Anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode

Abstract

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

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0076784, filed with the Korean Intellectual Property Office on June 23, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields in this area is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses such electrochemical energy is a secondary battery, and the range of its use is expanding more and more.

[0005] With the development of mobile device technologies and the increase in demand, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles with a high discharge capacity.

[0007] In particular, in response to the recent demand for high-density energy batteries, active research is being conducted into methods of increasing capacity using silicon-based compounds such as Si / C and SiOx as anode active materials, which have a capacity 10 times greater than that of graphite-based materials. While silicon-based compounds, which are high-capacity materials, have a higher capacity than conventionally used graphite, they suffer from the problem of rapid volume expansion during charging, which disrupts the conductive path and reduces battery performance.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as methods for adjusting the driving potential, methods for additionally coating a thin film on the active material layer, methods for suppressing volume expansion itself such as methods for adjusting the particle size of the silicon-based compound, and various methods for preventing the conductive path from being broken. However, these methods have limitations in their application because they may actually degrade battery performance, and there are still limitations in the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0009] In particular, research into binder composition for volume expansion has been conducted, and research is being conducted on the use of binder polymers with strong lateral stress to suppress the volume expansion of negative electrode active materials, which have large volume changes due to charging and discharging. However, these binder polymers alone have limitations in suppressing the increase in electrode thickness due to the contraction and expansion of negative electrode active materials and the resulting performance degradation of lithium secondary batteries.

[0010] In order to solve the problem of volume expansion of a negative electrode having such a silicon-based active material, an aqueous binder that has both dispersibility and adhesiveness has been used. While the aqueous binder has the advantage of improving dispersibility, it has the problem of breaking electrical contact between the active materials due to volume expansion of the active materials, which results in reduced lifespan, since cycling is performed in a state where the elongation is reduced.

[0011] Furthermore, a rubber-based binder may be used to improve the battery life. However, in the case of a silicon-based active material, if only a rubber-based binder is used, the rigidity of the binder is not sufficient, and this is also known to have limitations.

[0012] In addition, water-based binders have the problem of shrinking due to heat when the electrode dries, which is a disadvantage in the process, but SBR rubber-based binders, which have excellent flexibility, have the advantage of being less prone to shrinking when dried.

[0013] Therefore, when using high-capacity materials to manufacture high-capacity batteries, research is needed into binders that do not break the conductive network due to the volume expansion of the active material and have excellent adhesive strength. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Patent Publication No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0015] The present application relates to a binder that has excellent adhesive strength to a negative electrode current collector without disrupting the conductive network due to volume expansion of a silicon-based active material when manufacturing a high-capacity, high-density negative electrode. The present application has confirmed through research that the above-mentioned problems can be solved by adjusting the Young's modulus and tensile strain value of the binder and adjusting the binder content. Therefore, the present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0016] 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 negative electrode binder has a Young's modulus of 10 3 MPa or more, and a second binder having a tensile deformation rate (strain) of 15% or more, wherein the negative electrode binder satisfies the following formula 1: [Formula 1] 1≦X / Y<4 In the formula 1, Y represents the weight part of the first binder based on 100 parts by weight of the negative electrode binder; X represents the weight part of the second binder based on 100 weight parts of the negative electrode binder.

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

[0018] Finally, there is provided a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0019] The anode composition according to one embodiment of the present invention is characterized in that it uses a silicon-based active material, which is a high-capacity material, to fabricate a high-capacity battery, and solves the problem of volume expansion of the silicon-based active material by using a specific anode binder.

[0020] In particular, the negative electrode binder has a Young's modulus of 10 3 MPa or more, and a second binder having a tensile deformation rate (strain) of 15% or more, and the negative electrode binder satisfies the range of specific formula 1.

[0021] Specifically, the negative electrode composition according to the present application improves dispersibility for dispersing active materials even when silicon-based active materials are used, and also contains a first binder and a second binder of specific compositions to improve adhesive strength, thereby solving the problems of conductive network disconnection due to adhesive strength and volume expansion in the initial and later stages of batteries using silicon-based active materials.

[0022] That is, the negative electrode composition according to the present application has a high content of silicon-based active material particles, thereby enabling a high-capacity and high-density negative electrode to be obtained. Also, in order to solve problems such as volume expansion caused by having a high content of silicon-based active material particles, a binder with a specific composition and content is used to solve the problems, which is a main object of the present invention. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. [Figure 2] 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. [Figure 3] FIG. 1 is a diagram showing a method for evaluating curl in examples and comparative examples according to the present application. DETAILED DESCRIPTION OF THE INVENTION

[0024] Before describing the present invention, some terms will first be defined. In this specification, when a part is said to "comprise" a certain component, this does not mean that it may further include other components, unless specifically stated to the contrary, but rather that it does not exclude other components.

[0025] In this specification, "p to q" means "not less than p and not more than q." In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area can mean the specific surface area measured by the above-mentioned measurement method.

[0026] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, particle size distribution may also be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). When the particles pass through a laser beam, the difference in diffraction pattern due to particle size is measured to calculate the particle size distribution.

[0027] As used herein, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. As used herein, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

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

[0029] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0030] In one embodiment of the present application, the Young's modulus is measured by placing the binder solution in a coated container and drying it at room temperature for a long period of time to remove moisture. The film from which the moisture has evaporated is then vacuum-dried at 130°C for 10 hours, which corresponds to the electrode drying temperature, to obtain a dried film. The dried film is then cut or punched into a sample shape measuring 6 mm x 100 mm, and the tensile strength (Young's modulus) can be measured using UTM equipment.

