Negative electrode composition, negative electrode for lithium secondary battery containing the same, lithium secondary battery containing the negative electrode, and method for manufacturing the negative electrode composition

Abstract

The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, a lithium secondary battery including the negative electrode, and a method for producing the negative electrode composition.

Description

Technical Field

[0001] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2021-0131869, filed with the Korean Intellectual Property Office on October 05, 2021, and Korean Patent Application No. 10-2022-0007659, filed with the Korean Intellectual Property Office on January 19, 2022, and all of its contents are incorporated herein by reference.

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

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 fields of power generation and energy storage using electrochemical reactions are the most actively studied.

[0004] Currently, secondary batteries are representative examples of electrochemical devices using such electrochemical energy, and their 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, 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 released from the positive electrode, and as the negative electrode active material, silicon-based particles with a large discharge capacity can be used.

[0007] In particular, with the recent demand for high-density energy batteries, research has been actively conducted on methods to increase the capacity by using silicon-based compounds such as Si / C and SiOx, which have a capacity more than 10 times greater than that of graphite-based materials, as the negative electrode active material. However, in the case of silicon-based compounds, which are high-capacity materials, although the capacity is large compared to conventionally used graphite, there is a problem that the volume rapidly expands during the charging process, severing the conductive path and degrading the battery characteristics.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as the negative electrode active material, methods such as adjusting the driving potential, additionally coating a thin film on the active material layer, and adjusting the particle size of the silicon-based compounds to suppress the volume expansion itself, or various methods to prevent the conductive path from being severed have been discussed.

[0009] Nevertheless, silicon-based negative electrodes still have the characteristic of a poor tortuosity structure and disadvantageous ion movement due to the characteristics of silicon-based active material particles. Therefore, research on the particle size distribution of the silicon-based active material itself, which can improve the conductive path, is necessary.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] Silicon-based negative electrodes still have the characteristic of a poor tortuosity structure and disadvantageous ion movement due to the characteristics of silicon-based active material particles. As a result of research to improve the conductive path, it has been found that fine particles of the silicon-based active material hinder ion movement, and a large amount of SEI film is generated due to side reactions with the fine particles during the charge-discharge cycle process, resulting in a rapid deterioration of the diffusion resistance.

[0012] This application relates to a negative electrode composition capable of solving the above problems, a negative electrode for a lithium secondary battery including the same, a lithium secondary battery including the negative electrode, and a method for manufacturing the negative electrode composition.

Means for Solving the Problems

[0013] One embodiment of the present specification is a negative electrode composition including a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and based on 100 parts by weight of the silicon-based active material, 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less are included, and the silicon-based active material satisfies the particle size ratios of the following formulas (1) and (2).

[0014] [Formula (1)] 20 ≦ (X1 / Y) × 100 (%) [Formula (2)] (X2 / Y) × 100 (%) ≦ 230 In the above formulas (1) and (2), X1 represents the D5 particle size of the silicon-based active material, X2 represents the D95 particle size of the silicon-based active material, Y represents the median particle size (D50) of the silicon-based active material.

[0015] In another embodiment, a method for manufacturing a negative electrode composition includes the steps of mixing a negative electrode conductive material and a negative electrode binder to form a mixture; adding water to the mixture and performing first mixing; and adding a silicon-based active material to the first-mixed mixture and performing second mixing, wherein the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and based on 100 parts by weight of the silicon-based active material, 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less are included, and the silicon-based active material satisfies the particle size ratios of the following formulas (1) and (2).

[0016] [Formula 1] 20 ≦ (X1 / Y) × 100 (%) [Formula 2] (X2 / Y) × 100 (%) ≦ 230

[0017] In another embodiment, a negative electrode for a lithium secondary battery is provided, which includes a negative electrode current collector layer; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one or both surfaces of the negative electrode current collector layer.

[0018] Finally, a lithium secondary battery is provided, which includes 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]

[0019] In the case of a negative electrode using a conventional silicon-based active material, especially using pure Si particles has the characteristic that a high-capacity and high-density battery can be fabricated. However, the purer the Si particles are, the more problems occur due to volume expansion, and the problems are solved by including oxides such as SiO. However, this also has a poor tortuosity structure, and the disadvantageous characteristic of ion movement still exists. In the case of the negative electrode composition according to the present application, the main object of the present invention is to solve the problem by controlling the fine powder of silicon-based particles and using a silicon-based active material that satisfies a specific particle size range.

[0020] In the case of the negative electrode composition according to an embodiment of the present invention, when using a silicon-based active material, which is a high-capacity material, to fabricate a high-capacity battery, instead of adjusting the characteristics of the conductive material and the binder due to the volume expansion of the silicon-based active material, the characteristics of the silicon-based active material itself are changed. Specifically, the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and includes 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less based on 100 parts by weight of the silicon-based active material, and the particle size distribution of the silicon-based active material is adjusted to the ranges of the above Formula 1 and Formula 2.

[0021] That is, the negative electrode composition according to the present application contains a silicon-based active material with a controlled particle size distribution as described above. By removing fine particles from the perspective of tortuosity in the electrode, it has the advantage that the movement of lithium ions (conductive path) during charge and discharge becomes advantageous. In addition, fine silicon particles that hinder the movement of lithium ions during charge and discharge react with lithium ions to cause side reactions and increase diffusion resistance. However, by containing a silicon-based active material controlled within the ranges of Formula 1 and Formula 2 according to the present application, it is possible to significantly control the rate at which the diffusion resistance increases even as the charge and discharge process cycles continue.

[0022] That is, compared with the case of using a conventional silicon-based active material, a lithium secondary battery using a silicon-based active material adjusted to a certain particle size range (the ranges of Formula 1 and Formula 2) as in the present invention can solve the problems of reduced life and increased resistance during charging and discharging.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0024] Before explaining the present invention, first, several terms will be defined. In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components but may further include other components.

