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 lithium secondary battery including the same. The negative electrode includes both a carbon-based negative electrode active material and a silicon-based negative electrode active material as negative electrode active materials, and exhibits excellent characteristics in charge / discharge capacity and energy density. In addition, the negative electrode has an alignment degree (OI) of the carbon-based negative electrode active material after activation. a ) is the degree of alignment (OI) of the carbon-based negative electrode active material before activation. r ) has the advantage of exhibiting high charge characteristics and life characteristics during long-term charging and discharging.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery containing the same, which has excellent charge / discharge characteristics and life characteristics.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0169280 dated December 7, 2022 and Korean Patent Application No. 10-2023-0076626 dated June 15, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference. [Background technology]

[0003] In recent years, 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 and power storage devices. This has led to extensive research into batteries that can meet a variety of needs. In particular, research into lithium secondary batteries, which have high energy density and excellent life and cycle characteristics as power sources for medium- to large-sized devices, has been actively conducted.

[0004] A lithium secondary battery is a chargeable and dischargeable power generating device that consists of a laminated structure of a positive electrode, a separator, and a 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, and a lithium insertion reaction occurs in which lithium is reduced at the negative electrode and inserted into the negative electrode active material. In general, the desorption reaction at the positive electrode active material is faster than the insertion reaction at the negative electrode active material, so the charging speed and other performance characteristics of a lithium secondary battery are primarily determined by the negative electrode.

[0005] Carbon materials containing graphite are currently widely used as the negative electrode active material for the negative electrode. For example, graphite has a layered structure in which layers of carbon atoms are stacked in a network structure. As a result, lithium ions penetrate the edge surfaces (surfaces where layers overlap) of the carbon layers during charging and diffuse between the layers. During discharge, the diffused lithium ions are desorbed and released from the edge surfaces of the carbon layers. Furthermore, since the electrical resistivity of the carbon layers in the plane direction of graphite is lower than that in the stacking direction of the carbon layers, a bypass electron conduction path is formed along the plane direction of the carbon layers.

[0006] In this regard, a technique for magnetically orienting graphite contained in a negative electrode has been proposed to improve the charging performance of lithium secondary batteries using carbon materials such as graphite. Specifically, the (0,0,2) crystal plane of the graphite is oriented in a magnetic field during the formation of the negative electrode, and then fixed in place. In this case, the edge face of the graphite carbon layer faces the positive electrode active layer, facilitating the insertion and desorption of lithium ions. At the same time, the electron conduction path is shortened, improving the electronic conductivity of the negative electrode and thereby improving the charging performance of the battery.

[0007] On the other hand, when carbon materials such as graphite release lithium, the average potential is about 0.2 V (Li / Li + (reference), and the discharge potential exhibits a relatively flat pattern. Therefore, anodes containing graphite as anode active material have the advantage of high and constant voltage of secondary batteries. The theoretical electrical capacity per unit mass of carbon materials such as graphite is 372 mAh / g. However, since the capacity of the carbon materials increases close to the theoretical capacity, it is difficult to further increase the capacity, and there is a limit to how difficult it is to increase the energy density of the manufactured anode.

[0008] To improve the capacity and energy density of lithium secondary batteries, various anode active materials have been investigated. Silicon materials, such as silicon (Si) and silicon oxide (SiO2), have recently been the subject of extensive research due to their ability to reversibly adsorb and release large amounts of lithium through compound formation reactions with lithium. Silicon materials have a theoretical maximum capacity of approximately 4020 mAh / g (9800 mAh / cc, specific gravity 2.23). This is significantly higher than that of graphite-based materials, making silicon a useful anode material for high energy density and / or high capacity. However, silicon materials exhibit large volume changes (up to 300%) during charge and discharge. Therefore, although anodes containing both carbon and silicon materials have high energy density, they suffer from limited durability due to significantly reduced adhesion between the anode active layer and the anode current collector. In particular, when the (0,0,2) crystal plane of the graphite is oriented substantially parallel to the negative electrode current collector, the large volume change of the silicon material significantly damages and / or destroys the edge plane alignment of the carbon layer of the carbon material, resulting in a significant deterioration in the charging and life characteristics of the negative electrode when the negative electrode is charged and discharged for a long period of time.

[0009] Therefore, there is a strong need for a negative electrode technology for lithium secondary batteries that contains both a carbon material and a silicon material as negative electrode active materials and that not only has excellent charge / discharge capacity and energy density but also exhibits high charge characteristics and life characteristics even during long-term charge / discharge. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Publication No. 10-2020-0047287 Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a negative electrode for a lithium secondary battery, which contains both a carbon material and a silicon material as negative electrode active materials, has excellent charge / discharge capacity and energy density, and exhibits high charge characteristics and life characteristics even during long-term charge / discharge, and a lithium secondary battery containing the same. [Means for solving the problem]

[0012] To solve the above-mentioned problems, 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 and including a carbon-based negative electrode active material and a silicon-based negative electrode active material; The negative electrode active layer is The degree of alignment (OI) of the carbon-based negative electrode active material after activation a ) is less than or equal to 3, Provided is a negative electrode for a secondary battery that satisfies the following formula 1:

[0013] [Formula 1] 0.5≦[OI a ] / [OI r ]<1.0

[0014] In the above formula 1, OI r represents the degree of alignment (OI) of the carbon-based negative electrode active material measured before activation, OI a represents the degree of alignment (OI) of the carbon-based negative electrode active material measured after activation, The degree of alignment (OI) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy analysis of the negative electrode active layer.

[0015] In this case, the average particle size (Dc) of the carbon-based negative electrode active material may be 5 μm to 50 μm, the average particle size (Ds) of the silicon-based negative electrode active material may be 0.5 μm to 10 μm, and the ratio of the average particle sizes of the carbon-based negative electrode active material and the silicon-based negative electrode active material (Dc / Ds) may be 1 to 10.

[0016] The silicon-based negative electrode active material may be included in an amount of 1 wt % to 20 wt % based on the total weight of the negative electrode active material.

[0017] The carbon-based negative electrode active material may include at least one of natural graphite and artificial graphite.

[0018] The silicon-based negative electrode active material includes silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q , where 0.8≦q≦2.5).

[0019] The negative electrode active layer has a thickness of 150 mg / 25 cm 2 ~300mg / 25cm 2 and the average thickness may be 10 μm to 100 μm.

[0020] In one embodiment, the present invention further comprises: applying a negative electrode slurry containing a carbon-based negative electrode active material and a silicon-based negative electrode active material to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; drying and rolling the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer; The negative electrode active layer is The degree of alignment (OI) of the carbon-based negative electrode active material after activation a ) is less than or equal to 3, The present invention provides a method for manufacturing a negative electrode for a lithium secondary battery that satisfies the following formula 1:

[0021] [Formula 1] 0.5≦[OI a ] / [OI r ]<1.0

[0022] In the above formula 1, OI r represents the degree of alignment (OI) of the carbon-based negative electrode active material measured before activation, OI arepresents the degree of alignment (OI) of the carbon-based negative electrode active material measured after activation, The degree of alignment (OI) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy analysis of the negative electrode active layer.

