A negative electrode active material, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode

Abstract

This application relates to a negative electrode active material, a negative electrode for a lithium secondary battery, a method for manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including a negative electrode.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0141157, filed with the Korean Intellectual Property Office on October 20, 2023, and all of its contents are incorporated herein by reference.

[0002] This application relates to a negative electrode active material, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Background Art

[0003] 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 of power generation and energy storage using electrochemical reactions is one of the most actively studied areas.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage areas are increasingly expanding.

[0005] As technology development and demand related to 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, high 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.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and as the negative electrode active material, silicon-based particles having a large discharge capacity can be used.

[0007] In particular, with the recent 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 more than 10 times the capacity of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds are high-capacity materials, they have the problem that, compared to conventionally used graphite, their volume expands rapidly during the charging process, disrupting the conductive path and degrading battery performance.

[0008] Therefore, in order to resolve the problems that arise when silicon-based compounds are used as negative electrode active materials, various methods have been discussed, such as methods to adjust the driving potential, methods to further coat a thin film on the active material layer, methods to suppress volume expansion itself such as adjusting the particle size of the silicon-based compound, or methods to prevent the conduction path from being interrupted. However, in the case of the above methods, there is a limit to their application because they may actually degrade the performance of the battery, and there are still limitations to the commercialization of negative electrode battery manufacturing with a high content of silicon-based compounds.

[0009] Furthermore, when fabricating a negative electrode using silicon-based active materials, it is important that the pore structure of the negative electrode is simple, and it is known that increasing the size of the silicon-based active material particles is advantageous for this purpose. However, due to the properties of silicon-based active materials, significant swelling occurs during charging and discharging. Research has confirmed that this is because the larger the particle size, the greater the displacement of the volume change, and also because the contact surface with the negative electrode current collector layer decreases as the particle size increases, leading to the problem of electrode detachment.

[0010] To overcome the aforementioned problems, we found that while applying silicon-based active materials with small particle sizes can resolve the electrode desorption phenomenon, the small particle size causes the reaction to concentrate on the electrode surface, leading to problems with long-term lifespan.

[0011] Therefore, even when using silicon-based compounds as active materials to improve capacity performance, research is needed on silicon-based active material layers that can simplify the pore structure of the negative electrode, prevent damage to the conductive path due to volume expansion of the silicon-based compound, and ensure maximum lifetime characteristics. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Published Patent No. 2009-080971 [Overview of the project] [Problems that the invention aims to solve]

[0013] As mentioned above, silicon-based active materials have excellent capacity characteristics, and their application to negative electrodes is being discussed. However, their use is limited due to the complexity of the pore structure of the negative electrode caused by the size of the silicon-based active material itself, as well as problems such as volume expansion due to charging and discharging. However, we have confirmed that even when applying silicon-based active materials to negative electrodes, by adjusting the central particle size (D50) value of the silicon-based active material and mixing silicon-based active materials with adjusted central particle size in a certain proportion, the pore structure of the negative electrode can be simplified, and electrode detachment due to charging and discharging can be prevented, thereby ensuring lifespan characteristics.

[0014] Therefore, the purpose of this application is to provide a negative electrode active material having the above-mentioned features, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0015] One embodiment of this specification provides a negative electrode active material comprising a silicon-based active material, wherein the silicon-based active material consists of a first silicon-based active material having an average particle size (D50) of 2 μm or more and 5 μm or less, and a second silicon-based active material having an average particle size (D50) of 10 μm or more and 20 μm or less, and the weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0016] Another embodiment provides a negative electrode for a lithium secondary battery, comprising 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, wherein the negative electrode active material layer comprises a negative electrode active material layer composition comprising the negative electrode active material, negative electrode conductive material, and negative electrode binder according to this application.