[0025] In this specification, "p~q" means a range of "p or more and q or less". In this specification, the "specific surface area" is measured by the BET method. Specifically, it is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan, Inc. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0026] In this specification, "Dn" means the particle size distribution and means the particle size at the n% point of the cumulative particle number distribution according to the particle size. That is, D50 is the particle size (median particle size) at the 50% point of the cumulative particle number distribution according to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution according to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution according to the particle size. Also, D95 is the particle size at the 95% point of the cumulative particle number distribution according to the particle size, and D5 is the particle size at the 5% point of the cumulative particle number distribution according to the particle size. On the other hand, the median particle size 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 measuring device (for example, Microtrac S3500), and the difference in the diffraction pattern according to the particle size is measured when the particles pass through the laser beam to calculate the particle size distribution.

[0027] In one embodiment of this application, the particle size or particle diameter may mean the average diameter or representative diameter of individual particles forming the metal powder.

[0028] In this specification, that a polymer contains a certain monomer as a monomer unit means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when it is said that a polymer contains a monomer, this is interpreted in the same way as that the polymer contains the monomer as a monomer unit.

[0029] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless otherwise specified as "homopolymer".

[0030] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are the polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization as standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0031] Hereinafter, a detailed description will be given with reference to the drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention may be realized in various different forms and is not limited to the following description.

[0032] One embodiment of this specification is a negative electrode composition including a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and includes 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less based on 100 parts by weight of the silicon-based active material, and the silicon-based active material satisfies the particle size ratio of Formula 1 and Formula 2, and provides a negative electrode composition.

[0033] In the case of the negative electrode composition according to one embodiment of the present invention, when using a silicon-based active material, which is a high-capacity material, to fabricate a high-capacity battery, instead of adjusting the characteristics of the conductive material and the binder due to the volume expansion of the silicon-based active material, the characteristics of the silicon-based active material itself are changed. Specifically, the present invention is characterized by including silicon-based particles having a distribution with a particle size of 0.01 μm or more and 30 μm or less, including 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less based on 100 parts by weight of the silicon-based active material, and adjusting the particle size distribution of the silicon-based active material within the ranges of Formula 1 and Formula 2.

[0034] In one embodiment of the present application, a negative electrode composition comprising a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and based on 100 parts by weight of the silicon-based active material, the silicon-based particles having a particle size of 1 μm or less are included in an amount of 1 part by weight or more and 5 parts by weight or less, the D5 / D50 ratio of the silicon-based active material is 20% or more, and the D95 / D50 ratio of the silicon-based active material may be 230% or less.

[0035] In one embodiment of the present application, the Dx / Dy ratio of the silicon-based active material can be calculated by a general ratio calculation method, and as a calculation formula, it can be expressed as (Dx / Dy)×100 (%). That is, as an example, the D95 / D50 ratio of the silicon-based active material can be calculated by (D95 / D50)×100.

[0036] In one embodiment of the present application, a negative electrode composition is provided, wherein the silicon-based particles include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0037] In one embodiment of the present application, a negative electrode composition is provided, wherein the silicon-based particles include one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) is included in an amount of 70 parts by weight or more.

[0038] In one embodiment of the present application, a negative electrode composition is provided, wherein the silicon-based particles include SiOx (x = 0), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) is included in an amount of 70 parts by weight or more.

[0039] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included 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 included 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.

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

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

[0042] In one embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the impurities are metals that may generally be contained in the silicon-based active material. Specifically, they may be contained in an amount of 0.1 part by weight or less based on 100 parts by weight of the silicon-based active material.

[0043] In the case of silicon-based active materials, attempts to apply them have been increasing because their capacity is significantly higher compared to the conventionally used graphite-based active materials. However, during the charge and discharge process, since the silicon-based active material has a high volume expansion rate, it has remained at the level of being used by mixing a small amount with the graphite-based active material.

[0044] Therefore, in the case of the present invention, in order to improve the capacity performance, while using only the silicon-based active material as the negative electrode active material, instead of adjusting the composition of the conductive material and the binder to solve problems such as an increase in the tortuosity of the electrode and the diffusion resistance due to the charge and discharge cycles, the present invention has solved the conventional problems by adjusting the particle size distribution of the silicon-based active material itself.

[0045] In one embodiment of the present application, the silicon-based active material may contain silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

[0046] The statement that the silicon-based active material contains silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less means that a plurality of individual silicon-based particles having particle sizes within the above range are included, and the number of silicon-based particles included is not limited.

[0047] The particle size of the silicon-based particles can be indicated by its diameter in the case of spherical particles. However, even in the case of other non-spherical shapes, the particle size can be measured in comparison with the spherical case, and the particle size of individual silicon-based particles can generally be measured by methods used in the art.

[0048] In one embodiment of the present application, 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less may be included based on 100 parts by weight of the silicon-based active material.

[0049] In another embodiment, 1 part by weight or more and 5 parts by weight or less, preferably 1 part by weight or more and 4 parts by weight or less, 1.2 parts by weight or more and 4 parts by weight or less of silicon-based particles having a particle size of 1 μm or less may be included based on 100 parts by weight of the silicon-based active material.

[0050] That is, the silicon-based active material according to the present invention has silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and has silicon-based particles having a particle size of 1 μm or less within the above range, and can be represented as a silicon-based active material with controlled fine powder.