[0023] Here, the step of applying the magnetic field may be performed at a magnetic field strength of 3,000 G to 9,000 G for 1 second to 30 seconds.

[0024] The rolling can be carried out at a temperature of 20° C. to 35° C. and a pressure of 50 MPa to 200 MPa.

[0025] In one embodiment, the present invention further comprises: There is provided a lithium secondary battery including an electrode assembly including a positive electrode, the negative electrode according to the present invention, and a separator disposed between the positive electrode and the negative electrode.

[0026] In this case, the positive electrode may include a positive electrode active material 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:

[0027] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0028] [Chemical formula 2] LiM 2 p Mn 1-p O4

[0029] In the above Chemical Formula 1 and Chemical Formula 2, M 1is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, and v are 1.0≦x≦1.30, 0.5≦y<1, 0 <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 in the range of 0.05≦p≦1.0.

[0030] Furthermore, in one embodiment, the present invention provides activating a lithium secondary battery including an electrode assembly including a positive electrode, the negative electrode according to the present invention, and a separator disposed between the positive electrode and the negative electrode; The negative electrode active layer of the negative electrode is characterized by the degree of alignment (OI) of the carbon-based negative electrode active material after activation. a ) is 3 or less and satisfies the following formula 1:

[0031] [Formula 1] 0.5≦[OI a ] / [OI r ]<1.0

[0032] In the above formula 1, OI r represents the degree of alignment (OI) of the carbon-based negative electrode active material measured before activation, OI a represents the degree of alignment (OI) of the carbon-based negative electrode active material measured after activation, The degree of alignment (OI) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy analysis of the negative electrode active layer.

[0033] In this case, the activation step can be carried out by charging and discharging at a rate of 0.01C to 0.9C two or more times. [Effects of the Invention]

[0034] The negative electrode for a lithium secondary battery according to the present invention includes both a carbon-based negative electrode active material and a silicon-based negative electrode active material as negative electrode active materials, and exhibits excellent characteristics in charge / discharge capacity and energy density. In addition, the negative electrode has an alignment degree (OI) of the carbon-based negative electrode active material after activation. a ) is the degree of alignment (OI) of the carbon-based negative electrode active material before activation. r ) is realized in a predetermined range lower than that, it has an advantage that the secondary battery exhibits high charge characteristics and life characteristics during long-term charge and discharge. [Brief explanation of the drawings]

[0035] [Figure 1] 10A and 10B are images showing the alignment of the ab-axis crystal planes of graphite depending on whether or not a magnetic field is applied to a negative electrode slurry during the formation of a negative electrode active layer. (a) shows the case where no magnetic field is applied and the graphite crystal planes are not aligned, and (b) shows the case where a magnetic field is applied and the graphite crystal planes are aligned. DETAILED DESCRIPTION OF THE INVENTION

[0036] Because the present invention is susceptible to various modifications and embodiments, specific embodiments will be described in detail.

[0037] However, this is not intended to limit the invention to any particular embodiment, but rather to be understood as including all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0038] 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 may be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0039] 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.

[0040] Furthermore, in the present invention, "comprising as a main component" may mean containing 50 wt% or more (or 50 vol% or more), 60 wt% or more (or 60 vol% or more), 70 wt% or more (or 70 vol% or more), 80 wt% or more (or 80 vol% or more), 90 wt% or more (or 90 vol% or more), or 95 wt% or more (or 95 vol% or more) of the defined component relative to the total weight (or volume). For example, "comprising graphite as a main component as a negative electrode active material" may mean containing 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 graphite relative to the total weight of the negative electrode active material. In some cases, it may mean that the entire negative electrode active material is composed of graphite, with graphite accounting for 100 wt%.

[0041] Furthermore, in this 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) showing the two-dimensional planar structure of the carbon-based negative electrode active material constituting the negative electrode active material particles is aligned at a specific inclination relative to the surface of the negative electrode current collector. This may differ from the carbon-based negative electrode active material particles themselves being aligned in a specific direction within the negative electrode active layer.

[0042] Furthermore, "high orientation of the carbon-based negative electrode active material" may 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 may also 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 perpendicular, greater than 45°, specifically 60° or greater) with respect to the surface of the negative electrode current collector.

[0043] Furthermore, "a carbon-based negative electrode active material with 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 low angle (e.g., less than 45°) relative to the surface of the negative electrode current collector. Conversely, "a carbon-based negative electrode active material with 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 high angle (e.g., an angle close to perpendicular, 45° or greater, specifically 60° or greater) relative to the surface of the negative electrode current collector.

[0044] Furthermore, in this specification, the term "crystal plane of a 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 a crystal. In the present invention, this term may refer to a crystal plane including a flat surface of the carbon-based negative electrode active material, or a crystal plane including the a-axis, b-axis, and ab-axis of the carbon-based negative electrode active material crystal.

[0045] In addition, in this specification, "average particle size (D 50 )" 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.

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

[0047] <Anode for lithium secondary batteries>

[0048] 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 and a silicon-based negative electrode active material; The negative electrode active layer is The degree of alignment (OI) of the carbon-based negative electrode active material after activation a ) is less than or equal to 3, Provided is a negative electrode for a secondary battery that satisfies the following formula 1:

[0049] [Formula 1] 0.5≦[OI a ] / [OI r ]<1.0

[0050] In the above formula 1, OI r represents the degree of alignment (OI) of the carbon-based negative electrode active material measured before activation, OI a represents the degree of alignment (OI) of the carbon-based negative electrode active material measured after activation, The degree of alignment (OI) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy analysis of the negative electrode active layer.

[0051] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode current collector and a negative electrode active layer on at least one surface of the negative electrode current collector. The negative electrode active layer is a layer that realizes electrical activity of the negative electrode and includes a negative electrode active material that realizes an electrochemical oxidation-reduction reaction during charge and discharge of the battery.

[0052] Here, the present invention includes, as the negative electrode active material contained in the negative electrode active layer, a carbon-based negative electrode active material containing carbon atoms as a main component, and a silicon-based negative electrode active material containing silicon atoms as a main component.

[0053] The carbon-based negative electrode active material may have a layered structure in which layers formed of carbon atoms in a network structure are stacked. In a carbon-based negative electrode active material with such a structure, lithium ions penetrate into the edge surfaces (surfaces where layers overlap) of the carbon layers during charging and diffuse between the layers, and the diffused lithium ions are desorbed and released from the edge surfaces of the carbon layers during discharging. In the carbon-based negative electrode active material, the electrical resistivity in the plane direction of the carbon layers is lower than that in the stacking direction of the carbon layers, so that a bypass electron conduction path is formed along the plane direction of the carbon layers.

