Negative electrode for lithium secondary battery and method of manufacturing same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and method of manufacturing same, wherein the negative electrode includes a carbon-based negative electrode active material and a silicon-based negative electrode active material together in a negative electrode active layer, and thus exhibits a high charge and discharge capacity. In addition, the negative electrode active layer of the negative electrode has a two-layer structure, wherein, in the second negative electrode active layer positioned at the outermost layer, i) the order index (O.I) of the carbon-based negative electrode active material and ii) the ratio of the order index (O.I) and a specific X-ray diffraction peak area of the silicon-based negative electrode active material are adjusted to satisfy a predetermined range, resulting in the advantage of improving the high efficiency charging / discharging characteristics of a lithium secondary battery including same.

Description

Anode for lithium secondary battery and method for manufacturing the same

[0001] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2023-0076642, filed June 15, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same.

[0003]

[0004] Recently, lithium secondary batteries have been widely applied not only in small devices such as portable electronic devices, but also in medium and large-sized devices such as battery packs for hybrid and electric vehicles and power storage devices. In particular, with growing concern over environmental issues, research is being conducted on electric vehicles and hybrid electric vehicles that can replace fossil fuel-powered vehicles such as gasoline and diesel vehicles, which are a major cause of air pollution.

[0005] Due to their limited energy density, existing lithium secondary batteries are limited to short-range electric vehicles. Therefore, technology development has focused on further increasing the energy density of lithium secondary batteries.

[0006] However, developed lithium secondary batteries for automotive applications suffer from the long charging times required after discharging during driving. Consequently, as the adoption of electric vehicles increases, demand is growing for shorter charging times to a level acceptable to users. Furthermore, electric vehicles must be able to operate without issues even under high-power conditions, such as rapid acceleration. To achieve this, lithium secondary batteries must exhibit high-rate discharge performance, but currently, no technology exists to meet this requirement.

[0007] Meanwhile, lithium secondary batteries are rechargeable power generation devices composed of a stacked structure of anode / separator / cathode. 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, and a lithium insertion reaction 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, so the rapid charge / discharge performance of a lithium secondary battery is primarily determined by the cathode.

[0008] As the negative electrode active material of the above-mentioned negative electrode, a material containing graphite is widely used. 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.

[0009] Accordingly, various anode active materials are being studied to improve the high capacity and rapid charging performance of lithium secondary batteries. For example, since it has been known that silicon can reversibly adsorb and release large amounts of lithium through a compound formation reaction with lithium, much research has been conducted recently on this. 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, and thus has the advantage of being useful as a high-energy density and / or high-capacity anode material. However, silicon has limitations in that it not only induces a large volume change (~300%) during charge and discharge, but also does not have high high-rate discharge characteristics, limiting the lifespan and rapid discharge efficiency of lithium secondary batteries containing it.

[0010] Therefore, in order to fundamentally solve these problems, there is a high need for cathode technology that can simultaneously implement high-capacity characteristics and high-rate charge / discharge characteristics.

[0011]

[0012] The purpose of the present invention is to provide a negative electrode for a lithium secondary battery capable of simultaneously implementing high-capacity characteristics and high-rate charge / discharge characteristics, a method for manufacturing the same, and a lithium secondary battery including the negative electrode.

[0013]

[0014] To solve the above-mentioned problem,

[0015] In one embodiment of 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 second cathode active layer is

[0020] The alignment degree (OI) of the carbon-based negative electrode active material according to the following formula 1 is 2.5 or less,

[0021] A negative electrode for a lithium secondary battery is provided that satisfies the following equation 2 with a value of 8 or less:

[0022] [Formula 1]

[0023] OI = I 004 / I 110

[0024] [Formula 2]

[0025] I Si *OI

[0026] In equations 1 and 2,

[0027] I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer,

[0028] I 110 represents the area of ​​the peak representing the (1,1,0) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0029] I si It represents the area ratio of the peak representing the (1,1,1) crystal plane of the silicon-based negative electrode active material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0030] At this time, the alignment degree (OI) of the carbon-based negative electrode active material of the second negative electrode active layer may be 0.1 to 1.5, and Equation 2 may be 0.7 to 6.

[0031] Additionally, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may each include at least one of natural graphite and artificial graphite.

[0032] In addition, the above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q , but may include one or more of the following (0.8≤q≤2.5).

[0033] The above silicon-based negative electrode active material may be included in an amount of 1 wt% to 40 wt% based on the weight of the entire negative electrode active layer included in the first negative electrode active layer and the second negative electrode active layer.

[0034] In addition, the average particle diameter (Dc) of the second carbon-based negative electrode active material may be 1 µm to 50 µm, the average particle diameter (Ds) of the silicon-based negative electrode active material may be 0.1 µm to 10 µm, and the average particle diameter ratio (Dc / Ds) of the second carbon-based negative electrode active material and the silicon-based negative electrode active material may be 2 to 10.

[0035] In addition, the second cathode active layer may include a silicon-based cathode active material in an amount of 1 wt% to 40 wt% based on the weight of the entire cathode active layer.

[0036]

[0037] In addition, in one embodiment of the present invention,

[0038] A step of applying a first negative electrode slurry and a second negative electrode slurry such that the first negative electrode slurry is positioned on at least one surface of a negative electrode current collector and the second negative electrode slurry is positioned on the first negative electrode slurry;

[0039] A step of applying a magnetic field to the applied first cathode slurry and the second cathode slurry; and

[0040] A step of forming a cathode active layer by drying a first cathode slurry and a second cathode slurry to which a magnetic field is applied,

[0041] The above first negative electrode slurry includes a first carbon-based negative electrode active material,

[0042] The above second negative electrode slurry includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material,

[0043] The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the magnetic field is applied with a strength of 10,000 G or less.

[0044] At this time, the step of applying the magnetic field can be performed for 1 to 20 seconds.

[0045]

[0046] Furthermore, in one embodiment of the present invention,

[0047] A lithium secondary battery is provided having an electrode assembly including a positive electrode, a negative electrode according to the present invention, and a separator disposed between the positive electrode and the negative electrode.

[0048] At this time, the positive electrode is provided on at least one surface of the positive electrode current collector and may include one or more types of positive electrode active materials among lithium metal oxides represented by the following chemical formulas 1 and 2:

[0049] [Chemical Formula 1]

[0050] Li x [Ni y Co z Mn w M 1 v ]O2

[0051] [Chemical Formula 2]

[0052] LiM 2 p Mn 1-p O4

[0053] In the above chemical formulas 1 and 2,

[0054] M 1 is at least one element selected from the group consisting of 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,

[0055] x, y, z, w, and v are 1.0≤x≤1.30, 0.5≤y<1, 0, respectively. <z≤0.3, 0<w≤0.3, 0≤v≤0.1이되, y+z+w+v=1이고,

[0056] M 2 is Ni, Co or Fe,

[0057] p is 0.05≤p≤1.0.

