Negative electrode for lithium secondary battery and method for manufacturing same

Abstract

The present invention relates to a negative electrode and a method for manufacturing same. The negative electrode includes a carbon-based negative electrode active material and a silicon-based negative electrode active material at a predetermined content ratio, and, by the control of the degree of alignment (O.I) of the carbon-based negative electrode active material of the negative electrode active layer including the negative electrode active materials to be within a predetermined range, has high charge / discharge capacity and excellent lifespan characteristics. In addition, a lithium secondary battery comprising the negative electrode has the advantages of having excellent output characteristics, and enabling charging in a short time even at a 1C-rate.

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 from Republic of Korea Patent Application No. 10-2023-0105344, dated August 11, 2023, and all contents of the document in that Korean patent application are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries are now widely used not only in small devices like portable electronic devices, but also in medium- to large-sized devices like battery packs for hybrid and electric vehicles and power storage systems. In particular, with growing concern over environmental issues, research is being conducted on electric vehicles and hybrid electric vehicles as alternatives to fossil fuel-powered vehicles like gasoline and diesel, which are major contributors to 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 automobiles suffer from the problem of requiring a long time to recharge 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.

[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] Materials containing graphite are widely used as negative electrode active materials. The average potential when a material containing graphite releases lithium is approximately 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, so the lifespan and rapid discharge efficiency of lithium secondary batteries containing silicon are not high.

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

[0011]

[0012] [Prior Art Literature]

[0013] Republic of Korea Patent Publication No. 10-2020-0047287

[0014]

[0015] The purpose of the present invention is to provide a negative electrode for a lithium secondary battery having improved rapid charge / discharge performance, enabling charging of a secondary battery in a short time, and exhibiting high charge / discharge capacity and excellent life characteristics, and a method for manufacturing the same.

[0016]

[0017] To solve the above-mentioned problem,

[0018] The present invention,

[0019] 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 and a silicon-based negative electrode active material,

[0020] The above silicon-based negative electrode active material is included in an amount of 0.1 wt% to 10 wt% based on the weight of the total negative electrode active material.

[0021] The above negative electrode active layer provides a negative electrode having an alignment degree (OI) of a carbon-based negative electrode active material in the range of 5 to 15 according to the following formula 1:

[0022] [Formula 1]

[0023] OI = I 004 / I 110

[0024] In equation 1,

[0025] I 004 represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer,

[0026] I 110 It represents the area of ​​the peak representing the (110) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD)0 spectroscopy analysis of the negative electrode active layer.

[0027]

[0028] Here, the silicon-based negative electrode active material may be included in an amount of 0.1% to less than 5% by weight based on the weight of the entire negative electrode active material.

[0029] Additionally, the alignment index (OI) of the carbon-based negative electrode active material may be in the range of 0.01 to 10.

[0030] In addition, the average particle diameter (D) of the carbon-based negative electrode active material 50 ) may be in the range of 1㎛ to 30㎛, and the average particle diameter (D) of the silicon-based negative electrode active material 50 ) can range from 0.5㎛ to 20㎛.

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

[0032] In addition, the 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] Additionally, the average thickness of the cathode active layer may be in the range of 50 μm to 500 μm.

[0034]

[0035] In addition, the present invention, in an embodiment,

[0036] A step of applying a negative electrode slurry to at least one surface of a negative electrode collector;

[0037] A step of applying a magnetic field to the applied cathode slurry; and

[0038] The present invention provides a method for manufacturing a cathode, comprising a step of drying a cathode slurry to which a magnetic field is applied to form a cathode active layer.

[0039] At this time, the step of applying the magnetic field can be performed for 1 to 20 seconds.

[0040] Additionally, the step of applying the magnetic field can be performed with a magnetic field strength ranging from 1,000 G to 7,000 G.

[0041]

[0042] Furthermore, in one embodiment of the present invention,

[0043] An electrode assembly comprising an anode, a cathode according to the present invention, and a separator disposed between the anode and the cathode; and

[0044] A lithium secondary battery is provided, which includes an electrolyte composition in which the electrode assembly is impregnated.

[0045] At this time, the positive electrode may include a positive electrode active layer provided on at least one surface of the positive electrode current collector and including one or more types of positive electrode active materials among lithium metal oxides represented by the following chemical formulas 1 and 2:

[0046] [Chemical Formula 1]

[0047] Li x [Ni y Co z Mnw M 1 v ]O2

[0048] [Chemical Formula 2]

[0049] LiM 2 p Mn 1-p O4

[0050] In the above chemical formulas 1 and 2,

[0051] 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,

[0052] 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,

[0053] M 2 is Ni, Co or Fe,

[0054] p is 0.05≤p≤1.0.

[0055]

[0056] Specifically, 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 Mn1.3 O4, LiNi 0.5 Mn 1.5 O4 and LiNi 0.3 Mn 1.7 It may contain one or more of O4.

[0057] Meanwhile, the electrode assembly may be a stacked electrode assembly; a zigzag electrode assembly; or a zigzag-stacked electrode assembly.

[0058]

[0059] The negative electrode for a lithium secondary battery according to the present invention comprises a carbon-based negative electrode active material and a silicon-based negative electrode active material in a predetermined content ratio, and controls the alignment degree (OI) of the carbon-based negative electrode active material of the negative electrode active layer comprising them within a specific range, thereby exhibiting not only high charge / discharge capacity but also excellent life characteristics. In addition, a lithium secondary battery comprising the same has excellent output characteristics and the advantage of being capable of being charged in a short time even at a 1C-rate.

