Negative electrode and secondary battery

Abstract

Negative electrode for a secondary battery, comprising: a current collector; a first active material layer of the negative electrode provided on the current collector; and a second active material layer of the negative electrode, different from the first active material layer of the negative electrode, which is provided on the first active material layer of the negative electrode, wherein the first and second active material layers of the negative electrode comprise a silicon-based active material and natural graphite, wherein the natural graphite has an average particle diameter (D50) of 10 µm or less, wherein the average particle diameter (D50) is measured by laser diffraction, and an OI (004 / 110) of the first and second active material layer of the negative electrode is between 3 and 8, wherein the OI (004 / 110) is determined by X-ray diffraction analysis, wherein the OI value is given by I 004 / I 110 is represented, where I 004 the characteristic diffraction peak surface of the (004) crystal plane and I 110 represents the characteristic diffraction peak surface of the (110) crystal plane.

Description

Technical field

[0001] The present invention relates to a negative electrode for a secondary battery and a secondary battery including the same. State of the art

[0002] Secondary batteries are used not only universally for portable devices, but also for electric vehicles (EVs) and hybrid electric vehicles (HEVs) powered by electric drive sources.

[0003] Since such a secondary battery not only offers the main advantage of drastically reducing the use of fossil fuels, but also the advantage of producing no byproducts through energy use, the secondary battery is attracting attention as a new energy source because it is environmentally friendly and improves energy efficiency.

[0004] In general, a secondary battery comprises a positive electrode, a negative electrode, a separator placed between the positive and negative electrodes, and an electrolyte. Furthermore, an active material layer of the electrode, provided on a current collector, may be included.

[0005] With the increasing use of secondary batteries, different battery performance characteristics are required. Although attempts have been made to add additives to the active material layer to improve battery performance or durability, depending on the type of additive, one type of battery performance may be improved, while another type may be negatively affected. Therefore, research is needed regarding the selection or combination of materials included in an electrode to maintain or improve the performance of a secondary battery while also preserving or improving its durability. Brief description of the invention

[0006] The present invention relates to a negative electrode for a secondary battery with improved fast charging performance and a secondary battery including the same.

[0007] One embodiment of the present invention provides a negative electrode for a secondary battery, comprising: a current collector; a first active material layer of the negative electrode, which is provided on the current collector; and a second active material layer of the negative electrode, which is provided on the first active material layer of the negative electrode, wherein the first and second active material layers of the negative electrode contain a silicon-based active material and natural graphite, the natural graphite having an average particle diameter (D50) of 10 µm or less, the OI (004 / 110) of the first and second active material layer of the negative electrode is 8 or less.

[0008] In one embodiment, the thickness of the second active material layer of the negative electrode is 20% to 35% in relation to the total thickness of the first and second active material layers of the negative electrode.

[0009] Another embodiment of the present invention provides a secondary battery comprising the negative electrode for a secondary battery disclosed herein, a positive electrode and a separator.

[0010] Yet another embodiment provides a method for producing the negative electrode according to the present disclosure, wherein the method comprises the following: Formation of a first active material layer of the negative electrode on a current collector; Formation of a second active material layer of the negative electrode on top of the first active material layer of the negative electrode, and Exposure of the first and second active material layers of the negative electrode to a magnetic field during the formation of a first active material layer of the negative electrode on a current collector and the formation of a second active material layer of the negative electrode on the first active material layer of the negative electrode; wherein the first and second active material layers of the negative electrode comprise a silicon-based active material and natural graphite, and the natural graphite has an average particle diameter (D50) of 10 µm or less, and the OI (004 / 110) of the first and second active material layer of the negative electrode is 8 or less.

[0011] In the embodiments described in this specification, the weight load ratio of the second active material layer of the negative electrode is 20% to 35% relative to the weight load ratio of the first and second active material layers of the negative electrodes.

[0012] However, another embodiment of the present invention relates to a paste composition for producing the negative electrode for a secondary battery according to the embodiments of the invention, wherein the paste composition comprises a silicon-based active material and natural graphite, wherein the natural graphite has an average particle diameter (D50) of 10 µm or less.

[0013] According to the embodiments described in the present specification, the fast charging performance can be maximized by incorporating a silicon-based active material and natural graphite into a two-layer active material layer of the negative electrode and by controlling the graphite orientation degree of the active material layer of the negative electrode and simultaneously improving the particle diameter of the natural graphite.

[0014] In particular, compared to forming the active material layer of the negative electrode as a single layer, lithium-ion penetration and diffusion rates can be improved by using a two-layer structure for the active material layer of the negative electrode, as each layer is thinner than a single layer. Furthermore, the two-layer structure can improve battery characteristics by allowing the materials of each layer to be configured differently as needed. Battery durability or lifespan can also be improved after magnetic alignment in a two-layer structure compared to a single-layer structure.

[0015] Advantageously, a further improvement is achieved by adjusting the weight load ratio of the active material layer of the negative electrode, which is located far from the current collector, to a specific range; i.e., the weight load ratio of the upper layer of the two active material layers of the negative electrodes is adjusted to a specific range.

[0016] In particular, the curvature and orientation of the negative electrode can be reduced by magnetically aligning the graphite within it, thus enabling smooth lithium migration. Simultaneously, the use of small-diameter natural graphite can shorten the lithium diffusion path within the particles, resulting in faster charging.

[0017] Furthermore, by using natural graphite with a small particle size and advantageously by simultaneously adjusting the weight-load ratio of the upper layer (the second active material layer of the negative electrode) to the active material layer of the negative electrode to 20% to 35%, for example to 22% to 33%, or 35% to 30%, relative to the weight-load ratio of the first and second active material layers of the negative electrode, a rapid migration of lithium from the upper layer (the second active material layer of the negative electrode) into the interior of the active material layer of the negative electrode can be enabled, thereby further improving the fast-charging performance of the negative electrode. Detailed description

[0018] The present invention is described in more detail below to facilitate understanding. The present invention can be implemented in various forms and is not limited to the embodiments described herein.

[0019] In the present invention, the term “comprise”, “contain” or “have” is intended to indicate the presence of the feature, number, step, component or any implemented combination thereof and is to be understood as not excluding the presence or possibility of adding one or more other features or numbers, steps, components or any combination thereof.

[0020] When the term "approximately" is used, it can refer to a value that may vary by, for example, ±10% of the defined value, ±5% of the defined value, ±1% of the defined value, or ±0.1% of the defined value.