[0058] As an example, the positive electrode active material 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 O2, LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4 and LiNi 0.3 Mn 1.7 It may include one or more selected from the group consisting of O4.

[0059] Meanwhile, the electrode assembly may be a stacked electrode assembly; a zigzag electrode assembly; or a zigzag-stacked electrode assembly.

[0060]

[0061] The negative electrode for a lithium secondary battery according to the present invention exhibits a high charge / discharge capacity by including a silicon-based negative electrode active material together with a carbon-based negative electrode active material in the negative electrode active layer. In addition, the negative electrode active layer of the negative electrode has a two-layer structure, and i) the alignment degree (OI) of the carbon-based negative electrode active material of the second negative electrode active layer located at the outermost layer and ii) the ratio of the alignment degree (OI) and the specific X-ray diffraction peak area of ​​the silicon-based negative electrode active material are controlled to satisfy a predetermined range, thereby having an excellent advantage in that the high-rate charge / discharge characteristics of a lithium secondary battery including the same are improved.

[0062]

[0063] 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.

[0064] However, this is not intended to limit the present invention to a specific embodiment, but should be understood to include all modifications, equivalents, or substitutes included in the technical scope of the present invention.

[0065] 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.

[0066] Additionally, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "directly above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "directly below" the other part, but also cases where there is another part in between. Furthermore, in the present application, "on" may include cases where it is placed below as well as above.

[0067] In addition, in the present invention, "comprising as a main component" may mean comprising a defined component at 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 total weight (or total volume). For example, "comprising graphite as a main component as a negative electrode active material" may mean comprising graphite at 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 of the total weight of the negative electrode active material, and in some cases, it may mean that the entire negative electrode active material is made of graphite and comprises 100 wt% of graphite.

[0068] In addition, in the present specification, “the carbon-based negative electrode active material is oriented” or “the carbon-based negative electrode active material is aligned” means that a specific crystal plane (e.g., the ab-axis crystal plane of graphite) representing a two-dimensional planar structure of the carbon-based negative electrode active material constituting the negative electrode active material particles is arranged to have a predetermined inclination with respect to the negative electrode current collector surface, which 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.

[0069] In addition, "the carbon-based negative electrode active material has a high degree of orientation" may mean that a specific crystal plane (e.g., an ab-axis crystal plane of graphite) representing a two-dimensional planar structure of the carbon-based negative electrode active material contained in the negative electrode active layer frequently has a predetermined inclination with respect to the surface of the negative electrode current collector. Furthermore, in some cases, it may mean that the crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is arranged at a high angle (e.g., an angle close to vertical, exceeding 45°; specifically, 60° or more) with respect to the surface of the negative electrode current collector.

[0070] In addition, the term "the degree of alignment of the carbon-based negative electrode active material is high" means that the "degree of alignment (OI)" mentioned herein has a large value, which may mean that a specific crystal plane (e.g., the ab-axis crystal plane of graphite) representing the two-dimensional planar structure of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a low angle (e.g., less than 45°) with respect to the surface of the negative electrode current collector. Conversely, the term "the degree of alignment of the carbon-based negative electrode active material is low" means that the "degree of alignment (OI)" has a small value, which may mean that the crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle (e.g., an angle close to vertical, 45° or more; specifically, 60° or more) with respect to the surface of the negative electrode current collector.

[0071] Furthermore, in this specification, the “crystal plane of the carbon-based negative electrode active material” refers to a plane where atoms of the carbon-based negative electrode active material form the outer shape of the crystal, and in the present invention, it may mean a crystal plane including a plane of the carbon-based negative electrode active material, or a crystal plane including the a-axis / b-axis / ab-axis of the carbon-based negative electrode active material crystal.

[0072] Also, in this specification, "average particle diameter (D 50 )" refers to the particle size at which the accumulated value is 50% in the particle size distribution, and is also called the median diameter.

[0073]

[0074] Hereinafter, the present invention will be described in more detail.

[0075]

[0076] Cathode for lithium secondary batteries

[0077] In one embodiment of the present invention,

[0078] negative current collector,

[0079] 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

[0080] 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;

[0081] The second cathode active layer is

[0082] The alignment degree (OI) of the carbon-based negative electrode active material according to the following formula 1 is 2.5 or less,

[0083] A negative electrode for a lithium secondary battery is provided that satisfies the following equation 2 with a value of 8 or less:

[0084] [Formula 1]

[0085] OI = I 004 / I 110

[0086] [Formula 2]

[0087] I Si *OI

[0088] In equations 1 and 2,

[0089] I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer,

[0090] I 110 represents the area of ​​the peak representing the (1,1,0) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0091] I si It represents the area ratio of the peak representing the (1,1,1) crystal plane of the silicon-based negative electrode active material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0092]

[0093] The negative electrode for a lithium secondary battery according to the present invention 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 includes as a main component a negative electrode active material that implements an electrochemical redox reaction during charging and discharging of the battery.

[0094] At this time, the negative electrode active layer may have 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. Since the composition of each layer of the negative electrode active layer having a two-layer structure can be easily controlled, the performance of the negative electrode can be improved by controlling the type or content of 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.

[0095] 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.

[0096] At this time, 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. Specifically, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material refer to materials containing carbon atoms as a main component, and such carbon-based negative electrode active material may include graphite. The graphite may include at least one of natural graphite and artificial graphite. For example, the first carbon-based negative electrode active material and the second carbon-based negative electrode active material may include natural graphite or artificial graphite alone, and in some cases, may include a mixture of natural graphite and artificial graphite. In this case, the mixing ratio of natural graphite and artificial graphite may be 5 to 50:50 to 95, or 20 to 45:55 to 80, based on weight. The carbon-based negative electrode active material can contain natural graphite and artificial graphite in the above-mentioned mixing ratio, thereby strengthening the adhesion between the negative electrode current collector and the negative electrode active layer, and improving the orientation of the carbon-based negative electrode active material on the surface of the negative electrode current collector.

[0097] As an example, the first carbon-based negative electrode active material may include natural graphite and artificial graphite in a weight ratio of 30 to 50:50 to 70, and the second carbon-based negative electrode active material may include artificial graphite alone.

[0098] In addition, it is preferable that the first carbon-based negative electrode active material and the second carbon-based negative electrode active material are spherical graphite aggregates formed by aggregating a plurality of flake-shaped graphite. Examples of the flake-shaped graphite include, in addition to natural graphite and artificial graphite, mesophase calcined carbon (bulk mesophase) using tar and pitch as raw materials, and graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), and in particular, one aggregated using a plurality of highly crystalline natural graphites is preferable. In addition, one graphite aggregate can be formed by aggregating 2 to 100, preferably 3 to 20, flake-shaped graphite.