[0031] The Young's modulus may vary depending on the measurement method, speed, and measurement conditions of the binder, but the Young's modulus of the binder may refer to a value measured in a drying room at a dew point of -5°C to 10°C and a temperature of about 20°C to 22°C.

[0032] In this application, the dew point refers to the temperature at which condensation begins when humid air is cooled, and the partial pressure of water vapor in the air becomes equal to the saturated vapor pressure of water at that temperature. In other words, it can refer to the temperature at which dew begins to form when the temperature of a gas containing water vapor is lowered to 100% humidity.

[0033] A dew point of -5°C to 10°C and a temperature of about 20°C to 22°C can be defined as a normal dry room, and at this time, the humidity corresponds to a very low level.

[0034] In one embodiment of the present application, the tensile strain is measured by placing the binder solution in a coated container and drying it at room temperature for a long period of time to remove moisture. The film from which the moisture has evaporated is then vacuum dried at 130°C for 10 hours, matching the electrode drying temperature, to obtain a dried film. The dried film is then cut or punched into a sample shape measuring 6 mm x 100 mm, and the tensile strain can be measured using UTM equipment.

[0035] The tensile deformation rate of the binder varies depending on the measurement method, speed, and measurement condition of the binder, but the tensile deformation rate (strain) of the binder is the same as the measurement conditions for the Young's modulus.

[0036] DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily understand and practice the present invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the following description.

[0037] 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 negative electrode binder has a Young's modulus of 10 3 MPa or more, and a second binder having a tensile deformation rate (strain) of 15% or more, wherein the negative electrode binder satisfies the following formula 1:

[0038] [Formula 1] 1≦X / Y<4 In the formula 1, Y represents the weight part of the first binder based on 100 parts by weight of the negative electrode binder; X represents the weight part of the second binder based on 100 weight parts of the negative electrode binder.

[0039] Specifically, the negative electrode composition according to the present application, even when using a silicon-based active material, improves the dispersibility for dispersing the active material, and also includes a first binder and a second binder having a specific composition to improve the adhesion, thereby solving the problems of adhesion in the initial and later stages of a battery using a silicon-based active material and disconnection of the conductive network due to volume expansion.

[0040] In one embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0041] The active material of the present invention includes a silicon-based active material. The silicon-based active material may be SiOx, Si / C, or Si. SiOx may include a compound represented by SiOx (0 ≤ x < 2). In the case of SiO2, since it does not react with lithium ions and cannot store lithium, x is preferably within the above range. The silicon-based active material may be Si / C or Si composed of a composite of Si and C. Also, two or more of the above silicon-based active materials may be mixed and used. The negative electrode active material may further include a carbon-based active material together with the above silicon-based active material. The carbon-based active material can contribute to the improvement of the cycle characteristics or battery life performance of the negative electrode or secondary battery of the present invention.

[0042] Generally, it is known that a silicon-based active material has a capacity more than 10 times higher than that of a carbon-based active material. Thus, when applying a silicon-based active material to a negative electrode, it is expected that an electrode having a high level of energy density can be realized even with a thin thickness.

[0043] In one embodiment of the present application, there is provided a negative electrode composition in which the silicon-based active material includes 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 silicon-based active material.

[0044] In another embodiment, the silicon-based active material may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0045] The silicon-based active material according to the present application contains 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material, and when compared with a silicon-based active material using a SiOx (0 < x < 2) series as the main substance, the theoretical capacity is much higher than that of the silicon-based active material of the present application. That is, when using an active material of the SiOx (0 < x < 2) series, no matter what treatment is performed on the active material itself, it is impossible to realize conditions equivalent to the charge and discharge capacity compared with the case of having the silicon-based active material of the present invention.

[0046] In one embodiment of the present application, the silicon-based active material may use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material can mean, as described above, containing pure Si particles (SiOx (x = 0)) not combined with other particles or elements within the above range based on 100 parts by weight of the entire silicon-based active material.

[0047] Compared with the conventionally used graphite-based active material, the silicon-based active material has a significantly higher capacity, and attempts to apply it have increased. However, the volume expansion rate during the charge and discharge process is high, and it has remained at the level of using a small amount mixed with the graphite-based active material.

[0048] Therefore, in order to improve the capacity performance, the present invention uses a binder under specific conditions in order to solve the problems of maintaining the conductive path due to the above-mentioned volume expansion and maintaining the binding of the conductive material, binder, and active material while using a high content of the silicon-based active material as the negative electrode active material.

[0049] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within this range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This facilitates dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit of the range, the contact area between the silicon particles and the conductive material is excellent due to the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of maintaining a conductive network and improving capacity retention. Meanwhile, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0050] In one embodiment of the present application, the silicon-based active material usually 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~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is measured (using nitrogen) in accordance with DIN 66131. ​​The DIN 66131 measurement method corresponds to a method for measuring pore size by the amount of adsorption / desorption of nitrogen molecules.

[0051] In one embodiment of the present application, the silicon-based active material may be, for example, in crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or platelet-shaped particles. Alternatively, the silicon particles may have a fibrous structure or may exist in the form of a silicon-containing thin film or coating, but this is less preferred.

