Anode for lithium secondary battery and manufacturing method therefor

Abstract

The present invention relates to an anode for a lithium secondary battery and a manufacturing method therefor. The ratio of porosity to the degree of orientation (O.I) of a carbon-based anode active material in the anode satisfies a predetermined range such that movement paths of lithium ions in an anode active layer are shortened and diffusion resistance of the lithium ions is significantly lowered, and thus the anode has excellent fast-charging performance. In addition, the density of the anode active layer in the anode is improved within a range that does impair the shortened movement paths of lithium ions, and thus the anode has excellent energy density.

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 Korean Patent Application No. 10-2024-0097421, dated July 23, 2024, and Korean Patent Application No. 10-2024-0190271, dated December 18, 2024, 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 comprised 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. Because the desorption reaction in the cathode active material is faster than the insertion reaction in the anode active material, the charge / discharge performance of a lithium secondary battery, including its speed, is primarily determined by the anode.

[0006] Materials including graphite are widely used as the negative electrode active material of the above-mentioned negative electrode. Graphite has a layered structure, and carbon atoms form a network structure and are formed by stacking multiple layers in a planar shape. During charging, lithium ions can penetrate the edge surfaces (surfaces where the layers overlap) of these graphite layers and diffuse between the layers, and during discharge, lithium ions can be desorbed and released from the edge surfaces of the layers. In addition, since graphite has a lower electrical resistivity in the plane direction of the layers than in the stacking direction of the layers, a detoured conduction path for electrons is formed along the plane direction of the layers.

[0007] In conventional lithium secondary batteries using graphite, a technique for magnetically orienting the graphite contained in the negative electrode has been proposed to improve the charging performance of the negative electrode. Specifically, during the formation of the negative electrode, the (002) crystal plane of the graphite is oriented so that it is nearly perpendicular to the negative electrode current collector in a magnetic field, and the structure is configured to fix it. In this case, since the edge surface of the graphite layer faces the positive electrode active layer, the insertion and deintercalation of lithium ions can be performed smoothly, and at the same time, the conduction path of electrons can be shortened, thereby improving the electronic conductivity of the negative electrode. In addition, the negative electrode containing graphite can significantly accelerate the charging speed of the secondary battery.

[0008] However, even if the graphite's crystal plane is oriented nearly perpendicular to the negative electrode current collector using a magnetic field, the graphite's crystal plane inclines toward the negative electrode current collector when the negative electrode active layer is rolled to increase the energy density of the negative electrode, resulting in a decrease in orientation. In other words, there is a difficult limitation in simultaneously improving the rapid charging performance and energy density of the negative electrode using a magnetic field.

[0009] Accordingly, there is a need for technological development for cathodes with excellent rapid charging performance and high energy density.

[0010]

[0011] The purpose of the present invention is to provide a cathode having excellent rapid charging performance and high energy density, and a method for manufacturing the same.

[0012]

[0013] The present invention provides a negative electrode including a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector and including a carbon-based negative electrode active material.

[0014] The above carbon-based negative electrode active material has a total pore volume of 1×10 -5 ㎤ / g to 1×10 -1 Includes graphite in the range of ㎤ / g. For example, the total pore volume is 1×10 -5 ㎤ / g to 1×10 -1 Graphite in the ㎤ / g range can be abbreviated as 'low expansion graphite'.

[0015] The above cathode active layer satisfies a ratio in the range of 0.10 to 0.16 calculated by the following equation 1.

[0016] [Formula 1]

[0017] Y / X

[0018] In the above equation 1,

[0019] Y represents the orientation index (OI) of the carbon-based negative electrode active material,

[0020] X represents the porosity (vol.%) of the cathode active layer, and X is in the range of 22% to 30%.

[0021] The orientation index (OI) of the above carbon-based negative electrode active material is defined by the following equation 2.

[0022] [Formula 2]

[0023] OI= I 004 / I 110

[0024] In the above equation 2,

[0025] I 110represents the intensity of the peak representing the (110) crystal plane of the carbon-based negative electrode material when measuring X-ray diffraction (XRD) on the negative electrode active layer,

[0026] I 004 It represents the intensity of the peak representing the (004) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD) measurement of the negative electrode active layer.

[0027] The orientation index (OI) of the above carbon-based negative electrode active material may be in the range of 1.5 to 8.0.

[0028] In addition, the porosity (X) of the cathode active layer may range from 25% to 29.5% on average.

[0029] 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 in the range of 25 wt% to 100 wt% based on the total weight of the carbon-based negative electrode active material.

[0030] In addition, the carbon-based negative electrode active material may further include one or more of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, mesophase calcined carbon using tar and pitch as raw materials, and graphitized coke.

[0031] Additionally, the cathode active layer may have an average thickness of 100 ㎛ to 400 ㎛.

[0032]

[0033] In addition, the present invention provides a secondary battery including the negative electrode described above. The secondary battery is a lithium secondary battery and may be a cylindrical, pouch-shaped, or square battery.

[0034]

[0035] Furthermore, the present invention provides a method for manufacturing a cathode.

[0036] A method for manufacturing a negative electrode according to the present invention comprises a step (S1) of applying a negative electrode slurry containing a carbon-based negative electrode active material to at least one surface of a negative electrode current collector, a step (S2) of applying a magnetic field to the applied negative electrode slurry, a step (S3) of drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer, and a step (S4) of rolling the formed negative electrode active layer.

[0037] In the present invention, the carbon-based negative electrode active material has a total pore volume of 1×10 -5 ㎤ / g to 1×10 -1 Includes graphite in the ㎤ / g range.

[0038] The total pore volume above is 1×10 -5 ㎤ / g to 1×10 -1 The content of graphite in the range of ㎤ / g is in the range of 25 wt% to 100 wt% based on the total weight of the carbon-based negative electrode active material.

[0039] The step (S4) of rolling the above-mentioned negative electrode active layer is controlled so that, when fitting the orientation index (OI) of the carbon-based negative electrode active material to the porosity of the rolled negative electrode active layer, the average slope in the section where the porosity is 25% to 27% has a value of 0 or a positive value.

[0040] The above cathode active layer satisfies the ratio of the following equation 1 in the range of 0.10 to 0.16.

[0041] [Formula 1]

[0042] Y / X

[0043] In the above equation 1,

[0044] Y represents the orientation index (OI) of the carbon-based negative electrode active material,

[0045] X represents the porosity (vol.%) of the cathode active layer, and X is in the range of 22% to 30%.

[0046] In addition, the orientation index (OI) of the above carbon-based negative electrode active material is defined by the following equation 2.