[0099] These carbon-based negative electrode active materials may have a spherical particle shape. At this time, the sphericity of the graphite particles may be 0.75 or more, for example, 0.75 to 1.0; 0.75 to 0.95; 0.8 to 0.95; or 0.90 to 0.99. Here, the "sphericity" may mean the ratio of the shortest diameter (minor diameter) to the longest diameter (major diameter) among any diameters passing through the center of the particle. If the sphericity is 1, it means that the particle shape is spherical. The sphericity may be determined by measuring the shape of the particle using a particle shape analyzer, or by analyzing the measured result after measuring the shape of the particle using a scanning electron microscope (SEM) or an energy dispersive spectrometer.

[0100] The present invention can realize high electrical conductivity of the negative electrode active layer by implementing the shapes of the first carbon-based negative electrode active material and the second carbon-based negative electrode active material to be close to spherical. Therefore, the negative electrode including the spherical carbon-based negative electrode active material can improve the capacity of a secondary battery, and has the advantage of improving the adhesive strength between the negative electrode active layer and the current collector by increasing the specific surface area per unit weight of the negative electrode active material.

[0101] In addition, the silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and is contained only in the second negative electrode active layer. The present invention can increase the charge / discharge capacity of the negative electrode by containing the silicon-based negative electrode active material in the second negative electrode active layer adjacent to the positive electrode active layer. In addition, since the silicon-based negative electrode active material undergoes a large volume change during charge / discharge, there is a problem in that the durability of the negative electrode is reduced when included in the first negative electrode active layer. However, the present invention can maintain high durability of the negative electrode by applying the silicon-based negative electrode active material to the second negative electrode active layer.

[0102] Examples of the 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 second 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).

[0103] 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).

[0104] In addition, the carbon-based negative electrode active material and the silicon-based negative electrode active material contained in each layer of the negative electrode active layer may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the entire negative electrode active layer. Specifically, the carbon-based negative electrode active material and the silicon-based negative electrode active material contained in each layer of the negative electrode active layer 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 negative electrode active layer.

[0105] In addition, among these, 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 entire negative electrode active material contained in the first negative electrode active layer and the second negative electrode active layer, and specifically, 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%. The present invention can reduce lithium consumption and irreversible capacity loss during initial charge / discharge of a secondary battery while improving the charge capacity per unit mass by controlling the total content ratio of the entire negative electrode active material included in the negative electrode active layer and the content ratio of the silicon-based negative electrode active material included in the entire negative electrode active material within the above range. In addition, since the structural stability of the negative electrode active layer can be improved by minimizing the volume change of the negative electrode active layer during charge / discharge of the secondary battery, the lifespan of the secondary battery can be increased.

[0106] Furthermore, the negative electrode according to the present invention can further improve high-rate charge / discharge characteristics by controlling the crystal structure characteristics of negative electrode active materials contained in the second negative electrode active layer adjacent to the positive electrode.

[0107] As an example, the second carbon-based negative electrode active material contained in the second negative electrode active layer may have an alignment index (OI) of 2.5 or less according to the following equation 1:

[0108] [Formula 1]

[0109] OI = I 004 / I 110

[0110] In equation 1,

[0111] I 004 represents the area of ​​the peak representing the [0,0,4] crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer,

[0112] I110 represents the area of ​​the peak representing the [1,1,0] crystal plane of the carbon-based negative electrode material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0113]

[0114] The degree of alignment (OI) of the second carbon-based negative electrode active material can be an indicator of the degree to which the ab-axis 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). Specifically, the second 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 the second carbon-based negative electrode active material, when measured by X-ray diffraction. This represents the (0,0,2) plane, (1,0,0) plane, (1,0,1)R plane, (1,0,1)H plane, (0,0,4) plane, and (1,1,0) plane of graphite. Here, the peak appearing at 2θ=43.4±0.2° can be seen as an overlap between the peak corresponding to the (1,0,1)R plane of the second carbon-based negative electrode active material and the (1,1,1) plane of a current collector, for example, copper (Cu).

[0115] The alignment degree (OI) of the second carbon-based negative electrode active material can be measured through the ratio of the areas obtained by integrating the respective intensities of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane and the peak at 2θ=77.5±0.2° representing the (1,1,0) plane.

[0116] The peak at 2θ=54.7±0.2° is a peak indicating a crystal plane having an inclination with respect to the negative electrode current collector among the crystal planes of the second carbon-based negative electrode active material, so that the degree of alignment (OI) may mean that the closer the value is to 0, the closer the inclination with respect to the negative electrode current collector surface is to 90°, and the larger the value is, the closer the inclination with respect to the negative electrode current collector surface is to 0° or 180°. That is, the second negative electrode active layer according to the present invention may be aligned so that the second carbon-based negative electrode active material has 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. Accordingly, the second negative electrode active layer may have a lower degree of alignment (OI) of the second carbon-based negative electrode active material compared to a case where the second carbon-based negative electrode active material is aligned at a low angle of less than 60°. For example, the second negative electrode active layer may have an alignment degree (OI) of the carbon-based negative electrode active material according to Equation 1 of 2.5 or less, 2.0 or less, 1.3 or less, 1.0 or less, 0.5 or less, 0.1 to 2.5, 0.1 to 2.0, 0.1 to 1.5, 0.2 to 1.3, 0.4 to 1.3, 0.4 to 1.3, 0.4 to 1.0, 0.5 to 1.3, 1.1 to 1.3, 0.5 to 0.9, or 0.4 to 0.6. Here, the alignment degree (OI) represents the degree of alignment of the ab-axis crystal plane of the carbon-based negative electrode active material, and does not represent the degree to which the carbon-based negative electrode active material particles are aligned by self-rotation within the active layer.

[0117] The present invention can secure a shorter ion migration channel within the negative electrode active layer by controlling the degree of alignment (OI) of the second carbon-based negative electrode active material contained in the second negative electrode active layer as described above. Accordingly, the negative electrode of the present invention can prevent an increase in resistance due to a long migration distance of lithium ions, thereby preventing a decline in high-rate charging performance due to electrical resistance, and at the same time improving high-rate discharge efficiency.

[0118] As another example, the second positive electrode active layer can satisfy the following equation 2 with 8 or less:

[0119] [Formula 2]

[0120] I Si *OI

[0121] In equation 2,

[0122] OI represents the alignment degree of the second carbon-based negative electrode active material according to Equation 1,

[0123] I si It represents the area of ​​the peak representing the (1,1,1) crystal plane of the silicon-based negative electrode active material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0124]

[0125] Pure silicon with a crystal phase has different distances and densities between silicon elements forming the crystal depending on the type of crystal plane. Therefore, pure silicon (Si) with a crystal phase may exhibit different electrical properties, such as electron mobility, depending on the direction of each crystal plane exposed on the surface (i.e., crystal direction). For example, in a silicon crystal, among the crystal directions (1,0,0), (1,1,1), and (1,1,0), electron mobility may be high in the order of (1,0,0) > (1,1,1) > (1,1,0), and insertion of metal ions, etc. may be high in the order of (1,1,0) > (1,1,1) > (1,0,0).