[0052] In one embodiment of the present application, there is provided a negative electrode composition, wherein the silicon-based active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0053] In yet another embodiment, the silicon-based 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.

[0054] The negative electrode composition according to the present application uses a specific conductive material and binder that can control the volume expansion rate during charge and discharge even when a silicon-based active material with significantly high capacity is used within the above range, so that the negative electrode performance is not reduced even when the above range is included, and the negative electrode composition has the characteristic of excellent output characteristics during charge and discharge.

[0055] In one embodiment of the present application, the silicon-based active material may have a non-spherical morphology, and the sphericity thereof 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.

[0056] In this application, the circularity is determined by the following formula 1-1, where A is the area and P is the perimeter. [Formula 1-1] 4πA / P 2

[0057] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based compounds into negative electrode active materials have recently been increasing in response to growing demand for high-capacity batteries. However, even if the properties of silicon-based active materials are adjusted as described above, silicon-based compounds can experience rapid volume expansion during charge / discharge processes, potentially disrupting the conductive pathways formed within the negative electrode active material layer.

[0058] Therefore, in one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of dot-like conductive materials, planar conductive materials, and linear conductive materials.

[0059] In one embodiment of the present application, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode and has conductivity without inducing a chemical change. Specifically, the dot-like 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 derivatives, and preferably includes carbon black in view of realizing high conductivity and excellent dispersibility.

[0060] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more and 70m 2 / g or less, preferably 45m 2 / g or more and 65m 2 / g or less, more preferably 50m 2 / g or more and 60m 2 / g or less.

[0061] In one embodiment of the present application, the dot-like conductive material can satisfy a 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.

[0062] In particular, when the functional group content of the dot-like conductive material satisfies the above range, the functional groups present on the surface of the dot-like conductive material allow the dot-like conductive material to be smoothly dispersed in water as a solvent. In particular, the present invention uses silicon particles and a specific binder to reduce the functional group content of the dot-like conductive material, thereby providing an excellent effect in improving dispersibility.

[0063] In one embodiment of the present application, the silicon-based active material is characterized by including a dot-like conductive material having a functional group content within the above range, and the functional group content can be adjusted by the degree of heat treatment of the dot-like conductive material.

[0064] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0065] In one embodiment of the present application, the conductive material may include a planar conductive material. The planar conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode, while simultaneously suppressing the disconnection of conductive paths due to volume expansion. The planar conductive material may be referred to as a planar conductive material, a plate-shaped conductive material, or a bulk-type conductive material.

[0066] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0067] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size is within this range, the particle size is sufficient to facilitate dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when dispersing using the same equipment and time, the dispersion effect is excellent.

[0068] In one embodiment of the present application, there is provided a negative electrode composition in which the planar conductive material has a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0069] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material having a high BET specific surface area; or a sheet conductive material having a low specific surface area.

[0070] In one embodiment of the present application, the planar conductive material may be a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area without any restrictions. However, the planar conductive material of the present application may be particularly susceptible to dispersion effects that may affect electrode performance to some extent, and it is particularly preferable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0071] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​1 m 2 / g or more.

[0072] In another embodiment, the sheet conductive material has a BET specific surface area of ​​1 m 2 / g or more and 500m 2 / g or less, and preferably 5m 2 / g or more and 300m 2 / g or less, more preferably 5m 2 / g or more and 250m 2 / g.

[0073] The sheet conductive material according to the present application may be a sheet conductive material with a high specific surface area; or a sheet conductive material with a low specific surface area.

[0074] In another embodiment, the sheet conductive material is a sheet conductive material having a high specific surface area and a BET specific surface area of ​​50 m 2 / g or more and 500m 2 / g or less, preferably 80m 2 / g or more and 300m 2 / g or less, more preferably 100m 2 / g or more and 300m 2 / g or less can be satisfied.

[0075] In another embodiment, the sheet conductive material is a sheet conductive material having a low specific surface area, and a BET specific surface area of ​​1 m 2 / g or more and 40m 2 / g or less, preferably 5m 2 / g or more and 30m 2 / g or less, more preferably 5m 2 / g or more and 25m 2 / g or less can be satisfied.

[0076] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged parallel to each other or twisted with the longitudinal axes of the carbon nanotube units substantially aligned in the same direction, forming a bundle or rope. The carbon nanotube units each have a cylindrical graphite sheet with a nanosized diameter and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the carbon nanotube unit may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication and can smoothly form a conductive network within the negative electrode, thereby improving the conductivity of the negative electrode.

[0077] In one embodiment of the present application, the negative electrode composition is provided in which the negative electrode conductive material is present in an amount of 0.1 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode composition. Alternatively, the negative electrode conductive material may be present in an amount of, for example, 10 parts by weight or more and 40 parts by weight or less.

[0078] In yet another embodiment, the negative electrode conductive material may comprise, based on 100 parts by weight of the negative electrode composition, 0.1 parts by weight to 40 parts by weight, preferably 0.2 parts by weight to 30 parts by weight, more preferably 0.4 parts by weight to 25 parts by weight, and most preferably 0.4 parts by weight to 10 parts by weight.

[0079] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a planar conductive material and a linear conductive material.

[0080] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material comprises, based on 100 parts by weight of the negative electrode conductive material, 80 parts by weight or more and 99.9 parts by weight or less of the sheet conductive material; and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material.