[0060]

[0061] Figure 1 is an image showing the alignment of the ab-axis crystal planes of graphite depending on whether a magnetic field is applied to the cathode slurry during the formation of the cathode active layer. (a) shows a case where the crystal planes of graphite are not aligned because a magnetic field is not applied, and (b) shows a case where the crystal planes of graphite are aligned because a magnetic field is applied.

[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 spirit and 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 )" 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 that uses a laser diffraction scattering particle size distribution measurement method.

[0073] In addition, in this specification, "aspect ratio" means the ratio of the shortest dimension to the longest dimension passing through the center of a two-dimensional particle when performing a cross-sectional structural analysis of the negative electrode active material or projecting it into a two-dimensional particle. In addition, "average aspect ratio" means the number-weighted mean average of the aspect ratios of each particle in a population of active material particles. The aspect ratio can be determined by measuring the shape of the particle using a particle shape analyzer or by analyzing the measured results after measuring the shape of the particle using a scanning electron microscope (SEM) or an energy dispersive spectrometer.

[0074]

[0075] Hereinafter, the present invention will be described in more detail.

[0076]

[0077] Cathode for lithium secondary batteries

[0078] In one embodiment of the present invention,

[0079] 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 and a silicon-based negative electrode active material,

[0080] The above silicon-based negative electrode active material is included in an amount of 0.1 to 10 wt% based on the weight of the total negative electrode active material.

[0081] The above negative electrode active layer provides a negative electrode for a lithium secondary battery having an alignment degree (OI) of a carbon-based negative electrode active material in the range of 5 to 15 according to the following formula 1:

[0082] [Formula 1]

[0083] OI = I 004 / I 110

[0084] In equation 1,

[0085] I 004 represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer,

[0086] I 110 It represents the area of ​​the peak representing the (110) crystal plane of the carbon-based negative electrode active material in the X-ray diffraction (XRD)0 spectroscopy analysis of the negative electrode active layer.

[0087]

[0088] 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 charge and discharge of the battery. The negative electrode active material includes a carbon-based negative electrode active material and a silicon-based negative electrode active material.

[0089] Here, the carbon-based negative electrode active material refers to a material whose main component is carbon atoms. Such carbon-based negative electrode active materials may include graphite.

[0090] The above graphite may include at least one of natural graphite and artificial graphite. In addition to natural graphite and artificial graphite, the graphite may further include mesophase calcined carbon (bulk mesophase) made from tar or pitch, and graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.).

[0091] Specifically, the cathode active layer according to the present invention may comprise artificial graphite alone. The present invention, by including artificial graphite alone in the cathode active layer, significantly improves the lifespan of the cathode, which can be advantageous in conditions such as automobile batteries that must withstand frequent charging for long periods of time. Furthermore, artificial graphite offers the advantages of rapid charging and superior output performance compared to natural graphite.

[0092] In addition, the negative electrode active layer according to the present invention may include both natural graphite and artificial graphite, in which case the mixing ratio of the natural graphite and the artificial graphite may be 5 to 50%:50 to 95%, 20 to 45%:55 to 80%, or 5 to 15%:85 to 95% by weight. The present invention can maintain a high rapid charging speed and output performance by including both natural graphite and artificial graphite in the negative electrode active layer at the above content ratio. In addition, it can prevent the adhesive force between the negative electrode current collector and the negative electrode active layer from being reduced due to a large volume change of the silicon-based negative electrode active material during charge and discharge.

[0093] In addition, the carbon-based negative electrode active material may have a round particle shape rather than a plate-like, sheet-like, flake-like, or needle-like shape. Here, a round particle shape may mean a particle without a sharp edge. When performing a cross-sectional structural analysis of such particles or projecting them into two-dimensional particles, the shape may be spherical or ellipsoidal, and in some cases, it may be an amorphous shape (shapelessness) that is difficult to define.

[0094] For example, the carbon-based negative electrode active material may be graphite having a spherical particle shape. At this time, the spherical particles may be processed to have a spherical shape / form during manufacturing, or may be spherical graphite aggregates formed by aggregating a plurality of flake-shaped graphite. When the spherical particles are the aggregates, one graphite aggregate may be formed by aggregating 2 to 100, preferably 3 to 20, flake-shaped graphite. The present invention can further increase the electrical conductivity of the negative electrode active layer by controlling the shape of the carbon-based negative electrode active material as described above, and can improve the adhesive strength between the negative electrode active layer and the negative electrode current collector by maximizing the contact area with the negative electrode current collector.

[0095] Additionally, the carbon-based negative electrode active material may be spheroidal. In this case, the carbon-based negative electrode active material can more easily secure a path for lithium ions to move within the negative electrode active layer, thereby enabling charging to be completed in a shorter time even under the same conditions.

[0096] Furthermore, the size of the carbon-based negative electrode active material can be controlled within a certain range. Specifically, the average particle diameter (D) of the carbon-based negative electrode active material 50 ) may be in the range of 1 μm to 30 μm, and specifically, may be in the range of 1 μm to 20 μm; 1 μm to 15 μm; 1 μm to 10 μm; 1 μm to 8 μm; 1 μm to 5 μm; 1 μm to 3 μm; 10 μm to 20 μm; 11 μm to 19 μm; 8 μm to 15 μm; 13 μm to 24 μm; 13 μm to 19 μm; 14 μm to 17 μm; 5 μm to 8 μm; 7 μm to 14 μm; 9 μm to 13 μm; 2 μm to 6 μm; 5 μm to 9 μm; 1 μm to 4.5 μm; or 1 μm to 3 μm.