[0047] [Formula 2]

[0048] OI= I 004 / I 110

[0049] In the above equation 2,

[0050] I 110 represents the intensity of the peak representing the (110) crystal plane of the carbon-based negative electrode material when measuring X-ray diffraction (XRD) on the negative electrode active layer,

[0051] I 004 It represents the intensity of the peak representing the (004) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD) measurement of the negative electrode active layer.

[0052] The rolling ratio (vol.%) of the above cathode active layer is in the range of more than 30% and less than 42%.

[0053]

[0054] The negative electrode according to the present invention has a ratio of porosity to orientation index (OI) of a carbon-based negative electrode active material that satisfies a predetermined range, thereby shortening the movement path of lithium ions within the negative electrode active layer and significantly lowering the diffusion resistance of lithium ions, thereby exhibiting excellent rapid charging performance of the negative electrode. In addition, the negative electrode has the advantage of excellent energy density of the negative electrode because the density of the negative electrode active layer is improved within a range that does not damage the shortened movement path of lithium ions.

[0055]

[0056] Figure 1 is a graph showing the relationship between the porosity and the orientation index (OI) of carbon-based negative electrode materials for each example and comparative example.

[0057]

[0058] 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.

[0059] 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.

[0060] 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 a particle size analyzer or an analysis device using a laser diffraction scattering particle size distribution measurement method, but is not limited thereto.

[0061] 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.

[0062] 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.

[0063] In addition, the phrase "the degree of orientation of the carbon-based negative electrode active material is high" means that the "degree of orientation (OI)" mentioned in this specification has a large value, which may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a low angle with respect to the surface of the negative electrode current collector. Conversely, the phrase "the degree of orientation of the carbon-based negative electrode active material is low" means that the "degree of orientation (OI)" has a small value, which 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 surface of the negative electrode current collector.

[0064] Furthermore, in the present specification, "comprising as a main component" may mean comprising 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 comprising 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.

[0065] In addition, in this specification, the "average slope in a ~ section" may mean a value obtained by averaging n slopes calculated by dividing a defined section into n equal parts. However, n may be 5 or more, and preferably 5 to 10.

[0066]

[0067] Hereinafter, the present invention will be described in more detail.

[0068]

[0069] Cathode for lithium secondary batteries

[0070] The present invention provides a negative electrode including a negative electrode current collector and a negative electrode active layer provided on at least one surface of the negative electrode current collector and including a carbon-based negative electrode active material.

[0071] 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 comprising a carbon-based negative electrode active material 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 comprising 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.

[0072] The above-mentioned negative electrode active layer includes a carbon-based negative electrode active material composed of carbon atoms as a main component, which is a negative electrode active material exhibiting electrochemical activity, and the carbon-based negative electrode active material may include a graphite-based compound.

[0073] Specifically, the carbon-based negative electrode active material includes low-expansion graphite. In the present invention, "low-expansion graphite" means graphite having low expansion characteristics when charging a secondary battery. For example, when a secondary battery including graphite as an negative electrode active material is manufactured, if the expansion characteristics of the negative electrode active layer are low even when the charge and discharge cycle of the secondary battery is repeated, the graphite included in the negative electrode active layer can be referred to as "low-expansion graphite." At this time, the expansion characteristics of the low-expansion graphite can be known through the change in the thickness of the negative electrode active layer according to the charge and discharge cycle.

[0074] Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion artificial graphite. In the present invention, the low-expansion graphite may be manufactured by a cold isotropic pressing (CIP) method that uniformly applies pressure to each direction of the particles at a low temperature. The low-expansion graphite manufactured by the cold isotropic pressing method is isotropic graphite, and isotropic graphite has low electrical resistance, resistance to thermal shock, and excellent mechanical properties, so it can improve the life characteristics of the negative electrode itself. 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, so that not only is the expansion of the graphite suppressed when charging the secondary battery, but also the amount of impurities generated due to physical damage during the manufacturing of the carbon-based negative electrode active material and / or the manufacturing of the negative electrode using the same or the assembly of the battery is significantly reduced. In addition, the low-expansion graphite has the characteristic of a high porosity within the graphite particles. The high porosity of graphite particles can improve the volume expansion control capability of the negative electrode material itself, so that the volume expansion characteristic is small when the secondary battery is charged, and the orientation index (OI) of the carbon-based negative electrode material can be maintained low even after rolling.

[0075] For example, the above low-expansion graphite can have a total pore volume satisfying a predetermined range, specifically, an average of 1×10 -5 ㎤ / g to 1×10 -1 It can have a total pore volume of ㎤ / g. More specifically, the low-expansion graphite has an average 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 -2 It can have a total pore volume 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.

[0076] The above-described negative electrode active layer may include such low-expansion graphite as a main component of a carbon-based negative electrode active material. Specifically, the low-expansion graphite may be included in an amount of 25 wt% to 100 wt% based on the total weight of the carbon-based negative electrode active material. For example, the low-expansion graphite may be included in an amount of 30 wt% to 100 wt%; 40 wt% to 100 wt%; 50 wt% to 95 wt%; 50 wt% to 90 wt%; 50 wt% to 85 wt%; 50 wt% to 80 wt%; 50 wt% to 75 wt%; 50 wt% to 70 wt%; 60 wt% to 100 wt%; 70 wt% to 100 wt%; 80 wt% to 100 wt%; 90 wt% to 100 wt% based on the total weight of the carbon-based negative electrode active material. It can be comprised in an amount of 60 wt% to 95 wt%; 70 wt% to 90 wt%; 80 wt% to 99 wt%; 61 wt% to 99 wt%; or 75 wt% to 85 wt%. The present invention can maintain the orientation index (OI) of the carbon-based negative electrode active material comprised in the negative electrode active layer low even after rolling by controlling the content of the low-expansion graphite comprised in the negative electrode active layer within the above-described range.

[0077] The above negative active layer satisfies the ratio calculated by Equation 1 below in the range of 0.10 to 0.16 in order to have a short movement path of lithium ions and high energy density when charging a secondary battery:

[0078] [Formula 1]

[0079] Y / X

[0080] In the above equation 1,

[0081] Y represents the orientation index (OI) of the carbon-based negative electrode active material,

[0082] X represents the porosity (vol%) of the cathode active layer, and X is in the range of 22% to 30%.

[0083] In the above equation 1, the orientation index (OI) corresponding to the Y value is defined by the following equation 2, and can satisfy a certain range:

[0084] [Formula 2]

[0085] OI= I 004 / I 110

[0086] In the above equation 2,

[0087] I 110 represents the intensity of the peak representing the (110) crystal plane of the carbon-based negative electrode material when measuring X-ray diffraction (XRD) on the negative electrode active layer,

[0088] I 004 It represents the intensity of the peak representing the (004) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD) measurement of the negative electrode active layer.