[0051] By the silicon-based active material according to the present invention satisfying the above weight range, fine silicon-based particles are removed, an advantageous structure can be formed from the viewpoint of tortuosity in the electrode to prevent an increase in diffusion resistance, and the rate of increase in diffusion resistance can be significantly controlled even when the cycle of the charge and discharge process continues. This is the result of controlling the silicon-based active material with a small particle size that undergoes side reactions with lithium ions, and has the characteristic that the life and capacity of the electrode containing this increase.

[0052] In one embodiment of the present application, there is provided a negative electrode composition in which the D5 / D50 ratio of the silicon-based active material is 20% or more, and the D95 / D50 ratio of the silicon-based active material is 230% or less.

[0053] For the D5 / D50 ratio and the D95 / D50 ratio, the aforementioned formula may be applicable. Specifically, (D5 / D50)×100 (%) and (D95 / D50)×100 (%) may also be applicable.

[0054] In one embodiment of the present application, the D5 / D50 ratio of the silicon-based active material may be represented by Formula 1.

[0055] In one embodiment of the present application, Formula 1 may satisfy 20≦(X1 / Y)×100 (%).

[0056] In another embodiment, Formula 1 may be 20≦(X1 / Y)×100 (%), preferably 25≦(X1 / Y)×100 (%), more preferably 30≦(X1 / Y)×100 (%), and may satisfy the range of (X1 / Y)×100 (%)≦80, preferably (X1 / Y)×100 (%)≦70, more preferably (X1 / Y)×100 (%)≦55.

[0057] In one embodiment of the present application, the D5 / D50 ratio of the silicon-based active material may be 20% or more, preferably 25% or more, more preferably 30% or more, and may satisfy the range of 80% or less, preferably 70% or less, more preferably 55% or less.

[0058] In one embodiment of the present application, the D95 / D50 ratio of the silicon-based active material may be represented by Formula 2.

[0059] In one embodiment of the present application, Formula 2 may satisfy (X2 / Y)×100 (%)≦230.

[0060] In one embodiment of the present application, the D95 / D50 ratio of the silicon-based active material may satisfy the range of 230% or less, preferably 220% or less, and most preferably 210% or less, and may also satisfy the range of 180% or more, preferably 190% or more.

[0061] In one embodiment of the present application, the formula 2 may satisfy (X2 / Y)×100(%)≦230, preferably (X2 / Y)×100(%)≦220, more preferably (X2 / Y)×100(%)≦210, and may also satisfy the range of 180≦(X2 / Y)×100(%), preferably 190≦(X2 / Y)×100(%).

[0062] By adjusting the D5 / D50 ratio (formula 1) and the D95 / D50 ratio (formula 2) of the silicon-based active material according to the present application to the above ranges, a favorable structure can be formed from the perspective of tortuosity in the electrode, and it has the characteristic that the rate of increase in diffusion resistance can be controlled by the continuation of charge and discharge cycles.

[0063] In one embodiment of the present application, the Y represents the median particle size (D50) of the silicon-based active material. Specifically, the Y may satisfy the range of 3 μm or more and 10 μm or less, preferably 4 μm or more and 7 μm or less, and more preferably 4.5 μm or more and 7 μm or less.

[0064] In one embodiment of the present application, the X1 represents the D5 particle size of the silicon-based active material. Specifically, the X1 may satisfy the range of 2 μm or more and 5 μm or less, preferably 2.3 μm or more and 4 μm or less, and more preferably 2.5 μm or more and 4 μm or less.

[0065] In one embodiment of the present application, the X2 represents the D95 particle size of the silicon-based active material. Specifically, the X2 may satisfy the range of 6 μm or more and 15 μm or less, preferably 7 μm or more and 14 μm or less, and more preferably 8 μm or more and 14 μm or less.

[0066] In one embodiment of the present application, a negative electrode composition is provided in which the D5 / D95 ratio of the silicon-based active material is 20% or more.

[0067] The D5 / D95 ratio may be applied to the above-described formula. Specifically, (D5 / D95)×100(%) may be applied.

[0068] That is, in one embodiment of the present application, a negative electrode composition is provided in which the silicon-based active material satisfies the particle size ratio of the following formula 3.

[0069] [Formula 3] 10≦(X1 / X2)×100(%) In the formula 3, X1 represents the D5 particle size of the silicon-based active material, X2 represents the D95 particle size of the silicon-based active material.

[0070] In another embodiment, the formula 3 may satisfy the range of 10≦(X1 / X2)×100(%), preferably 15≦(X1 / X2)×100(%), more preferably 20≦(X1 / X2)×100(%), and (X1 / X2)×100(%)≦70, preferably (X1 / X2)×100(%)≦60, more preferably (X1 / X2)×100(%)≦55.

[0071] In one embodiment of the present application, a negative electrode composition is provided in which the silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less have a half-value width of 1 μm or more and 5 μm or less.

[0072] Satisfying the D5 / D95 ratio (formula 3) and the half-value width ratio means that the particle size distribution in the Particle-Size Distribution (PSD) graph is sharply formed. By satisfying the above range, even when a silicon-based active material that is pure silicon (Pure Si) is applied, side reactions due to charge and discharge can be suppressed and the problem of resistance increase can be solved.

[0073] In this application, the particle size distribution (PSD) means a mathematical function that defines the relative amount of particles present according to a list of values or sizes. This can provide information regarding the particle size span, and D10, D50, and D90 (known as D values or three-point specifications) are the most widely used values in PSD analysis. These values respectively indicate the diameters of the particles at 10%, 50%, and 90% of the cumulative distribution.

[0074] For example, assuming that D50 is 100 nm, it means that 50% of the particles in the sample are larger than 100 nm and 50% are smaller than 100 nm. Additional mediating variables related to the size distribution can be calculated with D10, D50, and D90. Specifically, Span can be calculated as follows. Span=(D90-D10) / D50

[0075] In one embodiment of this application, Dmax of the silicon-based active material may satisfy the range of 30 μm or less. Specifically, Dmax may satisfy the range of 30 μm or less, 27 μm or less, and may also satisfy 10 μm or more.