[0097] The present invention can easily suppress an increase in the electrical resistance of the negative electrode active layer by controlling the average particle diameter of the carbon-based negative electrode active material within the above range. In addition, within the above average particle diameter range, the carbon-based negative electrode active material can maximize the degree of disorder in the direction of expansion of each particle to prevent expansion of the particles due to lithium ion charging while increasing the specific surface area per unit weight, thereby further enhancing the adhesive strength between the negative electrode active layer and the negative electrode current collector. In addition, the carbon-based negative electrode active material can secure a movement path of lithium ions within the above average particle diameter range, so that the rapid charging performance is further improved. On the other hand, the carbon-based negative electrode active material has the advantage of further improving the rapid charging performance because the average particle diameter (D 50 ) has a particle diameter lower than the lower limit, a large amount of binder is required due to an increase in the number of particles per unit volume, which may deteriorate the electrical properties of the negative electrode active layer containing them. On the other hand, if the average particle diameter (D 50 ) has a high particle size exceeding the upper limit, the expansion rate of the negative electrode active material increases significantly during charging and discharging of the secondary battery, so that as charging and discharging 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 deteriorates, which may significantly reduce the cycle characteristics.

[0098] In addition, the silicon-based negative electrode active material refers to a material whose main component is silicon atoms. 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 (SiO2). q , but can be expressed as 0.8≤q≤2.5).

[0099] 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).

[0100] In addition, the size of the silicon-based negative electrode active material can be controlled within a certain range. Specifically, the average particle diameter (D) of the silicon-based negative electrode active material 50 ) may be in the range of 0.5 μm to 20 μm, and specifically, may be in the range of 0.5 μm to 15 μm; 0.5 μm to 13 μm; 0.5 μm to 9 μm; 0.5 μm to 6 μm; 0.5 μm to 4 μm; 0.5 μm to 2 μm; 9 μm to 18 μm; 10 μm to 17 μm; 7 μm to 14 μm; 14 μm to 18 μm; 12 μm to 18 μm; 11 μm to 15 μm; 4 μm to 8 μm; 4 μm to 13 μm; 5 μm to 12 μm; 7 μm to 11 μm; 1 μm to 5 μm; 3 μm to 8 μm; 1 μm to 3 μm; or 1 μm to 2 μm.

[0101] Here, the average particle diameter (Ds) of the silicon-based negative electrode active material may have a predetermined ratio with the average particle diameter (Dc) of the carbon-based negative electrode active material. For example, the ratio (Ds / Dc) of the average particle diameter of the silicon-based negative electrode active material to the average particle diameter of the carbon-based negative electrode active material may be 0.5 to 0.9. Specifically, the ratio may be 0.5 to 0.8; 0.5 to 0.7; 0.6 to 0.9; or 0.5 to 0.65. The present invention can realize high charge / discharge capacity of the negative electrode by maintaining the average particle diameter ratio (Ds / Dc) of the silicon-based negative electrode active material and the carbon-based negative electrode active material equal to or higher than the lower limit. In addition, by implementing a high degree of alignment of the carbon-based negative electrode active material within the negative electrode active layer, the movement path of lithium can be easily shortened, and thus high rapid charging performance can be realized.

[0102] In addition, by maintaining the average particle size ratio (Ds / Dc) equal to or lower than the upper limit, it is possible to prevent i) deterioration of the negative electrode active layer due to volume change of the silicon-based negative electrode active material during charge / discharge; and ii) reduction in adhesive strength between the negative electrode active layer and the negative electrode current collector; and iii) reduction in orientation of the carbon-based negative electrode active material.

[0103] In addition, the silicon-based negative electrode active material may be included in an amount of 0.1 to 10 wt% based on the weight of the total negative electrode active material. Specifically, the silicon-based negative electrode active material may be present in an amount of 0.1 to 9 wt%; 0.1 to 8 wt%; 0.1 to 7 wt%; 0.1 to 6 wt%; 0.1 to 5 wt%; 0.5 to 8 wt%; 1 to 6 wt%; 1 to 5 wt%; 3 to 7 wt%; 0.5 to 3 wt%; or 2 to 6 wt% based on the weight of the total negative electrode active material. The present invention can minimize the volume change rate due to the silicon-based negative electrode active material during charge and discharge by controlling the content ratio of the silicon-based negative electrode active material in the negative electrode active material within the above range, thereby maintaining the lithium movement path of the carbon-based negative electrode active material implemented in the negative electrode active layer due to the application of a magnetic field. Accordingly, the negative electrode according to the present invention can not only significantly improve the life characteristics while implementing a high charging capacity, but also significantly shorten the charging speed of a secondary battery.

[0104] Furthermore, the cathode according to the present invention can control the crystal structure characteristics of the carbon-based cathode active materials contained in the cathode active layer to realize a fast charging speed. Specifically, the cathode active layer can have an alignment degree (OI) of 5 to 15 of the carbon-based cathode active material according to the following equation 1:

[0105] [Formula 1]

[0106] OI = I 004 / I 110

[0107] In equation 1,

[0108] I004 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,

[0109] I 110 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.

[0110]

[0111] The degree of alignment (OI) of the above 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 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. This represents the (002) plane, (100) plane, (101)R plane, (101)H plane, (004) plane, and (110) plane of graphite. Here, 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).

[0112] The degree of alignment (OI) of the carbon-based negative electrode material can be measured by measuring the ratio of the areas obtained by integrating the respective intensities 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.

