Anode for lithium secondary battery and preparation method therefor

Abstract

The present invention relates to an anode and a preparation method therefor. The anode has excellent charging and discharging capacity due to the inclusion of a carbon-based anode active material together with a silicon-based anode active material, and by applying a magnetic field during preparation, the curvature of the entire anode active layer is reduced, and thereby, excellent rapid-charging performance is exhibited. In addition, even when a charge-discharge cycle of a secondary battery is repeatedly performed, the low electrical resistance can be maintained uniformly in the entire anode active layer, thereby suppressing deterioration, and thus, the anode exhibits excellent lifespan characteristics.

Description

Anode for lithium secondary battery and method for manufacturing the same

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

[0002] This application claims the benefit of priority to Republic of Korea Patent Application No. 10-2024-0097817, dated July 24, 2024, and Republic of Korea Patent Application No. 10-2025-0013944, dated February 4, 2025, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries are widely used not only in small devices like portable electronic devices, but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles and power storage systems. Recently, with growing concern for environmental issues, the demand base for high-capacity batteries is expanding, driven by the growth of the market for devices employing high-capacity batteries, such as electric vehicles and hybrid electric vehicles, which can replace fossil fuel-powered vehicles like gasoline and diesel, a major source of air pollution.

[0005] Lithium secondary batteries are rechargeable power generation devices consisting of a stacked structure of a cathode, separator, and anode. When charging a lithium secondary battery, a lithium desorption reaction occurs at the cathode, where lithium contained in the cathode active material is oxidized and released. A lithium insertion reaction also occurs at the anode, where lithium is reduced and inserted into the cathode active material. Generally, the desorption reaction in the cathode active material is faster than the insertion reaction in the anode active material. Therefore, the performance of a lithium secondary battery, including its charge / discharge speed, is primarily determined by the anode.

[0006] A material containing graphite is widely used as the negative electrode active material of the above negative electrode. The average potential when a material containing graphite releases lithium is about 0.2 V (Li / Li +) and the discharge potential shows a relatively flat pattern. Therefore, when graphite is used as an anode active material, the voltage of the secondary battery has the advantage of being high and constant. However, the electrical capacity per unit mass of the graphite material is small at 372 mAh / g. On the other hand, since the capacity of the current graphite material has been improved to be close to the theoretical capacity, further capacity increase is difficult. In addition, when graphite is used as an anode active material, the lithium ion insertion reaction proceeds at a slow rate, so there is a limitation that the rapid charging performance is low compared to cases where other anode active materials are applied.

[0007] To improve the high capacity and rapid charging performance of lithium secondary batteries, various anode materials are being studied. For example, silicon has recently been widely studied for its ability to reversibly adsorb and release large amounts of lithium through a compound formation reaction with lithium. Silicon has a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23), which is much higher than that of graphite-based materials, making it a useful anode material for high energy density and / or high capacity. However, silicon induces a large volume change (~300%) in the anode during charging of lithium secondary batteries and does not exhibit high high-rate discharge characteristics. Furthermore, silicon-based compounds applicable as anode active materials other than pure silicon (Si), such as silicon carbide (SiC), SiO, and silicon oxides such as SiO2, exhibit high electrical resistance under the temperature conditions encountered during charge and discharge of secondary batteries, potentially acting as resistors. This has the limitation that the lifespan characteristics of the negative electrode are significantly reduced as the cycle of the secondary battery progresses, as it accelerates the deterioration of the negative electrode active layer.

[0008] Therefore, there is a need for technological development for a lithium secondary battery cathode with excellent rapid charging performance and improved lifespan characteristics.

[0009]

[0010] [Prior Art Literature]

[0011] Republic of Korea Patent Publication No. 10-2024-0084840

[0012]

[0013] The purpose of the present invention is to provide a cathode having excellent rapid charging performance and excellent lifespan characteristics, and a method for manufacturing the same.

[0014]

[0015] The present invention,

[0016] negative current collector,

[0017] A first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material, and

[0018] A second negative electrode active layer is provided on the first negative electrode active layer and includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material;

[0019] The entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer provides a negative electrode in which the electrical resistance deviation between the points where the negative electrode active layer surface-based thickness ratio is 25±1% and 75±1% after 200 charge / discharge cycles is 1.0 Ω or less.

[0020] At this time, the silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but may include one or more of (0.5≤q≤2.5).

[0021] The above silicon-based negative electrode active material may be doped with one or more metals selected from the group consisting of Ni, Fe, Co, Ge, Li, Mg, Al, Ca, and Ti.

[0022] Additionally, the silicon-based negative electrode active material may be included in an amount of 1 wt% to 20 wt% based on the weight of the entire negative electrode active layer.

[0023] At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 It may further contain graphite in the range of ㎤ / g.

[0024] The total pore volume above is 1 × 10 -5 ㎤ / g to 1 × 10 -1 The content of graphite in the range of ㎤ / g may be 10 wt% to 70 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material.

[0025] In addition, the first carbon-based negative electrode active material may include at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0026] The above entire negative active layer can satisfy that the deviation between the average thickness measured at the BOL and the average thickness measured at the EOL of the lithium secondary battery is 30% or less based on the average thickness measured at the BOL.

[0027] The curvature of the entire cathode active layer may be in the range of 2.5 to 7.0.

[0028] Additionally, the average thickness of the entire cathode active layer may be in the range of 100 μm to 400 μm, and the average thickness of the second cathode active layer may have a ratio of 80% to 150% based on the average thickness of the first cathode active layer.

[0029]

[0030] Furthermore, the present invention,

[0031] A step (S1) of applying a first negative electrode slurry containing a first carbon-based negative electrode active material to at least one surface of a negative electrode current collector;

[0032] Step (S2) of applying a second negative electrode slurry containing a second carbon-based negative electrode active material and a silicon-based negative electrode active material on the applied first negative electrode slurry;

[0033] A step (S3) of applying a magnetic field to the applied first cathode slurry and the second cathode slurry, and

[0034] A step (S4) of drying the first cathode slurry and the second cathode slurry to which a magnetic field is applied to form a first cathode active layer and a second cathode active layer, respectively;

[0035] The entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer provides a method for manufacturing a negative electrode in which the electric resistance deviation between the points where the thickness ratio based on the surface of the negative electrode active layer is 25±1% and 75±1% after 200 charge / discharge cycles is 1.0 Ω or less.

[0036] The above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but may include one or more of (0.5≤q≤2.5).

[0037] At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 It may contain graphite in the range of ㎤ / g.

[0038] The above magnetic field can be performed with a magnetic field strength of 1,000 G to 10,000 G.

[0039]

[0040] The negative electrode according to the present invention has excellent charge / discharge capacity by including a silicon-based negative electrode active material together with a carbon-based negative electrode active material, and has excellent rapid charging performance because a magnetic field is applied during manufacturing to reduce the curvature of the entire negative electrode active layer. In addition, the negative electrode for a lithium secondary battery has the advantage of excellent life characteristics because even when the charge / discharge cycle of the secondary battery is repeated, low electrical resistance is uniformly maintained throughout the entire negative electrode active layer, thereby suppressing deterioration.

[0041]

[0042] Figure 1 is a cross-sectional view of a negative electrode schematically showing the ab-axis crystal plane state of a carbon-based negative electrode active material depending on the orientation of the carbon-based negative electrode active material. (a) is a case where the carbon-based negative electrode active material is not oriented, and (b) is a case where the carbon-based negative electrode active material is oriented.

[0043] Figure 2 is an image of a cross-section in the thickness direction of a cathode manufactured in Example 2 according to the present invention, taken with a scanning electron microscope (SEM), where (a) is a cross-section of the cathode active layer at BOL, and (b) is a cross-section of the cathode active layer at EOL.

[0044] Figure 3 is an image of a cross-section of a cathode active layer of a cathode manufactured according to the present invention, taken using a diffusion resistance atomic force microscope. (a) is a cross-section of a cathode active layer of Comparative Example 2, and (b) is a cross-section of a cathode active layer of Example 3.

[0045]

[0046] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0047] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0048] Also, in this specification, "average particle diameter (D 50 )" means the particle diameter at which the integrated value is 50% in the particle diameter distribution of the particles, and is also called the median diameter. The above average particle diameter can be measured by a method commonly applied in the art. For example, the above average particle diameter can be measured using an analysis device that utilizes a laser diffraction scattering particle size distribution measurement method.

[0049] In addition, in this specification, "the carbon-based negative electrode active material is oriented" means that the ab-axis crystal planes of the carbon-based negative electrode active material constituting the negative electrode active material particles are distributed to have a predetermined directionality with respect to the negative electrode current collector surface. This may be different from the case where the carbon-based negative electrode active material particles themselves are arranged to have a specific direction within the negative electrode active layer.

[0050] Additionally, “high alignment of the carbon-based negative electrode active material” may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high frequency with respect to the negative electrode current collector surface, and in some cases, may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle with respect to the negative electrode current collector surface.

[0051] Furthermore, in the present specification, "comprising as a main component" may mean including 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of the defined component with respect to the total weight (or total volume). For example, "comprising as a main component a carbon-based negative electrode active material" may mean including 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more with respect to the total 100 parts by weight of the negative electrode active layer, the negative electrode active material, and / or the negative electrode slurry. In some cases, it may mean that the entire negative electrode active layer, negative electrode active material and / or negative electrode slurry is comprised of 100 wt% carbon-based negative electrode active material.

[0052]

[0053] Hereinafter, the present invention will be described in more detail.

