Negative electrode active material, method for producing a negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery containing the same, and lithium secondary battery containing the negative electrode

Abstract

The negative electrode active material according to the present application contains a silicon-based active material having a crystal grain size of about 300 nm or less. The silicon-based active material has a value defined by (D90 - D10) / D50 of about 2.00 or less. The silicon-based active material contains one or more selected from SiOx (x = 0) and SiOx (0 < x < 2), and contains about 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. In the above formula, D90, D10, and D50 each mean the particle diameters corresponding to 90%, 10%, and 50% based on volume in the particle size distribution.

Description

Technical Field

[0001] This application relates to a negative electrode active material, a method for manufacturing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Background Art

[0002] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the field that has been most actively studied is the field of power generation and power storage using electrochemical reactions.

[0003] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and the use area of secondary batteries is increasingly expanding. For example, as the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, research on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively conducted.

Summary of the Invention

Problems to be Solved by the Invention

[0004] It has been found that, unlike spherical silicon particles formed by melting a conventional silicon raw material and atomizing it by gas atomizing, when increasing the cooling rate through a low-temperature ultrasonic treatment substrate, it is possible to achieve a reduction in the growth of crystal grains, and thus the silicon-based active material generated thereby can have a small crystal grain size and a uniform particle size distribution.

[0005] Therefore, the present application provides a negative electrode active material having relatively small crystal grain size and a uniform particle size distribution, a method for manufacturing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Means for Solving the Problems

[0006] One embodiment of the present specification includes a silicon-based active material having a crystal grain size of about 300 nm or less, the silicon-based active material has a value defined by the following formula 1 of about 2.00 or less, the silicon-based active material includes one or more selected from SiOx (x = 0) and SiOx (0 < x < 2), and the silicon-based active material includes about 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material, and provides a negative electrode active material. [Formula 1] (D90 - D10) / D50 In the above formula 1, each of D90, D10, and D50 means a particle diameter corresponding to 90%, 10%, and 50% based on volume in the particle size distribution.

[0007] Another embodiment is a method for manufacturing a negative electrode active material including a step of melting a silicon raw material; and a step of cooling the melted silicon raw material to form a silicon-based active material, wherein the step of cooling the melted silicon raw material to form a silicon-based active material includes a step of spraying and cooling the melted silicon raw material onto an ultrasonic vibration low-temperature substrate, the silicon-based active material has a crystal grain size of about 300 nm or less, and the silicon-based active material has a value defined by the following formula 1 of about 2.00 or less, and provides a method for manufacturing a negative electrode active material. [Formula 1] (D90 - D10) / D50 In the above formula 1, each of D90, D10, and D50 means a particle diameter corresponding to 90%, 10%, and 50% based on volume in the particle size distribution.

[0008] Another embodiment aims to provide a negative electrode composition including a negative electrode active material, a negative electrode conductive material, and a negative electrode binder according to the present application.

[0009] Still another embodiment aims to provide a negative electrode for a lithium secondary battery, including a negative electrode current collector layer and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer includes the negative electrode composition according to the present application or a cured product thereof.

[0010] Finally, a lithium secondary battery is provided, including a positive electrode, a negative electrode for a lithium secondary battery according to the present application, a separator provided between the positive electrode and the negative electrode, and an electrolyte.

Advantages of the Invention

[0011] The negative electrode active material of the present invention includes one or more selected from SiOx (x = 0) and SiOx (0 < x < 2) as a silicon-based active material, and includes about 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. That is, it has a pure Si active material, thereby solving the problem of volume expansion due to charge and discharge, which is a problem caused by it.

[0012] In the case of the negative electrode active material according to an embodiment of the present invention, different from the conventional spherical silicon particles formed by melting silicon raw materials and atomizing them with gas, the cooling rate is increased through an ultrasonic treatment substrate to which low-temperature ultrasonic waves are applied, so that a decrease in the growth of crystal grains is achieved, and the generated silicon-based active material has a small crystal grain size and a uniform particle size distribution.

[0013] For example, by forming a standing wave on the surface atomized by the force of ultrasonic treatment (Ultra sonication), it becomes possible to form droplets having a particle size within the range of Formula 1, and by using a low-temperature substrate instead of conventional air, the growth of crystal grains due to an increase in the cooling rate is reduced, thereby satisfying a specific range of crystal grain sizes.

[0014] This reduces the size of the crystal grains, thereby suppressing crack formation in the active material due to lithium insertion / desorption. Furthermore, by improving the grain size to the range of Equation 1, lithium ions are uniformly distributed within the lithium electrode, solving the problem of reduced lifespan performance due to uneven charging and discharging within the electrode. [Brief explanation of the drawing]

[0015] The following drawings accompanying this specification illustrate embodiments of the present invention and, together with the detailed description of the invention later, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited solely to the matters depicted in the drawings.

[0016] [Figure 1] This is an enlarged view showing a silicon-based active material according to one embodiment of this application. [Figure 2] This flowchart exemplifies a method for producing a negative electrode active material according to one embodiment of this application. [Figure 3] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 4] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Figure 5] This figure shows the manufacturing process of the silicon-based active material according to Example 1 of this application. [Figure 6] This figure shows the manufacturing process of the silicon-based active material of Comparative Example 1 of this application. [Figure 7] This figure shows a method for calculating the size of crystal grains according to one embodiment of this application.