[0089] Specifically, the orientation index (OI) defined by the above formula 2 can be a relative indicator indicating the degree to which the crystal plane of the carbon-based negative electrode active material is oriented in a certain direction, specifically, with respect to the negative electrode current collector surface, when measured by X-ray diffraction (XRD). The negative electrode active layer exhibits peaks of 2θ=26.5±0.2°, 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, 54.7±0.2°, and 77.5±0.2° for graphite, which is a carbon-based negative electrode active material, when measured by X-ray diffraction, which represent the (002) plane, (100) plane, (101)R plane, (101)H plane, (004) plane, and (110) plane. Additionally, the peak appearing at 2θ=43.4±0.2° can be seen as an overlap between the (101)R plane of the carbon-based negative electrode material and the peak corresponding to the (111) plane of a current collector, such as copper (Cu).

[0090] Among these, the orientation index (OI) of the carbon-based negative electrode active material can be measured through the intensity ratio of the peak at 2θ=54.7±0.2° representing the (004) plane and the peak at 2θ=77.5±0.2° representing the (110) plane. Here, the peak at 2θ=54.7±0.2° is a peak representing the (004) plane, which has a slope with respect to the negative electrode current collector among the crystal planes of graphite, and the (004) plane represents the ab-axis crystal plane of the carbon-based negative electrode active material. Therefore, the closer the orientation index (OI) value is to 0, the closer the slope with respect to the negative electrode current collector surface is to 90°, and the larger the value is, the closer the slope with respect to the negative electrode current collector surface is to 0° or 180°. That is, in the negative electrode active layer according to the present invention, the carbon-based negative electrode active material is aligned at a high angle with respect to the negative electrode current collector, specifically, at an angle of 60° or more, 70° or more, 70 to 90°, 80 to 90°, 65 to 85°, or 70 to 85° with respect to the negative electrode current collector, so that the orientation index (OI) of the carbon-based negative electrode active material can be lower compared to a case where the carbon-based negative electrode active material is aligned at a low angle.

[0091] For example, the negative active layer may have an orientation index (OI) defined by the above formula 2 controlled to 1.5 to 8.0. Specifically, the negative active layer may have an orientation index (OI) of 2.0 to 8.0; 3.0 to 8.0; 4.0 to 8.0; 5.0 to 8.0; 1.5 to 7.0; 1.5 to 6.0; 1.5 to 5.0; 3.0 to 7.0; 2.5 to 5.0; 3.0 to 5.0; 3.5 to 5.0; 4.0 to 5.0; 2.5 to 4.0; 2.5 to 3.5; 2.9 to 3.9; or 3.1 to 4.3.

[0092] Carbon-based anode active materials with ab-axis crystal planes oriented at a high angle relative to the surface of the anode current collector provide low tortuosity to the anode active layer. This shortens the path that lithium ions travel during charging of a secondary battery, thereby improving the charging speed.

[0093] In addition, the negative electrode active layer may have a rolled form, and thus may have a high energy density. In general, when the negative electrode active layer is rolled, even if the negative electrode active layer includes a carbon-based negative electrode active material with an ab-axis crystal plane aligned, the ab-axis crystal plane of the aligned carbon-based negative electrode active material collapses during the rolling process, increasing the orientation index (OI), so that the curvature of the negative electrode active layer increases again. In other words, since the alignment and / or orientation effect of the carbon-based negative electrode active material is offset by the rolling, the rolled negative electrode active layer has a minimal effect even if the rapid charging performance is improved.

[0094] However, the negative electrode active layer according to the present invention can improve both the energy density and the rapid charging performance of the negative electrode active layer by minimizing the increase in the orientation degree (OI) of the carbon-based negative electrode active material included therein during rolling. For example, the negative electrode active layer may have a ratio of the porosity to the orientation degree (OI) of the carbon-based negative electrode active material having a predetermined value. For example, the negative electrode active layer satisfies a ratio calculated by Equation 1 in the range of 0.10 to 0.16. Specifically, the negative electrode active layer may have a ratio calculated by Equation 1 in the range of 0.10 to 0.16; in the range of 0.10 to 0.15; in the range of 0.11 to 0.16; in the range of 0.10 to 0.15; or in the range of 0.10 to 0.14.

[0095] The negative electrode active layer according to the present invention may have i) a predetermined porosity range and ii) a composition of a carbon-based negative electrode active material in order to achieve energy density and excellent rapid charging performance.

[0096] Specifically, the change in orientation index (OI) of the carbon-based negative electrode active material due to rolling of the negative electrode active layer may be affected by the rolling degree of the negative electrode active layer. Therefore, the negative electrode active layer may have a porosity indirectly indicating the rolling degree within a predetermined range. The porosity of the negative electrode active layer may be in the range of 22% to 30% on average. For example, the porosity of the negative electrode active layer may be in the range of 25% to 30% on average; in the range of 22% to 28%; in the range of 28% to 30%; or in the range of 25% to 29.5%.

[0097] The above porosity is the porosity of the rolled negative electrode active layer, corresponds to the X value in the above equation 1, and can be an index indirectly indicating the degree of rolling of the negative electrode active layer. The above porosity tends to have a value that decreases as the density of the negative electrode active layer increases due to rolling. The method of measuring the porosity is not particularly limited, and in the present invention, for example, it can be measured by the BET (Brunauer-EmmettTeller) measurement method or the mercury penetration method (Hg porosimeter).

[0098] The present invention can prevent the orientation index (OI) of a carbon-based negative electrode active material from being reduced and resulting in a drop in rapid charging performance due to a porosity lower than the lower limit of the above-described range by controlling the porosity of the negative electrode active layer within the above-described range. In addition, the present invention can solve the problem of the energy density of the negative electrode active layer remaining low due to a high porosity exceeding the upper limit of the above-described range by controlling the porosity within the above-described range.

[0099] In addition, the carbon-based negative electrode active material may further include a negative electrode active material having a carbon component as a main component, along with low-expansion graphite. Specifically, the carbon-based negative electrode active material may further include one or more of natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, carbon microbeads, and other than mesophase calcined carbon using tar or pitch as a raw material (bulk mesophase, liquid crystal pitch-based carbon fiber, etc.), or graphitized carbon such as coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, coal coke, etc.).

[0100] The above carbon-based negative electrode active material may have 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 particles.