[0113] 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 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 negative electrode active layer according to the present invention may be aligned so that the carbon-based negative electrode active material contained in the layer 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 negative electrode active layer may have a lower degree of alignment (OI) of the carbon-based negative electrode active material compared to a case where the carbon-based negative electrode active material is aligned at a low angle of less than 60°.

[0114] Here, the alignment degree (OI) may indicate the degree to which carbon-based negative electrode active material particles are aligned on the surface of the negative electrode current collector. In addition, in some cases, the alignment degree (OI) may indicate the degree of alignment of the ab-axis crystal planes of the carbon-based negative electrode active material within the negative electrode active layer.

[0115] In the present specification, "the carbon-based negative electrode active material is oriented" or "the carbon-based negative electrode active material is aligned" may mean 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, as shown in (b) of FIG. 1, is arranged to have a predetermined inclination with respect to the negative electrode current collector surface. This may be different from the case where, as shown in (a) of FIG. 1, the ab-axis crystal planes of the crystal grains included in the carbon-based negative electrode active material particles are aligned internally in the particles but have no directionality with respect to the negative electrode current collector. In addition, when the ab-axis crystal planes of the carbon-based negative electrode active material are aligned, rotation of the particles of the carbon-based negative electrode active material contained in the negative electrode active layer may also be induced. However, since the particle rotation at this time is affected by the shape of the particle, it is not equivalent to the degree of alignment of the ab-axis crystal planes, so it may be difficult for the alignment degree (OI) to indicate that the particles of the carbon-based negative electrode active material are aligned.

[0116] Here, the carbon-based negative electrode active material contained in the negative electrode active layer may have an alignment index (OI) in the range of 5 to 15, and specifically, may have an OI in the range of 5 to 13; 5 to 11; 5 to 9; 7 to 15; 10 to 15; 7 to 13; 7 to 11; 7.5 to 10; 6 to 9.5; or 7.5 to 9.5.

[0117] If the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode active layer is lower than the lower limit described above, the adhesive strength with the negative electrode current collector may be reduced. Therefore, the present invention controls the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode active layer to be higher than the lower limit described above, thereby increasing the ratio of the crystal planes of the carbon-based negative electrode active material molecules constituting the negative electrode active material particles facing the negative electrode current collector, thereby improving the adhesive strength between the negative electrode active layer and the negative electrode current collector within a range in which the rapid charging performance of the negative electrode is not reduced. In addition, the present invention controls the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode active layer to be lower than the upper limit described above, thereby securing an ion migration channel through which lithium ions can move more briefly within the negative electrode active layer. Accordingly, the negative electrode of the present invention can prevent an increase in resistance due to a long movement distance of lithium ions, thereby increasing the movement speed of lithium ions during charging and discharging, thereby simultaneously improving rapid charging performance and output performance with high safety.

[0118] Specifically, conventional rapid charging of lithium secondary batteries has been applied to increase the speed by performing charging under high C-rate conditions exceeding the 1C-rate using the constant current-constant voltage (CC-CV) method. In general, constant current-constant voltage (CC-CV) charging inevitably causes concentration polarization due to the diffusion of lithium ions within the electrode during the constant current (CC) charging phase. This long-term diffusion inevitably causes concentration polarization. This concentration polarization of lithium ions easily causes lithium precipitation from the negative electrode, especially under high-rate conditions where the charging current (A) exceeds the standard value (i.e., the current at 1C-rate: 1A) compared to the rated capacity (Ah) of the secondary battery, which significantly lowers the safety of the secondary battery. In addition, high-rate constant current-constant voltage (CC-CV) charging reaches the upper limit voltage very quickly during the constant current (CC) charging phase, so the current may drop to a preset limit before the active material is completely consumed. That is, there is a problem that the effect of reducing the total time for charging a secondary battery is minimal because the charging time is significantly increased during the constant voltage (CV) charging stage.

[0119] However, the present invention can secure a short movement path of lithium ions in the negative electrode active layer, so that the resistance induced in the negative electrode active layer during charging can be significantly reduced. This resistance reduction can induce the execution time of the constant current (CC) charging step to be longer than the execution time of the constant voltage (CV) charging step during the total charging time when charging in the constant current-constant voltage (CC-CV) method. Here, since the same amount of current flows in the constant current (CC) charging step, the charge capacity per unit time is the same, but the constant voltage (CV) charging step shows a tendency for the current to be reduced in order to maintain the same voltage. In other words, since the charge capacity per unit time is rapidly reduced in the constant voltage (CV) charging step, the total charging time can be significantly reduced as the execution time of the constant current (CC) charging step increases. Therefore, the present invention can increase the execution time of the constant current (CC) charging step by controlling the degree of alignment (OI) of the carbon-based negative electrode active material, thereby completing the charging of the secondary battery in a significantly shorter time.

[0120] Furthermore, since rapid charging of these secondary batteries can be implemented under standard (e.g., 1 C-rate) conditions rather than high C-rate conditions, there is an advantage in overcoming the safety problem of lithium secondary batteries caused by the concentration polarization phenomenon of lithium ions induced in the negative electrode active layer during charging.