[0017] In some of the attached drawings, corresponding components are assigned the same reference numerals. Those skilled in the art will understand that the drawings are intended to show elements simply and clearly, and are not necessarily shown to scale. For example, to facilitate understanding of various embodiments, the dimensions of some elements shown in the drawings may be exaggerated compared to other elements. Furthermore, elements of the prior art that are useful or essential in commercially viable embodiments may often be omitted so as not to detract from the spirit of the various embodiments of the present invention. [Modes for carrying out the invention]

[0018] Before describing the present invention, let us first define some terms.

[0019] In this specification, when a part "includes" a component, it means that it may include other components rather than excluding them, unless otherwise stated.

[0020] In this specification, "p~q" means the range "p or greater and q or less".

[0021] In this specification, "specific surface area" is measured by the BET (Brunauer, Emmett, Teller) method, for example, calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0022] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution corresponding to the particle size. For example, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution corresponding to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution corresponding to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution corresponding to the particle size. On the other hand, the average particle size can be measured using the laser diffraction method. For example, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500), and the difference in diffraction patterns corresponding to the particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0023] In one embodiment of this application, particle size may refer to the average diameter or representative diameter of individual particles making up the metal powder.

[0024] In this specification, when a polymer is said to contain a monomer as a monomer unit, it means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. In this specification, when a polymer is said to contain a monomer, it is interpreted the same way as when a polymer contains a monomer as a monomer unit.

[0025] In this specification, unless otherwise specified, the term "polymer" is understood to be used in a broad sense, including copolymers.

[0026] In this specification, weight-average molecular weight (Mw) and number-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers of various degrees of polymerization (standard samples) as standard substances. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0027] Generally, secondary batteries or lithium secondary batteries consist of a positive electrode, a negative electrode, an electrolyte, and a separator. For example, in the case of a lithium secondary battery, the negative electrode contains a negative electrode active material that inserts and removes lithium ions released from the positive electrode, and silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0028] With the recent increase in demand for high-density energy batteries, research is actively being conducted on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx, which have a capacity approximately 10 times greater than graphite-based materials, as negative electrode active materials. However, while silicon-based compounds are high-capacity materials, they have the problem of rapidly expanding in volume during charging and / or discharging, disrupting conductive paths and degrading battery performance.

[0029] Therefore, in order to resolve the aforementioned problems when silicon-based compounds are used as negative electrode active materials, various methods have been studied to suppress volume expansion itself, such as methods to adjust the driving potential, methods to further coat a thin film on the active material layer, and methods to adjust the particle size of the silicon-based compound, or methods to prevent the conduction path from being interrupted. However, these methods may actually degrade the performance of the battery, so their application is limited, and there are still limitations to the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0030] The present invention provides a silicon-based active material that can prevent the conductive path from being damaged due to volume expansion of silicon-based compounds, even when a silicon-based active material is used as a negative electrode active material in order to improve capacity performance, a method for producing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode.

[0031] The present invention will be described in detail below with reference to the drawings so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention may be realized in various different forms and is not limited to the following description.

[0032] One embodiment of the present specification includes a silicon-based active material having a crystal grain size of about 300 nm or less, the silicon-based active material has a value defined by the following formula 1 of about 2.00 or less, the silicon-based active material includes one or more selected from SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, it includes about 70 parts by weight or more of the SiOx (x = 0), and provides a negative electrode active material. [Formula 1] (D90 - D10) / D50[[ID=【7】] In the above formula 1, each of D90, D10, and D50 means a particle size corresponding to 90%, 10%, and 50% based on volume in the particle size distribution.

[0033] In one embodiment of the present application, the silicon-based active material may have a value defined by formula 1 of about 2.00 or less, for example, about 1.98 or less, or about 1.97 or less, and may also be 1.20 or more, or may be 1.50 or more, or may be 1.60 or more. [[ID=1【6】]

[0034] [[ID=1【7】] [[ID=1【8】] <00*00224> The negative electrode active material of the present invention includes one or more selected from SiOx (x = 0) and SiOx (0 < x < 2) as the silicon-based active material, and based on 100 parts by weight of the silicon-based active material, it includes about 70 parts by weight or more of the SiOx (x = 0). For example, it has a pure Si active material, and solves the problem of volume expansion due to charge and discharge, which is a problem caused thereby, by adjusting the particle size (formula 1) and adjusting the crystal grain size within a certain range.

[0036] FIG. 1 is an enlarged view showing a silicon-based active material according to an embodiment of the present application. The silicon-based active material 1 is composed of a plurality of crystal structures 2. According to one embodiment, it can be confirmed that the crystal structure has a grain size distribution of about 1 nm or more and 300 nm or less. In addition, the space between crystal structures can be defined as a grain boundary. Generally, the crystal structure can be represented as crystal grains.

[0037] In one embodiment of the present application, the silicon-based active material contains one or more selected from SiOx (x = 0) and SiOx (0 < x < 2), and may contain about 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0038] In one embodiment of the present application, the silicon-based active material contains SiOx (x = 0), and may contain about 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0039] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of about 70 parts by weight or more, for example, 80 parts by weight or more, or 90 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, for example, 99 parts by weight or less, or 95 parts by weight or less.

[0040] In one embodiment of the present application, pure silicon (Si) particles may be used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material may mean that, as described above, pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are included within the above range based on 100 parts by weight of the silicon-based active material.

[0041] In one embodiment of the present application, the silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0042] According to one embodiment, the size of the SiOx (x=0) crystal grains may be about 300 nm or less.