[0054] Therefore, the present invention exhibits excellent charging performance by controlling the crystalline structure characteristics of the carbon-based negative electrode active material contained in the negative electrode active layer to shorten the ion path of lithium ions and reduce the resistance in the plane direction of the carbon layer.

[0055] As an example, the carbon-based negative electrode active material contained in the negative electrode active layer has an alignment degree (OI) that indicates the degree of inclination of the ab-axis crystal plane with respect to the negative electrode current collector. a ) may be 3.0 or less. Here, the degree of alignment (OI) is an alignment value calculated after activation of the secondary battery, and can be calculated by the following Equation 3:

[0056] [Formula 3] OI=I 004 / I 110

[0057] In Equation 3, 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.

[0058] The degree of alignment (OI) of the carbon-based negative electrode active material can be an index indicating 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 are the peaks for the carbon-based negative electrode active material, graphite, 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).

[0059] The degree of alignment (OI) of the carbon-based negative electrode active material can be measured by integrating the intensity of the peak at 2θ=54.7±0.2°, which indicates the (0,0,4) plane, and the intensity of the peak at 2θ=77.5±0.2°, which indicates the (1,1,0) plane, and then calculating the area ratio.

[0060] 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 may be aligned at an angle of 60° or more, 70° or more, 70-90°, 80-90°, 65-85°, or 70-85° relative to the negative electrode current collector. This may result in a lower OI of the carbon-based negative electrode active material in the negative electrode active layer compared to when the carbon-based negative electrode active material is aligned at an angle less than 60°.

[0061] For example, the negative electrode active layer may have a low degree of alignment (OI) of the carbon-based negative electrode active material. a) may be 3.0 or less, specifically 0.1 to 3.0, 0.5 to 2.9, 1.0 to 2.9, 1.5 to 2.9, 1.8 to 2.9, 1.7 to 2.7, 1.8 to 2.3, 2.2 to 2.8, or 1.9 to 2.5. Here, the degree of alignment (OI) indicates the degree of alignment of the ab-axis crystal plane of the carbon-based negative electrode active material, but does not indicate the degree to which the carbon-based negative electrode active material particles are rotated and aligned within the active layer.

[0062] The negative electrode active layer also contains a silicon-based negative electrode active material. Silicon-based negative electrode active materials have a theoretical maximum capacity of approximately 4020 mAh / g and are useful as high-energy density and / or high-capacity negative electrode materials. However, silicon-based negative electrode active materials exhibit large volume changes (up to 300%) during charge and discharge, which can reduce the durability of the electrode. In particular, when the ab-axis crystal plane of a carbon-based negative electrode active material is oriented substantially parallel to the negative electrode current collector to improve the charging performance of the negative electrode active layer, the silicon-based negative electrode active material can significantly damage and / or destroy this alignment during charge and discharge. Such damage to the orientation of the carbon-based negative electrode active material significantly reduces the charging and life characteristics of the negative electrode during long-term charge and discharge of the secondary battery.

[0063] However, the negative electrode according to the present invention has a low degree of alignment (OI) of the carbon-based negative electrode active material after activation. a ) is the degree of alignment (OI) of the carbon-based negative electrode active material before activation. r ) can overcome the problems caused by silicon-based negative electrode active materials.

[0064] As an example, the negative electrode may be characterized by the degree of alignment (OI) of the carbon-based negative electrode active material after activation. a ) is the degree of alignment (OI) of the carbon-based negative electrode active material before activation. r ) and may satisfy the following formula 1 at 0.5 or more and less than 1:

[0065] [Formula 1] 0.5≦[OI a ] / [OI r ]<1.0

[0066] In the above formula 1, OI r represents the degree of alignment (OI) of the carbon-based negative electrode active material measured before activation, OI a represents the degree of alignment (OI) of the carbon-based negative electrode active material measured after activation, The degree of alignment (OI) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy analysis of the negative electrode active layer.

[0067] Equation 1 above indicates that the ab-axis crystal plane of the activated carbon-based negative electrode active material is aligned at a higher angle relative to the negative electrode current collector, meaning that activation of the secondary battery improves the orientation of the carbon-based negative electrode active material in the negative electrode active layer.

[0068] Activation is a process of electrically activating a lithium secondary battery, which can ensure a path for lithium ion migration within the negative electrode active layer during charge and discharge. Lithium ions are intercalated between the layers of the carbon-based negative electrode active material and between the crystals of the silicon-based negative electrode active material during charge and deintercalated during discharge. Therefore, activation can be considered a process of ensuring the intercalation and deintercalation of lithium ions. As shown in FIG. 1, the ab-axis crystal plane of the carbon-based negative electrode active material is oriented at a high inclination, nearly perpendicular to the negative electrode current collector, thereby providing a short migration path for lithium ions generated from the positive electrode active layer. However, when a secondary battery is charged and discharged for a long period of time, the volume of the carbon-based negative electrode active material may continuously change due to the intercalation and deintercalation of lithium ions. Furthermore, the silicon-based negative electrode active material located between the carbon-based negative electrode active materials expands in volume due to the intercalation of lithium ions during charge. Such contraction and expansion of the negative electrode active material may reduce the inclination of the crystal plane of the carbon-based negative electrode active material relative to the negative electrode current collector.

[0069] Therefore, the negative electrode of the present invention can secure a lithium ion migration path while minimizing damage and / or loss of the inclination of the ab-axis crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer relative to the negative electrode current collector during activation. The secured lithium ion migration path is strong and undergoes little deformation even during long-term charge and discharge of the secondary battery, significantly reducing the possibility of damage and / or loss of the alignment of the carbon-based negative electrode active material in the negative electrode active layer.

[0070] The negative electrode of the present invention has an alignment degree (OI) of the carbon-based negative electrode active material after activation. a ) is the degree of alignment (OI) of the carbon-based negative electrode active material before activation. r ) and the above formula 1 is embodied as 0.5 or more and less than 1.0 (i.e., 0.5≦[OI a ] / [OI r Specifically, the negative electrode can satisfy the above formula 1 of 0.5 or more and 0.95 or less (i.e., 0.5≦[OI a ] / [OI r ]≦0.95), more specifically, the above formula 1 can be satisfied within a range of 0.6 to 0.95 (i.e., 0.6≦[OI a ] / [OI r ]≦0.95), 0.65~0.75 (i.e., 0.65≦[OI a ] / [OI r ]≦0.75), 0.85~0.95 (i.e., 0.85≦[OI a ] / [OI r ]≦0.95), 0.70~0.93 (i.e., 0.70≦[OI a ] / [OI r ] ≦ 0.93), or 0.72 to 0.90 (i.e., 0.72 ≦ [OI a ] / [OI r ]≦0.90). As a result, the negative electrode according to the present invention exhibits excellent effects on the charge characteristics and life characteristics during long-term charge and discharge of the secondary battery.