[0021] A case in which a part exists as a layer "above" or "on top" of another part includes a case in which the part is "immediately above" another part, but also a case in which another part is located in between. Conversely, the case in which a part is "immediately above" means that no other part is located in between. Furthermore, "above" or "on" a reference part means that something is located above or below the reference part, and not necessarily that it is located "above" or "on" it in the direction opposite to gravity.

[0022] When referring to the "upper layer" or the "upper active material layer of the negative electrode," it is understood that the "upper layer" is the layer located further away from the current collector; that is, the upper layer is the second active material layer of the negative electrode, which is arranged on top of the first active material layer of the negative electrode, with the first active material layer of the negative electrode being located on the current collector. Similarly, when referring to the "lower layer" or the "lower active material layer of the negative electrode," it is understood that the "upper layer" is the layer located closer to the current collector; that is, the lower layer is the first active material layer of the negative electrode, which is located on the current collector.

[0023] In this specification, particle diameter refers to the average particle diameter, represented by D50. D50 can be defined as the particle size based on 50% of the particle size distribution and can be measured using the laser diffraction method. For example, in the method for measuring the average particle diameter (D50), after the electrode particles are dispersed in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000) and irradiated with an ultrasonic wave at 28 kHz and a power of 60 W. The average particle diameter (D50), which corresponds to 50% of the cumulative volume in the analyzer, is then calculated.

[0024] In the present specification, the description referring to the “active material layer” without the expression “first” and “second” can be applied to both the first and the second active material layer.

[0025] The negative electrode for a secondary battery according to an embodiment of the present specification comprises: a current collector; a first active material layer of the negative electrode provided on the current collector; and a second active material layer of the negative electrode provided on the first active material layer of the negative electrode, wherein the first and second active material layers of the negative electrodes comprise a silicon-based active material and natural graphite, wherein the natural graphite has an average particle diameter (D50) of 10 µm or less, and wherein the OI (004 / 110) of the first and second active material layers of the negative electrodes is 8 or less.In other words, the negative electrode for a secondary battery can enable lithium to migrate more actively within the negative electrode, thus improving the fast charging performance of the negative electrode by forming a two-layer active material layer of the negative electrode while simultaneously using natural graphite with a small particle diameter and adapting the graphite orientation of the active material of the negative electrode to the above range.

[0026] If the OI (004 / 110) of the first and second active material layers of the negative electrode is 8 or less, the internal structure of the active material layer of the negative electrode becomes randomized and the degree of disturbance increases, making the movement and diffusion of lithium ions faster and easier, which is advantageous for fast charging performance.

[0027] The OI (004 / 110) of the first and second active material layer of the negative electrodes can be 8 or less, 7 or less, or 6 or less, between 1 and 8, or between 2 and 7, or between 3 and 6, and also advantageously by controlling the weight loading ratio of the upper layer relative to the upper and lower layers to 20% to 35%, for example to 22% to 33% or 35% to 30%, based on the weight loading ratio of the first and second active material layer of the negative electrodes, during the formation of a two-layer active material layer of the negative electrode.

[0028] The OI (004 / 110) of the first and second active material layers of the negative electrode is a value determined by X-ray diffraction analysis and can be determined using JIS K 0131-1996 or a general X-ray diffraction analysis procedure, such as with a Bruker D4 Endeavor X-ray diffraction analyzer. The OI (004 / 110) is measured for the first and second active material layers of the negative electrode as provided on the current collector. The OI is a value measured for the entire first and second active material layers of the negative electrode.The OI measured in this way includes not only the material from which the active material layer of the negative electrode is made, but also the properties of the active material layer of the negative electrode that are mediated by the manufacturing process including coating and rolling, so that it can be distinguished from the OI value that is measured when the electrode material is in a powder state.

[0029] The OI value of the negative electrode can be determined by I 0004 / I 110 are represented, where I 004 the characteristic diffraction peak surface of the (004) crystal plane and I 110The characteristic diffraction peak surface of the (110) crystal plane is represented. The (004) crystal plane has a parallel crystal structure, and the (110) crystal plane has a perpendicular crystal structure. These properties indicate the degree of orientation of graphite crystals in the active material layer of the negative electrode. The larger the OI value, the higher the orientation of the graphite, meaning that the graphite is aligned more parallel to the measuring plane. In this embodiment, by setting the OI value to 8 or less to reduce the curvature and degree of orientation of the negative electrode, the OI value can be controlled so that lithium ions can be easily introduced into or removed from the crystal structure of graphite. The OI value can be, for example, 1 or more and 8 or less, 2 or more and 7 or less, 3 or more and 6 or less, or 3 or more and 8 or less.The OI value can be measured in an electrode after the production of a negative electrode (after charging and discharging, including a fresh negative electrode, or after the activation process).

[0030] If the weight loading ratio of the upper layer (the second active material layer of the negative electrode) is controlled to 20% to 35% of the total weight loading of active material layers of the negative electrode (including the first and second active material layers of the negative electrodes), for example to 22% to 33% or 25% to 30%, during the formation of a two-layer active material layer of the negative electrode in the negative electrode for a secondary battery, the thickness of the upper layer is set to 20% to 35% of the total thickness of the upper and lower layers in order to reduce the migration distance of the lithium introduced from the surface of the upper layer and to allow lithium to migrate smoothly within the lower negative electrode layer by means of the orientation described above.

[0031] The weight-to-load ratio of the second active material layer of the negative electrode, which is the uppermost layer of the active material layer of the negative electrodes, can be 20% to 35%, for example, 25% to 35% or 28% to 32%, based on the total weight of the upper and lower layers. Since the weight-to-load ratio of each layer is proportional to its thickness, it can be confirmed by determining the thickness of each layer.

[0032] According to one embodiment, the thickness of the second active material layer of the negative electrode can be 40% to 60%, for example 45% to 55%, in particular 50% of the thickness of the first active material layer of the negative electrode.

[0033] In this specification, the boundary between the first and second active material layers of the negative electrode can be confirmed by measuring the electrode cross-section. For example, the boundary between the two layers can be confirmed by cutting the electrode cross-section using ion milling and measuring the cut electrode with a scanning electron microscope.

[0034] According to one embodiment, the content of the silicon-based active material in the first active material layer of the negative electrode and the second active material layer of the negative electrode can be different.

[0035] According to one embodiment, the content of the silicon-based active material in the second active material layer of the negative electrode can be higher than the content of the silicon-based active material in the first active material layer of the negative electrode. Even if the content of the silicon-based active material in the second active material layer of the negative electrode is high, as described above, it is possible to prevent the energy density from becoming too low by adjusting the thickness or weight-to-weight ratio of the second active material layer of the negative electrode to 20% or more.