[0017] Another embodiment provides a lithium secondary battery comprising 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. [Effects of the Invention]

[0018] In the case of a negative electrode active material according to one embodiment of the present invention, a silicon-based active material, which is a high-capacity material, is used to produce a high-capacity battery. In this case, the average particle size (D50) of the silicon-based active material is adjusted and arranged, and the silicon-based active material consists of a first silicon-based active material with an average particle size (D50) of 2 μm or more and 5 μm or less, and a second silicon-based active material with an average particle size (D50) of 10 μm or more and 20 μm or less, and the weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0019] In other words, a first silicon-based active material with a small average particle size and a second silicon-based active material with a large average particle size are mixed in a certain ratio, and the ratio of active materials with different average particle sizes is adjusted to 20% or more. When adjusted in this way, the volume expansion of the active material is small even during charging and discharging, the electrode detachment phenomenon can be prevented, the pore structure of the electrode can be simplified, and as a result the resistance of the negative electrode can be reduced.

[0020] In other words, the present invention adjusts the proportion of silicon-based active material in the negative electrode active material layer according to the average particle size of the silicon-based active material. The main features of this invention are that, having the above-mentioned characteristics, it is possible to maintain the high capacitance characteristics which are an advantage of negative electrodes containing silicon-based active material, while also preventing electrode desorption and resistance increase, thereby enhancing the lifespan characteristics. [Brief explanation of the drawing]

[0021] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0022] Before describing the present invention, let's first define some terms.

[0023] In this specification, when a part "includes" a component, it means that, unless otherwise stated, it may include other components rather than excluding them.

[0024] In this specification, "p to q" means the range "p or greater and q or less".

[0025] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan. In other words, in this application, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0026] 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. That is, D50 is the particle size (average particle size, central 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 particle size distribution can be measured using the laser diffraction method. Specifically, 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.

[0027] 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.

[0028] In this specification, unless otherwise specified, the term "polymer" is understood to be used in a broad sense, including copolymers.

[0029] 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 monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified.

[0030] 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.

[0031] In the case of a negative electrode active material according to one embodiment of the present invention, a silicon-based active material, which is a high-capacity material, is used to produce a high-capacity battery. In this case, the average particle size (D50) of the silicon-based active material is adjusted and arranged, and the silicon-based active material consists of a first silicon-based active material with an average particle size (D50) of 2 μm or more and 5 μm or less, and a second silicon-based active material with an average particle size (D50) of 10 μm or more and 20 μm or less, and the weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0032] The present invention adjusts the proportion of silicon-based active material in the negative electrode active material layer according to the average particle size of the silicon-based active material. The main objective of this invention is to maintain the high capacitance characteristics that are an advantage of negative electrodes containing silicon-based active material, while also preventing electrode desorption and enhancing lifespan characteristics.

[0033] Figure 1 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. Although Figure 1 shows the negative electrode active material layer formed on one side, it may also be included on both sides of the negative electrode current collector layer.

[0034] In one embodiment of the present application, the first silicon-based active material and the second silicon-based active material include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys, and provide a negative electrode for a lithium secondary battery.

[0035] In one embodiment of the present application, the first silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and may include 70 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the first silicon-based active material.

[0036] In one embodiment of the present application, the first silicon-based active material includes SiOx (x = 0), and may include 70 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the first silicon-based active material.

[0037] In another embodiment, based on 100 parts by weight of the first silicon-based active material, it may include 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more of SiOx (x = 0), and may include 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0038] In one embodiment of the present application, the first silicon-based active material may particularly use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean that, as described above, when based on 100 parts by weight of the first silicon-based active material, it includes pure silicon-based particles (SiOx (x = 0)) that are not bonded to other particles or elements within the above range.

[0039] In one embodiment of the present application, the first silicon-based active material may consist of silicon-based particles having 100 parts by weight of SiOx (x = 0).

[0040] In one embodiment of the present application, the second silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and may contain 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the second silicon-based active material.

[0041] In one embodiment of the present application, the second silicon-based active material contains SiOx (x = 0), and may contain 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the second silicon-based active material.

[0042] In another embodiment, the SiOx (x = 0) may be contained in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less, based on 100 parts by weight of the second silicon-based active material.

[0043] In one embodiment of the present application, the second silicon-based active material may use particularly pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean that, as described above, when based on 100 parts by weight of the second silicon-based active material, it contains pure silicon-based particles (SiOx (x = 0)) that are not bonded to other particles or elements within the above range.

[0044] In one embodiment of the present application, the second silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiOx (x = 0).