[0071] Furthermore, in order to firmly secure a migration path for lithium ions in the negative electrode active layer during activation of the secondary battery, the present invention can control the types of carbon-based negative electrode active material and silicon-based negative electrode active material constituting the negative electrode active layer, as well as the morphology, particle size, and content in the negative electrode active layer, to satisfy predetermined conditions.

[0072] First, the carbon-based negative electrode active material may include graphite. The graphite may include at least one of natural graphite and artificial graphite. For example, the carbon-based negative electrode active material may include natural graphite or artificial graphite alone, or may include a mixture of natural graphite and artificial graphite. In this case, the mixture ratio of natural graphite to artificial graphite may be 5-50:50-95 or 10-40:60-90 by weight. By including natural graphite and artificial graphite in the above-mentioned mixture ratio, the carbon-based negative electrode active material may achieve high orientation of the carbon-based negative electrode active material on the surface of the negative electrode current collector while strengthening adhesion between the negative electrode current collector and the negative electrode active layer.

[0073] As an example, the carbon-based negative electrode active material may contain natural graphite and artificial graphite in a weight ratio of 10-30:70-90.

[0074] As another example, natural graphite and artificial graphite may be contained in a weight ratio of 25-45:55-75.

[0075] As another example, the carbon-based negative electrode active material may include artificial graphite alone.

[0076] The carbon-based negative electrode active material is preferably a spherical graphite granule formed by the aggregation of multiple flake graphite particles. Examples of flake graphite include natural graphite, artificial graphite, mesophase calcined carbon (bulk mesophase) made from tar or pitch, and graphitized cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.). A graphite granule assembled from multiple highly crystalline natural graphite particles is particularly preferred. Each graphite granule may be formed by the aggregation of 2 to 100, preferably 3 to 20, flake graphite particles.

[0077] Such a carbon-based negative electrode active material may have a spherical particle shape. In this case, the sphericity of the graphite particles may be 0.75 or more, for example, 0.75 to 1.0, 0.75 to 0.95, 0.8 to 0.95, or 0.90 to 0.99. Here, "sphericity" refers to the ratio of the shortest diameter (minor axis) to the longest diameter (major axis) among any diameters passing through the center of a particle. A sphericity of 1 indicates that the particle shape is spherical. The sphericity can be measured using a particle shape analyzer or by measuring the particle shape using a scanning electron microscope (SEM) or an energy dispersive spectrometer, and then analyzing the measurement results.

[0078] The present invention provides a carbon-based negative electrode active material having a nearly spherical shape, thereby enabling the negative electrode active layer to have high electrical conductivity. Therefore, a negative electrode including a spherical carbon-based negative electrode active material can improve the capacity of a secondary battery and can increase the specific surface area per unit weight of the negative electrode active material, thereby improving the adhesion between the negative electrode active layer and the current collector.

[0079] Examples of the silicon-based negative electrode active material include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), and silicon dioxide (SiO2), which may be contained alone or in combination in the negative electrode active layer. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as the silicon-based negative electrode active material and contained in the negative electrode active layer, they are referred to as silicon oxide (SiO q , where 0.8≦q≦2.5).

[0080] The silicon-based negative electrode active material may be doped or alloyed with Li, Mg, Al, Ca, Ti, etc. When the silicon-based negative electrode active material contains oxygen (O), it may be surface-treated with a carbon coating layer or the like to suppress volume expansion during charging and improve the electrical conductivity of the negative electrode active material.

[0081] In addition, the carbon-based negative electrode active material and the silicon-based negative electrode active material contained in the negative electrode active layer, i.e., the total negative 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 total weight of the negative electrode active layer.

[0082] The silicon-based negative electrode active material may be included in an amount of 1 wt% to 20 wt%, specifically 5 wt% to 20 wt%, 1 wt% to 9 wt%, 5 wt% to 15 wt%, 3 wt% to 7 wt%, 11 wt% to 19 wt%, 13 wt% to 17 wt%, 15 wt% to 20 wt%, 8 wt% to 14 wt%, or 5 wt% to 9 wt%, based on the total weight of the negative electrode active material. By adjusting the ratio of the total content of the negative electrode active material in the negative electrode active layer and the content of the silicon-based negative electrode active material in the total negative electrode active material within the above ranges, the present invention can reduce lithium consumption and irreversible capacity loss during activation of a secondary battery while improving charge capacity per unit mass. Furthermore, volume change in the negative electrode active layer during charge and discharge of the secondary battery can be minimized, improving the structural stability of the negative electrode active layer and thereby improving the lifespan of the secondary battery.

[0083] The carbon-based negative electrode active material and the silicon-based negative electrode active material contained in the negative electrode active layer have a predetermined average particle size (D 50 Specifically, the carbon-based negative electrode active material may have an average particle size (D 50 , Dc) is 5 μm to 50 μm, and the average particle size (D 50 , Ds) may be 0.5 μm to 10 μm, and the ratio of the average particle sizes of the carbon-based negative electrode active material to the silicon-based negative electrode active material (Dc / Ds) may be 1 to 10.

[0084] Specifically, the carbon-based negative electrode active material has an average particle size (D 50, Dc), and may be selectively applied within the above ranges according to the average thickness of the negative electrode active layer. For example, the carbon-based negative electrode active material may have an average particle size (Dc) of 5 μm to 40 μm, 5 μm to 30 μm, 10 μm to 40 μm, 15 μm to 30 μm, 25 μm to 50 μm, 11 μm to 19 μm, 15 μm to 25 μm, 20 μm to 30 μm, 5 μm to 20 μm, 5 μm to 10 μm, 5 μm to 15 μm, 10 μm to 20 μm, 15 μm to 30 μm, 15 μm to 20 μm, 21 μm to 26 μm, 25 μm to 30 μm, 11 μm to 17 μm, 16 μm to 23 μm, 5 μm to 9 μm, 14 μm to 17 μm, or 16 μm to 19 μm. 50 ) can be observed. Spherical carbon-based negative electrode active materials are advantageously small in particle size to maximize the degree of disorder in the direction of expansion of each particle, preventing particle expansion during lithium ion charging. However, if the particle size of the carbon-based negative electrode active material is less than 5.0 μm, the number of particles per unit volume increases, requiring a large amount of binder, which can reduce the sphericity and sphericity yield. On the other hand, if the maximum particle size exceeds 50 μm, the expansion rate of the negative electrode active material during charge and discharge of the secondary battery increases significantly. This can reduce the adhesion between particles of the negative electrode active material and between the negative electrode active material particles and the current collector with repeated charge and discharge, resulting in a significant decrease in cycle performance.