[0101] Meanwhile, the carbon-based negative electrode active material included in the negative electrode active layer may have an average particle diameter satisfying a predetermined range. Specifically, the carbon-based negative electrode active material may have an average particle diameter (D) in the range of 0.5 μm to 20 μm. 50 ) can be represented. For example, the carbon-based negative electrode active material may 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.

[0102] The average particle size of the 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 lithium ion charging. However, when the particle size of the 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.

[0103] The negative electrode active layer including such a carbon-based negative electrode active material may have a structure in which the alignment and / or orientation of the carbon-based negative electrode active material is controlled by region.

[0104] Furthermore, the negative electrode active layer may optionally further include a silicon-based negative electrode active material, a conductive material, a binder, other additives, etc., as needed, in addition to the carbon-based negative electrode active material as the main component.

[0105] The above 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), silicon monoxide (SiO), or silicon dioxide (SiO2), and these may be included alone or in combination in the negative electrode active layer. When silicon monoxide (SiO2) and silicon dioxide (SiO2) are uniformly mixed or composited and included in the negative electrode active layer as the silicon-based negative electrode active materials, they are silicon oxide (SiO q , but can be expressed as 0.8≤q≤2.5).

[0106] In addition, the silicon-based negative electrode active material may be doped with Li, Mg, Al, Ca, or Ti, or may form an alloy. In addition, the silicon-based negative electrode active material may be surface-treated with a carbon coating layer or the like to suppress volume expansion during charging and improve electrical conductivity of the negative electrode active material when containing oxygen (O).

[0107] In addition, the silicon-based negative electrode active material may be included in an amount of 0.1 to 40 wt% based on the total weight of the negative electrode active layer. Specifically, the silicon-based negative electrode active material may be included in an amount of 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%, 10 to 30 wt%, 20 to 40 wt%, 25 to 35 wt%, 15 to 25 wt%, or 9 to 22 wt% based on the total weight of the negative electrode active layer. The present invention can reduce lithium consumption and irreversible capacity loss during initial charge and discharge of a secondary battery while improving the charge capacity per unit mass by controlling the content ratio of the silicon-based negative electrode active material included in the negative electrode active layer within the above range. 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.

[0108] The above-mentioned conductive material may include, but is not limited to, one or more types of carbon black such as acetylene black, Denka black, Ketjen black, Super-P, furnace black, lamp black, and summer black; graphene; carbon nanotubes, and carbon fibers.

[0109] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0110] The content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire 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. In addition, the present invention can prevent the problem of the charge capacity being lowered due to an increase in the content of the negative electrode active material due to an excessive amount of the conductive material exceeding the above range, or the electrical resistance from being increased due to an increase in the loading amount of the negative electrode active layer.

[0111] 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.

[0112] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire 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 the entire 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.

[0113] The 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, since 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 during the manufacturing process of the negative electrode active layer, there is a limitation in that the rapid charging performance of the manufactured negative electrode is low. Therefore, the present invention can adjust the average thickness of the negative electrode active layer within a predetermined range. Specifically, the negative electrode active layer may have an average thickness in the range of 100 ㎛ to 400 ㎛. For example, the 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 effect of improving rapid charging performance by controlling the average thickness of the negative electrode active layer to exceed the upper limit of the above-mentioned range and thus implementing a high orientation index (OI) of the carbon-based negative electrode active material by controlling the average thickness of the negative electrode active layer to the above-mentioned range, thereby minimizing the effect of improving rapid charging performance. 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.

[0114] 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, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used. In the case of copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the negative electrode current collector can be appropriately applied from 1 ㎛ to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0115]

[0116] The anode for a lithium secondary battery according to the present invention has the above-described configuration, thereby shortening the movement path of lithium ions within the anode active layer, thereby significantly reducing the diffusion resistance of lithium ions, and thus exhibiting excellent rapid charging performance. In addition, the anode has the advantage of excellent energy density of the anode, since the density of the anode active layer is improved within a range that does not damage the shortened movement path of lithium ions.

[0117]

[0118] lithium secondary battery

[0119] In addition, the present invention provides a lithium secondary battery including 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.

[0120] 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, equipped with the negative electrode of the present invention described above, has the advantage of not only improving lithium ion diffusion capacity and thus excellent rapid charging performance, but also having a high energy density.

[0121] At this time, since the cathode has the same configuration as the configuration described above, a detailed description is omitted.

[0122] In addition, the 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.

[0123] 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:

[0124] [Chemical Formula 1]

[0125] Li l [Ni m Co n Mn w M 1 v ]O2

[0126] [Chemical Formula 2]

[0127] LiM 2 p Mn q P r O4

[0128] In the above chemical formulas 1 and 2,

[0129] 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,

[0130] 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,

[0131] M 2 is Ni, Co or Fe,

[0132] p is 0.05≤p≤1.0,

[0133] q is 2-p,

[0134] r is either 0 or 1.

[0135]

[0136] 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 a high capacity and / or high voltage compared to conventional cathode active materials such as lithium iron phosphate oxide (LiFeO4).

[0137] 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., and 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 It may include O4, etc., and these may be used alone or in combination.

[0138] 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 entire 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.

[0139] The above positive electrode active layer may further include a conductive material, a binder, other additives, etc., along with the positive electrode active material.

[0140] The above-mentioned conductive material is used to improve the electrical performance of the anode, and can be applied to those commonly used in the art, but specifically, it can include one or more of natural graphite; artificial graphite; carbon black such as acetylene black, Denka black, Ketjen black, Super-P, furnace black, lamp black, and summer black; graphene; and carbon nanotubes.

[0141] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active layer. Specifically, the conductive material 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.

[0142] The above binder serves to bind the positive electrode active material 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.

[0143] Additionally, the binder may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the positive electrode active layer. Specifically, the binder may be included in an amount of 2 to 8 parts by weight based on 100 parts by weight of the positive electrode active layer; or in an amount of 1 to 5 parts by weight based on 100 parts by weight of the positive electrode active layer.

[0144] The total thickness of the positive electrode active layer is not particularly limited, but may specifically be in the range of 50 μm to 300 μm. More specifically, the total thickness of the positive electrode active layer may be 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.

[0145] 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, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. The average thickness of the current collector can be appropriately applied from 3㎛ to 500㎛, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0146] 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 be one comprising 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 comprising 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.

[0147] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery having 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.

[0148] Pouch-type secondary batteries and / or square secondary batteries have the advantage of high utilization in terms of energy density because the unit cells of the secondary batteries can be packed at a high density in a limited space.

