Negative electrode for lithium secondary battery and method for producing same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a method for manufacturing the same. The negative electrode has excellent adhesion to the negative electrode current collector due to the average aspect ratio of the carbon-based negative electrode active material contained in the negative electrode active layer and the degree of alignment (OI) relative to the negative electrode current collector being controlled to satisfy a predetermined range. Furthermore, a lithium secondary battery including the negative electrode has excellent output characteristics and can be charged in a short time even at a 1C rate.

Description

[Technical Field]

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

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0089499, filed on July 11, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference. [Background technology]

[0003] In recent years, lithium secondary batteries have been widely used not only in small devices such as portable electronic devices, but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles, power storage devices, etc. In particular, with the recent growing interest in environmental issues, much research has been conducted on electric vehicles and hybrid electric vehicles that can replace vehicles that use fossil fuels such as gasoline and diesel vehicles, which are one of the main causes of air pollution.

[0004] Existing lithium secondary batteries are limited in their energy density and can only be used in short-distance electric vehicles. Therefore, technological development has been focused on increasing the energy density of lithium secondary batteries.

[0005] However, the lithium secondary batteries currently being developed for automobiles have a problem in that they take a long time to charge after discharging during vehicle operation. Therefore, as the popularity of electric vehicles increases, there is an increasing demand to shorten the charging time to a level acceptable to users.

[0006] Meanwhile, lithium secondary batteries are chargeable and dischargeable power generating devices with a laminated structure of a positive electrode, separator, and negative electrode. When charging a lithium secondary battery, a lithium desorption reaction occurs in which lithium contained in the positive electrode active material is oxidized and released at the positive electrode inside the battery, and a lithium insertion reaction occurs in which lithium is reduced at the negative electrode and inserted into the negative electrode active material. Generally, the desorption reaction at the positive electrode active material is faster than the insertion reaction at the negative electrode active material, so the rapid charge and discharge performance of a lithium secondary battery is mainly determined by the negative electrode.

[0007] In reality, materials containing graphite are widely used as the negative electrode active material for the above-mentioned negative electrode. When materials containing graphite release lithium, the average potential is about 0.2 V (Li / Li + Therefore, when graphite is used as the negative electrode active material, it has the advantage of producing a high and constant voltage secondary battery.

[0008] Amorphous carbon or crystalline carbon is used as the negative electrode active material for a negative electrode, and crystalline carbon is the most widely used due to its high capacity. Examples of such crystalline carbon include graphite-based carbon such as natural graphite and artificial graphite.

[0009] The properties of graphite-based carbon vary depending on the type. For example, natural graphite is inexpensive and exhibits excellent adhesion to the current collector, but is relatively inferior to artificial graphite in terms of high-rate charge / discharge performance and lifespan. However, artificial graphite has few surface defects and functional groups, resulting in poor adhesion to the current collector. Furthermore, when propylene carbonate (PC) is mixed into the electrolyte to improve low-temperature performance, the propylene carbonate exfoliates and destroys the interlayer structure of the graphite.

[0010] Therefore, attempts have been made to use mixed graphite, which combines natural graphite and artificial graphite to utilize the advantages of each, as the negative electrode active material for lithium secondary batteries. However, such mixed graphite has limitations in that it has reduced adhesive strength to the current collector, making it difficult to achieve satisfactory levels of life characteristics and impact stability.

[0011] Therefore, in order to fundamentally solve these problems, there is a strong need for a negative electrode technology that has high adhesion to the current collector, excellent life characteristics, excellent output characteristics, and excellent fast charging characteristics. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Korean Patent Publication No. 10-2022-0064389 Summary of the Invention [Problem to be solved by the invention]

[0013] An object of the present invention is to provide a negative electrode for a lithium secondary battery which has high adhesion to a current collector, excellent life characteristics, excellent output characteristics, and excellent rapid charging characteristics, and a method for producing the same. [Means for solving the problem]

[0014] To solve the above problem, In one embodiment, the present invention comprises: a negative electrode current collector; and a negative electrode active layer provided on at least one surface of the negative electrode current collector, the negative electrode active layer including a carbon-based negative electrode active material having an average aspect ratio of 0.85 or less, The negative electrode active layer provides a negative electrode for a lithium secondary battery having an alignment degree (OI) of 10 or less of the carbon-based negative electrode active material represented by the following formula 1:

[0015] [Formula 1] OI=I 004 / I 110

[0016] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane of the carbon-based negative electrode active material when the negative electrode active layer is subjected to X-ray diffraction (XRD) spectroscopy.

[0017] In this case, the carbon-based negative electrode active material may have an average aspect ratio of 0.2 to 0.8.

[0018] In addition, the negative electrode active layer may have an alignment index (OI) of 0.01 to 10 for the carbon-based negative electrode active material represented by Formula 1.

[0019] The carbon-based negative electrode active material may include at least one of natural graphite and artificial graphite.

[0020] As one example, the carbon-based negative electrode active material may be artificial graphite.

[0021] In addition, the average particle size (D 50 ) can be 0.01 μm to 20 μm.

[0022] The negative electrode active layer may have a porosity of 20% to 30%.

[0023] The negative electrode active layer may have an average thickness of 50 μm to 500 μm.

[0024] In addition, the present invention provides, in an embodiment, applying a negative electrode slurry to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; and drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer.

[0025] At this time, the step of applying the magnetic field may be performed for 1 to 20 seconds.

[0026] The step of applying the magnetic field can be performed at a magnetic field strength of 1,000G to 7,000G.

[0027] Furthermore, in one embodiment, the present invention provides an electrode assembly including a positive electrode, the above-described negative electrode of the present invention, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte composition impregnated with the electrode assembly.

[0028] In this case, the positive electrode may include a positive electrode active layer provided on at least one surface of a positive electrode current collector and including one or more positive electrode active materials selected from lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2:

[0029] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0030] [Chemical formula 2] LiM 2 p Mn 1-p O4

[0031] In the above Chemical Formula 1 and Chemical Formula 2, M 1 is one or more elements selected from 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 <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつy+z+w+v=1であり、 M 2is Ni, Co or Fe, p is in the range of 0.05≦p≦1.0.