[0054]

[0055] cathode

[0056] The present invention,

[0057] negative current collector,

[0058] A first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material, and

[0059] A negative electrode is provided, which includes a second negative electrode active layer provided on the first negative electrode active layer and including a second carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0060]

[0061] The negative electrode according to the present invention refers to a negative electrode for a lithium secondary battery. The negative electrode includes a negative electrode active layer on at least one surface of a negative electrode current collector. The negative electrode active layer is a layer that implements electrical activity of the negative electrode, and is manufactured by applying a negative electrode slurry containing a negative electrode active material that implements an electrochemical redox reaction during charge / discharge of the battery to at least one surface of the negative electrode current collector, and then drying and rolling the same.

[0062] At this time, the negative electrode active layer has a two-layer structure in which a first negative electrode active layer and a second negative electrode active layer are sequentially laminated on a negative electrode current collector. The composition of each layer of the two-layer negative electrode active layer can be easily controlled. In this case, the performance of the negative electrode can be improved by controlling the type or content of the components contained in each layer according to a specific purpose, such as increasing the energy efficiency of the battery or improving the adhesion between the active layer and the current collector. For example, the negative electrode active layer may selectively include a silicon-based negative electrode active material having a high charge / discharge capacity of the battery only in the second negative electrode active layer in contact with the positive electrode. In addition, the negative electrode active layer may selectively include natural graphite having good adhesive properties as a negative electrode active material only in the first negative electrode active layer in contact with the negative electrode current collector, or may include a high content of a binder that provides binding properties to the components constituting the active layer.

[0063] In the present invention, the first negative electrode active layer includes a first carbon-based negative electrode active material, and the second negative electrode active layer includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0064] The above carbon-based negative electrode active material refers to a material whose main component is carbon atoms, and the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in each negative electrode active layer may be the same or different in type and / or content.

[0065] Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may include at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0066] The above carbon-based negative electrode active material may take the form of an assembly in which multiple particles are assembled. In this case, one graphite assembly may be formed by assembling 2 to 100 graphite particles, preferably 3 to 20. The graphite particles may refer to graphite crystal grains.

[0067] For example, the first carbon-based negative electrode active material may include natural graphite and artificial graphite. The artificial graphite may have a form of a graphite assembly in which 10 to 30 particles are aggregated. In addition, the mixing ratio of the natural graphite and the artificial graphite may be 5 to 50:50 to 95, or 30 to 49:51 to 70, based on weight. The first carbon-based negative electrode active material includes natural graphite and artificial graphite in the mixing ratio described above, thereby strengthening the adhesion between the negative electrode current collector and the negative electrode active layer, and maintaining the electrical resistance of the first negative electrode active layer low even when charge and discharge cycles of a lithium secondary battery are performed, thereby having the advantage of excellent life characteristics.

[0068] The second carbon-based negative electrode active material may include artificial graphite, and the artificial graphite may have the form of a graphite assembly in which 10 to 30 particles are aggregated. The artificial graphite has the advantage of superior high-rate charge / discharge performance and excellent life characteristics compared to natural graphite.

[0069] At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may further include low-expansion graphite. In the present invention, "low-expansion graphite" means graphite having low expansion characteristics when the secondary battery is charged. For example, when a secondary battery including graphite as the negative electrode active material is manufactured, if the expansion characteristics of the negative electrode active layer are low even when the secondary battery is subjected to repeated charge and discharge cycles, the graphite may be referred to as low-expansion graphite. The expansion characteristics of the low-expansion graphite can be determined through the change in thickness of the negative electrode active layer according to the charge and discharge cycle. Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion artificial graphite.

[0070] In the present invention, the low-expansion graphite may be manufactured by a cold isotropic pressing (CIP) method that uniformly applies pressure to each particle in all directions at a low temperature. The low-expansion graphite manufactured by the cold isotropic pressing method may be isotropic graphite. Since the isotropic graphite has low electrical resistance, resistance to thermal shock, and excellent mechanical properties, it can improve the life characteristics of the negative electrode itself.

[0071] In addition, the low-expansion graphite may refer to natural graphite particles coated with carbon. In this case, the low-expansion graphite has a carbon layer, which not only suppresses the expansion of the graphite when charging a secondary battery, but also has the advantage of significantly reducing the amount of impurities generated due to physical damage during the manufacturing of carbon-based negative electrode active materials and / or the manufacturing of negative electrodes using the same or the assembly of batteries.

[0072] The above low-expansion graphite has a high porosity within the graphite particles. Specifically, the low-expansion graphite can have a total pore volume that satisfies a predetermined range. For example, the low-expansion graphite has a porosity of 1 × 10 -5 ㎤ / g to 1 × 10 -1 The total pore volume can be in the range of ㎤ / g. The low expansion graphite is 5 × 10 -4㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 5 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -2 ㎤ / g; 5 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; or 5 × 10 -3 ㎤ / g to 2 × 10 -2 It can have a total pore volume in the range of ㎤ / g. The total pore volume of the low-expansion graphite can be measured through a BET measurement method using the adsorption of nitrogen (N2) gas. Since the low-expansion graphite can improve the volume expansion control ability of the negative electrode active material itself by satisfying the above-described range, the volume expansion characteristic can be implemented to be small when the secondary battery is charged. In addition, the low-expansion graphite having a total pore volume satisfying the above-described range can provide a path through which lithium ions and / or electrons can move inside the particle. Therefore, the low-expansion graphite can not only improve the charging speed of the secondary battery, but also effectively suppress the increase in electrical resistance of the negative electrode active layer according to the progress of the charge / discharge cycle of the secondary battery.

[0073] When the first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material includes low-expansion graphite, the low-expansion graphite may be included in a predetermined content ratio. Specifically, the low-expansion graphite may be included in a range of 10 wt% to 70 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material. For example, the low-expansion graphite may be included in a range of 10 wt% to 30 wt%; 20 wt% to 40 wt%; 15 wt% to 45 wt%; 10 wt% to 50 wt%; 30 wt% to 60 wt%; 50 wt% to 70 wt%; 40 wt% to 60 wt%; 15 wt% to 25 wt%; or 45 wt% to 69 wt% based on the total weight of the first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material.

[0074] The present invention can minimize the volume change of the first negative electrode active layer during charge and discharge of a secondary battery by controlling the content of low-expansion graphite within the above-described range when the first carbon-based negative electrode active material includes low-expansion graphite. Accordingly, the adhesive strength between the negative electrode current collector and the first negative electrode active layer can be improved. In addition, the low-expansion graphite controlled within the above-described content range can minimize the volume change of the first negative electrode active layer during charge and discharge of the secondary battery, thereby firmly fixing the negative electrode active material of the second negative electrode active layer. This can reduce the movement of the carbon-based negative electrode active material that occurs as the secondary battery cycles, thereby preventing an increase in the curvature of the second negative electrode active layer as the cycles progress and preventing a decrease in the orientation characteristics of the carbon-based negative electrode active material.

[0075] In addition, when the present invention includes low-expansion graphite in the second carbon-based negative electrode active material, electron movement and lithium movement can be improved by controlling the content of low-expansion graphite within the above-described range. Accordingly, the charge / discharge capacity of the second negative electrode active layer adjacent to the positive electrode active layer can be implemented high, and the volume expansion caused by the silicon-based negative electrode active material included in the second negative electrode active layer during charging of the lithium secondary battery can be significantly reduced. In addition, the increase in the curvature of the second negative electrode active layer can be suppressed until the end of the life of the lithium secondary battery. The curvature of the negative electrode active layer is a parameter that indirectly represents the length of the path provided inside the negative electrode active layer so that the electrolyte, etc. can move from the surface of the negative electrode active layer to the negative electrode current collector. The lower the curvature ratio, the shorter the path length, and the shorter the curvature ratio may be equivalent to the shorter movement degree of lithium ions and / or electrons during charge / discharge of the lithium secondary battery. However, in an actual lithium secondary battery, the volume expansion of the negative electrode active material inevitably occurs due to the insertion of lithium ions during charging, and the repeated volume change of the negative electrode active material due to charge and discharge may cause an increase in the curvature within the negative electrode active layer. The present invention can minimize the volume expansion of the second negative electrode active layer by including a low-expansion graphite as a second carbon-based negative electrode active material in a predetermined amount in a second negative electrode active layer including a silicon-based negative electrode active material having a large volume expansion during charging.

[0076] The negative electrode according to the present invention can be oriented so that the first carbon-based negative electrode active material and the second carbon-based negative electrode active material included in the first negative electrode active layer and the second negative electrode active layer, respectively, have a predetermined directionality with respect to the negative electrode current collector surface.

[0077] Carbonaceous negative electrode active materials, specifically graphite, have a particle form in which crystal planes (i.e., the ab-axis crystal planes of graphite) representing a two-dimensional planar structure composed of carbon atoms are stacked in the c-axis direction. If a separate treatment to orient the ab-axis crystal planes of graphite is not performed when forming the negative electrode active layer, the negative electrode active layer includes graphite (21) in a state in which the ab-axis crystal planes are not aligned with respect to the negative electrode current collector (10), as shown in (a) of FIG. 1. In this case, the negative electrode active layer (20) experiences volume expansion in both the thickness direction (e.g., the Z-axis direction) and the length direction (e.g., the Y-axis direction) due to the insertion of lithium ions when the secondary battery is charged.