[0036] According to one embodiment, the natural graphite can have an average particle diameter (D50) of 10 µm or less, or 9 µm or less, or 1 to 10 µm, or 2 to 9 µm, or 3 to 8 µm, or 4 to 7 µm, or 5 to 10 µm, or 6 to 9 µm. General natural graphite has an average particle diameter (D50) of more than 10 µm, but in the embodiments, the smaller the average particle diameter (D50) of 10 µm or less, the relatively shorter the diffusion distance of lithium ions, which is advantageous for improving fast-charging properties by accelerating the penetration and diffusion of lithium ions. In particular, the larger the particle diameter of natural graphite, the longer the scaled lithium distance in the particle, which slows down the charge.Conversely, the smaller the particle diameter of natural graphite, the shorter the lithium diffusion path, which can advantageously lead to faster charging performance. As an example of a method for controlling the particle diameter of natural graphite, it is possible to employ a process for spheroidizing natural flake graphite and coating the surface of the spheroidized natural graphite with carbon to reduce the specific surface area. Natural flake graphite can be spheroidized by an airflow classification process. The carbon coating on the surface can be achieved by applying a precursor to the modified spheroidized natural graphite and subsequently performing a heat treatment process.The precursor can be any precursor for carrying out a carbon coating treatment on the surface of natural graphite, with non-restrictive examples of precursor materials being materials such as pitch.

[0037] According to one embodiment, the first and second active material layers of the negative electrodes can further comprise synthetic graphite. The synthetic graphite can have an average particle diameter (D50) of 15 µm to 50 µm, for example, 20 µm to 45 µm, 25 µm to 40 µm, or 30 µm to 35 µm. With synthetic graphite having an average particle diameter (D50) of 15 µm or more, the binder can be applied uniformly to the surface of the active material, thereby improving the adhesion of the negative electrode to the current collector. Furthermore, the use of synthetic graphite with an average particle diameter (D50) of 50 µm or less, by effectively controlling the particle diameter of the synthetic graphite and facilitating lithium-ion diffusion, improves the fast-charging performance of the negative electrode.

[0038] Since synthetic graphite is a granulated secondary particle, controlling the particle size below 10 µm is difficult. Even if the size of the granulated synthetic graphite (secondary particles produced by assembling primary particles) is 10 µm, it does not have a positive effect on adhesion to the current collector. This is because the small particles result in more inert binders that become trapped between the particles and do not function properly as an adhesive, negatively impacting adhesion. Furthermore, the smaller the particle size of synthetic graphite, the denser the particles within the electrode, and the structure is more densely packed within the electrode after rolling, which is not advantageous for fast charging performance.The dense structure serves to lengthen the curvature within the electrode, i.e., the path of movement of lithium ions, which is disadvantageous for fast charging performance.

[0039] In this specification, "secondary particles" are particles formed by the aggregation of primary particles (for example, more than 50 or hundreds) generally as described herein. On the other hand, the term "primary particles" means particles that do not exhibit grain boundaries when viewed with a scanning electron microscope at 5,000x to 20,000x magnification.

[0040] In this specification, the term "particle" may be interpreted to include one or all secondary particles and primary particles.

[0041] According to one embodiment, each of the first and second active material layers of the negative electrodes may contain natural graphite in an amount of 10 parts by weight to 50 parts by weight, such as 15 parts by weight to 45 parts by weight, 20 parts by weight to 40 parts by weight, based on 100 parts by weight of the active material of the negative electrode.

[0042] According to one embodiment, each of the first and second active material layers of the negative electrodes can contain synthetic graphite in an amount of 50 to 89 parts by weight, such as 52 to 85 parts by weight, 55 to 80 parts by weight, and 58 to 72 parts by weight, based on 100 parts by weight of the active material of the negative electrode. If the synthetic graphite content is higher than the natural graphite content, the fast-charging performance can be improved.

[0043] According to one embodiment, the natural graphite content in the second active material layer of the negative electrode is lower than the natural graphite content in the first active material layer of the negative electrode. For example, the natural graphite content in the second active material layer of the negative electrode is 25 to 35 parts by weight based on 100 parts by weight of graphite in the second active material layer of the negative electrode, and the natural graphite content in the first active material layer of the negative electrode is 35 to 45 parts by weight based on 100 parts by weight of graphite in the first active material layer of the negative electrode. Synthetic graphite offers advantages over natural graphite in improving fast-charging performance.Natural graphite, on the other hand, has a higher capacity than synthetic graphite, which can increase the energy density and improve adhesion to the current collector of the negative electrode. Therefore, with a single-layer structure, it is difficult to simultaneously ensure the fast charging performance of synthetic graphite and the high energy density and adhesion to the current collector provided by natural graphite. However, in the two-layer structure of the present invention, the fast charging performance, energy density, and adhesion to the current collector are improved by a relative increase in the content of natural graphite in the first active material layer of the negative electrode, which is located close to the current collector, and by a relative increase in the content of synthetic graphite in the second active material layer of the negative electrode.

[0044] In one embodiment of this specification, the silicon-based active material comprises at least one of SiOx (0 ≤ x < 2), SiMy (M is a metal, 1 ≤ y < 4), and Si / C. Only one type of silicon-based active material may be present, or two or more types may be present together. If each layer of the active material layer of the negative electrode contains a silicon-based active material, each layer may contain the same type of silicon-based active material, or different types or combinations of silicon-based active materials.

[0045] In one embodiment of this specification, the silicon-based active material may be present in an amount ranging from 1 part by weight to 40 parts by weight, such as 5 parts by weight to 30 parts by weight or 10 parts by weight to 20 parts by weight, based on the total of 100 parts by weight of active materials contained in the active material layer of the negative electrode, including the silicon-based active material. The silicon-based active material in the first and second active material layers of the negative electrode may be present in the same amount or in different amounts.

[0046] The silicon-based active material, SiO₂ x (0≤x<2) contains a silicon-based composite particle including SiO x (0 <x<2) und Poren sein.

[0047] According to the present disclosure, the term composite particle, when referring to particles of a silicon-based active material, refers to particles comprising a silicon-based active material, optionally other elements or compounds, and pores. According to the present disclosure, a composite material refers to two or more materials that are physically aggregated but not chemically bonded.