[0032] 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 contain one or more of O4.

[0033] Meanwhile, the electrode assembly may be a stacked electrode assembly, a zigzag electrode assembly, or a zigzag-stacked electrode assembly. [Effects of the Invention]

[0034] The negative electrode for a lithium secondary battery according to the present invention has the advantage that the average aspect ratio of the carbon-based negative electrode active material contained in the negative electrode active layer and the degree of alignment (OI) relative to the negative electrode current collector are controlled to satisfy predetermined ranges, thereby enhancing adhesion to the negative electrode current collector and providing excellent life characteristics. Furthermore, a lithium secondary battery including the negative electrode has excellent output characteristics and can be charged in a short time even at a 1C rate. DETAILED DESCRIPTION OF THE INVENTION

[0035] Because the present invention is susceptible to various modifications and embodiments, specific embodiments are described in detail in the detailed description.

[0036] However, this is not intended to limit the invention to any particular embodiment, but rather it can be understood to include all modifications, equivalents, or alternatives falling within the scope of the present invention.

[0037] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and can be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0038] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0039] Furthermore, in the present invention, "comprising as a main component" can mean that the defined component is contained in an amount of 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) based on the total weight (or total volume). For example, "comprising graphite as a main component as a negative electrode active material" can mean that graphite is contained in an amount of 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 based on the total weight of the negative electrode active material. In some cases, it can mean that the entire negative electrode active material is composed of graphite, and that graphite is contained in an amount of 100 wt%.

[0040] Furthermore, in this 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) showing the two-dimensional planar structure of the carbon-based negative electrode active material constituting the negative electrode active material particles is arranged at a specific inclination with respect to the surface of the negative electrode current collector. This may be different from the case where the carbon-based negative electrode active material particles themselves are arranged in a specific direction within the negative electrode active layer.

[0041] Furthermore, "high orientation of the carbon-based negative electrode active material" can mean that a specific crystal plane (e.g., the ab-axis crystal plane of graphite) exhibiting 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. In some cases, it can mean that the crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a large angle (e.g., an angle close to perpendicular, greater than 45°; specifically, 60° or greater) with respect to the surface of the negative electrode current collector.

[0042] Furthermore, "a carbon-based negative electrode active material having a high degree of alignment" may mean that the "degree of alignment (OI)" referred to herein is large, and that a specific crystal plane (e.g., the ab-axis crystal plane of graphite) exhibiting a two-dimensional planar structure of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a small angle (e.g., less than 45°) relative to the surface of the negative electrode current collector. Conversely, "a carbon-based negative electrode active material having a low degree of alignment" may mean that the "degree of alignment (OI)" is small, and that the crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a large angle (e.g., an angle close to perpendicular, 45° or more; specifically, 60° or more) relative to the surface of the negative electrode current collector.

[0043] Furthermore, in this specification, the term "crystal plane of a carbon-based negative electrode active material" refers to a plane in which atoms of the carbon-based negative electrode active material form the outer shape of a crystal, and in the present invention, may refer to 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.

[0044] In addition, in this specification, "average particle size (D 50 The term "average particle size" refers to the particle size at which the cumulative value in the particle size distribution of particles is 50%, and is also called the median diameter. The above average particle size can be measured using a laser diffraction particle size analyzer.

[0045] In addition, the term "aspect ratio" used herein refers to the ratio of the shortest dimension to the longest dimension passing through the center of a two-dimensional particle when a cross-sectional structure of the negative electrode active material is analyzed or when the negative electrode active material is projected as a two-dimensional particle. The term "average aspect ratio" refers to the number-weighted mean average of the aspect ratios of each particle in a population of active material particles. The aspect ratio can be measured using a particle shape analyzer or by measuring the morphology of two-dimensionally projected particles using a scanning electron microscope (SEM) or an energy dispersive spectrometer, and then analyzing the measurement results.

[0046] The present invention will now be described in more detail.

[0047] <Anode for lithium secondary batteries> In one embodiment, the present invention comprises: a negative electrode current collector; and a negative electrode active layer provided on at least one surface of the negative electrode current collector, the negative electrode active layer including a carbon-based negative electrode active material having an average aspect ratio of 0.85 or less, The negative electrode active layer provides a negative electrode for a lithium secondary battery, in which the degree of alignment (OI) of the carbon-based negative electrode active material represented by the following formula 1 is 10 or less:

[0048] [Formula 1] OI=I 004 / I 110

[0049] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane of the carbon-based negative electrode active material when the negative electrode active layer is subjected to X-ray diffraction (XRD) spectroscopy.

[0050] 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 realizes electrical activity of the negative electrode and contains, as a main component, a negative electrode active material that realizes an electrochemical oxidation-reduction reaction during charge and discharge of the battery.

[0051] Here, the negative electrode active material is a carbon-based negative electrode active material, which refers to a material primarily composed of carbon atoms. Such a carbon-based negative electrode active material can include graphite. The graphite can include at least one of natural graphite and artificial graphite. In addition to natural graphite and artificial graphite, graphite can also include mesophase calcined carbon (bulk mesophase) made from tar or pitch, graphitized cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), and the like.

[0052] As one example, the negative electrode active layer according to the present invention may contain artificial graphite alone. Since the negative electrode active layer according to the present invention contains artificial graphite alone, the life of the negative electrode is significantly improved, which is advantageous in situations where the battery must withstand frequent charging for a long period of time, such as in an automobile battery. Furthermore, compared to natural graphite, artificial graphite has the advantage of being capable of being charged at a faster rate under the same C-rate conditions, resulting in superior output performance.

[0053] The average aspect ratio of a carbon-based negative electrode active material is one indicator of particle shape, and the electrical performance and adhesive strength of the negative electrode active layer may vary depending on the shape of the carbon-based negative electrode active material. The present invention controls the shape / morphology of the carbon-based negative electrode active material contained in the negative electrode active layer so that the average aspect ratio falls within a predetermined range, thereby increasing the adhesive strength between the negative electrode current collector and the negative electrode active layer and simultaneously improving the negative electrode output and fast charging.