[0126] Accordingly, the present invention is characterized by controlling the characteristics exhibited by the (1,1,1) plane among the crystal planes of pure silicon having a crystal phase. Specifically, the second negative electrode active layer according to the present invention exhibits a diffraction peak indicating a silicon-based negative electrode active material together with a diffraction peak indicating a crystal plane of the second carbon-based negative electrode active material when analyzed by X-ray diffraction (XRD) spectroscopy. For example, if the silicon-based negative electrode active material is silicon oxide (SiO q , but, in the case of 0.8≤q≤2.5), when measuring X-ray diffraction on the second cathode active layer, a gentle and broad curve spectrum indicating amorphous silicon oxide is shown, along with peaks indicating pure silicon (pure Si) at 2=28.4±0.2°, 47.3±0.5°, and 56.1±0.2°. The peaks represent the (1,1,1) plane, (2,2,0) plane, and (3,1,1) plane among the crystal planes of pure silicon (pure Si), respectively.

[0127] At this time, the diffraction peak representing the (1,1,1) crystal plane of pure silicon (pure Si) becomes stronger as the ab-axis crystal plane of the second carbon-based negative electrode active material is aligned at a higher angle with respect to the negative electrode current collector surface, and the area value obtained by integrating the intensity of the peak may also tend to increase. This means that the exposure of the (1,1,1) crystal plane of silicon on the surface of the second negative electrode active layer increases. However, as mentioned above, the degree of exposure of the (1,1,1) crystal plane can affect the mobility of electrons and metal ions, and the mobility of electrons and the mobility of metal ions can have a trade-off relationship, so it is preferable that the degree of exposure of the (1,1,1) crystal plane be adjusted to satisfy a predetermined range.

[0128] Accordingly, the present invention achieves this by adjusting the above formula 2 to 8 or less. Specifically, the second negative electrode active layer can satisfy formula 2 as 7 or less; 6 or less; 4 or less; 3.5 or less; 3 or less; 0.7 to 8; 0.7 to 6; 1 to 6; 1.75 to 6; 1.75 to 4; 1.75 to 3.5; 1.75 to 3; 1.75 to 2.5; 1.75 to 2.1; 2 to 6; 2 to 4; 2.1 to 3.5; 2.1 to 3.1; 3 to 5; or 2.5 to 3. Here, the above formula 2 calculates the alignment degree (OI) according to the above formula 1 from the diffraction peak for the second carbon-based negative electrode active material during X-ray diffraction spectroscopy analysis for the second negative electrode active layer; This means that the area integral of the diffraction peak intensity representing the (1,1,1) plane of the silicon-based negative electrode active material is reflected in the calculated alignment index (OI). The present invention can significantly increase the lithium ion mobility and insertion performance of the second negative electrode active layer composed of the second carbon-based negative electrode active material and the silicon-based negative electrode active material by satisfying Equation 2 within the above-described range, thereby significantly increasing the high-rate charge / discharge efficiency of the secondary battery including the same.

[0129] Furthermore, the second carbon-based negative electrode active material and the silicon-based negative electrode active material contained in the second negative electrode active layer may have predetermined particle sizes. Specifically, the average particle size (Dc) of the second carbon-based negative electrode active material may be 1 µm to 50 µm, the average particle size (Ds) of the silicon-based negative electrode active material may be 0.1 µm to 10 µm, and the average particle size ratio (Dc / Ds) of the second carbon-based negative electrode active material and the silicon-based negative electrode active material may be 2 to 10.

[0130] Specifically, the second carbon-based negative electrode active material has an average particle diameter (D) of 1 μm to 50 μm. 50, Dc) and can be selectively applied within the above range according to the average thickness of the second negative electrode active layer. For example, the second carbon-based negative electrode active material may have a thickness of 1 μm to 40 μm; 1 μm to 30 μm; 10 μm to 40 μm; 15 μm to 30 μm; 25 μm to 50 μm; 11 μm to 19 μm; 15 μm to 25 μm; 20 μm to 30 μm; 1 μm to 20 μm; 1 μm to 10 μm; 5 μm to 15 μm; 10 μm to 20 μm; 15 μm to 30 μm; 15 μm to 20 μm; 21 μm to 26 μm; 25 μm to 30 μm; 11 μm to 17 μm; 16 μm to 23 μm; 2 μm to 7 μm; 0.5 μm to 5 μm; Or an average particle diameter (D) of 1㎛ to 3㎛ 50 ) can be expressed. The second carbon-based negative electrode active material in a spherical shape may be advantageous in that the particle size is made smaller to maximize the disorder in the expansion direction for each particle so as to prevent expansion of the particles due to charging of lithium ions. However, when the particle size of the second carbon-based negative electrode active material is less than 1.0 ㎛, a large amount of binder is required due to an increase in the number of particles per unit volume, and the spheroidization degree and spheroidization yield may be reduced. On the other hand, when the maximum particle size exceeds 50 ㎛, the expansion rate of the negative electrode active material significantly increases during charge and discharge of the secondary battery, so that as charge and discharge are repeated, the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material particles and the current collector deteriorate, which may significantly reduce the cycle characteristics.

[0131] In addition, the silicon-based negative electrode active material has an average particle diameter (D) of 0.1 ㎛ to 10 ㎛. 50 , Ds) and specifically, the average particle diameter (D) of 0.1 ㎛ to 5 ㎛; 0.1 ㎛ to 3 ㎛; 0.1 ㎛ to 1 ㎛; 0.5 ㎛ to 2 ㎛; 0.5 ㎛ to 5 ㎛; 1 ㎛ to 5 ㎛; 3 ㎛ to 7 ㎛; 5 ㎛ to 10 ㎛; 1 ㎛ to 3 ㎛; 4 ㎛ to 9 ㎛; 0.1 ㎛ to 0.9 ㎛; 0.8 ㎛ to 1.2 ㎛; or 0.3 ㎛ to 0.8 ㎛ 50 ) can be expressed.