[0076] In one embodiment of this application, Dmin of the silicon-based active material may satisfy the range of 0.5 μm or more. Specifically, Dmin may satisfy the range of 0.5 μm or more, 1 μm or more, and may also satisfy 5 μm or less.

[0077] Dmax and Dmin may mean the particle sizes of the silicon-based particles having the largest particle size (Dmax) and the smallest particle size (Dmin) in the silicon-based active material containing silicon-based particles.

[0078] 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 m 2 / g~150.0 m 2 / g, more preferably 0.1 m 2 / g, preferably 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured in accordance with DIN 66131 (using nitrogen).

[0079] In one embodiment of the present application, the silicon-based active material may be present, for example, in crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or flaky particles. Alternatively, although less conveniently, the silicon particles may have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0080] In one embodiment of the present application, a negative electrode composition is provided in which the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0081] In another embodiment, the silicon-based active material may be 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0082] When the silicon-based active material with a significantly high capacity is used in the above range, the negative electrode composition according to the present application has the characteristic that problems of increased resistance and decreased lifespan can be solved by adjusting according to the particle size of the silicon-based active material itself.

[0083] In one embodiment of the present 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.

[0084] In the present application, the sphericity is determined by the following formula A-1, where A is the area and P is the boundary line. [Formula A-1] 4πA / P 2

[0085] 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, there has been an increasing attempt to use a silicon-based active material in combination to increase the capacity. However, in the case of a silicon-based active material, 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.

[0086] 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.

[0087] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, does not induce a chemical change, and has conductivity, and means a spherical or dot-shaped conductive material. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivative, and preferably may include carbon black in terms of achieving high conductivity and excellent dispersibility.

[0088] In one embodiment of the present application, the dot-shaped conductive material may have a BET specific surface area of 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0089] In one embodiment of the present application, the content of the functional groups (Volatile matter) in the dot-shaped conductive material may satisfy 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, more preferably 0.01% or more and 0.1% or less.

[0090] Particularly, when the content of the functional groups in the dot-shaped conductive material satisfies the above range, the functional groups present on the surface of the dot-shaped conductive material exist, and when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent.

[0091] In one embodiment of the present application, it is characterized by including a dot-shaped conductive material having a content of functional groups within the above range together with a silicon-based active material, and the adjustment of the content of the functional groups can be adjusted according to the degree of heat treatment of the dot-shaped conductive material.

[0092] That is, in the production of the dot-shaped conductive material, a high content of functional groups means a large number of foreign substances, and a low content of functional groups may mean that more heat treatment processes have been performed.

[0093] In one embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, more preferably 20 nm to 60 nm.

[0094] In one embodiment of the present application, the conductive material may include a sheet-shaped conductive material. The sheet-shaped conductive material can increase the surface contact between silicon particles in the negative electrode to improve conductivity and play a role in suppressing the interruption of the conductive path due to volume expansion, and can be represented as a plate-shaped conductive material or a bulk-shaped conductive material.

[0095] In one embodiment of the present application, the sheet-shaped conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0096] In one embodiment of the present application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, specifically, it may be 3 μm to 6 μm, and more specifically, it may be 4 μm to 5 μm. When the above range is satisfied, due to the sufficient particle size, excessive viscosity increase of the negative electrode slurry is not caused, and dispersion is easy. Therefore, when dispersing using the same apparatus and time, the dispersion effect is excellent.

[0097] In one embodiment of the present application, the sheet-like conductive material provides a negative electrode composition in which D10 is 0.5 μm or more and 1.5 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 7.0 μm or more and 15.0 μm or less.

[0098] In one embodiment of the present application, as the sheet-like conductive material, 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 may be used.

[0099] In one embodiment of the present application, as the sheet-like conductive material, 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 can be used without limitation. However, particularly for the sheet-like conductive material according to the present application, since the influence of dispersion can affect the electrode performance to a certain extent, it is particularly preferable to use a low specific surface area sheet-like conductive material that does not cause problems in dispersion.

[0100] In one embodiment of the present application, the sheet-like conductive material may have a BET specific surface area of 5 m 2 / g or more.

[0101] In another embodiment, the sheet-like conductive material may have a BET specific surface area of 5 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0102] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material with a high specific surface area, and the BET specific surface area is 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 / g or less may be satisfied.

[0103] In yet another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material with a low specific surface area, and the BET specific surface area is 5 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 / g or less may be satisfied.

[0104] Examples of 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 include a plurality of single carbon nanotubes. Specifically, here, the "bundle type" refers to a bundle or rope-like secondary shape in which a plurality of single carbon nanotubes are arranged side by side or intertwined in an orientation in which the axes in the length direction of the single carbon nanotubes are substantially the same, unless otherwise specified. The single carbon nanotube has a cylindrical shape with a nanosize diameter and a sp2 bond structure for the graphite sheet. At this time, depending on the angle and structure of the curling of the graphite sheet, it can exhibit the characteristics of a conductor or a semiconductor. The bundle-type carbon nanotubes can be uniformly dispersed during the production of the negative electrode compared to entangled-type carbon nanotubes, and a conductive network can be smoothly formed in the negative electrode, improving the conductivity of the negative electrode.

[0105] In one embodiment of the present application, the linear conductive material may include single-walled carbon nanotubes (SWCNT); or multi-walled carbon nanotubes (MWCNT).

[0106] In one embodiment of the present application, the negative electrode conductive material provides a negative electrode composition that is 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0107] In another embodiment, the negative electrode conductive material may be included in an amount of 10 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, more preferably 15 parts by weight or more and 25 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0108] In one embodiment of the present application, the negative electrode conductive material provides a negative electrode composition including a sheet-like conductive material; and a linear conductive material.