[0078] However, the negative electrode of the present invention may include a carbon-based negative electrode active material (22) oriented such that the ab-axis crystal plane of the entire negative electrode active layer (20) has a predetermined angle with respect to the surface of the negative electrode current collector (10) (the "black" portion in the drawing), as shown in (b) of FIG. 1. Here, the predetermined angle may mean a range of 30° or more, 45° or more, 60° or more, 70° or more, 70° to 90°, 80° to 90°, 65° to 85°, 70° to 85°, 30° to 60°, 45° to 70°, 45° to 90°, 60° to 90°, 60° to 80°, or 30° to 80° with respect to the surface of the negative electrode current collector (10). In this way, the carbon-based negative electrode active material oriented on the surface of the negative electrode current collector can significantly reduce the curvature of the negative electrode active layer, thereby improving the rapid charging performance of the negative electrode and realizing low electrical resistance. In addition, the oriented carbon-based negative electrode active material imparts directionality to the volume expansion of the negative electrode active layer due to lithium ion insertion. That is, since the negative electrode active layer is implemented in the length direction (i.e., Y-axis direction) rather than the thickness direction (i.e., Z-axis direction), even if volume expansion due to lithium ion insertion occurs repeatedly during charging, the volume expansion of the negative electrode active layer in the thickness direction can be suppressed. This has the advantage of improving the deterioration of the negative electrode because it can prevent the low electrical resistance of the negative electrode active layer from increasing.

[0079] For example, the negative electrode according to the present invention can satisfy the condition that the deviation between the average thickness measured at the BOL and the average thickness measured at the EOL of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer is 30% or less based on the average thickness measured at the BOL of the lithium secondary battery.

[0080] The "BOL" of a lithium secondary battery is an abbreviation for "Birth Of Life", and indicates the activated state after the lithium secondary battery is manufactured. In addition, the "EOL" of a lithium secondary battery is an abbreviation for "End Of Life", and indicates the state in which the life of the lithium secondary battery is determined to have ended. Here, the standard for determining that the life of a lithium secondary battery has ended may be that the capacity of the lithium secondary battery at the "BOL" of the lithium secondary battery may be 70% or less of the capacity of the lithium secondary battery, and in this case, the conditions for measuring the capacity of the lithium secondary battery at the BOL and the conditions for measuring the capacity of the lithium secondary battery at the EOL must be the same. The conditions for measuring the capacity may include C-rate conditions, voltage conditions, current conditions, etc.

[0081] The above condition is a parameter indicating the degree of volume expansion of the negative electrode active layer. The above condition can determine the degree of change in the average thickness of the entire negative electrode active layer through the deviation between the average thickness of the entire negative electrode active layer measured in a charged state at BOL, which represents the beginning of the life of a lithium secondary battery, and the average thickness of the entire negative electrode active layer measured in a charged state at EOL, which represents the end of the life. The negative electrode according to the present invention suppresses volume expansion in the thickness direction of the negative electrode active layer due to the insertion of lithium ions, even though it includes a silicon-based negative electrode active material having a large volume expansion when charged in the second negative electrode active layer. Therefore, the negative electrode can satisfy the condition of 30% or less by improving the volume expansion in the thickness direction of the entire negative electrode active layer. For example, the negative electrode can satisfy the condition of 0.01% to 30%; 0.01% to 25%; 0.01% to 20%; 0.01% to 15%; 1% to 30%; 5% to 30%; 10% to 30%; 15% to 30%; 20% to 30%; 24% to 29%; 24% to 27%; 22% to 28%; 0.01% to 10%; 0.01% to 8%; 0.01% to 6%; 0.01% to 4%; 0.01% to 2%; 0.1% to 9%; 0.5% to 5%; 1% to 5%; 2% to 7%; or 0.5% to 4%.

[0082] The above negative electrode may have a curvature of the entire negative electrode active layer, measured in a charged state at BOL, which represents the initial life of a lithium secondary battery, such that the ab-axis crystal planes of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material are oriented with respect to the surface of the negative electrode current collector, such that the curvature of the entire negative electrode active layer satisfies a predetermined range. Specifically, the entire negative electrode active layer of the negative electrode may have a curvature of 2.5 to 7.0. For example, the entire negative electrode active layer of the negative electrode may have a curvature of 2.5 to 6.0; 2.5 to 5.5; 2.5 to 5.0; 3.0 to 7.0; 3.5 to 7.0; 4.0 to 7.0; 4.5 to 7.0; 3.0 to 6.0; 3.1 to 5.5; 3.5 to 5.0; or 3.3 to 4.6. The present invention can achieve low electrical resistance of the cathode active layer by controlling the curvature of the entire cathode active layer within the aforementioned range. As a result, the cathode according to the present invention not only exhibits improved charge / discharge capacity, but also significantly enhanced rapid charging performance.

[0083] Furthermore, the negative electrode according to the present invention can uniformly maintain low electrical resistance of the entire negative electrode active layer by implementing a low curvature ratio of the entire negative electrode active layer and suppressing volume expansion in the thickness direction of the negative electrode active layer due to charge and discharge. Therefore, even if the negative electrode partially contains a silicon-based negative electrode active material having high electrical resistance, deterioration of the entire negative electrode active layer can be uniformly exhibited.

[0084] For example, the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer may have an electrical resistance deviation of 1.0 Ω or less at a point where the thickness ratio based on the surface of the negative electrode active layer is 25±1% and a point where the thickness ratio is 75±1% after 200 charge / discharge cycles. Specifically, the electrical resistance deviation may be in a range of 0.1 Ω to 1.0 Ω; 0.1 Ω to 0.9 Ω; 0.1 Ω to 0.7 Ω; 0.1 Ω to 0.5 Ω; 0.5 Ω to 1.0 Ω; 0.7 Ω to 1.0 Ω; 0.3 Ω to 0.8 Ω; 0.2 Ω to 0.6 Ω; or 0.2 Ω to 0.4 Ω. In the direction of the thickness of the entire negative electrode active layer, the resistance may refer to the vertical resistance measured by punching a circle having a predetermined diameter along the thickness direction of the entire negative electrode active layer and introducing a resistance measuring micrometer into the punched entire negative electrode active layer. At this time, by controlling the depth at which the resistance measuring micrometer is introduced, the electrical resistance at points where the thickness ratio is 25±1% and 75±1% based on the surface of the second negative electrode active layer can be measured.

[0085] The points where the surface-based thickness ratios of the entire negative electrode active layer are 25±1% and 75±1% are points located inside the first negative electrode active layer and the second negative electrode active layer, respectively, and the above-mentioned electrical resistance deviation represents the electrical resistance deviation between the second negative electrode active layer including the silicon-based negative electrode active material and the first negative electrode active layer not including the silicon-based negative electrode active material. Therefore, the fact that the electrical resistance deviations at the points where the surface-based thickness ratios of the negative electrode active layer are 25±1% and 75±1% are 1.0 Ω or less means that the electrical resistance of the entire negative electrode active layer remains uniform even after the charge and discharge cycle of the lithium secondary battery is performed.

[0086] Silicon-based negative electrode active materials, especially SiC or SiO q(However, 0.5≤q≤2.5) etc. have a large electrical resistance under the condition that the charging and discharging of the lithium secondary battery is normally performed, so they can act as electrical resistors. If the electrical resistance in the second negative electrode active layer increases due to the silicon-based negative electrode active material, the degradation of the corresponding point is accelerated, thereby reducing the life characteristics of the negative electrode. However, the negative electrode according to the present invention can improve the life characteristics of the negative electrode by slowing down the rapid degradation of the second negative electrode active layer by maintaining the deviation between the electrical resistance of the second negative electrode active layer including the silicon-based negative electrode active material and the electrical resistance of the first negative electrode active layer not including the silicon-based negative electrode active material small as in the above-described range.

[0087] For example, the negative electrode may have an average electrical resistance of the entire negative electrode active layer in a range of 1.0 Ω to 2.5 Ω after 200 charge / discharge cycles. Specifically, the negative electrode may have an average electrical resistance of the entire negative electrode active layer in a range of 1.0 Ω to 2.25 Ω; 1.0 Ω to 2.0 Ω; 1.0 Ω to 1.9 Ω; 1.0 Ω to 1.7 Ω; 1.0 Ω to 1.5 Ω; 1.25 Ω to 2.5 Ω; 1.5 Ω to 2.5 Ω; 2.0 Ω to 2.5 Ω; 1.1 Ω to 1.9 Ω; 1.2 Ω to 1.7 Ω; 1.4 Ω to 2.2 Ω; or 1.4 Ω to 1.8 Ω after 200 charge / discharge cycles. The average electrical resistance of the entire cathode active layer may be equal to the average value of the electrical resistance of the first cathode active layer and the electrical resistance of the second cathode active layer, and may be measured in the same manner as the method for measuring the electrical resistance deviation previously described.

[0088] Meanwhile, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may have an average particle diameter satisfying a predetermined range. Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may have an average particle diameter (D) of 0.5 μm to 20 μm, respectively. 50) can be represented. For example, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each have an average particle diameter (D) in the range of 0.5 µm to 15 µm; 0.5 µm to 10 µm; 5 µm to 20 µm; 10 µm to 20 µm; 12 µm to 18 µm; 2 µm to 7 µm; 0.5 µm to 5 µm; or 11 µm to 15 µm. 50 ) can be expressed.

[0089] The average particle size of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may be advantageously made smaller to maximize the disorder in the direction of expansion of each particle so as to prevent expansion of the particles due to charging of lithium ions. However, when the particle size of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material is less than 0.5 ㎛, a large amount of binder may be required due to an increase in the number of particles per unit volume. On the other hand, when the maximum particle size exceeds 20 ㎛, expansion becomes severe, and as charge and discharge are repeated, the adhesion between particles and the adhesion between the particles and the current collector deteriorates, which may significantly reduce the cycle characteristics.

[0090] The second negative electrode active layer includes a silicon-based negative electrode active material. The silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and can increase the charge / discharge capacity of the negative electrode. Examples of such silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), silicon monoxide (SiO), silicon dioxide (SiO2), and the like, silicon oxide (SiO). q ) can be included, and these can be included alone or used in combination in the cathode active layer.

[0091] When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as the above silicon-based negative electrode active material and included in the negative electrode active layer, they are silicon oxide (SiO q , but can be expressed as 0.5≤q≤2.5).