[0132] If the silicon-based negative electrode active material has a minimum particle size of less than 0.1 μm, it is difficult to uniformly distribute the second negative electrode active layer, and as the secondary battery is charged and discharged, the oxidation-reduction reaction is induced unevenly in the agglomerated and non-agglomerated regions of the silicon-based negative electrode active material, which may accelerate deterioration of the second negative electrode active layer. In addition, if the silicon-based negative electrode active material has a maximum particle size of more than 10 μm, it is difficult to control the crystal plane of the silicon-based negative electrode active material, and the expansion rate per unit area of ​​the second negative electrode active layer significantly increases during charge and discharge of the secondary battery, so there is a problem that the cycle characteristics significantly decrease as charge and discharge are repeated.

[0133] Furthermore, the average particle size ratio (Dc / Ds) of the second carbon-based negative electrode active material and the silicon-based negative electrode active material may be 2 to 10, and specifically, 2 to 7; 2 to 5; 3 to 7; 4 to 8; 5 to 10; or 6 to 9.

[0134] The present invention can induce a structure in which a silicon-based negative electrode active material is filled in voids formed by a plurality of second carbon-based negative electrode active materials by satisfying the average particle size ratio (Dc / Ds) of the second carbon-based negative electrode active material and the silicon-based negative electrode active material within the above range. At this time, the voids serve as a buffer that buffers the volume expansion of the silicon-based negative electrode active material during charge and discharge of the secondary battery, thereby minimizing the volume expansion of the second negative electrode active layer.

[0135] In addition, when the average particle size ratio (Dc / Ds) is less than the lower limit of the above-described range, the influence of the second carbon-based negative electrode active material on the silicon-based negative electrode active material is reduced, and thus there is a limitation in that it is difficult to control the crystal plane of pure silicon having a crystal phase. In addition, when the average particle size ratio (Dc / Ds) exceeds the upper limit of the above-described range, there is a problem in that the deterioration of the second negative electrode active layer is accelerated during charge / discharge of the secondary battery, thereby shortening the lifespan.

[0136] Meanwhile, the average thickness of the negative electrode active layer may be 100 ㎛ to 300 ㎛. Specifically, the average thickness of the negative electrode active layer may be 100 ㎛ to 250 ㎛; 100 ㎛ to 250 ㎛; or 130 ㎛ to 190 ㎛. The present invention can easily control the crystal characteristics of the negative electrode active material contained in the second negative electrode active layer by adjusting the average thickness of the negative electrode active layer within the above range, thereby improving the high-rate charge / discharge characteristics of a secondary battery including the negative electrode of the present invention.

[0137] In addition, the first negative electrode active layer and the second negative electrode active layer may have the same or different average thicknesses. Specifically, the average thickness (D1) of the first negative electrode active layer and the average thickness (D2) of the second negative electrode active layer may have a ratio of 1:0.5 to 3, and more specifically, a ratio of 1:0.8 to 2.5, 1:1 to 2.5, 1:1.1 to 2, 1:0.9 to 1.1, or 1:1.5 to 3. The present invention can maximize the charge / discharge capacity while maintaining high durability of the negative electrode by controlling the average thickness ratio of the first negative electrode active layer and the second negative electrode active layer within the above range.

[0138] In addition, the first cathode active layer and the second cathode active layer according to the present invention may optionally further include a conductive material, a binder, other additives, etc., as needed, along with the cathode active material as the main component.

[0139] The above-mentioned challenge material may include one or more of carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0140] As an example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0141] At this time, the content of the conductive material may be 0.1 to 10 parts by weight relative to 100 parts by weight of the entire negative electrode active layer. Specifically, the content of 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 relative to 100 parts by weight of the entire negative electrode active layer. By controlling the content of the conductive material within the above range, the present invention can prevent the resistance of the negative electrode from increasing due to a low content of the conductive material, thereby reducing the charging capacity, and can prevent the problem of the content of the negative electrode active material decreasing due to an excessive amount of the conductive material, thereby reducing the charging capacity, or the problem of the rapid charging characteristics from decreasing due to an increase in the loading amount of the negative electrode active layer.

[0142] In addition, the binder may be appropriately applied as 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 may be applied within a range that does not deteriorate the electrical properties of the electrode. Specifically, the binder may include at least one selected from the group consisting 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 fluororubber.

[0143] The content of the binder may be 0.1 to 10 parts by weight relative to 100 parts by weight of the entire negative electrode active layer. Specifically, the content of 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 relative to 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 electrode from being lowered due to an excessive amount of binder.

[0144] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and 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 in the range of 1 to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0145]

[0146] lithium secondary battery

[0147] In addition, in one embodiment of the present invention,

[0148] 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.

[0149]

[0150] 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, not only has a high charge / discharge capacity but also has excellent high-rate charge / discharge characteristics, and thus can be usefully used as a power source for medium- to large-sized devices such as electric vehicles.

[0151] At this time, since the cathode has the same configuration as the configuration described above, a detailed description is omitted.

[0152] 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.

[0153] 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:

[0154] [Chemical Formula 1]

[0155] Li x [Ni y Co z Mn w M 1 v ]O2

[0156] [Chemical Formula 2]

[0157] LiM 2 p Mn q P r O4

[0158] In the above chemical formulas 1 and 2,

[0159] M 1 is at least one element selected from the group consisting of 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,

[0160] x, y, z, w, and v are 1.0≤x≤1.30, 0.5≤y<1, 0, respectively. <z≤0.3, 0<w≤0.3, 0≤v≤0.1이되, y+z+w+v=1이고,

[0161] M 2 is Ni, Co or Fe,

[0162] p is 0.05≤p≤1.0,

[0163] q is 2-p,

[0164] r is either 0 or 1.

[0165]

[0166] 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 cathode active materials such as iron phosphate (LiFeO4) that are conventionally used.

[0167] 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 and LiNi 0.3 Mn 1.7 It may include O4, etc., and these may be used alone or in combination.

[0168] 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 positive electrode active layer.

[0169] In addition, the positive electrode active layer may further include a conductive agent, a binder, other additives, etc., along with the positive electrode active material.

[0170] At this time, the conductive material is used to improve the electrical performance of the anode, and can be applied to materials commonly used in the art, but specifically, can include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, summer black, graphene, and carbon nanotubes.

[0171] 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 each 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.

[0172] 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. As an example, the binder may include polyvinylidene fluoride.

[0173] In addition, the binder may be included in an amount of 1 to 10 parts by weight based on the weight of each positive electrode active layer, specifically 2 to 8 parts by weight; or 1 to 5 parts by weight.

[0174] The total thickness of the positive electrode active layer is not particularly limited, but may be specifically 50 µm to 300 µm. More specifically, the total thickness of the positive electrode active layer may be 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.

[0175] 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. In addition, the average thickness of the current collector can be appropriately applied in the range of 3 to 500 ㎛, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0176] In addition, the separator interposed between the positive and negative electrodes of each unit cell 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, but specifically, one including at least one polymer selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers having chemical resistance and hydrophobicity can be used. 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 to 10 μm, and an average thickness of 5 to 300 μm.