[0054] Specifically, the carbon-based negative electrode active material contained in the negative electrode active layer may have an average aspect ratio of 0.85 or less. For example, the carbon-based negative electrode active material may have an average aspect ratio of 0.2 or more and 0.8 or less, 0.10 to 0.85, 0.25 to 0.85, 0.25 to 0.80, 0.25 to 0.70, 0.25 to 0.60, 0.25 to 0.50, 0.25 to 0.40, 0.40 to 0.65, 0.50 to 0.80, 0.50 to 0.65, 0.60 to 0.85, 0.60 to 0.75, 0.70 to 0.85, 0.10 to 0.40, or 0.45 to 0.75.

[0055] In the present invention, an average aspect ratio of 0.85 or less, specifically 0.60 or less, may refer to an ellipsoid shape stretched in any direction relative to the particle center. That is, the present invention may include a carbon-based negative electrode active material in an ellipsoid shape stretched in any direction in a negative electrode active layer. In this case, the negative electrode active layer may further shorten the lithium ion migration path, thereby improving the output characteristics of the negative electrode and shortening the charging time. Specifically, when the average aspect ratio of the carbon-based negative electrode active material exceeds 0.85, the degree of curvature at the negative electrode surface increases, limiting the charging rate of the secondary battery.

[0056] Furthermore, the carbon-based negative electrode active material may have a shape that satisfies the above-mentioned average aspect ratio, and preferably have a round particle shape rather than a plate-like, sheet-like, scale-like, needle-like, etc. Here, a round particle shape may refer to particles that are not angular. When such particles are subjected to cross-sectional structure analysis or projected as two-dimensional particles, their shape may be spherical or ellipsoidal, or in some cases, may be shapeless, making it difficult to define their shape.

[0057] For example, the carbon-based negative electrode active material may be ellipsoidal. In this case, the carbon-based negative electrode active material may 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 under the same conditions.

[0058] The ellipsoid may be a graphite assembly formed by aggregating a plurality of flake graphite particles. In this case, one graphite assembly may be formed by aggregating 2 to 100, preferably 3 to 20, flake graphite particles. By controlling the shape of the carbon-based negative electrode active material as described above, the present invention can further increase the electrical conductivity of the negative electrode active layer and maximize the contact area with the negative electrode current collector, thereby improving the adhesive strength between the negative electrode active layer and the negative electrode current collector.

[0059] In addition, the carbon-based negative electrode active material has a predetermined average particle size (D 50 For example, the carbon-based negative electrode active material may have an average particle size (D 50 ) may be 0.1 μm to 20 μm, specifically 5 μm to 20 μm, 10 μm to 20 μm, 11 μm to 19 μm, 8 μm to 15 μm, 15 μm to 20 μm, 5 μm to 8 μm, 0.1 μm to 15 μm, 0.1 μm to 10 μm, 0.1 μm to 8 μm, 0.1 μm to 5 μm, 0.1 μm to 3 μm, 0.1 μm to 1 μm, 0.5 μm to 10 μm, 0.5 μm to 5 μm, 0.5 μm to 4.5 μm, 0.5 μm to 3 μm, 1 μm to 4.5 μm, 1 μm to 3 μm, or 0.8 μm to 1.8 μm.

[0060] Within this range, the present invention can suppress an increase in the electrical resistance of the negative electrode active layer. Furthermore, within this range, the carbon-based negative electrode active material can maximize the degree of disorder in the expansion direction of each particle, thereby preventing particle expansion due to lithium ion charging while increasing the specific surface area, thereby further enhancing the adhesion between the negative electrode active layer and the negative electrode current collector. Furthermore, within this range, the present invention has the advantage of being able to increase the electrical conductivity of the negative electrode active layer while simultaneously ensuring a path for lithium ion migration.

[0061] On the other hand, the carbon-based negative electrode active material has the above average particle size (D 50 If the particle size is smaller than the lower limit of the average particle size (D), a large amount of binder is required due to the increase in the number of particles per unit volume, which may result in a deterioration in the electrical properties of the negative electrode active layer containing them. 50 ), the expansion rate of the negative electrode active material during charge and discharge of the secondary battery increases significantly, and as a result, the adhesion between particles of the negative electrode active material and the adhesion between the negative electrode active material particles and the current collector decreases with repeated charge and discharge, which can significantly reduce cycle characteristics.

[0062] Furthermore, the carbon-based negative electrode active material can satisfy the following formula 2 in a range of 0.1 to 13:

[0063] [Formula 2] A*D 50

[0064] In the above formula 2, A represents the average aspect ratio of the carbon-based negative electrode active material, D 50 represents the average particle size (unit: μm) of the carbon-based negative electrode active material.

[0065] The average aspect ratio and average particle size of a carbon-based negative electrode active material are parameters that affect the adhesive strength between the negative electrode active layer and the negative electrode current collector and the lithium ion migration path within the negative electrode active layer, respectively. Smaller values ​​of the average aspect ratio and average particle size can enhance the adhesive strength between the negative electrode active layer and the negative electrode current collector, thereby extending the life of the negative electrode. However, if these values ​​are too small, the resistance of the negative electrode active layer may increase, resulting in deterioration of electrical properties. This may affect the charge / discharge capacity and output of the negative electrode.

[0066] However, the present invention can realize both high life characteristics and electrical performance of the negative electrode by controlling Equation 2, which shows the correlation between the average aspect ratio and average particle size of the carbon-based negative electrode active material, to satisfy a predetermined range. Equation 2 is a parameter that indicates whether the shape and size of the carbon-based negative electrode active material, which undergoes an electrochemical redox reaction during charge and discharge, function organically and / or complementarily. By satisfying Equation 2 within a predetermined range, the present invention can simultaneously realize excellent life characteristics and electrical performance of the negative electrode, even if either the average aspect ratio or average particle size of the carbon-based negative electrode active material has a significantly low value. Specifically, the negative electrode can satisfy Equation 2 within a range of 0.1 to 13. For example, the negative electrode can satisfy Equation 2 with 0.1 to 11, 0.1 to 10, 0.1 to 9, 0.1 to 8, 0.1 to 7, 0.1 to 5, 0.1 to 3, 0.5 to 5, 0.5 to 6.9, 0.5 to 8.9, 5 to 9, 2 to 7, 3 to 8, 1 to 8, 10 to 13, or 1 to 6.