[0043] In one embodiment of this application, the silicon-based active material may contain metallic impurities, in which case the impurities are metals that are commonly contained in silicon-based active materials, and may be present in an amount of about 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0044] In the case of silicon-based active materials, the capacity is significantly higher compared to conventionally used graphite-based active materials, and attempts to apply them are increasing. However, because of their high volume expansion rate during the charge-discharge process, their use is limited to cases where they are mixed in small amounts with graphite-based active materials.

[0045] Therefore, in the present invention, in order to improve capacity performance, only silicon-based active material is used as the negative electrode active material, and in order to resolve the volume expansion problem due to charging and discharging as described above, the conventional problem is solved by adjusting the average particle size (D50) and crystal grain size of the silicon-based active material itself, rather than adjusting the composition of the conductive material and binder.

[0046] In one embodiment of this application, the size of the crystal grains of the silicon-based active material may be about 300 nm or less.

[0047] In another embodiment, the crystal grain size of the silicon-based active material may be 300 nm or less, for example, 290 nm or less, 260 nm or less, 258 nm or less, 255 nm or less, or 253 nm or less. In one embodiment, the crystal grain size of the silicon-based active material may be in the range of about 10 nm or more, for example, 100 nm or more.

[0048] The silicon-based active material has the aforementioned grain size, and the grain size of the silicon-based active material can be adjusted by changing the manufacturing process conditions described later. In this case, by filling the aforementioned range and ensuring a wide distribution of grain boundaries, lithium ions will be inserted uniformly during insertion, reducing the stress applied to the silicon particles during lithium ion insertion, thereby mitigating the particle cracking phenomenon. As a result, the lifetime stability of the negative electrode can be improved.

[0049] In one embodiment of this application, a negative electrode active material is provided in which the silicon-based active material includes a crystalline structure having a grain distribution of about 1 nm to 300 nm, and the area ratio of the crystalline structure is about 5% or less based on the total area of ​​the silicon-based active material.

[0050] In another embodiment, the area ratio of the crystal structure may be about 5% or less, or about 3% or less, or about 0.1% or more, based on the total area of ​​the silicon-based active material.

[0051] The silicon-based active material according to this application has a crystal grain size of approximately 300 nm or less, and the size of each crystal structure is formed to be relatively small, thereby satisfying the aforementioned area ratio. As a result, the distribution of grain boundaries can be made relatively wide, which in turn allows for the aforementioned effect, for example, the suppression of volume expansion during charging and discharging.

[0052] In one embodiment of this application, a negative electrode active material is provided in which the number of crystal structures contained in the silicon-based active material is about 20 or more.

[0053] The number of crystal structures contained in the silicon-based active material may refer to the number of each crystal structure shown in Figure 1. In other words, the silicon-based active material itself may consist of multiple crystal structures, and in this case, the number of crystal structures may be approximately 20 or more.

[0054] In another embodiment, the number of crystal structures contained in the silicon-based active material may be 20 or more, 30 or more, 35 or more, and may satisfy the range of 60 or less, or 50 or less.

[0055] As mentioned above, when the size of the crystal grains of the silicon-based active material satisfies the aforementioned range, and the number of crystal structures also satisfies the aforementioned range, the strength of the silicon-based active material itself will be within a suitable range, which can impart flexibility when included in an electrode and efficiently suppress volume expansion.

[0056] In this application, "crystal grain" refers to a crystalline particle in a metal or material that is a collection of irregularly shaped particles of microscopic size, and the size of the crystal grain may refer to the diameter of the observed crystal grain. In other words, in this application, the size of the crystal grain refers to the size of domains within a particle that share the same crystal orientation, and is a different concept from particle size or particle size, which represents the size of a substance.

[0057] In one embodiment of this application, the grain size can be calculated using the FWHM (Full Width at Half Maximum) value obtained by XRD analysis. For example, Figure 6 shows how to calculate the grain size. In Figure 6, the remaining values, excluding L, are measured by XRD analysis of the silicon-based active material, and the grain size can be measured using the Debye-Scherrer equation, which shows that FWHM and grain size are inversely proportional. In this case, the Debye-Scherrer equation is as shown in Equation 1-1 below. [Formula 1-1] FWHM = (Kλ) / (LCOSθ) In the above formula 1-1, L represents the size of the crystal grain, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0058] Furthermore, the shape of the crystal grains varies and can be measured three-dimensionally. Generally, the size of the crystal grains can be measured using commonly used circle methods or diameter measurement methods, but is not limited to these.

[0059] The aforementioned diameter measurement method involves drawing 5 to 10 parallel lines, each with a length of L mm, on a micrograph of the target particle, and counting the number of crystal grains z along each line and averaging the results. In this process, only grains that fit entirely within the line are counted, and those that do not are excluded. If the number of lines is P and the magnification is V, the average grain size can be calculated using the following equation 1-2. [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0060] Furthermore, the circle method involves drawing a circle of a predetermined diameter on a micrograph of the target particles, and then determining the average area of ​​the crystal grains by the number of crystal grains that fall within the circle and the number of crystal grains that fall on the boundary line. This can be calculated using the following equations 1-3. [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)*V 2 )(μm 2 )

[0061] In equations 1-3 above, Fm represents the average particle area, Fk represents the measurement area on the photograph, z represents the number of particles within the circle, n represents the number of particles along the arc, and V represents the microscope magnification.

[0062] In one embodiment of this application, the silicon-based active material may include silicon-based particles having a particle size distribution of about 0.01 μm to 30 μm.

[0063] The statement that the silicon-based active material contains silicon-based particles having a particle size distribution of approximately 0.01 μm to 30 μm means that it contains multiple individual silicon-based particles having particle sizes within the aforementioned range, and the number of silicon-based particles included is not limited.