[0092] In addition, among the above silicon-based negative electrode active materials, the composite is a material containing silicon (Si) and carbon (C) as main components, such as silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q ) may mean a complex with carbon (C). For example, the complex may be silicon (Si), silicon carbide (SiC), silicon oxide (SiO q ) may have a core-shell structure in which carbon (C) is coated on the particle surface including the like. At this time, the carbon (C) may be formed by using CVD, PVD, ALD, etc. to form silicon (Si), silicon carbide (SiC), silicon oxide (SiO q ) or may have a form in which the particle surface is modified using plasma or UV, etc. In addition, the complex may include silicon (Si), silicon carbide (SiC), silicon oxide (SiO q ) and particles made of carbon (C) can be uniformly mixed / pulverized by applying mechanical and / or physical force to the mixture. In this case, the composite can mean that, unlike an alloy in which silicon (Si) atoms and carbon (C) atoms are physically and chemically bonded, particles including silicon (Si) components and particles made of carbon (C) are uniformly bonded while maintaining their original components.

[0093] These may be included alone or in combination in the second cathode active layer. For example, the silicon-based cathode active material may be SiC and SiO. q It may include one or more of the above SiC or SiO q Compared to the case where pure silicon particles are used, the SiC has the advantage of relatively small volume expansion during charging of a lithium secondary battery. However, the SiC has high electrical resistance at temperatures below 500°C and acts as a resistor. In addition, SiO q, that is, silicon oxide exhibits conflicting characteristics in that the higher the content of oxygen atoms, the higher the electrical resistance, which lowers the battery efficiency, and the lower the content of oxygen atoms, the shorter the lifespan. The silicon-based negative electrode active material with increased electrical resistance in this way can accelerate the deterioration of the negative electrode active layer as the cycle of the lithium secondary battery progresses, thereby significantly reducing the lifespan characteristics of the negative electrode. However, the negative electrode according to the present invention can uniformly implement low electrical resistance in the entire negative electrode active layer by maintaining a low curvature of the entire negative electrode active layer even after the charge and discharge cycle of the lithium secondary battery is performed.

[0094] The above silicon-based negative electrode active material may be doped with or alloyed with Ni, Fe, Co, Ge, Li, Mg, Al, Ca, Ti, etc. At least one of the above metals may be doped with or alloyed into the silicon-based negative electrode active material. In this case, the silicon-based negative electrode active material may be doped with or alloyed with a metal in an amount of 1 mol% to 10 mol%, specifically 1 mol% to 5 mol%, based on silicon atoms. When a metal is added to the silicon-based negative electrode active material in the form of doping or an alloy, the electrical conductivity may increase and the mechanical strength may be improved. However, since the metals have a higher atomic weight than silicon atoms, the energy density per unit weight may decrease as the content ratio increases. Therefore, the metals may be doped with or alloyed into the silicon-based negative electrode active material in the above-described amount in order to lower the electrical resistance without reducing the energy density per unit weight of the silicon-based negative electrode active material.

[0095] The above silicon-based negative electrode active material may be surface-treated with a carbon coating layer or complexed with carbon atoms for the purpose of suppressing volume expansion during charging of a secondary battery and improving electrical conductivity of the negative electrode active material.

[0096] The silicon-based negative electrode active material may be included in an amount of 0.1 to 30 wt% based on the weight of the entire negative electrode active layer. Specifically, the silicon-based negative electrode active material may be included in an amount of 0.1 to 25 wt%, 20 to 30 wt%, 10 to 30 wt%, 0.5 to 20 wt%, 1 to 9 wt%, 5 to 15 wt%, 3 to 7 wt%, 11 to 19 wt%, 13 to 17 wt%, 15 to 20 wt%, or 8 to 13 wt% based on the weight of the entire negative electrode active layer. The present invention can reduce lithium consumption and irreversible capacity loss during initial charge and discharge of a secondary battery by controlling the content ratio of the silicon-based negative electrode active material within the above range, while improving the charge capacity per unit mass. In addition, the structural stability of the negative electrode active layer can be improved by minimizing the change in volume of the negative electrode active layer during charging and discharging of the secondary battery, thereby increasing the lifespan of the secondary battery.

[0097] Furthermore, the first cathode active layer and the second cathode active layer may optionally further include a conductive material, a binder, other additives, etc., as needed, along with the cathode active material as the main component.

[0098] The above-mentioned challenge material may include, but is not limited to, one or more types of carbon black such as acetylene black, furnace black, lamp black, summer black, etc.; graphene; carbon nanotubes and carbon fibers.

[0099] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0100] In addition, the content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of each negative electrode active layer. Specifically, the conductive material may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight based on 100 parts by weight of the entire negative electrode active layer. The present invention can prevent the charge capacity from being lowered due to an increase in the resistance of the negative electrode caused by a low content of the conductive material by controlling the content of the conductive material within the above range, or the charge capacity from being lowered due to an increase in the loading amount of the negative electrode active layer. In addition, the present invention can prevent the problem of the negative electrode active material content being lowered due to an excessive amount of the conductive material exceeding the above range, thereby lowering the charge capacity, or the electrical resistance from being increased due to an increase in the loading amount of the negative electrode active layer.

[0101] The above binder is a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and can be appropriately applied within a range that does not deteriorate the electrical properties of the negative electrode. For example, the binder may include at least one of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluoroelastomer.

[0102] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of each negative electrode active layer. Specifically, the binder may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight based on 100 parts by weight of each negative electrode active layer. By controlling the content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the negative electrode from being lowered due to an excessive amount of binder.

[0103] The above negative electrode active layer may have a predetermined average thickness in order to realize a high charge / discharge capacity while achieving a fast charging speed. The negative electrode active layer exhibits a greater charge / discharge capacity as the loading amount of the negative electrode active material exhibiting electrochemical activity increases. However, in this case, it is difficult to orient the ab-axis crystal plane of the carbon-based negative electrode active material to have a predetermined inclination with respect to the negative electrode current collector, so there is a limitation in that the rapid charging performance of the manufactured negative electrode is low. To overcome this, the present invention can control the average thickness of the entire negative electrode active layer within a predetermined range. Specifically, the entire negative electrode active layer may have an average thickness in the range of 100 ㎛ to 400 ㎛. For example, the entire negative electrode active layer may have a thickness of 100 ㎛ to 350 ㎛; 100 ㎛ to 300 ㎛; 100 ㎛ to 250 ㎛; 100 ㎛ to 200 ㎛; 150 ㎛ to 400 ㎛; It can have an average thickness in the range of 200 ㎛ to 400 ㎛; 150 ㎛ to 300 ㎛; 150 ㎛ to 250 ㎛; or 150 ㎛ to 220 ㎛. The present invention can prevent the alignment of the carbon-based negative electrode active material from being sufficiently realized due to the average thickness of the negative electrode active layer exceeding the upper limit of the above-mentioned range by controlling the average thickness of the negative electrode active layer to the above-mentioned range. In addition, by controlling the average thickness of the negative electrode active layer to the above-mentioned range, it is possible to prevent the charge / discharge capacity and energy density of the negative electrode from being lowered due to a thickness thinner than the lower limit of the above-mentioned range.

[0104] In addition, the first negative electrode active layer and the second negative electrode active layer may have a predetermined thickness ratio. Specifically, the second negative electrode active layer may have a thickness ratio of 80% to 150% based on the average thickness of the first negative electrode active layer. For example, the second negative electrode active layer may have a ratio in the range of 80% to 120%; 80% to 100%; 80% to 99%; 100% to 150%; 125% to 150%; 90% to 120%; 110% to 140%; or 95% to 105% based on the average thickness of the first negative electrode active layer.

[0105] The present invention can prevent the effect of improving rapid charging performance from being minimal due to insufficient alignment of the first carbon-based negative electrode active material caused by an average thickness ratio of the first negative electrode active layer being lower than the lower limit of the above-described range by controlling the thickness ratio of the first negative electrode active layer and the second negative electrode active layer within the above-described range. In addition, it can prevent the charge / discharge capacity and rapid charging performance of the negative electrode from being reduced due to an average thickness ratio of the first negative electrode active layer being higher than the upper limit of the above-described range.

[0106] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be a thin plate or film containing copper, stainless steel, nickel, titanium, calcined carbon, etc. In the case of copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. may also be used. In addition, the average thickness of the negative electrode current collector may be appropriately applied from 1 ㎛ to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0107]

[0108] The anode according to the present invention has excellent charge / discharge capacity due to the above-described configuration, and since the movement path of lithium ions within the anode active layer is shortened, the diffusion resistance of lithium ions is significantly lowered, resulting in excellent rapid charging performance of the anode. In addition, the anode has the advantage of excellent life characteristics because even when the charge / discharge cycle of the secondary battery is repeated, low electrical resistance is uniformly maintained throughout the entire anode active layer, suppressing deterioration.

[0109]

[0110] lithium secondary battery

[0111] In addition, the present invention,

[0112] A lithium secondary battery is provided, comprising an electrode assembly including a positive electrode, a negative electrode of the present invention described above, and a separator disposed between the positive electrode and the negative electrode.

[0113]

[0114] A lithium secondary battery according to the present invention comprises an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately arranged and a separator is positioned between them. The lithium secondary battery comprises the negative electrode of the present invention described above, and thus has improved lithium ion diffusion capacity, thereby exhibiting superior energy density and rapid charging performance, as well as excellent lifespan characteristics.

[0115] At this time, since the cathode has the same configuration as the configuration described above, a detailed description is omitted.