[0085] In addition, the silicon-based negative electrode active material has an average particle size (D 50 , Ds), and specifically, an average particle size (D) of 0.5 μm to 5 μm, 0.5 μm to 3 μm, 0.5 μm to 2 μm, 0.5 μm to 1 μm, 1 μm to 5 μm, 3 μm to 7 μm, 5 μm to 10 μm, 1 μm to 3 μm, 4 μm to 9 μm, 0.8 μm to 1.2 μm, or 6 μm to 9.5 μm. 50 ) can be shown.

[0086] If the minimum particle size of the silicon-based negative electrode active material is less than 0.5 μm, uniform dispersion of the negative electrode active layer is difficult, and as the secondary battery is charged and discharged, oxidation-reduction reactions are unevenly induced between regions where the silicon-based negative electrode active material aggregates and regions where it does not aggregate, which can accelerate deterioration of the negative electrode active layer. Furthermore, if the maximum particle size of the silicon-based negative electrode active material exceeds 10 μm, the volume expansion of the silicon-based negative electrode active material during charging increases significantly, and the inclination of the ab-axis crystal plane of the carbon-based negative electrode active material decreases (i.e., the degree of alignment (OI) increases), resulting in a significant decrease in cycle performance as the secondary battery is repeatedly charged and discharged.

[0087] Furthermore, the ratio of average particle sizes of the carbon-based negative electrode active material to the silicon-based negative electrode active material (Dc / Ds) may be 1 to 10, specifically 2 to 7, 2 to 5, 3 to 7, 4 to 8, 5 to 10, 6 to 9, or 1.5 to 4.7.

[0088] By ensuring that the average particle size ratio (Dc / Ds) of the carbon-based negative electrode active material to the silicon-based negative electrode active material satisfies the above range, the present invention can induce a structure in which the silicon-based negative electrode active material fills voids formed between the carbon-based negative electrode active materials. The voids act as a buffer to prevent volumetric expansion of the silicon-based negative electrode active material during charge and discharge of the secondary battery, thereby minimizing volumetric expansion of the negative electrode active layer. Furthermore, if the average particle size ratio (Dc / Ds) exceeds the upper limit of the above range, deterioration of the negative electrode active layer during charge and discharge of the secondary battery may be accelerated, resulting in a shortened service life.

[0089] Meanwhile, the average thickness of the negative electrode active layer may be 10 μm to 100 μm, specifically 20 μm to 90 μm, 50 μm to 90 μm, 80 μm to 90 μm, 40 μm to 70 μm, or 55 μm to 68 μm.

[0090] The average loading amount of the negative electrode active layer is 150 mg / 25 cm 2 ~300mg / 25cm 2 Specifically, 180 mg / 25 cm 2 ~280mg / 25cm 2, 180mg / 25cm 2 ~250mg / 25cm 2 , 200mg / 25cm 2 ~250mg / 25cm 2 , or 200 mg / 25 cm 2 ~220mg / 25cm 2 It could be.

[0091] By adjusting the average thickness and / or average loading amount of the negative electrode active layer within the above range, the present invention can easily control the crystalline characteristics of the negative electrode active material contained in the negative electrode active layer, thereby further increasing the energy density of the negative electrode.

[0092] 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.

[0093] The conductive material may include, but is not limited to, one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and the like.

[0094] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0095] 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 low content of conductive material from increasing the resistance of the negative electrode and reducing the charge capacity. Furthermore, it can prevent problems such as a decrease in the content of the negative electrode active material due to an excessive amount of conductive material, thereby reducing the charge capacity, or a decrease in fast charge characteristics due to an increase in the loading amount of the negative electrode active layer.

[0096] The binder is a component that aids in bonding between the negative electrode active material and the conductive material, etc., and between the negative electrode active material and the current collector, and may be suitably used within a range that does not degrade 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.

[0097] 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, based on 100 parts by weight of the total 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 adhesive strength of the active layer due to a low content of binder or a decrease in electrical properties of the electrode due to an excessive amount of binder.

[0098] 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 also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector is preferably 1 μm to 500 μm, taking into account the conductivity and total thickness of the negative electrode to be manufactured.

[0099] <Method of manufacturing a negative electrode for a lithium secondary battery>

[0100] In one embodiment, the present invention further comprises: applying a negative electrode slurry containing a carbon-based negative electrode active material and a silicon-based negative electrode active material to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; drying and rolling the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer; The negative electrode active layer is The degree of alignment (OI) of the carbon-based negative electrode active material after activation a ) is less than or equal to 3, The present invention provides a method for producing a negative electrode for a lithium secondary battery that satisfies the following formula 1:

[0101] [Formula 1] 0.5≦[OI a ] / [OI r ]<1.0

[0102] In the above formula 1, OI r represents the degree of alignment (OI) of the carbon-based negative electrode active material measured before activation, OI a represents the degree of alignment (OI) of the carbon-based negative electrode active material measured after activation, The degree of alignment (OI) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy analysis of the negative electrode active layer.

[0103] The method for manufacturing the negative electrode according to the present invention refers to a method for manufacturing the above-described negative electrode according to the present invention, and may be performed by applying a negative electrode slurry to a negative electrode current collector, applying a magnetic field to the surface of the applied negative electrode slurry, and then drying and rolling the negative electrode slurry to form a negative electrode active layer.

[0104] 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 preferably, a die coating method can be used. The die coating method can be performed using a slot die equipped with a shim for controlling the 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 of the shim.

[0105] The negative electrode slurry contains a carbon-based negative electrode active material and a silicon-based negative electrode active material as main components, and may optionally further contain a conductive material, a binder, other additives, etc. In this case, the carbon-based negative electrode active material, the silicon-based negative electrode active material, the conductive material, the binder, other additives, etc. have the same configuration as the configuration of the negative electrode for a lithium secondary battery described above, and therefore a detailed description thereof will be omitted.

[0106] The step of applying a magnetic field to the negative electrode slurries may control the crystalline properties of the negative electrode active materials contained in the negative electrode slurries and reduce the degree of disorder of the carbon-based negative electrode active materials contained in the negative electrode slurries. Specifically, this step may align the ab-axis crystal planes of the carbon-based negative electrode active materials contained in each negative electrode slurry at a high angle relative to the negative electrode current collector by applying a magnetic field to the surface of the negative electrode slurries coated on the negative electrode current collector.

[0107] In this case, the magnetic field may be applied by magnets disposed above and below the moving negative electrode current collector with the negative electrode slurry coated on its surface, and the polarities of the magnets disposed above and below may be opposite to each other.

[0108] In addition, the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode slurry can be adjusted by adjusting the strength and application time of the applied magnetic field, and thus, the step of applying the magnetic field can be performed under predetermined magnetic field strength and application time conditions.

[0109] Specifically, the step of applying the magnetic field may apply a magnetic field of 10,000 G (Gauss) or less, and specifically, a magnetic field may be applied with an intensity of 3,000 G to 9,000 G, 3,000 G to 8,500 G, 3,500 G to 8,500 G, 4,000 G to 8,200 G, 3,600 G to 4,500 G, 4,500 G to 6,500 G, 5,000 G to 7,000 G, 6,000 G to 8,500 G, 7,000 G to 8,500 G, 6,000 G to 6,500 G, or 4,000 G to 5,000 G.