[0067] In the negative electrode according to the present invention, the crystalline structure characteristics of the carbon-based negative electrode active material contained in the negative electrode active layer may be controlled to achieve a high charging rate while maintaining adhesion between the negative electrode active layer and the negative electrode current collector.

[0068] For example, the negative electrode active layer may have an alignment index (OI) of 15 or less for the carbon-based negative electrode active material represented by the following formula 1:

[0069] [Formula 1] OI=I 004 / I 110

[0070] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane of the carbon-based negative electrode active material when the negative electrode active layer is subjected to X-ray diffraction (XRD) spectroscopy.

[0071] The degree of alignment (OI) of the carbon-based negative electrode active material can be an index 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, relative to the surface of the negative electrode current collector, as 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°, which correspond to the graphite carbon-based negative electrode active material, as measured by X-ray diffraction. These peaks represent 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° is thought to be an overlap of the peaks corresponding to the (1,0,1)R plane of the carbon-based negative electrode active material and the (1,1,1) plane of the current collector, for example, copper (Cu).

[0072] The degree of alignment (OI) of the carbon-based negative electrode active material can be measured by integrating the intensities of the peak at 2θ=54.7±0.2°, which indicates the (0,0,4) plane, and the peak at 2θ=77.5±0.2°, which indicates the (1,1,0) plane, and calculating the area ratio.

[0073] The peak at 2θ=54.7±0.2° indicates a crystal plane of the carbon-based negative electrode active material that is tilted relative to the negative electrode current collector. Therefore, the closer the OI value is to 0, the closer the tilt relative to the negative electrode current collector surface is to 90°, and the larger the OI value is, the closer the tilt relative to the negative electrode current collector surface is to 0° or 180°. That is, in the negative electrode active layer according to the present invention, the carbon-based negative electrode active material contained in the layer may be aligned at an angle of 60° or more, 70° or more, 70° to 90°, 80° to 90°, 65° to 85°, or 70° to 85° relative to the negative electrode current collector. Therefore, the negative electrode active layer may have a lower OI of the carbon-based negative electrode active material than a layer in which the carbon-based negative electrode active material is aligned at an angle less than 60°. Here, the degree of alignment (OI) indicates the degree of alignment of the ab-axis crystal planes of a carbon-based negative electrode active material. When the ab-axis crystal planes of the carbon-based negative electrode active material are aligned, the particles of the carbon-based negative electrode active material contained in the negative electrode active layer may also be induced to rotate. However, this particle rotation is affected by the particle morphology and is not equivalent to the degree of alignment of the ab-axis crystal planes. Therefore, it may be difficult to indicate that the particles of the carbon-based negative electrode active material are aligned using the degree of alignment (OI).

[0074] Here, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode active layer may be 10 or less, specifically 0.01 to 10, 0.01 to 9, 0.01 to 7, 0.01 to 5, 0.01 to 3, 1 to 9, 3 to 9, 5 to 9, 3 to 8, 4 to 7, 6 to 10, 6 to 9, 0.01 to 4, 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 1.0, 0.5 to 1.3, 1.1 to 1.3, 0.5 to 0.9, or 0.4 to 0.6.

[0075] By controlling the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode active layer as described above, the present invention can ensure a shorter ion migration channel within the negative electrode active layer, thereby preventing an increase in resistance due to the long migration distance of lithium ions, thereby further increasing the lithium ion migration rate during charge and discharge, and simultaneously improving fast charge performance and output performance with high safety.

[0076] Specifically, conventional fast charging of lithium secondary batteries has been achieved by increasing the charging rate by charging at a high C rate (above 1C rate) using a constant current-constant voltage (CC-CV) charging method. Generally, in CC-CV charging, lithium ion diffusion within the electrode occurs during the CC charging phase. However, prolonged diffusion inevitably leads to concentration polarization. This lithium ion concentration polarization easily leads to lithium deposition at the anode, particularly at high rates where the charging current (A) exceeds the standard value (i.e., 1A at 1C rate) relative to the rated capacity (Ah) of the secondary battery, significantly reducing the safety of the secondary battery. Furthermore, high-rate CC-CV charging reaches the upper voltage limit very quickly during the CC charging phase, which can cause the current to drop to a preset limit before the active material is completely consumed. That is, since the charging time increases significantly in the constant voltage (CV) charging stage, there is a problem that the effect of reducing the total time required to charge the secondary battery is small.

[0077] However, the present invention significantly reduces the resistance induced in the negative electrode active layer during charging by shortening the lithium ion migration path within the negative electrode active layer. This reduction in resistance can be induced so that the constant current (CC) charging stage is longer than the constant voltage (CV) charging stage during the entire charging time when charging using a constant current-constant voltage (CC-CV) method. Here, the constant current (CC) charging stage provides the same charge capacity per unit time because the same amount of current flows, while the constant voltage (CV) charging stage tends to reduce the current to maintain the same voltage. That is, because the charge capacity per unit time during the constant voltage (CV) charging stage decreases rapidly, the overall charging time can be significantly reduced as the constant current (CC) charging stage duration increases. Therefore, the present invention can increase the constant current (CC) charging stage duration by controlling the degree of alignment (OI) of the carbon-based negative electrode active material, thereby completing charging of a secondary battery in a significantly shorter time.

[0078] Furthermore, the fast charging of such secondary batteries can be realized under standard conditions (e.g., 1C rate) rather than high-rate C rate conditions, which has the advantage of overcoming safety issues of lithium secondary batteries due to the concentration polarization of lithium ions induced in the negative electrode active layer during charging.

[0079] Meanwhile, the negative electrode active layer may have a porosity of 20% to 30%, specifically 23% to 30%, 25% to 30%, 26% to 29%, or 24% to 28%.