[0048] The silicon-based composite particle comprises a SiO₂ x (0 <x<2)-Matrix einschließlich Si und SiO2, wobei das Si auch eine separate Phase innerhalb der SiO x can form a matrix. That is, x corresponds to the numerical ratio of O to Si in the SiO₂ matrix. x is included (0 <x<2). Ein siliziumbasiertes aktives Material, das SiO x (0≤x<2) can improve the discharge capacity of a secondary battery.

[0049] The silicon-based composite particles can further comprise at least one Mg compound and one Li compound. The Mg compound and the Li compound can be contained within a matrix of the silicon-based composite particle.

[0050] The Mg compound and / or Li compound can be found inside and / or on the surface of the SiO₂. x (0 <x<2) dispergiert sein. Der anfängliche Wirkungsgrad der Batterie kann durch die Mg-Verbindung und / oder Li-Verbindung verbessert werden.

[0051] The Mg compound can be any one selected from the group consisting of Mg silicates, Mg silicides, and Mg oxides. The Mg silicate can be any one selected from the group consisting of Mg₂SiO₄ and MgSiO₃. The Mg silicide can contain Mg₂Si. The Mg oxide can contain MgO.

[0052] In one embodiment of the present specification, the Mg element may be present in an amount of 0.1 wt.% to 20 wt.% or 0.1 wt.% to 10 wt.% based on a total of 100 wt.% of the silicon-based active material. Specifically, the Mg element may be present in an amount of 0.1 wt.% to 20 wt.%, 0.2 wt.% to 15 wt.%, 0.3 wt.% to 10 wt.%, 0.4 wt.% to 9 wt.%, 0.5 wt.% to 8 wt.%, 0.6 wt.% to 7 wt.%, 0.7 wt.% to 6 wt.%, 0.8 wt.% to 5 wt.%, or 0.8 wt.% to 4 wt.%. An amount of the Mg element that meets the above-mentioned range results in an appropriate content of the Mg compound contained in the silicon-based active material, so that the volume change of the silicon-based active material during charging and discharging of a battery can be easily suppressed, thus improving the discharge capacity and initial efficiency of the battery.

[0053] The lithium compound can be any one selected from the group consisting of lithium silicates, lithium silicides, and lithium oxides. The lithium silicate can be any one selected from the group consisting of Li₂SiO₃, Li₄SiO₄, and Li₂Si₂O₅. The lithium silicide can contain Li₇Si₂. The lithium oxide can contain Li₂O.

[0054] In one embodiment of the present invention, the Li compound can be present in the form of a lithium silicate. The lithium silicate is represented by the formula Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5) dargestellt und kann in kristallines Lithiumsilikat und amorphes Lithiumsilikat eingeteilt werden. Das kristalline Lithiumsilikat in den siliziumbasierten Verbundpartikeln kann in Form von mindestens einem Lithiumsilikat vorliegen, das aus der Gruppe bestehend aus Li2SiO3, Li4SiO4 und Li2Si2O5 ausgewählt ist, und das amorphe Lithiumsilikat kann in Form von Li a Si b Oc (2≤a≤4, 0<b≤2, 2≤c≤5) vorliegen.

[0055] In one embodiment of the present specification, the Li element may be present in an amount of 0.1 wt.% to 20 wt.% or 0.1 wt.% to 10 wt.% based on a total of 100 wt.% of the silicon-based active material. Specifically, the Li element may be present in an amount of 0.1 wt.% to 20 wt.%, 0.2 wt.% to 15 wt.%, 0.3 wt.% to 10 wt.%, 0.4 wt.% to 9 wt.%, 0.5 wt.% to 8 wt.%, 0.6 wt.% to 7 wt.%, 0.7 wt.% to 6 wt.%, 0.8 wt.% to 5 wt.%, or more precisely, 0.5 wt.% to 4 wt.%. An amount of Li element that meets the above-mentioned range results in an adequate content of the Li compound contained in the silicon-based active material, so that the volume change of the active material of the negative electrode during charging and discharging of a battery can be easily suppressed, thus improving the discharge capacity and initial efficiency of the battery.

[0056] The concentration of the Mg or Li element can be confirmed by inductively coupled plasma (ICP) analysis. For ICP analysis, a sample of the negative active material is obtained by aliquoting a predetermined amount (e.g., 0.01 g) of the active material from the negative electrode. The active material is then decomposed on a hot plate by transferring the aliquot to a platinum crucible and adding nitric, hydrofluoric, or sulfuric acid. A reference calibration curve is then generated by measuring the intensity of a standard liquid of known concentration, prepared with a standard solution of the Mg and Li compounds (5 mg / kg) at an intrinsic wavelength of the Mg or Li element, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300).Afterwards, the previously pretreated sample solution and a blank sample are each introduced into the device, an actual intensity is calculated by measuring each intensity, the concentration of each component is calculated in relation to the prepared calibration curve, and then the content of the Mg element or the Li element of the prepared silicon-based active material can be analyzed by converting the total sum into the theoretical value.

[0057] In one embodiment of the present specification, a carbon coating layer may be provided on the surface of the silicon-based composite particles and / or internal pores. The carbon coating layer disclosed herein imparts electrical conductivity to the silicon-based composite particles, and the initial efficiency, lifetime characteristics, and battery capacity characteristics of a secondary battery, including the active material of the negative electrode and the silicon-based composite particles, may be improved, thereby providing a more sustainable secondary battery. The total weight of the carbon coating layer may be 5 wt.% to 40 wt.%, 10 wt.% to 30 wt.%, or 15 wt.% to 20 wt.%, based on a total of 100 wt.% of the silicon-based composite particles.

[0058] In one embodiment of the present specification, the carbon coating layer may contain at least any amorphous carbon and crystalline carbon.

[0059] The silicon-based active material can achieve an average particle diameter (D 50 ) from 2 µm to 15 µm, in particular 3 µm to 12 µm, and in particular 4 µm to 10 µm. If the silicon-based composite particles have an average particle diameter (D 50 ) that fulfills the above-mentioned range, side reactions between the silicon-based composite particles and an electrolyte solution of the secondary battery can be controlled, and the discharge capacity and initial efficiency of the battery can be effectively implemented.

[0060] In the present specification, an average particle diameter (D) can be defined. 50) is defined as a particle diameter that corresponds to 50% of a cumulative volume in a particle diameter distribution curve of the particles. The average particle diameter (D 50 The particle size can be measured, for example, using a laser diffraction method. This method can typically measure particle diameters of approximately several millimeters in the submicrometer range, yielding results with high reproducibility and high resolution.