[0121]

[0122] Meanwhile, the average thickness of the negative electrode active layer may be in the range of 50 ㎛ to 500 ㎛, and specifically, may be in the range of 100 ㎛ to 400 ㎛; 200 ㎛ to 350 ㎛; 50 ㎛ to 180 ㎛; 80 ㎛ to 150 ㎛; 100 ㎛ to 250 ㎛; 100 ㎛ to 250 ㎛; or 130 ㎛ to 190 ㎛. The present invention can easily control the crystal characteristics of each carbon-based negative electrode active material contained in the negative electrode active layer by adjusting the average thickness of the negative electrode active layer within the above range. Accordingly, the negative electrode of the present invention not only can implement high adhesion between the negative electrode active layer and the negative electrode current collector, but also has the advantage of being capable of rapid charging that can complete charging within a short period of time even under standard conditions (1C-rate).

[0123] In addition, the negative electrode active layer according to the present invention may optionally further include a conductive agent, a binder, other additives, etc., as needed, along with the negative electrode active material as the main component.

[0124] 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.

[0125] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0126] At this time, 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, and specifically, 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. 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 deteriorating due to an increase in the loading amount of the negative electrode active layer.

[0127] 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.

[0128] 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, and specifically, 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. 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 by controlling the content of the binder contained in the negative electrode active layer within the above range.

[0129] 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.

[0130]

[0131] lithium secondary battery

[0132] In addition, in one embodiment of the present invention,

[0133] An electrode assembly comprising an anode, a cathode of the present invention described above, and a separator disposed between the anode and the cathode; and

[0134] A lithium secondary battery is provided, which includes an electrolyte composition in which the electrode assembly is impregnated.

[0135]

[0136] 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, which comprises the negative electrode of the present invention described above, has a large charge / discharge capacity and excellent lifespan characteristics, and can be charged in a short time even at a 1C-rate, so that it can be usefully used as a power source for medium- to large-sized devices such as electric vehicles.

[0137] At this time, since the cathode has the same configuration as the configuration described above, a detailed description is omitted.

[0138] 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.

[0139] 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:

[0140] [Chemical Formula 1]

[0141] Li x [Ni y Co z Mn w M 1 v ]O2

[0142] [Chemical Formula 2]

[0143] LiM 2 p Mn q P r O4

[0144] In the above chemical formulas 1 and 2,

[0145] M 1is 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,

[0146] 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,

[0147] M 2 is Ni, Co or Fe,

[0148] p is 0.05≤p≤1.0,

[0149] q is 2-p,

[0150] r is either 0 or 1.

[0151]

[0152] 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.

[0153] 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 Al0.1 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.

[0154] In addition, the positive electrode active material may be included in an amount of 85 parts by weight or more based on the weight of the positive electrode active layer, and specifically, 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.

[0155] 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.

[0156] 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, 7 graphene, and carbon nanotubes.

[0157] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on the weight of each positive electrode active layer, and specifically, 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.

[0158] In addition, the binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0159] 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.

[0160] The total thickness of the above-mentioned positive electrode active layer is not particularly limited, but may be specifically in the range of 50 µm to 300 µm, and more specifically in the range of 100 µm to 200 µm; 80 µm to 150 µm; 120 µm to 170 µm; 150 µm to 300 µm; 200 µm to 300 µm; or 150 µm to 190 µm.

[0161] 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.

[0162] 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.

[0163] 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. Specifically, the lithium secondary battery according to the present invention may be a pouch-type secondary battery or a square-shaped secondary battery.

[0164] 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.

[0165] Furthermore, in the lithium secondary battery, the electrolyte composition can be used without particular limitation as long as it is one that is commonly applied to lithium secondary batteries.

[0166] Specifically, the electrolyte composition may include a non-aqueous organic solvent, a lithium salt, and an electrolyte additive.

[0167] Here, the non-aqueous organic solvent can be applied without particular limitation as long as it is used in a non-aqueous electrolyte in the art. For example, the non-aqueous organic solvents include N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate (PC), propylene carbonate, butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), gamma-butyrolactone, 1,2-dimethoxyethane (DME), tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphoric acid, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate (MP), Non-protic organic solvents such as ethyl propionate (EP) and propyl propionate (PP) can be used.

[0168] In addition, the non-aqueous organic solvent used in the present invention may be used alone, or two or more types may be mixed in any combination or ratio according to the intended use. Among these, from the viewpoint of electrochemical stability against oxidation and reduction and chemical stability with respect to heat or reactions with solutes, it is particularly preferable to mix propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethylmethyl carbonate.

[0169] In addition, the lithium salt may be applied without particular limitation as long as it is used in a non-aqueous electrolyte in the art. Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, and (FSO2)2NLi.

[0170] The lower limit of the appropriate concentration range for properly using the above lithium salt is 0.5 mol / L or more, specifically 0.7 mol / L or more, more specifically 0.9 mol / L or more, and the upper limit is 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the concentration of the lithium salt is less than 0.5 mol / L, there is a concern that the ionic conductivity may decrease, thereby deteriorating the cycle characteristics and output characteristics of the non-aqueous electrolyte battery. In addition, if the concentration of the lithium salt exceeds 2.5 mol / L, the viscosity of the electrolyte for the non-aqueous electrolyte battery increases, which may also deteriorate the ionic conductivity, and there is a concern that the cycle characteristics and output characteristics of the non-aqueous electrolyte battery may also deteriorate.

[0171] In addition, when a large amount of lithium salt is dissolved in a non-aqueous organic solvent at once, the temperature of the electrolyte may rise due to the heat of dissolution of the lithium salt. If the temperature of the non-aqueous organic solvent rises significantly due to the heat of dissolution of the lithium salt in this way, in the case of a lithium salt containing fluorine, there is a concern that decomposition may be accelerated and hydrogen fluoride (HF) may be generated. Hydrogen fluoride (HF) is not desirable because it causes deterioration of battery performance. Therefore, the temperature when dissolving the lithium salt in the non-aqueous organic solvent is not particularly limited, but can be controlled to -20 to 80°C, and specifically, can be controlled to 0 to 60°C.

