisfy the following formulas 1 to 3.

[0488] (Equation 1) RB1 > RB2

[0489] (Equation 2) CD1 < CD2

[0490] (Equation 3) CD1 > RB2

[0491] (In Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.)

[0492] Aspect 22. In a method for manufacturing a negative electrode for a secondary battery according to any one of the aforementioned aspects, the difference value (CD2-CD1) between the content of the second cellulose derivative (CD1) included in the first negative electrode composite layer and the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer may be 0.2 wt% or more.

[0493] Aspect 23. In a method for manufacturing a negative electrode for a secondary battery according to any one of the aforementioned aspects, the first and second negative electrode slurries each have a viscosity of 6,000 cP to 11,000 cP, and the difference in solid content between the first and second negative electrode slurries may be 4% or less.

[0494] Aspect 24. In a method for manufacturing a negative electrode for a secondary battery according to any one of the aforementioned aspects, the first and second rubber-based binders may each be one or more selected from the group consisting of a styrene-butadiene-based binder, an acrylated styrene-butadiene-based binder, an acrylonitrile-styrene-butadiene copolymer-based binder, a styrene-acrylate-based binder, and a styrene-butadiene-styrene-based binder.

[0495] Aspect 25. In a method for manufacturing a negative electrode for a secondary battery according to any one of the aforementioned aspects, the first and second cellulose derivatives may each be one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethyl cellulose (CMC-Li), sodium salt of carboxymethyl cellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose.

[0496] Aspect 26. In a method for manufacturing a negative electrode for a secondary battery according to any one of the aforementioned aspects, in the step of providing the negative electrode composite layer, the first negative electrode slurry is coated on the negative electrode current collector, and the second negative electrode slurry is coated on the first negative electrode slurry, and then dried simultaneously to be manufactured.

[0497] Aspect 27. In a method for manufacturing a negative electrode for a secondary battery according to any one of the aforementioned aspects, in the step of providing the negative electrode composite layer, the first negative electrode slurry is coated on the negative electrode current collector and dried once, then the second negative electrode slurry is coated and dried twice.

[0498] Aspect 28. Another aspect of the present disclosure may include a secondary battery comprising a negative electrode for a secondary battery according to any one of the aforementioned aspects or a negative electrode for a secondary battery according to a method for manufacturing a negative electrode for a secondary battery.

[0499] A person skilled in the art to which this disclosure pertains will understand that this disclosure may be practiced in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of this disclosure is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalents thereof should be interpreted as being included within the scope of this disclosure.

Claims

1. Cathode current collector; A first cathode composite layer provided on the above-mentioned cathode current collector; and A second cathode composite layer provided on the first cathode composite layer; comprising The first cathode composite layer comprises a first cathode active material, a first rubber-based binder, and a first cellulose derivative, and The second cathode composite layer comprises a second cathode active material, a second rubber-based binder, and a second cellulose derivative, and A negative electrode for a secondary battery whose thermogravimetric analysis (TGA) results satisfy the following Equation 1: (Relationship 1) TW2 / TW 1+2 ≤ 0.95 (In relation 1, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and TW2 is the average weight loss ratio of the second cathode composite layer in a temperature range of 300°C to 500°C in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer.) 2. In Paragraph 1, In the above relationship 1, TW2 / TW 1+2 is a negative electrode for a secondary battery with a value of 0.9 or less.

3. In Paragraph 1, The above thermogravimetric analysis (TGA) results are a negative electrode for a secondary battery that further satisfies the following Equation 2: (Equation 2) 0.85 ≤ TW 1+2 (In relation 2, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit is %) 4. Cathode current collector; A first cathode composite layer provided on the above-mentioned cathode current collector; and A second cathode composite layer provided on the first cathode composite layer; comprising The first cathode composite layer comprises a first cathode active material, a first rubber-based binder, and a first cellulose derivative, and The second cathode composite layer comprises a second cathode active material, a second rubber-based binder, and a second cellulose derivative, and A negative electrode for a secondary battery whose pyrolysis-gas chromatography (Py-GC) results satisfy the following Equation 3: (Relationship 3) GW2 / GW 1+2 ≤ 0.99 (In relation 3, GW 1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 is a measured value in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer, and GW2 and GW 1+2 is the value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight.) 5. In Paragraph 4, In the above relationship 3, GW2 / GW 1+2 is a negative electrode for a secondary battery with a value of 0.9 or less.