[0061] The active material, including Si / C as a silicon-based active material, is a composite of Si and C and is distinct from silicon carbide, which is designated SiC. The silicon-carbon composite can be a silicon-graphite composite and can also form a structure in which a core of silicon-graphite composite or similar material is surrounded by graphene, amorphous carbon. In the silicon-carbon composite, the silicon can be nanosilicon, which is nanoscale silicon particles dispersed within the silicon-carbon composite.

[0062] In some embodiments, the active material layer of the negative electrode may comprise, in addition to the negative active materials, further ingredients or compounds, such as a binder or a conductive material. In one embodiment of the present specification, the active material of the negative electrode may be contained in 100 parts by weight of each of the active material layer of the negative electrodes in an amount of 80 parts by weight or more and 99.9 parts by weight or less, for example, from 80 parts by weight to 98 parts by weight, from 85 parts by weight to 95 parts by weight, preferably 90 parts by weight or more and 99.9 parts by weight or less, and preferably 95 parts by weight or more and 99.9 parts by weight or less.

[0063] According to a further embodiment of the present specification, the active material layer of the negative electrode may, in addition to the silicon-based active material and the carbon-based active material, also include a binder for the negative electrode.

[0064] The binder for the negative electrode can serve to improve the bond between the particles of the active material of the negative electrode and the adhesion between the particles of the active material of the negative electrode and the current collector of the negative electrode.Binders for the negative electrode may be those known in the field, and non-exhaustive examples thereof may include at least one selected from the group consisting of a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, an ethylene propylene diene monomer (EPDM), a sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid and a material in which the hydrogen of these is replaced by Li, Na, Ca or the like, and may also include various copolymers thereof.

[0065] The binder for the negative electrode may be contained in an amount of 0.1 parts by weight or more and 20 parts by weight or less, 0.2 parts by weight or more or 18 parts by weight or less, 0.3 parts by weight or more or 16 parts by weight or less, 0.4 parts by weight or more or 14 parts by weight or less, 0.5 parts by weight or more or 12 parts by weight or less, 0.6 parts by weight or more or 10 parts by weight or less, for example preferably 0.3 parts by weight or more and 20 parts by weight or less, and preferably 0.5 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the active material layer of the negative electrode.

[0066] The active material layer of the negative electrode must not contain any conductive material, but may contain a conductive material if necessary. The conductive material contained in the active material layer of the negative electrode is not particularly limited, as long as the conductive material exhibits electrical conductivity without causing a chemical change to the battery. Examples of permissible conductive materials include graphite, such as natural or synthetic graphite; carbon black, such as acetylene carbon black, ketine carbon black, sewer carbon black, furnace carbon black, flame carbon black, and thermal carbon black; a conductive fiber, such as carbon fiber or metal fiber; a conductive tube, such as a carbon nanotube; a metal powder, such as fluorocarbon powder, aluminum powder, and nickel powder; a conductive whisker, such as zinc oxide and potassium titanate; a conductive metal oxide, such as titanium oxide; a conductive material, such as polyphenylene derivatives; and the like.The content of conductive material in the active material layer of the negative electrode can be 0.01 to 20 parts by weight, 0.05 to 18 parts by weight, 0.10 to 16 parts by weight, 0.50 to 14 parts by weight, 1.50 to 12 parts by weight, 3 to 10 parts by weight, 5 to 8 parts by weight, preferably 0.03 to 18 parts by weight, based on 100 parts by weight of the active material layer of the negative electrode. For the purposes of this disclosure, if the carbon-based active material is graphite, such as natural or synthetic graphite, the weight fractions of the graphite used as the carbon-based active material are not to be taken into account when defining the total weight fractions of conductive material.Similarly, when selecting graphite as the conductive material for the negative electrode, the described weight fractions of the conductive material are not to be included in the definition of the total weight fractions of the active material of the carbon-based negative electrode. If graphite is selected both as the carbon-based active material for negative electrodes and as the conductive material for negative electrodes, the total weight fractions of graphite correspond to the sum of the weight fractions of graphite used as the active material for carbon-based negative electrodes and the weight fractions of graphite used as the conductive material for negative electrodes.

[0067] The conductive material contained in the active material layer of the negative electrode is, for example, carbon black such as acetylene carbon black, ketjen carbon black, kanal carbon black, furnace carbon black, flame carbon black and thermal carbon black; a conductive fiber such as carbon fiber or metal fiber; a conductive tube such as a carbon nanotube.

[0068] In one embodiment of the present specification, the first active material layers of the negative electrode may have a thickness of 1 µm or more and 50 µm or less, for example 2 µm or more and 40 µm or less, 5 µm or more and 30 µm or less, 10 µm or more and 25 µm or less; wherein the active material layers of the second negative electrode may have a thickness of 5 µm or more and 100 µm or less, for example 10 µm or more and 80 µm or less, 20 µm or more and 60 µm or less, 25 µm or more and 50 µm or less. The sum of the thicknesses of the first and second active material layers of the negative electrode can be 6 µm or more and 150 µm or less, 50 µm or more and 140 µm or less, 80 µm or more and 120 µm or less.

[0069] In one embodiment of the present application, the current collector with a negative electrode is sufficient as long as it exhibits electrical conductivity without causing a chemical change to the battery, and is not particularly restricted. For example, copper, stainless steel, aluminum, nickel, titanium, burnt carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, and the like can be used as the current collector. In particular, a transition metal, such as copper or nickel, which readily adsorbs carbon, can be used as the current collector. Although the current collector may have a thickness of 1 µm to 50 µm, for example, 2 µm to 40 µm, 5 µm to 30 µm, or 10 µm to 20 µm, the thickness of the current collector is not limited to these values.

[0070] An additional embodiment of the present specification provides a secondary battery comprising the positive electrode, the negative electrode and the separator according to the embodiment described above.

[0071] In one embodiment of the present specification, the positive electrode comprises a positive electrode current collector and an active material layer of the positive electrode formed on the positive electrode current collector and enclosing the active material of the positive electrode. The active material layer of the positive electrode can have a thickness of 20 µm or more and 500 µm or less, 30 µm or more and 400 µm or less, 50 µm or more and 300 µm or less, or 100 µm or more and 200 µm or less.

[0072] The positive electrode current collector is not particularly limited in its applications, as long as it exhibits electrical conductivity without causing a chemical change in the battery. Suitable materials include, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, and the like. Furthermore, the positive electrode current collector can typically have a thickness of 1 to 50 µm, for example, 2 µm to 40 µm, 5 µm to 30 µm, or 10 µm to 20 µm. Adhesion of the active material to the positive electrode can also be improved by the formation of fine irregularities on the current collector's surface. For example, the positive electrode current collector can be used in various forms, such as film, sheet, foil, mesh, porous body, foam body, and non-woven body.