[0172] Furthermore, the electrolyte additive may be included as an additional auxiliary component to improve the properties of the electrolyte composition. An electrolyte additive commonly used in the non-aqueous electrolyte of the present invention may be added in any ratio. Specifically, compounds having an overcharge prevention effect, a negative electrode film formation effect, and a positive electrode protection effect, such as cyclohexylbenzene, biphenyl, t-butylbenzene, carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate, may be mentioned. In addition, it is also possible to use an electrolyte for a non-aqueous electrolyte battery by solidifying it with a gelling agent or a crosslinking polymer, such as in the case of use in a non-aqueous electrolyte battery called a lithium polymer battery.

[0173]

[0174] The lithium secondary battery according to the present invention has the above-described configuration, and thus has the advantage of not only having a large charge / discharge capacity and excellent life characteristics, but also being capable of being charged in a short time even at a 1C-rate.

[0175]

[0176] Method for manufacturing cathode

[0177] In addition, in one embodiment of the present invention,

[0178] A step of applying a negative electrode slurry to at least one surface of a negative electrode collector;

[0179] A step of applying a magnetic field to the applied cathode slurry; and

[0180] A method for manufacturing a negative electrode for a lithium secondary battery is provided, including a step of drying a negative electrode slurry to which a magnetic field is applied to form a negative electrode active layer.

[0181]

[0182] 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.

[0183] 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, position, etc. of the shim, the loading amount, coating thickness, etc. of the negative electrode slurry applied onto the negative electrode current collector can be easily controlled.

[0184] 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 can align the ab-axis crystal planes of each carbon-based negative electrode active material contained in the negative electrode slurry to have a high angle with respect to the negative electrode collector by applying a magnetic field to the surface of the negative electrode slurry coated on the negative electrode current collector.

[0185] At this time, a magnetic field can be applied by magnets placed 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. The polarities of the magnets placed on the upper and lower portions may be different from each other.

[0186] In addition, the alignment degree (OI) of the carbon-based negative electrode active material contained in each negative electrode slurry can be controlled by the strength of the applied magnetic field, the application time, etc., and accordingly, the step of applying the magnetic field can be performed under predetermined magnetic field strength conditions.

[0187] Specifically, the step of applying the magnetic field may apply a magnetic field in a range of 10,000 G (Gauss) or less, and specifically, the magnetic field may be applied with a strength in a range of 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; 4,000 G to 7,000 G; 2,000 G to 4,000 G; 2,500 G to 3,500 G; 3,000 G to 6,500 G; or 2,700 G to 3,300 G.

[0188] 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; 7 seconds to 13 seconds; or 6 seconds to 11 seconds.

[0189] For example, in the step of applying the magnetic field, a magnetic field of 3,000±50 G may be applied to the cathode slurry for 9 to 11 seconds.

[0190] 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 in the range of 105% to 200% based on the width direction length of the negative electrode slurry, and specifically, may have a length ratio in the range 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.

[0191] The present invention can uniformly implement the alignment degree (OI) of a carbon-based negative electrode active material contained in a negative electrode slurry so as to satisfy a predetermined range 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.

[0192] 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.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] Specifically, the rolling can be performed at a temperature in the range of 50°C to 100°C, more specifically at a temperature in the range 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 in the range of 2 m / s to 7 m / s, more specifically at 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 ranging from 3.5 m / s to 5 m / s; from 5 m / s to 7 m / s; from 5.5 m / s to 6.5 m / s or from 6 m / s to 7 m / s. In addition, the rolling can be performed under a pressure condition ranging from 50 MPa to 200 MPa, and specifically, under a pressure condition ranging from 50 MPa to 150 MPa; from 50 MPa to 100 MPa; from 100 MPa to 200 MPa; from 150 MPa to 200 MPa or from 80 MPa to 140 MPa.

[0197] 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.

[0198]

[0199] Hereinafter, the present invention will be described in more detail through examples and experimental examples.

[0200] 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.

[0201]

[0202] Examples 1 to 9 and Comparative Examples 1 to 3. Preparation of negative electrode for lithium secondary battery

[0203] As carbon-based negative electrode active materials, flake-shaped primary particles were assembled to prepare artificial graphite as secondary particles, and natural artificial graphite, respectively, and as silicon-based negative electrode active materials, silicon dioxide (SiO2) was prepared. In addition, styrene butadiene rubber (SBR) was prepared as a binder and carboxymethyl cellulose (CMC) was prepared as a thickener.

[0204] Then, 96 parts by weight of carbon-based negative electrode active materials and silicon-based negative electrode active materials, 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 negative electrode slurry. At this time, i) the content ratio based on the total weight of negative electrode active materials of the carbon-based negative electrode active material and the silicon-based negative electrode active material and ii) their respective average particle diameters were controlled as shown in Table 1 below.

[0205] Once the cathode slurry was prepared, the cathode slurry was cast on a copper foil (thickness: 10 μm) being transported roll-to-roll (transport speed: 5 m / min) using a single die coater.

[0206] 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 collector, and a magnetic field was applied at a magnetic field strength of 3,000±20 G. The time for which the magnetic field was applied is shown in Table 1. The negative electrode slurry to which the magnetic field was applied was dried with hot air, and an negative electrode was formed in the form of a negative electrode active layer sequentially stacked on the negative electrode collector. The formed negative electrode active layer was rolled at 50±1℃, 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 negative electrode active layer: 160±5 μm, loading: 5 to 20 mg / cm2).