[0109] In one embodiment of the present application, the negative electrode conductive material includes a sheet-like conductive material; and a linear conductive material, and the linear conductive material may be included in an amount of 0.01 parts by weight or more and 10 parts by weight or less; and the sheet-like conductive material may be included in an amount of 90 parts by weight or more and 99.99 parts by weight or less based on 100 parts by weight of the negative electrode conductive material.

[0110] In another embodiment, the linear conductive material may be 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 5 parts by weight or less, more preferably 0.1 parts by weight or more and 3 parts by weight or less based on 100 parts by weight of the negative electrode conductive material.

[0111] In still another embodiment, the sheet-like conductive material may be 90 parts by weight or more and 99.99 parts by weight or less, preferably 95 parts by weight or more and 99.95 parts by weight or less, more preferably 97 parts by weight or more and 99.9 parts by weight or less based on 100 parts by weight of the negative electrode conductive material.

[0112] In particular, in one embodiment of the present application, the negative electrode conductive material includes a sheet-shaped conductive material and a linear conductive material. By satisfying the respective compositions and ratios, it does not significantly affect the life characteristics of conventional lithium secondary batteries, has many points where charging and discharging are possible, and has the characteristic of excellent output characteristics at a high C-rate.

[0113] In the case of the negative electrode conductive material according to the present application, it has a completely different configuration from the positive electrode conductive material applied to the positive electrode. That is, in the case of the negative electrode conductive material according to the present application, it serves to make contact between silicon-based active materials with a very large expansion of the electrode volume during charging and discharging. The positive electrode conductive material serves as a buffer during rolling and also serves to impart some conductivity, and its configuration and role are completely different from those of the negative electrode conductive material of the present invention.

[0114] Further, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different configuration from the conductive material applied to a graphite-based active material. That is, the conductive material used for an electrode having a graphite-based active material has characteristics of improving output characteristics and imparting some conductivity because it simply has smaller particles than the active material, and its configuration and role are completely different from those of the negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0115] In one embodiment of the present application, the sheet-shaped conductive material used as the above-described negative electrode conductive material generally has a different structure and role from the carbon-based active material used as a conventional negative electrode active material. Specifically, the carbon-based active material used as a negative electrode active material may be artificial graphite or natural graphite, and means a material processed into a spherical or dot shape to facilitate the storage and release of lithium ions.

[0116] In contrast, the sheet-like conductive material used as the negative electrode conductive material is a substance having a sheet-like or plate-like shape, and can be represented as plate-like graphite. That is, it is a substance contained to maintain a conductive path in the negative electrode active material layer, and does not play a role in storing and releasing lithium, but means a substance for ensuring a sheet-like conductive path inside the negative electrode active material layer.

[0117] That is, in the present application, using plate-like graphite as the conductive material means that it is processed into a sheet-like or plate-like shape and is used as a substance for ensuring a conductive path, rather than playing a role in storing or releasing lithium. At this time, the negative electrode active material contained together has high capacity characteristics for storing and releasing lithium and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0118] In contrast, in the present application, using a carbon-based active material as the active material means that it is processed into a dot-like or spherical shape and is used as a substance that plays a role in storing or releasing lithium.

[0119] That is, in one embodiment of the present application, artificial graphite or natural graphite, which is a carbon-based active material, is dot-like, and the BET specific surface area may satisfy the range of 0.1 m 2 / g or more and 4.5 m 2 / g or less. Also, the plate-like graphite, which is a sheet-like conductive material, may be sheet-like and have a BET specific surface area of 5 m 2 / g or more.

[0120] In one embodiment of the present application, the negative electrode binder may include at least any one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0121] The negative electrode binder according to one embodiment of the present application serves to hold the active material and the conductive material in order to prevent distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. If the above roles are satisfied, all general binders can be applied. Specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0122] In one embodiment of the present application, the negative electrode binder may be 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 also be 5 parts by weight or more, 10 parts by weight or more.

[0123] In one embodiment of the present application, a method for manufacturing a negative electrode composition includes: mixing a negative electrode conductive material and a negative electrode binder to form a mixture; adding water to the mixture and performing first mixing; and adding a silicon-based active material to the mixed mixture and performing second mixing. The silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and includes 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less based on 100 parts by weight of the silicon-based active material. The silicon-based active material satisfies the particle size ratios of the following Formula 1 and Formula 2, and provides a method for manufacturing a negative electrode composition.

[0124] [Formula 1] 20 ≦ (X1 / Y) × 100 (%) [Formula 2] (X2 / Y) × 100 (%) ≦ 230 In Formula 1 and Formula 2, X1 represents the D5 particle size of the silicon-based active material, X2 represents the D95 particle size of the silicon-based active material, Y represents the median particle size (D50) of the silicon-based active material.

[0125] In one embodiment of the present application, a method for manufacturing a negative electrode composition includes: mixing a negative electrode conductive material and a negative electrode binder to form a mixture; adding water to the mixture and performing first mixing; and adding a silicon-based active material to the mixed mixture and performing second mixing. The silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and includes 1 part by weight or more and 5 parts by weight or less of Si particles having a particle size of 1 μm or less based on 100 parts by weight of the silicon-based active material. The D5 / D50 ratio of the silicon-based active material is 20% or more, and the D95 / D50 ratio of the silicon-based active material is 230% or less, and provides a method for manufacturing a negative electrode composition.

[0126] In the method for manufacturing the negative electrode composition, each composition included in the negative electrode composition is the same as the description mentioned above.