[0064] When the silicon-based particles are spherical, their particle size may be represented by their diameter. However, even when they are not spherical but have other shapes, the particle size can be measured in comparison with the spherical case, and the particle size of individual silicon-based particles can be measured by a method generally used in the art.

[0065] On the other hand, the average particle diameter (D50 particle size) of the silicon-based active material of the present invention is about 1 μm or more and 9 μm or less, and may be, for example, about 2 μm to 8 μm, or about 3 μm to 8 μm. When the average particle diameter is within the above range, the specific surface area of the particles is within a suitable range, so that the viscosity of the negative electrode slurry is formed within a suitable range. As a result, the dispersion of the particles constituting the negative electrode slurry becomes smooth. In addition, since the size of the silicon-based active material has a value above the lower limit of the above range, the contact area between the silicon particles and the conductive material in the negative electrode slurry due to the composite composed of the conductive material and the binder becomes good, and the possibility of maintaining the conductive network is high, and the capacity retention rate increases. On the other hand, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is smoothly formed, thereby preventing the non-uniformity phenomenon of the current density during charge and discharge.

[0066] In the present application, there is provided a negative electrode active material in which the crystal grain size of the silicon-based active material is about 1 nm or more and 300 nm or less, and the average particle diameter (D50) of the silicon-based active material is about 3 μm or more and 8 μm or less.

[0067] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of the silicon-based active material is about 0.01 m 2 / g to 150 m 2 / g, 0.1 m 2 / g to 100 m 2 / g, about 0.2 m 2 / g to 80 m 2 / g, or 0.2 m 2 / g to 18 m​​​​ In one embodiment of this application, the silicon-based active material may exist in a crystalline or amorphous form, for example, and is non-porous. According to one embodiment, the silicon particles are spherical or fragmentary particles. Alternatively, the silicon particles may have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0069] In one embodiment of this application, the silicon-based active material may have a non-spherical shape, and its sphericity is, for example, about 0.9 or less, for example about 0.7 to 0.9, for example about 0.8 to 0.9, for example about 0.85 to 0.9.

[0070] In this application, the circularity is determined by the following formula 1-A, where A is the area and P is the boundary line. [Formula 1-A] 4πA / P 2

[0071] One embodiment of this application provides a negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0072] In one embodiment of this application, a negative electrode composition is provided in which the negative electrode active material is about 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0073] In another embodiment, the negative electrode active material may be about 40 parts by weight or more, for example, about 60 parts by weight or more, about 65 parts by weight or more, or about 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be about 95 parts by weight or less, about 90 parts by weight or less, or about 85 parts by weight or less.

[0074] The negative electrode composition according to this application uses a negative electrode active material that satisfies a specific crystal grain size that can suppress the volume expansion rate during the charge and discharge process, even when using a silicon-based active material with remarkably high capacity within the aforementioned range. This prevents a decrease in negative electrode performance and provides excellent output characteristics during charging and discharging, even when containing a silicon-based active material within the aforementioned range.

[0075] Traditionally, graphite-based compounds were used exclusively as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based active materials to increase capacity. However, in the case of silicon-based active materials, even if the properties of the silicon-based active material itself are adjusted as described above, a problem can still occur where the volume expands rapidly during the charge / discharge process, damaging the conductive paths formed in the negative electrode active material layer.

[0076] In one embodiment of this application, the negative electrode conductive material may include one or more selected from point conductive materials, sheet conductive materials, and linear conductive materials.

[0077] In one embodiment of this application, the point-shaped conductive material means a point-shaped or spherical conductive material that can be used to improve conductivity in a negative electrode, does not cause chemical changes, and is conductive. For example, the point-shaped conductive material may be at least one selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and according to one embodiment, carbon black may be included in order to achieve relatively high conductivity and excellent dispersibility.

[0078] In one embodiment of this application, the point-shaped conductive material has a BET specific surface area of ​​approximately 40 m². 2 / g or more 70m 2 It may be less than / g, for example, about 45m 2 / g or more 65m 2 / g or less, or approximately 50m 2 / g or more 60m 2 It may be less than / g.

[0079] In one embodiment of this application, the point-shaped conductive material may satisfy a functional group content (volatile matter) of about 0.01% to 1%, for example, 0.01% to 0.3%, or 0.01% to 0.1%.

[0080] When the functional group content of the dot-shaped conductive material satisfies the above range, functional groups are present on the surface of the dot-shaped conductive material, and when water is used as the solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. The present invention makes it possible to lower the functional group content of the dot-shaped conductive material by using a specific silicon-based active material, thereby providing an excellent improvement in dispersibility.

[0081] One embodiment of this application includes a silicon-based active material along with a point-type conductive material having a functional group content within the range described above, wherein the functional group content can be adjusted according to the degree of heat treatment of the point-type conductive material.

[0082] In one embodiment of this application, the particle size of the dot conductive material may be about 10 nm to 100 nm, for example, about 20 nm to 90 nm, or about 20 nm to 60 nm.

[0083] In one embodiment of this application, the conductive material may include a sheet-like conductive material.

[0084] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and can also suppress the disruption of the conductive path due to volume expansion. The sheet-like conductive material can also be described as a plate-like conductive material or a bulk conductive material.

[0085] In one embodiment of this application, the sheet-like conductive material may include at least one selected from plate graphite, graphene, graphene oxide, and graphite flakes, for example, plate graphite.