[0080] In this case, the negative electrode active layer has a thickness of 0.62 m 2 / g or less, specifically 0.615 m 2 / g or less, 0.6m 2 / g or less, 0.5m 2 / g or less, 0.20m 2 / g~0.62m 2 / g, 0.30m 2 / g~0.62m 2 / g, 0.40m2 / g~0.62m 2 / g, 0.40m 2 / g~0.60m 2 / g, 0.40m 2 / g~0.55m 2 / g, 0.40m 2 / g~0.50m 2 / g, or 0.58m 2 / g~0.62m 2 The BET specific surface area can be expressed as / g. Here, the specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method. For example, it can be measured by the BET 6-point method using a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) and a nitrogen gas adsorption / flow method.

[0081] The present invention can further increase the energy density of the negative electrode without reducing the wettability of the negative electrode active layer to the electrolyte by adjusting the porosity and / or BET specific surface area of ​​the negative electrode active layer, which is located at the outermost layer of the negative electrode active layer and is in direct contact with the electrolyte, within the above ranges.

[0082] The average thickness of the entire negative electrode active layer may be 50 μm to 500 μm, specifically 100 μm to 400 μm, 200 μm to 350 μm, 50 μm to 180 μm, 80 μm to 150 μm, 100 μm to 250 μm, or 130 μm to 190 μm. By adjusting the average thickness of the negative electrode active layer within the above range, the present invention can easily control the crystalline characteristics of each carbon-based negative electrode active material contained in the negative electrode active layer. As a result, the negative electrode of the present invention not only exhibits 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, which allows charging to be completed in a short time even under standard conditions (1C rate).

[0083] In addition, the negative electrode active layer according to the present invention may further include, in addition to the negative electrode active material as the main component, a conductive material, a binder, other additives, and the like, as needed.

[0084] The conductive material may include one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0085] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0086] The content of the conductive material may be 0.1 to 10 parts by weight, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight, based on 100 parts by weight of the total negative electrode active layer. By controlling the content of the conductive material within the above range, the present invention can prevent a decrease in charge capacity due to an increase in negative electrode resistance caused by a low content of conductive material, and can prevent problems such as a decrease in charge capacity due to a decrease in the content of negative electrode active material caused by an excessive amount of conductive material, or a decrease in fast charge characteristics due to an increase in the loading amount of the negative electrode active layer.

[0087] The binder is a component that aids in bonding between the negative electrode active material and the conductive material, and between the negative electrode active material and the current collector. It may be appropriately used within a range that does not degrade the electrical properties of the electrode. Specifically, the binder may include at least one of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0088] The content of the binder may be 0.1 to 10 parts by weight, specifically 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, per 100 parts by weight of the 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 a decrease in the adhesive strength of the active layer due to a small content of binder, or a decrease in the electrical properties of the electrode due to an excessive amount of binder.

[0089] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery, and may be made of, for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. In the case of copper or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector may be appropriately selected from 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0090] <Lithium secondary battery> In one embodiment, the present invention further comprises: an electrode assembly including a positive electrode, the above-described negative electrode of the present invention, and a separator disposed between the positive electrode and the negative electrode; and an electrolyte composition impregnated with the electrode assembly.

[0091] The lithium secondary battery according to the present invention includes an electrode assembly having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are alternately arranged with a separator disposed therebetween. The lithium secondary battery includes the negative electrode according to the present invention and has excellent output characteristics. Since the lithium secondary battery can be charged in a short time even at a 1C rate, the lithium secondary battery can be effectively used as a power source for medium- to large-sized devices such as electric vehicles.

[0092] In this case, the negative electrode has the same configuration as that described above, and therefore a detailed description thereof will be omitted.

[0093] 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, and the like, as needed.

[0094] The positive electrode active material is a material capable of undergoing an electrochemical reaction on a positive electrode current collector, and may include at least one lithium metal oxide represented by the following Chemical Formula 1 and Chemical Formula 2, which are capable of reversibly intercalating and deintercalating lithium ions:

[0095] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0096] [Chemical formula 2] LiM 2 p Mn q P r O4

[0097] In the above Chemical Formula 1 and Chemical Formula 2, M 1 is one or more elements selected from 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 <z≦0.3、0<w≦0.3、0≦v≦0.1であり、かつy+z+w+v=1であり、 M 2 is Ni, Co or Fe, p is 0.05≦p≦1.0, q is 2-p, r is 0 or 1.

[0098] The lithium metal oxides represented by the above Chemical Formula 1 and Chemical Formula 2 are materials containing high contents of nickel (Ni) and manganese (Mn), respectively, and when used as a positive electrode active material, have the advantage of being able to stably supply electricity with a high capacity and / or high voltage compared to conventionally commonly used positive electrode active materials such as lithium iron phosphate (LiFePO4).

[0099] In this case, the lithium metal oxide represented by the above 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 O2, etc. In addition, the lithium metal oxide represented by the above chemical formula 2 can be LiNi 0.7 Mn 1.3 O4, LiNi 0.5 Mn 1.5 O4, LiNi 0.3 Mn 1.7 O4, etc. The lithium metal oxides represented by Chemical Formula 1 and / or Chemical Formula 2 may be used alone or in combination.

[0100] In addition, the positive electrode active material may be included in an amount of 85 parts by weight or more, specifically 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more, based on the weight of the positive electrode active layer.

[0101] In addition, the positive electrode active layer may further include a conductive material, a binder, and other additives in addition to the positive electrode active material.

[0102] The conductive material is used to improve the electrical performance of the positive electrode, and may be a conductive material commonly used in the art. Specifically, the conductive material may include at least one of natural graphite, artificial graphite, carbon black, acetylene black, denka black, ketjen black, super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0103] The conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active layer, specifically 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.

[0104] The binder functions to bind the positive electrode active material, the positive electrode additive, and the conductive material together, and any material having this function may be used without particular limitation. Specifically, the binder may include one or more resins 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.

[0105] The binder may be included in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, based on 100 parts by weight of the positive electrode active layer.

[0106] The total thickness of the positive electrode active layer is not particularly limited, but may be specifically 50 μm to 300 μm, more specifically 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.