[0081] In another embodiment, the negative electrode conductive material may contain 80 parts by weight or more and 99.9 parts by weight or less, preferably 85 parts by weight or more and 99.9 parts by weight or less, and more preferably 95 parts by weight or more and 98 parts by weight or less of the sheet conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0082] In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.1 parts by weight or more and 15 parts by weight or less, and more preferably 0.2 parts by weight or more and 5 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0083] In one embodiment of the present application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each of which satisfies the above-mentioned composition and ratio, so that the life characteristics of conventional lithium secondary batteries are not significantly affected. In particular, when the negative electrode conductive material includes a planar conductive material and a linear conductive material, the number of points at which charging and discharging are possible increases, resulting in excellent output characteristics at a high C-rate and a reduced amount of gas generation at high temperatures.

[0084] In one embodiment of the present application, the negative electrode conductive material may be made of a linear conductive material. In particular, when a linear conductive material is used alone, it is possible to simplify the tortuosity of the electrode, which is a problem with silicon-based negative electrodes, and improve the electrode structure, thereby reducing the resistance to lithium ion migration within the electrode.

[0085] In one embodiment of the present application, when the negative electrode conductive material contains only a linear conductive material, the negative electrode conductive material may contain 0.1 parts by weight or more and 5 parts by weight or less, preferably 0.2 parts by weight or more and 3 parts by weight or less, and more preferably 0.4 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0086] The anode conductive material according to the present application has a completely different structure from the cathode conductive material used in the cathode. That is, the anode conductive material according to the present application controls the contact points between the silicon-based active material, which experiences a large volume expansion of the electrode during charging and discharging, while the cathode conductive material acts as a buffer during rolling and also provides some conductivity, and thus has a completely different structure and role from the anode conductive material of the present invention.

[0087] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0088] In one embodiment of the present application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material typically used as a negative electrode active material. 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-like shape to facilitate the storage and release of lithium ions.

[0089] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, which may be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not function to store and release lithium, but rather to ensure a planar conductive path within the negative electrode active material layer.

[0090] In other words, in this application, the use of plate-like graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material contained therein has high capacity characteristics for storing and releasing lithium and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0091] Meanwhile, in the present application, the term "carbon-based active material is used as an active material" means that the carbon-based active material is processed into a dotted or spherical shape and used as a material that stores or releases lithium.

[0092] In one embodiment of the present application, the negative electrode binder has a Young's modulus of 10 3 MPa or more, and a second binder having a tensile strain of 15% or more.

[0093] In one embodiment of the present application, there is provided a negative electrode composition, wherein the first binder includes one or more selected from the group consisting of PAA, PAN, and PAM, and the second binder is a rubber-based binder.

[0094] In one embodiment of the present application, the negative electrode binder has a Young's modulus of 10 3 MPa or more of a first binder.

[0095] In another embodiment, the negative electrode binder has a Young's modulus of 1×10 3 MPa or more, preferably 2×10 3 MPa, more preferably 5×10 3 MPa or more, most preferably 9 x 10 3 MPa or more, and 3 MPa or less, preferably 18 × 10 3 MPa or less, more preferably 15×10 3 MPa or less.

[0096] In still another embodiment, the Young's modulus of the negative electrode binder is 3×10 3 MPa or more, 4 x 10 3 MPa or more, 6×10 3 MPa or more, 7 x 10 3 MPa or more, 8 x 10 3 MPa or more, 10 x 10 3 MPa or more, 19 x 10 3 MPa or less, 17×10 3 MPa or less, 16×10 3 MPa or less, 14×10 3 MPa or less, 13×10 3 MPa or less, 12×10 3MPa or less, including all of the various combinations of ranges set forth above.

[0097] The first binder has both dispersibility for dispersing the negative electrode active material in a negative electrode slurry containing the negative electrode composition and adhesive strength for binding the negative electrode current collector layer and the negative electrode active material layer after drying, and corresponds to a binder with a relatively low adhesive strength. That is, the first binder according to the present application may refer to a binder having a surface-adhesive form, including an aqueous binder that satisfies the Young's modulus.

[0098] The first binder is a binder suitable for lithium secondary batteries in which a silicon active material that exhibits large volume expansion during charge and discharge is used in the negative electrode. If the first binder is below the lower limit of the range, it is difficult to effectively control the volume expansion of silicon. If the first binder is above the upper limit of the range, the binder is likely to crack during charge and discharge due to its excessive rigidity.

[0099] In one embodiment of the present application, the aqueous binder is soluble in an aqueous solvent such as water and includes at least one selected from the group consisting of polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM). Preferably, the aqueous binder may include at least one selected from the group consisting of polyacrylic acid (PAA) and polyacrylamide (PAM), more preferably polyacrylic acid (PAA) and polyacrylamide (PAM), in order to provide excellent resistance to volumetric expansion / contraction of the silicon-based active material.

[0100] More specifically, the first binder may be a PAM-based binder. In this case, the PAM-based binder is a binder mainly composed of PAM, and the ratio of PAM, PAA, and PAN may be adjusted, and the composition may be appropriately changed to satisfy the above-mentioned Young's modulus.

[0101] The first binder may include a binder in which hydrogen atoms in the first binder are substituted with Li, Na, Ca, or the like, in order to allow the first binder to be better dispersed in an aqueous solvent such as water during preparation of a negative electrode slurry for forming a negative electrode active material layer and to more smoothly coat the active material and improve binding strength.