[0045] In the case of silicon-based active materials, attempts to apply them have increased because their capacity is significantly higher compared to the conventionally used graphite-based active materials. However, due to their high volume expansion rate during the charge and discharge process, they have remained at the level of being used by mixing a small amount with graphite-based active materials.

[0046] 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 aforementioned problems, the conventional problems are solved by adjusting the ratio according to the average particle size of the silicon-based active material itself, rather than adjusting the composition of the conductive material and binder.

[0047] In one embodiment of this application, the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm to 30 μm.

[0048] The statement that the silicon-based active material contains silicon-based particles having a particle size distribution of 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.

[0049] The silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm to 30 μm, and the silicon-based active material includes a first silicon-based active material with an average particle size (D50) of 2 μm to 5 μm, and a second silicon-based active material with an average particle size (D50) of 10 μm to 20 μm.

[0050] In other words, the silicon-based active material may contain various silicon-based particles having a particle size distribution of 0.01 μm to 30 μm. In this case, the first silicon-based active material may contain silicon-based particles with an average particle size (D50) of 2 μm to 5 μm, and the second silicon-based active material may contain silicon-based particles with an average particle size (D50) of 10 μm to 20 μm.

[0051] The particle size of the silicon-based active material can be expressed by its diameter if it is spherical, but even if it is not spherical, the particle size can be measured by comparing it to the spherical case, and the particle size of each individual silicon-based particle can be measured using methods generally used in this industry.

[0052] In this application, the silicon-based active material contains silicon-based particles having a particle size distribution of 0.01 μm to 30 μm, and the negative electrode active material contains 5 parts by weight or less of particles smaller than 2 μm, based on 100 parts by weight of the silicon-based active material.

[0053] Specifically, based on 100 parts by weight of the silicon-based active material, particles smaller than 2 μm may be included in amounts of 5 parts by weight or less, 3 parts by weight or less, specifically 1 part by weight or less, or 0 parts by weight or more, or 0.1 parts by weight or more.

[0054] As described above, the silicon-based active material of this application does not contain fine powder. If fine powder is present, it is not possible to simplify the pore structure of the negative electrode, which leads to an increase in resistance, thus satisfying the above-mentioned limitations.

[0055] In one embodiment of this 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 preferably 0.01 to 150.0 m². 2 / g, more preferably 0.1~100.0m 2 / g, particularly preferably 0.2 to 80.0m 2 / g, most preferably 0.2 to 18.0m 2 The value is / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0056] In one embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon-based active material is preferably in the form of spherical or fragmentary particles. Alternatively, but less conveniently, the silicon-based active material may have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0057] In one embodiment of this application, the negative electrode active material may be included in an amount of 60 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0058] In another embodiment, the negative electrode active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0059] The negative electrode for lithium secondary batteries according to this application has the characteristic of not degrading the performance of the negative electrode and having excellent output characteristics in charging and discharging, even when a silicon-based active material with a remarkably high capacity is used within the aforementioned range, by distributing a silicon-based active material having a specific average particle size that can suppress the rate of volume expansion during the charging and discharging process within the negative electrode.

[0060] In one embodiment of this application, the silicon-based active material may have a non-spherical shape, and its sphericity is, for example, 0.9 or less, for example 0.7 to 0.9, for example 0.8 to 0.9, for example 0.85 to 0.9.

[0061] In this application, the degree of sphericity is determined by the following formula 1, where A is the area and P is the boundary line.

[0062] [Formula 1] 4πA / P 2

[0063] One embodiment of this application provides a negative electrode active material in which the weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:20.

[0064] In another embodiment, the weight ratio of the first silicon-based active material to the second silicon-based active material may be 20:80 to 80:20, preferably 30:70 to 70:30, and more preferably 35:65 to 65:35.

[0065] The silicon-based active material of this application comprises a first silicon-based active material having an average particle size (D50) of 2 μm or more and 5 μm or less, and a second silicon-based active material having an average particle size (D50) of 10 μm or more and 20 μm or less, and may satisfy the weight ratio described above.

[0066] In other words, if the first silicon-based active material is included in an amount of 40 parts by weight, based on 100 parts by weight of the silicon-based active material, the second silicon-based active material may be included in an amount of 60 parts by weight.