[0177] 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. As an example, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a square-shaped secondary battery.

[0178] 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.

[0179]

[0180] Method for manufacturing cathode

[0181] In addition, in one embodiment of the present invention,

[0182] A step of applying a first negative electrode slurry and a second negative electrode slurry such that the first negative electrode slurry is positioned on at least one surface of a negative electrode current collector and the second negative electrode slurry is positioned on the first negative electrode slurry;

[0183] A step of applying a magnetic field to the applied first cathode slurry and the second cathode slurry; and

[0184] A step of forming a cathode active layer by drying a first cathode slurry and a second cathode slurry to which a magnetic field is applied,

[0185] The above first negative electrode slurry includes a first carbon-based negative electrode active material,

[0186] The above second negative electrode slurry includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material,

[0187] The above magnetic field provides a method for manufacturing a negative electrode for a lithium secondary battery, wherein the magnetic field is applied with a strength of 10,000 G or less.

[0188]

[0189] The method for manufacturing a negative electrode according to the present invention refers to the method for manufacturing the negative electrode of the present invention described above. The method for manufacturing the negative electrode comprises: applying a negative electrode slurry on a negative electrode current collector, applying a magnetic field to the surface of the applied negative electrode slurry, and then drying each negative electrode slurry, thereby manufacturing a negative electrode having a negative electrode active layer in which the crystal characteristics of the negative electrode active material are controlled.

[0190] Here, the step of applying the negative electrode slurry is a step of discharging and coating the negative electrode slurry containing a carbon-based negative electrode active material onto the surface of the moving negative electrode current collector. This step can be applied without 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 through a slot die having a shim for controlling the discharging conditions of the negative electrode slurry. In this case, by controlling the shape of the shim, etc., the loading amount, coating thickness, etc. of the negative electrode slurry applied onto the negative electrode current collector can be easily controlled.

[0191] In the present invention, a dual die can be used to simultaneously apply the first negative electrode slurry and the second negative electrode slurry onto the negative electrode current collector. This has the advantage of significantly increasing process efficiency compared to applying each slurry sequentially.

[0192]

[0193] Meanwhile, the step of applying a magnetic field to the negative electrode slurry may be a step of controlling the crystal characteristics of the negative electrode active material contained in the negative electrode slurry. Specifically, this step applies a magnetic field to the surfaces of the first negative electrode slurry and the second negative electrode slurry coated on the negative electrode current collector, thereby aligning the ab-axis crystal plane of the carbon-based negative electrode active material contained in each negative electrode slurry to have a high angle with respect to the negative electrode current collector, and controlling the (1,1,1) crystal plane characteristics of the silicon-based negative electrode active material contained in the second negative electrode slurry.

[0194] At this time, a magnetic field may be applied by magnets disposed on the upper and lower portions of the negative electrode current collector, which is moved while the negative electrode slurry is applied to the surface. In addition, the polarities of the magnets disposed on the upper and lower portions may be different from each other.

[0195] In addition, the alignment degree (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry can be controlled by the strength of the applied magnetic field, etc., and accordingly, the step of applying the magnetic field can be performed under predetermined magnetic field strength conditions.

[0196] Specifically, the step of applying the magnetic field may apply a magnetic field of 10,000 G (Gauss) or less, and specifically, the magnetic field may be applied with a strength of 2,500 G to 9,000 G; 3,000 G to 8,500 G; 3,500 G to 8,500 G; 4,000 G to 8,200 G; 3,600 G to 4,500 G; 4,500 G to 6,500 G; 5,000 G to 7,000 G; 6,000 G to 8,500 G; 7,000 G to 8,500 G; or 6,000 G to 6,500 G.

[0197] Additionally, the step of applying the magnetic field may be performed for 1 second to 20 seconds, specifically, for 1 second to 15 seconds; 1 second to 10 seconds; 5 seconds to 20 seconds; 10 seconds to 20 seconds; 11 seconds to 18 seconds; 1 second to 5 seconds; 4 seconds to 9 seconds; or 6 seconds to 11 seconds.

[0198] As an example, in the step of applying the magnetic field, a magnetic field of 6,250±50 G may be applied to the cathode slurry for 1 to 5 seconds.

[0199] Furthermore, the step of applying the magnetic field is performed by magnets introduced to the upper and lower portions of the applied negative electrode slurry as mentioned above, and the size of the magnets may be adjusted to be larger than the size of the negative electrode slurry so that the magnetic field applied to the negative electrode slurry can be uniformly applied to the entire surface of the negative electrode slurry. For example, the magnets may have a length ratio of 105% to 200% based on the width direction length of the negative electrode slurry, and specifically, may have a length ratio of 110% to 180%; 110% to 160%; 110% to 140%; 110% to 130%; 130% to 150%; or 105% to 120% based on the width direction length of the negative electrode slurry.

[0200] The present invention can satisfy Equation 2 as 8 or less while satisfying the alignment degree (OI) of the carbon-based negative electrode active material contained in the second negative electrode slurry to 2.5 or less by controlling the strength of the magnetic field, the application time, and / or the size of the magnet portion as described above in the step of applying the magnetic field.

[0201] Additionally, the step of forming the cathode active layer may include a step of drying the cathode slurry; and a step of rolling the dried cathode slurry.

[0202] At this time, the step of drying the negative electrode slurry can be applied without any particular limitation as long as it is a method capable of maintaining the orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0203] For example, the drying step can dry the cathode slurry by applying heat energy to the cathode slurry using a hot air dryer, a vacuum oven, or the like.

[0204] In addition, the step of rolling the dried cathode slurry is a step of increasing the density of the cathode active layer by applying pressure to the dried cathode slurry using a roll press or the like. At this time, the rolling may be performed at a temperature higher than room temperature.

[0205] Specifically, the rolling can be performed at a temperature of 50°C to 100°C, more specifically at a temperature of 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. Specifically, the rolling can be performed at a rolling speed of 2 m / s to 7 m / s, more specifically at a rolling speed 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; The rolling can be performed at a rolling speed of 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. 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 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.

[0206] The present invention can increase the energy density of a negative electrode while minimizing changes in the alignment of a carbon-based negative electrode active material contained in a negative electrode active layer formed by performing rolling of a dried negative electrode slurry under the above-described temperature, speed, and / or pressure conditions.

[0207]

[0208] Hereinafter, the present invention will be described in more detail through examples and experimental examples.

[0209] However, the following examples and experimental examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0210]

[0211] Examples 1 to 5 and Comparative Examples 1 to 3. Preparation of negative electrode for lithium secondary battery

[0212] Natural graphite (average particle diameter (D)) as a carbon-based negative electrode material 50 ): 18±1㎛) and artificial graphite (average particle diameter (D 50 ): 16±1㎛) and silicon oxide (SiO2) were prepared as a silicon-based negative electrode active material, respectively, and the first negative electrode slurry and the second negative electrode slurry were prepared using the prepared carbon-based negative electrode active material and silicon-based negative electrode active material.