[0102] The first binder is hydrophilic and insoluble in electrolytes or electrolytic solutions typically used in secondary batteries. These properties can impart strong stress or tensile strength to the first binder when applied to anodes or lithium secondary batteries, thereby effectively suppressing the volume expansion / contraction problem of silicon-based active materials due to charge / discharge.

[0103] In one embodiment of the present application, there is provided a negative electrode composition, wherein the weight average molecular weight of the first binder is 100,000 g / mol or more and 2,000,000 g / mol or less.

[0104] More preferably, it may be 500,000 g / mol or more and 1,500,000 g / mol or less.

[0105] In one embodiment of the present application, the second binder may have a tensile strain of 15% or more, preferably 20% or more, more preferably 30% or more, and most preferably 40% or more, and may have a tensile strain of 300% or less, preferably 200% or less, and more preferably 150% or less.

[0106] In another embodiment, the tensile strain may be 25% or more, 35% or more, 45% or more, 75% or less, 65% or less, or 55% or less, and various combinations of these ranges may be included.

[0107] As described above, if the tensile strain value of the second binder is below the above range, the stress is high and it is difficult to effectively control the volume expansion of the silicon, and if it exceeds the above range, it is difficult to effectively control the adhesive strength between the electrodes.

[0108] The first binder satisfies the above modulus range and has strong stress, so if the first binder is used alone, there is a risk of bending of the negative electrode, cracking due to bending, and deterioration of life characteristics. The second binder is well soluble in the electrolyte or electrolytic solution typically used in secondary batteries, and when used together with the first binder, it can reduce the stress of the first binder to a certain level.

[0109] Therefore, the negative electrode composition of the present invention has the following characteristics: by using an anode binder containing the first binder and the second binder in a specific weight ratio, the problem of volume expansion / contraction of the silicon-based active material can be effectively resolved, thereby improving the life characteristics; during the manufacture of a thin film anode, the bending problem can be resolved, and the adhesive strength can be improved.

[0110] In this case, the tensile strain value of the second binder can be realized within the above range by adjusting the ST / BD ratio of the SBR binder within an appropriate range.

[0111] In one embodiment of the present application, the second binder may be defined as a material different from the first binder that is not well soluble in an aqueous solvent such as water but can be smoothly dispersed in an aqueous solvent. Specifically, the second binder having a tensile strain of 15% or more may include at least one selected from the group consisting of styrene butadiene rubber (SBR), hydrogenated nitrile butadiene rubber (HNBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, and fluororubber. Preferably, in terms of easy dispersion and excellent phase stability, the second binder may include at least one selected from the group consisting of styrene butadiene rubber and hydrogenated nitrile butadiene rubber, more preferably styrene butadiene rubber.

[0112] Generally, the second binder is a material that has a much higher electrolyte wettability than the first binder. When the second binder is located near the surface of the silicon-based anode, it can quickly supply the FEC solvent and LiPF6 salt that can form the SEI layer, thereby reducing the anode resistance.

[0113] In one embodiment of the present application, the formula 1 may satisfy 1≦X / Y<4, preferably 1.1≦X / Y<3.9, and more preferably 1.2≦X / Y<3.8.

[0114] More specifically, the ratios may be 1.3≦X / Y<3.7, 1.4≦X / Y<3.6, 1.5≦X / Y<3.5, 1.6≦X / Y<3.4, ​​1.7≦X / Y<3.3, 1.8≦X / Y<3.2, 1.9≦X / Y<3.1, 2.0≦X / Y<3.0, and 1.2≦X / Y<2.0.

[0115] In one embodiment of the present application, X is 50 parts by weight or more and 95 parts by weight or less, based on 100 parts by weight of the negative electrode binder, and Y is 5 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the negative electrode binder.

[0116] In another embodiment, X may be 50 parts by weight or more and 95 parts by weight or less, preferably 55 parts by weight or more and 90 parts by weight or less, more preferably 55 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the negative electrode binder. Alternatively, X may be 50 parts by weight or more and 70 parts by weight or less, 55 parts by weight or more and 67 parts by weight or less, or 60 parts by weight or more and 67 parts by weight or less.

[0117] In another embodiment, Y may be 5 parts by weight or more and 50 parts by weight or less, preferably 10 parts by weight or more and 45 parts by weight or less, more preferably 20 parts by weight or more and 45 parts by weight or less, based on 100 parts by weight of the negative electrode binder, or may be 33 parts by weight or more and 45 parts by weight or less, 35 parts by weight or more and 45 parts by weight or less, or 40 parts by weight or more and 45 parts by weight or less.

[0118] As described above, the negative electrode binder according to the present application has the characteristics of improving dispersibility and solving the problem of adhesive strength even when using a silicon-based active material, since the first binder and the second binder satisfy the above contents.

[0119] The first binder has a high modulus within the above range and therefore has a high stress. Therefore, if the first binder is used alone, there is a risk of bending of the negative electrode, cracking due to bending, and deterioration of life characteristics. The second binder is well soluble in the electrolyte or electrolytic solution typically used in secondary batteries, and when used together with the first binder, it can reduce the stress of the first binder to a certain level.

[0120] Therefore, the negative electrode composition of the present invention has the following characteristics: by using an anode binder containing the first binder and the second binder in a specific weight ratio, the problem of volume expansion / contraction of the silicon-based active material can be effectively resolved, thereby improving the life characteristics; the problem of bending during the manufacture of a thin film negative electrode can be resolved; and the adhesive strength can also be improved.