[0127] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode composition, wherein the steps of the first mixing and the second mixing are steps of mixing at 2,000 rpm to 3,000 rpm for 10 minutes to 60 minutes.

[0128] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, including a negative electrode current collector layer; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one or both sides of the negative electrode current collector layer.

[0129] FIG. 1 is a diagram showing 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 including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10 can be confirmed. FIG. 1 shows that the negative electrode active material layer is formed on one side, but it may be included on both sides of the negative electrode current collector layer.

[0130] Specifically, FIG. 2 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. As described above, the negative electrode active material layer is included on both sides of the negative electrode current collector layer, and a negative electrode 100 for a lithium secondary battery including a negative electrode active material layer 20 on both sides of the negative electrode current collector layer 10 can be confirmed. Substantially, it is rare to coat on one side as shown in FIG. 1, and the active material layer can be coated on both sides of the current collector layer and used as shown in FIG. 2. At this time, when the negative electrode composition of the present invention is included on at least one side of the current collector layer, the negative electrode can be manufactured. That is, the compositions of the active material layers coated on both sides may be the same or different from each other. When the compositions are different, generally used active material layers such as carbon-based and silicon-based may be used. Most preferably, the negative electrode active material layer including the negative electrode composition according to the present application is coated on both sides.

[0131] In one embodiment of the present application, the negative electrode for the lithium secondary battery may be formed by applying and drying a negative electrode slurry containing the negative electrode composition on one or both sides of a negative electrode current collector layer.

[0132] At this time, the negative electrode slurry may include the above-described negative electrode composition; and a slurry solvent.

[0133] In one embodiment of the present application, the solid content of the negative electrode slurry may satisfy 5 wt% or more and 40 wt% or less.

[0134] In another embodiment, the solid content of the negative electrode slurry may satisfy a range of 5 wt% or more and 40 wt% or less, preferably 7 wt% or more and 35 wt% or less, and more preferably 10 wt% or more and 30 wt% or less.

[0135] The solid content of the negative electrode slurry means the content of the negative electrode composition contained in the negative electrode slurry, and may mean the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0136] When the solid content of the negative electrode slurry satisfies the above range, it has the characteristics that the viscosity during the formation of the negative electrode active material layer is appropriate, the particle aggregation phenomenon of the negative electrode composition is minimized, and the negative electrode active material layer can be efficiently formed.

[0137] In one embodiment of the present application, the slurry solvent can be used without limitation as long as it can dissolve the negative electrode composition. Specifically, water or NMP may be used.

[0138] In one embodiment of the present 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 induce a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with a surface treatment of carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used. Further, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0139] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, 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 20 μm or more and 500 μm or less.

[0140] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0141] In one embodiment of the present application, the porosity of the negative electrode active material layer may satisfy the range of 10% or more and 60% or less.

[0142] In another embodiment, the porosity of the negative electrode active material layer may satisfy the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, more preferably 30% or more and 45% or less.

[0143] The porosity varies according to the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, by containing the silicon-based active material and conductive material according to the present application in specific compositions and content parts, the above range is satisfied. Thereby, it is characterized in that the electric conductivity and resistance in the electrode have an appropriate range.

[0144] In one embodiment of the present application, a lithium secondary battery is provided, which includes 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.

[0145] FIG. 3 is a diagram showing a laminated 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 confirmed on one side of a 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 confirmed on one side of a positive electrode current collector layer 50, indicating that the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are formed in a structure laminated with a separator 30 interposed therebetween.

[0146] A secondary battery according to one embodiment of the present specification may particularly include 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, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0147] 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.

[0148] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0149] The positive electrode active material may be a commonly used positive electrode active material. Specifically, examples of the positive electrode active material include layered compounds such as lithium cobalt oxide (LiCoO 2 ), lithium nickel oxide (LiNiO 2 ), and compounds substituted with one or more transition metals; lithium iron oxide such as LiFe 3 O 4 ; lithium manganese oxides such as the chemical formula Li 1+c1 Mn 2-c1 O 4 (0 ≦ c1 ≦ 0.33), LiMnO 3 , LiMn 2 O 3 , LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); vanadium oxides such as LiV 3 O 8 , V 2 O 5 , Cu 2 V 2 O 7 ; Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1-c2 Mc 2 O 2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3); lithium manganese composite oxide represented by the chemical formula LiMn 2-c3 M c3 O 2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1), or Li 2 Mn 3 MO 8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn 2 O 4 in which part of Li in the chemical formula is substituted with an alkaline earth metal ion, etc., but is not limited thereto. The positive electrode may be lithium metal (Li-metal).

[0150] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0151] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances 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 thereof may be used.

[0152] Further, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force 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, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of these alone or a mixture of two or more thereof may be used.

[0153] As the separator, it separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any material that can be used as a separator in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolyte and excellent in the ability to hold the moisture of the electrolyte. Specifically, a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made from high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0154] 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. Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0155] Examples of the non-aqueous organic solvent include 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 derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0156] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used as high-viscosity organic solvents because they have a high dielectric constant and can well dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, at an appropriate ratio and used, an electrolyte having high electrical conductivity can be produced, so they can be more preferably used.

[0157] As the metal salt, a lithium salt may be used. 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 - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 )3 PF 3 - 、(CF 3 ) 4 PF 2 - 、(CF 3 ) 5 PF - 、(CF 3 ) 6 P - 、CF 3 SO 3 - 、CF 3 CF 2 SO 3 - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、(SF 5 ) 3 C - 、(CF 3 SO 2 ) 3 C - 、CF 3 (CF 2 ) 7 SO 3 - 、CF 3 CO 2 - 、CH 3 CO 2 - 、SCN - 、および(CF 3 CF 2 SO 2 ) 2 N - One or more selected from the group consisting of may be used.