6. In Paragraph 4, A negative electrode for a secondary battery in which the above pyrolysis-gas chromatography (Py-GC) results further satisfy the following relationship 4: (Relationship 4) GW 1+2 ≥ 5,000,000 (In relation 4, GW 1+2 is a measured value across the entire area of ​​the first and second cathode composite layers.) 7. In Paragraph 1 or 4, The content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first cathode composite layer, and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second cathode composite layer satisfy the following formulas 1 to 3 for a secondary battery cathode: (Equation 1) RB1 > RB2 (Equation 2) CD1 < CD2 (Equation 3) CD1 > RB2 (In Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.) 8. In Paragraph 1 or 4, A negative electrode for a secondary battery, wherein the difference value (CD2-CD1) between the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer and the content of the first cellulose derivative (CD1) included in the first negative electrode composite layer is 0.2 wt% or more.

9. In Paragraph 1 or 4, The average composite density of the first cathode composite layer and the second cathode composite layer is 1.5 g / cc to 1.7 g / cc, and A negative electrode for a secondary battery, wherein the content of the second rubber-based binder in the second negative electrode composite layer is 0.2 wt% or more.

10. In Paragraph 1 or 4, A negative electrode for a secondary battery, wherein the loading weight (LW) per unit area for the entire first and second negative electrode composite layers is 4 mg / cm² to 20 mg / cm².

11. In Paragraph 1 or 4, The content (RB1) of the first rubber-based binder included in the first cathode composite layer is 1.0 wt% to 2.4 wt%, and The content (RB2) of the second rubber-based binder included in the second cathode composite layer is 0.2 wt% to 0.8 wt%, and The content (CD1) of the first cellulose derivative included in the first cathode composite layer is 0.8 wt% to 1.4 wt%, and A negative electrode for a secondary battery, wherein the content (CD2) of the second cellulose derivative included in the second negative electrode composite layer is 1.2 wt% to 1.8 wt%.

12. In Paragraph 1 or 4, The first and second rubber-based binders are each one or more selected from the group consisting of a styrene-butadiene-based binder, an acrylated styrene-butadiene-based binder, an acrylonitrile-styrene-butadiene copolymer-based binder, a styrene-acrylate-based binder, and a styrene-butadiene-styrene-based binder, and are negative electrodes for a secondary battery.

13. In Paragraph 1 or 4, The first and second cellulose derivatives are each one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethyl cellulose (CMC-Li), sodium salt of carboxymethyl cellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose, respectively, for a negative electrode for a secondary battery.

14. In Paragraph 1 or 4, A negative electrode for a secondary battery having an average coating adhesion strength of the first and second negative composite layers to the negative current collector of 0.29 N / 18 mm or more.

15. A slurry preparation step for preparing a first cathode slurry comprising a first solvent, a first conductive material, a first rubber-based binder, a first cellulose derivative, and a first cathode active material; a second cathode slurry comprising a second solvent, a second conductive material, a second rubber-based binder, a second cellulose derivative, and a second cathode active material; and A step of providing a cathode composite layer by coating the first cathode slurry and the second cathode slurry onto a cathode current collector, drying and rolling to sequentially provide a first cathode composite layer and a second cathode composite layer on the cathode current collector; A method for manufacturing a negative electrode for a secondary battery in which the thermogravimetric analysis (TGA) results satisfy the following Equation 1: (Relationship 1) TW2 / TW 1+2 ≤ 0.95 (In relation 1, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and TW2 is the average weight loss ratio of the second cathode composite layer in a temperature range of 300°C to 500°C in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer.) 16. In Paragraph 15, In the above relationship 1, TW2 / TW 1+2 A method for manufacturing a negative electrode for a secondary battery having a value of 0.9 or less.