[0067] When fabricating a negative electrode using silicon-based active materials, it is important that the pore structure of the negative electrode is simple, and it is known that increasing the size of the silicon-based active material particles is advantageous for this purpose. However, due to the properties of silicon-based active materials, significant swelling occurs during charging and discharging. This is because the larger the particle size, the greater the displacement of the volume change, and the smaller the particle size, the smaller the surface area in contact with the negative electrode current collector layer, leading to the problem of electrode desorption. To overcome the above problems, it was found that applying silicon-based active materials with small particle sizes can eliminate the problem of electrode desorption, but because of the small particle size, the reaction concentrates on the electrode surface, causing problems with long-term lifespan.

[0068] To further address the aforementioned problems, we attempted to improve both capacitance characteristics and lifespan characteristics by adjusting the arrangement of silicon-based active materials with different average particle sizes (D50), placing silicon-based active materials with smaller average particle sizes on the negative electrode current collector layer side and silicon-based active materials with larger average particle sizes on the surface.

[0069] However, even in this case, loading limitations made coating with this arrangement difficult, and problems such as desorption at interfaces with different average particle sizes occurred.

[0070] Therefore, as described above, this application is characterized by the fact that the silicon-based active material comprises a first silicon-based active material with an average particle size (D50) of 2 μm or more and 5 μm or less, and a second silicon-based active material with an average particle size (D50) of 10 μm or more and 20 μm or less, with their ratio adjusted, thereby ensuring lifespan characteristics and improving the clogging phenomenon of surface particles.

[0071] In other words, a mixture of a first silicon-based active material and a second silicon-based active material with different particle sizes was applied. In particular, when the proportion of silicon-based active materials with different reference particle sizes in the entire negative electrode active material layer was adjusted to 20% or more, it was possible to ensure lifetime characteristics and improve the clogging phenomenon of surface particles.

[0072] One embodiment of this application provides a negative electrode for a lithium secondary battery, wherein the average particle size (D50) of the first silicon-based active material is 2 μm or more and 5 μm or less, and the average particle size (D50) of the second silicon-based active material is 10 μm or more and 20 μm or less.

[0073] In this application, the average particle size (D50) of the first silicon-based active material may be 2 μm or more and 5 μm or less, preferably 2 μm or more and 4.5 μm or less, and more preferably 2.5 μm or more and 4 μm or less.

[0074] In this application, the average particle size (D50) of the second silicon-based active material may be 10 μm or more and 20 μm or less, preferably 10 μm or more and 19 μm or less, and more preferably 12 μm or more and 18 μm or less.

[0075] 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 provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode active material layer composition comprising the negative electrode active material, negative electrode conductive material, and negative electrode binder according to this application.

[0076] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, in recent years, as the demand for high-capacity batteries has increased, attempts have been made to mix and use silicon-based compounds to increase the capacity. However, in the case of silicon-based compounds, even if the characteristics of the silicon-based active material itself are adjusted as described above, there may be a problem that the volume rapidly expands during the charge / discharge process, damaging the conductive path formed in the negative electrode active material layer.

[0077] Therefore, in one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of a dot-shaped conductive material, a sheet-shaped conductive material, and a linear conductive material. <​​​​​​​​​​​​​​​​​​​​​​In one embodiment of this application, the point-shaped conductive material may satisfy the functional group content (Volatile matter) of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0081] In particular, when the content of functional groups in the point-shaped conductive material satisfies the above range, functional groups are present on the surface of the point-shaped conductive material, and when water is used as the solvent, the point-shaped conductive material can be smoothly dispersed in the solvent.

[0082] In the production of point-shaped conductive materials, a high functional group content means a high amount of foreign matter, and a low functional group content means that more heat treatment processing has been performed. In order for the functional group content of the point-shaped conductive material according to this application to satisfy the aforementioned range, a certain portion of the point-shaped conductive material can be heat-treated to satisfy the aforementioned functional group content range.

[0083] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0084] In one embodiment of this application, the negative electrode conductive material may include a sheet-like conductive material.