[0121] Furthermore, when the negative electrode binder and the negative electrode conductive material contain a sheet conductive material and a linear conductive material, the adhesive strength problem can be improved and the negative electrode internal resistance can also be improved.

[0122] In one embodiment of the present application, the negative electrode binder may include at least 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, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0123] In one embodiment of the present application, there is provided a negative electrode composition, in which the negative electrode binder is contained in an amount of 1 part by weight to 20 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0124] In one embodiment of the present application, the negative electrode binder may be included in an amount of 20 parts by weight or less, preferably 15 parts by weight or less, or may be 1 part by weight or more, 5 parts by weight or more, or 10 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0125] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer comprising the negative electrode composition according to the present application.

[0126] 1 is a diagram showing the laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0127] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by coating one or both sides of a current collector with a negative electrode slurry containing the negative electrode composition.

[0128] In one embodiment of the present application, the negative electrode slurry may include a negative electrode composition; and a slurry solvent.

[0129] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0130] In another embodiment, the solid content of the negative electrode slurry may satisfy the range of 5% to 40%, preferably 7% to 35%, more preferably 10% to 30%.

[0131] The solid content of the negative electrode slurry may refer to the content of the negative electrode composition contained in the negative electrode slurry, or may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0132] When the solid content of the negative electrode slurry satisfies the above range, the viscosity is appropriate during the formation of the negative electrode active material layer, and the caking phenomenon of particles of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0133] In one embodiment of the present application, the negative electrode current collector layer typically has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, plastic carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be provided with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0134] 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.

[0135] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0136] In one embodiment of the present application, the porosity of the negative electrode active material layer can satisfy the range of 10% or more and 60% or less.

[0137] In another embodiment, the porosity of the negative electrode active material layer can satisfy the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0138] The porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to the present application are contained in specific compositions and content portions to satisfy the above range, thereby providing the electrode with appropriate ranges of electrical conductivity and resistance.

[0139] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the adhesive strength of a surface of the negative electrode active material layer in contact with the negative electrode current collector layer satisfies 100 gf / 5 mm or more and 500 gf / 5 mm or less under conditions of 25°C and normal pressure.

[0140] In yet another embodiment, the adhesive strength of the surface of the negative electrode active material layer in contact with the negative electrode current collector layer may be 100 gf / 5 mm or more and 500 gf / 5 mm or less, preferably 300 gf / 5 mm or more and 450 gf / 5 mm or less, more preferably 350 gf / 5 mm or more and 430 gf / 5 mm or less, at 25°C and normal pressure.

[0141] In particular, the negative electrode according to the present application includes a specific negative electrode binder in the negative electrode composition, thereby improving adhesion as described above. Furthermore, even when the silicon-based active material expands and contracts repeatedly during repeated charging and discharging of the negative electrode, the specific composition of the negative electrode binder and negative electrode conductive material maintains the conductive network, preventing disconnection and suppressing an increase in resistance.

[0142] The adhesive strength was measured using a peel strength tester with 3M 9070 tape at a 90° angle and a speed of 5 mm / s. Specifically, one side of the negative electrode active material layer of the negative electrode for the lithium secondary battery was attached to one side of a slide glass (3M 9070 tape) with an adhesive film attached. Then, a 2 kg rubber roller was rolled back and forth 5 to 10 times to adhere the layer, and the adhesive strength (peel strength) was measured at a 90° angle and a speed of 5 mm / s. The adhesive strength was measured at 25°C and atmospheric pressure.

[0143] Specifically, the adhesive strength was measured on a 5 mm x 15 cm electrode at 25°C and normal pressure.

[0144] In one embodiment of the present application, normal pressure may refer to pressure in a state where no specific pressure is applied or reduced, and may be used in the same sense as atmospheric pressure. Usually, normal pressure may be expressed as 1 atmosphere.

[0145] In one embodiment of the present application, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0146] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are shown stacked with a separator 30 sandwiched between them.

[0147] A secondary battery according to an embodiment of the present specification may include the above-described negative electrode for a lithium secondary battery. 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 above-described negative electrode. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0148] 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 including the positive electrode active material.

[0149] The positive electrode current collector in the positive electrode is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, plastic carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0150] 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; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMn 2-c3 M c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (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 can be at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion. The positive electrode may be metallic lithium (Li-metal).

[0151] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material described above.

[0152] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0153] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), polyvinylidene 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, and various copolymers thereof. These may be used alone or in combination.

[0154] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator with low resistance to electrolyte ion movement and excellent humidifying ability for the electrolyte is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. Furthermore, a coated separator containing a ceramic component or a polymeric material to ensure heat resistance or mechanical strength may be used, and may be selectively used in a single-layer or multi-layer structure.

[0155] Examples of the electrolyte include 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 manufacturing lithium secondary batteries, but are not limited to these. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0156] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0157] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably used because they are high-viscosity organic solvents with high dielectric constants and good dissociation of lithium salts. Furthermore, when such cyclic carbonates are mixed with chain carbonates such as dimethyl carbonate and diethyl carbonate, which have low viscosity and low dielectric constants, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and therefore these cyclic carbonates are more preferably used.

[0158] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be 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 - One or more selected from the group consisting of:

[0159] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in the capacity of the battery, and improving the discharge capacity of the battery.