[0107] In addition, the positive electrode can use a positive electrode current collector that has high conductivity without inducing 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, those that have been surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately selected from 3 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0108] The separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film with high ion permeability and mechanical strength, and may be any material commonly used in the art. Specifically, it may contain one or more polymers selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers, which are chemically resistant and hydrophobic. The separator may be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the above-mentioned polymers. In some cases, the separator may be in the form of a composite separator, in which organic or inorganic particles are coated on the porous polymer substrate with an organic binder. The separator may have an average pore diameter of 0.01 μm to 10 μm and an average thickness of 5 μm to 300 μm.

[0109] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery having a form that can include a stack type, a zigzag type, or a zigzag-stack type electrode assembly. For example, the lithium secondary battery according to the present invention may be a pouch type secondary battery or a prismatic type secondary battery.

[0110] Pouch-type secondary batteries and / or prismatic secondary batteries have the advantage of being highly usable in terms of energy density since unit cells of the secondary battery can be packed at high density in a limited space.

[0111] Furthermore, in the lithium secondary battery, the electrolyte composition can be any composition that is commonly used in lithium secondary batteries, without any particular limitation.

[0112] Specifically, the electrolyte composition may include a non-aqueous organic solvent, a lithium salt, and an electrolyte additive.

[0113] Here, the non-aqueous organic solvent may be used without any particular limitation as long as it is used in the art for non-aqueous electrolytes. For example, examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), γ-butyrolactone, 1,2-dimethoxyethane (DME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP).

[0114] The non-aqueous organic solvent used in the present invention may be a single type, or two or more types may be mixed in any combination or ratio depending on the application. Among them, from the viewpoints of electrochemical stability against oxidation-reduction and chemical stability with respect to heat and reactions with solutes, it is particularly preferable to mix propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0115] In addition, the lithium salt may be any lithium salt used in non-aqueous electrolytes in the art without any particular limitation. Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO, or the like. 4、 LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, and (FSO2)2NLi.

[0116] The lower limit of the appropriate concentration range for the lithium salt to be used appropriately 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 of the appropriate concentration range is 2.5 mol / L or less, specifically 2.0 mol / L or less, more specifically 1.5 mol / L or less. If the lithium salt concentration is below 0.5 mol / L, the ionic conductivity may decrease, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery. Furthermore, if the lithium salt concentration exceeds 2.5 mol / L, the viscosity of the electrolyte for the nonaqueous electrolyte battery may increase, which may also result in a decrease in ionic conductivity, which may result in a deterioration in the cycle characteristics and output characteristics of the nonaqueous electrolyte battery.

[0117] Furthermore, 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, decomposition of the fluorine-containing lithium salt may be accelerated, resulting in the production of hydrogen fluoride (HF). Hydrogen fluoride (HF) is undesirable because it can cause deterioration of battery performance. Therefore, the temperature at which the lithium salt is dissolved in the non-aqueous organic solvent is not particularly limited, but may be adjusted to −20° C. to 80° C., specifically, 0° C. to 60° C.

[0118] Furthermore, the electrolyte additives may be included as additional auxiliary components to improve the physical properties of the electrolyte composition. Commonly used electrolyte additives may be added to the nonaqueous electrolyte of the present invention in any proportion. Specific examples include compounds that have overcharge prevention effects, anode film formation effects, and cathode protection effects, such as cyclohexylbenzene, biphenyl, t-butylbenzene, carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propane sultone, succinonitrile, and dimethylvinylene carbonate. Furthermore, the electrolyte for nonaqueous electrolyte batteries can be solidified using a gelling agent or crosslinked polymer, similar to when used in nonaqueous electrolyte batteries known as lithium polymer batteries.

[0119] The lithium secondary battery according to the present invention has the above-mentioned configuration, and therefore has the advantage that it not only has excellent battery output characteristics but also can be charged in a short time even at a 1C rate.

[0120] <Method of manufacturing the negative electrode> In one embodiment, the present invention further comprises: applying a negative electrode slurry to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; and drying the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer.

[0121] The method for manufacturing a negative electrode according to the present invention refers to a method for manufacturing the above-described negative electrode according to the present invention. The method for manufacturing a negative electrode includes coating a negative electrode slurry on a negative electrode current collector, applying a magnetic field to the surface of the coated negative electrode slurry, and then drying the negative electrode slurry, thereby manufacturing a negative electrode having a negative electrode active layer in which the crystalline properties of the negative electrode active material are controlled.

[0122] The negative electrode slurry coating step involves discharging and coating the negative electrode slurry containing a carbon-based negative electrode active material onto the surface of a moving negative electrode current collector. This step can be performed using any method commonly used in the art, but is preferably performed using a die coating method. The die coating method can be performed using a slot die equipped with a shim for controlling the discharging conditions of the negative electrode slurry. In this case, the loading amount and coating thickness of the negative electrode slurry coated on the negative electrode current collector can be easily controlled by controlling the shape and position of the shim.

[0123] Meanwhile, the step of applying a magnetic field to the negative electrode slurry may be a step of controlling the crystalline properties of the negative electrode active material contained in the negative electrode slurry. Specifically, this step may align the ab-axis crystal plane of the carbon-based negative electrode active material contained in the negative electrode slurry at a large angle relative to the negative electrode current collector by applying a magnetic field to the surface of the negative electrode slurry coated on the negative electrode current collector.

[0124] In this case, the magnetic field may be applied by magnets disposed above and below the negative electrode current collector, which is moved to a state where the negative electrode slurry is coated on its surface, and the polarities of the magnets disposed above and below the negative electrode current collector may be opposite to each other.

[0125] In addition, the degree of alignment (OI) of the carbon-based negative electrode active material contained in each negative electrode slurry may be adjusted by adjusting the strength and application time of the applied magnetic field, and thus, the step of applying the magnetic field may be performed under a predetermined magnetic field strength condition.

[0126] Specifically, the magnetic field applying step may apply a magnetic field of 10,000 G (Gauss) or less, specifically, a magnetic field of strength 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 may be applied.

[0127] Furthermore, the step of applying the magnetic field can be carried out for 1 to 20 seconds, specifically 1 to 15 seconds, 1 to 10 seconds, 5 to 20 seconds, 10 to 20 seconds, 11 to 18 seconds, 1 to 5 seconds, 7 to 13 seconds, or 6 to 11 seconds.