[0086] In one embodiment of this application, the average particle size (D50) of the sheet-like conductive material may be about 2 μm to 7 μm, for example, about 3 μm to 6 μm, or 3.5 μm to 5 μm. When the above range is met, the particle size is sufficient to prevent an excessive increase in the viscosity of the negative electrode slurry and facilitates dispersion. Therefore, the dispersion effect is excellent when dispersed using the same apparatus and time.

[0087] In one embodiment of this application, a negative electrode composition is provided in which the sheet-like conductive material has a D10 of about 0.5 μm to 2.0 μm, a D50 of about 2.5 μm to 3.5 μm, and a D90 of about 6.5 μm to 15.0 μm.

[0088] In one embodiment of this application, the sheet-like conductive material may be a high-specific-surface-area sheet-like conductive material with a high BET specific-surface-area; or a low-specific-surface-area sheet-like conductive material.

[0089] In one embodiment of this application, the sheet-like conductive material can be any sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area without limitation. However, as the sheet-like conductive material according to this application, since dispersion can affect electrode performance to some extent, a sheet-like conductive material with a low specific surface area that does not cause dispersion problems may be used.

[0090] In one embodiment of this application, the sheet-like conductive material has a BET specific surface area of ​​approximately 1 m². 2 It may be more than / g.

[0091] In another embodiment, the sheet-like conductive material has a BET specific surface area of ​​approximately 1 m². 2 / g or more 500m 2 It may be less than / g, for example, about 5m 2 / g or more 300m 2 / g or less, or approximately 5m 2 / g or more 250m 2 It may be less than / g.

[0092] The sheet-like conductive material used in this application may be a sheet-like conductive material with a high specific surface area, or a sheet-like conductive material with a low specific surface area.

[0093] In another embodiment, the sheet-like conductive material is a sheet-like conductive material with a high specific surface area, and its BET specific surface area is approximately 50 m². 2 / g or more 500m 2 Less than / g, for example, about 80m 2 / g or more 300m 2 / g or less, or approximately 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0094] In another embodiment, the sheet-like conductive material is a low specific surface area sheet-like conductive material with a BET specific surface area of ​​approximately 1 m². 2 / g or more 40m 2 Less than / g, for example, about 5m 2 / g or more 30m 2 / g or less, or approximately 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0095] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Here, "bundle type" refers to a bundle-like or rope-like secondary shape in which multiple carbon nanotube units are arranged side by side or intertwined with substantially the same orientation along the length direction of the carbon nanotube units. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the graphite sheet can exhibit conductive or semiconductor properties depending on the angle and structure at which it is curled. Compared to entangled-type carbon nanotubes, the bundle-type carbon nanotubes can be dispersed more uniformly during anode manufacturing, smoothly forming a conductive network within the anode and improving the conductivity of the anode.

[0096] In one embodiment of this application, the negative electrode conductive material is provided in an amount of about 10 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0097] In another embodiment, the negative electrode conductive material may be approximately 0.1 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition, for example, approximately 0.2 parts by weight or more and 30 parts by weight or less, approximately 0.4 parts by weight or more and 25 parts by weight or less, or approximately 0.4 parts by weight or more and 10 parts by weight or less.

[0098] In one embodiment of this application, the negative electrode composition is provided, wherein the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material.

[0099] In one embodiment of this application, the negative electrode conductive material is provided as a negative electrode composition comprising approximately 80 to 99.9 parts by weight of the sheet-like conductive material and approximately 0.1 to 20 parts by weight of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0100] In another embodiment, the negative electrode conductive material may contain approximately 80 to 99.9 parts by weight of the sheet-like conductive material, for example, approximately 85 to 99.9 parts by weight, or approximately 95 to 98 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0101] In another embodiment, the negative electrode conductive material may contain approximately 0.1 to 20 parts by weight of the linear conductive material, for example, approximately 0.1 to 15 parts by weight, or approximately 0.2 to 5 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0102] In one embodiment of this application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, satisfying the aforementioned composition and proportions. This does not significantly affect the lifespan characteristics of conventional lithium secondary batteries, and when sheet-like and linear conductive materials are included, the number of charge and discharge points increases, resulting in excellent output characteristics at a high C-rate and reduced high-temperature gas generation.

[0103] In one embodiment of this application, the negative electrode conductive material may be a linear conductive material.

[0104] According to one embodiment, when a linear conductive material is used alone, the electrode tortuosity, which is a problem with silicon-based negative electrodes, can be simplified, thereby improving the electrode structure and reducing the resistance to lithium ion movement within the electrode.

[0105] In one embodiment of this application, when the negative electrode conductive material includes a linear conductive material alone, the negative electrode conductive material may be included in an amount of about 0.1 parts by weight or more and 5 parts by weight or less, for example, about 0.2 parts by weight or more and 3 parts by weight or about 0.4 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0106] The negative electrode conductive material according to this application has a completely different structure from the positive electrode conductive material applied to the positive electrode. In the case of the negative electrode conductive material according to this application, it plays the role of providing contact between silicon-based active materials, which undergo very large volume expansion during charging and discharging, while the positive electrode conductive material plays the role of a buffer during rolling and imparts some conductivity, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0107] Furthermore, the negative electrode conductive material according to this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and thus have the properties of improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0108] In one embodiment of this application, the sheet-like conductive material used as the negative electrode conductive material described above has a different structure and role from the carbon-based active material generally used as a negative electrode active material. For example, the carbon-based active material used as a negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot shape to facilitate the storage and release of lithium ions.