[0158] In addition to the constituent components of the electrolyte, for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc., the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0159] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the 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 and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

Examples

[0160] Hereinafter, preferred examples are presented to assist in understanding the present invention. However, these examples are merely for illustrative purposes of this description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of this description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the appended claims.

[0161] <Production Example> <Manufacture of the negative electrodes of Examples 1 to 3 and Comparative Examples 1 to 3> <Manufacture of the negative electrode> A silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder satisfying the particle sizes and weight ratios in Table 1 below were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 80:9.6:0.4:10 to produce a negative electrode slurry (solid content concentration: 25% by weight).

[0162] Specifically, the first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0163] As a specific mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homomixer, and after adding the silicon-based active material, they were dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0164] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector layer at a loading amount of 85 mg / 25 cm 2 and 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 used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity 40.0%).

[0165]

Table 1

[0166] In Table 1 above, Formula 1 can be calculated as (D5 / D50)×100 (%), Formula 2 can be calculated as (D95 / D50)×100 (%), and Formula 3 can be calculated as the value of (D5 / D95)×100 (%). Also, in Table 1 above, the ratio of silicon-based particles with a particle size of 1 μm or less can indicate the weight ratio based on 100 parts by weight of the silicon-based active material.

[0167] <Example 4> In Example 1, a negative electrode was produced in the same manner as in Example 1, except that a polyacrylamide was added as a silicon-based active material, a first conductive material, a second conductive material, a third conductive material, and a binder at a weight ratio of 80:5:4.6:0.4:10 to distilled water as a solvent for forming a negative electrode slurry.

[0168] At this time, the first conductive material in Example 4 was carbon black (specific surface area: 58 m 2 / g, diameter: 37 nm), the second conductive material in Example 4 was plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the third conductive material in Example 4 was SWCNT.

[0169] <Example 5> In Example 1, except that a silicon-based active material, a first conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 80:10:10 to produce a negative electrode slurry, a negative electrode was produced in the same manner as in Example 1.

[0170] At this time, the first conductive material in Example 5 was carbon black (specific surface area: 58 m 2 / g, diameter: 37 nm).

[0171] <Experimental Example> Experimental Example 1: Life Evaluation of Monocell As a positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 O 2 (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 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry at a weight ratio of 97:1.5:1.5 to produce a positive electrode slurry (solid content concentration: 78% by weight).

[0172] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) as a positive electrode current collector at a loading amount of 537 mg / 25 cm 2 , 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), and a positive electrode was produced (thickness of the positive electrode: 77 μm, porosity: 26%).

[0173] A polyethylene separator was interposed between the positive electrode and the negative electrodes of Examples 1 to 5 and Comparative Examples 1 to 3, an electrolyte was injected, and secondary batteries were manufactured respectively.

[0174] The electrolyte was prepared by adding 3% by weight of vinylene carbonate based on the total weight of the electrolyte to an organic solvent obtained by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) at a volume ratio of 30:70, and adding LiPF 6 at a concentration of 1 M.

[0175] For the secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 3, life evaluation was performed using an electrochemical charge and discharge device, and the capacity retention rate was evaluated. The secondary battery was charged (0.33C CC / CV charge 4.2V 0.05C cut) and discharged (0.33C CC discharge 3.0V cut), which was taken as the first cycle. Then, from the second cycle under the conditions of charging (1.0C CC / CV charge 4.2V 0.05C cut) and discharging (0.5C CC discharge 3.0V cut), the cycles were confirmed until the capacity retention rate reached 80% and the charge and discharge were carried out.

[0176] The capacity retention rate at the Nth cycle was evaluated by the following formula. The results are shown in Table 2 below. Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0177] Experimental Example 2: Evaluation of the increase rate of discharge resistance at SOC50 (after 300 cycles) In Experimental Example 1, after measuring the capacity retention rate up to 300 cycles during the test, the resistance was measured by discharging at SOC50 with a 2.5C pulse, and the increase rate of resistance was compared and analyzed. The results are shown in Table 2 below.

[0178]

Table 2

[0179] As can be confirmed from Table 1 and Table 2 above, in the case of the negative electrode for a lithium secondary battery using the silicon-based active material according to the present application, it was confirmed that the life evaluation and the rate of increase in discharge resistance were superior to those of Comparative Examples 1 to 3. This is the result of using a silicon-based active material having silicon-based particles with controlled fine powder and satisfying the ranges of Formula 1 and Formula 2 according to the present application.

[0180] That is, by the silicon-based active materials according to Examples 1 to 5 satisfying the characteristic parts according to the present application, fine silicon-based particles were removed, and it was confirmed that an advantageous structure was formed from the viewpoint of tortuosity in the electrode, preventing an increase in diffusion resistance. Also, even when the cycles of the charge / discharge process continued, since the rate of increase in diffusion resistance due to the removal of fine silicon particles could be significantly controlled, it was confirmed from Examples 1 to 5 that the life and capacity of the electrode including this were significantly increased.

[0181] Comparative Example 1 corresponds to the case where the range of Formula 1 is not satisfied, Comparative Example 2 corresponds to the case where Formula 2 is not satisfied, and Comparative Example 3 corresponds to the case where neither Formula 1 nor Formula 2 is satisfied. In this case, it contains a pure silicon active material in which the fine powder is not controlled as compared with Examples 1 to 5, and it was confirmed that side reactions occurred during the charge / discharge process and the life and the rate of increase in discharge resistance were not good. That is, in the case of Comparative Examples 1 to 3, it was confirmed that they contain fine silicon particles and have an unfavorable structure from the viewpoint of the tortuosity of the electrode. Also, by repeating the charge / discharge, it was confirmed that the rate of increase in diffusion resistance due to the formation of the SEI film by the reaction between the fine silicon particles and lithium ions increased, and the life and the rate of increase in resistance were not good.