[0160] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore may be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0161] In one embodiment of the present application, a method for manufacturing a negative electrode using the negative electrode composition is provided. More specifically, a solvent is added to the negative electrode composition to obtain a negative electrode slurry. The negative electrode slurry is applied to at least one surface of a negative electrode current collector layer to form a negative electrode active material layer. The negative electrode active material layer coated on the negative electrode current collector layer is then dried and rolled to manufacture a negative electrode.

[0162] In the present application, the solvent contained in the negative electrode slurry may be, for example, distilled water. In one embodiment of the present application, the negative electrode slurry may have a solid content of 5% or more and 40% or less.

[0163] In another embodiment, the negative electrode slurry may have a solids content range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0164] The solid content of the negative electrode slurry may refer to the amount of the negative electrode composition contained in the negative electrode slurry, or may refer to the amount of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0165] When the negative electrode slurry satisfies the solid content range of 5% to 40%, the negative electrode active material layer has an appropriate viscosity when formed, thereby minimizing particle agglomeration of the negative electrode active material to form an electrode composition, thereby enabling efficient formation of the negative electrode active material layer.

[0166] Below, preferred examples are presented to help understand the present invention, but these examples are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present description, and it is natural that such changes and modifications fall within the scope of the claims. [Example]

[0167] <Production of negative electrode composition> Negative electrode compositions having the compositions and contents shown in Table 1 below were prepared.

[0168] [Table 1]

[0169] In Table 1, the silicon-based active material is Si (average particle size (D50): 5 μm), and the plate-shaped conductive material A has a BET specific surface area of ​​17 m 2 / g, D10: 1.7 μm, D50: 3.5 μm, D90: 6.8 μm, and the SWCNTs have a BET specific surface area of ​​1000 m 2 / g~1500m 2 / g and an aspect ratio of 10,000 or more were used.

[0170] In addition, in Table 1, as the first binder, PAM-1 has a Young's modulus of 15×10 3 MPa (=15GPa), and PAM-2 has a Young's modulus of 9×10 3 MPa (9GPa), and PAN has a Young's modulus of 10 2 MPa.

[0171] Also, in Table 1, as the second binder, SBR-1 is a binder with a tensile deformation rate (strain) of 60%, SBR-2 is a binder with a tensile deformation rate (strain) of 40%, and SBR-3 is a binder with a tensile deformation rate (strain) of 10%.

[0172] In this case, the Young's modulus of the first binder was achieved by adjusting the mixing ratio of PAA and PAN with a binder having PAM as the main component, and the tensile deformation rate (Strain) of the second binder was achieved by adjusting the ST / BD ratio with an SBR binder to achieve the same range.

[0173] The weight average molecular weight of the first binder is 5.0×10 5~1.5×10 6 Although the weight average molecular weight of the second binder before cross-linking can be measured, the weight average molecular weight is not measured because the second binder is in the form of spherical particles in practical use.

[0174] In Table 1, the content may refer to the weight ratio (parts by weight) of each component based on 100 parts by weight of the total negative electrode composition.

[0175] Anode manufacturing The negative electrode composition having the composition shown in Table 1 was added to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry (solid concentration: 25 wt %).

[0176] Then, a negative electrode with a thickness of 38 μm was applied on a copper foil (Cu foil) with a thickness of 8 μm to a weight of 76.34 mg / 25 cm. 2 After coating the negative electrode active material layer on the coated substrate, the coated substrate was dried at 130° C. for 12 hours and rolled to a porosity of 40% to prepare a negative electrode.

[0177] <Secondary battery manufacturing> As the positive electrode active material, 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 a positive electrode slurry to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0178] The positive electrode current collector was an aluminum current collector (thickness: 12 μm) and the positive electrode slurry was applied to both sides of the aluminum current collector at a rate of 537 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to prepare a positive electrode (thickness: 77 μm, porosity: 26%).

[0179] A polyethylene separator was interposed between the positive electrode and the negative electrode of Example 1 and Comparative Example, and an electrolyte was injected therein to prepare a lithium secondary battery.

[0180] The electrolyte was prepared by adding 3 wt% vinylene carbonate (based on the total weight of the electrolyte) to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0181] Mono-cells were fabricated in the same manner as described above, except that the negative electrodes of the Examples and Comparative Examples were used, and life characteristics were evaluated in the range of 4.2-3.0V.

[0182] Experimental example 1: Evaluation of mono-cell life characteristics at room temperature (25℃, 4.2-3.0V) The secondary batteries including the negative electrodes prepared in the Examples and Comparative Examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate the capacity retention rate. The secondary batteries were subjected to a cycle test at 4.2-3.0 V, 1 C / 0.5 C, and the number of cycles at which the capacity retention rate reached 80% was measured. Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100 The results are shown in Table 2 below.

[0183] Experimental Example 2: Measurement and Evaluation of Mono-cell Resistance Increase Rate (250 cycles, @SOC50, discharge) In the test 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, and then the resistance was measured by discharging at 2.5C pulses at SOC50, and the resistance increase rate was compared and analyzed. For the resistance increase rate measurement evaluation, data at 250 cycles was calculated, and the results are shown in Table 2 below.