[0085] The aforementioned sheet-like conductive material refers to a conductive material that improves conductivity by increasing surface contact between silicon particles within the negative electrode, and also suppresses the disruption of the conductive path due to volume expansion. The aforementioned sheet-like conductive material can also be described as a plate-like conductive material or a bulk conductive material.

[0086] In one embodiment of this application, the sheet-like conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0087] In one embodiment of this application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this 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.

[0088] In one embodiment of this application, a negative electrode composition is provided in which the sheet-like conductive material has a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 4.0 μm or more and 5.0 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0089] 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.

[0090] In one embodiment of this application, a sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area can be used without limitation as the sheet-like conductive material. However, in particular, since the sheet-like conductive material according to this application may be affected to some extent by dispersion, it is especially preferable to use a sheet-like conductive material with a low specific surface area that does not cause dispersion problems.

[0091] In one embodiment of this application, the sheet-like conductive material has a BET specific surface area of ​​5 m². 2 It may be more than / g.

[0092] In another embodiment, the sheet-like conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 It may be less than / g.

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

[0094] In yet another embodiment, the sheet-like conductive material is a low-specific surface area sheet-like conductive material, with a BET specific surface area of ​​5 m². 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 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. Specifically, unless otherwise specified, "bundle type" here 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, a negative electrode composition is provided in which the negative electrode conductive material includes a linear conductive material, and the linear conductive material is a carbon nanotube.

[0097] In one embodiment of this application, the negative electrode conductive material may include a sheet-like conductive material and a linear conductive material.

[0098] In one embodiment of this application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, and the ratio of the sheet-like conductive material to the linear conductive material may satisfy 1:0.01 to 1:0.1.

[0099] In one embodiment of this application, the negative electrode conductive material is provided in an amount of 5 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0100] In another embodiment, the negative electrode conductive material may be 5 to 40 parts by weight, preferably 10 to 30 parts by weight, and more preferably 15 to 25 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0101] In one embodiment of this application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, and satisfies the aforementioned composition and proportions, thereby having a large number of charging and discharging points, and exhibiting excellent output characteristics at a high C-rate, without significantly affecting the life characteristics of conventional lithium secondary batteries.

[0102] The negative electrode conductive material of this application has a completely different structure from the conductive material applied to the positive electrode. Specifically, the negative electrode conductive material of this application 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 also imparts some conductivity, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0103] Furthermore, the negative electrode conductive material described in 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.

[0104] In one embodiment of this application, the sheet-like conductive material used as the negative electrode conductive material described above has a structure and role different from the carbon-based active material generally used as a negative electrode active material in the conventional method. Specifically, the carbon-based active material used as the 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.

[0105] In contrast, sheet-like conductive materials used as negative electrode conductive materials are substances that have a sheet-like or plate-like shape and can be described as plate-like graphite. That is, they are substances included in the negative electrode active material layer to maintain conductive pathways, and do not play a role in the storage and release of lithium, but rather are substances that secure conductive pathways in a sheet-like form within the negative electrode active material layer.

[0106] In other words, in this application, when plate-shaped graphite is used as a conductive material, it 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.

[0107] In contrast, 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.

[0108] In other words, 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 ​​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 ​​5m². 2 It may be more than / g.

[0109] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of 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 hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0110] 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. Any general binder that fulfills the above role can be applied, and specifically, an aqueous binder may be used, or more specifically, a PAM-based binder may be used.

[0111] In one embodiment of this application, the negative electrode binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 5 parts by weight or more, or 10 parts by weight or more.

[0112] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the negative electrode active material layer is a single-layer negative electrode active material layer; or a multi-layer negative electrode active material layer.

[0113] In other words, in the case of a negative electrode for a lithium secondary battery according to this application, it may include a single-layer negative electrode active material layer or a double-layer negative electrode active material layer, and except that the negative electrode active material layer is single-layer or multi-layer, the proportion of silicon-based active materials with different particle sizes contained in the entire negative electrode active material layer may be applied similarly.

[0114] In one embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 10 μm or more and 250 μm or less.

[0115] However, the thickness can vary considerably depending on the type and application of the negative electrode used, and is not limited thereto.