17. In Paragraph 15, The above thermogravimetric analysis (TGA) results further satisfy the following relationship 2, a method for manufacturing a negative electrode for a secondary battery: (Equation 2) 0.85 ≤ TW 1+2 (In relation 2, TW 1+2 is the average value of the weight loss ratio in the temperature range of 300 ℃ to 500 ℃ over the entire area of ​​the first and second cathode composite layers, and the unit is %) 18. A slurry preparation step for preparing a first cathode slurry comprising a first solvent, a first conductive material, a first rubber-based binder, a first cellulose derivative, and a first cathode active material; a second cathode slurry comprising a second solvent, a second conductive material, a second rubber-based binder, a second cellulose derivative, and a second cathode active material; and A step of providing a cathode composite layer by coating the first cathode slurry and the second cathode slurry onto a cathode current collector, drying and rolling to sequentially provide a first cathode composite layer and a second cathode composite layer on the cathode current collector; A method for manufacturing a negative electrode for a secondary battery in which the pyrolysis-gas chromatography (Py-GC) results satisfy the following relationship Equation 3: (Relationship 3) GW2 / GW 1+2 ≤ 0.99 (In relation 3, GW 1+2 is a measured value over the entire area of ​​the first and second cathode composite layers, and GW2 is a measured value in an area corresponding to 40% of the total depth of 100% of the first and second cathode composite layers, in the direction from the surface of the second cathode composite layer toward the first cathode composite layer, and GW2 and GW 1+2 is the value obtained by dividing the peak area obtained from pyrolysis-gas chromatography measured in each region by the sample weight.) 19. In Paragraph 18, In the above relationship 3, GW2 / GW 1+2 A method for manufacturing a negative electrode for a secondary battery having a value of 0.9 or less.

20. In Paragraph 18, A method for manufacturing a negative electrode for a secondary battery in which the above pyrolysis-gas chromatography (Py-GC) results further satisfy the following relationship 4: (Relationship 4) GW 1+2 ≥ 5,000,000 (In relation 4, GW 1+2 is a measured value across the entire area of ​​the first and second cathode composite layers.) 21. In Paragraph 15 or Paragraph 18, A method for manufacturing a negative electrode for a secondary battery, wherein the content of the first rubber-based binder (RB1) and the content of the first cellulose derivative (CD1) included in the first negative electrode composite layer, and the content of the second rubber-based binder (RB2) and the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer satisfy the following formulas 1 to 3: (Equation 1) RB1 > RB2 (Equation 2) CD1 < CD2 (Equation 3) CD1 > RB2 (In Equations 1 to 3, RB1 is the weight ratio of the first rubber-based binder based on the solid contained in the first cathode composite layer, RB2 is the weight ratio of the second rubber-based binder based on the solid contained in the second cathode composite layer, CD1 is the weight ratio of the first cellulose derivative based on the solid contained in the first cathode composite layer, and CD2 is the weight ratio of the second cellulose derivative based on the solid contained in the second cathode composite layer.) 22. In Paragraph 15 or Paragraph 18, A method for manufacturing a negative electrode for a secondary battery, wherein the difference value (CD2-CD1) between the content of the second cellulose derivative (CD2) included in the second negative electrode composite layer and the content of the second cellulose derivative (CD1) included in the first negative electrode composite layer is 0.2 wt% or more.

23. In Paragraph 15 or Paragraph 18, The first and second cathode slurries each have a viscosity of 6,000 cP to 11,000 cP, and A method for manufacturing a negative electrode for a secondary battery in which the difference in solid content between the first and second negative electrode slurries is 4% or less.

24. In Paragraph 15 or Paragraph 18, A method for manufacturing a negative electrode for a secondary battery, wherein the first and second rubber-based binders are each one or more selected from the group consisting of a styrene-butadiene-based binder, an acrylated styrene-butadiene-based binder, an acrylonitrile-styrene-butadiene copolymer-based binder, a styrene-acrylate-based binder, and a styrene-butadiene-styrene-based binder.

25. In Paragraph 15 or Paragraph 18, A method for manufacturing a negative electrode for a secondary battery, wherein the first and second cellulose derivatives are each one or more selected from the group consisting of carboxymethyl cellulose, lithium salt of carboxymethyl cellulose (CMC-Li), sodium salt of carboxymethyl cellulose (CMC-Na), carboxymethyl cellulose ether, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethyl cellulose.

26. In Paragraph 15 or Paragraph 18, In the step of providing the cathode composite layer above, A method for manufacturing a negative electrode for a secondary battery by coating the first negative electrode slurry onto the negative current collector, coating the second negative electrode slurry onto the first negative electrode slurry, and then drying simultaneously.

27. In Paragraph 15 or Paragraph 18, In the step of providing the cathode composite layer above, A method for manufacturing a negative electrode for a secondary battery by coating the first negative electrode slurry onto the negative electrode current collector and drying it once, then coating the second negative electrode slurry, and then drying it twice.

28. A secondary battery comprising a negative electrode for a secondary battery according to either Paragraph 1 or Paragraph 4.

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