[0128] For example, in the step of applying a magnetic field, a magnetic field of 3,000±50 G may be applied to the negative electrode slurry for 9 to 11 seconds.

[0129] Furthermore, the step of applying the magnetic field is performed by magnets introduced above and below the applied negative electrode slurry, as described 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 across 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 of the negative electrode slurry, and more 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 of the negative electrode slurry.

[0130] In the present invention, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry can be uniformly achieved within a predetermined range by controlling the magnetic field strength, application time, and / or size of the magnet unit in the magnetic field application step as described above.

[0131] The step of forming the negative electrode active layer may include the steps of drying the negative electrode slurry and rolling the dried negative electrode slurry.

[0132] At this time, the step of drying the negative electrode slurry may be performed in any manner that can maintain the orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0133] For example, the drying step can dry the negative electrode slurry by applying heat energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0134] The step of rolling the dried negative electrode slurry is a step of increasing the density of the negative electrode active layer by applying pressure to the dried negative electrode slurry using a roll press, etc. Here, the rolling may be performed at a temperature higher than room temperature.

[0135] Specifically, the rolling can be carried out 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, 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. The rolling can be carried out under a pressure of 50 MPa to 200 MPa, specifically 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.

[0136] The present invention can increase the energy density of the negative electrode while minimizing changes in the alignment of the carbon-based negative electrode active material contained in the negative electrode active layer formed by rolling the dried negative electrode slurry under the above-mentioned temperature, speed, and / or pressure conditions.

[0137] The present invention will be described in more detail below with reference to examples and experimental examples.

[0138] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0139] <Examples 1 to 8 and Comparative Examples 1 to 3. Production of negative electrodes for lithium secondary batteries> As a carbon-based negative electrode active material, artificial graphite was prepared, which was formed by granulating scale-like primary particles and having a secondary particle form. Carbon black was also prepared as a conductive material, and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) were also prepared as binders. The average particle size (D 50The results are shown in Table 1 below.

[0140] Next, 96 parts by weight of artificial graphite, 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 a solid content of 50% to prepare a negative electrode slurry.

[0141] After the negative electrode slurry was prepared, the negative electrode slurry was cast onto a copper thin plate (thickness: 10 μm) that was being transferred roll-to-roll (transfer speed: 5 m / min) using a single die coater.

[0142] Permanent magnets with a length ratio of 110% to 120% of the width of the negative electrode slurry were placed above the applied negative electrode slurry and below the negative electrode current collector, and a magnetic field of 3,000±20 G was applied. 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 to form a negative electrode in the form of a negative electrode active layer laminated on the negative electrode current collector. The formed negative electrode active layer was rolled at 50±1°C under a pressure of 100 MPa to 150 MPa and a transfer speed of 3 m / s to form a negative electrode for a lithium secondary battery (average thickness of negative electrode active layer: 190±5 μm, loading amount: 5 mg / cm). 2 ~20mg / cm 2 ) was manufactured.

[0143] For each manufactured negative electrode, a cross-section of the negative electrode active layer was analyzed using a scanning electron microscope (SEM) to obtain a spectral image. The obtained image was analyzed to calculate the average aspect ratio of the artificial graphite contained in the negative electrode active layer. Here, the average aspect ratio refers to the ratio of the shortest dimension to the longest dimension passing through the center of an artificial graphite particle. The results are shown in Table 1 below.

[0144] In addition, X-ray diffraction spectroscopy (XRD) was performed on the negative electrode active layer of each of the manufactured negative electrodes to measure the spectrum. At this time, the measurement conditions for X-ray diffraction (XRD) were as follows:

[0145] - Target: Cu (Kα line) graphite monochromator - Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree - Measurement area: (1,1,0) plane: 76.5°<2θ<78.5° / (0,0,4) plane: 53.5°<2θ<56.0°

[0146] From the spectra measured under the above conditions, the average degree of alignment (OI) of the carbon-based active material contained in each negative electrode active layer was calculated using Equation 1. The results are shown in Table 1:

[0147] [Formula 1] OI=I 004 / I 110

[0148] In Equation 1, I 004 represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, I 110 represents the area of ​​the peak indicating the (1,1,0) crystal plane of the carbon-based negative electrode active material when the negative electrode active layer is subjected to X-ray diffraction (XRD) spectroscopy.

[0149] [Table 1]

[0150] <Comparative Examples 4 and 5: Production of negative electrodes for lithium secondary batteries> A negative electrode for a lithium secondary battery was prepared in the same manner as in Example 2, except that natural graphite having an ellipsoidal shape or artificial graphite having a scaly shape was used as the carbon-based negative electrode active material.

[0151] For the fabricated negative electrodes, (1) a scanning electron microscope (SEM) analysis was performed on the cross section of the negative electrode active layer to calculate the average aspect ratio of the carbon-based negative electrode active material contained in the negative electrode active layer. (2) X-ray diffraction (XRD) was also performed on the negative electrode active layer to determine the degree of alignment (OI) of the carbon-based negative electrode active material. The results are shown in Table 2 below.

[0152] [Table 2]

[0153] <Examples 9 to 16 and Comparative Examples 6 to 10. Production of Lithium Secondary Batteries> LiNi with a particle size of 5 μm is used as the positive electrode active material. 0.7 Co 0.1 Mn 0.1 Al 0.1 O2 was prepared and mixed with polyvinylidene fluoride as a carbon-based conductive material and binder in N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 to form a slurry, which was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to produce a positive electrode.

[0154] A separator made of polypropylene having a thickness of 18 μm was interposed between the obtained positive electrode and the negative electrode prepared in each of Examples 1 to 8 and Comparative Examples 1 to 5, and the positive electrode was inserted into a case, and then an electrolyte composition was injected to assemble a 1 Ah class lithium secondary battery.

[0155] The type of negative electrode used in each lithium secondary battery is shown in Table 3 below.

[0156] [Table 3]

[0157] <Experimental Example> In order to evaluate the performance of the negative electrode according to the present invention, the following experiments were carried out on the negative electrodes and lithium secondary batteries prepared in the examples and comparative examples.