[0073] In one embodiment of this specification, the positive electrode may comprise a lithium composite transition metal compound including nickel (Ni) and cobalt (Co) as active materials. The lithium composite transition metal compound may further comprise at least one manganese and one aluminum. The lithium composite transition metal compound may contain 80 mol% or more, for example, 80 mol% or more and less than 100 mol% nickel, based on the total moles of nickel, cobalt, and any additional metal M of the lithium composite transition metal compound, excluding lithium.

[0074] According to the present invention, the lithium composite transition metal compound comprises the metals lithium (Li), nickel (Ni), and cobalt (Co) and may optionally also include one or more additional metals M. Preferably, the one or more additional metals are selected from the group consisting of Mn, Al, Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

[0075] In one embodiment, the active material of the positive electrode can be contained in 100 parts by weight of the active material layer of the positive electrode in an amount of 80 parts by weight or more and 99.9 parts by weight or less, for example from 80 parts by weight to 98 parts by weight, from 85 parts by weight to 95 parts by weight, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0076] According to a further embodiment of the present specification, the active material layer of the positive electrode according to the embodiment described above may further comprise a binder for the positive electrode and a conductive material.

[0077] The binder for the positive electrode can serve to improve the bonding between the particles of the active material of the positive electrode and the adhesion between the particles of the active material of the positive electrode and the current collector of the negative electrode. Binders known in the field can be used for the positive electrode; these include, among others, polyvinylidene fluoride (PVDF), a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, an ethylene propylene diene monomer (EPDM), a sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof; one of these or a mixture of two or more of them can be used.

[0078] The binder for the positive electrode can be contained in an amount of 0.1 parts by weight or more and 20 parts by weight or less, for example preferably 0.3 parts by weight or more and 35 parts by weight or less, and more preferably 0.5 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the active material layer of the positive electrode.

[0079] The conductive material contained in the active material layer of the positive electrode is used to impart electrical conductivity to the electrode and can be used without particular restriction as long as the conductive material exhibits electronic conductivity without causing a chemical change in a battery. Specific examples include graphite, such as natural or synthetic graphite; a carbon-based material such as carbon black, acetylene carbon black, ketine carbon black, sewer carbon black, furnace carbon black, flame carbon black, thermal carbon black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; a conductive whisker such as zinc oxide and potassium titanate; a conductive metal oxide such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and any of these, or a mixture of two or more, can be used.

[0080] In particular, the conductive material in one embodiment can comprise one or more single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material can be present in an amount of 0.1 parts by weight or more and 2 parts by weight or less, for example preferably 0.3 parts by weight or more and 1.5 parts by weight or less, and more preferably 0.5 parts by weight or more and 1.2 parts by weight or less, based on 100 parts by weight of the composition for an active material layer of the positive electrode.

[0081] The positive and negative electrodes can be manufactured using a typical process for producing a positive and a negative electrode, with the exception that the aforementioned active materials are used for the positive and negative electrodes. Specifically, after applying a composition for forming an active material layer, which includes the aforementioned active material and optionally a binder and a conductive material to the current collectors, the positive and negative electrodes can be manufactured by drying and rolling the current collectors. In this case, the types and contents of the active materials of the positive and negative electrodes, the binder, and the conductive materials are as described above.The solvent may be a solvent commonly used in the field; examples include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, or similar solvents; and any one of these, or a mixture of two or more, may be used. The amount of solvent used is sufficient as long as it dissolves or disperses the active material, the conductive material, and the binder, taking into account the application thickness and the preparation yield of the paste, and has a viscosity that provides excellent thickness uniformity in subsequent application for the fabrication of the positive and negative electrodes.Alternatively, the positive electrode and the negative electrode can be produced by another method, by casting the composition to form an active material layer onto a separate support and then laminating a film obtained by peeling it off the support onto a current collector.

[0082] The separator separates the negative electrode from the positive electrode and provides a passage for the movement of lithium ions. It can be used without particular restrictions as long as it is typically used as a separator in a secondary battery. In particular, a separator with excellent moisture retention capacity in an electrolyte solution and low resistance to ion movement within the electrolyte is preferable. Specifically, it is possible to use a porous polymer film, for example, a porous polymer film formed from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof.Furthermore, a typical porous nonwoven fabric, such as one made of high-melting-point glass fiber, polyethylene terephthalate fiber, or the like, can be used. Additionally, a coated separator comprising a ceramic component or polymer material can be employed to ensure heat resistance or mechanical strength, and can be selectively used as a single-layer or multi-layer structure.

[0083] Examples of electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten-type inorganic electrolytes, and the like, which can be used to manufacture a lithium secondary battery.

[0084] In particular, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0085] For example, a non-aqueous organic solvent such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfrance, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triesters, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, or the like may be used.

[0086] In particular, among carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate can be preferably used, since the cyclic carbonates, as high-viscosity organic solvents, have a high permittivity and thus dissociate a lithium salt well, and such cyclic carbonates can be used preferentially because the cyclic carbonate can be mixed with a linear carbonate with low viscosity and low permittivity, such as dimethyl carbonate and diethyl carbonate, in a suitable ratio and used to prepare an electrolyte with high electrical conductivity.

[0087] A lithium salt can be used as the metal salt, wherein the lithium salt is a material that dissolves readily in the non-aqueous electrolyte solution, and, for example, it is possible to use one or more of the following anions as the lithium salt: F-, Cl-, I-, NO3-, N(CN)2-, BF4-, ClO4-, PF6-, (CF3)2PF4-, (CF3)3PF3-, (CF3)4PF2-, (CF3)5PF-, (CF3)6P-, CF3SO3-, CF3CF2SO3-, (CF3SO2)2N-, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN-, and (CF3CF2SO2)2N-.

[0088] To improve the lifespan characteristics of a battery, to suppress capacity degradation, and to improve the battery's discharge capacity, and thus to provide a more sustainable secondary battery, one or more additives may be included in addition to the electrolyte components mentioned above, such as a halogenated carbonate-based compound like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphotriamide, a nitrobenzene derivative, sulfur, a quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0089] An additional embodiment of the present invention provides a paste composition for producing the negative electrode for a secondary battery according to the embodiments described above, wherein the paste composition comprises a silicon-based active material and natural graphite according to the embodiments described above, wherein the natural graphite has an average particle diameter (D50) of 10 µm or less, as disclosed above.