[0109] Sheet-like conductive materials used as negative electrode conductive materials are substances having a sheet-like or plate-like shape and can be described as plate-like graphite. In other words, they are substances included in the negative electrode active material layer to maintain conductive pathways, and do not play a role in lithium storage or release, but rather are substances that secure conductive pathways in a sheet-like form within the negative electrode active material layer.

[0110] In this application, the use of plate-shaped graphite as a conductive material means that it is processed into a sheet or plate shape and used not to store or release lithium, but as a material to secure a conductive path. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0111] In this application, the use of a carbon-based active material as an active material means that it is processed into a point-like or spherical shape and used as a substance that stores or releases lithium.

[0112] In one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, is point-like and has a BET specific surface area of ​​approximately 0.1 m². 2 / g or more 4.5m 2 The range of less than or equal to / g may also be satisfied. In addition, plate graphite, which is a sheet-like conductive material, is in sheet form and has a BET specific surface area of ​​approximately 5 m². 2 It may be more than / g.

[0113] In one embodiment of this application, the negative electrode binder may contain at least one selected from 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, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogens of these are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0114] The negative electrode binder according to one embodiment of this application plays a role in holding the active material and conductive material to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material, and any general binder that fulfills the above role can be applied, for example, an aqueous binder or a PAM-based binder may be used.

[0115] In one embodiment of this application, the negative electrode binder may be about 30 parts by weight or less, for example, about 25 parts by weight or less, or about 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and in one embodiment, it may be about 5 parts by weight or more, or 10 parts by weight or more.

[0116] Figure 2 is a flowchart illustrating an exemplary method for manufacturing a negative electrode active material according to one embodiment of the present application. Referring to Figure 2, the method for manufacturing a negative electrode active material according to one embodiment of the present application includes the steps of: melting a silicon raw material (S100); spraying the molten silicon raw material onto an ultra-vibrating low-temperature substrate and cooling it (S200); and measuring the crystal grain size and (D90-D10) / D50 of the silicon-based active material (S300). Subsequently, the method for manufacturing a negative electrode active material according to one embodiment of the present application includes the step of determining whether the crystal grain size measured in the measurement step is between 1 nm and 300 nm, and whether the measured (D90-D10) / D50 value is 2 or less (S400).

[0117] Unlike conventional methods that involve melting metallic grade silicon (MG-Si) and forming spherical silicon particles by gas atomizing, the manufacturing method described in this application allows for the production of silicon-based active materials having small crystal grains and a uniform particle size distribution as shown in Equation 1, via an ultrasonically treated substrate to which low-temperature ultrasound is applied. Due to these characteristics, crack formation in the active material due to lithium insertion / desorption can be suppressed, and the uniform particle size improvement allows lithium ions to enter the lithium electrode uniformly, thereby solving the problem of reduced lifespan performance due to uneven charging and discharging within the electrode.

[0118] In this application, a method for producing a negative electrode active material is provided, wherein the vibration frequency of the ultra-vibrating low-temperature substrate is approximately 1 kHz or more and 1500 kHz or less.

[0119] In another embodiment, the vibration frequency of the ultra-vibrating cryogenic substrate may be approximately 1 kHz to 1500 kHz, for example, 5 kHz to 1300 kHz, or 10 kHz to 1000 kHz.

[0120] In one embodiment of this application, a method for producing a negative electrode active material is provided, wherein the cooling temperature in the step of cooling the molten silicon raw material to form a silicon-based active material is about 20°C or lower.

[0121] In another embodiment, the cooling temperature in the step of cooling the molten silicon raw material to form a silicon-based active material may be about 20°C or lower, or it may be -20°C or higher, or -10°C or higher.

[0122] In this application, the cooling is performed by adjusting the cooling temperature of a solvent using a cooling solvent. The cooling solvent can be used without limitation as long as it satisfies the cooling temperature requirement, but according to one embodiment, water or ethylene glycol may be used.

[0123] The method for producing a negative electrode active material according to this application applies the manufacturing process described above, and by adjusting the cooling rate, it was possible to obtain a silicon-based active material that satisfies the crystal grain size and grain size distribution (Equation 1).

[0124] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, the negative electrode composition according to this application or a cured product thereof.

[0125] Figure 3 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Referring to Figure 3, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one surface of the negative electrode current collector layer 10. Figure 4 shows the negative electrode active material layer 20 formed on one surface of the negative electrode current collector layer 10, but is not limited to this, and for example, the negative electrode active material layer 20 may be formed on both surfaces of the negative electrode current collector layer 10.

[0126] In one embodiment of this application, the negative electrode 100 for the lithium secondary battery may be formed by applying and drying a negative electrode slurry containing the negative electrode composition to one or both sides of the negative electrode current collector layer 10.

[0127] In this case, the negative electrode slurry may contain the aforementioned negative electrode composition and slurry solvent.

[0128] In one embodiment of this application, the solid content contained in the negative electrode slurry may be approximately 5% or more and 40% or less based on 100 parts by weight of the negative electrode slurry.

[0129] In another embodiment, the solid content in the negative electrode slurry may be in the range of approximately 5% to 40% based on 100 parts by weight of the negative electrode slurry, for example, approximately 7% to 35%, or approximately 10% to 30%.

[0130] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity during the formation of the negative electrode active material layer is suitable, minimizing particle aggregation of the negative electrode composition and enabling efficient formation of the negative electrode active material layer.

[0131] In one embodiment of this application, the slurry solvent can be any solvent capable of dissolving the negative electrode composition, such as water or NMP (N-methyl-2-pyrrolidone).