[0110] Furthermore, the step of applying the magnetic field may be carried out for 1 to 30 seconds, specifically 1 to 20 seconds, 1 to 15 seconds, 1 to 10 seconds, 5 to 20 seconds, 10 to 20 seconds, 11 to 19 seconds, 14 to 18 seconds, 4 to 9 seconds, or 6 to 11 seconds.

[0111] As one example, in the step of applying a magnetic field, a magnetic field of 4,700±50 G may be applied to the negative electrode slurry for 3 to 8 seconds.

[0112] As another example, in the step of applying a magnetic field, a magnetic field of 4,700±50 G may be applied to the negative electrode slurry for 12 to 17 seconds.

[0113] Furthermore, the magnetic field application may be performed using magnets installed above and below the coated negative electrode slurry, with the size of the magnets being adjusted to be larger than the size 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. In this case, the magnetic field applied to the negative electrode slurry is uniformly applied across the entire surface of the negative electrode slurry, thereby achieving a uniform degree of alignment (OI) of the carbon-based negative electrode active material.

[0114] In addition, the step of forming the negative electrode active layer may refer to a process of drying the negative electrode slurry under a magnetic field and firmly fixing the oriented carbon-based negative electrode active material. Therefore, the step of forming the negative electrode active layer may be applied without any particular limitation as long as it can maintain the degree of alignment (OI) of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0115] For example, the drying can be performed by applying heat energy to the negative electrode slurry using a hot air dryer, a vacuum oven, or the like.

[0116] The rolling step 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. The rolling step may be performed under conditions that do not increase the degree of alignment (OI) of the carbon-based negative electrode active material in the dried negative electrode slurry.

[0117] Specifically, the rolling can be carried out at a temperature close to room temperature, more specifically at a temperature of 20°C to 35°C, 20°C to 30°C, or 20°C to 25°C.

[0118] The rolling may 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.

[0119] 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.

[0120] 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.

[0121] For example, the negative electrode active layer formed under the above conditions minimizes the change in the degree of alignment of the carbon-based negative electrode active material, and the degree of alignment (OI) of the carbon-based negative electrode active material after rolling is maintained. r ) may be 5 or less and may satisfy the following formula 2:

[0122] [Formula 2] 0.1≦[OI c ] / [OI r ]≦0.7

[0123] In the above formula 2, OI c represents the degree of alignment (OI) of the carbon-based negative electrode active material measured before rolling the negative electrode active layer, OI r represents the degree of alignment (OI) of the carbon-based negative electrode active material measured after rolling the negative electrode active layer, The degree of alignment (OI) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy analysis of the negative electrode active layer.

[0124] Specifically, the negative electrode active layer has an alignment degree (OI) of the carbon-based negative electrode active material after rolling. r ) can be 4.5 or less, 4.0 or less, 1.0 to 4.0, 2.0 to 4.0, 2.0 to 3.5, 2.0 to 3.0, 3.0 to 4.0, 3.0 to 3.5, 1.8 to 2.5, or 1.8 to 3.4.

[0125] In addition, the negative electrode active layer has an alignment degree ratio (OI) of the carbon-based negative electrode active material before and after rolling. c / OI r ) to 0.1 to 0.7 (i.e., 0.1 ≦ [OI c ] / [OI r]≦0.7), specifically, 0.1 to 0.65 (i.e., 0.1≦[OI c ] / [OI r ]≦0.65), 0.3~0.65 (i.e., 0.3≦[OI c ] / [OI r ]≦0.65), 0.4~0.65 (i.e., 0.4≦[OI c ] / [OI r ]≦0.65), 0.50~0.63 (i.e., 0.50≦[OI c ] / [OI r ]≦0.63), 0.45~0.55 (i.e., 0.45≦[OI c ] / [OI r ]≦0.55), or 0.55 to 0.65 (i.e., 0.55≦[OI c ] / [OI r ]≦0.65).

[0126] The method for manufacturing a negative electrode for a lithium secondary battery according to the present invention has the above-described configuration, and therefore can manufacture a negative electrode having excellent charge / discharge capacity and energy density, and having excellent charge characteristics and life characteristics during long-term charge / discharge of the secondary battery.

[0127] <Lithium secondary battery>

[0128] In one embodiment, the present invention further comprises: There is provided a lithium secondary battery including an electrode assembly including a positive electrode, the negative electrode according to the present invention, and a separator disposed between the positive electrode and the negative electrode.

[0129] 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 charge / discharge capacity and energy density, as well as excellent charge / discharge characteristics and life characteristics even during long-term charge / discharge. Therefore, the lithium secondary battery can be useful as a power source for medium- to large-sized devices such as electric vehicles.

[0130] In this case, the negative electrode has the same structure as that described above, and therefore a detailed description thereof will be omitted.

[0131] 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 further include a conductive material, a binder, other additives, and the like, as needed.

[0132] The positive electrode active material is a material capable of undergoing an electrochemical reaction on a positive electrode current collector, and may include one or more lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2, which are capable of reversibly intercalating and deintercalating lithium ions:

[0133] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0134] [Chemical formula 2] LiM 2 p Mn q P r O4

[0135] In the above Chemical Formula 1 and Chemical Formula 2, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, and v are 1.0≦x≦1.30, 0.5≦y<1, 0 <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.

[0136] The lithium metal oxides represented by Chemical Formula 1 and Chemical Formula 2 above are materials containing high amounts 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 at a high capacity and / or high voltage compared to conventionally commonly used positive electrode active materials such as iron phosphate oxide (LiFeO4).

[0137] 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., 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 O 4、 LiNi 0.3 Mn 1.7 O4, etc., which may be used alone or in combination.

[0138] 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.

[0139] The positive electrode active layer may further include a conductive material, a binder, and other additives in addition to the positive electrode active material.

[0140] In this case, 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 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, thermal black, graphene, and carbon nanotubes.

[0141] The conductive material may be contained in an amount of 0.1 to 5 parts by weight based on the weight of each 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.

[0142] 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. As one example, the binder may include polyvinylidene fluoride.

[0143] The binder may be contained 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 the weight of each positive electrode active layer.

[0144] 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.

[0145] The positive electrode may use a current collector having high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the current collector may be preferably 3 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0146] The separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film having high ion permeability and mechanical strength. It may be any material commonly used in the art, including at least one polymer 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 polymer. 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.

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

[0148] Pouch-type secondary batteries and / or prismatic secondary batteries have the advantage of being highly usable in terms of energy density since secondary batteries can be packed at high density in a limited space.

[0149] <Method of manufacturing lithium secondary batteries>

[0150] Furthermore, in one embodiment, the present invention provides a method for manufacturing the above-described lithium secondary battery.