[0149]

[0150] Method for manufacturing a negative electrode for a lithium secondary battery

[0151] Furthermore, the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery according to the present invention described above.

[0152]

[0153] A method for manufacturing a negative electrode for a lithium secondary battery according to the present invention includes a step (S1) of applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector, a step (S2) of applying a magnetic field to the applied negative electrode slurry, a step (S3) of drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer, and a step (S4) of rolling the formed negative electrode active layer.

[0154] The above step (S1) refers to a process of coating at least one surface of a moving negative electrode current collector by discharging a negative electrode slurry containing a carbon-based negative electrode active material.

[0155] This step (S1) can be applied without any particular limitation as long as it is a method commonly applied in the art, but preferably, a die coating method can be used. The die coating method can be performed using a slot die equipped with a shim for controlling the discharge conditions of the negative electrode slurry. The slot die 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, position, etc. of the shim.

[0156] The above-mentioned negative electrode slurry contains a carbon-based negative electrode active material as a main component, and the carbon-based negative electrode active material includes "low-expansion graphite." In the present invention, "low-expansion graphite" refers to graphite having low expansion characteristics when a secondary battery is charged. The expansion characteristics of the low-expansion graphite can be determined through changes in the thickness of the negative electrode active layer according to charge and discharge cycles.

[0157] Examples of such low-expansion graphite include low-expansion natural graphite and low-expansion artificial graphite. 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.

[0158] The above low-expansion graphite may refer to natural graphite particles coated with carbon. 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 a carbon-based negative electrode active material and / or the manufacturing of an negative electrode using the same or the assembly of a battery. In addition, the low-expansion graphite has the characteristic of high porosity within the graphite particles. The high porosity of the graphite particles can improve the volume expansion control ability of the negative electrode active material itself, so that the volume expansion characteristics are small when charging a secondary battery, and the orientation index (OI) of the carbon-based negative electrode active material can be maintained low even after rolling.

[0159] A more detailed description of the above low-expansion graphite is quoted from the above-mentioned.

[0160] The present invention can maintain the orientation index (OI) of a carbon-based negative electrode active material contained in a negative electrode active layer low even after rolling by controlling the content of low-expansion graphite contained in a negative electrode slurry within the above-described range.

[0161] The above-mentioned negative electrode slurry may further include a carbon-based negative electrode active material in addition to low-expansion graphite, and may further include a conductive material, 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.

[0162] Meanwhile, the orientation of the carbon-based negative electrode active material can be induced by applying a magnetic field after this step (S1).

[0163] Specifically, the above step (S2) means a process of applying a magnetic field to the negative electrode slurry to align and / or orient the ab-axis crystal plane of the carbon-based negative electrode active material included in the negative electrode slurry.

[0164] At this time, the degree to which the ab-axis crystal planes of the carbon-based negative electrode active material included in the negative electrode slurry are aligned and / or oriented may vary depending on the conditions of the applied magnetic field, specifically, the strength of the applied magnetic field.

[0165] Here, the magnetic field applied to the negative electrode slurry may have a strength in the range of 1,000 G to 9,000 G (Gauss) to enhance the effect of aligning and / or orienting the ab-axis crystal plane of the carbon-based negative electrode active material. Specifically, the magnetic field applied to the negative electrode slurry is 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 7,500 G; 5,500 G to 6,500 G; 1,000 G to 7,000 G; 2,000 G to 6,000 G; 1,500 G to 5,000 G; 1,500 G to 4,500 G; The magnetic field can be applied with a strength in the range of 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 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 formed after drying the negative electrode slurry containing the carbon-based negative electrode active material.

[0167] Next, the above step (S3) refers to a process of forming a cathode active layer by drying the cathode slurry to which a magnetic field is applied.

[0168] At this time, the 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 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] Next, the above step (S4) refers to a process of rolling the negative electrode active layer formed by drying. 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 negative electrode active layer formed using a roll press or the like.

[0170] The above rolling can be 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 to manufacture a negative electrode having a final negative electrode active material layer formed on a current collector.

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

[0172] Specifically, the rolling can be performed under heating conditions, but it is preferable to perform the rolling without heating in order to suppress changes in the physical properties of the electrode. For example, the rolling can be performed at a temperature in the range of 18°C ​​to 35°C, and more specifically, at a temperature of 18°C ​​to 30°C; 18°C ​​to 23°C; 22°C to 25°C; 20°C to 25°C; 20°C; or 25°C.

[0173] In addition, the rolling can be performed at a rolling speed in the range of 2 m / s to 7 m / s, and more specifically, it 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] In addition, the rolling can be performed under a pressure condition of 50 MPa to 200 MPa, and specifically, it can be performed under a pressure condition in the range of 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]

[0176] Additionally, the vacuum drying conditions may be performed for 1 to 15 hours at, for example, a temperature range of 150°C to 250°C, a range of 160°C to 200°C, or a range of 175°C to 185°C.

[0177] The present invention can maximize the energy density of the negative electrode active layer while minimizing the decrease in the orientation index (OI) of the carbon-based negative electrode active material of the negative electrode active layer formed by performing rolling under the above-mentioned temperature, speed, and / or pressure conditions.

[0178] In general, when rolling a negative electrode active layer, even if the negative electrode active layer includes a carbon-based negative electrode active material with an ab-axis crystal plane aligned, the aligned ab-axis crystal plane of the carbon-based negative electrode active material collapses during the rolling process, increasing the orientation index (OI), thereby increasing the curvature of the negative electrode active layer again. In other words, since the alignment and / or orientation effect of the carbon-based negative electrode active material is offset by rolling, the rolled negative electrode active layer has a minimal effect even if the rapid charging performance is improved.

[0179] However, the method for manufacturing a negative electrode according to the present invention can improve both the energy density and the rapid charging performance of the negative electrode active layer by minimizing the increase in the orientation index (OI) during rolling of the dried negative electrode active layer. For example, in the present step (S4), when fitting the orientation index (OI) of the carbon-based negative electrode active material to the porosity, the rolled negative electrode active layer may have an average slope of 0 or a positive value in the section where the porosity is 25% to 27%. For example, when fitting the orientation index (OI) of the carbon-based negative electrode active material to the porosity, the negative electrode active layer may have an average slope of 0 or more and 0.5 or less; 0 or more and 0.4 or less; 0 or more and 0.3 or less; 0 or more and 0.2 or less; 0 or more and 0.15 or less; 0 or more and 0.11 or less; 0.05 or more and 0.15 or less; 0.05 or more and 0.2 or less; 0.1 or more and 0.3 or less; 0.2 or more and 0.4 or less; 0.25 or more and 0.5 or less; or 0.01 or more and 0.19 or less.