[0132] In one embodiment of this application, the negative electrode current collector layer generally has a thickness of about 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has relatively high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0133] The negative electrode for a lithium secondary battery provided by one embodiment of this application has a negative electrode current collector layer thickness of approximately 1 μm to 100 μm, and a negative electrode active material layer thickness of approximately 5 μm to 500 μm.

[0134] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0135] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of approximately 10% to 60%.

[0136] In another embodiment, the porosity of the negative electrode active material layer may be in the range of approximately 10% to 60%, for example, approximately 20% to 50%, or approximately 30% to 45%.

[0137] The aforementioned porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. By including the silicon-based active material and conductive material according to this application in specific compositions and content amounts, the aforementioned range is satisfied, thereby providing the electrode with an appropriate range of electrical conductivity and resistance.

[0138] A lithium secondary battery provided by one embodiment of this application includes a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0139] Figure 4 shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. Referring to Figure 4, a negative electrode 100 for a lithium secondary battery, including a negative electrode active material layer 20, can be seen on one side of the negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery, including a positive electrode active material layer 40, can be seen on one side of the positive electrode current collector layer 50, indicating that the negative electrode 100 and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separator 30 interposed between them.

[0140] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0141] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of about 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0142] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited thereto. For example, the positive electrode may be Li metal.

[0143] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0144] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. Examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0145] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0146] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. It is not particularly limited to any material commonly used as a separator in secondary batteries, and may be made of a material that has low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity. For example, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0147] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0148] According to one embodiment, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0149] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used.

[0150] Among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be used as non-aqueous solvents because they are high-viscosity organic solvents, have high dielectric constants, and relatively easily dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with relatively high electrical conductivity can be produced, and therefore they can be used as non-aqueous solvents.

[0151] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, as the anion of 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 - You may use one or more selected from the list.

[0152] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0153] One embodiment of the present invention provides a battery module and a battery pack containing the secondary battery as a unit cell. Because the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0154] Examples are provided below to aid in understanding the present invention. However, the examples described below are merely illustrative of this description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of this description and the technical concept. It goes without saying that such variations and modifications fall within the scope of the appended claims. [Examples]

[0155] <Manufacturing example> <Manufacturing of the negative electrode active material in Example 1> The manufacturing method shown in Figure 5 differs from conventional gas atomizing methods in that the substrate is subjected to sonication and gas atomizing is performed at a relatively lower temperature through cooling, thereby producing a silicon-based active material with a more uniform particle size distribution and relatively smaller crystal grains.

[0156] The silicon raw material was crushed and heated to liquefy it, and then gas atomized. During this process, the substrate was subjected to ultrasonic treatment using an ultrasonic device to form standing waves on the surface in a liquid state, thereby ensuring that the particles were formed to a more uniform size. Furthermore, during the crystallization of the silicon particles, rapid cooling was suppressed to suppress grain growth, and silicon-based active materials satisfying the physical properties of the size shown in Table 1 were produced. Table 1 shows the physical properties of Examples 1-8, which were produced by varying the ultrasonic treatment frequency, solvent cooling temperature, and type of cooling solvent applied to the substrate.

[0157] <Manufacturing of the negative electrode active material in Comparative Example 1> The manufacturing method shown in Figure 6 involves melting the silicon raw material and then gas atomizing it. For example, a silicon block, such as MG-Si, was crushed by physical force, melted, and then gas atomized.

[0158] In this process, during gas atomization, a silicon-based active material with a smooth surface is formed due to the influence of surface tension between the liquid and gas. However, the overall particle size distribution was broad, and the crystal grain size was relatively large. The physical properties can be confirmed in Table 1 below. Table 1 shows the physical properties of Comparative Examples 1-7, which were manufactured by varying the ultrasonic treatment frequency, solvent cooling temperature, and type of cooling solvent applied to the substrate.

[0159] [Table 1]

[0160] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by adding the aforementioned silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10 to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 25% by weight).

[0161] For example, the first conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 The second conductive material was single-walled carbon nanotubes (SWCNTs), with a particle size of 3.5 μm (D50) per g.

[0162] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0163] As the negative electrode current collector layer, the negative electrode slurry is applied to both sides of a copper current collector (thickness: 8 μm) at a rate of 85 mg / 25 cm². 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was then used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0164] <Manufacturing of secondary batteries> LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the cathode slurry to prepare a cathode slurry (solid content concentration 78% by weight).

[0165] As the positive electrode current collector, an aluminum current collector (thickness: 12 μm) is coated on both sides with the positive electrode slurry at a rate of 537 mg / 25 cm². 2 The material was coated with the specified loading amount, rolled (roll press), and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), thereby manufacturing the positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

[0166] A polyethylene separator was interposed between the positive electrode and the negative electrodes of the above-mentioned examples and comparative examples, and an electrolyte was injected to manufacture a lithium secondary battery.

[0167] The electrolyte in question was prepared by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90 in an organic solvent, adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0168] <Example of experiment> [Experimental Example 1: Cycle Life Data] The lifespan of secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples was evaluated using an electrochemical charger / discharger, and the capacity retention rate was assessed. The secondary batteries underwent in-situ cycle testing at 4.2-3.0V 1C / 0.5C, and the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during the test. Life retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0169] [Experimental Example 2: Cycle Resistance Increase Rate] In Experimental Example 1, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during testing. Then, the resistance was measured by discharging with a 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0170] For the measurement and evaluation of the aforementioned resistance increase rate, data was calculated for 200 cycles, and the results are shown in Table 2 below.