[0207] For each manufactured cathode, X-ray diffraction (XRD) spectroscopy was performed on the cathode active layer to measure the spectrum. The measurement conditions for X-ray diffraction (XRD) were as follows:

[0208] - Target: Cu(Kα line) graphite monochromator

[0209] - Slit: Diverging slit = 1 degree, Receiving slit = 0.1 mm, Scatter slit = 1 degree

[0210] - Measurement area: (110) plane: 76.5° < 2θ < 78.5° / (004) plane: 53.5° < 2θ < 56.0°.

[0211]

[0212] The average alignment index (OI) of the carbon-based active material contained in each cathode active layer was calculated from the spectra measured under the above conditions using Equation 1. The results are shown in Table 1:

[0213] [Formula 1]

[0214] OI = I 004 / I 110

[0215] In equation 1,

[0216] I 004 represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode material in the X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer,

[0217] I 110 represents the area of ​​the peak representing the (110) crystal plane of the carbon-based negative electrode material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

[0218] Content ratio [weight %]Average particle size [D 50, ㎛]Cathode active layer alignment (OI)Magnetic field appliedNatural graphiteArtificial graphiteSiOCarbon-basedSilicon-basedWhetherTimeExample 1-95.05.015108O9~11Second embodiment 27.687.45.015109O9~11Second embodiment 37.485.67.015108O9~11Second embodiment 47.282.810.015109O9~11Second embodiment 57.687.45.01538O9~11Second embodiment 67.687.45.01569O9~11Second embodiment 77.687.45.01512.58O9~11Second embodiment 87.687.45.0151511O9~11 First Example 97.687.45.0151015O1~2 First Comparative Example 1892.0015107O9~11 First Comparative Example 26.878.215.0151010O9~11 First Comparative Example 37.687.45.0151023XO First

[0219]

[0220]

[0221] Examples 10-18 and Comparative Examples 4-6. Manufacturing of lithium secondary batteries.

[0222] LiNi with a particle size of 5㎛ as a cathode active material 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 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.

[0223] A separator made of 18 μm polypropylene was interposed between the positive electrode obtained above and the negative electrode manufactured in Examples 1 to 9 and Comparative Examples 1 to 3, respectively, and inserted into a case, and then an electrolyte composition was injected to assemble a 1 Ah-class lithium secondary battery.

[0224] At this time, the types of negative electrodes applied to each lithium secondary battery are shown in Table 2 below.

[0225] Type of applied cathode Example 10 The cathode manufactured in Example 1 Example 11 The cathode manufactured in Example 2 Example 12 The cathode manufactured in Example 3 Example 13 The cathode manufactured in Example 4 Example 14 The cathode manufactured in Example 5 Example 15 The cathode manufactured in Example 6 Example 16 The cathode manufactured in Example 7 Example 17 The cathode manufactured in Example 8 Example 18 The cathode manufactured in Example 9 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

[0226]

[0227]

[0228] Experimental example.

[0229] In order to evaluate the performance of the negative electrode according to the present invention, the following experiments were conducted on each negative electrode and lithium secondary battery manufactured in the examples and comparative examples.

[0230]

[0231] 1) Life characteristics evaluation

[0232] Each of the lithium secondary batteries manufactured in Examples 10 to 18 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.

[0233] Each activated lithium secondary battery was charged at a temperature of 25℃ at a rate of 1.0C to 4.2V under CC-CV conditions, and discharged at a rate of 1.0C to 2.5V under CC conditions, which was set as one cycle, and one cycle of charge-discharge was performed on each lithium secondary battery manufactured in the examples and comparative examples. At this time, the capacity during charge-discharge was measured to confirm the charge-discharge capacity of the first cycle. After that, 499 cycles of charge-discharge were performed on each lithium secondary battery, and a total of 500 cycles of charge-discharge were performed. At this time, the charge-discharge capacity of the 500th cycle was confirmed when the last cycle was performed. The charge-discharge capacity retention rate of the 500th cycle was calculated based on the measured charge-discharge capacity of the 1st cycle. The results are shown in Table 3 below.

[0234]

[0235] 2) 1C-rate rapid charging evaluation

[0236] Each of the lithium secondary batteries manufactured in Examples 10 to 18 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.

[0237] Each activated lithium secondary battery was charged at 25°C using the constant current-constant voltage (CC-CV) method, and the time required for the state of charge (SOC) to reach 80% was measured. At this time, the charging was performed using constant current (CC) charging at a current of 1.0 C-rate until the voltage reached 4.2 V, followed by constant voltage (CV) charging, which maintained 4.2 V and cut-off when the current reached 0.005 C-rate. The measured charging times are shown in Table 3 below.

[0238] Type of negative electrode Capacity retention rate [%] Charging time (SOC 80%) Example 10 Negative electrode manufactured in Example 1 8020 Example 11 Negative electrode manufactured in Example 2 8119 Example 12 Negative electrode manufactured in Example 3 7621 Example 13 Negative electrode manufactured in Example 4 7423 Example 14 Negative electrode manufactured in Example 5 7228 Example 15 Negative electrode manufactured in Example 6 7527 Example 16 Negative electrode manufactured in Example 7 5329 Example 17 Negative electrode manufactured in Example 8 4930 Example 18 Negative electrode manufactured in Example 9 8035 Comparative Example 4 Negative electrode manufactured in Comparative Example 1 6823 Comparative Example 5 Negative electrode manufactured in Comparative Example 2 624 Comparative Example 6Cathode 8151 manufactured in Comparative Example 3

[0239]

[0240] As shown in Table 3 above, it can be seen that the negative electrode for a lithium secondary battery according to the present invention not only has excellent life characteristics, but also completes charging at a fast rate under 1C-rate conditions.