[0090] An additional embodiment provides a method for producing a negative electrode for a secondary battery according to the embodiments described above, wherein the method comprises: forming a first active material layer of the negative electrode on a current collector; forming a second active material layer of the negative electrode on the first active material layer of the negative electrode; and exposing the first and second active material layers of the negative electrode to a magnetic field during the formation of a first active material layer of the negative electrode on a current collector and the formation of a second active material layer of the negative electrode on the first active material layer of the negative electrode;wherein the first and second active material layers of the negative electrodes comprise a silicon-based active material and natural graphite, the natural graphite having an average particle diameter (D50) of 10 µm or less, and the OI (004 / 110) of the first and second active material layers of the negative electrodes is 8 or less. Coating the first active material layer of the negative electrode on a current collector;The coating of the second active material layer of the negative electrode onto the first active material layer of the negative electrode can all be carried out by applying magnetism. Optionally, the coating of the first and second active material layers of the negative electrode can each additionally include a drying step. That is, the first active material layer of the negative electrode can be coated and dried while magnetism is applied, and the second active material layer of the negative electrode can be coated and dried while magnetism is applied.

[0091] It is advantageous that the weight-to-weight ratio of the second active material layer of the negative electrode is 20% to 35% relative to the weight-to-weight ratio of the first and second active material layers of the negative electrode. If the weight-to-weight ratio of the second active material layer of the negative electrode is less than 20% relative to the weight-to-weight ratio of the first and second active material layers of the negative electrode, this can result in a low energy density and the second active material layer of the negative electrode may not meet the cell specifications of similar quality.

[0092] In one embodiment, the method can further include adjusting the OI to 8 or less by magnetically aligning the first and second active material layers of the negative electrode. The degree of alignment can be controlled by the intensity or duration of the magnetic alignment. The greater the intensity or the longer the exposure time, the better the magnetic alignment and the lower the OI value.

[0093] The secondary battery according to one embodiment of the present invention, which may be a lithium secondary battery, comprises an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte. The lithium secondary battery according to the present disclosure exhibits excellent fast-charging performance. For example, as illustrated by the experimental examples described below, the state of charge (SOC) during 3C lithium plating of a lithium coin half-cell manufactured using a negative electrode according to the present invention and incorporated into the secondary battery can be 27% or more, preferably 28% or more, or 29% or more.

[0094] An additional embodiment of the present invention provides a battery module that includes the secondary battery described above as a unit cell, and a battery pack that includes this. The battery module and the battery pack comprise the secondary battery according to the present invention, which has a high capacity, high rate characteristics, and cycle characteristics, and can therefore be used as a sustainable energy source for a medium-sized and large device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and an energy storage system.

[0095] Since the secondary battery according to embodiments of the present invention exhibits excellent discharge capacity, performance characteristics, and cycle life, the lithium secondary battery can be used as a sustainable power source for portable devices such as mobile phones, notebooks, and digital cameras, as well as medium-sized and large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. For example, the battery module or battery pack can be used as a power source for one or more medium-sized and large power tools; an electric vehicle, including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); and an energy storage system.

[0096] Preferred embodiments are suggested below to facilitate understanding of the present invention, but these embodiments are provided for illustrative purposes only. Example 1.

[0097] A copper foil with a thickness of 15 µm was coated with a composition to form a first active material layer of the negative electrode, including synthetic graphite with a D50 of 21 µm, SiO₂, and natural graphite with a D50 of 9 µm as the active material of the negative electrode, and subsequently dried to form a first active material layer of the negative electrode. The first active material layer of the negative electrode was then coated with a composition to form a second active material layer of the negative electrode, also including synthetic graphite with a D50 of 21 µm, SiO₂, and natural graphite with a D50 of 9 µm as the active material of the negative electrode, and subsequently dried to form a second active material layer of the negative electrode, thus producing a negative electrode.During the coating of the compositions to form the first and second active material layer of the negative electrodes, the composition was exposed to magnetic equipment, and in this case, the magnetic orientation was carried out by a method for controlling the magnetic strength and the total exposure time.

[0098] The compositions for forming the first and second active material layers of the negative electrode were prepared by mixing the above-described active material of the negative electrode Super C65 as a conductive material, styrene-butadiene rubber (SBR) as a binder, and carboxymethylcellulose (CMC), which is a thickening agent, in a weight ratio of 96 (artificial graphite / natural graphite / SiO 60 / 39 / 1):1:2:1 (first active material layer of the negative electrode) and 96 (artificial graphite / natural graphite / SiO 70 / 29 / 1):1:2:1 (second active material layer of the negative electrode) and adding water.

[0099] The loading quantity of the composition for the formation of the second active material layer of the negative electrode was set at 30 wt% based on the total quantity of the compositions for the formation of the first and second active material layers of the negative electrode, and the OI of the prepared first and second active material layers of the negative electrodes was 6.

[0100] Vinylene carbonate was dissolved in 0.5 wt% in a mixed solution of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) in a mixing volume ratio of 7:3, and an electrolyte solution containing LiPF6 dissolved at a concentration of 1 M was injected therein to produce a lithium coin half-cell.

[0101] The OI was measured as follows.

[0102] The orientation index I (004) / I (110) indicates the extent to which the crystal structures within the active material layer of the negative electrode are oriented in a specific direction. It can assess the direction in which the crystals within the active material layer of the negative electrode are aligned and can be measured by X-ray diffraction (XRD). More precisely, the orientation index is an area ratio ((004) / (110)) obtained by measuring the planes (110) and (004) of the active material contained in the active material layer of the negative electrode by XRD and integrating the peak intensities of the planes (110) and (004). - Goal: Copper graphite monochromator (Kα line) - Gap: Deviating gap = 1 degree, Receiving gap = 0.1 mm, Scattering gap = 1 degree - Measuring range and step angle / measuring time: (110)-plane: 76.5 degrees < 2θ < 78.5 degrees, 0.01 degrees / 3 seconds (004)-plane: 53.5 degrees < 2θ < 56.0 degrees, 0.01 degrees / 3 seconds, Above, 2θ represents the diffraction angle. Example 2

[0103] An experiment was conducted in the same manner as in Example 1, except that the D50 of the natural graphite contained in the first and second active materials of the negative electrode was 7 µm. The loading amount of the composition for forming the second active material of the negative electrode was set at 30 wt% based on the total amount of compositions for forming the first and second active materials of the negative electrode, and the OI of the prepared first and second active material layers of the negative electrodes was 3. By increasing the exposure time of the magnetic equipment compared to Example 1, the curvature and degree of alignment caused by the graphite magnet arrangement in the negative electrode were reduced. Example 3