[0116] The above positive electrode includes a positive electrode active layer including a positive electrode active material on a positive electrode current collector, and the positive electrode active layer may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0117] The above cathode active material is a material capable of causing an electrochemical reaction on the cathode current collector, and may include at least one lithium metal oxide represented by the following chemical formulas 1 and 2, which is capable of reversibly intercalating and deintercalating lithium ions:

[0118] [Chemical Formula 1]

[0119] Li l [Ni m Co n Mn w M 1 v ]O2

[0120] [Chemical Formula 2]

[0121] LiM 2 p Mn q P r O4

[0122] In the above chemical formulas 1 and 2,

[0123] M 1 is at least one element among W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0124] l, m, n, w and v are 1.0≤l≤1.30, 0.5≤m<1, 0, respectively. <n≤0.3, 0<w≤0.3, 0≤v≤0.1이되, m+n+w+v=1이고,

[0125] M 2 is Ni, Co or Fe,

[0126] p is 0.05≤p≤1.0,

[0127] q is 1-p or 2-p,

[0128] r is either 0 or 1.

[0129]

[0130] The lithium metal oxides represented by the above chemical formulas 1 and 2 are substances containing high contents of nickel (Ni) and manganese (Mn), respectively, and when used as a cathode active material, they have the advantage of being able to stably supply electricity at high capacity and / or high voltage compared to conventional cathode active materials such as lithium iron phosphate oxide (LiFeO4).

[0131] At this time, the lithium metal oxide represented by the chemical formula 1 is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may include O2, etc. The lithium metal oxide represented by the above chemical formula 2 is LiNi 0.7 Mn 1.3 O4; LiNi 0.5 Mn 1.5 O4; LiNi 0.3 Mn 1.7 O4, etc. may be included. The lithium metal oxides represented by the above chemical formulas 1 and 2 may be used alone or in combination.

[0132] In addition, the positive electrode active material may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the positive electrode active layer. Specifically, the positive electrode active material may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more based on 100 parts by weight of the entire positive electrode active layer.

[0133] Meanwhile, the positive electrode active layer may further include a conductive agent, a binder, other additives, etc., along with the positive electrode active material.

[0134] The conductive material is used to improve the electrical performance of the anode, and can be applied as a material commonly used in the art. Specifically, the conductive material may include one or more of natural graphite; artificial graphite; carbon black such as acetylene black, furnace black, lamp black, or summer black; graphene; and carbon nanotubes.

[0135] The conductive agent may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of each positive electrode active layer. Specifically, the conductive agent may be included in an amount of 0.1 to 4 parts by weight; 2 to 4 parts by weight; 1.5 to 5 parts by weight; 1 to 3 parts by weight; 0.1 to 2 parts by weight; or 0.1 to 1 part by weight based on 100 parts by weight of each positive electrode active layer.

[0136] In addition, the binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0137] The above binder may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of each positive electrode active layer. Specifically, the binder may be included in an amount of 2 to 8 parts by weight or 1 to 5 parts by weight based on 100 parts by weight of the positive electrode active layer.

[0138] The total thickness of the above-mentioned positive electrode active layer is not particularly limited, but may be specifically in the range of 50 µm to 300 µm, and more specifically in the range of 100 µm to 200 µm; 80 µm to 150 µm; 120 µm to 170 µm; 150 µm to 300 µm; 200 µm to 300 µm; or 150 µm to 190 µm.

[0139] In addition, the positive electrode can be used as a positive electrode current collector that has high conductivity without causing chemical changes in the battery. For example, a thin plate or film containing stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used. In the case of containing aluminum or stainless steel, a surface-treated material with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately applied from 3 µm to 500 µm, taking into account the conductivity and total thickness of the positive electrode being manufactured.

[0140] The separator interposed between the positive and negative electrodes of the lithium secondary battery is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the art. Specifically, the separator may include at least one polymer selected from the group consisting of chemically resistant and hydrophobic polypropylene; polyethylene; and polyethylene-propylene copolymers. The separator may have a porous polymer substrate form, such as a sheet or non-woven fabric, including the above-described polymer, and in some cases, may have a composite separator form in which organic or inorganic particles are coated on the porous polymer substrate using an organic binder. In addition, the separator may have an average pore diameter of 0.01 μm to 10 μm, and an average thickness of 5 μm to 300 μm.

[0141] The lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery in a form that may include a stacked, zigzag, or zigzag-stacked electrode assembly. For example, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a square-shaped secondary battery.

[0142] The above pouch-type secondary battery and / or square secondary battery has the advantage of high utilization in terms of energy density because the unit cells of the secondary battery can be packed at a high density in a limited space.

[0143]

[0144] Method for manufacturing cathode

[0145] Furthermore, the present invention provides a method for manufacturing a cathode according to the present invention described above.

[0146] Specifically, the method for manufacturing a negative electrode according to the present invention includes a step (S1) of applying a first negative electrode slurry including a first carbon-based negative electrode active material to at least one surface of a negative electrode current collector, a step (S2) of applying a second negative electrode slurry including a second carbon-based negative electrode active material and a silicon-based negative electrode active material on the first negative electrode slurry, a step (S3) of applying a magnetic field to the applied first negative electrode slurry and the second negative electrode slurry, and a step (S4) of drying the first negative electrode slurry and the second negative electrode slurry to which the magnetic field is applied to form a first negative electrode active layer and a second negative electrode active layer, respectively.

[0147] At this time, the steps (S1) and (S2) refer to a process of coating the surface of a moving negative electrode current collector by simultaneously or continuously discharging a first negative electrode slurry containing a first carbon-based negative electrode active material and a second negative electrode slurry containing a second carbon-based negative electrode active material. Accordingly, the first negative electrode slurry is applied to at least one surface of the negative electrode current collector, and the second negative electrode slurry is applied on the applied first negative electrode slurry.

[0148] The above steps (S1) and (S2) can be applied without particular limitation as long as they are methods commonly applied in the art, but preferably, a die coating method can be used. The die coating method is performed using a slot die coater, and the slot die coater can be equipped with a shim for controlling the discharge conditions of the slurry. The slot die coater can easily control the loading amount, coating thickness, etc. of the negative electrode slurry applied on the negative electrode current collector by controlling the shape and position of the shim.

[0149] For example, the present invention can simultaneously apply a first negative electrode slurry and a second negative electrode slurry onto a negative electrode current collector using a dual die coater. In this case, there is an advantage in that process efficiency can be significantly increased compared to applying each slurry sequentially.

[0150] In addition, the first negative electrode slurry and the second negative electrode slurry each contain a first carbon-based negative electrode active material and a second carbon-based negative electrode active material as main components. Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each contain at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0151] The above first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each have the form of an assembly in which a plurality of particles are assembled. In this case, one graphite assembly may be formed by assembling 2 to 100 graphite particles, preferably 3 to 20 particles.

[0152] For example, the first carbon-based negative electrode active material may include natural graphite and artificial graphite. The artificial graphite may have a form of a graphite assembly in which 10 to 30 particles are aggregated. In addition, the mixing ratio of the natural graphite and the artificial graphite may be 5 to 50:50 to 95, or 30 to 49:51 to 70, based on weight. The first carbon-based negative electrode active material includes natural graphite and artificial graphite in the mixing ratio described above, thereby strengthening the adhesion between the negative electrode current collector and the first negative electrode active layer, and maintaining the electrical resistance of the first negative electrode active layer low even when charge and discharge cycles of the secondary battery are performed, thereby having the advantage of excellent life characteristics.

[0153] In addition, the second carbon-based negative electrode active material may include artificial graphite, and the artificial graphite may have the form of a graphite assembly in which 10 to 30 particles are aggregated. The artificial graphite has the advantage of superior high-rate charge / discharge performance and excellent life characteristics compared to natural graphite.

[0154] The first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material may further include low-expansion graphite. In the present invention, "low-expansion graphite" refers to graphite having low expansion characteristics when the secondary battery is charged. For example, when a secondary battery including graphite as the negative electrode active material is manufactured, if the expansion characteristics of the negative electrode active layer are low even when the secondary battery undergoes repeated charge and discharge cycles, the graphite included in the secondary battery may be referred to as low-expansion graphite. Here, the expansion characteristics of the low-expansion graphite can be determined through the change in thickness of the negative electrode active layer according to the charge and discharge cycle. Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion artificial graphite.

[0155] In the present invention, the low-expansion graphite may be manufactured by a cold isotropic pressing (CIP) method in which plate-shaped natural graphite is spheroidized and then pressure is uniformly applied to each particle in all directions at a low temperature. The low-expansion natural graphite manufactured by the cold isotropic pressing method may be isotropic graphite. Since the isotropic graphite has low electrical resistance, resistance to thermal shock, and excellent mechanical properties, it can improve the life characteristics of the negative electrode itself.

[0156] The above low-expansion graphite may refer to natural graphite particles coated with carbon. In this case, the low-expansion graphite has a carbon layer, which not only suppresses the expansion of the graphite when charging a secondary battery, but also significantly reduces the amount of impurities generated due to physical damage during the manufacturing of carbon-based negative electrode active materials and / or the manufacturing of negative electrodes using the same, or the assembly of batteries.

[0157] In addition, the low-expansion graphite has a high porosity inside the graphite particles. The low-expansion graphite can satisfy a predetermined range in total pore volume, specifically, 1 × 10 -5 ㎤ / g to 1 × 10 -1 It can have a total pore volume in the range of ㎤ / g. For example, the low expansion graphite has a pore volume of 5 × 10 -4 ㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 5 × 10 -3 ㎤ / g to 1 × 10 -1 ㎤ / g; 1 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; 1 × 10 -3 ㎤ / g to 1 × 10 -2 ㎤ / g; 5 × 10 -3 ㎤ / g to 5 × 10 -2 ㎤ / g; or 5 × 10 -3 ㎤ / g to 2 × 10 -2It can have a total pore volume in the range of ㎤ / g. The total pore volume of the low-expansion graphite can be measured through a BET measurement method using the adsorption of nitrogen (N2) gas. The low-expansion graphite can reduce the diffusion resistance of lithium ions while minimizing the volume change during charging of a secondary battery by satisfying the above-described range.