[0151] A method for manufacturing a lithium secondary battery according to the present invention includes the steps of inserting an electrode assembly including a positive electrode, a negative electrode according to the present invention, and a separator disposed between the positive electrode and the negative electrode into a battery case, injecting a non-aqueous electrolyte solution, and then activating the assembled lithium secondary battery.

[0152] The activation step may refer to a process of electrically activating a lithium secondary battery and securing a path for lithium ions to move within the negative electrode active layer during charging and discharging.

[0153] Here, the present invention may be carried out under specific conditions to ensure a lithium ion migration path while minimizing damage and / or loss of the inclination of the ab-axis crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer relative to the negative electrode current collector during activation of the secondary battery.

[0154] Specifically, the activation step may involve two or more charge / discharge cycles under a constant current condition of less than 1 C. More specifically, the activation step may involve charge / discharge cycles under a constant current condition of a C rate of 0.01 C to 0.9 C, 0.01 C to 0.75 C, 0.01 C to 0.5 C, 0.05 C to 0.5 C, or 0.05 C to 0.3 C. The activation step may involve two or more charge / discharge cycles, three or more cycles, four or more cycles, two to five times, or two to four times.

[0155] The present invention provides a secondary battery that can be activated by repeatedly charging and discharging at a low current density of less than 1 C, thereby minimizing changes in the alignment of the ab-axis crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer and ensuring lithium ion migration paths. The thus-secured lithium ion migration paths can reduce contraction and expansion of the carbon-based negative electrode active material and silicon-based negative electrode active material during charge and discharge after activation. As a result, the lithium secondary battery of the present invention can maintain a high degree of alignment of the ab-axis crystal plane of the carbon-based negative electrode active material even during long-term charge and discharge, thereby exhibiting excellent charge and discharge characteristics and life characteristics.

[0156] The present invention will be described in more detail below with reference to examples and experimental examples.

[0157] 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.

[0158] <Examples 1 to 3 and Comparative Examples 1 to 6. Production of Lithium Secondary Batteries>

[0159] <Production of negative electrodes>

[0160] Natural graphite (average particle size (D 50 ): 18±1 μm) and artificial graphite (average particle size (D 50 ):16±1μm) and silicon oxide (SiO2) were prepared as a silicon-based negative electrode active material, and negative electrode slurries were produced using the prepared carbon-based negative electrode active material and silicon-based negative electrode active material.

[0161] Specifically, the mixed graphite (average particle size (D 50A negative electrode active material was prepared by mixing 95 parts by weight of the prepared negative electrode active material, 1 part by weight of carbon black as a conductive material, 1.5 parts by weight of carboxymethyl cellulose (CMC) as a binder, and 2.5 parts by weight of styrene butadiene rubber (SBR) with water to a solid content of 50%.

[0162] After the negative electrode slurry was prepared, it was cast onto a copper sheet (thickness: 10 μm) that was being transferred roll-to-roll (transfer speed: 5 m / min) using a dual die coater. The loading amount of the applied negative electrode slurry was 208 to 210 mg / 25 cm. 2 It was.

[0163] Permanent magnets with a length ratio of 110-120% 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 was applied at a magnetic field strength of 4,700 G for the time 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 active layer on the negative electrode current collector in which the carbon-based negative electrode active material was oriented. The formed negative electrode active layer was subjected to X-ray diffraction (XRD) spectroscopy analysis to measure the spectrum. The X-ray diffraction measurement conditions were as follows:

[0164] - 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 degrees < 2θ < 78.5 degrees / (0,0,4) plane: 53.5 degrees < 2θ < 56.0 degrees

[0165] The formed negative electrode active layer was then rolled at 22±1°C under a pressure of 100 MPa to 150 MPa and a transfer speed of 3 m / s to prepare a negative electrode for a lithium secondary battery (average thickness of negative electrode active layer before rolling: 87 to 88 μm / average thickness after rolling: 58 to 66 μm). X-ray diffraction (XRD) spectroscopy was additionally performed on the rolled negative electrode active layer to measure its spectrum.

[0166] The degree of alignment (OI) of the mixed graphite was calculated from the spectra measured before and after rolling using the following equation 3, and the results are shown in Table 1 below.

[0167] [Formula 3] OI=I 004 / I 110

[0168] In Equation 3, 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.

[0169] [Table 1]

[0170] <Production of positive electrodes>

[0171] 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 N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 with polyvinylidene fluoride as a binder and carbon-based conductive material to form a cathode slurry, which was then applied to an aluminum sheet. The aluminum sheet coated with the cathode slurry was then dried in a vacuum oven at 120°C and rolled to produce a cathode (average thickness of the cathode active layer: 100±10μm).

[0172] <Manufacturing lithium secondary batteries>

[0173] An electrode assembly was fabricated by interposing a separator made of polypropylene having a thickness of 18 μm between the obtained positive electrode and each of the negative electrodes fabricated in Examples 1 to 3 and Comparative Examples 1 to 6. The fabricated electrode assembly was inserted into a case, and a non-aqueous electrolyte composition was injected into the case to fabricate a lithium secondary battery.

[0174] The assembled lithium secondary battery was activated at 22±1° C. to manufacture a lithium secondary battery. The activation was performed under constant current conditions with the current density shown in Table 2 below.

[0175] The negative electrode was disassembled from each activated lithium secondary battery, and the negative electrode active layer was subjected to X-ray diffraction (XRD) spectroscopy analysis. The XRD conditions were the same as those used previously. The degree of alignment (OI) of the mixed graphite was determined from the measured XRD spectrum. a ) was calculated. In addition, the degree of alignment of the carbon-based negative electrode active material (OI a ) and the degree of alignment of the carbon-based negative electrode active material (OI r The results are shown in Table 2 below.

[0176] [Table 2]

[0177] <Experimental Example>

[0178] In order to confirm the performance of the negative electrode according to the present invention, the initial charge / discharge capacity and life characteristics of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 6 were evaluated.

[0179] Specifically, each of the lithium secondary batteries activated in Examples 1 to 3 and Comparative Examples 1 to 6 was charged and discharged once. The batteries were charged at a constant current (CC) of 1.0 C at 25°C until the voltage reached 5 mV, and then charged at a constant voltage (CV) until the charge current reached 0.005 C (cut-off current). After leaving the batteries for 20 minutes after charging, the batteries were discharged at a constant current (CC) of 1.0 C at 25°C until the voltage reached 1.5 V. The charge and discharge capacities of each lithium secondary battery were measured, and the measured charge and discharge capacities were determined to be the initial charge and discharge capacities of each lithium secondary battery. The results are shown in Table 3 below.