[0184] Experimental Example 3: Evaluation of high temperature life characteristics of mono-cell (45℃, 4.2-3.0V) The secondary batteries including the negative electrodes prepared in the Examples and Comparative Examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate the capacity retention rate. The secondary batteries were subjected to a cycle test at 4.2-3.0 V, 1 C / 0.5 C, and the number of cycles at which the capacity retention rate reached 80% was measured. The results are shown in Table 2 below.

[0185] Experimental Example 4: Electrode curl measurement The bending strength was measured by measuring the height of the center of the coated electrode with the coating facing up as shown in Figure 3. That is, when the binder dries, tensile force acts on the coating, causing it to dent, resulting in curling. The degree of curling was measured, and the results are shown in Table 2 below.

[0186] [Table 2]

[0187] As in Examples 1 to 6, the battery contains a first binder and a second binder, satisfies specific formula 1, and is blended with SBR having a certain range of tensile strain. This allows the contact points between the active materials to be maintained even when the volume expands with the progress of cycles, resulting in a low resistance increase rate and excellent life performance at room temperature and high temperature.

[0188] For reference, when Examples 1, 3, and 4 were compared with Comparative Examples 1, 4, and 5, it was confirmed that a higher SBR ratio reduced the occurrence of electrode curl and was advantageous for process stability. However, when the SBR ratio was less than the ratio of the present application, as in Comparative Example 4, it was confirmed that the curl phenomenon became severe.

[0189] For reference, Comparative Example 1 is a case where a second binder is not included, Comparative Example 2 is a case where a first binder is not included, Comparative Example 3 is a case where a first binder and a second binder are included but the content range exceeds the range of Formula 1, Comparative Example 4 is a case where the content range is below the range of Formula 1, Comparative Example 5 is a case where the range of Formula 1 is satisfied but the Young's modulus of the first binder is below the range of the present application, and Comparative Example 6 is a case where the range of Formula 1 is satisfied but the tensile deformation rate (strain) of the second binder is below the range of the present application.

[0190] When the comparative examples 1 to 6 were examined, it was confirmed that the life characteristics were lower and the resistance increase rate was higher than those of the examples 1 to 6 of the present application, and that the curl phenomenon also occurred frequently.

[0191] That is, it was confirmed that the negative electrode composition according to the present application improves dispersibility for dispersing active materials even when using silicon-based active materials, and contains a first binder and a second binder of specific compositions to improve adhesive strength, thereby solving the problems of conductive network disconnection due to adhesive strength and volume expansion in the initial and later stages of batteries using silicon-based active materials.

[0192] That is, it has been confirmed that the negative electrode composition according to the present application has a high content of silicon-based active material particles, thereby enabling a high-capacity and high-density negative electrode to be obtained, and also solves problems such as volume expansion caused by having a high content of silicon-based active material particles. [Explanation of symbols]

[0193] 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 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, The negative electrode binder has a Young's modulus of 10 ３ MPa or more, and a second binder having a tensile deformation rate (strain) of 15% or more; The negative electrode binder has a negative electrode composition that satisfies the following formula 1: [Formula 1] 1≦X / Y<4 In the formula 1, Y represents the weight part of the first binder based on 100 parts by weight of the negative electrode binder; X represents the weight part of the second binder based on 100 weight parts of the negative electrode binder.

2. X is 50 parts by weight or more and 95 parts by weight or less based on 100 parts by weight of the negative electrode binder, The negative electrode composition according to claim 1 , wherein Y is 5 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the negative electrode binder.

3. The negative electrode composition of claim 1 , wherein the negative electrode binder is present in an amount of 1 part by weight to 20 parts by weight based on 100 parts by weight of the negative electrode composition.

4. the first binder comprises one or more selected from the group consisting of PAA, PAN, and PAM; The negative electrode composition according to claim 1 , wherein the second binder is a rubber-based binder.

5. The negative electrode composition according to claim 1 , wherein the silicon-based active material is present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

6. 2. The negative electrode composition according to claim 1, wherein the silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and a Si alloy.

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

8. The negative electrode composition according to claim 1 , wherein the negative electrode conductive material is present in an amount of 0.1 parts by weight to 40 parts by weight based on 100 parts by weight of the negative electrode composition.

9. The negative electrode composition according to claim 1 , wherein the negative electrode conductive material comprises at least one selected from the group consisting of a dot-like conductive material, a sheet-like conductive material, and a linear conductive material.

10. 10. The negative electrode composition according to claim 9, wherein the negative electrode conductive material comprises 80 parts by weight or more and 99.9 parts by weight or less of the sheet conductive material and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

11. The negative electrode composition of claim 1 , wherein the weight average molecular weight of the first binder is 100,000 g / mol or more and 2,000,000 g / mol or less.

12. a negative electrode current collector layer, and a negative electrode active material layer comprising the negative electrode composition according to any one of claims 1 to 11, formed on one or both surfaces of the negative electrode current collector layer; A negative electrode for a lithium secondary battery comprising:

13. 13. The negative electrode for a lithium secondary battery according to claim 12, wherein an adhesive strength of a surface of the negative electrode active material layer in contact with the negative electrode current collector layer satisfies a range of 100 gf / 5 mm to 500 gf / 5 mm under conditions of 25°C and normal pressure.

14. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 13. The negative electrode for a lithium secondary battery according to claim 12, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

15. positive electrode, The negative electrode for a lithium secondary battery according to claim 12 . a separator disposed between the positive electrode and the negative electrode; and electrolyte, A lithium secondary battery comprising:

Images