[0158] When the first carbon-based negative electrode active material and / or the second carbon-based negative electrode active material includes low-expansion graphite, the low-expansion graphite may be included in a predetermined content ratio. Specifically, the low-expansion graphite may be included in an amount of 10 wt% to 70 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material. For example, the low-expansion graphite may be included in an amount of 10 wt% to 30 wt%; 20 wt% to 40 wt%; 15 wt% to 45 wt%; 10 wt% to 50 wt%; 30 wt% to 60 wt%; 50 wt% to 70 wt%; 40 wt% to 60 wt%; 15 wt% to 25 wt%; or 45 wt% to 69 wt% based on the total weight of the first carbon-based negative electrode active material or the second carbon-based negative electrode active material.

[0159] In addition, the second cathode slurry includes a silicon-based cathode active material. The silicon-based cathode active material is a material containing silicon (Si) as a main component, and can increase the charge / discharge capacity of the cathode. Examples of such silicon-based cathode active materials include Si, SiC, and SiO. q (However, 0.5≤q≤2.5) etc. can be mentioned, and these can be included alone or in combination in the second negative electrode active layer. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or complexed as the silicon-based negative electrode active material and included in the negative electrode active layer, they are silicon oxide (SiO q, but may be expressed as 0.5≤q≤2.5). In addition, the SiC may mean silicon carbide, and in some cases, may mean a composite in which a carbon coating layer is formed on the surface of silicon particles, or a composite in which silicon particles and carbon particles are complexed.

[0160] For example, the above silicon-based negative electrode active material is SiC and SiO q It may include one or more of the following:

[0161] The above silicon-based negative electrode active material may be doped with or alloyed with Ni, Fe, Co, Ge, Li, Mg, Al, Ca, Ti, etc. At this time, at least one of the above metals may be doped with or alloyed with the silicon-based negative electrode active material. In this case, the silicon-based negative electrode active material may be doped with or alloyed with a metal in an amount of 1 mol% to 10 mol%, specifically 1 mol% to 5 mol%, with respect to silicon atoms. When a metal is added to the silicon-based negative electrode active material in the form of doping or an alloy, the electrical conductivity may increase and the mechanical strength may be improved. However, since the metals have a higher atomic weight than silicon atoms, the energy density per unit weight may decrease as the content ratio increases. Therefore, the metals may be doped with or alloyed with the silicon-based negative electrode active material in the above-described amount in order to lower the electrical resistance without reducing the energy density per unit weight of the silicon-based negative electrode active material.

[0162] In addition, the silicon-based negative electrode active material may be included in an amount of 0.1 to 30 wt% based on the weight of the entire negative electrode active layer. Specifically, the silicon-based negative electrode active material may be included in an amount of 0.1 to 25 wt%, 20 to 30 wt%, 10 to 30 wt%, 0.5 to 20 wt%, 1 to 9 wt%, 5 to 15 wt%, 3 to 7 wt%, 11 to 19 wt%, 13 to 17 wt%, 15 to 20 wt%, or 8 to 13 wt% based on the weight of the entire negative electrode active layer. The present invention can reduce lithium consumption and irreversible capacity loss during initial charge and discharge of a secondary battery by controlling the content ratio of the silicon-based negative electrode active material in the above range, while improving the charge capacity per unit mass. In addition, the structural stability of the negative electrode active layer can be improved by minimizing the change in volume of the negative electrode active layer during charging and discharging of the secondary battery, thereby increasing the lifespan of the secondary battery.

[0163] The above-mentioned negative electrode slurry may further include a conductive agent, a binder, and additives in addition to the negative electrode active material. Since each component included in the above-mentioned negative electrode slurry is the same as the negative electrode active layer of the negative electrode for a lithium secondary battery, a detailed description thereof will be omitted.

[0164] Meanwhile, the above step (S3) refers to a process of applying a magnetic field to the first negative electrode slurry and the second negative electrode slurry applied after steps (S1 and S2) to orient the ab-axis crystal plane of the carbon-based negative electrode active material included in the negative electrode slurry with respect to the negative electrode current collector surface.

[0165] The degree to which the ab-axis crystal planes of the carbon-based anode active material included in each anode slurry are oriented may vary depending on the strength of the applied magnetic field. The magnetic field applied to each anode slurry may have a strength in the range of 1,000 G to 10,000 G (Gauss) to enhance the effect of orienting the ab-axis crystal planes of the carbon-based anode active material. Specifically, the magnetic field applied to the anode slurry is 1,000 G to 9,000 G; 1,000 G to 8,000 G; 2,000 G to 8,000 G; 3,000 G to 8,000 G; 5,000 G to 9,000 G; 5,000 G to 7,5000 G; 5,500 G to 6,5000 G; 1,000 G to 7,000 G; The magnetic field can be applied with a strength in the range of 2,000 G to 6,000 G; 1,500 G to 5,000 G; 1,500 G to 4,500 G; 4,000 G to 8,000 G; 4,500 G to 7,000 G; 3,000 G to 6,500 G; or 3,500 G to 6,500 G.

[0166] Accordingly, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material can be oriented so that the ab-axis crystal plane has a predetermined inclination with respect to the negative electrode current collector surface. This can be indirectly confirmed through X-ray diffraction analysis (XRD) of the negative electrode active layer generated after drying each negative electrode slurry containing the carbon-based negative electrode active material.

[0167] The above step (S4) refers to a process of forming a cathode active layer by drying a cathode slurry to which a magnetic field is applied.

[0168] The above drying can be applied without particular limitations as long as it is a method that can be commonly applied in the art. For example, the above drying can be performed by applying heat energy to the cathode slurry using a hot air dryer, a vacuum oven, or the like, thereby drying the cathode slurry.

[0169] After the above step (S4), a step (S5) of rolling the formed negative electrode active layer may be further included. The rolling refers to a process of increasing the density of the entire negative electrode active layer by applying pressure to the surface of the formed negative electrode active layer using a roll press or the like.

[0170] At this time, the rolling is performed using rolling equipment such as a roll press, etc., under a pre-pressure condition that reaches the target thickness and target porosity, and then vacuum drying is performed to manufacture a negative electrode having a final negative electrode active material layer formed on a current collector.

[0171] For example, the above rolling can be performed under conditions where the target thickness (i.e., the average thickness of the cathode active layer) is in the range of 100 μm to 400 μm and the target porosity (i.e., the void ratio) is in the range of 21% to 30%.

[0172] Specifically, the rolling may be performed at a temperature in the range of 20°C to 100°C, more specifically, at a temperature in the range of 20°C to 80°C; 20°C to 60°C; 20°C to 40°C; 20°C to 30°C; 30°C to 100°C; 40°C to 100°C; 60°C to 100°C; 75°C to 100°C; 85°C to 100°C; 50°C to 90°C; 60°C to 80°C; or 65°C to 90°C.

[0173] The above rolling can be performed at a rolling speed in the range of 2 m / s to 7 m / s, and more specifically, can be performed at a rolling speed in the range of 2 m / s to 6.5 m / s; 2 m / s to 6 m / s; 2 m / s to 5.5 m / s; 2 m / s to 5 m / s; 2 m / s to 4.5 m / s; 2 m / s to 4 m / s; 2.5 m / s to 4 m / s; 2.5 m / s to 3.5 m / s; 3.5 m / s to 5 m / s; 5 m / s to 7 m / s; 5.5 m / s to 6.5 m / s or 6 m / s to 7 m / s.

[0174] The above rolling can be performed under pressure conditions ranging from 50 MPa to 200 MPa, and specifically, can be performed under pressure conditions ranging from 50 MPa to 150 MPa; 50 MPa to 100 MPa; 100 MPa to 200 MPa; 150 MPa to 200 MPa or 80 MPa to 140 MPa.

[0175] Additionally, the vacuum drying conditions may be performed, for example, at 100°C to 150°C for 1 hour to 15 hours.

[0176] The present invention can maximize the energy density of the negative electrode active layer while minimizing the loss of orientation of the carbon-based negative electrode active material formed by performing rolling under the above-mentioned temperature, speed and / or pressure conditions.

[0177] The negative electrode manufactured by the method for manufacturing the negative electrode according to the present invention can suppress the volume change during charge / discharge of the second negative electrode active layer including the silicon-based negative electrode active material, thereby improving the increase in electrical resistance.

[0178] As an example, the negative electrode manufactured by the above manufacturing method may have an electrical resistance deviation of 1.0 Ω or less at a point where the surface-based thickness ratio of the entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer is 25±1% and a point where the thickness ratio is 75±1% after 200 charge / discharge cycles.

[0179]

[0180] The method for manufacturing a negative electrode according to the present invention has the above-described configuration, so that not only is the charge / discharge capacity excellent and the rapid charging performance excellent, but even when the charge / discharge cycle of the secondary battery is repeated, a low electrical resistance is uniformly maintained throughout the entire negative electrode active layer, thereby manufacturing a negative electrode with improved degradation.

[0181]

[0182] Hereinafter, the present invention will be described in more detail through examples and comparative examples.

[0183] However, the following examples and comparative examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and comparative examples.

[0184]

[0185] Examples 1 to 7 and Comparative Examples 1 to 3. Preparation of cathode

[0186] Natural graphite (average particle diameter (D 50 ): about 11~13㎛), artificial graphite (average particle diameter (D 50 ): about 15~16㎛) and low-expansion natural graphite (average particle diameter (D 50 ): about 16~20㎛, total pore volume: about 0.006~0.012㎤ / g) was prepared as a carbon-based negative electrode active material.