[0241] Specifically, the cathodes of the examples exhibited a high charge-discharge capacity retention rate of over 70% after 500 charge-discharge cycles. Furthermore, the secondary batteries of the examples including these cathodes reached an 80% state of charge (SOC) in less than 30 seconds under standard constant current-constant voltage (CC-CV) charging conditions of 1 C-rate.

[0242] On the other hand, the negative electrode of Comparative Example 1, which does not include silicon dioxide (SiO2), a silicon-based negative electrode active material, as a negative electrode active material, showed a relatively high charge / discharge capacity retention rate of about 68% after 500 charge / discharge cycles, but was confirmed to have a significantly lower charge / discharge capacity per cycle compared to the negative electrodes of the examples including silicon dioxide (SiO2).

[0243] In addition, the negative electrode of Comparative Example 2 containing an excessive amount of silicon dioxide (SiO2) was confirmed to have a significantly low charge-discharge capacity retention rate of approximately 6% after 500 charge-discharge cycles. Furthermore, the negative electrode of Comparative Example 3 containing silicon dioxide (SiO2) but not applying a magnetic field during the formation of the negative electrode active layer reached a state of charge (SOC) of 80% after a long time exceeding 50 seconds under standard constant current-constant voltage (CC-CV) charging conditions of 1 C-rate.

[0244] This means that the life characteristics of the negative electrode and the charging speed under standard C-rate conditions can be improved by controlling the alignment degree (OI) of the carbon-based negative electrode active material included in the negative electrode active layer and the content of the silicon-based negative electrode active material.

[0245]

[0246] From these results, it can be seen that the negative electrode for a lithium secondary battery according to the present invention has a large charge / discharge capacity and excellent life characteristics, and that a lithium secondary battery including the negative electrode can be charged in a short time even at a 1C-rate.

[0247]

[0248] 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 various modifications and changes to the present invention can be made without departing from the spirit and technical scope of the present invention as set forth in the claims to be described below.

[0249] 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. 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 and a silicon-based negative electrode active material, The above silicon-based negative electrode active material is included in an amount of 0.1 to 10 wt% based on the weight of the total negative electrode active material. The above negative electrode active layer is a negative electrode having an alignment degree (OI) of a carbon-based negative electrode active material in the range of 5 to 15 according to the following formula 1: [Formula 1] OI = I 004 / I 110 In equation 1, I 004 represents the area of ​​the peak representing the (004) crystal plane of the carbon-based negative electrode material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak representing the (110) crystal plane of the carbon-based negative electrode material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer.

2. In paragraph 1, An anode in which the above silicon-based anode active material is included in an amount of 0.1 to 5 wt% based on the weight of the total anode active material.

3. In paragraph 1, A cathode having an alignment index (OI) of the carbon-based cathode active material in the range of 7 to 11.

4. In paragraph 1, The average particle diameter (D) of the above carbon-based negative electrode active material 50 ) is in the range of 1㎛ to 30㎛, The average particle diameter (D) of the above silicon-based negative electrode active material 50 ) is a cathode having a range of 0.5㎛ to 20㎛.

5. In paragraph 1, The above carbon-based negative electrode active material is a negative electrode including at least one of natural graphite and artificial graphite.

6. In paragraph 1, The above silicon-based negative electrode active materials include silicon (Si), silicon carbide (SiC), and silicon oxide (SiO). q , but a cathode including at least one of 0.8≤q≤2.5).

7. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the average thickness of the negative active layer is in the range of 50 ㎛ to 500 ㎛.

8. A step of applying a cathode slurry to at least one surface of a cathode current collector; A step of applying a magnetic field to the applied cathode slurry; and A method for manufacturing a cathode according to claim 1, comprising the step of drying a cathode slurry to which a magnetic field is applied to form a cathode active layer.

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

10. In paragraph 8, A method for manufacturing a cathode, wherein the step of applying the magnetic field is performed with a magnetic field strength in the range of 1,000 G to 7,000 G.

11. An electrode assembly comprising a positive electrode, a negative electrode according to claim 1, and a separator disposed between the positive electrode and the negative electrode; and A lithium secondary battery comprising an electrolyte composition in which the electrode assembly is impregnated.

12. In paragraph 11, The above positive electrode is provided on at least one side of the positive electrode current collector and includes a positive electrode active layer including at least one type of positive electrode active material among lithium metal oxides represented by the following chemical formulas 1 and 2: A lithium secondary battery: [Chemical Formula 1] Li x [Ni y Co z Mr w M 1 v ]O 2 [Chemical formula 2] Glue 2 p Mn 1-p O 4 In the above chemical formulas 1 and 2, 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, 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.

13. In paragraph 12, The above cathode active material is LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.9 Co 0.05 Mn 0.05 O 2 , LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O 2 , LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O 2 , LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O 2 , LiNi 0.7 Mn 1.3 O 4 , LiNi 0.5 Mn 1.5 O 4 and LiNi 0.3 Mn 1.7 O 4 A lithium secondary battery comprising at least one of the following:

14. In paragraph 11, A lithium secondary battery wherein the electrode assembly is a stacked electrode assembly; a zigzag electrode assembly; or a zigzag-stacked electrode assembly.

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