[0182] For reference, Examples 1 to 3 correspond to the case where a sheet-like conductive material and a linear conductive material are used as the conductive material (two types of conductive materials). In this case, when compared with Example 4 (three types of conductive materials) and Example 5 (one type of conductive material), it can be confirmed that the life evaluation results are particularly excellent and the discharge resistance increase rate is also low. This is because the two types of conductive materials included do not have a great influence on the life characteristics of conventional lithium secondary batteries, and there are many points where the conductive path increases and charging and discharging are possible, and it has the characteristic of excellent output characteristics at a high C-rate.

[0183] Experimental Example 3: R ion Resistance evaluation (measurement of pore resistance using a coin half-cell) [Manufacture of symmetric cell] The negative electrodes manufactured in Example 1 and Comparative Example 1 were punched out with a 15-pi punching machine, and a coin cell was assembled using two electrodes with similar thickness and weight (negative electrode / separator / negative electrode, and the electrolyte was the same). After sufficiently impregnating the electrolyte, EIS was measured at room temperature from 300 kHz to 100 mHz at 100 points with an amplitude of 5 mV to measure the pore resistance of the electrode, and the results are shown in Table 3 below.

[0184]

Table 3

[0185] As can be confirmed from Table 3 above, when the silicon-based active material according to the present application satisfies the ranges of specific Formulas 1 and 2, it can be confirmed from the measurement of the resistance that a favorable structure is formed from the viewpoint of the tortuosity in the negative electrode. Specifically, in order to prevent non-uniform deterioration and improve the performance of the cell as it enters from the surface part to the inside of the negative electrode, R ion needs to be low, and it was confirmed that this was improved by using a silicon-based active material controlled under specific conditions according to the present application.

[0186] That is, the negative electrode containing the silicon-based active material according to the present application has a structure that is advantageous from the viewpoint of tortuosity, and it has been confirmed that the diffusion resistance of the cell can be improved by improving the conductive path, thereby increasing the life durability of the lithium secondary battery.

Description of Reference Numerals

[0187] 10 ··· Negative electrode current collector layer 20 ··· Negative electrode active material layer 30 ··· Separator 40 ··· Positive electrode active material layer 50 ··· Positive electrode current collector layer 100 ··· Negative electrode for lithium secondary battery 200 ··· Positive electrode for lithium secondary battery

Claims

1. A negative electrode composition comprising a silicon-based active material, a negative electrode conductive material, and a negative electrode binder, wherein the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, the silicon-based active material contains 1 part by weight or more and 5 parts by weight or less of silicon-based particles having a particle size of 1 μm or less based on 100 parts by weight of the silicon-based active material, the silicon-based active material satisfies the particle size ratios of the following Formula 1 and Formula 2: Negative electrode composition [Formula 1] 20 ≤ (X1 / Y) × 100 (%) [Formula 2] (X2 / Y) × 100 (%) ≤ 230 In Formula 1 and Formula 2 above, X1 represents the D5 particle size of the silicon-based active material, X2 represents the D95 particle size of the silicon-based active material, Y represents the median particle size (D50) of the silicon-based active material.

2. The negative electrode composition according to Claim 1, wherein the silicon-based particles include one or more selected from the group consisting of SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloys.

3. The negative electrode composition according to Claim 1, wherein the silicon-based particles include one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and the silicon-based active material contains 70 parts by weight or more of the SiO x (x = 0) based on 100 parts by weight of the silicon-based active material.

4. The negative electrode composition according to Claim 1, wherein the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

5. The negative electrode composition according to Claim 1, wherein the silicon-based active material satisfies the particle size ratio of the following Formula 3: [Formula 3] 10 ≤ (X1 / X2) × 100 (%) In Formula 3 above, X1 represents the D5 particle size of the silicon-based active material, X2 represents the D95 particle size of the silicon-based active material.

6. The negative electrode composition according to Claim 1, wherein the silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less have a half-value width of 1 μm or more and 5 μm or less.

7. The negative electrode composition according to Claim 1, wherein the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material.

8. A method for manufacturing a negative electrode composition, comprising the steps of mixing a negative electrode conductive material and a negative electrode binder to form a mixture, adding water to the mixture and performing first mixing, and adding a silicon-based active material to the first-mixed mixture and performing second mixing. ​ The silicon-based active material contains silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less, and contains 1 to 5 parts by weight of silicon-based particles having a particle size of 1 μm or less based on 100 parts by weight of the silicon-based active material, The silicon-based active material satisfies the particle size ratio of the following Formula 1 and Formula 2, Method for manufacturing a negative electrode composition: [Formula 1] 20 ≤ (X1 / Y) × 100 (%) [Formula 2] (X2 / Y) × 100 (%) ≤ 230 In Formula 1 and Formula 2 above, X1 represents the D5 particle size of the silicon-based active material, X2 represents the D95 particle size of the silicon-based active material, Y represents the median particle size (D50) of the silicon-based active material.

9. The step of the first mixing and the step of the second mixing are steps of mixing at 2,000 rpm to 3,000 rpm for 10 to 60 minutes, The method for manufacturing a negative electrode composition according to Claim 8.

10. A negative electrode current collector layer, and A negative electrode active material layer including the negative electrode composition according to any one of Claims 1 to 7 formed on one or both sides of the negative electrode current collector layer, A negative electrode for a lithium secondary battery including.

11. The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, The thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less, The negative electrode for a lithium secondary battery according to Claim 10.

12. A positive electrode, The negative electrode for a lithium secondary battery according to Claim 10, A separator provided between the positive electrode and the negative electrode, and An electrolyte, A lithium secondary battery including.

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