[0116] In one embodiment of this application, the negative electrode current collector layer generally has a thickness of 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 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.

[0117] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0118] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0119] One embodiment of this application provides a lithium secondary battery comprising: 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.

[0120] Figure 2 shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. Specifically, 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. 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.

[0121] A secondary battery according to one embodiment of this specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0122] 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.

[0123] 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 3 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.

[0124] 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 the group consisting of 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 the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or 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. The positive electrode may also be Li-metal.

[0125] 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.

[0126] 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. Specific 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. One of these alone or a mixture of two or more may be used.

[0127] 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. Specific 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.

[0128] The separator separates the negative and positive electrodes and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries is acceptable without particular limitations, and it is especially preferable that it has low resistance to electrolyte ion movement and excellent electrolyte moisture retention capacity. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from 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 these may be selectively used as single-layer or multi-layer structures.

[0129] 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.

[0130] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0131] 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.

[0132] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents because they have high dielectric constants and dissociate lithium salts well. Furthermore, 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 high electrical conductivity can be produced, making them even more preferable.

[0133] 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 group consisting of the following:

[0134] 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.

[0135] 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 the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Examples]

[0136] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative examples, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of this description and the technical concept, and such variations and modifications will naturally fall within the scope of the appended claims.

[0137] <Manufacturing example> <Manufacturing Example 1> Negative electrode of SLC A negative electrode active material layer composition was formed using silicon-based active materials (first silicon-based active material, second 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. This composition was then added to distilled water as a solvent for negative electrode slurry formation to produce a negative electrode slurry.

[0138] The first conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 The second conductive material was SWCNT, with a particle size of 3.5 μm (d / g) and an average particle size of 3.5 μm.

[0139] The mixing method involved dispersing the first conductive material, binder, and water using a homomixer at 1500 rpm for 30 minutes, then adding the silicon-based active material and dispersing at 2500 rpm for 30 minutes, followed by adding the second conductive material and dispersing at 2500 rpm for 10 minutes. Subsequently, 20 mg / 25 cm of the negative electrode active material slurry was applied to both sides of a copper current collector (thickness: 15 μm) to serve as the negative electrode current collector. 2 It was coated and dried with the specified loading amount.

[0140] In this case, the average particle size and parts by weight of the first silicon-based active material and the second silicon-based active material contained in the negative electrode slurry are as shown in Table 1 below.

[0141] [Table 1]

[0142] <Manufacturing Example 2> DLC Negative Electrode A first negative electrode active material layer composition was formed using silicon-based active materials (first silicon-based active material, second 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. This composition was then added to distilled water as a solvent for negative electrode slurry formation to produce a negative electrode slurry.

[0143] The first conductive material is plate-shaped graphite (specific surface area: 17 m²). 2 The second conductive material was SWCNT, with a particle size of 3.5 μm (d / g) and an average particle size of 3.5 μm.

[0144] Subsequently, 8 mg / 25 cm of the first negative electrode active material slurry was applied to both sides of a copper current collector (thickness: 15 μm) to serve as the negative electrode current collector. 2 After coating with the loading amount, the second negative electrode active material layer slurry was added at a rate of 12 mg / 25 cm³. 2 The electrodes were manufactured by coating them with the specified loading amount.

[0145] In this case, the average particle size and parts by weight of the first silicon-based active material and the second silicon-based active material contained in the negative electrode slurry are as shown in Table 2 below.

[0146] [Table 2]

[0147] <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).

[0148] 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%).

[0149] 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.

[0150] 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 3% by weight of vinylene carbonate based on the total weight of the electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0151] <Example of experiment> Experimental Example 1: Cycle Life Data The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries underwent in-situ cycle testing at 4.2-3.0V 1C / 0.5C, and during the test, they were charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles to measure the capacity retention rate.

[0152] Life retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0153] [Table 3]

[0154] 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 the test. Then, the resistance was measured by discharging with a 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0155] For the measurement and evaluation of the aforementioned resistance increase rate, data was calculated for 200 cycles, and the results are shown in Table 4 below.