[0213] Specifically, a first carbon-based negative electrode active material was prepared by mixing mixed graphite, which was a mixture of natural graphite and artificial graphite in a weight ratio of 3.5 to 4.5:5.5 to 6.5, and carbon black as a conductive material and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as binders. Then, 95 parts by weight of mixed graphite, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethyl cellulose (CMC), and 2.5 parts by weight of styrene butadiene rubber (SBR) were mixed with water to obtain a solid content of 50% to prepare a first negative electrode slurry.

[0214] In addition, a negative electrode active material was prepared by mixing artificial graphite and silicon oxide (SiO2) in a weight ratio of 85 to 90:10 to 15, and carbon black as a conductive material and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) as binders were prepared. Then, 95 parts by weight of mixed graphite, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethyl cellulose (CMC), and 2.5 parts by weight of styrene butadiene rubber (SBR) were mixed with water to obtain a solid content of 45% to prepare a second negative electrode slurry.

[0215] When each cathode slurry was prepared, the first cathode slurry and the second cathode slurry were simultaneously cast on a copper foil (thickness: 10 μm) being transported roll-to-roll (transport speed: 5 m / min) using a dual die coater.

[0216] A permanent magnet having a length ratio of 110 to 120% of the widthwise length of the negative electrode slurry was placed on the upper side of the applied negative electrode slurry and on the lower side of the negative electrode current collector, and the magnetic field strength was adjusted as shown in Table 1 below and applied for 2 to 3 seconds. The negative electrode slurry to which the magnetic field was applied was dried with hot air to form a negative electrode active layer in the form of a first negative electrode active layer and a second negative electrode active layer sequentially stacked on the negative electrode current collector. The formed negative electrode active layer was rolled at 50±1℃ under a pressure of 100 to 150 MPa and a conveying speed of 3 m / s to manufacture a negative electrode for a lithium secondary battery (average thickness of the first negative electrode active layer and the second negative electrode active layer: each 110±5 μm).

[0217] In addition, for each manufactured cathode, X-ray diffraction (XRD) spectroscopy was performed on the second cathode active layer to measure the spectrum. At this time, X-ray diffraction (XRD) spectroscopy analysis was performed once each targeting the second carbon-based cathode active material and silicon-based cathode active material contained in the second cathode active layer. The measurement conditions for X-ray diffraction (XRD) were as follows:

[0218] - Target: Cu(Kα line) graphite monochromator

[0219] - Slit: Diverging slit = 1 degree, Receiving slit = 0.1 mm, Scatter slit = 1 degree

[0220] - Measurement area: (1,1,0) plane: 76.5°< 2θ < 78.5° / (0,0,4) plane: 53.5°< 2θ < 56.0°.

[0221]

[0222] Then, ① from the spectrum measured targeting the second carbon-based negative electrode material, the integral values ​​of each area of ​​the peak representing the (0,0,4) crystal plane and the peak representing the (1,1,0) crystal plane were obtained, and the ratio of these areas (I 004 / I 110 ) was calculated to derive the degree of alignment (OI) of the mixed graphite by region. In addition, ② the area integral (I) of the peak representing the (1,1,1) crystal plane from the spectrum measured targeting the silicon-based negative electrode material was derived. Si ) was calculated. The calculated values ​​are shown in Table 1 below.

[0223] D of SiO2 50 Magnetic field strength O.II Si I Si *OI Comparative Example 16±1 ㎛-5.181.608.34 Comparative Example 20.5±0.05 ㎛6,250G0.811.941.57 Comparative Example 316±1 ㎛6,250G0.831.921.59 Exemplary Example 16±1 ㎛3,500G2.192.645.79 Exemplary Example 26±1 ㎛4,000G1.202.813.37 Exemplary Example 36±1 ㎛6,250G0.753.732.80 Exemplary Example 46±1 ㎛8,050G0.494.242.07 Exemplary Example 56±1 ㎛10,100G0.364.501.62

[0224]

[0225] Examples 6 to 10 and Comparative Examples 4 to 6. Manufacturing of lithium secondary batteries

[0226] 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.

[0227] A separator made of 18 μm polypropylene was interposed between the positive electrode obtained above and the negative electrode manufactured in Examples 1 to 5 and Comparative Examples 1 to 3, respectively, and inserted into a case, and then an electrolyte composition was injected to assemble a lithium secondary battery.

[0228] At this time, the type of negative electrode applied to each lithium secondary battery is shown in Table 2 below.

[0229] Type of applied cathode Example 6 The cathode manufactured in Example 1 Example 7 The cathode manufactured in Example 2 Example 8 The cathode manufactured in Example 3 Example 9 The cathode manufactured in Example 4 Example 10 The cathode manufactured in Example 5 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

[0230]

[0231] Experimental example.

[0232] In order to evaluate the performance of the negative electrode according to the present invention, the following experiments were conducted on lithium secondary batteries manufactured in Examples 6 to 10 and Comparative Examples 4 to 6.

[0233]

[0234] 1) Evaluation of the expansion rate of secondary batteries during charging

[0235] Each lithium secondary battery of the examples and comparative examples was charged to 4.2 V under CC-CV conditions at a rate of 0.3 C at 25°C, and then discharged to 2.5 V under CC conditions at a rate of 0.3 C to activate it. Thereafter, the volume of the activated lithium secondary battery in the discharged state was measured using the Archimedes principle.

[0236] Each activated lithium secondary battery was charged to 4.5 V at a rate of 2.0 C at 25°C under CC-CV conditions, and the volume of the charged lithium secondary batteries was measured in the same manner as the volume measurement above. The volume change rate during charging of each lithium secondary battery was calculated using Equation 3 below, and the volume change rate thus calculated was judged as the expansion rate of the negative electrode provided in each lithium secondary battery. The results are shown in Table 3 below.

[0237] [Formula 3]

[0238] Volume change rate when charging = [(volume when charging - volume when discharging) / volume when discharging] Х100

[0239]

[0240] 2) Evaluation of initial charge capacity and high-rate charge / discharge characteristics

[0241] Each of the lithium secondary batteries manufactured in Examples 6 to 10 and Comparative Examples 4 to 6 was charged to 4.2 V under CC-CV conditions at a rate of 0.3 C at 25°C, and then discharged to 2.5 V under CC conditions at a rate of 0.3 C to activate them.