[0180] When fitting the orientation index (OI) of the carbon-based negative electrode active material to the porosity, the average slope of 0 or more in the section where the porosity is 25% to 27% means that the orientation index (OI) of the carbon-based negative electrode active material does not increase but is maintained or decreases as the rolling density increases in the section where the porosity is 25% to 27%. This indicates that even if the rolling density of the negative electrode active layer increases due to rolling, a low orientation index (OI) of the carbon-based negative electrode active material is implemented in the section, which means that the negative electrode active layer according to the present invention has high energy density and excellent rapid charging performance.

[0181] In contrast, when fitting the orientation index (OI) of the carbon-based negative electrode active material to the porosity of the negative electrode active layer, if the average slope in the section where the porosity is 25% to 27% is less than 0, the bending rate increases during rolling, which may reduce the rapid charging performance. In addition, if the average slope in the section where the porosity of the negative electrode active layer is 25% to 27% exceeds the upper limit described above, there is a limitation in that the contact characteristics at the interface between the negative electrode active layer and the negative electrode current collector deteriorate, resulting in a decrease in durability.

[0182] In addition, the rolled cathode active layer satisfies the ratio calculated by Equation 1 below in the range of 0.10 to 0.16.

[0183] [Formula 1]

[0184] Y / X

[0185] In the above equation 1,

[0186] Y represents the orientation index (OI) of the carbon-based negative electrode active material,

[0187] X represents the porosity (vol%) of the cathode active layer, where X is in the range of 22% to 30%.

[0188] A more detailed explanation of Equation 1 is the same as previously mentioned.

[0189] In addition, the orientation index (OI) of the above carbon-based negative electrode active material is defined by the following equation 2.

[0190] [Formula 2]

[0191] OI= I 004 / I 110

[0192] In the above equation 2,

[0193] I 110 represents the intensity of the peak representing the (110) crystal plane of the carbon-based negative electrode material when measuring X-ray diffraction (XRD) on the negative electrode active layer,

[0194] I 004It represents the intensity of the peak representing the (004) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD) measurement of the negative electrode active layer.

[0195] A more detailed explanation of Equation 2 is the same as previously mentioned.

[0196] The negative electrode active layer of the negative electrode manufactured according to the present invention can improve both the energy density and the rapid charging performance of the negative electrode active layer by adjusting the ratio calculated by the above-described Equation 1. In addition, the negative electrode active layer can have a predetermined rolling ratio in order to realize the energy density and excellent rapid charging performance. The rolling ratio is a value obtained by dividing the thickness difference before and after rolling by the thickness before rolling, and represents the ratio of the thickness of the negative electrode active layer reduced due to rolling. The rolling ratio, as opposed to the porosity, tends to increase as the density of the negative electrode active layer increases due to rolling. The negative electrode active layer according to the present invention can have a rolling ratio (vol%) in the range of 30% to 42% on average. Specifically, the rolling ratio of the negative electrode active layer can be in the range of 30% to 40%; 32% to 40%; or 30% to 39% on average.

[0197] The present invention can prevent the energy density of the negative electrode active layer from being lowered due to a rolling rate lower than the lower limit of the above-described range by satisfying the rolling rate of the negative electrode active layer within the above-described range. In addition, the present invention can prevent the orientation index (OI) of the carbon-based negative electrode active material from being reduced due to a high rolling rate exceeding the upper limit of the above-described range by controlling the rolling rate within the above-described range, thereby deteriorating the rapid charging performance.

[0198]

[0199] The method for manufacturing a negative electrode for a lithium secondary battery according to the present invention can manufacture a negative electrode having a low tortuosity of a negative electrode active layer due to application of a magnetic field and an improved energy density due to rolling by having the above-described configuration.

[0200]

[0201] Hereinafter, the present invention will be described in more detail through examples and comparative examples.

[0202] 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.

[0203]

[0204] Examples 1 to 3 and Comparative Examples 1 to 4. Preparation of negative electrode for lithium secondary battery

[0205] 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 ): approximately 12~16㎛, total pore volume: approximately 0.006~0.012㎤ / g) was prepared as a carbon-based negative electrode active material. In addition, styrene butadiene rubber (SBR) was prepared as a binder, carboxymethyl cellulose (CMC) was prepared as a thickener, and carbon black (Super-P) was prepared as a conductive material.

[0206] Then, as shown in Table 1 below, ① a carbon-based negative electrode active material was prepared, and 96.85 wt% of the prepared carbon-based negative electrode active material, 1.05 wt% of carboxymethyl cellulose (CMC), 1.6 wt% of styrene butadiene rubber (SBR), and 0.5 wt% of carbon black were mixed with water to obtain a solid content of 50% to prepare a negative electrode slurry. At this time, the viscosity of the prepared negative electrode slurry at room temperature (22±3℃) was 7,000 to 12,000 cps.

[0207] The prepared cathode slurry was applied (S1) onto a copper foil (thickness: 6 μm) being transported roll-to-roll (transport speed: 6 m / min) using a die coater. Thereafter, a magnetic field of 8,050±50 G (Gauss) was applied (S2) for 2 to 11 seconds from the bottom of the applied cathode slurry using a magnet. The application of the magnetic field was controlled as shown in Table 1 below.

[0208] A negative electrode slurry to which a magnetic field was applied was hot-air dried to form a negative electrode active layer on a negative electrode current collector. The thickness of the formed negative electrode active layer was measured to calculate the average thickness, and the negative electrode current collector with the negative electrode active layer was slit into multiple pieces with the same width. Each slit negative electrode current collector was rolled using a roll press to obtain a porosity of 21–30% to manufacture a negative electrode for a lithium secondary battery. The average thickness of each manufactured negative electrode was measured, and it was confirmed that the average thickness of each negative electrode was 170–205 ㎛. ② The rolling ratio was calculated from the average thickness of the negative electrode active layer measured before and after rolling. In addition, ③ the porosity of the negative electrode active layer was calculated using the previously measured average thickness of the negative electrode active layer. In addition, X-ray diffraction (XRD) analysis was performed on the negative electrode active layer of the manufactured negative electrode to measure the X-ray diffraction of the carbon-based negative electrode active material contained in the negative electrode active layer. The measurement conditions were as follows:

[0209] - Target: Cu(Kα-ray) graphite monochromator

[0210] - Slit: Diverging slit = 1°, Receiving slit = 0.1mm, Scattering slit = 1°

[0211] - Measurement area: (110) plane: 76.5°<2θ<78.5° / (004) plane: 53.5°<2θ<56.0°.