[0156] [Table 4]

[0157] As can be seen from Tables 3 and 4, a first silicon-based active material with a small average particle size and a second silicon-based active material with a large average particle size are mixed in a fixed ratio, and the ratio between the active materials with different average particle sizes is particularly adjusted. When adjusted in this way, the volume expansion of the active material is small even during charging and discharging, the electrode detachment phenomenon can be prevented, the pore structure of the electrode can be simplified, and as a result, the resistance of the negative electrode can be reduced.

[0158] Comparative Example 1 is a case where a silicon-based active material with small particle size is included alone, while Comparative Example 2 is a case where a silicon-based active material with large particle size is included alone. In the case of Comparative Example 1, although it shows better cycle performance than Comparative Example 2, after a certain number of cycles, the reaction concentrates on the surface, causing sudden death and problems. In the case of Comparative Example 2, large volume expansion of the Si active material occurs from the initial cycle, causing desorption from the surface of the current collector, resulting in inferior cycle performance.

[0159] In the cases of Comparative Examples 3 and 4, large-particle silicon-based active materials and small-particle silicon-based active materials were applied as in the present invention, but the ratio of each fell outside the scope of the present invention. Specifically, it was confirmed that when the amount of small-particle active material was less than the scope of the present application, as in Comparative Example 3, it showed low cycle performance similar to Comparative Example 2, which had 100% large-particle active material, and when the amount of large-particle active material was less than the scope of the present application, as in Comparative Example 4, it showed performance similar to Comparative Example 1.

[0160] In the case of Comparative Example 5, although the weight ratio satisfies the scope of this application, the particle size itself falls outside the scope of this application. Regardless of the ratio, the performance is inferior due to large volume expansion. Furthermore, if the active material has a small particle size and falls outside the scope of this application, there is no difference in initial lifespan performance, but the problem arises that the point of sudden death becomes earlier.

[0161] For reference, Examples 14 and 15, and Comparative Examples 6 and 7 are active material double-layer structures (DLD) and have the same principles as the aforementioned examples and comparative examples. [Explanation of Symbols]

[0162] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30 ···Separator 40...Cathode active material layer 50 ···Positive electrode current collector layer 100 ···Negative electrode for lithium secondary batteries 200 ···Positive electrode for lithium secondary batteries

Claims

1. A negative electrode active material containing a silicon-based active material, The silicon-based active material comprises a first silicon-based active material having an average particle size (D50) of 2 μm or more and 5 μm or less, and a second silicon-based active material having an average particle size (D50) of 10 μm or more and 20 μm or less. The anode active material wherein the weight ratio of the first silicon-based active material to the second silicon-based active material is 20:80 to 80:

20.

2. The negative electrode active material according to claim 1, wherein the weight ratio of the first silicon-based active material to the second silicon-based active material is 35:65 to 65:

35.

3. The silicon-based active material comprises silicon-based particles having a particle size distribution of 0.01 μm to 30 μm. The negative electrode active material according to claim 1, wherein the silicon-based active material contains 5 parts by weight or less of particles smaller than 2 μm, based on 100 parts by weight of the silicon-based active material.

4. The negative electrode active material according to claim 1, wherein the first silicon-based active material and the second silicon-based active material include one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and Si alloys.

5. The negative electrode active material according to claim 1, wherein the first silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0 < x < 2), and contains 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the first silicon-based active material.

6. The negative electrode active material according to claim 1, wherein the second silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0) and SiOx (0 < x < 2), and comprises 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the second silicon-based active material.

7. A negative electrode for a lithium secondary battery comprising 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 a negative electrode active material layer composition containing a negative electrode active material, a negative electrode conductive material, and a negative electrode binder as described in any one of claims 1 to 6.

8. The negative electrode for a lithium secondary battery according to claim 7, wherein the negative electrode active material is included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

9. The negative electrode for a lithium secondary battery according to claim 7, wherein the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material.

10. The negative electrode for a lithium secondary battery according to claim 7, wherein the negative electrode active material layer is a single-layer negative electrode active material layer; or a plurality of layers of negative electrode active material layers.

11. 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 7, wherein the thickness of the negative electrode active material layer is 10 μm or more and 250 μm or less.

12. positive electrode; A negative electrode for a lithium secondary battery according to claim 7; A separator provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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