[0242] Each activated lithium secondary battery was subjected to constant current / constant voltage (CC / CV) charging at a temperature of 25°C, and the initial charge capacity was measured. The charging was performed with a constant current of 0.1C rate until the voltage reached 4.2 V, and then cut-off at a current of 0.005C rate in constant voltage mode to maintain 4.2 V. In addition, each charged secondary battery was subjected to constant current discharge (CC discharge), and the initial discharge capacity was measured. At this time, the constant current discharge was performed with a 1.0C rate until the voltage reached 1.5 V.

[0243] After that, each lithium secondary battery was fully charged at 25℃ with a charge current of 2.0C rate to a charge terminal voltage of 4.2~4.25V, and the charge capacity was measured. From the measured charge capacity, the relative charge capacity ratio based on the initial charge capacity was calculated to evaluate the high-rate charge characteristics of each lithium secondary battery. After that, the discharge capacity was measured while discharging the lithium secondary batteries in the range of 1.0~2.0C at 0.2C intervals. From the measured discharge capacity, the relative discharge capacity ratio based on the initial discharge capacity for each discharge rate was calculated to evaluate the high-rate discharge characteristics of each lithium secondary battery. The measured results are shown in Table 3.

[0244] Initial capacity [mAh / g] High-rate charge characteristics [%] High-rate discharge characteristics [%] Expansion rate [%] Charge Discharge 1.0C 1.2C 1.4C 1.6C 1.8C 2.0C Comparative example 445939985.493.892.489.787.585.383.241.8 Comparative example 546440188.394.393.091.189.787.586.140.2 Comparative example 646340087.294.292.890.589.386.985.540.6 Example 646240390.194.893.492.691.089.588.139.7 Example 746440490.695.193.992.791.489.888.438.6 Example 846640691.795.694.393.191.890.388.637.5 Example 946640590.895.294.092.991.690.088.438.9 Example 1046540390.394.693.592.491.289.688.339.3

[0245]

[0246] As shown in Table 3 above, it can be seen that the lithium secondary battery according to the present invention has a reduced expansion rate during charging, a high charge / discharge capacity, and excellent high-rate charge / discharge efficiency.

[0247] Specifically, the lithium secondary batteries of the examples had a high charge capacity of 462 mAh / g or more, and exhibited excellent high-rate charge / discharge characteristics of 90% or more and 88% or more, respectively, during high-rate charging and discharging under 2C rate conditions. In addition, the lithium secondary batteries of the examples showed a reduced volume increase with an expansion rate of less than 40% during charging.

[0248] This shows that the cathodes of the examples have a two-layer structure of cathode active layers, and by controlling the crystal characteristics of the carbon-based cathode active material and the silicon-based cathode active material contained in the second cathode active layer located at the outermost layer to satisfy the conditions of Equations 1 and 2, the charge / discharge capacity of the lithium secondary battery is increased and the high-rate charge / discharge characteristics are improved.

[0249] From these results, it can be seen that the negative electrode for a lithium secondary battery according to the present invention has a high charge / discharge capacity and excellent high-rate charge / discharge characteristics.

[0250]

[0251] 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 scope of the present invention as set forth in the claims to be described below.

[0252] 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, 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 second cathode active layer is, The alignment degree (OI) of the carbon-based negative electrode active material according to the following formula 1 is 2.5 or less, A negative electrode for a lithium secondary battery satisfying the following equation 2 with a value of 8 or less: [Formula 1] OI = I 004 / I 110 [Formula 2] I Si *OI In equations 1 and 2, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak representing the (1,1,0) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer. I si It represents the area ratio of the peak representing the (1,1,1) crystal plane of the silicon-based negative electrode active material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

2. In paragraph 1, The second negative electrode active layer is a negative electrode for a lithium secondary battery, wherein the alignment degree (OI) of the carbon-based negative electrode active material is 0.1 to 1.

5.

3. In paragraph 1, A negative electrode for a lithium secondary battery, characterized in that the second negative active layer has a formula 2 of 0.7 to 6.

4. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first carbon-based negative electrode active material and the second carbon-based negative electrode active material each include at least one of natural graphite and artificial graphite.

5. In paragraph 1, The above silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q , but, 0.8≤q≤2.5) containing at least one of the following:

6. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the silicon-based negative electrode active material is included in an amount of 1 to 40 wt% based on the weight of the entire negative electrode active layer included in the first negative electrode active layer and the second negative electrode active layer.

7. In paragraph 1, The average particle diameter (Dc) of the second carbon-based negative electrode active material is 1 ㎛ to 50 ㎛, The average particle diameter (Ds) of the above silicon-based negative electrode active material is 0.1 ㎛ to 10 ㎛, A negative electrode for a lithium secondary battery, wherein the average particle size ratio (Dc / Ds) of the second carbon-based negative electrode active material and the silicon-based negative electrode active material is 2 to 10.

8. A step of applying a first negative electrode slurry and a second negative electrode slurry so that the first negative electrode slurry is positioned on at least one surface of the negative electrode collector and the second negative electrode slurry is positioned on the first negative electrode slurry; A step of applying a magnetic field to the applied first cathode slurry and the second cathode slurry; and A step of forming a cathode active layer by drying a first cathode slurry and a second cathode slurry to which a magnetic field is applied, The above first negative electrode slurry includes a first carbon-based negative electrode active material, The above second negative electrode slurry includes a second carbon-based negative electrode active material and a silicon-based negative electrode active material, A method for manufacturing a negative electrode for a lithium secondary battery according to claim 1, wherein the magnetic field is applied with a strength of 10,000 G or less.

9. In paragraph 8, A method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of applying the magnetic field is performed for 1 to 20 seconds.

10. A lithium secondary battery having an electrode assembly including a positive electrode, a negative electrode according to claim 1, and a separator disposed between the positive electrode and the negative electrode.

11. In paragraph 10, A lithium secondary battery comprising a cathode active layer provided on at least one surface of a cathode current collector and including at least one cathode active material among lithium metal oxides represented by the following chemical formulas 1 and 2: [Chemical Formula 1] Li x [Ni y Co z Mr w M 1 v ]O2 [Chemical Formula 2] LiM 2 p Mn 1-p O4 In the above chemical formulas 1 and 2, M 1 is at least one element selected from the group consisting of 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, x, y, z, w and v are 1.0≤x≤1.30, 0.5≤y<1, 0 respectively <z≤0.3, 0<w≤0.3, 0≤v≤0.1이되, y+z+w+v=1이고, M 2 is Ni, Co or Fe, p is 0.05≤p≤1.

0.

12. In paragraph 11, The above cathode active material 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 O2, LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4 and LiNi 0.3 Mn 1.7 A lithium secondary battery comprising at least one selected from the group consisting of O4.

13. In paragraph 10, A lithium secondary battery wherein the electrode assembly is a stacked electrode assembly; a zigzag electrode assembly; or a zigzag-stacked electrode assembly.