[0104] The same procedure as in Example 1 was carried out, except that natural graphite with a D50 of 10 µm was used instead of natural graphite with a D50 of 9 µm for the production of the first and second active material layers of the anode, and the OI of the first and second active material layers of the anode was adjusted to 8. Comparative example 1

[0105] An experiment was conducted in the same manner as in Example 1, except that during the coating of the compositions for forming the first and second active material layers of the negative electrodes, the composition was not exposed to any magnetic equipment. The loading amount of the composition for forming the second active material of the negative electrodes was adjusted to 30 wt% relative to the total amount of compositions for forming the first and second active material of the negative electrodes, and the OI of the prepared first and second active material layers of the negative electrodes was 14. Comparative example 2

[0106] An experiment was conducted in the same manner as in Example 1, except that a natural graphite was used, which is contained in the first and second active materials of the negative electrode with a D50 of 18 µm. By adjusting the loading amount of the composition for forming the second active material of the negative electrode to 30 wt% relative to the total amount of compositions for forming the first and second active materials of the negative electrode and by reducing the exposure time to the magnetic device compared to Example 1, the OI of the prepared first and second active material layer of the negative electrodes was adjusted to 10. Comparative example 3

[0107] An experiment was conducted in the same manner as in Example 1, except that the loading quantity of the composition for forming the second active material of the negative electrode was adjusted to 70 wt% relative to the total quantity of the compositions for forming the first and second active materials of the negative electrode. By shortening the exposure time to the magnetic equipment compared to Example 1, the OI of the prepared active material layers of the first and second negative electrode was 10. Comparative example 4

[0108] An experiment was conducted in the same manner as in Example 1, except that natural graphite was used, which is contained in the first and second active materials of the negative electrode with a D50 of 20 µm. By adjusting the loading amount of the composition for forming the second active material of the negative electrode to 30 wt% relative to the total amount of compositions for forming the first and second active materials of the negative electrode and by skipping exposure to the magnetic device, the OI of the prepared first and second active material layer of the negative electrodes was adjusted to 22. Comparative example 5

[0109] The same procedure as in Example 1 was carried out, except that natural graphite with a D50 of 20 µm was used for the fabrication of the first active material layer of the negative electrode, the orientation of the negative electrode was adjusted to 24, and the second active material layer of the negative electrode was not formed. Due to the nature of the material, which contained many small fine particles in the particle size distribution, the electrode orientation increased after rolling the electrodes, leading to an increase in the OI value.

[0110] After three charge and discharge cycles of the manufactured half-cell at 0.1C, the fast-charging performance was evaluated using a method to determine the Li-plating state of charge (SOC). This involved identifying a slope change point by differentiating the output voltage as a function of the SOC variation with respect to capacity during charging in constant current (CC) mode (3C) for 15 minutes, based on the discharge capacity of the third cycle at 1C. The Li-plating SOC is the SOC point at which lithium precipitates. [Table 1] 3C Li-Plating SOC (%) Example 1 29 Example 2 32 Example 3 27 Comparative example 1 24 Comparative example 2 25 Comparative example 3 25 Comparative example 4 17 Comparative example 5 16

[0111] As shown in Table 1, it could be confirmed that the half-cells produced in the examples according to the present invention exhibit excellent fast charging performance compared to comparison examples 1 to 5. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] JIS K 0131-1996

[0028]

Claims

[1] Negative electrode for a secondary battery, comprising: a current collector; a first active material layer of the negative electrode provided on the current collector; and a second active material layer of the negative electrode, different from the first active material layer of the negative electrode, which is provided on the first active material layer of the negative electrode, wherein the first and second active material layers of the negative electrode comprise a silicon-based active material and natural graphite, wherein the natural graphite has an average particle diameter (D50) of 10 µm or less, wherein the average particle diameter (D50) is measured by laser diffraction, and an OI (004 / 110) of the first and second active material layer of the negative electrode is between 3 and 8, wherein the OI (004 / 110) is determined by X-ray diffraction analysis, wherein the OI value is given by I 004 / I 110 is represented, where I 004 the characteristic diffraction peak surface of the (004) crystal plane and I 110 represents the characteristic diffraction peak surface of the (110) crystal plane. [2] Negative electrode according to claim 1, wherein the thickness of the second active material layer of the negative electrode is 40% to 60% of the thickness of the first active material layer of the negative electrode. [3] Negative electrode according to one of claims 1 or 2, wherein the natural graphite has an average particle diameter (D50) of 6 µm to 9 µm. [4] Negative electrode according to any one of claims 1 to 3, wherein the first and second active material layers of the negative electrode further comprise artificial graphite. [5] Negative electrode according to claim 4, wherein the artificial graphite has an average particle diameter (D50) of 15 µm to 50 µm. [6] Negative electrode according to any one of claims 1 to 5, wherein each of the first and second active material layers of the negative electrode comprises a silicon-based active material in an amount of 1 part by weight to 40 parts by weight based on 100 parts by weight of the active material of the negative electrode. [7] Negative electrode according to any one of claims 1 to 6, wherein the silicon-based active material comprises at least one of SiOx, wherein 0≤x<2, SiMy (M is a metal, 1≤y≤4) and Si / C. [8] Negative electrode according to any one of claims 1 to 7, wherein each of the first and second active material layers of the negative electrode comprises natural graphite in an amount of 10 parts by weight to 50 parts by weight based on a total of 100 parts by weight of the active material of the negative electrode. [9] Negative electrode according to any one of claims 1 to 8, wherein each of the first and second active material layers of the negative electrode comprises artificial graphite in an amount of 50 parts by weight to 99 parts by weight based on 100 parts by weight of the active material of the negative electrode. [10] Secondary battery comprising the negative electrode according to any one of claims 1 to 9, a positive electrode and a separator. [11] Secondary battery according to claim 10, wherein the positive electrode comprises a lithium composite transition metal compound comprising nickel (Ni) and cobalt (Co) as the active material. [12] Secondary battery according to claim 11, wherein the lithium composite transition metal compound further comprises at least one of manganese and aluminium. [13] Paste composition for producing the negative electrode for a secondary battery according to any one of claims 1 to 9, wherein the paste composition comprises a silicon-based active material and natural graphite, wherein the natural graphite has an average particle diameter (D50) of 10 µm or less, wherein the average particle diameter (d50) is measured by a laser diffraction method.