[0187] In addition, silicon monoxide (SiO, average particle size (D)) as a silicon-based negative electrode active material 50 ): approximately 6±0.5㎛); Styrene butadiene rubber (SBR) as a binder and carboxymethyl cellulose (CMC) as a thickener were prepared, and carbon nanotubes (CNT) and carbon black (Super-P) were prepared as conductive materials.

[0188] Then, 95 wt% of the first carbon-based negative electrode active material, 1 wt% of carbon black, 3.0 wt% of styrene butadiene rubber (SBR), and 1 wt% of carboxymethyl cellulose (CMC) were mixed with water to obtain a solid content of 50% to prepare a first negative electrode slurry.

[0189] Separately, a second negative electrode slurry was prepared by mixing 95.55 wt% of a mixture of a second carbon-based negative electrode active material and a silicon-based negative electrode active material, 1.13 wt% of carboxymethyl cellulose (CMC), 2.3 wt% of styrene butadiene rubber (SBR), 0.02 wt% of carbon nanotubes, and 1 wt% of carbon black with water to a solid content of 50%.

[0190] At this time, ① the composition of the first carbon-based negative electrode active material, ② the composition of the second carbon-based negative electrode active material, and ③ the content ratio of the silicon-based negative electrode active material included in the second negative electrode slurry were adjusted as shown in Table 1 below.

[0191] The prepared cathode slurry was applied (S1 and S2) onto a copper foil (thickness: 6 μm) being transported roll-to-roll (transport speed: 6 m / min) using a dual die coater. Thereafter, a magnetic field was applied (S3) for 9 to 11 seconds from the bottom of the applied cathode slurry using a magnet. ④ Whether or not a magnetic field was applied and ⑤ the strength of the applied magnetic field were controlled as shown in Table 2 below.

[0192] The cathode slurry to which a magnetic field was applied was dried with hot air to form a cathode active layer on the cathode current collector (S4). The cathode (average thickness: approximately 135±5㎛) was manufactured by rolling the cathode active layer using a roll press so that the porosity of the cathode active layer was 25±2% (S5). At this time, the thickness ratio of the first cathode active layer and the second cathode active layer was 1:1.

[0193] Composition of the first carbon-based negative electrode active materialComposition of the second carbon-based negative electrode active materialContent of the silicon-based negative electrode active materialExample 1 Artificial graphite: low-expansion natural graphite = 1:2 (wt% / wt%) Artificial graphite = 100 wt% 12 wt%Example 2 Artificial graphite: low-expansion natural graphite = 1:1 (wt% / wt%) Artificial graphite = 100 wt% 12 wt%Example 3 Artificial graphite: low-expansion natural graphite = 2:1 (wt% / wt%) Artificial graphite = 100 wt% 12 wt%Example 4 Artificial graphite: natural graphite = 2:1 (wt% / wt%) Artificial graphite: low-expansion natural graphite = 1:1 (wt% / wt%) 12 wt%Example 5 Artificial graphite: natural graphite = 2:1 (wt% / wt%) Artificial graphite = 100 Weight % 12 Weight % Example 6 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 30 Weight % Example 7 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 12 Weight % Comparative Example 1 Artificial graphite: natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 12 Weight % Comparative Example 2 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 12 Weight % Comparative Example 3 Artificial graphite: low expansion natural graphite = 2:1 (weight % / weight %) Artificial graphite = 100 weight % 12 Weight %

[0194] Magnetic field strengthExample 1: 6,000±1,000 GExample 2: 6,000±1,000 GExample 3: 6,000±1,000 GExample 4: 6,000±1,000 GExample 5: 6,000±1,000 GExample 6: 6,000±1,000 GExample 7: 10,000±1,000 GComparative Example 1X-Comparative Example 2X-Comparative Example 3: 1,000±100 G

[0195]

[0196] Examples 8 to 14 and Comparative Examples 4 to 6. Manufacturing of lithium secondary batteries

[0197] LiNi with a particle size of 5㎛ as a cathode active material 0.7 Co 0.1 Mn 0.1 Al0.1 O2 was prepared, and polyvinylidene fluoride as a carbon-based conductive agent and binder was mixed with N-methyl pyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was cast on an aluminum sheet, dried in a vacuum oven at 120°C, and then rolled to manufacture a cathode.

[0198] A separator made of 18 μm polypropylene was interposed between the positive electrode obtained above and the negative electrode manufactured in Examples 1 to 7 and Comparative Examples 1 to 3, respectively, and inserted into a case, and then an electrolyte composition was injected to assemble a 1 Ah-class lithium secondary battery.

[0199] At this time, the types of negative electrodes applied to each lithium secondary battery are shown in Table 3 below.

[0200] Type of applied cathode Example 8 The cathode manufactured in Example 1 Example 9 The cathode manufactured in Example 2 Example 10 The cathode manufactured in Example 3 Example 11 The cathode manufactured in Example 4 Example 12 The cathode manufactured in Example 5 Example 13 The cathode manufactured in Example 6 Example 14 The cathode manufactured in Example 7 Comparative Example 4 The cathode manufactured in Comparative Example 1 Comparative Example 5 The cathode manufactured in Comparative Example 2 Comparative Example 6 The cathode manufactured in Comparative Example 3

[0201]

[0202] Experimental example.

[0203] In order to evaluate the properties and performance of the cathode manufactured according to the present invention, the following experiments were conducted.

[0204]

[0205] 1) Measurement of the curvature of the entire cathode active layer

[0206] Two of the cathodes manufactured in Examples 1 to 7 and Comparative Examples 1 to 3 were prepared, and symmetrical cells were manufactured by stacking them in the order of separator / cathode / separator / cathode / separator. An electrolyte was injected into the manufactured symmetrical cell to completely wet it, and it was mounted on an electrochemical impedance spectroscopy (EIS) device while fastened to a jig. Thereafter, the impedance was measured over the range of 300 kHz to 300 mHz, and the measured data was fitted to calculate the curvature. The calculated curvature is shown in Table 4.

[0207]

[0208] 2) Measurement of the average thickness deviation from BOL to EOL of the entire cathode active layer

[0209] One of the prepared lithium secondary batteries was charged at a constant current of 1 / 3 C at 22±3°C until the voltage reached 4.35 V, and the charge capacity was measured. Then, the lithium secondary battery was disassembled, and the average thickness of the entire negative electrode active layer in the BOL was measured.

[0210] At this time, the average thickness of the entire cathode active layer was measured by argon ion milling (Ar) under an acceleration voltage condition of 6 kV for the thickness direction cross-section of the entire cathode active layer. + Ion milling was performed. Afterwards, scanning electron microscopy (SEM) analysis on the ion-milled cross-section was performed under conditions of an acceleration voltage of 5 kV and a working distance of 7 mm, and the thickness at three arbitrary points in the obtained image was measured to calculate the average thickness of the entire negative electrode active layer. The ion milling was performed using an IM5000 from Hitachi, and the scanning electron microscopy analysis was performed using an IT800SHL from JEOL.

[0211] After that, charging was performed at 22±3℃ with a constant current of 1 / 3C until the voltage reached 4.35 V, and discharging was performed with a constant current of 1 / 3C until the voltage reached 3.0 V, which was set as one cycle. These charge / discharge cycles were repeated until the charge capacity at the BOL of the lithium secondary battery reached 70% or less. When the charge capacity reached 70% of the charge capacity at the BOL, the average thickness of the entire negative electrode active layer at the EOL was measured in the same manner as previously used to measure the average thickness of the entire negative electrode active layer.

[0212] The average thickness deviation was calculated from the average thickness of each entire cathode active layer measured at BOL and EOL, and the deviation rate based on the measured value at BOL was calculated from the calculated value. The results are shown in Table 4 below.

[0213]

[0214] 3) Measurement of the vertical resistance of the entire cathode active layer

[0215] The lithium secondary batteries manufactured in Examples 8 to 14 and Comparative Examples 4 to 6 were subjected to 200 cycles of charge and discharge. At this time, one cycle was set to be charged at a constant current of 1 / 3C at 22±3°C until the voltage reached 4.35 V, and discharged at a constant current of 1 / 3C until the voltage reached 3.0 V.

[0216] After each lithium secondary battery subjected to 200 charge-discharge cycles was transferred to a dry room, the negative electrode was separated, and the negative electrode active layer of the separated negative electrode was punched into a circle with a diameter of 2.5 cm along the thickness direction. A resistance measuring micrometer was introduced into the entire punched negative electrode active layer to measure the vertical resistance of the entire negative electrode active layer.

[0217] In addition, the depth at which the micrometer for measuring the resistance was introduced was adjusted to a point where the thickness ratio was 25±1% and a point where the thickness ratio was 75±1% based on the surface of the second cathode active layer, and the electrical resistance at each point was measured. The deviation was calculated from the electrical resistance of the two measured points. The results are shown in Table 4 below.

[0218] Separately, the thickness-direction cross-sections of the cathodes manufactured in Comparative Example 2 and Example 3 were subjected to argon ion milling (Ar) under an acceleration voltage condition of 6 kV. + Ion milling was performed, and scanning spread resistance microscope (SSRM) analysis was performed on the ion-milled cross-section. The results are shown in Fig. 3 below.

[0219]

[0220] 4) Rapid charging performance evaluation

[0221] The positive electrode was manufactured in the same manner as in Examples 8 to 14 and Comparative Examples 4 to 6, and separately, Li4Ti5O 12 (LTO) electrodes were prepared.