[0212]

[0213] The orientation index (OI) of the carbon-based negative electrode material ⑤ was calculated from the measured spectrum using the following equation 2:

[0214] [Formula 2]

[0215] OI= I 004 / I 110

[0216] In the above equation 1,

[0217] I 110 represents the intensity of the peak representing the (110) crystal plane of the carbon-based negative electrode material when measuring X-ray diffraction (XRD) on the negative electrode active layer,

[0218] I 004 It represents the intensity of the peak representing the (004) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD) measurement of the negative electrode active layer.

[0219]

[0220] The orientation index (OI) of the carbon-based negative electrode active material was fitted to the porosity of the previously calculated negative electrode active layer, and the average slope in the section where the porosity was 25% to 27% was calculated. All measured and calculated results are shown in Table 1 below.

[0221] Classification ① Composition of carbon-based negative electrode active material ② Application of magnetic field ③ Rolling ratio ④ Porosity ⑤ Orientation (OI) ⑥ Average slope in the 25 to 27% range Example 1-a Low-expansion graphite = 100 wt% O 3 7% 25% 4.0 About 0.1 Example 1-b 3 5% 27% 4.2 Example 1-c 3 2% 29.5% 3.4 Example 2-a Low-expansion graphite: artificial graphite = 80:20 (wt% / wt%) O 3 6% 25% 3.7 About 0.05 Example 2-b 3 5% 27% 3.8 Example 2-c 3 1% 29.5% 3.2 Example 3-a Low-expansion graphite: artificial graphite = 50:50 (wt% / wt%) O 3 7% 25% 3.5 About 0.05 Example 3-b 34% 27% 3.6 Example 3-c 30% 29.5% 3.0 Comparative Example 1-a Low-expansion graphite: Artificial graphite = 20:80 (wt% / wt%) 0 36% 25% 2.48 Approximately -0.06 Comparative Example 1-b 34% 27% 2.36 Comparative Example 1-c 29% 29.5% 1.84 Comparative Example 2-a Low-expansion graphite = 100 wt% X 36% 25% 23.5 Approximately -1.1 Comparative Example 2-b 34% 27% 21.3 Comparative Example 2-c 30% 29.5% 20.6 Comparative Example 3-a Artificial graphite = 100 wt% 0 36% 25% 2.1 Approximately -0.1 Comparative Example 3-b 34% 27% 1.9 Comparative Example 3-c 29% 29.5% 1.5 Comparative Example 4-a Natural graphite = 100 wt% O 38% 25% 5.6 approx. -0.05 Comparative Example 4-b 36% 27% 5.5 Comparative Example 4-c 34% 29.5% 4.9

[0222] In addition, Fig. 1 graphically illustrates the relationship between the porosity and the orientation index (OI) of the carbon-based negative electrode active material in the above examples and comparative examples. Fig. 1 illustrates the calculation results for Examples 1 to 3 and Comparative Examples 1 to 3. In addition, Fig. 1 also illustrates cases where the porosity is 21% and 33%.

[0223]

[0224] Examples 4 to 12 and Comparative Examples 8 to 16. Manufacturing of lithium secondary batteries.

[0225] LiNi with a particle size of 5㎛ as a cathode active material 0.7 Co 0.1 Mn 0.1 Al 0.1O2 was prepared, and polyvinylidene fluoride as a carbon-based conductive agent and binder and N-methyl pyrrolidone (NMP) were mixed 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.

[0226] An electrode assembly was manufactured using the manufactured positive electrode, the negative electrode manufactured in Examples 1 to 3 and Comparative Examples 1 to 4, the LTO electrode, and the separator, respectively. The separator used was a 14 μm polypropylene separator. The LTO electrode was manufactured by coating LTO on a copper (C9) wire. The electrode assembly was inserted into a case, and then an electrolyte composition was injected to manufacture a lithium secondary battery.

[0227] At this time, the types of negative electrodes applied to each lithium secondary battery are shown in Table 2 below.

[0228] Types of cathodes applied separately Example 4 Anode manufactured in Example 1-a Example 5 Anode manufactured in Example 1-b Example 6 Anode manufactured in Example 1-c Example 7 Anode manufactured in Example 2-a Example 8 Anode manufactured in Example 2-b Example 9 Anode manufactured in Example 2-c Example 10 Anode manufactured in Example 3-a Example 11 Anode manufactured in Example 3-b Example 12 Anode manufactured in Example 3-c Comparative Example 5 Anode manufactured in Comparative Example 1-a Comparative Example 6 Anode manufactured in Comparative Example 1-b Comparative Example 7 Anode manufactured in Comparative Example 1-c Comparative Example 8 Anode manufactured in Comparative Example 2-a Comparative Example 9 Comparative Example Cathode manufactured in Comparative Example 10 Cathode manufactured in Comparative Example 2-c Cathode manufactured in Comparative Example 11 Cathode manufactured in Comparative Example 3-a Cathode manufactured in Comparative Example 12 Cathode manufactured in Comparative Example 3-b Cathode manufactured in Comparative Example 13 Cathode manufactured in Comparative Example 3-c Cathode manufactured in Comparative Example 14 Cathode manufactured in Comparative Example 4-a Cathode manufactured in Comparative Example 15 Cathode manufactured in Comparative Example 4-b Cathode manufactured in Comparative Example 16 Cathode manufactured in Comparative Example 4-c

[0229]

[0230] Experimental example.

[0231] In order to evaluate the properties and performance of the cathode manufactured according to the present invention, the following experiments were conducted.

[0232]

[0233] 1) Rapid charging performance evaluation

[0234] The rapid charging performance of the lithium secondary batteries manufactured in Examples 4 to 12 and Comparative Examples 5 to 16 was evaluated. Specifically, charge and discharge were performed between the cathode and LTO, and the LTO was charged to 50% of the SOC to adjust the potential to 1.53 V. The LTO voltage profile showed that 1.53 V was maintained throughout most of the SOC range. In addition, the voltage profile of the cathode potential was confirmed by measuring the cathode-LTO and anode-cathode voltages using an EC-lab charger and discharger. The portion where a plateau appeared in the profile for the cathode during charging was determined as the charge capacity (charge depth). The C-rate was increased from 0.5 C to 3 C in 0.5 C increments, and the charge depth at each C-rate was confirmed, and then the required charging time was measured. The measured charging times are shown in Table 3 below.

[0235]

[0236] 2) Energy density measurement

[0237] The loading per unit area was measured for the negative electrodes for lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4.