[0158] 1) Evaluation of adhesive strength to the negative electrode current collector The negative electrodes prepared in Examples 1 to 8 and Comparative Examples 1 to 5 were cut into specimens measuring 25 mm in width and 70 mm in length. The specimens were attached to a glass plate using double-sided tape, with the current collector facing the glass plate. The specimens attached to the glass plate were then attached to a tensile tester, and the negative electrode active layer of each negative electrode was peeled off at a 90° angle from the negative electrode current collector at a rate of 100 mm / min at 25°C. The peel force measured in real time was defined as the interfacial adhesion strength between the negative electrode current collector and the negative electrode active layer, and the measurement results are shown in Table 4 below.

[0159] 2) 1C rate fast charging evaluation Each of the lithium secondary batteries prepared in Examples 9 to 16 and Comparative Examples 6 to 10 was activated by charging at 25°C at a rate of 0.3C to 4.2V under CC-CV conditions and discharging at a rate of 0.3C to 2.5V under CC conditions.

[0160] Each activated lithium secondary battery was charged at 25°C using a constant current-constant voltage (CC-CV) method, and the time required for the state of charge (SOC) to reach 80% was measured. The charging was performed at a constant current (CC) rate of 1.0C until the voltage reached 4.2V, and then constant voltage (CV) charging was performed, maintaining 4.2V and cutting off when the current reached a 0.005C rate. The measured charging times are shown in Table 4 below.

[0161] [Table 4]

[0162] As shown in Table 4 above, the negative electrode for a lithium secondary battery according to the present invention not only has excellent adhesion between the negative electrode active layer and the negative electrode current collector, but also completes charging at a fast rate under 1C rate conditions.

[0163] Specifically, the negative electrodes of the examples exhibited a high adhesive strength between the negative electrode active layer and the negative electrode current collector of 31 gf / cm or more (particularly, 33 gf / cm or more).Furthermore, the secondary batteries of the examples including such negative electrodes reached a state of charge (SOC) of 80% in a short time of 21 seconds or less (particularly, less than 20 seconds) under standard constant current-constant voltage (CC-CV) charging conditions at a 1 C rate.

[0164] On the other hand, the negative electrodes of the comparative examples showed a low adhesive strength of 30 gf / cm or less between the negative electrode active layer and the negative electrode current collector. However, the negative electrode of Comparative Example 4 showed an adhesive strength of 30 gf / cm between the negative electrode active layer and the negative electrode current collector, and it was confirmed that a secondary battery including it took 22 seconds or more to reach a state of charge (SOC) of 80%.

[0165] This means that by controlling the average aspect ratio and degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode active layer, the adhesive strength between the negative electrode current collector and the negative electrode active layer and the charging speed under standard C-rate conditions can be improved.

[0166] These results show that the negative electrode for a lithium secondary battery according to the present invention has excellent life characteristics due to its high adhesive strength to the negative electrode current collector, and that a lithium secondary battery containing it has excellent output characteristics and can be charged in a short time even at a 1C rate.

[0167] Although the present invention has been described above with reference to preferred embodiments, it will be understood by those skilled in the art or those with ordinary knowledge in the art that the present invention can be modified and changed in various ways without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0168] Therefore, the technical scope of the present invention is not limited to the content described in the Summary of the Invention of the specification, but can be defined by the 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, the negative electrode active layer including a carbon-based negative electrode active material having an average aspect ratio of 0.85 or less, The negative electrode active layer has an alignment degree (O.I) of 10 or less of the carbon-based negative electrode active material represented by the following formula 1: [Formula 1] O.I=I ００４ / I １１０ In Formula 1, I ００４ represents the area of ​​the peak representing the (0,0,4) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopic analysis of the negative electrode active layer, I １１０ represents the area of ​​the peak indicating the (1,1,0) crystal plane of the carbon-based negative electrode active material in X-ray diffraction (XRD) spectroscopy analysis of the negative electrode active layer, negative electrode for lithium secondary battery.

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the carbon-based negative electrode active material has an average aspect ratio of 0.2 to 0.

8.

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active layer has an alignment degree (O.I) of the carbon-based negative electrode active material represented by Formula 1 of 0.01 to 10.

4. The negative electrode for a lithium secondary battery according to claim 1 , wherein the carbon-based negative electrode active material comprises at least one of natural graphite and artificial graphite.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the carbon-based negative electrode active material is artificial graphite.

6. The average particle size (D ５０ 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the first electrode is 0.01 μm to 20 μm.

7. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active layer has a porosity of 20% to 30%.

8. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the average thickness of the negative electrode active layer is 50 μm to 500 μm.

9. 2. A method for producing a negative electrode for a lithium secondary battery according to claim 1, comprising: applying a negative electrode slurry to at least one surface of the negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; and drying the negative electrode slurry to which the magnetic field has been applied to form the negative electrode active layer.

10. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 9, wherein the step of applying the magnetic field is performed for 1 to 20 seconds.

11. 10. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 9, wherein the step of applying a magnetic field is performed at a magnetic field strength of 1,000 G to 7,000 G.

12. an electrode assembly including a positive electrode, the negative electrode of claim 1, and a separator disposed between the positive electrode and the negative electrode; an electrolyte composition impregnated with the electrode assembly.

13. The positive electrode includes a positive electrode active layer provided on at least one surface of a positive electrode current collector and including one or more positive electrode active materials selected from lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2: [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ [Chemical formula 2] LiM ２ ｐ Mn １－ｐ O ４ In the above Chemical Formula 1 and Chemical Formula 2, M １ is one or more elements selected from 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 in the ranges 1.0≦x≦1.30, 0.5≦y<1, 0<z≦0.3, 0<w≦0.3, 0≦v≦0.1, respectively, and y+z+w+v=1; M ２ is Ni, Co or Fe, 13. The lithium secondary battery according to claim 12, wherein p is in the range of 0.05≦p≦1.

0.

14. The positive electrode 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 The lithium secondary battery according to claim 13, comprising one or more of:

15. The lithium secondary battery of claim 12, wherein the electrode assembly is a stacked electrode assembly, a zigzag electrode assembly, or a zigzag-stacked electrode assembly.

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