[0222] A three-electrode cell was manufactured by stacking the prepared positive and LTO electrodes and the negative electrodes prepared in Examples 1 to 7 and Comparative Examples 1 to 3 so that a separator was interposed between them, and then assembling the stacked LTO electrodes by coating a copper wire.

[0223] Charging and discharging were performed between the positive electrode and the LTO electrode so that the state of charge (SOC) of the LTO electrode reached 50%, and the three-electrode cell was charged to adjust the potential to 1.53 V.

[0224] Afterwards, the voltage of the positive and LTO electrodes and the voltage between the positive and negative electrodes were measured using an EC-Lab charger and discharger to perform charging and discharging of the three-electrode cell. The charging was performed under constant current conditions of 0.5C, 1.0C, 1.5C, 2.0C, 2.5C, or 3.0C, respectively, and the charging time was calculated after confirming the depth of charge at each C-rate condition. In addition, the depth of charge was determined by checking the negative voltage profile, and when a plateau was confirmed in the negative profile during charging, that point was determined as the charge capacity (charge depth). The calculated charging times are shown in Table 5 below.

[0225]

[0226] 5) Energy density measurement

[0227] The loading amount per unit area and porosity of the cathodes manufactured in Examples 1 to 7 and Comparative Examples 1 to 3 were measured.

[0228] The energy density of a large-sized secondary battery cell was calculated using the measured loading per unit area and porosity. The large-sized secondary battery cell was designed as a cell with dimensions of 99.7 mm × 301.5 mm × 8.2 mm that satisfies a discharge capacity of 40 Ah under 1 / 3C conditions. The calculated values ​​are shown in Table 5 below.

[0229]

[0230] 6) Life characteristics

[0231] The charge-discharge capacity retention rate at room temperature was measured for the lithium secondary batteries manufactured in Examples 8 to 14 and Comparative Examples 4 to 6. Specifically, one cycle was set as charging at a constant current of 1 / 3C at 22±3°C until the voltage reached 4.35 V, and discharging at a constant current of 1 / 3C until the voltage reached 3.0 V. Then, 300 cycles of charge-discharge were performed on each lithium secondary battery.

[0232] At this time, when charging and discharging each lithium secondary battery, 1 st Discharge capacity of cycles and 300th The discharge capacity of the cycle was measured. The measured 1 st 300 based on discharge capacity per cycle th The discharge capacity retention rate of each lithium secondary battery was evaluated by calculating the discharge capacity retention rate of the cycle. The results are shown in Table 5 below.

[0233] (BOL→EOLAverage thickness deviation rateCurvatureVertical electrical resistance[Ω]Electrical resistance deviation[Ω] at the point where the thickness ratio is 25±1% and 75±1%Example 8Approximately 2.5%4.131.820.31Example 9Approximately 2.7%4.171.850.33Example 10Approximately 3.0%4.211.870.34Example 11Approximately 4.3%4.451.890.48Example 12Approximately 6.8%5.291.930.56Example 13Approximately 18.1%6.321.940.90Example 14Approximately 1.7%4.131.800.35Comparative Example 4Approximately 106%8.892.081.47Comparative Example 5Approximately 80.9%8.242.011.28Comparative Example 6Approximately 10.5%7.421.951.06

[0234] Fast charging time [minutes] Energy density [Wh / L] 300 th Cycle Discharge Capacity Retention Rate [%] Example 8 27.4 5 9 7.4 8 6.4 Example 9 27.2 5 9 7.3 8 6.0 Example 10 27.1 5 9 7.5 8 4.4 Example 11 28.6 5 9 5.1 8 1.6 Example 12 28.9 5 9 5.8 8 2.1 Example 13 31.1 6 20.4 8 0.2 Example 14 28.7 6 0 0.2 8 1.3 Comparative Example 4 42.1 5 9 5.5 7 1.2 Comparative Example 5 38.0 5 8 1.0 8 3.6 Comparative Example 6 35.9 5 8 7.7 7 8.9

[0235] As shown in Tables 4 and 5 above, it can be seen that the negative electrode according to the present invention has excellent rapid charging performance and excellent energy density and lifespan characteristics.

[0236] Specifically, it was confirmed that the lithium secondary batteries manufactured in the examples took approximately 31 minutes or less to charge to a depth of charge. In addition, the lithium secondary batteries manufactured in the examples exhibited a high energy density of approximately 595 Wh / L or more, and it was confirmed that the discharge capacity retention rate after 300 charge / discharge cycles was approximately 80% or more.

[0237] In addition, referring to (a) of FIG. 3, in the case of the cathode of Comparative Example 2, after 200 cycles, when the entire cathode active layer was analyzed by atomic force microscopy for diffusion resistance, the color of the second cathode active layer including the silicon-based cathode active material (e.g., light gray) was significantly different from the color of the second cathode active layer not including the silicon-based cathode active material (e.g., dark gray). This means that the deterioration of the second cathode active layer including the silicon-based cathode active material was accelerated, thereby increasing the resistance of the second cathode active layer.

[0238] In contrast, referring to (b) of FIG. 3, in the case of the negative electrode of Example 3, after 200 cycles, the color (e.g., dark gray) of the first negative electrode active layer and the second negative electrode active layer was uniform in the diffusion resistance atomic force microscope analysis of the entire negative electrode active layer. This means that the deterioration of the second negative electrode active layer was improved, and the increase in electrical resistance was improved even as the secondary battery cycle progressed.

[0239] From these results, it can be seen that the electrical resistance of the negative electrode active layer can be implemented to be low even if a silicon-based negative electrode active material having a high electrical resistance is included, and that this low electrical resistance is maintained even when charge and discharge are performed repeatedly, thereby improving the life characteristics of the negative electrode.

[0240] Therefore, the negative electrode according to the present invention has the advantages of excellent rapid charging performance and superior energy density and lifespan characteristics.

[0241]

[0242] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that the present invention can be variously modified and changed within a scope that does not depart from the technical features of the present invention described in the claims to be described later.

[0243] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

[0244]

[0245] [Explanation of symbols]

[0246] 10: Negative current collector

[0247] 20: Cathode active layer

[0248] 21: Aligned and / or unoriented carbon-based negative electrode material

[0249] 22: Aligned and / or oriented carbon-based negative electrode material

Claims

1. Negative current collector, A first negative electrode active layer provided on at least one surface of the negative electrode current collector and including a first carbon-based negative electrode active material, and A second negative electrode active layer is provided on the first negative electrode active layer and includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material; The average thickness of the second cathode active layer has a ratio of 80% to 150% based on the average thickness of the first cathode active layer; The entire negative electrode active layer including the first negative electrode active layer and the second negative electrode active layer has an electrical resistance deviation of 1.0 Ω or less between a point where the thickness ratio based on the surface of the negative electrode active layer is 25±1% and a point where the thickness ratio based on the surface of the negative electrode active layer is 75±1% after 200 charge / discharge cycles.

2. In paragraph 1, The above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but a cathode containing at least one of 0.5≤q≤2.5).

3. In paragraph 1, The above silicon-based negative electrode active material is a negative electrode characterized in that it is doped with one or more metals selected from the group consisting of Ni, Fe, Co, Ge, Li, Mg, Al, Ca, and Ti.

4. In paragraph 1, A negative electrode in which the above silicon-based negative electrode active material is included in a range of 1 wt% to 30 wt% based on the weight of the entire negative electrode active layer.

5. In paragraph 1, At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 A cathode further containing graphite in the range of ㎤ / g.

6. In paragraph 5, The total pore volume above is 1 × 10 -5 ㎤ / g to 1 × 10 -1 An anode having a graphite content in the range of ㎤ / g of 10 wt% to 70 wt% based on the total weight of the first carbon-based anode active material or the second carbon-based anode active material.

7. In paragraph 1, The above first carbon-based negative electrode active material is a negative electrode including at least one of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

8. In paragraph 1, An anode characterized in that the deviation between the average thickness measured at BOL and the average thickness measured at EOL of the lithium secondary battery is 30% or less based on the average thickness measured at BOL.

9. In paragraph 1, A cathode having a curvature of the entire cathode active layer in the range of 2.5 to 7.

0.

10. In paragraph 1, A cathode having an average thickness of the entire cathode active layer in the range of 100 ㎛ to 400 ㎛.

11. A step (S1) of applying a first negative electrode slurry containing a first carbon-based negative electrode active material to at least one surface of a negative electrode current collector; Step (S2) of applying a second negative electrode slurry containing a second carbon-based negative electrode active material and a silicon-based negative electrode active material on the first negative electrode slurry; A step (S3) of applying a magnetic field to the applied first cathode slurry and the second cathode slurry, and A step (S4) of drying the first cathode slurry and the second cathode slurry to which a magnetic field is applied to form a first cathode active layer and a second cathode active layer, respectively; The average thickness of the second cathode active layer has a ratio of 80% to 150% based on the average thickness of the first cathode active layer; A method for manufacturing a cathode, wherein the entire cathode active layer including the first cathode active layer and the second cathode active layer has an electrical resistance deviation of 1.0 Ω or less between a point where the thickness ratio based on the surface of the cathode active layer is 25±1% and a point where the thickness ratio based on the surface of the cathode active layer is 75±1% after 200 charge / discharge cycles.

12. In paragraph 11, The above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), a composite containing silicon (Si) and carbon (C), and silicon oxide (SiO). q , but, a method for manufacturing a cathode including at least one of 0.5≤q≤2.5).

13. In paragraph 11, At least one of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material has a total pore volume of 1 × 10 -5 ㎤ / g to 1 × 10 -1 A method for manufacturing a cathode comprising graphite in the range of ㎤ / g.

14. In paragraph 11, A method for manufacturing a cathode, wherein the above magnetic field is performed with a magnetic field strength of 1,000 G to 10,000 G.

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