[0238] Thereafter, the energy density of a large secondary battery cell was calculated using the previously measured porosity. At this time, the large 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 results are shown in Table 3 below.

[0239] Classification Carbon-based negative electrode active material composition Porosity SOC 10 → SOC 80 Charging time [minutes] Energy density [Wh / L] Example 4 Low expansion graphite = 100 wt% 25% 28.86 0 3.1 Example 5 27% 29.15 9 ​​6.1 Example 6 29.5% 27.95 8 7.0 Example 7 Low expansion graphite: artificial graphite = 80:20 (wt% / wt%) 25% 29.36 0 4.0 Example 8 27% 29.55 9 6.2 Example 9 29.5% 27.85 8 6.8 Example 10 Low expansion graphite: artificial graphite = 50:50 (wt% / wt%) 25% 29.86 0 4.3 Example 1 1 27% 29.85 9 6.6 Example 1229.5%27.8586.5Comparative Example 5 Low-expansion graphite: artificial graphite = 20:80 (wt% / wt%)25%30.9603.5Comparative Example 627%30.1596.0Comparative Example 729.5%28.5586.5Comparative Example 8 Low-expansion graphite = 100 wt%25%41.8603.4Comparative Example 927%39.2596.0Comparative Example 1029.5%36.7585.1Comparative Example 11 Artificial graphite = 100 wt%25%31.9602.7Comparative Example 1227%30.5596.3Comparative Example 1329.5%28.4586.5Comparative Example 14 Natural graphite = 100 Weight %25%33.4590.2Comparative Example 1527%31.2579.0Comparative Example 1629.5%30.7572.4

[0240]

[0241] As shown in Table 3 above, it can be seen that the negative electrode according to the present invention has excellent rapid charging performance and high energy density at the same time. Specifically, the lithium secondary batteries manufactured in the examples showed that the energy density improved by about 1.3% from about 586 Wh / L to about 604.3 Wh / L as the porosity was lowered from 29.5% to 25% by rolling. In addition, it was confirmed that the time required for the lithium secondary batteries manufactured in the examples to charge from 10% to 80% of the state of charge (SOC) was 30 minutes or less. In particular, the lithium secondary batteries showed that the phenomenon of delayed charging time was suppressed even when the porosity was lowered from 27% to 25%.

[0242] These results indicate that the negative electrode according to the present invention includes oriented low-expansion graphite as a carbon-based negative electrode active material, and when the ratio of the orientation degree (OI) of the carbon-based negative electrode active material to the porosity of the negative electrode active layer satisfies a predetermined range, not only does the energy density of the negative electrode increase, but also the increase in the orientation degree (OI) of the carbon-based negative electrode active material is improved.

[0243] Therefore, it can be seen that the negative electrode according to the present invention has excellent rapid charging performance and energy density.

[0244]

[0245] 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.

[0246] 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.

Claims

1. Negative current collector, and A negative electrode active layer provided on at least one surface of the negative electrode current collector and including a carbon-based negative electrode active material; The above carbon-based negative electrode active material has a total pore volume of 1×10 -5 ㎤ / g to 1×10 -1 Contains graphite in the range of ㎤ / g; The above cathode active layer satisfies the ratio calculated by the following equation 1 in the range of 0.10 to 0.16, The orientation index (OI) of the above carbon-based negative electrode active material is defined by the following equation 2: [Formula 1] Y / X In the above equation 1, Y represents the orientation index (OI) of the carbon-based negative electrode active material, X represents the porosity (vol%) of the cathode active layer, wherein X is in the range of 22% to 30%, [Formula 2] OI= I 004 / I 110 In the above equation 2, I 110 represents the intensity of the peak representing the (110) crystal plane of the carbon-based negative electrode material when measuring X-ray diffraction (XRD) on the negative electrode active layer, I 004 It represents the intensity of the peak representing the (004) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD) measurement of the negative electrode active layer.

2. In paragraph 1, An anode having an average orientation index (OI) of the above carbon-based anode active material in the range of 1.5 to 8.

0.

3. In paragraph 1, A cathode having a porosity (X) of the above cathode active layer in the range of 25% to 29.5% on average.

4. In paragraph 1, Total pore volume is 1×10 -5 ㎤ / g to 1×10 -1 The graphite content in the range of ㎤ / g is A negative electrode having a range of 25 wt% to 100 wt% based on the total weight of the carbon-based negative electrode active material.

5. In paragraph 1, The above carbon-based negative electrode active material further comprises 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.

6. In paragraph 1, The above cathode active layer is a cathode having an average thickness of 100 ㎛ to 400 ㎛.

7. A secondary battery including a negative electrode according to paragraph 1.

8. Step (S1) of applying a negative electrode slurry containing a carbon-based negative electrode active material to at least one surface of a negative electrode current collector; Step (S2) of applying a magnetic field to the applied cathode slurry; Step (S3) of drying the cathode slurry to which a magnetic field is applied to form a cathode active layer, and It includes a step (S4) of rolling the formed cathode active layer, The above carbon-based negative electrode active material has a total pore volume of 1×10 -5 ㎤ / g to 1×10 -1 Contains graphite in the range of ㎤ / g, The total pore volume above is 1×10 -5 ㎤ / g to 1×10 -1 A method for manufacturing a negative electrode, wherein the content of graphite in the range of ㎤ / g is in the range of 25 wt% to 100 wt% based on the total weight of the carbon-based negative electrode active material.

9. In paragraph 8, The step (S4) of rolling the above negative active layer is: A method for manufacturing a rolled negative electrode active layer, wherein when fitting the orientation index (OI) of a carbon-based negative electrode active material to a porosity, the average slope in the section where the porosity is 25% to 27% is controlled to have a 0 or positive value.

10. In paragraph 8, The above cathode active layer satisfies the ratio of the following formula 1 in the range of 0.10 to 0.16, The orientation index (OI) of the above carbon-based negative electrode active material is defined by the following formula 2: [Formula 1] Y / X In the above equation 1, Y represents the orientation index (OI) of the carbon-based negative electrode active material, X represents the porosity (vol%) of the cathode active layer, wherein X is in the range of 22% to 30%, [Formula 2] OI= I 004 / I 110 In the above equation 2, I 110 represents the intensity of the peak representing the (110) crystal plane of the carbon-based negative electrode material when measuring X-ray diffraction (XRD) on the negative electrode active layer, I 004 It represents the intensity of the peak representing the (004) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD) measurement of the negative electrode active layer.

11. In paragraph 8, A method for manufacturing a cathode, wherein the rolling ratio (vol%) of the cathode active layer is in a range of more than 30% and less than 42%.

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