[0171] [Table 2]

[0172] In the case of a negative electrode active material according to one embodiment of the present invention, by forming a standing wave within the atomized surface using the force of ultrasonic treatment, it becomes possible to form droplets with a particle size within the range of Equation 1. By using a low-temperature substrate instead of conventional air, the cooling rate increases, reducing crystal grain growth and thus resulting in a crystal grain size within a specific range. As a result, it has been confirmed that crack formation in the active material due to lithium insertion / desorption can be suppressed by reducing the crystal grain size, and that by improving the particle size to the range of Equation 1, lithium ions can be uniformly distributed within the lithium electrode, thereby solving the problem of reduced lifespan performance due to uneven charging and discharging within the electrode.

[0173] Referring to Table 2, it was confirmed that when adjusting the range of Equation 1, the higher the frequency within a specific range and the lower the temperature within a specific range during manufacturing, the better the performance in cell lifetime evaluation and resistance evaluation.

[0174] Comparative Example 1 does not involve cooling or ultrasonic vibration; Comparative Examples 2 and 3 do not involve cooling; and Comparative Examples 4 to 7 involve a cooling process but do not involve ultrasonic vibration.

[0175] When both ultrasonic vibration and cooling are performed, the crystal grain size and range of Equation 1 are satisfied according to this application. In Comparative Examples 1 to 3, since the cooling process is not performed, the crystal grain size is formed to be larger than in the examples, and it was confirmed that the range of Equation 1 is also formed to be larger. In Comparative Examples 4 to 7, since the cooling process is performed, the crystal grain size is within the range of this application, but since ultrasonic vibration is not performed, it was confirmed that the grain size relationship (Equation 1) is not satisfied.

[0176] In Comparative Examples 1 to 7, because the crystal grain size and / or the range of Equation 1 were not met, lithium ions could not enter the lithium electrode uniformly. As a result, it was confirmed that a problem of reduced lifespan performance due to non-uniform charging and discharging within the electrode occurred.

[0177] As described above with reference to the embodiments of this disclosure, any person skilled in the art or with ordinary knowledge in the art can understand that various embodiments of this disclosure can be modified and altered in various ways without departing from the technical scope of the various embodiments of this disclosure as described in the claims below. Therefore, the technical scope of the various embodiments of this disclosure is not limited to what is described in the detailed description of the specification, but must be determined by the claims.

Claims

1. It contains a silicon-based active material with a crystal grain size of 300 nm or less. The silicon-based active material has a value of 2.00 or less, as defined by the following formula 1. The silicon-based active material comprises one or more selected from SiOx (x=0) and SiOx (0 < x < 2), and the negative electrode active material comprises 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material: [Formula 1] (D90-D10) / D50 In the above formula 1, D90, D10, and D50, respectively, refer to particle sizes that account for 90%, 10%, and 50% of the particle size distribution based on volume.

2. The negative electrode active material according to claim 1, wherein the size of the crystal grains of SiOx (x=0) is 300 nm or less.

3. The negative electrode active material according to claim 1, wherein the silicon-based active material includes a crystalline structure having a grain distribution of 1 nm to 300 nm.

4. The negative electrode active material according to claim 1, wherein the average particle size (D50) of the silicon-based active material is 1 μm or more and 9 μm or less.

5. The crystal grain size of the silicon-based active material is 1 nm or more and 300 nm or less. The negative electrode active material according to claim 1, wherein the average particle size (D50) of the silicon-based active material is 3 μm or more and 8 μm or less.

6. The step of melting the silicon raw material; and A method for producing a negative electrode active material, comprising the step of cooling the molten silicon raw material to form a silicon-based active material, The step of cooling the molten silicon raw material to form a silicon-based active material includes the step of spraying the molten silicon raw material onto an ultra-vibration low-temperature substrate and cooling it. The silicon-based active material has a crystal grain size of 300 nm or less. The silicon-based active material has a value of 2.00 or less as defined by the following formula 1, and is used to manufacture the negative electrode active material: [Formula 1] (D90-D10) / D50 In the above formula 1, D90, D10, and D50, respectively, refer to particle sizes that account for 90%, 10%, and 50% of the particle size distribution based on volume.

7. The method for producing a negative electrode active material according to claim 6, wherein the vibration frequency of the ultra-vibrating low-temperature substrate is 1 kHz or more and 1500 kHz or less.

8. The method for producing a negative electrode active material according to claim 6, wherein the cooling temperature in the step of cooling the molten silicon raw material to form a silicon-based active material is 20°C or lower.

9. A negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder according to any one of claims 1 to 5.

10. The negative electrode composition according to claim 9, wherein the negative electrode active material is 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

11. The negative electrode composition according to claim 9, wherein the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material.

12. The negative electrode composition according to claim 11, wherein the negative electrode conductive material comprises 80 to 99.9 parts by weight of the sheet-like conductive material and 0.1 to 20 parts by weight of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

13. The negative electrode composition according to claim 9, wherein the negative electrode conductive material is 20 parts by weight or less based on 100 parts by weight of the negative electrode composition.

14. A negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, The negative electrode for a lithium secondary battery comprises the negative electrode composition or a cured product thereof according to claim 9, wherein the negative electrode active material layer includes the negative electrode composition or a cured product thereof according to claim 9.

15. The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less. The negative electrode for a lithium secondary battery according to claim 14, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

16. positive electrode; A negative electrode for a lithium secondary battery according to claim 14; A separator provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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