[0180] Each lithium secondary battery whose initial charge / discharge capacity had been measured was subjected to 299 charge / discharge cycles under the same conditions. After the 299th charge / discharge cycle, the charge and discharge capacities of each lithium secondary battery were measured. The measured charge and discharge capacities were considered to be the 300th charge / discharge capacity of each lithium secondary battery, and the capacity retention rate was calculated based on the initial charge / discharge capacity. The results are shown in Table 3 below.

[0181] [Table 3]

[0182] As shown in Table 3, it can be seen that the negative electrode according to the present invention has excellent charge / discharge capacity and life characteristics.

[0183] Specifically, the lithium secondary battery of the example has the following characteristics: (1) the degree of alignment (OI) of the carbon-based negative electrode active material after activation; a ) is adjusted to 3 or less, and (2) the degree of alignment (OI) of the carbon-based negative electrode active material before and after activation a / OI r ) is controlled to be 0.5 or more and less than 1. This shows that the lithium secondary battery has a charge capacity and a discharge capacity at the initial charge / discharge time of 461 mAh / g or more and 398 mAh / g or more, respectively, and a capacity retention rate after 300 charge / discharge cycles of 87% or more.

[0184] On the other hand, the lithium secondary batteries of the comparative examples did not include all of the above components, and although their initial charge / discharge capacities were lower or equal to those of the examples, it was confirmed that their capacity retention rates after 300 charge / discharge cycles were significantly low.

[0185] This indicates that the negative electrode of the example contains both a carbon-based negative electrode active material and a silicon-based negative electrode active material, and has high charge / discharge capacity and energy density. Furthermore, the negative electrode secures a strong path for lithium ions to move within the negative electrode active layer during activation, thereby suppressing contraction and expansion of the negative electrode active material due to intercalation and deintercalation of lithium ions even during long-term charge / discharge of the secondary battery, and minimizing damage and / or loss of the degree of alignment (OI) of the carbon-based negative electrode active material.

[0186] These results show that the negative electrode for a lithium secondary battery according to the present invention has excellent charge characteristics and life characteristics during long-term charge and discharge.

[0187] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0188] 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 is defined by the claims.

Claims

1. A lithium secondary battery comprising an electrode assembly comprising a positive electrode, a negative electrode, and a separator membrane disposed between the positive electrode and the negative electrode, The negative electrode is 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 negative electrode active layer is The degree of alignment (O.I.) of the carbon-based negative electrode active material after activation ａ ) is 3 or less, A lithium secondary battery that satisfies the following formula 1: [Formula 1] 0.5≦[O.I] ａ ] / [O.I ｒ ]<1.0 In the formula 1, O.I. ｒ represents the degree of alignment (O.I) of the carbon-based negative electrode active material measured before activation, O.I. ａ represents the degree of alignment (O.I) of the carbon-based negative electrode active material measured after activation, The degree of alignment (O.I) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the area integral value of the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy of the negative electrode active layer.

2. The carbon-based negative electrode active material has an average particle size (Dc) of 5 μm to 50 μm, The silicon-based negative electrode active material has an average particle size (Ds) of 0.5 μm to 10 μm, and 2. The lithium secondary battery according to claim 1, wherein the ratio (Dc / Ds) of the average particle diameters of the carbon-based negative electrode active material and the silicon-based negative electrode active material is 1 to 10.

3. 2. The lithium secondary battery of claim 1, wherein the silicon-based negative electrode active material is contained in an amount of 1 wt % to 20 wt % based on the total weight of the negative electrode active material.

4. The 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. The silicon-based negative electrode active material is silicon (Si), silicon carbide (SiC), and silicon oxide (SiO ｑ 2. The lithium secondary battery according to claim 1, wherein q is selected from the group consisting of 0.8≦q≦2.

5.

6. The negative electrode active layer has a thickness of 150 mg / 25 cm ２ ~300mg / 25cm ２ 2. The lithium secondary battery according to claim 1, wherein the loading amount is

7. 2. The lithium secondary battery according to claim 1, wherein the negative electrode active layer has an average thickness of 10 μm to 100 μm.

8. A method for manufacturing a lithium secondary battery comprising an electrode assembly comprising a positive electrode, a negative electrode, and a separator membrane disposed between the positive electrode and the negative electrode, comprising: The negative electrode is applying a negative electrode slurry containing a carbon-based negative electrode active material and a silicon-based negative electrode active material to at least one surface of a negative electrode current collector; applying a magnetic field to the applied negative electrode slurry; drying and rolling the negative electrode slurry to which the magnetic field has been applied to form a negative electrode active layer; The negative electrode active layer is The degree of alignment (O.I.) of the carbon-based negative electrode active material after activation ａ ) is 3 or less, A method for producing a lithium secondary battery according to any one of claims 1 to 7, which satisfies the following formula 1: [Formula 1] 0.5≦[O.I] ａ ] / [O.I ｒ ]<1.0 In the formula 1, O.I. ｒ represents the degree of alignment (O.I) of the carbon-based negative electrode active material measured before activation, O.I. ａ represents the degree of alignment (O.I) of the carbon-based negative electrode active material measured after activation, The degree of alignment (O.I) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the area integral value of the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy of the negative electrode active layer.

9. The method for manufacturing a lithium secondary battery according to claim 8, wherein the step of applying a magnetic field is performed at a magnetic field strength of 3,000 G to 9,000 G.

10. The method for manufacturing a lithium secondary battery according to claim 8, wherein the step of applying the magnetic field is performed for 1 to 30 seconds.

11. 9. The method for producing a lithium secondary battery according to claim 8, wherein the rolling is carried out at a temperature of 20° C. to 35° C. and a pressure of 50 MPa to 200 MPa.

12. 2. The lithium secondary battery of claim 1, wherein the positive electrode is provided on at least one surface of a positive electrode current collector and includes 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 Mn2-pO ４ In the above Chemical Formula 1 and Chemical Formula 2, M １ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, and v are 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, p is in the range of 0.05≦p≦1.

0.

13. A method for producing a lithium secondary battery comprising: activating the lithium secondary battery of claim 1; The negative electrode active layer of the negative electrode is The degree of alignment (O.I.) of the carbon-based negative electrode active material after activation ａ ) is 3 or less, A method for producing a lithium secondary battery that satisfies the following formula 1: [Formula 1] 0.5≦[O.I] ａ ] / [O.I ｒ ]<1.0 In the formula 1, O.I. ｒ represents the degree of alignment (O.I) of the carbon-based negative electrode active material measured before activation, O.I. ａ represents the degree of alignment (O.I) of the carbon-based negative electrode active material measured after activation, The degree of alignment (O.I) represents the ratio of the area integral value of the peak at 2θ=54.7±0.2° representing the (0,0,4) plane to the area integral value of the peak at 2θ=77.5±0.2° representing the (1,1,0) plane in X-ray diffraction spectroscopy of the negative electrode active layer.

14. The method for producing a lithium secondary battery according to claim 13, wherein the activation step is performed by charging and discharging the battery at a rate of 0.01 C to 0.9 C at least twice.

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